How do I determine which controller to use

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Last seen: 12 years 11 months ago
Joined: Wednesday, January 2, 2008 - 13:50
Points: 13
How do I determine which controller to use

Back again in my attempt to gain some useful knowledge.
My basic question is how do I calculate if a controller will be sufficient for my use.
Specifically I am planning on running 24v through 2 350w motors in series (I'm assuming this is equivalent to 1 700w motor. Will a 24v 40a controller work for this application.

racermike39's picture
Last seen: 9 years 7 months ago
Joined: Thursday, November 15, 2007 - 09:21
Points: 127
Re: How do I determine which controller to use

Many here will be able to provide excellent info on this subject. My suggestion would be to email controller manufacturers with the same info you provided. Kelly Controls has always responded to my questions, and been very supportive after the purchase. I'm sure AltraX, Curtis, or any of their dealers would also be happy to help.

You can take the info provided by the manufacturers, and post further questions here based on the info provided.

Keep us posted on your project!

Mike K.

5 years ago I met Jesus and he total ruined my life. I have never been happier.

jdh2550_1's picture
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Joined: Tuesday, July 17, 2007 - 09:35
Points: 2335
Re: How do I determine which controller to use

Here's what I think (not sure so feel free to correct me!)

I'm not sure you can run two motors in series from one controller. You can run two in parallel though (andrew has done it on one of his project bikes).

A 24v 40A controller gives you a max wattage of 24*40 = 960W.

If wired in parallel then each motor will get the 24V and that 960W output will need to be split between both motors (i.e. 20A each in most simplistic form) - that means that each motor will get up to 480W.

That's probably not quite enough to get the max from your setup - although 480W is more than 350W - remember that 350W is the constant rating - a peak rating is probably 2 to 3 times that. So, if you want 700W per motor in parallel then you'll need a controller that can output 1400W, which at 24V requires a peak amperage of around 60A...

John H. Founder of Current Motor Company - opinions on this site belong to me; not to my employer
Remember: " 'lectric for local. diesel for distance" - JTH, Amp Bros || "No Gas.

andrew's picture
Last seen: 11 years 2 months ago
Joined: Tuesday, November 28, 2006 - 17:21
Points: 1361
Re: How do I determine which controller to use

John pretty much covered it. You can run two motors in series, but I don't think hendu wants to do that. That will result in full current to each motor, but half the voltage, and double the terminal resistance of the motor system (lower efficiency). Or, double the torque and half the speed, as if they were wired in parallel. In theory one could switch between series and parallel wiring of two motors for a sort of two-speed transmission, but this is really just a way to get more power past the bottleneck of the controller, and this is why it is done for racing. I could explain why, but that's not really the focus of this thread.

You most likely want to run the motors in parallel, and you will probably want a controller with double the amperage that would be suitable for one motor. I don't know the motor, and I don't know what your intentions are. Because 40 amps at 24v will provide 960 watts and the motors are probably about 80% efficient (just a guess) than this will provide a maximum of 768 watts output. As jdh mentions, you may want considerably more peak power depending on the application.

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Last seen: 12 years 11 months ago
Joined: Wednesday, January 2, 2008 - 13:50
Points: 13
Re: How do I determine which controller to use

Wow, just got back in town thanks for all the great info. I'll give a 40a 24v controller a go with the motors wired in parallel. I'm pretty much in the experimental, on the cheap stage, so that sounds perfect. Thanks again for all the info. I'll let you all know how it turns out.

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