how to size your mppt charge controller ?

[bluefox140]

hi, I have 4 arrays . 1= 4s2p 800w ,2=4s2p 800w, 3rd = 4s2p 800w and the fourth is 3s2p of 200w 12v panels total 1200w .
I was thinking using one 60amp mppt for the 3 sets of 800w and one for my 1200w or should I use 4mppt one for each ? I am on 24v system ..please advise thanks

 

[gnubie]

You have to work backwards a little. Step 1. What's the recommended charge rate for your battery (bank). You now know the maximum combined current that all your chargers can supply. It may be more appropriate to use 2 40A chargers and accept loss at the top of production but ensuring that your battery never gets more than 80A, assuming 80A is safe for it of course, while 3 40A chargers could see you pushing 95A and the battery getting charged at a faster rate than you desired.

It goes deeper too. If you have multiple lithium batteries in some sort of parallel arrangement you have to keep in mind what happens if the BMS on one trips. The remainder now have the current that battery was drawing available to them. If you scale things properly they should be able to handle the current even though it might be more than you want to charge them at. If you have 3 and two disconnect, will the remaining one be happy charging at 95A?

A lot, almost all really, cheap controllers do not let you adjust the amp limit. What is on the box is the limit, no more, no less. More expensive controllers will often let you artificially limit the amps the charger will output.

*edit to add information about parallel batteries*

 

[bluefox140]

You have to work backwards a little. Step 1. What's the recommended charge rate for your battery (bank). You now know the maximum combined current that all your chargers can supply. It may be more appropriate to use 2 40A chargers and accept loss at the top of production but ensuring that your battery never gets more than 80A, assuming 80A is safe for it of course, while 3 40A chargers could see you pushing 95A and the battery getting charged at a faster rate than you desired.

A lot, almost all really, cheap controllers do not let you adjust the amp limit. What is on the box is the limit, no more, no less. More expensive controllers will often let you artificially limit the amps the charger will output.

how to find out my battery bank upper amp limit ? I have 8 x 138ah valence battery in 2s 4p at 24v 552 AH
thank you

 

[gnubie]

Best thing I can think of would be to Google search the battery model, unless the recommended and maximums are on the label.

 

[bluefox140]

doesn't say

 

[Supervstech]

1C would be 552A, .1C is often the charge rate, so 55A
If there is a spwc sheet for the batteries you can follow that.

 

[Forbisher]

1C would be 552A, .1C is often the charge rate, so 55A
If there is a spwc sheet for the batteries you can follow that.

His Valence batteries are LFP so 0.5C charging is ok