LIFEPO4 and Lithium ion in parallel ?????????

I recently built my first LIFEPO4 packs. I ordered 80 K2 energy cells from battery hookup. The first 6S pack was solderless but took up a lot more space than desired so I got a new 80 watt iron and some large tips and soldered a second 6S pack and a 4S pack.

I thought LIFEPO4 charged to 3.7V per cell but they settled at 3.3V per cell.

Standing voltage is 53V. - 16S.

The problem is I only used 16 gauge wire. I can only draw 600 watts from the pack safely but need about 1,200W.

About a year ago I bought a 13S - 7P pack rated at 20 Ah and 1,000W. I need about 200 watts more as am running a 26" - 1,000W direct drive hub motor. The top speed should be like 30 mph or at least 28 mph but not even close and it is about useless up hills with the 13S lion pack.

1,000W / 48V = 20.8 * 53 = 1,104 watts.

Basically I do not want to take the LIFEPO4s apart and re solder 12 gauge wire. I also built three packs each with a balance plug to charge with my 6S LiPo chargers. The packs are illustrated below.

After extensive searching I see people have paralleled up LiPo to lithium ion and both of those to SLAs but I have NOT seen LIFEPO4 in parallel with anything except LTOs I think.

Since the LIFEPO4s are brand new and never ran them and the Lithium ion pack is > 100 cycles all batteries are close in age and use as well as standing voltage.

Even the capacity is within 1Ah.

The 13S - 7P - Lion pack is rated at 20 AH and the 16S LIFEPO4 at 19 AH. 3.8 Ah * 5 cells in parallel = 19AH. I was thinking that I would not need to charge everything separate if all in parallel as the 13S - Lion pack has a charge port and I have 3 balancers if I need to balance one of the LIFEPO4 packs.

Here is the diagram.

Will it work ???????

Please let me know.

Thanks.

LC. out.

I'd asked a similar question recently, along with suggesting various elaborate schemes in a attempt to match the characteristics of the different chemistries and keep within the limitations of each and the answers boil down to "hook them up together and try it". However! That was with new cells for both chemistries and you're hooking up used cells in series with new ones and imo that's a recipe for disaster.

The very first thing I'd suggest doing is testing the packs, hook them up to a load and see how they behave. I think it's very likely you'll get so much difference between them that the old cells will be pushed under voltage and destroyed. For a load, I'd use 24v truck headlamp bulbs or heater plugs as I have them to hand, an old electric heater may work if you have one or just a big coil(s) of wire will work, anything that has the right resistance and current handling to match the loads you'll be putting on them.

If they pass that test then it shouldn't be too hard to work out how they'll behave when in parallel, how they sag 'should' tell you how much of the load they'll be carrying at various currents and if that's within their ratings you 'should' be good to go. 'Should' is in inverted commas because that's all theory, I'll be doing the same tests myself at some point but so far haven't come across any similar tests/figures to use as a basis.

Since the LIFEPO4s are brand new and never ran them and the Lithium ion pack is > 100 cycles all batteries are close in age and use as well as standing voltage.

Click to expand...

That is my quote.

Add capacity to that also.

It might be only 50 cycles or less than 100 on the lithium ion pack. It is basically new and the LIFEPO4 never been run.

The lithium ion pack has a BMS and the LIFEPO4 no BMS. Balance plugs.

It is not like the Lithium ion pack with the BMS can tell the difference in battery chemistry or type, It should just detect a similar voltage ???????????????????????

Please let me know.

Thanks.

LC out.

That crazy system will work fine but tricky.. take care about voltage limits details!

usefull total voltage range for this parallel working range --> 54,6V(upper lithium ion cells charger) to 40V (lower LiFePO4 cutoff voltage)

LiFePO
Minimum -->2.5x16S = 40V cutoff
Maximum --> 3.6Vx16S= 57,6V max

LithIon
Minimum -->2,7Vx13S= 35,1V cutoff
Maximum --> 4,2Sx13S=54,6V max

54,6V max voltage limited by lithium ion top limit
system cut off LiFePO4 @40V and after that maybe only 13S lithium battery keep drain solo until 35,1V ..

at math is minimum multiple common calculation..

TAKE CARE because is a parallel, LithIon battery will force LiFePO4 voltage to be tha same, if your LithION battery goes 35,1V, so there will be this voltage at LiFePO4 battery package(minimum 40V forced to 35,1V)
make sure LiFePO4 BMS will cutoff/open circuit for sure at 40V! otherwise, LiFePO4 pack will be discharged until 35,1V means 2,19V per cell (under 2.5V lower limit but maybe still safe..)

there is also an unknown behavior at Lifepo4 bms cutoff voltage limits, because x3 serial LiFePO4 batteries. since each of 3 batteries have individual bms. three serial bms's(serial bms's not recommended..) .. it would be more stable if use a single 16S LiFePO4 BMS..


think about this "boom"

U could get more capacity from this system by charging all this stuff to 57,6V , but...
you have to MAKE SURE that Lithion ION 13S BMS cutoff/opens circuit at 54,6V!
this way, since LithION battery is full, it keep putting more charge at LiFePO4 packs until max 57,6V

NOT recommend doing this..

if LithION pack bms does not have superior cutoff,it will put 57,6V at lithION 13S cells, meaning 4,43V for each cell. maybe still workin..

