# 'Undervolting' Siemens motors (Siemens 1PV5135-4WS14)



## gunnarhs (Apr 24, 2012)

boekel said:


> Does anyone have experience with using the 'low voltage' Siemens motors on an even lower voltage?
> 
> Using the Siemens 1PV5135-4WS14 with a small controller (Sevcon? Curtis? ...?) on 48, 72 or 96 volt, what kind of output is to be expected?
> 
> ...


Hi, this motor is not really made for low Voltage/ low RPM as you can see in the datasheet http://media3.ev-tv.me/Azure300VDC-400Acurve.pdf.

But it can be used for 96V, then it would deliver about 10-20 kW continuous with about 100-200A. The motor frequency would still be about +/- 1000 RPM ( 16 Hz) . So you would need a reduction gearbox for your boat. Not sure Sevcon /Curtis - controllers will be able to work with this motor but some options are mentioned in http://www.diyelectriccar.com/forums/showthread.php/siemens-1pv5135-4ws14-83007p1.html.
http://www.hec-drives.nl/ has also an inverter (400 V) and a reduction gearbox.


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## CKidder (Dec 12, 2009)

You can pretty much use any motor at a lower voltage than it is rated for. The issue is really one of speed. An A/C motor is spun at a certain speed based upon the input frequency. When a motor says it will spin 1725 RPM at 60hz that means it would spin half that fast at 30Hz, twice that fast at 120Hz, etc. But, voltage comes into play as well. When an A/C motor is spinning there is an induced counter voltage (called back EMF) that tries to oppose the forward voltage you are sending it. The BEMF is speed dependent. When a motor is rated at 240V, 60Hz that means that if you give it 240v at 60Hz you will get full power out of it and it'll spin the rated RPM. The back EMF will balance against the forward EMF and leave you with just enough volts to drive the motor at full power. If you were to attempt to lower the voltage to, say, half the voltage then you would find that the point where forward EMF and back EMF match up for full power is at a much lower RPM. You would actually be unable to drive the motor too fast as the back EMF would quickly rise to such a point where it perfectly matches the forward EMF and thus no current flows. Obviously you can't power at motor at no current so it will be free wheeling at that point. (EDIT) I should also note that it is possible to use field weakening to counter the back EMF. But, this takes away from the max power the more you do it. It lets you spin faster in exchange for less torque. This quickly burns away your torque such that you can't go forward any faster because you've run out of torque.

To some extent you could look at an A/C motor as a device that runs at some constant voltage V which might only be about 10-20V. At low speed the motor is really only running at such a low voltage. As the back EMF raises so does your forward voltage so that it is around V volts above the back EMF (if you're trying for full power. You can send less volts if you don't need to drive it at full power but always must send more voltage than the back EMF unless you're hoping to do regen braking). As I said, you can go faster by weakening the field but it steals away your max torque.

So, it would work and it would work just the same as always right up until you hit the limit of your forward voltage. Halving the voltage is going to halve the speed. Going to 96 volts is going to cut your max speed basically to a quarter. You'll be able to get a bit more speed with weakening but with a quarter the voltage your torque will very quickly suffer. If that's OK with you then you can do that. Otherwise you need more voltage so that you can drive the motor faster.


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## boekel (Nov 10, 2010)

Thanks for the reply's!

got it spinning...
https://www.youtube.com/watch?v=4jiGilR1QMk

Now either put it against another motor with a bigger controller (dmoc?) as a dyno....

Or put it on a water-brake....(also called a boat)..

to be continued...


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