adding a bank of batteries

[Callinger]

So, our bank of Lithium batteries is proving to insufficient to carry us through the night. We are looking to add another bank in parallel.
Currently we have 2 banks of about 16 KWH each (rated - but we bought them used). We want to add one more bank of 15-16 KWH batteries (48v).
I know the market for lithium batteries is ever changing so I am looking for some advice on where to get the best bang for our buck these days if anyone has any advice. Thank you!

 

[timselectric]

Lithium-ion, or Lithium iron phosphate (AKA LiFePo4, LFP)?

 

[Callinger]

I'm not 100% sure. Are you asking because the charge / discharge profiles would be different? I think LiFePo4. Here is the data plate:

 

[timselectric]

Not sure from the picture.
I was going to suggest two options if LFP.
1) pre maid server rack batteries.
2) buy individual cells and a BMS to build your own battery.

 

[Vigo]

Would depend on age but i would guess most A123 products in existence today predate their use of lifepo4.. are those EV modules? Admittedly i didn't run the number so i'm being lazy in asking.

 

[Callinger]

All I know is they were military.
Is it bad to mix a bank of Lithium-ion, with a bank of Lithium iron phosphate?

 

[Callinger]

When I have tried to "run the numbers" I have found nothing and A123 was no help.

 

[Callinger]

so, Is it bad to mix a bank of Lithium-ion, with a bank of Lithium iron phosphate?

 

[timselectric]

You just have to choose a charging voltage that is acceptable for both types.

 

[Callinger]

So, we added a rack of 6 EG4 48v batteries in parallel to our A123 bank of batteries. The LV6548s only seem to be drawing power from the EG4 rack. The EG4 rack is at 52.27 V the A123 bank is at 52.21 V. Why is it only drawing from the EG4 batteries?

 

[Vigo]

Is it possible to capture the wiring evtween the two banks to the inverters, in a picture?

Wiring differences contributes. The millivolt difference contributes. The difference in internal resistance of the two battery strings contributes.

But if you drain the eg4s to an identical voltage as the a123s, the current contribution of the 123s should start increasing, and while they are both draining the difference in current between them is caused by the differences in wiring and internal resistances.

 

[Callinger]

Thanks, Vigo for your insights. I don't think a picture would help much in this situation because of the cramped nature of the equipment room but the 2 banks are wired in parallel to busbars ahead of the 2 LV6548's. The cables to the A123 bank of batteries is a couple feet longer though.
Something strange that I cannot understand - I disconnected the solar array to let the EG4 bank of batteries' voltage drop to the point where it was equal to the A123 bank, expecting to see the A123 bank begin to contribute to the load. As the EG4 bank dropped in voltage, so did the A123 bank even though the A123 bank never showed any flow of amps. (true RMS DC clamp meter). Any idea why this could happen?

 

[Vigo]

I can imagine several possibilities for that but it really depends on the hardware in place. For example, does the a123 bank have a bms? If so do you know what it disconnects at?

current flowing in or out of a battery does not begin to be measurable at the first little millivolt of voltage differential unless everything between the two points of different voltages has extremely low resistance, but that would have to include the batteries themselves. for example if I have a car battery charged to 12.7 V and I hooked something that is 12.75 V to it I will probably not move measurable current. So it’s possible that the 123 bank was at a lower resting voltage than what you were seeing on the screen and the eg4 bank through the paralleled wiring was essentially holding that circuit up to its own voltage level without creating enough of a voltage differential to force any current into the 123s. Sort of like if you hooked one end of a wire to the eg4 and the other end not hooked to anything you would see the eg4s voltage everywhere on that wire. Its possible that at the voltage differential that existed in your situation, the 123s were functionality identical to a ‘dead end’ at the end of that shared wire. If that’s the case the voltage could fall all the way to slightly below the actual resting voltage of the 123s before you had measurable current. It depends where the voltage measurements are taken whether that’s plausible.

 

[Callinger]

you bring up a good point; I don't think I disconnected the A123 bank from the system when I checked the voltages. I will try to absorb your input and check all my parameters on the controllers and BMS's before a trip to the transmitter site tomorrow.

 

[Vigo]

Let us know what you find. Having non marching battery banks in parallel is an interesting thing. I have seen a ‘mysterious’ lack of current flow many times when paralleling lifepo4 and lead acid banks at different voltages in my rv.

 

[Callinger]

Still waiting for weather to improve to go to the transmitter site but I want to keep the topic open.

 

[Callinger]

Went to the transmitter site today. I did not have time to work on this issue; the snow chased us off the mountain! I guess I will have to re-open the topic later when I have more time to chase it down. Thanks for standing by!

 

[Callinger]

The generator surges on both gasoline and propane. It only surges under load. I was not able to stop the surging by careful adjustment of the main propane tank valve or any other adjusting screws. Is it possible that there is a problem with the governor? If so, how can I trouble shoot the governor?

 

[Bossrox]

So, we added a rack of 6 EG4 48v batteries in parallel to our A123 bank of batteries. The LV6548s only seem to be drawing power from the EG4 rack. The EG4 rack is at 52.27 V the A123 bank is at 52.21 V. Why is it only drawing from the EG4 batteries?

Newer batts have a lower internal resistance than older so the new 1's will draw the most & the others will follow as they equalize.

 

[crossy]

The generator surges on both gasoline and propane. It only surges under load. I was not able to stop the surging by careful adjustment of the main propane tank valve or any other adjusting screws. Is it possible that there is a problem with the governor? If so, how can I trouble shoot the governor?

It's probably time for a new thread on genset issues, but when our (gasoline only) genset misbehaved by surging on load it turned out to be an air-leak between the carb and manifold.

I'd start by looking for anything loose, split pipes etc.