Inverter DC voltage drop causing low voltage cutoff.

[protryon]

So my batteries measure according to my charge controller and multimeter to be 12.5 V. My inverter reads 10.5 and under load as low as 9.5 V. If it hasn't been loaded in a few hours, it'll only drop .4 V saying 12.4V at 12.8 real volts.
Has anyone else had this problem? Have you found the solution? I'm considering opening it up and bolstering some electrical connections to reduce resistance.

 

[tx2sturgis]

I think you have a voltage drop in your cabling or connectors.

Test the voltage drop in the cables.

Hook your multimeter up with one probe at one end of a cable, and the other probe at the other end of the SAME cable.

Set it for DC voltage. 

Keep it there and put a load on the inverter.

Tell us what you see.

I'm guessing you have 2 or 3 volts drop in one or both cables.

 

[protryon]

The voltage drop from my batteries to my inverter is .3 V, with the load of my refrigerator running, while my inverter drops .4 V for a total drop of .7 V

 

[protryon]

That is right now, this morning it was hitting 9.5 V. I'll try it again when it's singing.

 

[tx2sturgis]

A total drop of .7v is not bad at all.

The internal voltage measuring circuit in the inverter could be incorrectly calibrated, there is usually a small potentiometer for setting meter accuracy, and there might be an internal switch to set cut-off voltage. Or maybe not.

Do you have the original manual?

 

[John61CT]

With such a high current load, you need a bank that doesn't drop so much.

This can be achieved to some extent by going to a much larger bank.

Also it needs to be fresh, once the 20-hour AH capacity gets down to 80% of new, that drop-off accelerates and for such high-amp usage the bank needs replacing sooner rather than later.

Finally spending more on higher quality chemistries yields a flatter curve, but no lead comes close to LFP's.

 

[Ticklebellly]

I'm thinking leads to the inverter need to be looked at first to assess size is adaquate.

That said, one low power inverter I have needs to be turned on, no load, else I get a low volt alarm. Once going, a load can be connected without further fuss (load within the inverter specs, that is).

 

[Weight]

1; What is your battery bank? Size,chemistry,number. 2; What is the size and length of the cables from your bank to inverter? 3; What inverter are you using? make,wattage.

 

[highdesertranger]

^what weight said. also at 12.5 volts your batteries are low. highdesertranger

 

[protryon]

I figured it out, I touched the negative battery wire and the voltage shot up over two volts. Damn bolt holding the connection to the inverter had shaken loose -- tightened now. The poor connection increased resistance which under any load caused voltage drops.
@highdesertranger 12.5 isn't low under consistent 200 W load.
Thanks for the help guys.

 

[Weight]

wow. operator error.