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In an electric vehicle the motive power comes from the battery. Electrical power is volts multiplied by amps so that 40 amps drain from a 12v battery is 480 watts. But 480 watts is also given from a 24v battery by a current of only 20 amps.Therefore, for a particular performance, the higher the voltage, the lower the current.
However, electrical current causes heating. Motor, wiring and the controller will all waste heat. The heat wasted is proportional to the square of the current multiplied by the resistance. Generally a 24v motor will have twice the resistance of a 12v one but even so a 24v motor would waste half as much power in heat as would a 12v motor (½; x ½; x 2). The controller and wiring will pobably be the same for 12v or 24v, so they will waste only ¼ as much power on 24v as on 12v.
It is clear from this that a 24v system is always better than a 12v system - provided
you can use two batteries. By the same token 36 or 48v would be even better - but require
different controllers which are not so readily available. Nevertheless really heavy
current systems (milk floats, electric cars, fork lift trucks) often use 72v or even 96v
to reduce heating.
Motors are specified to run at a specified rpm at a particular voltage with a specified
loading. The specified loading is usually that at which the motor takes its maxi mum
continuous current. If you run the motor under a lighter load than this specification its
current consumption will reduce and its speed will increase. If you increase the load,
then the motors current consumption will increase and its speed will reduce. Obviously you
are now exceeding the motors continuous rating so it will start to get hot. the greater
the overload, the quicker the motor will heat so there is a time limit on this overload.
However it is usually safe to run a motor under a 300% over current for, perhaps, a minute
although this will vary from motor to motor.
If you run a 12v motor from 24v its current drain and speed will still depend on the mechanical loading. However under no load it will run at twice the speed that it ran with 12v. Heating in the motor is still related to the current so you can still run it at its full rated mechanical load/current. However if the motor is badly balanced you may expect noise and vibration as the general construction may be inadequate for the faster speed. There may also be a problem with brush wear since the brushes are being asked to switch the current twice as fast. These effects are, however not very likely and usually the speed increase is quite OK.
If you overload the motor, its current rises in the same way whether the motor is running from 12v or 24v. However on stall the current from 24v could be twice that from 12v, so the motor could get f4QD's times as hot (heating is proportional to the square of the current). This however won't happen when you are using a good controller as the controller will limit the current to its designed value. Also the controller varies the voltage on the motor so you are probably not going to use the motor at full voltage in any case.
Another consideration is that, if you put too much current through a permanent magnet motor, it is possible to slightly demagnetise the magnets. This is cumulative: the motor's performance will drop slightly each time you do it. However, for battery motors, is is probably fairly safe to assume that, at the rated voltage, the current drawn when the motor is stalled will not reach this demagnetisation level. If you were to run a 12v motor off a 24v battery the stall current would then be excessive if it weren't limited by the controller.
Therefore, provided you chose a controller suitable for the motor you use, you can
usually run a motor 12v motor from a 24v battery with no effect except that full speed is
doubled.
Generally an ammeter on a battery system is of little use: it can be interesting to know
how much current you are taking, but once the system is set up - so what? If the motor
takes 25 amps up that incline, then that is what it will always take - unless there is a
mechanical fault such as a seized bearing. A meter might be useful before you bought the
controller, so you know which controller to get, but once the system is working OK, who
needs one?
A battery voltmeter is more useful: as the battery discharges, its voltage drops, so this will tell you the charge state of the battery. Also, under heavy load, the battery voltage dips. If the voltage dips too far then either the load has increased or the battery is getting old.
4QD have LED meters available (3 LED for 12v systems, 5 LED for 24v, 36v and 48v systems) which can be useful. They will show the voltage dips as you accelerate and will indicate the charge state. LED meters, working in steps, can never be as good an indication as an expensive voltmeter, but they can be very useful and better than most of the cheaper battery state indicators. They also give a nice display!
Or you can get a proper digital voltmeter: these can be bought for about £30 from most
electronic stores. If there is a demand, 4QD could stock them.
4QD controllers get used for a very wide variety of purposes. We list a few below.
