# dc motor



## richerson (Mar 7, 2010)

Hi all

Is this any good?
http://www.ebay.co.uk/itm/Large-DC-...arts_Vehicles_CarParts_SM&hash=item4acb002b20


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## major (Apr 4, 2008)

richerson said:


> Hi all
> 
> Is this any good?
> http://www.ebay.co.uk/itm/Large-DC-...arts_Vehicles_CarParts_SM&hash=item4acb002b20


DC---good. 72V rated---good. Brush & comm look good. 4 equal leads--probably series wound---good. Usable shaft---good.

Nice motor. Looks like it weighs a lot. But I imagine it would run fine and put out a lot of torque.


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## richerson (Mar 7, 2010)

great.

ill see if i can win it.

I'm guessing that it should be ok for 144v if the writing on the side is correct. 72v 2200rpm 30.5rpm/v 144v * 30.5= 4392 rpm.

Can this sort of motor take that sort of rpm without self destructing?


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## major (Apr 4, 2008)

richerson said:


> great.
> 
> ill see if i can win it.
> 
> ...


144 battery will probably be o.k. And 4000 RPM will be probably be o.k. But, if this is a series motor, which I think it is, then RPM is more load dependent than voltage dependent. Look up the speed torque curve for series dc motors and notice how the RPM curve goes asymptotic at zero load. So you could run it to well over the 4000 RPM with 72V. That is why you can find like a thousand posts on here warning to never test (run) and unloaded motor with more than 12V.

So you take the ratio of voltage and proportion the RPM to get 4400. That only applies at the load. That load was 8 hp @ 2200 RPM, so 4400 would apply for 16 hp when on 144V. Lesser loads on 144V would be faster.

The good news is that your motor controller can reduce the voltage to the motor so you can avoid overspeed. Or you can permanently couple the motor to a load (vehicle drive) such that it is incapable of driving it that fast. Or get a tacho and speed limiter circuit.


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## richerson (Mar 7, 2010)

Ok I will look that up, next question how many amps?

Is this just trial and error. test at lower amps and see how hot the motors getting. Then increase in stages checking temps?


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## major (Apr 4, 2008)

richerson said:


> Ok I will look that up, next question how many amps?
> 
> Is this just trial and error. test at lower amps and see how hot the motors getting. Then increase in stages checking temps?



Do you understand that current (amps) is drawn dependent on load? So your question doesn't make any sense to me. What controller you use, battery you have, and load will determine what you ask. 

Since this is an older motor without a readable nameplate, it is a guess as to insulation class, so what is the allowable operating temperature?

Any idea of the truck it came from? What size? speed? controller?

I'm pretty familiar with motors and give you some opinions, but that's about it. You throw up some photos and ask if it's a good motor. But for what? You haven't said if your EV is a go-kart or a 10 ton truck. 10 mph or 100.


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## richerson (Mar 7, 2010)

I cant tell you much about the motor or what it came from. I have asked the seller and i'm waiting for a reply. The motor is hopefully powerful enough for a classic vw beetle conversion. partly why I was asking how many amps it could take is so I can choose a controller. My goal would be to have a top speed of 70mph but mostly used for driving around London, lots and lots of start stop in traffic so wants to have good 0-40mph time.


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## Hollie Maea (Dec 9, 2009)

I could be wrong, but that thing looks a bit more massive than I would put in a VW Bug.


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## z_power (Dec 17, 2011)

I've never seen one myself, neither do I know anybody who's sister's husband's father seen one  but I think it's so called "milkfloat motor" judging on size, coupling and location. Search for "milkfloat" here on forums...


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## richerson (Mar 7, 2010)

Great, thanks for the input, if it is a milk float motor it should be plenty powerful for what I want. It may be a little large for a bug, but i'll give a punt.


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## favguy (May 2, 2008)

Hi,

At 120Kg and that diameter, it is far too large for a classic beetle... a 9" diameter would be a much better fit.


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## richerson (Mar 7, 2010)

ok

9" motors about 70kg makes sense for a bug.

would the bigger motor be ok in a mazda rx8 or is it still to heavy?


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## jjmillsy (Jul 17, 2012)

Not sure whether you would have the clearance in an RX8 - I was reading one of skoolers threads and IIRC 9 or 10" should fit ok, but 13" probably wouldn't.

I did see this on ebay too, however the price has now gone up by £50!


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