2 Controllers one motor

Hi All.

I don't know if I am being silly BUT I was wondering, I have a KT setup 4 KW motor and a 22amp max controller @ 48 volts, it equates to just over 1kW, and according to the screen, I am getting close to that, now to my question, AT LAST. Would it be possible to put 2 controllers on one motor to share the load? Before you all ridicule me and say just buy another controller well, come and live here where we have to pay between 12 and 14 N$ for a single US$, the picture becomes somewhat different, now, the reason I ask obviously is heat, the controller gets pretty warm pulling almost a kW and with our lovely summer temps from 30 -40 odd degrees C it does not help much, would it be able to work? I have two identicle controllers, if possible 1: what would the connection parameters be? 2: a diagrame would be welcome.
Thank you in advance.

Charles Gibbs said:

Would it be possible to put 2 controllers on one motor to share the load?

Click to expand...

Not for brushless motors, unless you take the motor apart and rewire it, etc. (assuming your motor is suitable for that process). (See John in CR's Hubmonster threads about that)

There's a few threads about two controllers on one motor, within this search list
https://endless-sphere.com/forums/search.php?keywords=controllers+motor&terms=all&author=&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search
and there's others I recall that don't come up in that search, don't know a simple one that would find them all.

This one has some good answers in it
https://endless-sphere.com/forums/viewtopic.php?f=30&t=91515&hilit=controllers+motor

@ amberwolf. Thank you for the reply will check out the links, did not know quite how to serch for it...... Thanks again.

Consider mod to your actual controller. Most can be mod easily, to feed at least twice watt they were made for. :wink:

MadRhino said:

Consider mod to your actual controller. Most can be mod easily, to feed at least twice watt they were made for. :wink:

Click to expand...

He's not looking to double his power, but rather half the heat generated inside one controller by spreading the load across 2 controllers. (Note:30-40deg C summer temps).

Buk___ said:

MadRhino said:

Consider mod to your actual controller. Most can be mod easily, to feed at least twice watt they were made for. :wink:

Click to expand...

He's not looking to double his power, but rather half the heat generated inside one controller by spreading the load across 2 controllers. (Note:30-40deg C summer temps).

Click to expand...

Depending of the mosfets in the controller and the winding of the motor, to upgrad and feed higher Amps might run cooler. That is because Amps limiting is a major factor of controller heat.

MadRhino said:

Depending of the mosfets in the controller and the winding of the motor, to upgrad and feed higher Amps might run cooler. That is because Amps limiting is a major factor of controller heat.

Click to expand...

Same number and type of mosfets; more amps, less heat. Cool!

(I wonder why they bother producing 9/12/18 mosfet controllers for high power; when according to the above 6 mosfets with more amps should run colder?!)

Buk___ said:

MadRhino said:

Depending of the mosfets in the controller and the winding of the motor, to upgrad and feed higher Amps might run cooler. That is because Amps limiting is a major factor of controller heat.

Click to expand...

Same number and type of mosfets; more amps, less heat. Cool!

(I wonder why they bother producing 9/12/18 mosfet controllers for high power; when according to the above 6 mosfets with more amps should run colder?!)

Click to expand...

Ok, I see that you need it clear:
A 18 X 4110 controller feeding 40 A to a fast winding hub motor in a 26’’ wheel, will run cooler feeding 80A after beefing the traces and wire size upgrade. But, the same controller with a smaller wheel or a slow winding, won’t run cooler after upgrade. That is because, when the motor wants to pull higher power than the controller is set to feed, current limiting is making heat.

Controller heating is primarily caused by i squared r in the FETs. Limiting the current is normal and required. Current limiting creates negligible heat in a properly designed controller.

Paralleling hall sensored brushless controllers has been done successfully. If the identical hall signals as well as power, ground and throttle are fed to both controllers they should stay in sync.

Changing to better FETs helps by lowering FET resistance, which is a major factor in FET heating. Beefing up traces and adding bus bars reduces heat in those areas. Bypassing or paralleling shunts disables the protection in the controller and reduces reliability. Less heat is desirable, more current is not. Raising current increases controller heat significantly since it is driven by current squared.

Improving the drivers, or just getting a better controller can also help. Properly driven FETs generate significantly less heat.

Quality controllers will protect themselves against high temperature. Cheap controllers may have little or no effective protection. Building in reliability and self protection takes engineering and costs more.

Hacked controllers will generally have bypassed their protection and will produce more heat and self destruct more easily. They will produce more power but have little or no protection.

Alan B said:

Raising current increases controller heat significantly since it is driven by current squared.

Click to expand...

