shallow cycling agm... am I killing them softly ie reducing cycle life

[b0ardski]

Four 12v 92 ah durastart in parallel. I know I know but uneducated mistake$ were made and this winter we'll have to make do.
most days only getting down to 90% soc. should I add more load to take it down to 70-80% to take better advantage of limited cycle life?

[inetdog]

Four 12v 92 ah durastart in parallel. I know I know but uneducated mistake$ were made and this winter we'll have to make do.
most days only getting down to 90% soc. should I add more load to take it down to 70-80% to take better advantage of limited cycle life?

Although many people will assert that FLA batteries benefit from an occasional deeper discharge, I do not see that adding additional loads that are not really necessary is going to do you any good in the long run.

Instead of getting 1000 cycles (~ 3 years) of shallow discharge you would get 700 cycles (~2 years) of deeper discharge. You will have used more of the energy handling capacity of the battery but you will have shortened the life.

The argument that you will see in various threads about designing around increased DOD is that you can use a smaller battery bank, costing less in the long run even though you will replace the batteries more frequently.
Once you have the batteries already, adding more load to try to increase life simply does not make sense to me.

You will, however, see some arguments, especially if generator supplementing is needed to reach full charge, that going for several days in a row not getting above 80 or 90% SOC is not a bad thing. To some extent, even for FLA batteries, the wear on the battery plates of getting all the way from 90% up to 100% SOC is disproportionate to the wear on the battery plates of going from 80% to 90%.
Once again, the action to take would be to defer charging to full SOC rather than to add load.

[Sunking]

The deeper you discharge a battery, the shorter the life. A good true deep cycle battery life cycle looks something like:

10% DOD 3000 cycles.
20-30% DOD 2500 cycles.
50% DOD 1000 cycles.
90% DOD 150 cycles.

Solar battery systems are designed for 5 day capacity or more meaning only discharging 10 to 20% per day.

[PNjunction]

... should I add more load to take it down to 70-80% to take better advantage of limited cycle life?

YES

Very shallow cycling on a non-sli battery (like these dual-purpose agm's) less than about 10% DOD tends to promote clumping of the sulfate due to the shallow discharge, rather than a smoother overall covering that occurs when going just a bit deeper. (This is the natural sulfation effect that happens with all discharge). Eventually you run the risk of "hot spots" from the clumping effect.

The queston is, will that degradation occur before your battery ages and dies of it's own accord in 4 years or so? Your usage patterns will determine that. But on the whole, for a non-sli battery, very shallow cycling is not ideal.

The key word here is cycling. At some point, you may be better off thinking about a constant-float, ie 13.8v at all time with no 2 or 3 stage charging. Although this again depends on your usage. Are you truly cycling, or are you in a standby/backup situation?

Without knowing any more details, my inclination would be to use just a single battery rather than putting an extra load on the pair you have now. Keep the other one fully charged for a "hot-swap" for any unexpected loads that would take a single one past 50% DOD.

[b0ardski]

that ? brought some meat to chew on

Thanks for the info all ya'all; love this forum and the no nonsense sharing of experience

more info; recent storms causing prolonged outages necessitated a good backup set up. Gas gen gets crap mileage, and our tiny contribution toward creating demand and main stream acceptance can only be a good thing. We have good friends living off grid on solar. I just found this site and have been reading a lot to try and get up to speed.
We purchased gear without studying or guidance so now have to make do with mismatched gear till we can afford to expand and make adjutments.

starting setup; 4 100w windy nation pvs paired to 24v; 50ft 8awg from panels to xantrex conext xw mppt 60a-150v cc (just installed); 4 12v 92ah agms, (soon to be 6) paralleled with 4awg per smartgage


36" of 4awg to 12v 2000w xantrex prowatt xw; been running satellite internet and tv a few hours a night just to learn the system.
Will add wind next month to get thru sunless winter storm cycles.

[SunEagle]

Thanks for the info all ya'all; love this forum and the no nonsense sharing of experience

more info; recent storms causing prolonged outages necessitated a good backup set up. Gas gen gets crap mileage, and our tiny contribution toward creating demand and main stream acceptance can only be a good thing. We have good friends living off grid on solar. I just found this site and have been reading a lot to try and get up to speed.
We purchased gear without studying or guidance so now have to make do with mismatched gear till we can afford to expand and make adjutments.

starting setup; 4 100w windy nation pvs paired to 24v; 50ft 8awg from panels to xantrex conext xw mppt 60a-150v cc (just installed); 4 12v 92ah agms, (soon to be 6) paralleled with 4awg per smartgage


36" of 4awg to 12v 2000w xantrex prowatt xw; been running satellite internet and tv a few hours a night just to learn the system.
Will add wind next month to get thru sunless winter storm cycles.

That 4awg is only good for about 125 to 130 amps and your 2000watt inverter can draw up to 167amp at 12volts. So make sure you have a fuse or breaker to protect that 4awg wire.

You will also need over-current protection for the wires between your xantrex charge controller and batteries.

[b0ardski]

Thanks for the heads up,
The recommended 250a anl fuse & 0awg cables are on the way.
will go to 2 gauge battery links soon also
80 amp dc breaker to the battery 60a from pv