LiPO battery packs use din parallel

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Hey all,

To keep a unit that floats balanced I am looking to use two battery packs, one on each side of the device.  Each pack is 7.4v/3600maH.  I would like to connect them in parallel in the unit to extend the runtime, and I was wondering if there is any issue with doing this?  Packs are made by Turnigy and have the associated protection circuit in them.

 

The packs will be removed from the unit and charged independently when needed.

 

To me I think there will be no issue as the packs have their own protection circuits built in, but I thought I would get a second(or third, fourth etc...) opinion on this.

 

Thanks

 

Jim

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Last Edited: Mon. Jul 16, 2018 - 10:57 AM
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Hi Jim.

I do not have experience with this type of battery but working on privat boat and assemble a lot of lithium LiFePo4 pack set in parallelle without problem.

But just make a test and measure current between 2 pack without load if current is "zero" all good. 

when charging natur will make your live easy. if on pack is less charge he will take more current into both has same "charge level" and share current.

Thierry

Thierry Pottier

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I would be a bit concerned about charging them independently, then connecting in parallel. With this scheme, there is nothing to guarantee that they are anywhere close to the same voltage at the time they are connected. Maybe one is not even fully charged? If it were my project, I would try to charge them in parallel, also.

 

West Coast Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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The charger is a commercial unit for charging R/C hobby packs. The packs themselves have a secondary harness that connects to the charger for status monitoring so I am pretty confident that the packs will be properly charged.

I will charge both packs and try Thierry's suggestion to see.

Thanks

ECJ

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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If your worried about 1 pack charging the other, why not put a diode inline with the packs!

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Jim in aviation modelling such a thing is common place. What you describe would be 1S2P. But the very fact the packs are already 7.2V means they're already 2S (and I guess 1P unless they are already paralleled to make the 3600mAh) so you'll just end up with 2S2P.
.
In such packs it's normal to bring out monitoring points on each so individual cells can be monitored during charging though I have to say I never really bothered but the I tend to stick to just 2S1P or 3S1P (11V)

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@Cliff,
So there should not be any issue parallel connecting the packs correct?

I will probably put the diodes in place as well. The .6v loss is nothing considering the device.

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Well, putting packs that are highly mismatched could lead to rather high currents and disaster (due to the high currents).  Say for some accident one was nearly completely empty & the other was tip-top full....hooking them together would lead to a rush of current.

 

Why not put a polyswitch between them, say 5 amps (or whatever makes sense) to limit the current of the initial marriage.  You mention some protection is built in--so maybe this is redundant.

 

Also, here is some info on parallel charging considerations:

 

https://www.rchelicopterfun.com/parallel-lipo-charging.html

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Thaks for the info.

 

Just for clarity:

avrcandies wrote:
Also, here is some info on parallel charging considerations:

 

I wrote:

jgmdesign wrote:
The packs will be removed from the unit and charged independently when needed.

 

I like the link you posted even though the packs will be charged on their own and not at the same time.

 

avrcandies wrote:
Why not put a polyswitch between them, say 5 amps (or whatever makes sense) to limit the current of the initial marriage.

 

Great idea, But as Cliff mentions what I want to do is commonplace.  I do plan on adding the series diode on each pack output anyway so in theory they should not sense each other.

 

Great tips all....Thank you

 

JIm

 

 

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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 The .6v loss is nothing

Schottky would be lower & its uA leakage is rather minimal concern for this. 

 

Of course diode will prevent charging, so need extra wire/connection to pump in current.

Or put the diodes on PCB, if possible (not sure if you are even designing a PCB). 

 

The packs themselves have a secondary harness that connects to the charger

Maybe that will do the trick.  Since you mentioned pack has protection, maybe they already have a diode in the non-charge cable.

 

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Jim,

 

I'd say THE place to find out about all this stuff is:

 

https://www.rcgroups.com/batteri...

 

They've got experts there that have been doing this "pack building" thing for decades and know all there is to know about how and when you need to monitor packs.

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Thanks Cliff. That's a great link and I am purchasing the packs from Hobby King as well.

I have my answer to this which there is no issue connecting the two packs together for the most part. Charging is no issue as they will be removed from the device and connected to my commercial R/C charger one at a time to recharge the pack.

Thanks all.

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user