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Dual battery controller

We developed this dual battery controller for running two batteries in parallel.


Hi @gcelec,

Cool! What exactly does the controller do, in addition to being being a convenient parallel adapter?


I saw a few people on the Forum asking if it’s possible to run LiOn batteries in parallel and as we have some experience with this and understand the dangers of getting it wrong, we made this circuit. It’s designed for running two Blue Robotics batteries in parallel.

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it looks like that guy’s got a cool job.

That’s Ed, who designed and built the batteries. Also a machinist and mechanic. Smartest guy I know!

I run 4 LiPo’s in parallel, never had a problem directly connecting them, but I understand the potential issues. How can this product help me? what does it do? Can we get them?

It would be nice if the battery controller had a cut off relay/switch which could be activated with the small water linked contact

Does it suppose to do the same thing like this : switch between lipo and liion batteries ?

I second the motion. What’s this protecting?

Bad things happen if you charge a LiPo too quickly - at best, you reduce the life of the battery, at worst it will explode. When you parallel two LiPo batteries, one will discharge and the other will recharge until they reach equilibrium. The difference in voltage can be 0.1v for the the current to be over 10 amps (the recommended charge current for BlueRobotics 14.8V, 18Ah battery). So if you repeatedly parallel a pair of batteries after they’ve charged, you’ll probably be shortening their life, but the main danger is accidentally paralleling batteries that have a greater difference in voltage.
Discharging too fast and charging too fast are both bad for batteries.

Thanks for the detailed explanation. I can say from experience that this would be a necessary item as I now believe I lost a battery that could have been saved with your device presumably. I have a dual battery set up and got lazy only hooking one battery up for testing, running it down a bit then hook both together for operations. Now one battery is out of balance and won’t recharge.

So does Seaview have a price and availability for these? I am actually looking into a quad battery set up for a design I am working on.

Also, can you address difference between switch referred to by @kikislater and yours.

I"m looking at pricing ours at $150. The one referenced by @kikislater is for a quadcopter and you manually switch between the batteries. Apparently it’s more efficient to have a high current battery for for taking off, then you switch to the other battery for flying.
Our board just safely combines the two batteries without overloading them or damaging them. I’ve bench tested it with dummy load, but haven’t field tested it yet.

@gcelec, does it just limit the current between the two batteries, or is there more to it than that? Does it shut off the parallel connection if the voltage delta is too high?


Seems a bit pricey. Kind of like paying 50% of new battery for insurance. I’m sure it comes down to economies of scale but would be more viable at a price sub $100.

Thanks for the feedback @dtrail It is a matter of economy of scale and if it’s worth it to SeaView to sell low value items.

I would spend the money on this to make my setup more robust, but I am still curious, how exactly does your device protect the packs from high charge/discharge rates when unbalanced packs are connected in parallel? Does it limit the charge rate to something safe so the packs equalize over a longer period of time? Or does it cut the connection, or switch from one pack to the other?
Could you configure more than one of these to handle 4 or more packs in parallel?

@nperry, @adam It switches between batteries, discharging the higher voltage battery until they balance.
In theory I think you could connect four batteries into two circuit boards, then connect those two boards into a third one - let me test it and get back to you!

Just to be precise, it’s used in VTOL (virtual take off and landing) for RC planes. You take off in multirotor mode with high C rate lipo which use a lot of current due to no efficiency of multirotor design concept. Then you switch to plane with one or two motors depending on design and use a liion with lower C rate which don’t need a lot of power due to aerodynamic design. Finally switch back to lipo for landing in multirotor mode …