Les amps, less heat. Make sense to me

Note that controller heating is motor current dominated, reducing battery current by increasing battery voltage does not reduce controller heating significantly because motor current is not affected by this, the only thing that reduces motor current is reducing torque or changing windings.

I live in the desert too, and run controllers hard when climbing hills. ( southern rockies) Just mount it where it gets good cooling, and if really worried, add some more heat sink to it.

If really thrashing it, carry a spray bottle to cool both controller and motor.

Alan B said:

Note that controller heating is motor current dominated, reducing battery current by increasing battery voltage does not reduce controller heating significantly because motor current is not affected by this, the only thing that reduces motor current is reducing torque or changing windings.

Click to expand...

Current does make controller heat, according to the combined impedance of the controller fets and power circuit. To reduce controller impedance is the first thing to do when you want to feed more current. So a controller can be upgraded to run cooler yet feeding higher current than it was feeding in its original state, especially when it had high impedance from the start. Of course, any cooling means can also improve the max current tolerance of a controller.

Then, once you know the new controller limits, the optimal combination of motor winding and wheel size will determine the max performance that can be achieved with it.

Impedance is the combination of resistance with inductance or capacitance. Only the resistive part dissipates power and generates heat.

The loss in the controller comes from a combination of the FET resistance, the body diode voltage drop (not exactly resistance in that case), and the traces carrying the motor and battery currents. There is also a short time during switching when the FET is not saturated and the FET dissipation is quite large, but this is tempered by the short period of time the FET is in this state.

The largest loss component is often the body diode voltage drop. If the FET is poorly driven (as in many cheap controllers), the switching loss can be high as well. Paralleling controllers spreads this loss across the devices, but does not reduce the total. Spreading the dissipation across controllers has another benefit in that the junction temperature of the FETs is reduced, and this reduces the resistance of the junctions. There is a modest overall savings from this.

The forward resistance of the saturated FET can be improved by changing to a better FET, or paralleling controllers. In this case the total loss is reduced as well as spread across multiple controllers (since it is I squared R dropping the current to half in a controller will drop the power there to one quarter, so the total power loss from this loss component is reduced to one half.

The switching losses of the FET can be reduced by improving the driving circuitry. In practical terms this means buying a better controller.

The large losses in the body diode don't change much with different FETs, but can be reduced significantly by changing to Synchronous Rectification (again, buying a better controller). Of course then the controller would not be suitable for parallel operation.

There are plenty of threads talking about hacking controllers and increasing their power output (while generally making them less reliable). But this thread is about paralleling controllers.

Alan B said:

Impedance is the combination of resistance with inductance or capacitance. Only the resistive part dissipates power and generates heat.

The loss in the controller comes from a combination of the FET resistance, the body diode voltage drop (not exactly resistance in that case), and the traces carrying the motor and battery currents. There is also a short time during switching when the FET is not saturated and the FET dissipation is quite large, but this is tempered by the short period of time the FET is in this state.

The largest loss component is often the body diode voltage drop. If the FET is poorly driven (as in many cheap controllers), the switching loss can be high as well. Paralleling controllers spreads this loss across the devices, but does not reduce the total. Spreading the dissipation across controllers has another benefit in that the junction temperature of the FETs is reduced, and this reduces the resistance of the junctions. There is a modest overall savings from this.

The forward resistance of the saturated FET can be improved by changing to a better FET, or paralleling controllers. In this case the total loss is reduced as well as spread across multiple controllers (since it is I squared R dropping the current to half in a controller will drop the power there to one quarter, so the total power loss from this loss component is reduced to one half.

The switching losses of the FET can be reduced by improving the driving circuitry. In practical terms this means buying a better controller.

The large losses in the body diode don't change much with different FETs, but can be reduced significantly by changing to Synchronous Rectification (again, buying a better controller). Of course then the controller would not be suitable for parallel operation.

There are plenty of threads talking about hacking controllers and increasing their power output (while generally making them less reliable). But this thread is about paralleling controllers.

Click to expand...

Thanks for this. Such concise descriptions of circuit limitations/boundaries is very rare to to find.

Buk___ said:

Thanks for this. Such concise descriptions of circuit limitations/boundaries is very rare to find.

Click to expand...

Exactly, Alan thanks for taking the time to inform others. Much appreciated and food for thought.

FWIW, doesn't the controller heat a lot less at WOT, because it runs most efficient when the fets are not switching?

Its true, accelerating with the big motor on a smaller controller will heat it, but it should stand it if you run more or less wide open all the time. 8)

At the very least, give it full throttle when starting up. Once cruising at say, 30 kph, your fets will be switching, but your wattage will be moderate, unless riding in deep sand.

