Charging an AGM battery

[-robw-]

My thinking is you have either a problem with your controller wiring/setup or with your battery wiring/setup or batteries.

I have only used series batteries for my house. Firstly FLA and now sealed.

If I had your problem I would turn off all loads and use my external A/C charger and charge the bank taking note of the charge current. They should taper off to 0 amps current or almost. If all is well this will give you a true 100% Soc but faulty batteries can also taper off to 0 amps current.

I would do that coming up to dark so that you then start the night with a known 100% soc and reset meter. Turn the loads back on.

Assuming a nice sunny day next day monitor what happens.

It is just on daybreak here, my meter is telling me I am -70Ah, so I know I what I need to get back today.

FWIW; a couple of things seem to be true about these Renogy 200ah AGM's.

1) Their efficiency is a lot better then 85%. Granted they're only a month old, but they're tracking closer to 100%, which my wet cells could never do. This was observed by, once ammeter showed full, shutting the system down and connecting my NOCO charger to a battery in each bank. They were indeed full.

2) It'll take warmer weather to confirm but I doubt they're 200ah @ C20. I now have them registered on my ammeter at 175ah, which is tracking perfectly with battery box at ~50 degrees.

[-robw-]

But if I used my generator at 80% I wouldn't be able to brag to my two woke girls how much greener I am then them

Thanks again.

[Bala]

I went to sealed for same reason. Do not need to worry about water. I can't remember the last time I looked at my batteries, it could be 12 months.

I never let my soc get below 80%. If the batteries are down I run the generator to charge and at the same time heat water, wash and dry clothes etc.

I have lithium in my caravan and Ute auxiliary. The house will get lithium next.

[-robw-]

Yes, I'm convinced, although now not so much that it's a problem. A disadvantage, for sure, but if I can now escape this homestead for a couple of weeks w/o wet cells going dry it's well worth it. Luckily I have the AGM's on a pretty powerful array so as long as I get some sun, and in Texas we obviously get a lot, I should be good. Thanks for the term "gassing", got me thinking about that and reaching this conclusion.

I've now converted to lithium and AGM's on two systems, at costs borderline more expensive than my prior floodeds, and am a happy camper. God, those things were horrid..

[Bala]

I don't know enough about your system, your usage or sun hrs to help much.

I suggested one option to try to diagnose the system.

Another would be to try running each string separately with one controller.

I thought I had a failed Lithium in my caravan but it was just slightly loose connection. A friend had a charging problem with a lithium that was just a slightly loose connection.

You seem convinced it is the type of battery causing the problem. I am not so sure.

[-robw-]

Yeah, I think what I'm observing here is just a difference between a battery that will gas, and one that will not. Since floodeds gas, we can throw as much amperage as we want, regardless of SOC, which will then be converted to literally gas. But AGM's don't gas (much) so they can't convert the extra amperage, and "tell" the CC that.

Got that right?

[Bala]

I have BAE VRLA. 2V Cells 12V system.

I have not had to Eq.

They are set to Charge Bulk and Absorb at 2.366 V Per cell, so 28.4V for my system. For these batteries, new a bit over 3 years ago, I fitted a new Morningstar tri star regulator. It rarely goes into float even though they are 100% soc. It will only go into float when we are not home so seems to act on minimal current draw. Basically a max smoke set up.

I old system with FLA and different controllers would float by noon.

The specs for my batteries give 2.4V per cell as a gassing Voltage. When I had them new I had settings given to me by the supplier that were 2.4V or higher and I could hear them gassing so went by the manufactures data and dropped it back to the 2.366.

Your initial question is can you go higher in Voltage than specs. I would say no, you need to stay under gassing V.

[-robw-]

Ok, you have AGM's? So what result do you get if you charge your bank to 100% and then start EQ?

[Bala]

My thinking is you have either a problem with your controller wiring/setup or with your battery wiring/setup or batteries.

I have only used series batteries for my house. Firstly FLA and now sealed.

If I had your problem I would turn off all loads and use my external A/C charger and charge the bank taking note of the charge current. They should taper off to 0 amps current or almost. If all is well this will give you a true 100% Soc but faulty batteries can also taper off to 0 amps current.

I would do that coming up to dark so that you then start the night with a known 100% soc and reset meter. Turn the loads back on.

Assuming a nice sunny day next day monitor what happens.

It is just on daybreak here, my meter is telling me I am -70Ah, so I know I what I need to get back today.