Aerial rotators . . . . . . . . . . . . . . . 2 off 2QDs in servo system or NCC with joystick board Agricultural equipment . . . . . . . . . . . . 1QD, 2QD, NCC series, Pro-120 and 4QD series Camera dollies . . . . . . . . . . . . . . . . NCC or Pro-120 Caravan shifters . . . . . . . . . . . . . . . NCC or Pro-120 Carnival floats . . . . . . . . . . . . . . . NCC or Pro-120 Conveyors . . . . . . . . . . . . . . . . . . NCC or Pro-120, 2QD or 1QD Dog walking machines . . . . . . . . . . . . . 2QD Electric boats . . . . . . . . . . . . . . . . 1QD or 2QD series Electric bicycles . . . . . . . . . . . . . . 1QD or 2QD series Electric library trolleys . . . . . . . . . . 1QD or 2QD series Electric wheelbarrows . . . . . . . . . . . . 1QD or 2QD series Factory stores vehicles . . . . . . . . . . . NCC or Pro-120 Floor cleaning machines . . . . . . . . . . . NCC or Pro-120 Go Karts . . . . . . . . . . . . . . . . . . . Pro-120 or 4QD series Golf buggies . . . . . . . . . . . . . . . . . NCC-100, Pro-120 or 4QD series Golf caddies . . . . . . . . . . . . . . . . . Eagle or 1QD Invalid vehicles . . . . . . . . . . . . . . . Pro-120, NCC or 4QD series Kiddie cars . . . . . . . . . . . . . . . . . Pro-120, NCC series Lathes & milling machines . . . . . . . . . . 1QD or 2QD Materials handling . . . . . . . . . . . . . . Pro-120, NCC, 2QD Miniature railways, 3", 5" and 7¼" gauge . . . NCC, Pro-120 or 4QD Mobile targets . . . . . . . . . . . . . . . . Pro-120, NCC series Motorised library, filing and storage racking. NCC series, Pro-120 or 4QD series Mountain rescue vehicles . . . . . . . . . . . 4QD, Pro-120 or NCC series Potter's wheels . . . . . . . . . . . . . . . 2QD or 1QD Remote guided vehicles . . . . . . . . . . . . Pro-120, NCC series Ride on golf buggies . . . . . . . . . . . . . 4QD, Pro-120 or NCC series Voltage dropper for battery lighting . . . . . 1QD or 2QD Winches . . . . . . . . . . . . . . . . . . . Pro-120 or NCC series Window cleaning machines . . . . . . . . . . . Pro-120 or NCC series
Car batteries are intended for sudden, heavy surges (i.e. starting currents) then to be
steadily recharged. Their structure is such that they don't last very long if they are
continuously discharged almost completely and then recharged. They will in fact be
destroyed by over discharging.
The other type of battery is known as the 'traction' or 'deep discharge' battery. These are not designed for the 300 - 500 amp discharge that can occur on starting, but they are designed to be continually discharged to near full discharge and then recharged on a cyclic basis. They are used to power golf vehicles and for caravan use.
4QD don't actually make vehicles so we have no first hand experience of the batteries.
We know from 4QD's customers that lead acid batteries are the weak link in electric
vehicles and they do cause trouble. The problem is that a battery's performance today will
depend not only on its present state of charge, but also on how it has been treated during
its life. All batteries can be damaged by overcharge, over discharge and by leaving too
long in a discharged state. It also does no good to leave then unused for long, even
though fully charged. Batteries that are used regularly (and properly) tend to last
longest.
Most battery motor applications are land based and only draw high currents intermittently
(when accelerating or climbing a gradient). Motor controllers are designed to cope with
this market and will give high currents for short periods but soon get hot so their
continuous output must be de-rated from their short term rating. Boats are different from
terrestrial vehicles in that the current drain is continuous and also increases as the
propeller speed ncreases. The limitation on current is caused by the balance between
heating (I²R losses in the controller, where I is the current and R the equivalent
resistance in the controller) and cooling. The temperature the controller reaches will be
down to how much heat it dissipates and how quickly you can remove the heat. For instance
at 33 amps, the 2QD-70 will dissipate (33 x 33 x .009) 10 watts. The 2QD heatsink is about
5.6°C per watt, so it will rise (10*5.6) or 56°C above ambient, i.e. 80°C for 24°C
ambient. The 2QD-100 has a resistance of about 0.006 Ohms (and a slightly larger heatsink,
say 5°C per watt) so at 33 amps it would rise only about 33°C above ambient. The moral
is - the larger the controller the better, but expect to use extra heatsinking. It is OK
to run the heatsink at 100°C - apart from the risk of burns - but not much higher, so you
must expect to mount the controller on a significant external heatsink.
The NCC series may be used instead of the 2QD where reversing is required. 4QD are also
working on a controller specially aimed at the boat market. To be called the 'Cruiser', it
should have a continuous current rating of 70 amps and a peak current of only about 140
amps, giving a peak/continuous rating of 2:1 - rather more than most available
controllers.
Most customers tend to buy controller larger than necessary. This is fine: 4QD's drives
are so cheap you can do this. A larger controller will also stay cooler so will be more
efficient. There is no such thing as 'too large a current' - the motor will only take what
it requires. The only exception to this is that, if you run a 12v motor on 24v and stall
the motor, then a current limited by the controller is a good idea to prevent damage to
the motor.
Historically most controllers haven't included current limit so you have needed to use a larger controller than necessary for safety, mainly because stalling the motor could otherwise destroy the controller. 4QD's controllers have a current limit so you won't damage them by overloading them or by stalling the motor - unless you do this for so long the system overheats.
