Controller Question For Electrical Gurus

[dumbass]

I run twin brushed motors 24v 450w with twin 35a controllers. I want to change to a single controller (24v) so I am assuming I need a 24v 70a controller for brushed motors. Right??? I want to maintain the option to run a single motor or both motors using switches to turn on/off each motor. My question is what will happen when running a single motor on this high amp controller? Is this going to over power the motor or ??? For that matter if I use a controller with say 100a capasity is this going to be a problem even when running both motors? Or is there a maximum amount of current the motor will take and therefore, no big deal?

Here's a few of the controllers I am considering; The basic difference between them is cost, Continuous current rating and the last offers is a 24v/48v.

http://kellycontroller.com/kds24100100a12v-24v-mini-brushed-controller-p-73.html
http://kellycontroller.com/kds24100e100a12v-24v-mini-brushed-controller-p-74.html
http://kellycontroller.com/kds24200200a12v-24v-mini-brushed-controller-p-76.html

http://kellycontroller.com/kds48100e100a24v-48v-mini-brushed-controller-p-285.html

Bob

 

[dumbass]

No one has a thought?

 

[amberwolf]

Sorry, been sick last week and a half, so not poking into new threads much.

I run twin brushed motors 24v 450w with twin 35a controllers. I want to change to a single controller (24v) so I am assuming I need a 24v 70a controller for brushed motors.

Mmmm...running parallel motors on one controller will work, but any difference between them means that one motor will get more current flow thru it than the other. Dunno if that will make a difference in operation compared to one motor per controller.

Personally I would prefer the separate controllers just for the backup capability, so that if one dies the other controller and motor will continue and get me home.

I used to use a single rebuilt/modded controller for the twin ex-fan motors on DayGlo Avenger's friction drive, and it worked fine until the night one of the shafts broke from a big bump. At that point there was no load on that motor, so it revved way way up and the other one just got no power to it, until I cut the wire to the broken one.


Unless your existing controllers are limiting the power the motors take, it won't make any difference how powerful the controller is, as far as how the motor reacts to it--only how much throttle you use does that. A motor only pulls as much power as it is loaded to and fed by throttle. Even a 50000-amp controller wouldn't feed any more power to the motor than a 50-amp controller, as long as that motor isn't being loaded enough to take more than 50 amps.

However, if the controller is limiting power, to 35A, then a controller with a higher limit is going to supply more power to the motors when in individual mode, so that it draws as much total power as it is physically capable of, up to the 70A limit of the new controller.

When running both motors, the limit would still be the same as before, as each gets half the current (assumign they're identical).

So if you can also switch the current limit on the controller down to 35A at the same time you switch off a motor, it should essentially work the same as a single controller.


With the extra complication, you might be better staying with the existing pair of controllers. What particular reason is there to change to a single one?

 

[dumbass]

Sorry, been sick last week and a half, so not poking into new threads much.

"mmm...running parallel motors on one controller will work, but any difference between them means that one motor will get more current flow thru it than the other. Dunno if that will make a difference in operation compared to one motor per controller.

Personally I would prefer the separate controllers just for the backup capability, so that if one dies the other controller and motor will continue and get me home.

I used to use a single rebuilt/modded controller for the twin ex-fan motors on DayGlo Avenger's friction drive, and it worked fine until the night one of the shafts broke from a big bump. At that point there was no load on that motor, so it revved way way up and the other one just got no power to it, until I cut the wire to the broken one.

Unless your existing controllers are limiting the power the motors take, it won't make any difference how powerful the controller is, as far as how the motor reacts to it--only how much throttle you use does that. A motor only pulls as much power as it is loaded to and fed by throttle. Even a 50000-amp controller wouldn't feed any more power to the motor than a 50-amp controller, as long as that motor isn't being loaded enough to take more than 50 amps.

However, if the controller is limiting power, to 35A, then a controller with a higher limit is going to supply more power to the motors when in individual mode, so that it draws as much total power as it is physically capable of, up to the 70A limit of the new controller.

When running both motors, the limit would still be the same as before, as each gets half the current (assumign they're identical).

So if you can also switch the current limit on the controller down to 35A at the same time you switch off a motor, it should essentially work the same as a single controller.


With the extra complication, you might be better staying with the existing pair of controllers. What particular reason is there to change to a single one?

Soory about your illness, hope your feeling better now. You didn't pass any germs onto my thread did you? LOL

I totally agree and would prefer to stay with twin controllers. The problem with my current controllers is they don't play nice together. Hence, I have to use twin throttles and they have to be mounted on the same hand (right). I know others use a throttles but one on each hand. I can not do that because of my Nuvinci shifter on the left. I indicated in an old thread that my controllers will falt if wired to the same throttle. One or the other always get a feed back from the other causing it to shut down. I and others on the forum concluded that maybe diodes on the 5v output of the controller may prevent the feedback but of cours cause some lose of power. So I thought I would try a single large controller and switch the motors individually on/off and needed.

