Parallel connection Lipo with Lithium Ion

[chronosgarage]

Have anyone here ever try to combine rc lipo with li ion battery?
I have a 20S9P about 20A battery from old recycled laptop battery, it doesn’t have enough current drain I need.
I’m thinking about using 5 pcs of 4S rc lipo (4500 mah) connected in series, and connect it in parallel with the 20S9P battery. So when there’s a need of high current draw, the lipo will supply the current, is this possible?
I will use 4S 1.2A active balancer For the lipo battery.

What do you think about this setup?


Any help is appreciated...

 

[Hillhater]

I’m thinking about using 5 pcs of 4S rc lipo(4500 mah) connected in series, and connect it in parallel with the 20S9P battery. ...

Are those “ 5 pcs of 4S rc lipo”. ..5 pieces of 4S ?.... ie 20S in total ?
.....if yes, then it can be done providing you match the voltages of both 20S groups before yo connect them.
And watch the voltage on the RC packs doesnt get drawn down too low as the packs discharge.

 

[chronosgarage]

I’m thinking about using 5 pcs of 4S rc lipo(4500 mah) connected in series, and connect it in parallel with the 20S9P battery. ...

Are those “ 5 pcs of 4S rc lipo”. ..5 pieces of 4S ?.... ie 20S in total ?
.....if yes, then it can be done providing you match the voltages of both 20S groups before yo connect them.
And watch the voltage on the RC packs doesnt get drawn down too low as the packs discharge.

That’s correct, 20S in total.
What if I use a 20s bms for the 5 piece of 4s lipo connected in parallel with the balance lead connected to the lipo balance cable, so that when there is a voltage drop in one of the group, the bms will shut off?

 

[Hillhater]

I dont know what will happen, i never use a BMS !
...but i suspect that you will have some issues since the discharge rates , nd instantaneous voltages may vary on the dofferent packs depending on the load.

 

[dogman dan]

The bms can work, or use low voltage alarms to wake you up to when its time to slow down, and limp home on just the lithium ion chemistry pack.

The lipo, if this was not made clear enough to others reading, will reach 0% at a higher voltage than the other pack. So you need some way to disconnect it before it gets over discharged.

Disconnect to charge them separately, bms or no bms. Then connect only when the voltages are equal.

 

[chronosgarage]

The bms can work, or use low voltage alarms to wake you up to when its time to slow down, and limp home on just the lithium ion chemistry pack.

The lipo, if this was not made clear enough to others reading, will reach 0% at a higher voltage than the other pack. So you need some way to disconnect it before it gets over discharged.

Disconnect to charge them separately, bms or no bms. Then connect only when the voltages are equal.

Thank you for your reply.

What is the lowest recommended safe voltage for lipo?
Is it possible to charge the lipo together with the li ion? Because i want to build an on board charger system.

 

[Hillhater]

If you push RC lipo below 3.6 - 3.5v you are is risky territory.
You are proposing ideas which, whilst technically possible , no professional battery “expert”. Would recommend ...
... (IE:- mixed chemistry, mixed recycled cells, different capacity parallel groups, and now a common charge system)
Remember there are serious consequences of fire and injury if something unpredicted happens
Be careful,..and make sure you fully understand what you are doing. And the potential risks..
Do not just rely on advice from this or any other forum ! :wink:

 

[neptronix]

The biggest thing i'd be worried about is the RC Lipo, which has >10x more power than a saggy recycled battery pack, pushing large amounts of current into the weaker pack after the weak pack is done sagging like crazy after you nail the throttle.

Recycled batteries and lipo are also the holy grail for sketchy battery setups. You've got one chemistry that's super powerful but will burn your garage if you look at it wrong, paired to aged cells which are full of dendrites which could cause a short on their own spontaneously.. what could go wrong?

In other words, don't do it :lol:

 

[chronosgarage]

If you push RC lipo below 3.6 - 3.5v you are is risky territory.
You are proposing ideas which, whilst technically possible , no professional battery “expert”. Would recommend ...
... (IE:- mixed chemistry, mixed recycled cells, different capacity parallel groups, and now a common charge system)
Remember there are serious consequences of fire and injury if something unpredicted happens
Be careful,..and make sure you fully understand what you are doing. And the potential risks..
Do not just rely on advice from this or any other forum ! :wink:

Thank you for your reply.
Agree with you. I think the dangers outweighs the benefit.

 

[chronosgarage]

The biggest thing i'd be worried about is the RC Lipo, which has >10x more power than a saggy recycled battery pack, pushing large amounts of current into the weaker pack after the weak pack is done sagging like crazy after you nail the throttle.

Recycled batteries and lipo are also the holy grail for sketchy battery setups. You've got one chemistry that's super powerful but will burn your garage if you look at it wrong, paired to aged cells which are full of dendrites which could cause a short on their own spontaneously.. what could go wrong?

In other words, don't do it :lol:

Thank you for the reply.
I have a cell level fuse as a precaution. But I think I will discard this idea, because of the potential danger.