The current ratings on 4QD's drives are realistic ratings. The drives will, for short periods, give considerably more than we claim, thus the 50 amp drive will, from cold, give around 70 amps. However if you run it at 70 amps it starts to heat up. Internal circuitry detects this heating and reduces the output current to keep the drive safe.
So, if you chose too small a controller for your application no damage will result, but the controller will get hot. If this does happen you can easily and cheaply upgrade to a larger unit, or you can add extra heatsinking. The larger the heatsink, the longer the drive will take to reduce its output current. However a larger drive will also be more efficient so is a better choice.
4QD's range is getting large enough to make choice difficult. The first choice is: do you want reversing? If so, then the choice is the Pro-120, the NCC series or the 4QD series - but don't forget that you can add reversing to a simple controller by a double pole switch to reverse the armature connections, so a 2QD is also a possible choice. However you must make sure that the switch cannot be operated whilst the motor is still rotating.
The choice is simply down to 'do I want regen braking?'. The 1QD series incorporates the
same circuitry as the 2QD's braking since this, as a side effect, makes it far more
efficient than the industry standard controllers for golf caddies etc. If you want regen
braking, then the 2QD is indicated. If you definitely do not want regen braking, then the
1QD is indicated. In practise the choice is usually down to the style.
As an alternative to 1QD, we offer the Eagle series. This is an economy controller aimed
at golf caddies, electric bicycles etc and it is available cased (or, for larger
quantities, as a bare board). The Eagle (in common with other golf caddy controllers) has
no main decoupling capacitor: this is no problem if the battery leads are short but long
leads cause the MOSFETs to work harder and therefore get hotter.
The 4QD is designed for high current golf carts, 100 amps plus. The current ratings are
shown in the specification sheets There is usually little to chose between the 4QD series
and a pair of NCC controllers so the choice is down to individual preference and ease of
wiring. The Pro-120 and the NCC-100 are very similar in performance but the Pro has
reverse polarity protection, all the terminals are at one end and a cover is available,
making it physically similar to other 'industry standard' 110 amp controllers, albeit
giving considerably more power at a much better price!
In a moving vehicle or on moving machinery it is often useful to be able to take evasive
action when the vehicle collides with an object. Naturally the action required is down to
the vehicle's stopping distance - a car travelling at 60mph would need sophisticated radar
to be of any practical use. However a vehicle travelling at, say, 4mph may be able to stop
sensibly within 10cm or so. The safe stopping distance is down to the vehicle's mass and
speed and is not something that we can completely control in the electronics.
However the NCC, Pro-120 and the 4QD series controllers all have 'dual slope' reversing. This means that, if the reverse switch is operated at speed the controller will automatically slow to zero speed (under control of the deceleration ramp), reverse and then start up again backwards. This means that if you have a sprung bumper at the front of the vehicle and place an auxiliary reversing switch so that it is operated when the springs of the bumper start to compress, the controller will go into reverse, slow down then back off until the switch opens again. The vehicle will now hover at the switch's operating point. Naturally for complete safety the bumper's free travel should be greater than the vehicle's stopping distance or crushing will occur during braking.
Above is a suitable circuit showing how to use two switches, one at front and one at rear for 'both end' collision detection.
When using 4QD's joystick board with the NCC, a slightly different arrangement is required. The diagram shows the direction output of the JSB (an NPN transistor with a pull-up resistor to +24v (or +12v) and the direction input to the NCC which senses at about 6v. The NCC's direction input is high to engage reverse. If S1 is closed, the NCC will always go in reverse, so if this is closed by forward travel, the machine will hit the switch, stop, reverse and back off to the switch's operating point where it will hover until the joystick is reversed. The extra 10K stops S1 fighting the JSB's output transistor.
Similarly if S3 is closed, then the NCC will always travel forward.Alternatively S2 can be fitted. When this is open the joystick can never give a reverse signal to the NCC. Naturally in a machine you must consider what will happen if both end stops get operated simultaneously or is one switch sticks. In the circuit above, S1 will always win. Note that the daughter version of the Joystick interface has end stop circuitry included.
4QD sell a magnetically operated reed switch which can be very useful for this purpose.
Or you could arrange a rod straight through the vehicle, moved by the (sprung) bumpers. If
a front collision occurs the rod moves backwards moving the magnet to close the reed
switch so the vehicle automatically reverses. More information on Reed
Switches
A motor converts electrical energy into mechanical energy. In the conversion some of the
electrical energy is wasted as heat. Some of the mechanical energy also goes as heat
because of friction losses. The mechanical energy is used partly to accelerate the loco -
i.e. it is turned into Kinetic energy, some is used to climb hills - it gets turned into
Potential energy. It is quite easy to work out the current you require if you have all
units in Metres, Kilogrammes and seconds.
