LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[diugo]

The four 260Ah cells have arrived from Balqon! They weighed 19lb each and came in a 24lb wooden crate for a total of 100lb, sent to Yuma, AZ via UPS for $88.

All four bear a date code of 101206, which means built on Dec 6, 2010---so about 25 months old. Serial numbers were not consecutive. Initial voltages were 3.292, 3.293, 3.292, and 3.289---but that doesn't mean much, since Balqon could have simply recharged all four to 3.300V just prior to shipment.

First order of business is to take them each down to 3.100V, then wire them in parallel for a good bottom balance. As someone else already suggested, a halogen headlight bulb is a great power resistor for doing this.

[deckofficer]

Doug,

Now the fun begins. If you have a big load, you will be amazed at the no voltage sag of these cells. Unlike lead acid, these cells hold voltage under big loads like no other battery chemistry I've ever used.

[diugo]

Can't wait to experience that Bob! Right now, my AGMs sag down to 11.9V whenever I run the microwave in the evening---and I always have to triple the cooking time. The inverter should be much happier getting a steady 13.3V.

[Lagoon4us]

Below is what i received prior to my order, VAT free to Croatia but i'll be due to pay probably 20% on arrival, just sorting an agent now see how we go.

Solar Panels 230P - 135.55 EURO
As installation parts we have 5m long special outdoor cable EV-Power | Connection cable 5 m solar MC4 M/F (4mm black) and connectors EV-Power | MC4 T- branch connector 1 to 2 (set Male + Female)

CellLogger (up to 8cells) - 23,90 EURO
The Logger have standard input connector, you can see more details here : lithium & solar power LiFePO4

400Ah cell - 395,07 EURO
Voltage of all cells is double checked at factory, cells come charged to 50% and should be charged to 100% before use

Cheers.

[Lagoon4us]

Have a look at these, what are thoughts? EV-Power | Simple Battery Management Board 4 cells (12V/60A)

Cheers

[mcarling]

Originally Posted by Lagoon4us

Have a look at these, what are thoughts? EV-Power | Simple Battery Management Board 4 cells (12V/60A)

It appears that it disconnects both the charger and the load upon detection of either under-voltage or over-voltage. I would want independent disconnection of the load in case of under-voltage and of the charger in case of over-voltage.

[Lagoon4us]

Originally Posted by mcarling

It appears that it disconnects both the charger and the load upon detection of either under-voltage or over-voltage. I would want independent disconnection of the load in case of under-voltage and of the charger in case of over-voltage.

Is it feasible to therefore have one there to do it's job whilst the boat is unattended BUT with an override to be able to go to a manual i.e. we go ashore, the solars pumping away etc etc.

[Lagoon4us]

Two other BMS units i think more Battery Monitoring than management. We offer ethier fully featured monitoring/balancing system RT-BMS (EV-Power | Real Time BMS 2.1 - Main Control Unit 64 cells + accessories) or for example EV-Power | BMS123 - BMS Main Controller

Cheers

[Lagoon4us]

Some more from their website,

After deep discharge, how to restore the function of the battery pack?
First of all the SBM should be used only as a „last resort“ protection measure. This means you should monitor the battery pack and stop discharging before the voltage goes too much down. The SBM should not be used to replace such monitoring.
Secondly, if the pack gets discharged deeply and the SBM makes the protection, we suggest recharging the battery pack as soon as possible.
In order to restore the function of the SBM, you need to disconnect the load. After the disconnection, the voltage of the cells may go up and the SBM function should get released.
In some cases, the voltage may get too deep or the cells maybe misbalanced – in such cases you may need to recharge the cells first to restore the function of the SBM.
What about overcharge?
The same rules apply to the overcharge protection. You should stop charging before the SBM cuts-off the battery pack. In case the overcharge protection disconnects the pack, you may need to wait for some time until the voltage of the cells drops down to allow the SBM to reconnect.


Has some promise if under 60 amp?

[mrm]

Originally Posted by Lagoon4us

Some more from their website,

[...]
What about overcharge?
The same rules apply to the overcharge protection. You should stop charging before the SBM cuts-off the battery pack. In case the overcharge protection disconnects the pack, you may need to wait for some time until the voltage of the cells drops down to allow the SBM to reconnect.

Personally I think what they propose is a wrong approach. Since an overvoltage condition is a charging controller(s) fault, charging path should be isolated from the bank. Why disable power to other boat systems when there is plenty available?

[goboatingnow]

Originally Posted by mrm

Personally I think what they propose is a wrong approach. Since an overvoltage condition is a charging controller(s) fault, charging path should be isolated from the bank. Why disable power to other boat systems when there is plenty available?

Because all these simple BMS do is disconnect at the battery feed. Hence load and charge get disconnected. It's more complicated on a boat with multiple charging sources, some of which can not get arbitrarily disconnected.

Dave

[mcarling]

Originally Posted by goboatingnow

Because all these simple BMS do is disconnect at the battery feed. Hence load and charge get disconnected.

That's not a design I would buy.

[goboatingnow]

Originally Posted by mcarling

That's not a design I would buy.

No me either. It's not suitable for boats.

Dave

[diugo]

The approach is reasonable if you consider that it's the responsibility of the charge controller to disconnect charging. My charger should stop charging at 13.6V, but if it fails to do so, my voltage monitor will isolate the cells at 14V.

[mcarling]

Originally Posted by diugo

The approach is reasonable if you consider that it's the responsibility of the charge controller to disconnect charging. My charger should stop charging at 13.6V, but if it fails to do so, my voltage monitor will isolate the cells at 14V.

I don't want the loads disconnected in that case. I want only the charging systems disconnected.

Similarly, if the voltage drops too low, I don't want the charging systems disconnected. I want only the loads disconnected.

In my opinion, there is no battery voltage which justifies disconnecting both the charging systems and the loads. In my opinion, disconnecting both charging systems and loads together is just bad design.