Matias Käkelä avatar image
Matias Käkelä asked

Voltage drop started after 3 years of working flawlessly

I have an EasySolar 24/1600. It's connected to two 12v/240ah Victron AGM Deep Cycle batteries. I have had the same setup working without any issues for the past three years, but suddenly, this summer I've started to get voltage drops when high loads (such as the coffee maker) are turned on. After a few seconds, the inverter turns off. Nothing really has changed in the setup.

The problem does not seem to happen if the battery SOC is around 100%, but for instance this morning it was around 94%, and the problem occurred. At the lowest, the voltage dropped to around 20.6v, and the current drawn was around 55A (according to VRM).

The batteries have never been discharged under 75%, and they are most of the time in the range of 90-100%, and only actively used about one month a year. For about five months per year, they are connected but idling, and for six months, they are disconnected and stored fully charged.

What could this mean? If I had problems with cabling wouldn't such an issue have occurred sooner? Are the batteries somehow damaged or worn? If yes, how could that happen as they've been treated like royalty? Why does the problem not occur when the SOC is 100%?

voltage drop
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Alexandra avatar image Alexandra ♦ commented ·

Batteries calendar age as well.

But out simply the internal resistance has changed (higher now) they are showing their age.

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Matias Käkelä avatar image Matias Käkelä Alexandra ♦ commented ·

Victron data sheet indicates service their Deep cycle battery life to be 7-10 years. Batteries becoming noticeably degraded only in three years with fairly little usage sounds surprising (in a bad way).

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Alexandra avatar image Alexandra ♦ Matias Käkelä commented ·
I think it says 7-10 years in float service.

So not exactly how you have been taking care if them by the short usage you have described.

AGMs can't be stored they self discharge and sulphate just exisiting. Or at least that is what i have seen in my experience.

Are they rated for the discharge amps for the inverter (66A)? To be honest we have never used Victron AGMs. Last AGM install was over 5 years ago and most are rated at C10, so a 20A discharge. Not worth it really.

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Matias Käkelä avatar image Matias Käkelä Alexandra ♦ commented ·

About six months per year they are continuously connected to VictronConnect MPPT and thus remaining mostly in float.

The other six months (winter) they are stored fully charged without any load. I recharge them one additional time during the winter, in addition to the initial charging before putting them to storage.

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2 Answers
geomz avatar image
geomz answered ·

That seems suspect to me as well. While AGM —lead-acid in general — ages rather unwell, 3 years is a really short time, even for lead, except for batteries that have been abused or are defective. It sounds like abuse is not the case here.

This might be a bit of a pain, but I would try to isolate each battery out from the system, attach a volt meter to it, and monitor what happens directly as a heavy load is applied externally. Simulating a high-amp 12v load can be difficult, so a load tester would be very handy. Some auto-parts stores will let you rent one. If not, you might have to devise something.

You can try reversing this test, by isolating the battery to a single one and using the inverter to generate the load on it. Just have a meter directly on the terminals to isolate wiring problems, loose connections, mice-chewed cables, etc :)

Edit: OK, reread your original post and saw you’re running a 24v system, so the individual battery test using the inverter is obviously not doable. I would still try to isolate the batteries from one another and test them individually. In a series system, it’s possible one of the batteries is out of sync with the other and is not charged nearly as full.

It’s unlikely(hopefully) that they’re both bad, unless something catastrophic happened, but this might get you closer to isolating the culprit.

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kevgermany avatar image kevgermany ♦♦ commented ·
Problem is under heavy load, so no testing needed.
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kevgermany avatar image
kevgermany answered ·

Batteries deteriorate for a number of reasons. Your description points to batteries which have reached middle age or more.

There's a low voltage alarm/cut out in the EasySolar, which can be adjusted with an mk3 to usb adapter and VE configure software. This can be adjusted downwards.

Suggest that when these batteries do get past their useful life, you consider either Lead Carbon or Lithium.

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