Electrical energy = volts x amps x time. So a 12v battery giving 10 amps for one minute
(60 seconds) will give 12 x 10 x 60 (or 7200) Joules and a motor taking 20 amps at 10
volts for 60 seconds will deliver 20 x 10 x 60 (or 12000) Joules.
Kinetic energy is defined as 1/2 x mass x velocity². Mass should be in kilograms,
velocity in metres/second. So a train weighing 250kg travelling at 4.47 metres/sec (which
is 10mph) would have an energy of 0.5 x 250 x 4.47 x 4.47, or 2497 Joules
If we require 4QD's vehicle to accelerate smoothly to top speed in, say, 60 seconds
then current must flow for this full 60 seconds and the electrical energy used in
accelerating will equal the kinetic energy gained.
So: volts x amps x time = 12 x amps x 60 = 2497 (the K.E. gained).
Therefore amps = 2497/60/12 = 3.47 amps
So we only need less than 4 amps of motor current for this acceleration.
Potential energy is Mass x g x height, where g is 9.80 metres/second/second. the
acceleration due to gravity. If we have a gradient of 1 in 50, 30 metres long, then the
height gained on this incline will be 1/50 x 30 or 0.66 metres. In ascending this incline
4QD's vehicle will have gained a potential energy of
250 x 9.8 x .66 or 1617 Joules
At top speed the train will travel at 4.47 metres/second so it will take 30/4.47 seconds
to travel the 30 metre incline, i.e. 6.71 seconds. The current must flow for this time so
amps = 1617/12/6.71 = 20.08 amps
So we need 20 amps of motor current for this incline.
It doesn't help at all to go slowly up the incline (unless you have mechanical gear change): if it takes 20 amps of motor current at full speed, the motor current will still be 20 amps at half speed, because full speed is 12v on the motor (which we used in 4QD's calculation) so half speed will be 6v on the motor. Halving the motor voltage halves the power, so the motor current won't change. Yes - the battery current will halve, but it will flow for twice the time, so there is no overall benefit. At high motor currents the motors and controller will get hot (wasting power). The power wasted is only down to the motor current: the quicker you get up the incline therefore the shorter the time for which you will be wasting power, so the smaller the overall losses.
Kinetic energy is defined as : ½; x mass x velocity²;.
Electrical energy = volts x amps x time.
Equating the two and rearranging to get current,
½ x mass x velocity² = volts x amps x time.
Amps = ½; x mass x velocity² / volts / time.
Current = ½ x (vehicle laden weight) x (max vehicle speed)² / battery volts / (time to top speed)
Potential energy is Mass x g x height,
where the vehicle's mass is measured in Kilograms,
height is in metres and
g is 9.80 metres/second/second. the acceleration due to gravity.
If we have a gradient of T%, then the height gained will be
T/100 x Length (the length of the incline in metres)
the potential energy will be Mass x g x T/100 x Length
4QD's vehicle will traverse the incline in Length / Speed seconds.
Current must flow for this time so electrical energy will be: Volts x Amps x Length/Speed
Equating electrical to mechanical energy we get
Mass x g x T/100 x Length = Volts x Amps x Length/ Speed
So the motor current must be
Mass x g x T/100 x Speed/Volts
Volts and amps in the calculation must be the motor volts and amps, not the battery
volts and amps but, at top speed, motor volts and amps are equal to battery volts and amps
and the calculation approximates to
Current =1/10 x (Vehicle laden weight) x (gradient) x (Top vehicle speed) / (Battery
voltage)
The above calculations are simplified and do not include friction losses (or resistive
losses). You cannot really calculate these: either measure the current the motor draws on
level track or guesstimate. Say 10 amps at 12v for a 5@quot loco and 15 amps for a 7 1/4
gauge loco at 12v. Halve these for 24v operation.
The current you need then is the frictional part plus either the K.E or the P.E.,
whichever is greater. Unless, that is, you are going to stop on the incline!
Several of 4QD's controllers are ideal for electrically assisted cycles (e.g.2QD, 1QD,
Eagle, Scooota'). your choices are partly mechanical and partly electrical and partly
depend on the proposed use. The 2QD has regenerative braking. This means that, with a
permanent magnet motor, your speed is controlled by the motor. If the cycle tries to go
faster than the motor speed then braking will come in. This is ideal for stop-start town
work, where a high top speed is not required and where the regenerative braking is a great
boon. However for country work you don't want a restricted top speed - you want to be able
to coast down one hill to gain momentum to help carry you up the next. Regenerative
braking stops this and is then a nuisance. However don't forget that, if you have a free
wheel between the motor and wheel, braking won't occur anyway and if you don't have a
freewheel then any pedalling is against the friction of the motor. If you don't want regen
braking, 4QD's 1QD-70 is perfect: it is similar to the 2QD-70 but without regen braking.
In practise most existing cycles don't want regen braking and use a standard golf caddy
controller. 4QD's Eagle series is then indicated - but better that most other
manufacturer's offerings because it doesn't have a high-dissipation flywheel diode to fail
at high currents. For a technical description
of what a flywheel diode does.
