# Over-volting a motor - how much more heat can I expect?

#### RogueRose

Joined Oct 10, 2014
375
I'm looking at some motors for a few different applications and there are a number of times where over-volting would be a HUGE benefit for a number of reasons.

I'm looking at basically 2 setups:
12v motor normally running @ 12 v but supplies of 24, 36 or 48v are available (supply can produce more than adequate amperage for any demands)

48v motor (normal running voltage). 72, 96 & 120v supplies available as well.

Motor 1
What I need from these motors:
-over-voltage would occur for 2-4 seconds/min with normal voltage operation @ other operating times. Load on motor will vary and here is a rough breakdown of the load demand the motor might expect (so if it was a 100w motor, 50% in the chart means it would draw 50watts)

Power draw - % of time drawing this
100% w/ Over-voltage - 5% or less
100% - ~55%
90-95% - ~10%
70-90% - ~10%
30-70% - ~10%
15-30% = ~5%
0% - ~5%
There are times where it might be beneficial to reverse the flow (turn motor into generator) during the 0% but this would then be a 100% generation load, possibly even at a higher than nominal/standard rating voltage. I'm assuming this will also generate the same heat as if electricity was supplying the motor? Is there equal heat production as a motor vs generator for same amount of power input vs output? If this is the case, then no generation would be used.

Since a 12v motor drawing 10 A = 120watts & putting 48v through it will net 480watts, what I want to know is how much more heat is generated from this, is it exactly 4x more or is it higher and what is the best way to figure this out or at least estimate it?

If that 12v motor was given 48v using a PWM at a 25% rate, effectively cutting it down to 120w - will this setup produce more heat than a 12v motor getting 12v 100% of the time?

Motor 2
The second application would GREATLY benefit from the smallest sized motor possible but it needs to put out a lot of power in a couple 2-5 seconds bursts per minute, couple/few 1-2 second bursts in that minute as well. The rest of the time it wouldn't have any load/demand though running at normal voltage might be desired as the output could be used but not 100% necessary (& it could have a built in fan for cooling). So I'm wondering if I could get away with a 12v motor with 36, 48, 60 or 72v to get the higher max power. Total on times in seconds - 6min to 16 max - seconds/min.
If the motor gets to hot the motor and output/load can be shut off and taken out of the system until it cools down - basically bypassed. There's a lot that can be worked with and around.

As far as for how long a motor like this would be used, I would think many times for 1-5 minutes before getting a break of 5-20 mins (maybe much longer), so it won't be used at the cycle use in the paragraph above for hours on end, unless safety & bypass/minimal duty features can be installed that monitor heat and even then it wouldn't be used for more than an hour MAYBE 2. This application would be used to

Both of these motors would be custom fabricated for their specific purposes unless a pre-made one could be found, though I doubt it. I think it would be possible to co-mount an auxiliary motor in the primary motor to power a fan that can constantly run to cool the primary motor. For motor 1 I suspect a nominal rating of 5-10Kw in a horizontal/pancake (is there a proper name for this type of motor) arrangement. It's also possible to fluid cool this motor and also include an auxillary motor to power a fan as well, if those things would help allow them to run with over-voltage and keep them from burning up or to make them last longer.

Joined Jul 18, 2013
25,469
One avenue to explore when High current is expected is to use gearing if possible, this allows the benefit in economizing on motor size and drive, if the maximum rpm of the motor is not required when driven direct.
Commercial industrial control motors typically are supplied with a spec sheet showing continuous torque (current) rating and also the peak torque rating, where the motor can be overdriven, typically for a very brief time, a few minuets.
Continuous torque curve goes from zero to max rpm.
Motors can also be purchased with temp sensors buried in the winding's to use as an auto shut down if required.
Max.

#### shortbus

Joined Sep 30, 2009
9,441
Another thing that used to be a problem on over volting a DC motor was the commutator throwing a segment from the excess speed. Don't know if it would apply to modern motors and the way they are made.

But with a DC motor there is a design element that comes into play -

Joined Jul 18, 2013
25,469
Depends on the motor, most of the industrial ones I use, DC, BLDC servo's etc, the torque curve is fairly flat from maximum at zero RPM up to the rated max RPM.
Max.

#### cmartinez

Joined Jan 17, 2007
7,745
Depends on the motor, most of the industrial ones I use, DC, BLDC servo's etc, the torque curve is fairly flat from maximum at zero RPM up to the rated max RPM.
Max.
What about an ordinary universal motor? The torque curve resembles more like the one that Shortbus posted, right?

Joined Jul 18, 2013
25,469
Close, The Series field motor is very high torque at zero RPM due to the field current increase with load.
One prime reason they are used for automotive starter.
Max.

#### Bernard

Joined Aug 7, 2008
5,788
No serious adverse effects were noted when new 12 V system trucks were mated with older 6 V Ford starter motors driving cable reels. What a ride in picking up cable driving at 30 mph- lost a glove or two but never a hand. Where was OSHA ?