# over-volting controller



## Guest (Mar 19, 2011)

NO. Don't try. If you need more get a controller that will handle your needs and still operate safely. If you do over volt your controller and are out on a drive and it fails on you will be in trouble. Others will also be at risk. Don't over volt a controller. I have a controller that will supply safely 156 volts. I run it at a lower voltage. I can go up to 156 but I won't ever take it over that. 

Pete


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## majortom (Mar 19, 2011)

What I have is an old 48 volt EV. It'll hold 45 mph, tops out at 50mph on 8 12 volt truck batteries. Room is not a factor, money is. I plan to double the batteries to achieve my 40+ mile range. It has two 7" GE motors, one on each rear wheel. The motors and the controller do not get hot. My target speed is 55mph, but the way the car acts, I need to push the motors a little harder. I don't think I'm out of rpms, I'm out of volts. It's not worth putting thousands of dollars in it even though for what it is, it is very well done.


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## Guest (Mar 19, 2011)

I think you might get away with maybe one extra battery. Remember you need to know the final fully charged voltage of your pack and what the max your controller can handle. One extra battery may not do much for you but then the next question is what about your charger? I suspect your charger is just a 48 volt unit and won't accept an extra cell. Which leaves you in the same boat your in now. Live with what it is or upgrade voltage to the next level and upgrade your charger and controller too.

Pete


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## Coulomb (Apr 22, 2009)

majortom said:


> What I have is an old 48 volt EV. It'll hold 45 mph, tops out at 50mph on 8 12 volt truck batteries. Room is not a factor, money is.


If the controller won't take a higher voltage pack, the cheaper way to get more speed would be to weaken the field. Possibly a contactor with a very low resistance (perhaps a suitable length of cable) that can be switched across the field (a sort of "overdrive" switch). You'd probably want to leave the switch off at lower speeds so you get full starting torque, and only throw the switch when higher speed is needed. The controller should current limit to prevent a sudden surge of speed (the size of the surge will depend on the pedal setting; with low pedal, the surge would be mild).

To add extra capacity for extra range, put another 4 batteries (perhaps of lower capacity than the existing pack) in parallel with the existing. So the controller and motor still see 48 V nominal, but with larger capacity (range) and current (peak power).

Of course, the motor and controller will heat up more quickly with sustained higher speeds. Whether they heat up too quickly or not is hard to judge; you might just have to try it and see. You can try the overdrive contactor by itself (without adding to the pack) to get an idea.


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## major (Apr 4, 2008)

Coulomb said:


> If the controller won't take a higher voltage pack, the
> cheaper way to get more speed would be to weaken the field. Possibly a contactor with a very low resistance (perhaps a suitable length of cable) that can be switched across the field (a sort of "overdrive" switch). You'd probably want to leave the switch off at lower speeds so you get full starting torque, and only throw the switch when higher speed is needed. The controller should current limit to prevent a sudden surge of speed (the size of the surge will depend on the pedal setting; with low pedal, the surge would be mild).


Hey Coul,

I don't think you should field weaken a series motor unless your controller is full on (100% dc). And why would you want to? And this guy says he has two motors. From the one controller? Anyway, it might not be easy (or cheap) to implement, and depending on his load, the effectiveness questionable.

But you did make a good point about adding batteries. I really don't like trying to advise on performance modifications without any data. I wonder what is voltage sag is. It could be that a stiffer battery pack could get him another 5 mph.

Hey majortom,

Can you get us some numbers, like battery volts and amps at full speed?

Regards,

major


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## Coulomb (Apr 22, 2009)

major said:


> I don't think you should field weaken a series motor unless your controller is full on (100% dc).


Well, I'm not big on DC motors... but I don't see what the problem is. There is plenty (?) of inductance from the armature. Weakening the field is just changing the motor characteristics, such that the back EMF per RPM is lower.

Ah, is that the issue... when the back EMF changes abruptly, the current will try to change (increase, when the switch comes on) abruptly, and there could be a kick of some sort from the armature's inductance?



> And why would you want to?


To get the motor to run at higher speed, and draw some current. Like putting the transmission into overdrive, except electrically.



> And this guy says he has two motors. From the one controller?


Oh, I missed that. So perhaps series/parallel switching instead of field weakening?



> Anyway, it might not be easy (or cheap) to implement, and depending on his load, the effectiveness questionable.


I thought one contactor and one resistor was pretty simple; I suppose if the field terminals aren't brought out of the motor it gets messy.

But I'll defer to your far greater experience with DC motors.


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## major (Apr 4, 2008)

Coulomb said:


> There is plenty (?) of inductance from the armature.


Maybe not. The field inductance is typically much higher than that of the armature.



> Weakening the field is just changing the motor characteristics, such that the back EMF per RPM is lower.


If you're less than 100% dc and want more speed or torque and not in current limit, just increase the dc. Weakening the field while chopping would be counterproductive and could prove to be bad news for the controller. I think the fork trucks with the GE EV1 would lock out FW until it went into 1A (bypass).


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## piotrsko (Dec 9, 2007)

hows about: gearing or tire diameter changes? unless you've hit the drag wall.


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## DJBecker (Nov 3, 2010)

It may be possible to replace some of the internal components to handle a moderately higher voltage, and perhaps increase efficiency at the same time.

You'll need to open the case and research the drive section components.

One problem that you are likely to encounter is getting replacement diodes. Curtis often used diodes that had a reverse configuration. Standard diodes have the cathode on the tab, with the leads (e.g. two outer leads) being anodes. Curtis sourced diodes with the anode on the tab, which simplifies the design as it allows a electrically common heatsink. Good for Curtis. Bad for you.

You should note that your controller won't be considered "safe". Systems that use over 50V have much more stringent isolation requirements. 60 volts has very little risk, but is clearly on the wrong side of 50V.


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## majortom (Mar 19, 2011)

DAF-E has two drive motors connected "parallel" to a curtis 1221. I tried it today with 8 used group 31 batts, 2 banks of 4. car peaked at 45mph and slowly dropped to 35mph after 13 miles. Volts dropped from 50 to 36 on the only guage it has. It's 12 miles to town, so i think 16 batts, 4 banks of 4 might just make it there and back. The motors are belt drive, and the pulleys are close in size. It excels good maybe i can swap the pulleys around for a little more speed.


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## majortom (Mar 19, 2011)

DAF-E has two drive motors connected "parallel" to a curtis 1221. I tried it today with 8 used group 31 batts, 2 banks of 4. car peaked at 45mph and slowly dropped to 35mph after 13 miles. Volts dropped from 50 to 36 on the only guage it has. It's 12 miles to town, so i think 16 batts, 4 banks of 4 might just make it there and back. The motors are belt drive, and the pulleys are close in size. It excels good maybe i can swap the pulleys around for a little more speed.


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