For high performance machines 4QD's new 'Scoota' is ideal: this is based on the Pro-120 but without the reversing features. It also has the ability to reduce the regen current limit for applications where excessive braking could be undesirable.
Also you will probably chose about 50 amps for the motor and controller. 50 amps at 12v
is 600 watts, which sound a lot, but if your 600 watts will drive you at 15mph on the
level, then it won't drive you at 15mph up hill. You will have to much slower uphill and
slower speed means a lower motor voltage. Lowering the motor voltage also lowers the motor
power, so you actually have less power for going up hills. You really need a gear change
so the motor can keep at top speed (i.e. at top voltage therefore at maximum power) even
when the cycle is going slow up a steep hill.
There are several ways of arranging a dead man's handle with the 2QD or NCC controllers.
With the NCC series controllers any of these methods will work properly as they have a sophisticated ramp system where the acceleration and deceleration ramps are independently adjustable to suit the vehicle and the ignition circuitry is timed so that the controller decelerates to zero before the ignition goes off.
The 2QD only has a very small internal ramp so deceleration will be very fast if precautions are not taken. As well as causing mechanical shock this also cases a high energy dissipation in the controller as the braking MOSFETs absorb the energy of the vehicle. If the vehicles energy is too high (heavy vehicle, travelling fast) this can lead to failure of the MOSFETs. Possibilities are:
When using two motors on opposite sides of a vehicle, some people ask whether differential
drive is required. In practise it is not. It is common practise now for ride-on golf
buggies (which can have a small turning circle) to simply drive two motors in parallel
from one controller. This causes no problem at all and the differential action is no
problem.
In theory, with two motors, better differential action if obtained with
series-connected motors because the current through the two motors is always the same.
When turning, the inner motor slows (reduced back EMF) and the outer one speeds up
(increased back EMF). The motor torque is proportional to the current flowing so both
motors will always give the same torque. For parallel motors the inner motor will slow
down, drawing more current and increasing the torque. The outer motor will speed up,
increasing the back EMF and so reducing the motor current and torque. The parallel
connected motors will then, in theory at least, fight the turn whilst series connected
motors will not. The trade off is that parallel connected motors will be better at getting
out of ruts! The problem is that the current through each motor is doubled so the motors
are not as easy to make and brush wear is increased. Generally 24v motors in parallel are
therefore to be preferred to 12v motors in series.
4QD's controllers are quite suitable for use from a digital control system. Most PLCs and
micro controllers have a PWM output which will normally be the best interface. The
controllers have a ramping circuit which acts as a low pass filter. It will average out
the PWM signal, accepting the mean d.c. voltage as the speed reference input. To alter the
speed, simply vary the mark/space ratio of the signal.
You will of c4QD'sse need to fit a resistor in place of the pot, to override the pot
fault detection circuit.
A lot of users are concerned about battery life. 4QD's controllers are carefully designed to minimise losses and and therefore to maximise battery life. Older controllers used low (audible) frequency for switching: this increases losses in the motor, so the motor runs hotter. 4QD's controllers use 20kHz to reduce motor losses to a minimum. Also, 4QD's controllers draw very low current for the control circuitry. Lastly, we employ regenerative braking which actually uses the motor as a generator during braking and recovers some of the energy which is returned to the battery. There is also some advantage in using a higher current controller and the thickest wiring practical - the higher the current handling ability of these the less power will be wasted as heat.
Other causes of loss are inefficient motors: a permanent magnet motor will always be a
better choice than a field wound motor since the field draws current, the permanent magnet
doesn't. We can do nothing about this in 4QD's controllers.
Historically most industrial vehicles, including fork-lift trucks, have used Series wound
motors. Modern trucks still tend to use these motors, because they are cheap and a tried
and tested technology. There is also a large service industry supplying spare parts
(contactors, resistors etc) for them.
See section on 'Series wound motors' for more information.
You can get electronic controllers specifically for series wound motors: the
controllers also have outputs for the direction change contactors, to switch these at the
correct time to control reversing. Switching the contactors at zero current stops arcing
and extends the contactor life.
Unfortunately there is much confusion in nomenclature: golf cart and golf trolley are both
indiscriminately used to describe both passenger carrying golf buggies and also motorised
golf bags, or caddies.
For passenger carrying golf buggies the current required is determined by the maximum
speed, vehicle weight and payload (weight of rider) and the required hill climbing ability
(usually 1 in 3 or 1 on 4). Given all these parameters we can work out the required
current but we would generally recommend 4QD's 4QD-150D-24 for 6 mph vehicles and 4QD's
4QD-200D-24 for 8 mph vehicles, assuming you want to climb the 1 in 4 hills some c4QD'sses
have.
