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murphy-r avatar image
murphy-r asked

Multiplus Low Battery Alarm

Hello everyone,

I have a multiplus on our boat that is connected to two 8D AGM that are about 6 years old. Battery bank size 500 Ah.

What I have seen recently is that the multiplus is reporting a low battery alarm in the last 2 out of 3 uses. The two times it has thrown the alarm were with no load introduced that would cause such a sudden drop in voltage level. See attached two charts.

I did a quick test for 30 minutes on the inverter while on the dock. That was with about 140W pulling continuously with one of our fridges periodically kicking in. At the end I put a 1400W additional load on the batteries for 36 seconds and the batteries dropped from 12.5V -> 11.8V

Do folks think that the AGM may just be at the end of their life?




low-battery-alarm-1.pngLow Battery 1

low-battery-alarm-2.pngLow Battery 2

test-load.pngLoad Test


Cheers,

Robert


MultiPlus Quattro Inverter Chargermultiple inverters
test-load.png (162.2 KiB)
low-battery-alarm-1.png (97.2 KiB)
low-battery-alarm-2.png (107.1 KiB)
low-battery-alarm-1.png (113.7 KiB)
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2 Answers
Mike Dorsett avatar image
Mike Dorsett answered ·

At 6 years old, your AGM's are probably past their use by date...

Do check that all terminals are clean etc. On our yacht we went through 2 sets of batteries in 11 years, and were close to expiring the 3rd set. 4 years seemed to be about average life, but they were cycled every day. Looking at the dips when the fridge switches on and your 150A discharge test, I'd say the batteries are sulphated.


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murphy-r avatar image
murphy-r answered ·

Hi Mike,

We recently had to replace the Multiplus last month so I know all the contacts are clean and I went down and checked to make sure no loose connections. This is the original set of batteries with the boat at six years and I already had to replace the generator AGM battery that failed. I could look to see if the Multiplus software supports running de-sulfacation. We were planning on doing an upgrade next season of the battery systems on board and converting to Lithium.

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