But that motor does deserve a better controller, if your battery can hack it. For now, I'd just ride it, and not worry unless you actually scald a hand touching the controller. You are correct though, that if your wheel is large, and the winding fast, your controller could be at risk. Best thing you could do, a bit on the cheap, would be to make your wheel a 20 inch one. You should be careful about overloading it if you have a big wheel, such as trailers, extreme steep hills, or riding in deep sand.

Reading this back, maybe I just confused you. What I'm saying is your controller has a 22 amps limit because it CAN handle that rate. I'm not suggesting your climate is good for increasing it. The danger though, is that the big motor will pull hard on it, and when its doing that, dont stall out the motor with too much sand around the wheel, or towing a trailer up hills. Controller WOT, plus the wheel is loaded too much to spin fast, is where you might pop your controller.

Wide Open Throttle, or WOT is often mentioned as a "solution" to reduce heat in the controller. This is a complex issue, and the devil is in the details.

The way it is usually justified is to use WOT to avoid switching losses in the FETs. As we have already stated, the magnitude of switching losses depends greatly on the FET driver circuit design. In a well designed high quality controller the switching losses will be fairly low, so avoiding PWM won't be as helpful in reducing controller heat. But there's much more.

The throttle is only a "request" to the controller to increase the PWM duty cycle. The controller also takes into account the battery current and an estimate (or a measurement) of the motor current in deciding the actual PWM duty cycle to use. If these values are nearing their limits the controller will override the throttle input and not allow full duty cycle to the FETs anyway. This occurs at low speeds where the back EMF is low. So using WOT at low speeds will not provide 100% duty cycle anyway, so switching losses are not reduced. Above some speed the back EMF from the motor is high enough to limit these currents and only then will the controller go to 100% duty cycle. Applying WOT above this speed will reduce those switching losses, however much they might be. The speed above which this full duty cycle is available is a function of the battery voltage, motor winding, system resistance and the values of the battery and motor current limits. The more voltage your battery has the higher speed will be required before this full duty cycle will be available. So called "torque windings" are really higher voltage windings, and these reduce the speed at which 100% PWM can be reached, whereas "speed windings" will increase this speed due to the greater or lesser back EMF the motor produces. But there's still more.

There may be an optimal throttle setting for going up a hill. It isn't easy to find this value, but it is easy to find some "wrong" throttle settings. For example if we set the throttle to make enough torque to exactly compensate for the gradient the velocity will be zero, and there will be no progress up the hill (assuming we don't pedal) and power will be consumed till the battery is exhausted or something fails, depending on the power level and the dissipation capacity of the controller and motor. So clearly there is a throttle setting that is too low.

As we apply more throttle the torque goes up in proportion to motor current, while the power dissipated goes up with motor current squared. The time it takes to climb the hill goes down with distance divided by speed. The total integral of the power dissipation goes down as this time becomes shorter, but it goes up with the power dissipation. The difficulty of climbing the hill also increases as the air resistance goes up with higher speed. There will be some throttle setting that will minimize this integral of dissipated power to top the hill, but this could be at a setting that is lower or even higher than WOT. So there may be an available optimal choice for the throttle setting, but it is unlikely that wide open throttle is precisely it. It depends on the setup and on the hill. Other factors enter such as the safe speed to navigate the terrain. At high speeds on the hill the additional air resistance loss becomes a factor, so the best throttle setting is likely the one that produces only moderate speed.

For some combinations of hill and ebike system there will not be an optimal throttle setting, the system just doesn't have enough torque. For those you just need to pedal up the hill. Applying the throttle will provide some help and heat the motor and controller, they may or may not overheat before the crest is reached. The more throttle you apply the more power dissipation and the higher temperature you will reach. Applying WOT in this condition will produce the maximum help and the maximum temperature. It may destroy the motor or controller as well, so saying WOT is optimal here is questionable.

If the controller is getting hot and the motor is not, then you don't have enough controller. Better quality or more FETs in parallel is indicated.

If you have enough controller the motor temperature will be the indicator to watch, the controller won't be as hot as the motor. Set the controller's battery and motor current limit to reasonable values for each device's capability. The motor current limit should be set high enough to push the motor, but not high enough to reach magnetic saturation where losses grow even faster. Then you can pedal hard and use WOT at low speed (even though the controller PWM limiting may not reach 100% duty cycle), the goal being to get to a reasonable speed for the hill, reducing the throttle and pedaling to continue at moderate speed, and watch motor temperature. If the motor is heating too much your only choice is to reduce throttle and pedal harder.