Alternatively 4QD's NCC-70 is recommended. This is designed so two controllers can be used in tandem, one driving each motor. This gives the required current and has independent current limits for each motor, so if one motor gets damaged, the other sill still work and should get you home with little chance of a burn out. Both 4QD and NCC series have reversing full regenerative braking so are ideal controllers.
The NCC-100 is another choice. However this is similar in output to the controller used on some of the lighter golf buggies which are sometimes considered to be underpowered: this will depend on your own weight and the vehicle weight as well as the nature of your normal golf c4QD'sses. The 4QD is, generally, a safer choice.
Commercial carts almost all use EMD motors, the smaller ones use two EMD 180w motors (PM50-63) with a 110 amp controller and a top speed of 6 mph. However these are distinctly under-powered. A better choice, as used in the better buggies, are two EMD 300 watt motors (PM63-50) with a 4QD-150 amp controller. This combination is OK up to 8mph on even the hilliest c4QD'sses
Two Sinclair C5 motors are a similar power to two EMD PM63s, but, although they can be used safely on 24v, their top speed is then 6000 rpm, so they need appropriate gearing. Otherwise use them in series, when they each will get 12v from a 24v controller.
For a cheaper, non-reversing system, you can just about get away with one of 4QD's 2QD-100 controllers or, better, two 2QD-70 controllers, one for each motor. This still gives regenerative braking.
For motorised golf bags 12v at about 30 amps is adequate: less than 30 amps may mean that
the trolley needs help up hills. 4QD's 1QD-35 is designed specifically for this market or
for heavier use, the 1QD-70 may be used. These both have reverse polarity protection and
do not give regenerative braking since most commercial caddies have a freewheel device
which renders regen braking useless.
However if the wheels are fixed, the regenerative braking of the 2QD can be useful. Or, if you really want to impress your friends, you could use an NCC-35 to give regen braking and reversing.
For volume users we can also supply a small, economical card controller - the Eagle
All components or wires which are carrying any current get hot. How hot it eventually gets
depends on the rate that heat is generated in the item and on how quickly heat can get out
of the item into the surroundings. How quickly the item reaches this steady temperature
also depends on how much heat the item can absorb or how 'large' it is, i.e. on its
'thermal mass'. The situation is more complicated in most motor control application
because heat generation is very intermittent.
Electrical heat is generated by electrical current (amps) flowing through a wire or
component which has electrical 'resistance' (ohms). All electrical components and wires
have resistance but the larger the wire, the lower its resistance. The heat generated is
the square of the current multiplied by the resistance. Electricians refer to current as
'I' and resistance as 'R' so the heat generated is I²R. Note that the voltage does not
come into this: heat generation has nothing directly to do with the voltage. However the
power the device is handling is directly concerned with the voltage since power is volts
times amps. This is why a 24v system is better than a 12v one: it can give double the
power at the same heat or, if you halve the current, the same power for ¾ the
heat.
A hot object dissipates heat, i.e. it looses heat into the surroundings. The loss rate
depends on the area over which the heat is dissipated, how good the 'contact' with the
surroundings, hot much hotter the object is and even the col4QD's of the object. In
practise the dissipation is eventually to the air (unless you are on a boat and can use
water) so the 'contact' is down to the surface roughness (whether the object is finned)
and the airflow: blowing air over your coffee cools it quicker than standing it in still
air.
Usually the object which is getting hot is not the same object that is loosing the heat to
the air. The heat has to flow from one object to another, usually through other objects on
the way. The heat conduction path does not let the heat flow unless there being a
temperature drop: the objects 'resist' the flow of heat. An object which has a high
resistance (be it to heat flow or to electricity) has a poor 'conductivity'. A good
conductor does not resist the flow of heat so much as a poor conductor (this is the same
for heat as for electricity: usually the two are linked). If there are several objects
through which the heat has to flow the contact between each item and the next must be
good: a very small gap, even in the form of surface roughness, can dramatically reduce the
heat flow (i.e. it can add resistance to the thermal path). Obviously this is bad so it is
common practise to use 'heatsink compound' to fill the gaps caused by roughness when
joining two metal parts through which heat must flow.
If an object has a lot of 'thermal mass' it takes a lot of heat to increase its
temperature. If we do not want an object to heat quickly, then we must have a large
thermal mass. Thermal mass can even out the heating, so a few short, high bursts of heat
don't cause overheating. However thermal mass alone won't cool an object. The mass only
stores the heat which must still get dissipated safely. A High thermal mass increase the
time the object takes to get hot, but its final temperature is still determined by the
balance between heating and cooling rates.
