Possible to bond two battery packs?

Batteries, Chargers, and Battery Management Systems.

Possible to bond two battery packs?

Postby rollin » Fri May 19, 2017 1:14 pm

Thanks to everyone for this great forum I'm learning as fast as I can so I apologize in advance if this is a particularly stupid question.
I have a Raleigh Tekoa ie with a 48v 8.7ah Currie battery on the down tube I also have a rack-mounted 52v 10.5 ah pack from a hub conversion I did last year. I'd like to increase my range on the Tekoa ie by bonding the batteries, if both batteries were fully charged could I just plug the 52v output into the charging port of the Currie 48v (which would remain in place supplying the Currie motor with power) and expect it to work? Thus more than doubling my available power and extending the time I could spend out exploring local fire roads.

Good idea or will I need some kind of extra circuitry to make it work?

Thanks to all who read this post and all advice welcomed.
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Re: Possible to bond two battery packs?

Postby 999zip999 » Fri May 19, 2017 3:03 pm

What are the batteries we are talking about ? Link.
Do you have a volt meter ?
Last edited by 999zip999 on Fri May 19, 2017 3:04 pm, edited 1 time in total. View post history.
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Re: Possible to bond two battery packs?

Postby fechter » Fri May 19, 2017 3:24 pm

If the batteries are different voltages, you can't connect them together directly. One of my bikes has two batteries with different voltages and I use a switch to swap between them. When the first battery gets low, I can change over to the second one.
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Re: Possible to bond two battery packs?

Postby spinningmagnets » Fri May 19, 2017 3:36 pm

Its absolutely vital to learn the differences between connecting two battery packs in "series" and in "parallel".

The 48V and 52V names are the "nominal" ratings which show the average of the packs voltage over the curve of a discharge cycle.

If you connect the two packs in series, it can be done, and...the result will be a 100V nominal pack. Which will likely damage your controller.

If you connect them in parallel, it will be an absolute disaster. Best case scenario they are both damaged when they try to balance out and attain a 50V nominal voltage. The rapid equalization attempt will absolutely result in a lot of heat, and it is quite likely they will catch on fire, ruining two battery packs, and also resulting in every other consequence that a fire brings.
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Re: Possible to bond two battery packs?

Postby e-beach » Fri May 19, 2017 4:07 pm

Yep, more information needed before you blow anything up.

What type of batteries are you running?
What chemestry are they?
What is your charging and balancing set up like?
Can you access any internal wiring?
What do you have to check voltages?
How are your electronics skills?

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Re: Possible to bond two battery packs?

Postby rollin » Fri May 19, 2017 9:30 pm

Yep I thought it might be beyond my minimal electronic skills (though I did build a Dynaco Preamp 50 years ago) I think spinningmagnets has convinced me to put the kibosh on this particular project. I am trying to be super careful when handling these Li-on packs and am quite amazed at the amount of energy they store so I think I'll just leave well enough alone. Thanks for the rapid replies.
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Re: Possible to bond two battery packs?

Postby spinningmagnets » Fri May 19, 2017 9:59 pm

If you are carrying two battery packs and you don't want to unplug one in order to plug in the other, then you can wire up a 3-position switch that has a dead position in the center.

I haven't done this, but since your two packs will have different voltages, the controller will have a low voltage cutoff (LVC) that only works for one of them. You could use one controller if both packs have the same nominal voltage, but...I don't really see any other way to do it.
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Re: Possible to bond two battery packs?

Postby 999zip999 » Fri May 19, 2017 10:14 pm

Just unplug one and plug in the other simple. Don't run batteries to cutoff as the rule. Do get a multi meter now. Check voltage, check polarity. Important. Free at harbor freight with coupon. If you answer all questions it would help.
Last edited by 999zip999 on Fri May 19, 2017 10:15 pm, edited 1 time in total. View post history.
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Re: Possible to bond two battery packs?

Postby e-beach » Fri May 19, 2017 11:40 pm

Don't get turned off by the answers, we will help as much as we can. :wink:

As far as "lvc...low voltage cutoff" goes....are you using a BMS?

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Favorite Quote: "This is L.A., sugar. There is no 'over the top." --- Chris Erskine

Current build: Liahona w/ cheap front suspension and suspension seat post. Yescomusa 36v 800w generic front hub motor. 15ah Headway triangle mounted pack. Tronsung 30 amp,

Previous Build:1992 Trek Antelope 800 - Bone Crusher (no suspension) - Yescomusa 800 watt 36 volt front wheel kit. Don't do it! Get suspension!!!
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Re: Possible to bond two battery packs?

Postby dogman dan » Sun May 21, 2017 6:28 am

Bummer they are different. one is 13 cells, the other 14.

So all you can really do, is ride one till its empty, then switch to the other. ( or buy another 13cell, or another 14 cell)

People make it out like stopping for 60 seconds to swap is a pain beyond tolerance. Really? on a two hour ride you won't stop for 60 seconds along the way? Puuuleeeze.

Nothing wrong with multiple batteries, and long range, however you have to do it. Before all my shit burned, I had up to 43 ah of battery, half if it 13 cell, the other half 14. For sure, on an 80 mile ride I'll be stopping many times, so no problem to swap packs as needed.
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Re: Possible to bond two battery packs?

Postby 999zip999 » Sun May 21, 2017 4:08 pm

Don't assume any color wire means anything check polarity before hooking up. With multi meter.
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