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joshairstream avatar image
joshairstream asked

Mppt voltage spike/ ripple

Hi, I've installed a solar system on an airstream caravan for a friend in conjuction with an electrician. I have screenshot-20230620-182436.jpgImage Captiona lifepo4 300ah 12v sterling power with built in bms.....the problem seems to be when charging in most states apart from long durations of "float". In bulk ,absorption and partly float I get voltage changes enough to trigger the alarm on the multiplus compact 12/1200. When viewing the solar charger on the app, voltages spike upwards of 16v and power flicks between 5w upto 189w for 600w installed solar power. I've disconnected the panels and measured a smooth dc signal on panel output. When mppt is disconnected there is no alarms from the inverter. Mppt is set to run lifepo4 battery.... I assume the built in bms is at fault but I have changed cell protection settings, etc temporarily without any major effect. Could anyone shed any light please many thanks. screenshot-20230620-182401.jpg

MPPT Controllers
screenshot-20230620-182436.jpg (274.2 KiB)
screenshot-20230620-182401.jpg (317.4 KiB)
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Alexandra avatar image Alexandra ♦ commented ·
@Joshairstream

Your next step is to test it with a totally different battery.

But it is almost 100% of the time a loss of battery reference during power production that causes the spiking, especially if there is no load for it to go to otherwise.

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joshairstream avatar image joshairstream Alexandra ♦ commented ·
Ah OK ill have a look into it, problem is trying to get my friend to buy another battery!
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Alexandra avatar image Alexandra ♦ joshairstream commented ·

@Joshairstream

A simple one would be to put a car battery on it. You are not cycling the battery just testing the charging. Program accordingly.

Possibly you could lower the charged voltages for the one you have already installed.

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joshairstream avatar image joshairstream Alexandra ♦ commented ·
Cheers ill give it a shot!
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1 Answer
snoobler avatar image
snoobler answered ·

This is classic BMS charge protection behavior and is very common on "canned" LFP batteries with built-in BMS.

Reduce absorption to 13.8V

Set absorption time to Fixed, 4 hours

Diable tail current

Set float to 13.6V

Behavior may improve immediately, and should improve after several days. After several days, change absorption to 14.4V, time to 1 hour and float to 13.5. If behavior returns, try at lower absorption voltages until the behavior stops. Dwell for several days and repeat as needed until the behavior goes away completely.



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joshairstream avatar image joshairstream commented ·
Thanks, I'll give it a try later on. It seems under load (had a 240w fridge running) it work great smooth voltage from the mppt and the inverter is happy fast forward 5 hours....when I left I turned the fridge off and back to dipping in and out.
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