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jasonshanahan avatar image
jasonshanahan asked

Strange power loss

I am having some questions about my inverter its a multiplis II 12/3000/120. Last night, i unplugged shore power and had an immediate total power failure in the bus. Everything restarted on its own, but since then, operating on my battery bank which is 800ah of renogy lifepo4 batteries, i get intermittent power failures, specifically when drawing power for the air conditioning. The ac will start and run for a few minutes and then the multiplus will cut off, showing a red low battery indicator on the display panel. After about 10 seconds the system auto restarts, shows no faults or alarms. I know my battery bank is completely charged because i have 13.3 volts holding in each battery. Any ideas what could be causing this? I hooked back up to shore power, and no issues now, a/c is working and no shutdowns, so it seems to be an inverter issue? Why would it think the batteries are too low? The a/c only draws about 750 watts when running.

Multiplus-II
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3 Answers
derrick thomas avatar image
derrick thomas answered ·

This is most likely the same cause as your other thread (improper settings). You need to first verify that you don't actually have a low voltage situation by checking with a vm at the multi battery posts while running the AC in inverter mode, while the multi gives the low battery alarm. If you can verify that you do not have a low voltage situation, then you will need to adjust your battery voltage settings on the inverter tab in veconfig. You can also check the notifications on the touch display to see if it is the battery or the multi that is issuing the alarm and shutdown.

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jasonshanahan avatar image jasonshanahan commented ·
Ok im going to work on adjusting those settings. In the mean time, i did infact use a voltmeter to check all my battery terminals, they are all charged to 13.3 volts. There is a battery disconnect switch inline between the batteries and the distributor to the multiplus, i read 0 resistance across the battery terminal connections, the cable leading to the switch, the cable leading away from the switch, and 28ohms across the switch terminals inside the disconnect itself. I think this is a bad switch, so im going to swap that out and see if it makes a difference. At the moment running on shore power, seems to be working fine. And so far since the start of this there have been a total of 0 alarms or notifications.
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Rob Fijn avatar image
Rob Fijn answered ·

Also a good test is using a Amp Clamp meter and see if every battery is able to give current when discharging and take current for charging.. All should be equal.
Rob

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Alexandra avatar image
Alexandra answered ·

@Jasonshanahan

First and most common reason is undersized cabling. 3k at 12v is quite a few amps.

If you have daisy chained your batteries, that will also be where an issues is. Current sharing.

You might find batteries are tripping then waking up again, particularly the end ones.

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jasonshanahan avatar image jasonshanahan commented ·

We sized the cables according to the installer recommendations, the batteries are connected in parallel with 00 gauge cables. I am going to replace what i found to be a faulty battery disconnect switch, tested with a voltmeter set to read resistance, as i moved through the system i read an open loop across the switch, so im hoping that is the issue. I am still going to be checking everything else also as i work on this today.

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Alexandra avatar image Alexandra ♦ jasonshanahan commented ·
Cool. Yeah high resistance connection.. it will do that too. Causes the voltage drop and hence the power outage.
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jasonshanahan avatar image jasonshanahan Alexandra ♦ commented ·
Additionally, do you think having the battery bank disconnected and only running on shore power would affect the dc system? Now, i am seeing lights dimming when i turn on my 12v water pump, and also my cerbo touch 50 has been cycling on and off most of the evening. I am going to pick up a new continuous duty disconnect switch this morning and put it back inline and reconnect the battery bank and see what that does for it all...
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nickdb avatar image nickdb ♦♦ jasonshanahan commented ·
Multis are not designed nor supported to run without a battery bank attached. It is ill advised to do so.
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jasonshanahan avatar image jasonshanahan nickdb ♦♦ commented ·
@nickdb I have it hooked back up now with a new disconnect switch and everything seems to be back in fine working order. Can you expand a bit more on the downside of running this way? The disconnect switch was fried completely melted, so i had to remove it. I kept a small load on the system overnight, like the fridge and a light, i got it all hooked back up this morning so a total down time of about 10 hours or so. In the future what should be done differently?
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