reconfigure strings when moving from 24 to 48 v

[jtdiesel65]

I was wondering it there is some advantage to reconfiguring strings when moving from 24 to 48 volt. The sizing tool says the controller wants to see 130% of high battery volts. My high battery volts are now ~58v.  Panels are 43.8 voc, 35.2 vmp. But the tool indicates that if I move from 2 panels per string to 3 per string, the config is borderline with hypervoc. Attached screen shots of the two scenarios. Is there a more efficient setup? Or does the fact that the 3 string config has possible hypervoc make it a showstopper?

[Vic]

Hi jt..,

WIth a 48 V  Flooded LA battery,  and a Classic 150,  it has always seemed to me that one has essentially no choice to run strings of three 72 cell PVs.   EQing cool batteries may well require Veq of about 64-ish volts,  and a string Vmp of 70-ish V (STC) is just too low,  even with Legacy P&O,  and perhaps LoMax= ON.

There would probably be some cold days,  or at least cold mornings,  where the CC would probably be in Hyper VOC,  with strings of three,  until the PV cells are warmed.

Strings of two PVs would be a bit more efficient than with three PVs,  but it is all a tradeoff.

My system is running strings of three 72 cell PVs  --  string Vmp of 106-ish volts at STC,  but we have a mild climate,  here in CA,  so,  we have never been in Hyper VOC.

Tough decision,  IMO.   MN Tech may have some added guidance.   73,   GL,   Vic

[jtdiesel65]

thx

Yeah, I'm not sure which is better.

[Vic]

Hi jt..,

Did skim your previous posts,   and it  appears that you are now using FLA batteries (forklift bat,  IIRC).   If you will continue to use FLAs,  then  it seems that strings of two of your 170s will probably not have enough string Vmp to extract MPP power.

On the other hand,  if you were thinking of some Li batts,  then strings of two might be fine,  as no Temp Comp for charging,  and no EQ.

Forget your future plans.    IMO,    FWIW,  Vic

[jtdiesel65]

I have 560 ah of LFP. It's either an expensive experiment or it's going to work out really well. I figured I would try them and just sell and buy an FLA if things didn't work out. I've only been using them for a few days now. So far there are some quirks, but nothing that seems impossible to overcome.


thx