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rd10153 avatar image
rd10153 asked

Double-Checking MPPT Settings for Flooded Lead Acid

I added a solar setup to my teardrop. Would someone be so kind as to double-check my MPPT settings?


I'm running a pair of 6v Duracell GC2 flooded lead acid golf cart batteries in series at 12v. They are 215 amp hours each, so 215 amp hours total at 12v. I can't find specs for this exact battery but have read they are the same as the Deka GC10 with specs here.


Editing to add links again as I'm not seeing them above when I view the post.

Duracell GC2: https://www.samsclub.com/p/duracell-golf-car-battery-group-size-gc2/prod3590228

Deka GC10 Specs:


Batt Voltage: 12v

Max Charge Current: 15A

Absorption Voltage: 14.7

Float Voltage: 14.1

Equalization Voltage: 15.3

Auto Equalization: Enabled, Every 45 Days (I've read every 1-3 months for flooded)

Temp Compensation: -18v/C (because I have 6 cells, right?)

Low Temp Cuttoff: Disabled



One other noob question that I think I know the answer to: If the MPPT is sending current to the batteries and I connect to shore power, it will detect the voltage from the power center and regulate current from the solar panel, correct? I'm running a basic WFCO power center.


Thanks!



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JohnC avatar image
JohnC answered ·

Hi @rd10153

GC2's are generic floodeds. All major makers have them, so do I (different brand).

I use 48V but equiv Abs 14.4V. Float 13.6V, TC -20mV/C. I don't Equalize them, they get daily cycled down to ~75% SOC, and I don't think they need it then. They don't need to be pushed hard, gentle does it, they just boil water and get hot if you do.

I don't know this WFCO device, but 2 charge sources always interact via V. Which one takes priority when V reaches the set targets depends on the targets set on each unit. The lower will back off.

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rd10153 avatar image rd10153 commented ·
Thanks for the info! Excess max charge current is what would boil them, correct? Or, excess voltage?


When I'm not camping, it will sit in my driveway for months on end so I'm thinking would be good to have the equalization turned on, though I don't pretend to understand all the chemistry stuff.


I do have a hydrometer so maybe I'll learn a bit more so I can monitor and tweak as I go.


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JohnC avatar image JohnC ♦ rd10153 commented ·
@rd10153

They can handle a lot of current without harming them. Like I sometimes use up to 55A with a genset, but commonsense tells me 20-30A max from a solar bellcurve is likely more conducive to a long life. Heat is the enemy, and leaving them sit at Absorb V for hours can only harm them. I have my system set to drop to Float at 7A (~3% A/Ah). At that point they're 99.0% charged (monitored), the last 1% under Float.

*Warning, Anecdote*. My bank is 6yo and still ok, not once Equalized. They replaced a motley bunch of the same, but of different brands and ages. I pensioned the best 6x of the oldies off into a lightly loaded 12V system, and they get a daily dose of of a flat 13.6V for 2-3 hours. Should all be long dead by now, but nope, they roll on. One is at least 13yo (unknown, I inherited it).

Up to you whether you equalize, I did long ago, but no more. And if I did I'd do it manually and supervise it.

I tried hydrometers but they never showed what they were supposed to. And I always broke them, useless for me..

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nesswill avatar image nesswill JohnC ♦ commented ·
Completely agree with @JohnC if looked after they can last 14 to 20 years this will depend on brand but mine have a design life of 16y.
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rd10153 avatar image rd10153 JohnC ♦ commented ·

Great info, @JohnC. Thanks again!


So to set when it drops to float, I assume you're using expert mode and setting the tail current at 7A? Are you using fixed mode or adaptive?


The specs sheet says "Charge until change in current < 0.10A per Hr / Max Time: 12H"


I am a bit worried about overcharging given that there's usually little to no draw on the batteries when in storage. I'm also in a very hot area, 85-95 degrees during the day in Summer, which probably doesn't help with overheating.


I tried to bump up the max charge current to 25 amps but it seems to max out at 15. Spec sheet says 20% of amp hours max, which would be 43 amps.


Thanks again!


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kevgermany avatar image kevgermany ♦♦ rd10153 commented ·
Float is tail current and detectio time once charger in absorption. As well as the absorption time limits.

Charge current will be limited by the battery as well as what's available from the MPPT. The fuller the battery, the lower the charge current.



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JohnC avatar image JohnC ♦ rd10153 commented ·
@rd10153

Yes, I use the mppt Tail, which is a great feature. Networked across to a Smartshunt, so I get the actual batt amps, and the loads ignored (loads are always there for me). 3hr Fixed mode, but that's just an emergency thing. Typically get an hour or so Absorb time using the Tail limit. These are quite reactive batts and charge current tails quickly when they're almost done. Something to always keep an eye on, whether or not you use the automated features.

Makers specs, hey. 12hrs max at what V? Ignore, you're beyond that level of care already.

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