I have two 36 v batteries 10.1 ah. Is it safe to use them in parallel on my e bike to increase capacity of battries. And can i charge them togather with one charger? 2 batteries as in pic

I have two 36 v batteries 10.1 ah. Is it safe to use them in parallel on my e bike to increase capacity of battries. And can i charge them togather with one charger? 2 batteries as in pic

... If both batteries are initially discharged fully, you could pair them and charge them as a set, then provided they remain as Siamese twins everything will be fine. You can charge and discharge them in tandem till the cows come home.

Each battery as been fitted with its own battery management system, and they may have a slightly different voltage eg 41.1 and 41.5 . If both were charged and then brought together there would be an imbalance of 0.4v, which does not seem a lot, but as the batteries can source a lot of current, here could be massive current from one to the other while the voltages stabilise.

What would be much more terrible would be to connect a fully charged battery accross an empty one as the voltage difference could be 41 - 32 , and the current flow into and out of each battery would heat both probably destructive ly.

You can't charge them while joined in parallel because the one will charge the other through its discharge terminals, which can have disastrous consequences because it by-passes the battery's charge safety controls, and that can cause a serious fire.

 

Charge them separately when not in parallel, then when they're at the same voltage, you can connect them. Under no circumstances should you join them when they're at different voltages - say more than 1v difference.

I have two 36 v batteries 10.1 ah. Is it safe to use them in parallel on my e bike to increase capacity of battries. And can i charge them togather with one charger? 2 batteries as in pic

.. both dvh8 and myself are saying the same thing, but it might not be particularly useful to you unless you have access to a multimeter and know how to use it. .. The following process will work and you don't need to be technically competent to use it.

.. get a torch bulb and two leads ... even a A 1.5 v flashlamp bulb is suitable. Maplin have suitable bulb holders for these or Halfords have 6v and 12v wired holders

connect this bulb between the positive terminals of both batteries

. Then connect a single lead between the negatives of both batteries.

If the batteries are initially at different voltages, which inevitably they will be, current will flow through the the lamp and it will glow, eventually when and as the voltages stabilise, the lamp will glow less and less bright , go towards red and eventually extinguish. A lower voltage bulb is more sensitive toa minor voltage difference .

When there is no visible light Then both batteries can be joined together safely.

and charged and discharged in parallel indefinitely.

The battery management system of the lowest overall voltage battery will determine the overall peak voltage attained, but this is only going to be fractions of a volt.

 

 

This use of a bulb is an old electrical power engineering trick.

I connected lion's and lipo's in Parallel, they are usually within 0.5v of each other often I will ride the lion for a 2 or 3 miles before connecting up the lipo as I charge them to a lower value. Having a watt meter wired in line takes all the guess work out.

If the voltage is far out 1-2v for example, then wiring will get very warm or hot until cells equalise. If the wiring is rated and up to it you should be ok as a one off, I have only done this once when I realised a paralleled and series lipo brick had come disconnected and was about 1v out.

Edited May 23, 20178 yr by Nealh

Thanks everyone