# Battery Questions



## hyper24 (Jun 13, 2008)

Say I have the X91-4001 motor which is rated at 144v, I can run that off 12 12V deep cycle batteries.
Now if i wanted to upgrade this later, would I have to buy another 12 and connect them in parallel.
Or is it possible to only add a couple in series which would increase the voltage of the pack, would the motor like this?


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## e_canuck (May 8, 2008)

Hello.

I am not shure what overvolting the motor would do. I am guessing more arcing at the brushes. Probably a shorter life. Maybe more wear in general.

Now 156V versus 144V is probably not that bad overall, but who knows.
Where will to much start?

The controller have maximum to. You might have to change your controller. Or buy more than you need in the first place. Again what will overvolting do?
And how much is to much?

More voltage also affect your contactor, and dc-dc converter.

I think adding batteries and splitting the pack in pairs with a lower voltage, within limits, would be acceptable.

Hope that help, take care,

DP


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## hyper24 (Jun 13, 2008)

Ok so any batteries that are connected in parallel must be of equal series lenght correct?

So if i had one pack of 12 batteries, I would need another 12 to connect them in parrell?

Or if i wanted to add only 8 batteries, I would have 20 so would need two series of 10 length each.

Also this would just double the AH rating?


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## e_canuck (May 8, 2008)

Hi Hyper.

Yes, you got it. say you have 20 batteries, you can connect them in pairs and have one string of 10 pairs. or you could have two strings of 10 batteries.

If only a few batteries were doubled. It would be like mixing big and small batteries. The pack will empty unenvenly. And batteries will die. A string of batteries is like one battery. So two strings should be matched. 

Think of it like rower on a boat. Every rower should pull evenly.

Actualy if you look at a single battery. It is made of several batteries.

http://cache.eb.com/eb/image?id=238&rendTypeId=4

A 12V is actually 6 batteries of 2V. A 6V is actually 3 batteries of 2V.

They are strung together in series. Well we do the same building the traction pack. Making one big battery.

Now your original question was about adding batteries. You can but keep the pack ballanced. Older and new batteries are like big and small. They will pull differently. The older and the newer they are, the more different they are.

And again I do not kinow what overvolting the components will do.

DP


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## ElectriCar (Jun 15, 2008)

RE overvolting. I spoke with an Advanced engineer about some things, one being running the FB1 at 156V. He said he's seen them run successfully at 192V with no problems, however they recommend 120V max.

In the electrical world I work in, 5% variation of specified voltage is not uncommon and for motors isn't an issue. For DC motors the only problem I can see for this is potential arcing but I can't say for sure that would be an issue. I could see problems running one at say 200-300V but not at 10-15% over.


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## Nate (Jul 10, 2008)

*If the manufacturer rated the motor at a true 144 volts then you could add more batteries to your single string. How many would depend on how much your amp load pulled the battery pack down. A 144V battery pack may not be at 144 volts when under load. This voltage drop would determine how many batteries you could use to get back to 144V under load.*


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## Gibles (Jul 14, 2008)

My question is this: why would you want to overvolt the pack? What do you get from this?


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## Qer (May 7, 2008)

Gibles said:


> My question is this: why would you want to overvolt the pack? What do you get from this?


Three things:


Easier to add batteries. If you have, for example, a Zilla 1kHV and want to run the motor on 144 Volt tops the battery pack has to be between 144-375 Volt (the Zilla can't handle above 375 Volt IIRC) so you can have anything from 24 to almost 60 6 Volt batteries. If you can fit, for example, exactly 35 batteries in your car and you can't over volt you'd have to go for 2*17 which would give you 102 Volt while 35 batteries in a single string would give you 210 Volt that can be limited to 144 in the controller.
No voltage drop over the motor. If the pack has, for example, 180 Volt and drops to 150 Volt at acceleration the motor can still get 144 Volt. If your pack is on 144 Volt and drops to 120 Volt during acceleration your 0-60 will be slower.
The cables from the battery pack to the controller can be thinner since the current will be equally lower.
The problem is that high voltage controllers (like the Zilla 1kHV) cost. In the long run it's no biggie, but it stabs the wallet pretty bad when you buy it...


