# How much can you overvolt a motor



## itchyback (May 28, 2014)

So I was weighing up getting a new kostov or netgain vs a forklift motor. 
I rang the local shop, they have a 48v 11inch diameter motor for $200aus. lets assume in good condition (I haven't been to check it out yet, make and condition unknown).

144volts seems acceptable in these circumstances but I cant find any information about higher voltages/ amps or how much is too much. 
It would be used to power a 1800kg jag. P.S not aiming for a rocket ship, just respectable modern performance like a holden commodore. 

So is there a limit to the volts/ amps I can put through a motor (assuming I can add a fan for cooling) bonus points for links to info on cooling the motor.


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## Duncan (Dec 8, 2008)

Hi Itchy
The thread above is long but well worth reading

Basically - a forklift motor is a Netgain motor with advanced timing and a nice paint job

Voltage limit
Your controller acts by modulating the motor voltage until the desired current is achieved,

This is dependent on the current and the motor speed,

Effectively you can't "overvolt" a motor - but you can overspeed or over current it

A 10Kw 48v motor will probably run at about 1500rpm and 200amps - for a long time

200 amps - hours
500 amps - minutes
1000 amps - seconds

Higher speed means more air flow = more cooling = higher current capacity

An 11inch motor (I believe) will be OK at 4000rpm - May be OK at 5000rpm

At $200 I would grab two - one to use, one as a spare


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## itchyback (May 28, 2014)

Thank you zsnemeth, I have been reading that thread. I'm up to page 46 and that has taken a fair bit of time.i did a search in the forums and that thread for 'over volt' but only came up with a few relevant posts. Up to 144v seems common place but wasnt sure about anything after that. I started to wonder if no one had asked it. I am new though maybe I'm not looking in the right places.

Thank you Duncan for the summary. Things are starting to make more sense.


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## dougingraham (Jul 26, 2011)

itchyback said:


> Thank you zsnemeth, I have been reading that thread. I'm up to page 46 and that has taken a fair bit of time.i did a search in the forums and that thread for 'over volt' but only came up with a few relevant posts. Up to 144v seems common place but wasnt sure about anything after that. I started to wonder if no one had asked it. I am new though maybe I'm not looking in the right places.
> 
> Thank you Duncan for the summary. Things are starting to make more sense.


It isn't really over volting the motor. A series DC motor wants to turn at a given RPM depending on the voltage under a load. The motor will draw current in an effort to reach that RPM. If you increase the load the current will go up and the RPM will drop somewhat. If you increase the voltage the RPM will go up and the current will increase. The voltage limit of 48 volts will allow a motor that has not been advanced to operate in both directions without much issue. If you are going to run higher voltages then you will need to advance the timing or you will see trailing edge erosion on the comm segments and one of the brush pairs will have excessively fast wear. Increasing the voltage will increase the torque band. Using a low voltage setup will require a lot of gears in the transmission.


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## PhantomPholly (Aug 20, 2008)

itchyback said:


> So is there a limit to the volts/ amps I can put through a motor (assuming I can add a fan for cooling) bonus points for links to info on cooling the motor.


The answer can be derived empirically. Increase current until smoke emerges...

Unfortunately, this method of determining the limit leaves the motor unusable. There used to be an outfit selling smoke kits to restore the smoke into the motor, but they went out of business.


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## itchyback (May 28, 2014)

I understand. Thank you all for your responses. 
Essentially a large car needs a large motor because a smaller motor could not sustain the amps at a given rpm to move a large car. the motor would burn out or the car would go painfully slow/ stop, whichever happened first (in the absence of a well programmed controller).
A large motor also has its limits, presumably 1000amps/ 5000rpm or thereabouts when the smoke comes out (LOL PhantomPholly).

So in my circumstances 11inch ex-forklift motor should suffice (with advanced timing etc). Add a cooling fan, a big one. Get a gearbox/ diff to keep the rpm to under 4000-5000. Set the controller to limit the amps to maybe 800ish, limitingperformance to sustain longevity of motor, more if i'm game, less if im a grandpa). and add as many volts and amp hours as i can fit batteries

Getting the hang of this. now up to page 50 of the choosing a forklift motor thread.


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