Bob

 

[amberwolf]

Another method would be to use Op-Amps (each powered by it's own controller) to isolate each controller from the single throttle, and power the throttle from only one controller.

There are a number of 8-pin DIP single or dual-op-amp chips that should run on 5V ok, and operate rail-to-rail, to be able to copy a single throttle's output voltage into a pair of non-inverted but high-impedance-buffered outputs to run to each controller.

The basic circuit is the second one here:
http://www.pic101.com/op_amp.htm
Figure 21, and is very simple to build. Since you want zero gain (1:1 ratio of input to output), the input resistors and feedback resistor are identical (almost, there is a bit of fiddling to get this, see the formula on that part of the page). Higher values (100Kohm and up) are probably better for isolation from one controller to the other, in general.

Build two of these circuits, and connect the throttle's signal output wire to the non-opamp-end of the input resistor on both. Connect the output of each opamp to one controller. The whole thing can fit in a space the size of the end of your thumb, or less. If you prefer, you could stick each opamp circuit inside each controller's housing, secured down somewhere out of the way.

Since it is possible that both controllers/motors don't respond exactly identical to the throttle, and there are tolerances in resistors, use a potentiometer for one of the feedback resistors in one opamp circuit, and tune it so that both controllers respond identically.


If you find you can power both opamps from a single controller and still feed their outputs to the pair of them, then use a dual-opamp chip to save space. Otherwise use two single-opamp chips and power each one from it's own controller.

If I did it right, this link should go to a Mouser search already narrowed down to 24 possible easy-to-work-with (physically) chips, in single and dual opamp packages:
Mouser Search

I've used this one:
http://www.mouser.com/ProductDetail/STMicroelectronics/LM358AN/?qs=sGAEpiMZZMtCHixnSjNA6NYMOzdu7NqZVYO9CfoYmkQ%3d
this one:
http://www.mouser.com/ProductDetail/STMicroelectronics/LM358N/?qs=sGAEpiMZZMtCHixnSjNA6NZSRdSRwPq0Mk%252bI3N7wYew%3d
and this one:
http://www.mouser.com/ProductDetail/STMicroelectronics/LM2904N/?qs=sGAEpiMZZMtCHixnSjNA6MwNigq1a7AoalbK%2fMMy2lY%3d
for buffering signals before, in non-bike related projects.

There is also info here:
http://en.wikipedia.org/wiki/Operational_amplifier_applications
about various opamp stuff, and lots of good electronics tutorials around online, should you want to delve deeper into it.

 

[johnrobholmes]

You should be fine with one controller, but if a wheel comes off the ground or starts running faster it would allow the other motor to start taking more than half the amount of current since the other wheel is spinning faster. Don't try to ride wheelies up hills, make sure the front wheel isn't peeling out, and one controller should be just fine.

Now that I think about it, would the rear motor naturally want to take more load going up a hill since it has more weight on it? Like carrying a fridge up stairs and being on the lower end?

 

[Wattever]

IMO you should be fine with one controller to both motors, however, you should be able to connect both controllers to the same throttle. have you tried connecting one controller to its throttle and adding only the ground and signal leads from the second controller? are these the same controllers?

 

[dumbass]

WOW. dude you are way over my head on this one. But I'll take another run at it when I'm sobbor but I don't think it will help. Electronics is my thing. Thanks, Bob

 

[dumbass]

You should be fine with one controller, but if a wheel comes off the ground or starts running faster it would allow the other motor to start taking more than half the amount of current since the other wheel is spinning faster. Don't try to ride wheelies up hills, make sure the front wheel isn't peeling out, and one controller should be just fine.

Now that I think about it, would the rear motor naturally want to take more load going up a hill since it has more weight on it? Like carrying a fridge up stairs and being on the lower end?

YOur misunderstandingthe setup. I am running non-hub motors and they are both connected to teh rear wheel.

 

[dumbass]

IMO you should be fine with one controller to both motors, however, you should be able to connect both controllers to the same throttle. have you tried connecting one controller to its throttle and adding only the ground and signal leads from the second controller? are these the same controllers?

Yeah, they are both Currie 35a matching controllers. I thought I tried connecting the controllers in every way I could think of but I will try again. Teh problem was everytime The problem is I could make it work but as soon as I powered up the second controller the back feed of 5v from the first controller would cut off the second controller. I am assuming it is a built in safety and the controller thinks there is a short and shuts down. But the first controller (no matter which it is) always runs fine.

Bob

 

[johnrobholmes]

YOur misunderstandingthe setup. I am running non-hub motors and they are both connected to teh rear wheel.

If this is the case it won't matter if it is one or two controllers. You can wire the motors series or parallel. Series will half the speed vs one motor, parallel will half the resistance and double the amp draw vs one motor.

 

[dumbass]

YOur misunderstandingthe setup. I am running non-hub motors and they are both connected to teh rear wheel.

If this is the case it won't matter if it is one or two controllers. You can wire the motors series or parallel. Series will half the speed vs one motor, parallel will half the resistance and double the amp draw vs one motor.

