any comments on this LiFePO4 pack & charging plan?

[Ben]

If I used a 48v supply on plugged into a wall timer for example, this should be a safe way to quickly bulk charge without constant monitoring?

You'd have to make sure that the timer would correspond to the state of charge of the pack.

Another option would be to make up a time delay relay circuit using a 555 timer or something similar, so after a certain time the bulk charger could switch over and charge the other 12s1p string. This would also have to be done carefully so as to not overcharge the pack.

 

[fechter]

13 contacts cool, I can't visualise what shared in-between connections means. I understand the basic concepts of series & parallel pack building from the voltage and amps/ah perspective but large pack building and efficient layout methodology alludes me. I've googled pack building but haven't found a good explanation.

Here's a crude pic: Imagine extending it to 12 cells...

 

[voicecoils]

Awesome I understand that So I need to sort out connectors but otherwise done with my single cell charger plan.

I've ordered a 48v 8a power supply $40+40 shipping to Australia which I can trim to 43.8V (3.65v/cell) I wanted to buy two, but it doubled the shipping...

Hopefully the charger will be able to supply the full 400w charging power to charge each 12s1p string quickly.

 

[fechter]

Yes, that should work except you need to be careful that none of the cells get overcharged. A BMS would be safer. If you time the charge so that none of the cells get past the bulk charge phase and start rising in voltage it should be OK.

If you had a series-parallel pack that broke a connection or a cell lost capacity over time, you could fry some cells.

 

[jeffkay]

Charge like you said? You can do this all day--get it? Just kidding. If you do go this route, buy at least one or two extra chargers. I only have one and it has become crippled...
Jeff K. "Deep Cycle" project

 

[voicecoils]

Yes, that should work except you need to be careful that none of the cells get overcharged. A BMS would be safer. If you time the charge so that none of the cells get past the bulk charge phase and start rising in voltage it should be OK.

If you had a series-parallel pack that broke a connection or a cell lost capacity over time, you could fry some cells.

Cool, if an inexpensive and not too complex bms capable of 72v (or 12v modular groups for example) came along I'd be interested.

For unattended charing I'll just use the voltphreaks. But the powersupply looks like a good way to charge in a hurry.

I think I'll need to be sure both 36v strings are fully charged (or at least at the same SOC) before I reconnect them, otherwise I'd imagine the imbalance would not be healthy for them.

 

[voicecoils]

Does this sound do-able or am I missing something critical? If you do go this route, buy at least one or two extra chargers. I only have one and it is crippled...
Jeff K. "Deep Cycle" project

Crap, I've already ordered...exactly 12