Alternating battery banks for increased range.

[JasonG]

Just to clarify, I'm not talking addind additional weight,motors,Tesla coils, etc.

I am asking if taking an "existing" say 400AH battery pack, and dividing it in half. (OK I added 2 large relays)

Would the rest time give the batteries more range the using them in parrallel thereby stressing them less ? ?

[dcb]

Pretty sure it wont help. The batteries will be twice as stressed when they are being used, and the peukert effect isn't linear, it gets worse the more you stress a battery.



Also the battery is part of the circuit, if you have two in parallel, you effectively "halve" the internal resistance of one battery.

[byte312]

I agree. You need exacly the right size motor and batteries to match the size of the car.
The performace will not get better by carrying batteries that are not active in the circuit.

[Frank Lee]

Maybe you just need to P&G.

[byte312]

Oh but, the performance gets better if you stop and replace the batteries every few miles. That way you only carry the weight required to run the motor until the next stop.

[Phantom]

I have thought about this and posted in a different thread, what would be the difference in run time if:

1: Run two banks both at 40v only having one connected till it is at 20v then run the second bank till it's at 20v. When both are at 20v run them in series for a total voltage of 40 again.

2: Run the same number of batteries in parallel/series for the same starting 40v.

[byte312]

Interesting thought. I think just regulating voltage from a series string of batteries might help keep the car runnng at a constant speed for a longer time. What if you have 120 volts to start and the motor only needs 96v. If you can use a regulator to hold the output at 96 you can discharge 24 volts before the car slows down. Changeing from series to parralled or vice versa will not change available watts but you can choose either higher current or higher voltage.

[Daox]

Its all about amperage with batteries, especially lead acid. The faster you drain them, the less capacity they have (aka the peukert effect). Keep the amperage as low as possible and they last longer. Thats really about all there is to it. The more voltage you have, the less amperage you need. Therefore higher voltage is better for your pack.

[Ryland]

Originally Posted by Phantom

1: Run two banks both at 40v only having one connected till it is at 20v then run the second bank till it's at 20v. When both are at 20v run them in series for a total voltage of 40 again.

What kind of battery can you drain that low tho? my 48v pack starts out at 100% full with a at rest voltage of around 52v once the at rest voltage is around 46 volts the pack is dead but in normal use I try to keep it above 47.5v to make my pack last longer as the deeper I discharge the fewer cycles I can get out of the pack.
Also the comment about a 120v battery pack and reducing the voltage to 96v going to the motor, that is more or less how speed controllers work, you give the motor the voltage it needs to go the speed you want to go, crawling along in traffic? your 120v pack might be reduced down to 20v via the speed controller.
The fact of the matter remains, stress your batteries to much and you will be replacing then every year or two instead of every 5-6 years, take really good care of them and they might last you ten years.

[DJBecker]

Originally Posted by byte312

Interesting thought. I think just regulating voltage from a series string of batteries might help keep the car runnng at a constant speed for a longer time. What if you have 120 volts to start and the motor only needs 96v. If you can use a regulator to hold the output at 96 you can discharge 24 volts before the car slows down. Changeing from series to parralled or vice versa will not change available watts but you can choose either higher current or higher voltage.

That's a slightly misleading explanation.

If you need 96V from a 128V battery, the motor controller uses a 75% pulse. During the 25% 'off' period the motor current is provided by diodes or diode-like freewheel switching. Also during the off period the controller's smoothing capacitors recharge to provide part of the current for the next pulse.

As the voltage drops, the pulse width increases to compensate. Less of the current comes from the freewheel devices, and more current comes from the batteries.

A modern controller can do this very efficiently, at a frequency so high the motor current is almost constant. This is *far* more efficient than slowly switching banks of batteries in various combinations of serial, parallel and anti-series. (Anti-series is reversing/recharging one bank to effectively drop the voltage across the motor.)