Outback Equalization/RTS Questions in the Cold Cold Winter

Dan-A-Canuck

Hi all: I can't seem to find answers anywhere, comments or help would be appreciated. I have an off grid remote setup with about 1100 hours storage with Trojan L-16's.... @12v - yea.. I know , and about 1200 watts of panels. I'm running a pair of Outback FM 80's both with an RTS, one is set up as slave. My questions revolve around the RTS and the charge limit. 1) The Trojans have a -4 f limit on operating range. My inclination is to use that number to calculate the limit setting for the Outback CC. i.e.  the compensation per cell added to the absorb recommendation of 14.8v. That works out to a limit setting of about 17.6v, my inclination is to set it to about 17.2 as a factor of safety. Comments? Suggestions? 2) I can't find this answer anywhere: the recommended eq. for the batteries is 15.5v. Does the RTS come into play with the eq. charge. i.e. does the Outback bump the charge above 15.5 using the RTS? And would my set limit throttle the eq. charge to my limit setting of 17.2v? The equalization charge almost seems redundant in cold weather if it only reaches the absorb setting.  A little more info: yes, my batteries probably spend the bulk of the winter down close to -4 depending on the winter and, I don't usually get to visit my batteries between October and May.  Thanks for any help: Dan
Afterthought: I've always wondered this. Do my batteries get a "Mulligan" in winter when they are so cold? i.e. a longer life because they are "hibernating". Heat kills, does cold do the opposite?

Estragon

The short answer is yes, the batteries get a sort of mulligan (on sulfation) in winter. The chemical reactions that cause self-discharge and eventual sulfation happen much more slowly at temps that low. Fully charged, they should be fine. Partly discharged though, they would be at risk of freezing.

I assume you tilt the panels to near vertical for winter to be sure of shedding snow? If they stayed covered for long, FM self-consumption could run the batteries down far enough to freeze. I've had this happen with my panels at ~70° tilt.

EQ should definitely be temp compensated to be effective. I never auto-EQ, as IMHO the risk of running low on water etc is too high. Limiting absorb voltage temp compensation is probably wise as that reduces the chance of running low on water. Assuming there are no loads, the bank should get lots of float time.

westbranch

An option is to have  a  couple of panels mounted vertically and a PWM CC to keep the bank topped off overwinter as you have no other loads than the CC... MN Brat  30A max   >> http://www.midnitesolar.com/productPhoto.php?product_ID=615&productCatName=Charge Controllers - Brat&productCat_ID=49&sortOrder=1&act=p    $89 US  +  shipping ... from NAWS    https://www.solar-electric.com/midnite-solar-brat-pwm-solar-charge-controller.html

Vic

Hi Dan-A..

We always want MORE info;

What make/model Inverter are you using?
Do you use a Mate?  If so what model Mate?
What is the model number of L-16 that you are using?

We always use a Temperature Compensated EQ voltage.

Believe that the OB FM CC still do not have temperature comped EQs,   at least without a Mate 3 (?).
Believe that the OB FM CCs are set at -5 mV/Cell/C  for compensation,   does this match the needs of your batteries?

Thanks for added answers,  when you have a chance.    Vic

Estragon

> @westbranch said:
> An option is to have  a  couple of panels mounted vertically and a PWM CC to keep the bank topped off overwinter as you have no other loads than the CC... MN Brat  30A max   >> http://www.midnitesolar.com/productPhoto.php?product_ID=615&productCatName=Charge Controllers - Brat&productCat_ID=49&sortOrder=1&act=p    $89 US  +  shipping ... from NAWS    https://www.solar-electric.com/midnite-solar-brat-pwm-solar-charge-controller.html

That's what I ended up doing for when panels get covered while I'm away. The "winter" panels produce enough to keep batteries topped off, and handle the self-consumption of classics.

petertearai

 Hi my understanding  is that the EQ  voltage is not temp compensated , however if the temp gets to 50 deg c , EQ will stop .

Dan-A-Canuck

Thanks for the great input all. A few comments in reply to the above: batteries remain fully charged all winter, this is year 4 and the few times that I get up to camp in the winter, and in the spring, always fully charged according to the hydrometer. Locals tell me that they get 15+ years from lead/acids if they treat them well. I seldom discharge more that 20% (80% remaining) so I'm hoping that my have a similar long run. Yes, the panels go vertical in the fall, The top rail is hinged, I drop them when I leave in early November - they stay 100% clear. Water is never an issue, even in summer - the batteries seldom see 77f. I only top up water a couple of times a year, maybe 3 oz. a cell. No loads in winter, just the panels, batts and the CC's. I can't find that setting/option so I'm guessing Vic is right since I don't run a Mate -  I just set one CC as a slave with settings i.e. only one is set on auto-EQ every 30 days and one slightly lower on absorb charge. The batteries go into absorb every day but they spend most of the time in float. The Trojans are L16EAC's, no load in winter except the CC's. I calc'd the OB temp compensation, it was pretty close to the Trojan spec. I'll probably hear about this one, but my guess is that temp compensation being spot on is more important on the hot end of things rather than the cold... intuition - no more. And, the auto-EQ works in the very cold, according to the log, and I actually saw the CC auto- EQ last time I was up, air temp was -25C (-10ish), batteries were close to that. Again, thanks for the input!