Author Topic: DC Motor Driver.  (Read 8640 times)

Offline Stot

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DC Motor Driver.
« on: May 12, 2012, 05:12:20 AM »
Hi,

I have a DC 180v 1250w 4400rpm motor from a treadmill that I'm going to put on a belt grinder I'm building.   Unfortunately the treadmill was an advanced type lots of ICs, no pots etc and I cant use the control board that came with it to power the motor.

I have seen a 240v DC 1000W SCR Motor Speed controller on ebay.  My understanding is that this would drive and even overdrive the motor but not quite at full torque is that right?

So I could expect to see up to 5800rpm at full speed but would only see 80% of the full power the motor is capable of?

Cheers
Stot
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Offline hopefuldave

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Re: DC Motor Driver.
« Reply #1 on: May 12, 2012, 07:55:21 AM »
Hi Stot,

I can only speak from my own experience, but I'd recommend one of the KBIC speed controller boards, probably the KBIC240 for that motor load and supply voltage, as they have Useful Features like current limiting, presets for max/min speed, IR compensation (helps maintain motor speed under load).
 The max speed setting basically sets the max voltage to the motor armature, so you can stick a meter on it and be sure you don't go over your motor's 180V rating, and the plug-in current-limiting ("HP") resistors let you set an initial ballpark limit for motor horsepower *before* trimming it a bit with the CL setting on the board - probably the 1+1/2 HP @ 240V would be a good choice.

 Wiring in is about as simple as you could get, 2 wires for 220AC in, 2 wires to the motor, 3 for the potentiometer to set the speed. BE WARNED - the potentiometer is at half line voltage and shorting its leads to earth (ground) WILL kill the board instantly... Don't ask me how I know... (OK, OK, it wasn't mine, it was a customer's "rewire"!)

I'd suggest putting a fuse (10A would be plenty) between motor and controller as well as the fuse and switch on the AC side, could save the PCB if the motor fails short-circuit or you have a major overload-and-stall - stalling a DC motor can send the current way higher than the nameplate current!

If you're planning to reverse the motor, it's pretty important to cut the power to the board *before* reversing the motor connections, the induced voltage from generator-effect in the motor can be a fair bit higher than the actual motor voltage, so you need the motor to slow before throwing arcs in the switch / spikes at the speed control board!

Dave H. (the other one)
Rules are for the obedience of fools, and the guidance of wise men.

Offline Stot

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Re: DC Motor Driver.
« Reply #2 on: May 12, 2012, 01:48:32 PM »
Thanks Dave,

The KBIC is the away to go, if it were for me.  The grinder is for a... Ill say 'frugal'... friend so hes trying to get everything on a budget of nothing :doh:.

The 1000W one is ~£22 and by my reckoning should get me ~1.3hp out of my motor rather than the ~1.7hp its capable of? which I think would be enough for the grinder.

Saying that I may be able to get a 240D for not too much more than the 1000W one I've seen pending inquiries and luck.  :med:

Cheers
Stot
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Offline andyf

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Re: DC Motor Driver.
« Reply #3 on: May 12, 2012, 06:24:31 PM »
Dave H will know much more about this than me, Stot, but personally I'd be wary of running a 1250W motor off a controller which is only good for 1000W. That said, if it's just powering a grinder, the motor probably won't ever be required to run at its max HP and thus draw 1250W, so you should get away with it.

I use a KBIC240 (max output voltage 180VDC, I think; I'm away in France just now so can't easily look it up) to power a 220V treadmill motor which alleges itself to be 2HP, and it works just fine. As Dave says, they are simplicity itself to wire up if you don't need to reverse the motor. But mine cost around £70 three or four years back, so your eBay job would be more economical. I'd be interested to see the eBay offering; after the auction is over would be fine if you don't want to publicise it widely while you are bidding.

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline Stot

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Re: DC Motor Driver.
« Reply #4 on: May 12, 2012, 07:20:41 PM »
This is the controller.  Its a BIN so no bother about bidding.

http://www.ebay.co.uk/itm/230759601008

Cheers
Stot
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Offline Stot

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Re: DC Motor Driver.
« Reply #5 on: May 16, 2012, 03:33:31 PM »
This board looks equivalent to the KBIC-240 to me and should run my motor well.

http://www.grahammotorsandcontrols.com/products/s1000.php

I can get it ~£30-£50, Import VAT dependent, so looks a better option than the 1000W version.

Cheers
Stot
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Offline Stot

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Re: DC Motor Driver.
« Reply #6 on: May 20, 2012, 08:07:21 AM »
Well I ended up finding another 'broken' treadmill locally for £20 and it actually worked fine once I bent the dead man switch key to stop it pushing its-self back out, i managed 9 mins of a 15min workout...  :palm:

This one had a 200V DC 2.75hp motor in it and the controller is a 230vdc 8a continuous, 12a max and can be controlled with a 4K7 pot instead of the digital panel.  :clap:



Cheers
Stot
Chronographing: www.chronoconnect.com