Floating below 100% SOC

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Floating below 100% SOC

Postby JRHill on Mon Apr 18, 2016 1:15 pm

Not being nit picky but just wondering about fine tuning:

Example: I'm fully through the bulk and absorb cycles and into float. After a bit (1-2 hours) and with no loads other than the normal light draw of household stuff, I see the SOC falling back to 99, then 98, etc during full sun. I have Absorb End Amps set at "0" and I'm thinking this is where I need to add some value. Correct? If so, what is the best way to estimate a beginning value? I'm thinking that if I can catch the charge value just as the batteries go to float after the 3.5 hour absorb cycle, this would be a good beginning set point? (At least, for this time of the season?)

TIA,
Jim
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Re: Floating below 100% SOC

Postby Vic on Mon Apr 18, 2016 4:41 pm

Hi JRHill,

So, are you saying that your batteries are not maintaining 100% SOC with normal household loads, with the FM CC showing that it is in Float, not Float-MPPT (or whatever the FMs say when there is too little PV input to maintain Vfloat)?

Yes, when you set EA to a non-zero value, the FM CC should end Absorb either by the Absorb time setting, or the EA setting, which ever occurs first.

If your FM remains in Float, with normal household loads, and you see the SOC diminishing from 100% SOC (assuming that the device that shows SOC is actually accurate), then, probably, your Vfloat is a bit too low. IMO, the best Temperature Compensated Float voltage is one that will just barely keep a fully-charged battery, fully-charged. It is quite possible that the SOC measuring device could well be inaccurate.

It is true that many battery monitoring devices will measure battery temperature, and change the displayed SOC, based on battery temperature, but it is difficult to imagine that your batteries would cool enough between the beginning of Float, and some minutes or an hour later, with any reasonably-sized batteries.

Also IMO, relying on a battery monitoring device for accurate indications of actual SOC, is really a waste of time ... Battery Monitoring devices are more like rough indicators of approximate SOC, not absolute indicators, and, perhaps should step in 10% steps, or show some indicator that they know that they know only showing approximations, etc.

FWIW, Vic
4/20/08: 18 Shell SQ 175-106 Vmpp, Stacked 5548 SW+, 1350 AH Surrette 4KS25's, MX-60, Kubota SQ-3250 25 KVA Polyphase Diesel genset. Thanks OutBack for this Forum + the great Support and Service.
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Re: Floating below 100% SOC

Postby larrywa on Mon Apr 18, 2016 7:14 pm

I started at a charge/discharge factor of about 85% and have been raising it to 90% over the last few weeks to keep my SOC not triggerring my notification system in my Home Automation system.

I have also been playing with my float level where the inverters will suck it down to, while monitoring the float current on the grapgic chart. Batt In and Batt Out.


Trouble with this whole Outback system is you have all these battery cycles and a temperature compensation for nothing.

If you run a Mate3 when grid-tie mode is on it changes all the CC floats to the absorb voltage so that the inverters can have excess voltage to make them feed energy back into the grid. Now you have a non-temperature compensated float setting for your batterries based on the sell setting in the Mate3....duh!

I can't believe after all these years that OutBack can be so first year in their understanding of how battery charging is supposed to work. Lef hand, right hand thing?
It does seem like OB had really good equipment and then software writers come along with Mate3 and they started from their first year of developement again.
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