How do various materials perform? The table to be inserted below will shows relative
values for several metals. Specific heat is the ratio of 'thermal mass' to actual mass,
note how very good water is. If you want a high thermal mass, use a bucket of water! Not
very practical: electronics does not like water! The second best is aluminium. A kilogram
of aluminium can absorb twice as much as a kilogram of copper or steel. However, steel is
about 3 times denser than aluminium, so a 10cm cube of steel is actually about 1.5 times
better than the same size block of aluminium. However, when you examine the thermal
conductivity, the differences become more obvious. Thermal conductivity is related to the
volume, so a rod of silver will conduct heat twice as well as a rod of aluminium the same
size. Steel is 5 times worse than aluminium. Anyone who has tried welding these materials
will appreciate the difference! Copper is pretty good too but, because of its low density,
aluminium is, weight-for-weight, the best. Steel, weight-for-weight, is very bad indeed
and, where heat conduction is important (as it always is in a heatsink) should not be
used, except where there can be a very good contact area into a large mass or where there
is sufficient thermal mass to even out the heatflow. If you need to mount on steel, then a
heat spreader made from aluminium (or copper will get the heat out of the s4QD'sce, spread
it over a wide area and pass it into the steel.
2QD controllers are ideal for industrial use as a 'building block' for designing into a
system. We have many years experience in the design and manufacture of industrial
machinery control systems and can usually help. We can also usually supply suitable
circuitry.
The 1QD, 2QD and NCC controllers do not incorporate internal armature voltage sensing. For
most applications this is an unnecessary complication since the operator compensates for
speed changes automatically. The 4QD series does incorporate armature voltage sensing.
However this alone gives a limited improvement since the motor's speed still changes
because of the voltage loss in its internal resistance (IR loss). It is possible to
compensate for motor IR loss, but the controller then must be set up for each different
motor: this causes much confusion as setting up requires much skill, or a tachometer and a
method of loading the motor whilst measuring the speed. The other problem is that the
existing internal current sensing (which could be used for IR compensation, is sensitive
to the MOSFETs internal temperature, so the IR compensation would drift.
The best method of closed loop control is via a tachogenerator. It is relatively simple to add on to the 4QD series as the internal circuitry used for armature voltage sensing can accept a tacho generator circuitry with minimal change.
It is also possible to add a tachometer to the 2QD and NCC series but and you will require an error amplifier to compare tacho feedback voltage with the demand speed. A suitable bi-directional circuit can be made quite easily using one quad op-amp. 4QD can supply a circuit on request: if there seems adequate demand we could even make a suitable module available.
It is also possible to use a pulse generator to measure motor speeds. If using analogue control this needs to be processed via a frequency to voltage convertor to be used as feedback. The slowest motor speed will determine the maximum time between pluses and this will determine the minimum response speed of the F to V convertor: if it responds too quickly the motor will accelerate between pulses! Pulse circuitry is not direction sensitive (unlike a tacho generator) so the error amplifier need only be uni-directional.
Pulse generators are often used with computer control systems: in this case the computer can give the controller a demand speed via a Digital to analogue convertor: the software can control response times and difference amplification (if the demand speed is input digitally), or the D-A can output to a conventional analogue error amplifier, working direct from the demand speed control.
The NCC series has, at its input, sophisticated analogue ramps: ideally the error amplifier should be inserted after the ramping circuit and before the modulator: contact 4QD for more assistance.
The 2QD can be used in constant torque mode, i.e. in current limit mode. The current limit
can be reduced to virtually any value by adjusting one resistor. The main consideration is
that current sensing is done by using the MOSFET Rds(on) so it is temperature sensitive
because of the MOSFET's positive temperature coefficient. Therefore if the MOSFETs get
hot, the current drops. You should therefore use a high current controller with the
current limit set well back to avoid self heating if you require reasonable stability.
Note that the current limit circuit used in the 2QD-100 is not suitable for this as it
cannot be altered much (it uses a transistor Vbe as a reference voltage). We will change
this on future production batches.
In the 2QD there is a built in CR ramp (100K and 1µ). This can easily be altered or
removed completely when the slew rate is limited by an internal CR of 10K and 100n, so
response can be very fast.
When increasing the ramp time you should be aware that there is a 'dead band' at the bottom of the speed control range. Adding a long ramp will increase the time delay spend in this dead band. Contact the factory if this is a problem.
You can use the 1QD, 2QD and NCC controllers as a voltage follower: 100% output occurs for
about 4v input (adjustable). You must use a resistor in place of the pot to operate the
'ignition switch' circuitry. Details are in the manual.
Motorised jockey wheels normally use a 12v system: an EMD PM63 motor and a speed
controller. The motor may take 60 amps or more for short periods. An NCC-70-12v will be
ideal or you can use a 2QD if you don't want reversing.
Several commercial units exist: mostly these use the EMD motor.
A 'Joystick' is a control operated so that the centre of stick travel is zero speed. Move
the control forward to run forward and move the control back to run backwards. Some of
4QD's reversing controllers can be used in this way, others not. The 'Joystick' can be a
linear control or, more usually, a rotary pot with a lever, used only over the centre of
its rotation. This is a 'Single axis Joystick' which will control speed and reversing but
not steering. To control steering two controllers are required, each controlling a
separate motor, with a 'Dual axis Joystick' system.