AKE CARE because is a parallel, LithIon battery will force LiFePO4 voltage to be tha same, if your LithION battery goes 35,1V, so there will be this voltage at LiFePO4 battery package(minimum 40V forced to 35,1V)
make sure LiFePO4 BMS will cutoff/open circuit for sure at 40V! otherwise, LiFePO4 pack will be discharged until 35,1V means 2,19V per cell (under 2.5V lower limit but maybe still safe..)

Click to expand...

The LIFEPO4 packs have no BMS. I am using balance plugs and have two 6S LiPo chargers.

I do not plan on running the packs low. Standing voltage will be around 54V and will run them down to 47 or 46V maybe and then re charge them back to 54V. That is the plan. I will get more cycle life that way. Also I will have an onboard meter which will show standing voltage and voltage SAG under load.

Not sure if you know but I am forced to charge the Lithium ion packs to 4.2V per cell only because of the BMS. A BMS is not always a good thing. I bought the pack off e bay and ordered the charger. For maximum cell life charging to 3.92V you can get > 2,000 charge cycles. Charging at 4.2V < 500 cycles.



I thought about putting a 1S - 7P pack in series with the Lithium ion pack but a BMS in series with another battery outside the BMS is even more tricky than running a BMS in parallel with a pack with no BMS and different chemistry like I intend to do after I weigh all the information.

For one thing the BMS needs 4.2V per cell to properly balance the pack so stuck with about 500 cycles. I do plan on building a 15S pack and charging it at 14S so 14 * 4.2V = 58.8V. so 58.8V / 15 = 3.92V. However a BMS will not work. External balancers will though and I own three. I also have a bag with about 20 - 6S balance cable extensions. If you want to get four times the cycle life from 18650 batteries they need to be balanced separate.

I have about 200 - 18650 cells I got from Battery Hookup but are in plastic holders and are wired up for 3S. They were used in a life vest for people with heart conditions and all the cells need to be extracted and glue was used between the cells so the cell wrap comes off and the little rubber top ring for the positive top also so I re - wrap them with electric tape and use liquid tape to put the little rings back on so no short. My method does work and already have several 1S - 10P battery banks built.



Notice the packs with all the wires sticking out. Back then I was soldering a 3 or 4" piece of wire to each cell then twisting them together. I learned how to use a single piece of wire across the top and bottom. I use strips of gorilla tape over the edges where the rings go and wrap electric tape on the wire as well for extra protection as the wire heats up considerably. Those above I just cut the long wires off and re soldered the connections. I started using a single piece with the LIFEPO4 but should have went with 12 gauge wire.

When using a wire for each cell it adds up and < 10 gauge. The problem with a single wire is 16 gauge is not thick enough. That is what happened with the LIFEPO4s There are 16 banks of 5 in series so a few feet at least of 16 gauge wire only rated for 600 watts or 10 amps. That could be a problem. That is why running in parallel with the 13S - pack with the BMS could solve that problem as then together I can safely use it as a 1,200 watt battery.

Thanks.

LC. out.

latecurtis said:

The LIFEPO4 packs have no BMS. I am using balance plugs and have two 6S LiPo chargers.

I do not plan on running the packs low. Standing voltage will be around 54V and will run them down to 47 or 46V maybe and then re charge them back to 54V. That is the plan. I will get more cycle life that way. Also I will have an onboard meter which will show standing voltage and voltage SAG under load.

Click to expand...

U think all the world into a project, but U need to check some details..
"am running a 26" - 1,000W direct drive hub motor"
This means maybe 30A max peak draw from this system and average current from system will be arround 15A
Using only a 7P lithium ion means 4,2A max per cell and average is half aprox 2,1A So this is not a real stress for good cells.. (no worry about SAG)



Now U add a parallel with 2P LiFePO4 low internal resistence. Its a mixed 7S lithium +2P LiFeP
So work from Lithium pack will be a fraction . maybe 2A max and 1A average per cell for 7P13S li ion ...

since U are only discharging a fraction of batteries capacity, this means U never need to worry about cycles, because at this current and depth of discharge, good cells last much more than 1K cycles.
your cycles will go to many thousands..

But system not optimized.. because U're losing a lot of capacity with parallel voltage window range 54V to 46V
anyway this is someway good, your cells (lithium + LiFePO4) will last 4k cycles and last more than 10years.. like a duracell..

Yea.

I wont be paralleling them. I am just tearing the LIFEPO4 pack apart and starting from scratch. I bought 10 gauge wire. However after attempting to solder a piece to the top of cells found it to be impossible. Solder really does not want to stick to 26650 cells anyway.

I have to go back to my old method of soldering cells.




It is way easier than striping a single strand of wire and solder it across 5 battery terminals. I just put a decent size bead of solder on the top or bottom of the cell and tin the end of the wire , then heat the bead back up and stick the wire in. 10 seconds or so and it is done. About 20 seconds though for 26650 cells as the larger surface area needs more heat to stick.

I ordered a new Weller 100 watt iron , lead base solder and rosin core flux for the wires. The big drawback with that method is dealing with five wires on either side of the 1S - 5P battery bank. The wires will need to solder to a 10 gauge wire for the series connections. That is where the flux comes into play. It is a very large solder joint. five 16 gauge soldered to 10 gauge.

The other major problem is stacking the banks. Lots of wires to deal with. The wires take up almost as much room as the cells. Now I know why bus bars and spot welding is popular. Less space.

Thanks.

LC. out.