Advice for skip days during winter

[coniferous]

Hi All,

We have closed up our off grid trailer for the winter and now are getting ready for the canadian winter. I'd like to know if

1) a full absorb cycle is required every day and
2) If not, how often should we absorb the batteries?

Currently we have a constant draw of about 40 watts for internet equipment on a 1000 amp hour AGM battery bank. overnight we consume about 40 Ah ish.

My absorb is set to end at 9 amps, or 5 hours at 14.7 volts. Float is 13.9 volts.

How often is a full absorb cycle needed? I know there aren't any hard and fast rules on this, but I'm curious about what other people are doing and general advice on long term winter maintaining.

[ClassicCrazy]

I know it is recommended for flooded batteries to use skip days when there are only small loads . That is because the electrolyte can stratify and cause sulfation. So in that case letting the batteries go down a bit means that there will be a longer absorb cycle that can bubble and mix up the electrolyte.

But with AGM batteries that is probably different. I would check with the battery manufacturer and ask their recommendations . It might be that no problem having them float all day everyday  because some agm batteries are very happy with that.

Larry

[boB]

AGMs need absorb cycles too although they aren't as needy as flooded as I understand.

Just letting lead acid batteries sit for too long without an absorb cycle once in a while and they will sulfate.

It's just that they don't need to be absorbed for several hours every single day.  That can supposedly wear them out early.

But yes, really have to check the manufacturer's specifications on charging.  Lead antimony, Lead calcium and the different chemistries "should" all be the same I would think. 

But we, as a company can't tell customers how to charge a certain companies batteries.  That would be dangerous

[mike90045]

Since AGM has a pretty good recharge efficiency , in your winter, how long does it take to harvest 30-40ah ?

You want to daily get them above 80%, and maybe 1x a week, a full absorb.

[coniferous]

Hi All,

I've taken a look at the white paper for my batteries (https://www.usbattery.com/wp-content/uploads/2018/07/usb_agm_31_DATA_2018.pdf) and I didn't find any specific advice about how often they should go through absorb. perhaps I should just email them...

"Since AGM has a pretty good recharge efficiency , in your winter, how long does it take to harvest 30-40ah"

like, two hours. or less. we have 1.4kw of panels. Absorb takes longer then that, as we aren't using the panels to the fullest in that stage. but even on the cloudiest of days I can't see them not filling entirely. 

"But we, as a company can't tell customers how to charge a certain companies batteries.  That would be dangerous"

Totally understand that, I never knew the extent of the difference between batteries until I started this project, even within the same AH class and chemistry types they are all so very different.

[Westbranch]

A few questions
1 what is the standby use of your  Inverter?
2 are you only using the Inverter for the Net connection?
3 can you use a smaller inverter to cover the Tare consumption?

discuss later...

[coniferous]

1) about 10 - 15 watts
2) Yes
3) We actually have two inverters and this is the smaller one. Our main 3000 watt one will be off for the winter, this is a smaller 300 watt modified sine wave one. Should i get an even smaller one?

[Westbranch]

Hi All,

"Since AGM has a pretty good recharge efficiency , in your winter, how long does it take to harvest 30-40ah"

like, two hours. or less. we have 1.4kw of panels. Absorb takes longer then that, as we aren't using the panels to the fullest in that stage. but even on the cloudiest of days I can't see them not filling entirely. 

Did you adjust your  panels to a more vertical position to keep them snow free?

Is there ANY  possibility of shadows of tree branches AT ALL? if so, your power production can be easily reduced to less than half of your SUMMER production.

[coniferous]

they are at a 45ish degree angle right now, we changed their orientation for winter so snow can fall over. we have no trees on our site at all.