Any electrical engineers here?

[gotime]

I couldn't quite nail down where to post this, but I'm guessing this is a good a place as any.

I have an electric bike that currently uses 3 12v batteries. I think they are connected in Series. The controller and charger are 36v types. I recently came into an extra 12v that I'd like to add to the bike. Would I need a different controller? As far as charging, I can use my car battery tender for that 4th one.

[ShadowX]

The controller or the motor has to be able to handle 48V for it to work. As for the charger, yes you need a 48V charger unless you take the extra battery out each time. Even though you can connect the original charger to the 3 batteries, leaving the 4th one in series and attaching another charger may not be a good idea. Its better if you put a switch to disconnect the extra battery. Either way, adding a new battery does not sound like a good idea unless the system is designed to handle it.

An alternative option is if you can get two more 12V batteries, you can wire those 3 new batteries in series and then connect to the original set in parallel. The voltage will be the same, but you have additional capacity due to the 3 new batteries.

[gotime]

Thanks, that's exactly the info I was looking for. The last bit is clever, but I'm looking for more acceleration, not range. I guess I'll find some other application for the spare 12v.

[Epaphroditus]

How much more acceleration would result (don't forget the extra battery is more weight which works against your stated purpose)?

[sd_shooter]

Why not put it parallel with one of the existing ones? Same 36v charger. Done.

[gotime]

These are small, not like the ones you find in cars. I'd imagine if I added the extra battery plus the proper controller, it'd be a noticeable difference. It's not exact, but I'd imagine it's analogous to adding 25% more displacement to your car engine.

[RobertMW]

Why not put it parallel with one of the existing ones? Same 36v charger. Done.

Because then the two parallel batteries are draining or charging at half the rate of the other two. This creates battery balancing issues which, best case cause some of the batteries to fail in fewer charge/discharge cycles, or worst case cause a fire.

[SkyHawk]

Adding another 36v battery string in parallel not only increases the capacity (by 2x assuming the same capacity batteries are used throughout) but also halves the resistance of the battery supply, allowing more current delivery (amps). This could (very well depending on the controller) result in greater acceleration. But adding voltage is the best way to increase acceleration and top speed. However if the speed controller is not rated for 48v input, it will fry.

[Jimi Jah]

Exceed voltage inputs and you will let the smoke out. The manufacturer should have stated limits on supply voltage. Current is another story, you can parallel more batteries to extend the life of the charge.

Charging batteries in series takes longer than charging each alone. There are also possible variations in each batteries storage and charge times, placing them in series adds more variables. I would charge a 12 volt battery with a 12 volt charger, it's 'tuned' to the current load and the heat dissapation. Run stuff in series and all bets are off.