Lifepo4 battery too cheap?

[Tony1]

1 hour ago, 170968 said:

 

Nice sunny day. Getting lots of free power.

 

Would you (or anyone else) mind sharing your settings for absorbtion voltage and length? I am trying to achieve 85% with a lowish voltage setting. I tried it at 13.6v absorbtion and for only 15 minutes. It went into float whilst the SOC is down at 81%, so that's no good. Should I leave the voltage and increase the absorbtion time so that it stays at 13.6V while getting to 85%, or what do you suggest?

 

I have thought about using the excess to heat water, but not an air-conditioner. It's a great idea and I do have space. Only thing I don't like is the amount of noise the bloody things make.

 

In winter I set the absorption at 14.4v and for I think 6 hours. The idea is that the MPPTs wont often fill up the batteries enough anyway in winter, so I have them charging flat out, and eventually the BMV712 switches them off when they get to 85% full.  

If the BMV712 fails to switch off the MPPTs for some reason, the 14.4v setting means they will get up to maybe 99% full before they go into float (which I set at 12.75v). Getting them up to 99% full is not what you want to do on a day to day basis, but its ok as a one-off.

And bear in mind you'll want to get them up to 100% SoC every few weeks anyway, to re-synchronise the BMV712 and keep its SoC reading accurate. 

 

If I wanted to be less aggressive I would set the absorption to 13.9v, but there's no guarantee the MPPT will go into float at 85% or even 90%.

On a summer day for example you might get 90amps of charge in, and the voltage will rise more quickly than if it was a winter day and you only had 15 amps coming in.

So at 15amps charge and 13.9v absorption voltage, your batteries might get to 95% full before they go into float. But at 90 amps charge at 13.9v setting, the batteries might only get to 80% full before the MPPTs decides to go into float. 

Thats why I like using SoC as the criteria to decide when the charging stops- it removes the variable factor of the charging current.

 

 

 

 

 

 

 

 

Edited March 10, 2023 by Tony1

[170968]

Makes sense. Thanks Tony.

Edited March 10, 2023 by 170968