# Limits of Overvolting DC series wound motors



## rmay635703 (Oct 23, 2008)

Even the most advanced series wound only goes to about 200 volts and past that you gain nothing anyway.

The only way this would work out would be with a higher end dc controller that can limit voltage applied to the motor, you could feed 400 volts in and get 144 volts out


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## Meni Menindorf (Mar 17, 2018)

rmay635703 said:


> Even the most advanced series wound only goes to about 200 volts and past that you gain nothing anyway.
> 
> The only way this would work out would be with a higher end dc controller that can limit voltage applied to the motor, you could feed 400 volts in and get 144 volts out


Thank you rmay~ Is a dc controller like that a stand-alone unit from the motor/speed controller, or is it built in? Any recommendations? Otherwise. . . I'm kind of looking forward to tearing the batteries apart and playing with them  

If you have knowledge/time to share. Would a 200V situation be that much more desirable than a ~150V . . . does it depend heavily on specific the motor(s) I end up with? Thinking of running two DC motors in mechanical series~ Would it possibly behoove me keep the Leaf battery in it's current configuration and wire the motors in series instead of parallel to bring the voltage from the 400 to 200 range? 

I'm hoping for higher efficiency and range rather than top-speed if it makes a difference~


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## major (Apr 4, 2008)

Meni Menindorf said:


> I am curious to learn more about over-volting DC series wound motors. I have heard over and over that you can run a forklift motor at 140-150V. Is it absolutely necessary to advance the timing in order for this to work? How far can we push the envelope here . . . what happens if I use a Leaf battery with a forklift motor without reconfiguring the modules for a lower voltage. . . does the forklift motor blow-up. . . or get damaged in some way? Is it possible to advance the timing this much up to 360-400V?
> 
> I feel like a moron talking to salvage people and having them ask "Are you looking for 36V or 48V motors?" and my (inner) response is. . . "Doesn't matter, I'm gonna run it at 148V anyway!!!" Can someone help me understand the theory here? Or point me in the right direction?
> 
> ...


Yep, I can read it. 

About the voltage. Other limiting factors come in to play. Namely the controller, and the load. Trying to keep this simple, the higher the voltage, the higher the RPM. But there's a limit on the RPM which the armature can tolerate. Let's say 5kRPM. So if you're motoring along at 4000 with 48V applied to the motor and all of a sudden switch to 96V, the motor changes to 8000 RPM. Armature goes boom. So at that load, you'd never want much more than 60V on the motor in a steady state condition (meaning no acceleration). If you have a 150V battery, then the controller is reducing voltage to the motor.

What really happens when you suddenly change from 48 to 96V on the motor in the above example is that the motor can't change RPM instantly due to the inertia of the load (vehicle mass). So you have 96V on the motor spinning at 4000 RPM and the result is a huge sudden increase in current accompanied by tremendous torque. Great for acceleration but likely more than the tires and battery can handle. So Mr. controller steps in with current limit and keeps current and torque reasonable. How is this accomplished? By reducing voltage to the motor.

So using a 48V rated motor in a conversion with a 150V battery does not necessarily mean the motor will ever see 150V. Why use the high voltage battery then? Under load battery voltage sags. Towards end of charge battery voltage drops off and sag can become even more pronounced. Cold tends to decrease battery voltage and increase sag. And finally, it gives you ability to draw high current at high speed if needed.

A lot depends on a lot of factors but the motor will likely see the same voltage range using a 150V battery as it would with a 300V battery. The advance in the motor aids commutation at those times of high current especially at high RPM. 

Hope that helps.

major


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## Duncan (Dec 8, 2008)

Hi Meni

I am using a 48v DC Hitachi motor with a 340v battery

What happens is that you "demand" some amps and the controller alters the mark space ratio until it reaches that demand - effectively it increases the voltage until the current meets the demand

Full throttle is 1200 amps

When I start off it only takes about 15 volts across the motor to get 1200 amps
As the motor spins it produces Back EMF - so more voltage is required to push the current through the motor

I had all this worked out on my thread but its disappeared so this is a bit rough

Speed/Rpm ---- Motor Current - Motor Voltage -------Battery Current-- Battery voltage 
0/0-------------------1200------------15---------------------60------------------300
20mph/1000rpm----1200------------100--------------------400-----------------300
40mph/2000rpm----1200------------200-------------------800------------------300
60mph/3000rpm----1200------------300-------------------1200-----------------300

At this point the voltage cannot increase and the current has to drop down

80mph/4000rpm----800------------300----------------------800----------------300

At 85 rpm I am at the end of the 1/8th mile strip and I back off

Except last time when I vaporized part of my armature

Another motor cost me $150 and I'm back driving 

It is possible that I am a little bit cruel to my motors

The "Back EMF" is roughly proportional to rpm and current so if I did this at 600 amps

Speed/Rpm ---- Motor Current - Motor Voltage -------Battery Current-- Battery voltage 
0/0-------------------600------------7.5---------------------15------------------300
20mph/1000rpm----600------------50--------------------100-----------------300
40mph/2000rpm----600------------100-------------------200------------------300
60mph/3000rpm----600------------150-------------------300-----------------300
80mph/4000rpm----600------------200--------------------400----------------300


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## MattsAwesomeStuff (Aug 10, 2017)

Who knows where this community is headed, so, I'll take the time now while it's topical to say thanks to Major and Duncan for your respective efforts. Some fantastic, easy-to-digest content there.


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## jonerickson3 (5 mo ago)

Duncan said:


> Hi Meni
> 
> I am using a 48v DC Hitachi motor with a 340v battery
> 
> ...


Where do you buy motors?


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## piotrsko (Dec 9, 2007)

What flavor motor? For series wound, and some shunt wound

Forklift hitachi and GE motors: motor repair shops or forklift repair shops particularly if they have a scrap pile / used forklifts. Thyssen Krupp elevator repair places if they have a scrap yard. Not sure if you can still buy Kostovs in bulgaria but the EU has similar manufacturers for EV motors

Ge has industrial motors out the wazoo but maybe $ 3-5000 new


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