Overvolting a controller

I recently purchased a 48v 1000w motor kit off eBay and I have 2x 48v battery’s what will happen if I connect both 48v battery’s and ride it will it blow the controller straight away? Thanks

If you connect them is series then yes, two use a pair of batteries at the same time you need to make up a parallel Y lead connecting from the controller to each battery.

All connections need to be Black, Black to Black & Red, Red to Red, at no time must any connection cross Black to Red.

 

In parallel you will still have a 48v battery, the capacity will increase as will the continuous discharge current to that of both added together. If paralleling make sure both batteries are charged to within 0.025v or closer and charge separately and not in parallel.

Ok thank you for reply I’m new to this lol for now I have red to red black to black going from one battery terminal

To the other so they are both linked will that be ok to connect them both

I want to try it but worried in case the thing goes boom on me lol

You MUST charge the batteries seperately, then BEFORE you connect them, measure the output voltage of each battery.

They must be as near equal voltage as makes no difference.

Very important - do check.

Ok so will I be fine to try it

Ok thank you for reply I’m new to this lol for now I have red to red black to black going from one battery terminal

To the other so they are both linked will that be ok to connect them both

Yes sounds ok, take pic and show us.

You MUST charge the batteries seperately, then BEFORE you connect them, measure the output voltage of each battery.

They must be as near equal voltage as makes no difference.

Very important - do check.

 

I've not connected two e-bike battery packs in parallel before. I'm curious, what happens if you connect them to the same charger if both packs are at about the same voltage? I can understand with old lead acid systems that the charger ideally would supply at constant current, then switch to constant voltage at some point, so you wanted to have a charger for each battery pack to get them optimally charged. However, with lithium packs, doesn't the BMS in each pack handle the complexities of the charging process and nowadays, the charger itself is just a dumb power source at 54V?

There’s the image

If you connect them is series then yes, two use a pair of batteries at the same time you need to make up a parallel Y lead connecting from the controller to each battery.

All connections need to be Black, Black to Black & Red, Red to Red, at no time must any connection cross Black to Red.

 

In parallel you will still have a 48v battery, the capacity will increase as will the continuous discharge current to that of both added together. If paralleling make sure both batteries are charged to within 0.025v or closer and charge separately and not in parallel.

 

One way I've thought about getting around the problem of connecting two batteries of different states of charge without having lots of smoke and sparks is to put two Schottky diodes in the Y splitter cable, so current can't flow from one pack into the other. You can get them for solar panels up to 60Amps for just a few pounds and they only cause about 0.1V drop.

https://www.flyingtech.co.uk/cables-connectors/xt60-y-lead-parallel-battery-harness-2x-male-1x-female

I will take your word for it, that it's ok. From that lash up I can't tell.

You can tidy it up a bit by using spiral wrap for the wiring.

One way I've thought about getting around the problem of connecting two batteries of different states of charge without having lots of smoke and sparks is to put two Schottky diodes in the Y splitter cable, so current can't flow from one pack into the other. You can get them for solar panels up to 60Amps for just a few pounds and they only cause about 0.1V drop.

 

If both batteries are widely different using diodes they will never equalise and one will discharge sooner then to the so defeats the object of paralleling.

I tried it nothing different lol

If both batteries are widely different using diodes they will never equalise and one will discharge sooner then to the so defeats the object of paralleling.

 

I don't mean one almost empty and the other full. I'm thinking of it as a safety feature. So if one pack is say 10% discharged and the other is full, with the diodes in place you could connect them in parallel without worrying about them being at exactly the same voltage. Then the full one would discharge down to 10% discharged, where they would be matched and then the two packs would discharge at the same rate together (assuming equal pack Ah capacities).

I don't mean one almost empty and the other full. I'm thinking of it as a safety feature. So if one pack is say 10% discharged and the other is full, with the diodes in place you could connect them in parallel without worrying about them being at exactly the same voltage. Then the full one would discharge down to 10% discharged, where they would be matched and then the two packs would discharge at the same rate together (assuming equal pack Ah capacities).

I use a 40 Amp (duel 2 X 20 diodes, controller is 14amp) Schottky and it works exactly as you said. It will pull more current from the higher voltage battery for only a very short period and then equalize. Indeed, I have forgotten on occasions to fully charge one of the batteries so there would have been a big difference but it still works, the higher voltage fully charged battery being drawn down until it levels with the half discharged other battery and then both batteries will be drawn on.

The battery packs do not need to be matched (other than nominal voltage) but each diode (and battery and BMS) should be rated and capable of carrying the full current in this case.

If the individual batteries have a lower discharge rating than the controller, then the batteries need to be similar and kept equalized , as Nealth says above.

Edited June 9, 20205 yr by Sturmey