I would be paralleling the motors. But the existing controllers I have are only rated at 35a. So not matter how mucg the motors wanted to draw they would be limited to 35a. That's why I was looking at the ladger controllers that putouy a constant 60a or 80a. With one of these controllers and wiring the 2 motors in parallel I should have plenty of power. But if I switched both motors so I could turn one or the other off when added power isn't needed I could run a little more efficently. Right?

Bob

 

[TylerDurden]

But if I switched both motors so I could turn one or the other off when added power isn't needed I could run a little more efficently.

The opposite.. two motors will run more efficiently: each one is carrying half the load (half the current).

 

[johnrobholmes]

But you would also have twice the no load current. It is more efficient to use one larger motor.

If you switched off one motor while using one controller, you would have to be careful that you didn't feed 80a through the single motor.

 

[dumbass]

But you would also have twice the no load current. It is more efficient to use one larger motor.

If you switched off one motor while using one controller, you would have to be careful that you didn't feed 80a through the single motor.

OK, so based on what you and Tyler are saying it sounds like my best bet is to use 1 large controller (lets say 60 to 80a) and only run on 1 motor in an emergency if a motor failed. That way I still get home but need to be careful. Agreed?

 

[johnrobholmes]

That is certainly how I would do it.

 

[liveforphysics]

Parallel brushed motors works on paper, sucks in practice. Go series. It's forces current to be matched in the motors.

 

[johnrobholmes]

As long as they are pretty closely matched, they work well enough. While I agree that series is best for load sharing when they are connected together, is there an easily available brushed controller that can take twice the voltage?

The downside to running then in series is that if one gives out, you are forced to rewire them to limp home. With a parallel setup you can remove a brush or clip a wire and continue.

 

[liveforphysics]

Yes. 48v brushed controllers are not a rare item.


With series, you just jumper the failed motor out, or snip the leads and twist them together or whatever. It's not like it's a lot more difficult or something. With series, not only are much much less prone to having a motor failure (due to inherently perfect current sharing), but if you get a failure, it doesn't take your controller down with it.

 

[dumbass]

Well now I'm confused again. The way I would understand it is in parallel and running at 24v the motors could actually run slightly out of sink with each other because they are likely not perfectly match. However, the way I felt was so what.....so motor A works a little harder then motor B. But if ether motor goes down and is wired to an on/off switch all I do is turn off the failed motor. However, if I wire the motors with a 48v controller in series this assures the motors stay perfectly in sink and both motors do exactly the same amount of work. While this is a better situation as long as both motor are running it creats a problem if one motor fails. Should a motor fail and the controller is 48v when I turn off the failed motor the remaining motor is now getting the full 48v. I'm thinking htis is not a good thing. John.....your saying this is not a problem? How so? Please elaborate so I can understand. Thanks guys, Bob

 

[Wattever]

You said both your motors are the same, and both are connected to the same rear wheel, they will pull approx the same power.
You really should parallel them and use 24V, have you tried using both controller with the same throttle when only one controller feeds the +5V (red) of the throttle?

 

[johnrobholmes]

If you did run a 48v controller you would need to use roughly half throttle to keep from blowing a single motor, in case of an emergency ride. From an electrical standpoint the 48v system is superior otherwise. Half the amps, easier on the batteries, less copper loss in the wires. Either way will work, just decide what your needs are for limping home, if you even care about that situation.

 

[dumbass]

You said both your motors are the same, and both are connected to the same rear wheel, they will pull approx the same power.
You really should parallel them and use 24V, have you tried using both controller with the same throttle when only one controller feeds the +5V (red) of the throttle?

Yeah, I have tried using both controllers with 1 throttle but I can't get it to work because of voltage feedback on the +5v. Only 1 controller will actually work at a time. But I am going to retest.

Bob

 

[dumbass]

If you did run a 48v controller you would need to use roughly half throttle to keep from blowing a single motor, in case of an emergency ride. From an electrical standpoint the 48v system is superior otherwise. Half the amps, easier on the batteries, less copper loss in the wires. Either way will work, just decide what your needs are for limping home, if you even care about that situation.

Is the throttle controlling the controllers voltage output or amperage. I really do worry about limping home on one motor that's why I have 2 of them. I had a single motor bike crap out on me 2 years ago. I was about 10 miles from my car. My knees are over due for full replacement and it nearly killed me peddling the 10 miles without any motor assist. Actually it would come on for about a 1/2 mile now and then so when it was running I ran it as fast as I could go. Got back to me car and had to rest before loading it on the car. So it is supper important to me to have a backup system. And yes I do carry a spare throttle with me and even presized chains and tube patches too.

Bob

 

[johnrobholmes]

The throttle controls both amperage and voltage.

Really there is no best method in case of failure. If you wire them parallel, there is a chance of overamping one motor if ran alone. If ran in series, there is a chance of over volting a motor if ran alone.

Did you try tying the grounds together between your controllers to help the throttle issue? Sounds like a floating ground problem, which I have seen discussions on how to solve this.