Dual axis joysticks also allow transverse movement (in addition to front-to-back). In some applications (e.g. a remote controlled pan and tilt head for a camera) the two motors can be controller one by each axis, i.e. one controlled by front to back movement and the other by transverse movement. This is two separate 'Single-axis' controls rather than a true 'Dual-axis' control.
In other applications two motors are used (with separate controllers) one to drive each wheel of a vehicle. In this case transverse movement of the stick must speed up one motor whilst slowing the other so the vehicle steers by the difference in speed. This is a true 'sum and difference', 'dual-axis' system, offered by 4QD's Dual-Axis JSI.
4QD-150 series. This has circuitry for joystick control: all that is required is a small modification, to be done at the factory.
NCC-35 & NCC-50 Early versions are not suitable as they use 'pre-select' reversing. This only reverses when the speed is reduced to zero so you would have to hold the joystick at the centre position long enough for the relays to drop out. This is impractical. Later versions are the same as the NCC-70 series.
NCC-70 & NCC-100 Early versions used preselect reversing (same as the NCC35/50). They now have 'dual ramp reversing'. With this, the controller reacts immediately the direction is changed so that if you are going at full speed forward and throw the reverse switch the controller will slow to a halt, reverse and start up backwards automatically. This is suitable for interfacing to a joystick.
4QD offer a Single-axis interface for the NCC series. We also offer a 'Dual-axis
interface' for differential steering.
This was one of the applications we considered in designing 4QD's NCC range of
controllers. The NCC-35 should prove a good choice, unless the car is particularly heavy,
very fast or to run on very rough ground, when the NCC-50, NCC-60, NCC-70 or even the
NCC-100 would be a better choice.
The current you actually require will depend on the weight of the child, the weight of the vehicle, the performance you expect (i.e. the top speed and the hill climbing/rough ground ability) and the voltage. For an average car operating at 12v with a top speed of 4 mph, a 35 amp controller should generally give adequate performance. If the top speed is more than 4 mph then you need proportionally more current. For 24v operation, halve the required current - or double the top speed, depending on your gearing. Because of the reduced current requirements, 24v is preferable - if you don't mind the extra battery.
For the reversing switch you can use any ordinary single pole switch with the NCC series. Or you could mount a reed switch with the magnet on the gear lever to give a proper floor mounted reversing switch. For more information on the reed switch, see section.
Alternatively, if you don't want reversing, 4QD's 2QD controllers are ideal. They include regenerative braking which is very useful.
For the speed pot (for either range of controller) you can use a simple rotary panel
mounted potentiometer, 4QD's 'Bicycle Bell' throttle or, if you want a foot pedal, the
Plunger operated pot is easy to fit, but expensive. Otherwise you can use a rotary pot
with a lever attached, since the controllers have adjustable gain to suit a rotary pot
with only a few degrees of movement, but you will need to be ingenious with the operating
linkage. The naked mechanism from 4QD's 'Bicycle bell' throttle lends itself well to this
application.
Low voltage lighting circuits may be run off a 2QD controller: this enables a vehicle with
24v, 36v or 48v battery to use a 12v circuit for lighting, horn etc. The 2QD can of
c4QD'sse also be varied, so you can have a variable voltage lighting circuit. The only
problem is that the 2QD's output is between +ve and live output, so battery positive is
the common connection: you cannot then normally use a negative earth system. However 4QD's
controllers do have a fast high side current limit so it is possible to use the
controllers 'upside-down', i.e. with a common negative. The problem here is that the
circuit won't switch on properly as it is designed to start up smoothly with a common
negative. Contact 4QD for more advise - we are working on this.Send an email to 4QD
The current a locomotive will take depends on the loco's mass (including passengers), the
top speed of the loco and the size of any gradients it will have to climb. Given all these
figures, we can actually calculate the current required. However a 5 loco takes typically
about 30 amps at about 15 amps at 24v while an average 7¼ gauge loco may draw
50 amps at 12v or 25 amps at 24v. It is probably best to chose a controller slightly
larger than you anticipate, but a typical loco could be built by choosing the controller
from the chart below (to be inserted later).
For more heavy duty 7¾ locos consider either an NCC-100 or a 4QD series controller - these are also available for 36v operation.
Some people prefer the regen braking that these controllers give - others dismiss it as 'unrealistic'. This depends on who is driving the machine. If it is a garden railway and the kids will be using it, we strongly recommend regen braking and a reversing controller that will handle this safely.
If you really don't want regen, then choose the 1QD (or the Eagle). Since the controller doesn't measure the speed of the train, it cannot do the reversing safely - it has no way of knowing when the train is 'standing in the station'. Therefore you will have to reverse with a changeover switch or relay that is controlled by the driver and only operated at a standstill.
