RC controllers and current limit questions

Are there any controllers that have a manually adjustable current limit? And, also, is it ok to use a "20 amp" controller with this motor?

Would a ping battery trip if it were used with a 20 amp controller(and it can sustain 25 continuous amps)?

Are RC controllers functionally equivalent to crystalyte controllers in terms of the relationship between v_motor and throttle and the current limiting region? That is, would 50% throttle convert 48 volts from the battery into 24 volts fed to the motor assuming the battery current isn't being limited? And do RC controllers limit the battery current or the motor current?

I am not aware of any rc controller that has an adjustable current limiter function. The CC controllers have the ability to limit the current to the max the controller can handle or no current limiting. If your 20 amp controller can limit itself, then it may be safe to use with your motor. if all you want is 20 amps, you could use a smaller motor.

I would not expect the over current limiter of the bms on the Ping battery to trip at 25 amps. Max amps on his smallest battery is 45 amps.

I believe the controllers for brushless motors use PWM. My understanding is that the pulse going from the controller to the motor is full battery voltage ( minus voltage drop though the electronics). Averaging the pulses over time gives you the current draw from the battery.

The load on the motor determines how much current is needed. Unless the controller has a max current function, it does not limit the current from the battery or going to the motor. The controller will try to give the motor all of the current it asks for. If that exceeds the capacity of the Fets in the controller, then the controller blows. It all has to to do with that back emf stuff.

Just remember that these answers are roughly right.

Bubba

Most of them are fixed as far as I know. Some may be programmable.

I designed an add-on current limiter that ties into the servo tester a while back. This seemed to work well and was adjustable on the fly. The actual interface is dependent on the servo tester used, so the schematic I have may need tweaking.

I'll try to locate that one (on another computer).

dontsendbubbamail said:

The controller will try to give the motor all of the current it asks for. If that exceeds the capacity of the Fets in the controller, then the controller blows. It all has to to do with that back emf stuff.

Click to expand...

Oh crap. I hope I didn't blow my 20amp pedal first controller. My simulator seems to predict the current the motor will draw at lower speeds would be at about 70 amps whereas the >407 motors demand 40-50ish amps. I noticed that Justin guaranteed the controller on 48 volts for the 407,408,409,etc. motors and all the 40x motors at 36 volts suggesting that my controller might be destroyed by the motor which is as current hungry, if not more, than say the 404. I'm using a 48 volt battery, so I was getting a little concerned...

If they blow, I can just replace the FETs, right? Or... when they "blow"... they actually short out, don't they? That doesn't seem good.

fechter said:

Most of them are fixed as far as I know. Some may be programmable.

I designed an add-on current limiter that ties into the servo tester a while back. This seemed to work well and was adjustable on the fly. The actual interface is dependent on the servo tester used, so the schematic I have may need tweaking.

I'll try to locate that one (on another computer).

Click to expand...

I was noticing that the "most programmable" RC controller out there, the Castle Creations ones, didn't have an explicitly programmable current limit. The closest that they seemed to have was throttle profiles... but I'm not sure that'd work as effectively as I'd imagine.

Anyways, with your idea, are you suggesting that limiting the throttle signal can be used to limit the battery current? I was planning on creating my own arduino-based throttle system, and if the battery current can be sensed somehow(Possibly halls? Shunt resist?), then i guess the arduino can automatically adjust the throttle signal to keep the battery current in check and provide "ramping up" on the battery current so it won't get near the battery's current cut out. But, yes, please add your schematic as it may be very helpful. Is it a "throttle divider" in a sense, and the division amount is determined manually(By like, say, a pot and amp-meter)?

dirty_d made a good suggestion of using two smt resistors for current monitoring. http://endless-sphere.com/forums/viewtopic.php?f=28&t=4625&p=96093#p96093.

This build has another way of doing the current limiting. http://www.recumbents.com/mars/tetz/E-Assist.htm

Personally I am using a hall effect device to measure current and a Arduino for the control. I should say that I am providing design specifications to my buddy who is doing the programming. It has a max current setting and will reduce the throttle setting to say under the limit. There are two throttle input modes in the first version.

In mode one, the throttle input will be used to set the current level you want to run at. That would be between 0 and the max limit that has been set. This will give you a constant power input from the motor. Any pedaling makes you go faster and current is constant.

In mode two it acts as if you are using a servo tester as the throttle input with max current limiting. . The good thing is that you don't need to buy a servo tester and can use a pot or a hall effect throttle as the input. Any pedaling reduces the current draw and doesn't do much for increasing speed.

It is just waiting on me to get my new trailer together for some testing.

Bubba

I designed the current limiter for Tetz. As I recall, he snapped off the shaft of a motor before using the limiter circuit.

Here's what he finally ended up using:
He wanted a push button on/off throttle, but the same circuit would work for a normal throttle.
We had to really slow down the response of the amp (feedback capacitor) to prevent oscillation in the system.

The new Castle Creation industrial software seems to allow complete control over current limit:
http://www.castlespecialprojects.com/csp_software.html

Very interesting. But I also noticed that..

Castle Industrial Link (CIL) will only operate with controllers that are programmed at the factory to be compatible with the CIL system. CIL will NOT work with standard Castle controllers programmed with our RC controller code.

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So I take it that it's a special feature you have to ask for(Or is it exclusive for the Phoenix Ice system?). Also, I wonder if some sort of current ramping option is provided, but I guess that's a part of the throttle profile or whatever it's called.

Edit: I just noticed the phoenix controllers at the Castle Special Projects page are described as CIL compatible, so it seems it's an option! Now I wonder if they charge for the software.

P.P.S. It appears they do. It also has that ominous

Pricing: call Castle for details at (913) 390-6939 ext. 122

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Suggesting a tad more than 30 dollars. :lol:

Yes, you need to buy a controller configured to use it - I thought the cost of the software was included in the price of the controllers, for CIL, but I may be wrong... Anyway, you'd save the cost of the servo tester

swbluto said:

Are there any controllers that have a manually adjustable current limit? And, also, is it ok to use a "20 amp" controller with this motor?

Would a ping battery trip if it were used with a 20 amp controller(and it can sustain 25 continuous amps)?

Are RC controllers functionally equivalent to crystalyte controllers in terms of the relationship between v_motor and throttle and the current limiting region? That is, would 50% throttle convert 48 volts from the battery into 24 volts fed to the motor assuming the battery current isn't being limited? And do RC controllers limit the battery current or the motor current?

Click to expand...

The Castle Creations "HV" series has a variable current limiter; settings range in four or five increments between very sensitive/conservative, to a disabled limiter.

As Miles pointed out, CC's industrial software appears to only function with their industrial models.

I don't know how the crystalyte controllers function, but brushless RC controllers are effectively a DC-->AC converter. The brushless outrunners are electrically nothing more than three-phase AC motors. The R/C style ESCs measure back-EMF to accurately measure and regulate RPM...so no flimsy little wires or hall-effect sensors, are necessary. A 1-2ms length pulse-width-modulated (PWM) signal is used to signal your desired throttle position, and my $30 "servo tester" allows for very fine-grained PWM signals; translating into a very fine-grained throttle control.