How to connect two 36v batteries and NOT getting 72v

[minexplorer]

Hi ive got a bottle mounted battery on my bbs01 and am adding a second pannier one for long range.Can anyone tell me how i connect both sets of battery wires permanently ,without accidently blowing up my controller with 72v or something.Just want 40ah of 36v without having to unplug one when its empty and plug in the other.Thanks

 

[chris_n]

Connect them in parallel, positive to positive and negative to negative. Make sure the voltages are close to identical (0.2v ish) when connecing them. Disconect them from each other before charging or you will bypass the BMS.

 

[minexplorer]

Connect them in parallel, positive to positive and negative to negative. Make sure the voltages are close to identical (0.2v ish) when connecing them. Disconect them from each other before charging or you will bypass the BMS.

Cheers chris .So id need some kind of splitter connectors attached to the controller wires then .Have to see whats about.

 

[chris_n]

I would use XT60 connectors. Just put XT60 splitter into Ebay for a ready made one, of course you will have to solder plugs on to the wires yourself. On mine I was able to solder directly to the bottom of the battery connection terminals on the battery holder.

 

[Paultr]

Just a small point but get into the habit of always connecting - ve to - ve first.

EDIT: and take the - ve off last when disconnecting.

 

[chris_n]

Just a small point but get into the habit of always connecting - ve to - ve first.

EDIT: and take the - ve off last when disconnecting.

Why? XT 60 connectors make and break both together and are keyed so they can't be fitted the wrong way round.

 

[footpump]

my collection of xts for most occasions, actually got quite good at soldering them in the end
the one on the left is parrellel lead of ebay for linking 2 batteries

 

[minexplorer]

my collection of xts for most occasions, actually got quite good at soldering them in the end
the one on the left is parrellel lead of ebay for linking 2 batteries
View attachment 25624

Thanks everyone for the info.Well it looks simple to do.It bothers me the having to ensure both are equally charged.Im very lackadasical .Has anyone found just unplugging the 1st batt when exhausted and plugging in the second easier. Esp if say ones 100% charged and the others 75 %

 

[chris_n]

When mine are charged fully they go together without problems. The advantage of running parallel is you put less stress on the batteries and probably don't fully cycle them. Both of these will lead to longer life.
If you are not comfortable you could just run them sequentially.

 

[Benjahmin]

If you are, as you say, lackadasiacal, then I wouldn't parallel them. You have to be sure to disconnect the batteries from each other EVERY time you charge. Otherwise it is possible for one battery to charge the other (via the output cable) by passing the bms. This is a fire risk.
I measure my battery voltages every time before I connect them together, just to be sure. They are normally 41.2 and 41.5v, this causes no problems. It takes about a minute to do.
As already said there are great advantages, for battery longevity and for your own decrease in range anxiety, but you have to be mindful of what you are doing.

 

[Nealh]

As Ben has mentioned his are with in 0.3v when paralleled, 0.5v is the most mine have been connected up as. When equalising only half of the voltage difference amount will flow as they equalise.
The important thing is not to have the wiring too thin to cause a bottle neck with flow and heat issues.
Use 12 or 14awg silicone wire, the bigger the gauge the better and the better for heat dispersal.

 

[Paultr]

Why? XT 60 connectors make and break both together and are keyed so they can't be fitted the wrong way round.

Yes of course, if using connectors you have no choice. My advice was only relevant if dealing with loose wires. The op might have had a trial run before fitting the XT 60 connectors for a permanent solution.
It is not a set in stone thing anyway, just good practice to get into.

 

[minexplorer]

When mine are charged fully they go together without problems. The advantage of running parallel is you put less stress on the batteries and probably don't fully cycle them. Both of these will lead to longer life.
If you are not comfortable you could just run them sequentially.

Im going to def parallel them then. When im running full 18amps a lot i see im working them too hard. 6p and 5p 29E im getting only 15amp & 12.5amp continous.11p will be 27amp cont. Far less strain.

Same principle when i picked a 30q battery for my bbshd rather than the Ga cells .Which would be getting hammered with loads of 25amp + use.

Like the engines of a 2.5 L and a 1.6 L cars both doing 80mph. Ones being worked a lot harder.

 

[Nealh]

Longevity wise your batteries will be less stressed and amp draw kinder to them so they will /should have a longer life span holding capacity better, mileage/ range wise you will see at least the same as the two individual batteries would give and should see a little improvement but it won't be massive.

 

[minexplorer]

Longevity wise your batteries will be less stressed and amp draw kinder to them so they will /should have a longer life span holding capacity better, mileage/ range wise you will see at least the same as the two individual batteries would give and should see a little improvement but it won't be massive.

The 8 months ive been running my 350w bbs 29E 6p battery at 15 -18 amps.To fully discharged most rides too,has probably reduced its capacity. The case is prob worse on the 5p LG battery for the missus bike which only has a throttle and pulls 19amps alot. Ive only just learned that u cant trust many battery specs 'continous' ratings. They often claim 20- 25amp continous .More than these mid range cells are meant to deliver at a continous level. Adding the 2nd batt was intended for range .I wasnt realising til now ,it will actually be a great benefit to the other batt.