# Need advice on controllers



## TX_Dj (Jul 25, 2008)

Clyde,

If you're dead set on building a controller as an exercise, then by all means don't let me stop you.

It just seems more sensible to buy a pre-built controller for something that size. A 30A 36v controller for that type of motor is only about $40-60. I have one that I use in my little scooter, it works great. It's no speed demon, but I've won the NTEAA Scooter Challenge Championship two years in a row with it.


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## Clyde (Jun 11, 2010)

Hmm- in that case I think I'll look into that instead... one thing has been confusing me though... I see some motor controllers that are advertised as being rated for 30A 36V and 500W but wouldn't the wattage actually be 1080W? or is there some reason it is shown lower...


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## TX_Dj (Jul 25, 2008)

Could be a very inefficient design with inflated numbers (i.e. showing what you'd get for amps on the input side, rather than the output side). Could be 500w continuous with 1000+ in spurts.

Mine would hold 30A until it blew, if the motor was geared tall enough. I've had it geared such to go about 20-25 mph top speed, and even climbing a stiff hill (which it didn't like, performance-wise) the controller was still barely warm. 

Geared for about 15-17 mph, it will hold a reasonable speed up the same hill, and accelerates much quicker.

But, if your application needs more torque, you'll need bigger amp capability. There doesn't seem to be much in the 36v range to bridge you from 30A to 300A, the next size up controller that I see that I would trust to deliver anything remotely near its rated capacity is an Altrax unit, which is about $300.

I found some controllers that looked promising a while back, rated 100-180 amps at 36v, but they're really designed for some sort of RC application, I'm not sure how reliable they would be at even half the rated current output.

Depending on how heavy this moped is, that motor is probably undersized, or you will have a hard time coming up with a cheap controller. My scooter has a curb weight around 70 lbs including batteries.


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## major (Apr 4, 2008)

Clyde said:


> Hmm- in that case I think I'll look into that instead... one thing has been confusing me though... I see some motor controllers that are advertised as being rated for 30A 36V and 500W but wouldn't the wattage actually be 1080W? or is there some reason it is shown lower...


Don't know for sure cause I ain't seen the spec sheet. But could be a 30 amp current limit and 500 watt continuous rating. And you don't want to skimp on the controller. Look into one with a 50A current limit and maybe 800W rating. Or even bigger. Might be a few bucks more, but work a lot better.


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## Clyde (Jun 11, 2010)

Does this one look any good- or is it at least worth the money?

http://cgi.ebay.com/ebaymotors/Electric-E-Scooter-36v-1000w-Controller-Throttle-Kit-/170395874327


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## major (Apr 4, 2008)

Clyde said:


> Does this one look any good- or is it at least worth the money?
> 
> http://cgi.ebay.com/ebaymotors/Electric-E-Scooter-36v-1000w-Controller-Throttle-Kit-/170395874327


Hard to say. I think it would be marginal at best. The 1000W rating is likely for max voltage, 60V. So at 36, you're at around the 650W which you say is the rating for your motor. It says it is for a minibike and I think your bike is larger. It may be a good controller for what it is. Is it right for you? Looks wimpy to me, but I'm used to big ones


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## Clyde (Jun 11, 2010)

I got a 1000w 36v controller, and the motor seems to be able to push the bike a little bit without me on it, but when I get on the bike it cannot move-

Also it is making this loud high-pitched whine...

Is this because the motor just isn't strong enough?


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## major (Apr 4, 2008)

Clyde said:


> I got a 1000w 36v controller, and the motor seems to be able to push the bike a little bit without me on it, but when I get on the bike it cannot move-
> 
> Also it is making this loud high-pitched whine...
> 
> Is this because the motor just isn't strong enough?


How is it geared? What is the battery voltage and current when this happens?


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## Clyde (Jun 11, 2010)

I'm supplying 36v to the controller from a lab power supply, the voltage to the motor is 7 volts when I'm sitting on the bike, and its sitting still.
I'm not sure how to measure the current through the motor though.

The gear on the motor has 9 teeth and the gear fixed to the rear wheel has 42 teeth, giving a ratio of 3:14


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## Tesseract (Sep 27, 2008)

Clyde said:


> I'm supplying 36v to the controller from a lab power supply...


Is that a *30A* lab power supply? Because if it isn't then you aren't actually testing the controller, you're testing the power supply's current limiting circuit...


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## Clyde (Jun 11, 2010)

The power supply maxes out at 8 amps- but the controller is only drawing 3-4 amps when I'm on the bike and its trying to move but not moving...


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## major (Apr 4, 2008)

Clyde said:


> I'm supplying 36v to the controller from a lab power supply, the voltage to the motor is 7 volts when I'm sitting on the bike, and its sitting still.
> I'm not sure how to measure the current through the motor though.
> 
> The gear on the motor has 9 teeth and the gear fixed to the rear wheel has 42 teeth, giving a ratio of 3:14


Hi Clyde,

It sounds like to me that the system is in current limit because of excessive load. And this is because your drive ratio is way, way off. I'm thinking you need like a 20:1 ratio, off the top of my head. Figure it out. What is the rated speed of that motor, like 4000 RPM. Go thru the math and set that equal to 10 mph. What reduction ratio do you get? Ain't 4.67:1 which is what you have now, is it?

major


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## major (Apr 4, 2008)

Clyde said:


> The power supply maxes out at 8 amps- but the controller is only drawing 3-4 amps when I'm on the bike and its trying to move but not moving...


So you're testing a 1000 watt controller with a 288 watt supply


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## major (Apr 4, 2008)

Clyde said:


> The power supply maxes out at 8 amps- but the controller is only drawing 3-4 amps when I'm on the bike and its trying to move but not moving...


And the other thing, power supplies act differently than batteries. The power supply can be limiting the "on pulse" where as the battery supply the full "on pulse". That may be why the controller is limiting to only about half of the power supply limit.

But if you have only 4A at 36V going to the controller, you got 144 watts. And less than that to the motor. Likely less than rated current and therefore a fraction of torque as opposed to 3 to 5 times torque like I spoke of earlier.


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## Clyde (Jun 11, 2010)

Tried hooking up some batteries, and got the same result as with the power supply...

It's probably the gearing... which is going to be trouble since the rear sprocket is bolted directly to the wheel. I suppose I'll have to unbolt that and swap it out for something else-


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