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## Whitey_87 (May 30, 2008)

I have a question regarding a battery / controller combination.

I want to run a minimum of 144 volts. I plan to use 24 - 12v batteries. My choices between controllers are the (appropriately sized) curtis or the largest Zilla. Keeping cost out of the equation and focusing on performance / safety. Should I run two parallel strings of 12 batteries giving me 144v, or should I series them all and go for 288? Obviously the latter combo would require the zilla. Since I will have the same power available in the pack, what is the difference between having 144v with ~200A and 288v with ~100A?

Thanks.


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## Gibles (Jul 14, 2008)

Whitey_87 said:


> I have a question regarding a battery / controller combination.
> 
> I want to run a minimum of 144 volts. I plan to use 24 - 12v batteries. My choices between controllers are the (appropriately sized) curtis or the largest Zilla. Keeping cost out of the equation and focusing on performance / safety. Should I run two parallel strings of 12 batteries giving me 144v, or should I series them all and go for 288? Obviously the latter combo would require the zilla. Since I will have the same power available in the pack, what is the difference between having 144v with ~200A and 288v with ~100A?
> 
> Thanks.


From my understanding you will have a longer runtime with the parallel configuration.


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## Nate (Jul 10, 2008)

*I would think the higher voltage pack is going to generate more motor amps at slower speeds, which could cause higher motor temperatures.*


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## rfengineers (Jun 2, 2008)

Nate said:


> *I would think the higher voltage pack is going to generate more motor amps at slower speeds, which could cause higher motor temperatures.*


Actually, motor Amps are constant for a given torque. What changes is PWM duty cycle.

For example: 

Say you have a hypothetical 72-Volt system that draws 50 Amps from the battery when your motor is delivering 60 ft-lbs of torque and drawing 100 motor-Amps. This means that your PWM duty-cycle is about 50%. That is, your controller is sending 72-Volts at 100-Amps to the motor for '1/2X' seconds and then 0-Volts at 0-Amps for another '1/2X' seconds. This results in 100 motor Amps but an average of only 50 battery Amps.

Now, double your pack voltage. Your 144-Volt system will draw 25 Amps from the battery. Your motor (still delivering 60 ft-lbs of torque) will use the same 100 motor Amps but the PWM duty cycle will be 25%. That is, your controller will send 144-Volts at 100-Amps to the motor for '1/4X' seconds and 0-Volts at 0-Amps for '3/4X' seconds. This results in 100 motor Amps but an average of 25 battery Amps.


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## Nate (Jul 10, 2008)

*Rfengineers, I see what you are saying. Something is not calculated correctly though. I have seen too many series wound motors get hotter on higher voltage than they did when they were running lower voltage at slow speeds (10MPH and slower). I have also noticed the freewheel diodes in the controller get warmer as well. As the vehicles sped up the motors actually ran cooler as did the controllers to a point before the heat started building again. What am I missing here?*


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## rfengineers (Jun 2, 2008)

Nate said:


> *Rfengineers, I see what you are saying. Something is not calculated correctly though. I have seen too many series wound motors get hotter on higher voltage than they did when they were running lower voltage at slow speeds (10MPH and slower). I have also noticed the freewheel diodes in the controller get warmer as well. As the vehicles sped up the motors actually ran cooler as did the controllers to a point before the heat started building again. What am I missing here?*


That may be due to the motor RPM's being lower for a given torque at a higher voltage. Low RPM means reduced cooling air being forced through the motor. That could be the reason for increased heat.

But wait... shouldn't the RPM be the same for a given vehicle speed??

hmmmmm I need to think about this one.....


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## Nate (Jul 10, 2008)

*Yes RPM is the same at a given speed and same gear ratio and same vehicle so weight is also the same. I think the inductance of the motor has a big part in this. I also noticed that motors with higher inductance are less sensitive to high voltage at slow speeds. I would not think that the entire field could collapse in 1/15,000 of a second (controller frequency) am I wrong about that?*


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