[-robw-]

A couple of things to make communication easier.
Have a look at this info. Max Smoke Method. Basicially just set Bulk, Absorb and Float to same setting.

https://www.solarpaneltalk.com/forum/off-grid-solar/batteries-energy-storage/19316-are-you-killing-your-batteries

https://www.solarpaneltalk.com/forum/off-grid-solar/batteries-energy-storage/351396-are-you-killing-your-batteries-part-2

I'm aware of that smoke method, and I applied it to my last floodeds bank which was toasted during Arctic vortex of '21. I would not apply it to a new bank though, especially a voltage sensitive AGM bank. I can also reset SOC on my ammeter, which I do occasionally because most ammeters - like mine - don't have config adjustments to account for 85% efficiency of LA batteries.

Since no one has addressed my original question, I guess juicing my absorb voltage +.2vdc (allowed per Renogy but I'm skeptical - would rather charge at lowest voltages) won't help me here.

[Bala]

A couple of things to make communication easier.

An ammeter measures current draw, it will tell you the current in/out at any given time. A battery monitor like Victron BMV will use that info and calculate SOC.

Amps is what the panels are putting in or what is being drawn from the batteries.

Ah is the overall amount of power that has been used or is still available over time.

The victron BMV battery monitors use power that is not recorded by them. So the battery needs a full charge to reset the 100% factor. Yours may be the same, if you have not had 100%Soc for some time it may not be giving you an accurate reading.

The agms may well have different charging characteristics to your previous lead acids.

Have a look at this info. Max Smoke Method. Basicially just set Bulk, Absorb and Float to same setting.

https://www.solarpaneltalk.com/forum/off-grid-solar/batteries-energy-storage/19316-are-you-killing-your-batteries

https://www.solarpaneltalk.com/forum/off-grid-solar/batteries-energy-storage/351396-are-you-killing-your-batteries-part-2

[-robw-]

Follow the manufactures recommendations for charge voltage. You will possibly find their Max v is below gassing. Unless otherwise stated you do not want to equalise sealed batteries.

How are you determining soc?

Hi. With an ammeter. It's pretty accurate, now showing 74% SOC @ 49.33vdc under 7 amp draw.

I'm not sure I've been clear here. What I'm curious about is the following example:

Forecast calls for heavy clouds the next few days. The CC is in absorb mode but I only have 2 hours of daylight left and I want to top off bank by EOD. So I start EQ

Same wiring and interconnects:

Before with floodeds: max amps is delivered (50-80ah) - bank gets fully charged
Now with AGM's: EQ no better than absorb, with restrained ~30ah supply - bank gets to ~90 SOC and I run out of sunlight

Why? Is that just a characteristic of sealed batteries?

- recommended EQ for these batteries is .2v higher than absorb
- set at 4 hour absorb
- set at 10 ending amps
- don't pick on my example. same thing happens everyday, with CC going into float @ 90 SOC while delivering 30 ah

[Bala]

I'm thinking Renogy voltage specs are wrong.

I'm having the damndest time charging 8 Renogy 12v/200AH batteries running for a few weeks now. I noticed something odd before, in that once they get to about 70% charge they won't accept enough current to finish charge by EOD. One of my FM-80's will drop off ("charged") and the other supplies only about 20 amps when far more is available via my array. But now I'm really lost. Us Texans were just hit with a bad storm and, for the first time since living here, we actually had 4 straight days of very dark skies. These batteries got as low as ~25% (47 and change), but when charging them today I had to put my CC's in EQ mode at around 60% SOC to finish charging, and even then my they wouldn't fully accept what my CC could supply.

That seems to me to be the result of too low an absorb voltage, but I've read that AGM's are susceptible to high voltages and don't want to kill them. Renogy specs call for 57.6 vdc absorb, which is 1/2 volt lower than my prior floodeds. I'd like to experiment with higher voltage but before I do I'm wondering if anyone else has had such an experience with Renogy/AGMs and found a solution. Or if this just how AGM's behave.

I've communicated this problem with Renogy but their team is utterly useless.

Thank you.

Follow the manufactures recommendations for charge voltage. You will possibly find their Max v is below gassing. Unless otherwise stated you do not want to equalise sealed batteries.

How are you determining soc?

[SunEagle]

Hey, I didn't say I believed it! Just saying that's how the bank is acting.

I understand your dilemma. I hope you can find the issue and save your batteries.

[-robw-]

Hey, I didn't say I believed it! Just saying that's how the bank is acting.