Joining batteries together ?

[stevenatleven]

My Oxygen e mate has a 15Ah battery which sits vertical alongside the seat tube. At the bottom it engages with 2 prongs to connect to the controller housed in a little compartment below it.It is charged by a XLR 3 pin socket at the top. I also have another bike with a 13Ah battery which is rear carrier mounted and plugs into the controller with a IEC male kettle type plug. So I wondered if I could also mount my 13Ah battery on the Oxygen rear carrier and using a lead I can make up, plug the 13Ah battery into the 15Ah battery XLR socket, in effect making a 28Ah battery to use for some long runs I have planned for next year. Hope that is not to vague, the rear carrier mounted battery plugs straight into the top of the 15Ah battery which sits in position above the controller which it is plugged into.

 

[EmSeeDee]

I wouldn't recommend that. The circuitry behind the xlr connector is expecting to see a charger, not a battery. At best it won't work; at worst you could end up killing either or both of the batteries and perhaps setting fire to something.

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[stevenatleven]

Thanks for the explanation, back to the drawing board then.

 

[EmSeeDee]

Thanks for the explanation, back to the drawing board then.

If you're prepared to dig into the electronics, it might be possible to interrupt the wire that goes from the "2 prong socket" to the controller circuit and re-route it via a changeover switch so that you could bring the second battery into play when the first one goes flat.

 

[stevenatleven]

Thanks for this suggestion. I have it opened up and I can probably solder 2 wires into the circuit and take them off to a connector to the other battery.
Will investigate this further.

 

[EmSeeDee]

Thanks for this suggestion. I have it opened up and I can probably solder 2 wires into the circuit and take them off to a connector to the other battery.
Will investigate this further.

Just to clarify ( not knowing how much you know about electrics), you need to arrange the switching so that only one battery can every be connected at a time. This means that you need to remove the wire between the existing battery and the controller, and re-route it via the switch. You'd need a switch a bit like this: http://uk.farnell.com/arcolectric/c3960bbaaa/switch-dpdt-16a-250vac-solder/dp/7674309?ost=c3960&selectedCategoryId=&categoryNameResp=All+Categories&searchView=table&iscrfnonsku=false and you could fit a sealing boot to keep the water out.

 

[Benjahmin]

Yeh, you would need to check that it's a 'break before make' switch to ensure that two batteries, at different voltages, could never be accidently connected together.

 

[stevenatleven]

Both batteries being 36v. If when the first battery was spent I switched it off with the key but it was still in contact with the prongs and so the controller, would it be possible to connect up the tails I took off the circuit and connect to the 2nd battery. Or would the 1st battery have to be disconnected altogether ?

 

[Alan Quay]

Both batteries being 36v. If when the first battery was spent I switched it off with the key but it was still in contact with the prongs and so the controller, would it be possible to connect up the tails I took off the circuit and connect to the 2nd battery. Or would the 1st battery have to be disconnected altogether ?

The first really does need to be disconnected.

If it were me, I find a way to cut the power cable from battery/controller, put a connector on it, and corresponding connectors on both the batteries. When one was exhausted, I'd swap over to the other.

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[D8ve]

There needs to NO way the two batteries can be connected together when in different state of charge. That could lead to very high current causing melted wires or even start of a battery thermal runaway event.
Google ;for what that looks like

 

[Benjahmin]

There needs to NO way the two batteries can be connected together when in different state of charge. That could lead to very high current causing melted wires or even start of a battery thermal runaway event.
Google ;for what that looks like

Absolutely, with knobs on. Big blue flash and hot stuff everywhere.

 

[stevenatleven]

Thanks for all the advice, I think I,ve got it no communication between the batteries. I will have to consult someone who is a bit more knowledge than me before I go ahead.

 

[Deleted member 4366]

Thanks for this suggestion. I have it opened up and I can probably solder 2 wires into the circuit and take them off to a connector to the other battery.
Will investigate this further.

That will work. You can even have both batteries connected together provided that they're at the same voltage (fully charged) when you join them. Don't leave them joined while charging one of them because the one will charge the other through the discharge port, which has no charge controls.

The Oxygen key-switch isolates the cell-pack from the output wires, so, you charge them both in situ with the key turned off, then switch it on when both are fully charges. You need to check that they're fully charged (about 41.6V) before switching on because if there were a fault charging one of them so that there was a significant voltage difference between them when you switch on, you could see fireworks.

 

[stevenatleven]

Thanks Dave, I am currently tidying the space for extra wiring below the battery just now. I have been told the Oxygen battery is open circuit so turning the key to the off position should in theory be fine but to be on the safe side I will put a switch inside the controller box and when I want to switch over go inside and do it manually, that way it will separate the batteries from each other.