Lithium Lipo + LifePo4 batteries in parallel

[Christophe]

Subject divided since solar-photovoltaic / assistant for-my-installation-solar-t16166.html

It concerns the placing of Lifepo4 and Lipo lithium batteries. It doesn't work and here's why ...

If you put a 275 Ah pack in parallel to your existing 150 Ah pack, you will quickly destroy your lower capacity pack.

Exact, never mix different batteries! Whether in parallel or in series!

I tried on one of my electro road prototypes from Lipo 12 Ah with LifePo4 10 Ah in parallel... capacities quite close so I was confident but in fact not!

LifePo4 simply didn't discharge at all or almost not, 99% of the current was drawn on the Lipo!

I do not know the exact physical reason but it must certainly be related to their discharge capacity, 30C for lipos, 3C for Lifepo4 ...

It is as if the section of the "electron valve" of the lipo is 10 times larger and the lipo electrons push the lifepo4 electrons into the lifepo4 battery.

[dede2002]

If you put a 275 Ah pack in parallel to your existing 150 Ah pack, you will quickly destroy your lower capacity pack.

Exact, never mix different batteries! Whether in parallel or in series!

I tried on one of my electro road prototypes from Lipo 12 Ah with LifePo4 10 Ah in parallel... capacities quite close so I was confident but in fact not!

...

Hello,

Theoretically, batteries of different capacities can be put in parallel, provided that they have the same voltage, and therefore the same technology.

In practice, the more batteries there are, the more problems there are, whether in series or in parallel. A defective battery leads to the destruction of the others.

[izentrop]

If you put a 275 Ah pack in parallel to your existing 150 Ah pack, you will quickly destroy your lower capacity pack.

Exact, never mix different batteries! Whether in parallel or in series!

I tried on one of my electro road prototypes from Lipo 12 Ah with LifePo4 10 Ah in parallel... capacities quite close so I was confident but in fact not!
LifePo4 simply didn't discharge at all or almost not, 99% of the current was drawn on the Lipo!

I do not know the exact physical reason but it must certainly be related to their discharge capacity, 30C for lipos, 3C for Lifepo4 ...

I don't know anything about it but it's not the same technologies
LIPO Rated voltage 3,7V: Charging voltage 4,2 Volts per cell. http://www.ni-cd.net/accusphp/theorie/l ... charge.php
Li Fe Po 4 Nominal cell voltage: 3,3V Charging voltage: 3,6V http://www.ni-cd.net/accusphp/theorie/lifepo4/index.php

When the LIPO is discharged the LIFE is only partially discharged or not, on the other hand if the charger is configured for the LIPO, the LIFE is overcharged ... to be avoided with lithium (fire). You were lucky if the Li Fe did not swell.

[Christophe]

Thank you I know all this and I obviously thought balanced voltages ... otherwise one of the 2 batteries would have been completely unthinkable in overvoltage ...

24S in lifepo4 and 20S in lipo.

both are wired to a dedicated bms and one independent

the experience did not last long

[Christophe]

Hello,

Theoretically, batteries of different capacities can be put in parallel, provided that they have the same voltage, and therefore the same technology.

In practice, the more batteries there are, the more problems there are, whether in series or in parallel. A defective battery leads to the destruction of the others.

Theoretically and to troubleshoot yes ... practically and for cycling it is completely not recommended.

My mixed drum experience was educational above all ...

[izentrop]

Thank you I know all this and I obviously thought balanced voltages ... otherwise one of the 2 batteries would have been completely unthinkable in overvoltage ...
24S in lifepo4 and 20S in lipo.
both are wired to a dedicated bms and one independent
the experience did not last long

20s, BMS are Chinese for me. You talk about balanced voltages, it makes me think that the charge of a computer battery is done independently by elements. In this case, no charging problem, but if you put the batteries in parallel, when using the 4,2 V battery will immediately discharge in the one charged at 3.7 V.

Just the 4 battery or maybe 8 of 275amp and nothing else.
Of course new batteries.

It is true that we are in a wasteful society , but on the other hand if they have been mistreated, they must no longer have their original capacity, putting them in parallel with new ones would not have been balanced either.

As you have several chargers, you can charge your 150 Ah pack independently and switch it manually when your other batteries are exhausted. It can also be done automatically with a PLC.

[Christophe]

20s, BMS are Chinese for me. You talk about balanced voltages, it makes me think that the charge of a computer battery is done independently by elements. In this case, no charging problem, but if you put the batteries in parallel, when using the 4,2 V battery will immediately discharge in the one charged at 3.7 V.

So it's completely HS but I will answer.

These are 2 batteries that I wired myself starting from each element.

a) BMS = Battery Manager System, 3 main functions
- this balances the voltage of each element of the battery.
- this limits the discharge and charge currents.
- this cuts the voltage to protect against overloads and overloads

b) 20s = 20 elements in series .... xs = x element in series ...

A BMS is made to work on X elements in series.

So I had:

lipo

Nominal voltage: 20 * 3,7 = 74 V
Max voltage 20 * 4,2 = 84 V
Min voltage (cut-out by configurable BMS) 20 * 3.2 = 64 V

LiFePO4

Nominal voltage: 24 * 3,2 = 76,8 V (the mounted BMS is sold for a 72V)
Max voltage 24 * 3,6 = 86,4 V (can be increased to 3,65 V)
Voltage min 24 * 2,8 = 67,2 V

Both were charged at 2V with the same charger but not at the same time

The LifePo4 therefore worked less high in self-tension than the Lipo ... but that does not explain why it did not work at all in landfill. It is indeed a story of differential electromotive force on the same circuit! A bit like connecting 1 compressed air circuit with 2 compressors, 1 to 10 bars and the other to 1 bar on a common outlet: the 10 bars will work.

When I unplugged the Lipo the Lifepo4 worked.

Besides, I have a mysterious element on the LifePo4 (not mounted on the battery) whose voltage oscillates (?!?) I will make it a subject!

[sicetaitsimple]

The LifePo4 therefore worked less high in self-tension than the Lipo ... but that does not explain why it did not work at all in landfill.

Subject to all reserves, the internal resistance of a LifePo4 battery is around 10 times that of a Lipo. On a parallel installation, it does not seem abnormal to me that the LifePo4 does not charge anything or almost as soon as we start to shoot it.
Once again with all reservations ... I have no certainties in electrical engineering!

[Christophe]

Yes, that's exactly that kind of explanation ... hence my analogy with a water valve or air pressure.

I have a "pro" charger which gives the internal resistances cell by cell of lipo batteries (calculated via a load algo since obviously we cannot measure them directly).

Some, washed out, can go up to 400-500 Ohm but a healthy cell has an internal resistance to the load of 0 Ohm.

In discharge I ignore these values, I imagine that the more we shoot inside the more it heats and the higher they are.

[sicetaitsimple]

Yes, that's exactly that kind of explanation ... hence my analogy with a water valve or air pressure.

The analogy would be rather two compressors at 10bar in //, one of which delivers through a pipe of 1/4 "and the other through a pipe of 3". But we are not going to quibble!