Hi,
I am need to control a 12v motor that has a stall current of 68 Amps.
What is the best way to control this motor?
I was thinking combining 2 vnh5019 dual motor controllers might work. I am going to combine four of these motors so I was thinking I could get six vnh5019’s and have each motor use 1 and a half.
Thanks for all help,
Joel
Do you need PWM?
Parallelling H bridges is dangerous, because there will be some difference in timing between them, and during that timing, you will see shoot-through from one H-bridge to the other, which may very well fry the bridges.
Is 68A the instantaneous max stall current, or a continuous-duty current? If stall, then your continuous duty current shouldn’t be more than about 15A, so something like a 60A Sabretooth controller should deal with it (it’s rated for up to 120A for very short pulses) or the RoboClaw 2x60A (same thing there; rated for higher fast-pulse current.)
Another brand that’s more towards industrial automation is Roboteq. For example, the LDC1430 does 30V and 120A (I don’t know if those are 120A-peak or 120A-continuous.)
Or you can build your own, with some fat discrete N-channel MOSFETs like IRFB75400 and high-speed N-channel MOSFET drivers like Intersil 83204.
However, at those current levels, the real problem is not part selection; it’s PCB design to avoid melting or de-laminating the traces, and cooling for the switching parts…
This is the motor:http://www.robotmarketplace.com/products/AME-226-3003.html
It has a stall current of 68 amps.
What is the difference between PWM and Analog, in terms of motor control?
I want to have the most variations of speed possible, so if the motor runs between 0-100rpm and I use an Analog pin does that mean that I have 1024 different speeds between 0-100rpm? Does PWM only give me 255?
On the description of the VNH5019 is says that it can provide continuous 24 A (60 amp max) to one motor, how would I control the motor if it is connected like that?
If I were to build a great cooling system (multiple fans, heat sinks, and thermal compound) for the VNH5019, would that increase its continuous current rate? If so by how much?
I was looking at the RoboClaw and it looks awesome, however it is expensive and I would have to buy 2 so it would cost me $100 more than 6 VNH5019. If there is any way to use the VNH5019 I would prefer, but I DONOT WANT TO SACRIFICE QUALITY FOR COST, would it be better to use the RoboClaw or VNH5019?
The analog pins on an Arduino are INPUT not OUTPUT. Thus, there is no getting 1023 different duty cycle values from an analog pin on an Arduino.
If you use a Leonardo or Mega, those have a few timers that have better resolution (up to 65536, although then only at 240 Hz.) You can custom control these timers to generate higher-resolution duty cycles, but that’s not supported by the default Arduino library AFAIK.
There existed, in the old pre-historic times, something called “motor amps” which worked much like regular loudspeaker amplifiers; provide more analog voltage for louder volume. Unfortunately, this requires BJT transistors that bleed off a lot of heat and thus become very inefficient. PWM achieves the same thing by switching the signal fully-on and fully-off very quickly, so it averages out. Switching “fully on” without loss is quite effective using MOSFET transistors, assuming you can switch them on/off fast enough.
If the rated stall current is 68 Amps, then using any controller with an impulse rating less than 68A is unlikely to be safe. Most controllers will shut down and give an error signal if they see anything exceeding the rated load. And, when you switch direction of a motor, it may temporarily look like up to twice the rated stall current (!) so you really want something rated 120A for that to be robust.
I’d go with the RoboClaw 2x60A, or the Robotech 2x120A, if you need servo (closed loop, encoder) control, and the Sabretooth 2x60A if you don’t need encoder support.
I don’t know how much harder you can push the VNH5019 with active cooling – if I were to guess, I’d say that the specs in the data sheet for that part assume efficient cooling of some sort, so you could look it up there. Or perhaps our friends from Pololu staff have a better answer?
Hello, Joel and jwatte.
In single-channel mode, the VNH5019 shield might work with your motor, but the motor drivers that jwatte suggested would probably be safer. You can find instructions for using the VNH5019 shield in single channel mode in the “Using the Driver in Single-Channel Mode” section in its user’s guide.
Please note that the VNH5019 has over-current protection that might kick in before reaching the stall current of your motor (the driver’s over-current protection can kick in as low as 30A per channel, so in single-channel mode, it might kick in as low as 60A). Unfortunately, we have not characterized our drivers with heat sinks, so I cannot say how much more current it can handle continuously with sufficient cooling. If you do try it, we would love to hear about it.
- Jeremy
I am leaning towards the Roboclaw 2x60A because I would rather be safe than sorry. I get the motor today, I will hook it up to my car battery and use an ammeter to determine how many amps it take during operation (I will just set it to full speed).
Unfortunately, a free-running motor will only draw a fraction of its full power, because there is nothing to exert power against. Your measurement will show how much the motor draws when there is no load, which may be interesting for certain characteristics, but not particularly useful to determine what max draw or even working (with load) draw will be.
