Inverter Panel Issue

[velacreations]

I have a Xantrex Prosine 2 inverter.  It works great, and we have had it for several years without issue.  I have started noticing, however, that the battery voltage on the panel of the inverter reads .4 volts higher (12.8 vs 12.4) than my cheap multimeter.  I put the multimeter on other batteries and power sources, and it reads correctly.

I have a charge controller that reads the same voltage as the Xantrex panel.

So, I assume it is the multimeter, but the fact that it reads correctly on other things with a known voltage (vehicle batteries, etc), makes me think that maybe there is an issue with the inverter and/or charge controller connection.

Any thoughts?

[Frank S]

How do you know the multimeter reads correctly? vehicle batteries can vary quite a bit I have a Toyota that will show 13.4 with my Fluke 81438  engine off my forklift after running for 2 or 3 hours  and resting for 1/2 an hour usually is around 12.8 
 my Bank might read 14.1 on my Zantrex 3000plus while the PDM will be reading 13.8 the fluke might show  14.0  I know my fluke is not the most expensive or the most accurate meter on the market  but it serves my needs. since I don't deal with mili-volts I don't get too worried about a few points variation.
 As long as things are within 1 to 2% if figure goodernuff.

[velacreations]

well, this is more than 3% difference

I just saw the inverter and the controller read 12.7, and the mm reads 12.3

That's a big difference in condition of a battery, really.

I don't know that the mm is accurate, it is a cheap, harbor freight model, but it does read accurate (not .4 volts less) on a car battery that has been sitting for several days (it was reading 12.6).

I am just wondering which should I assume is right, the inverter and the charge controller or the cheap mm?

[klsmurf]

Can you take specific gravity readings and compare?

[velacreations]

Can you take specific gravity readings and compare?

no, the batteries are sealed.

[joestue]

a new alkaline battery is 1.56 volts. i don't trust anything btw.
i have a weston cell and all my meters read either 1.018 or 1.019 volts on it.

[velacreations]

well, I dug around and found a 7812, which should output 12 volts.

I hooked the MM to it, and it shows 11.6 volts

I can't really test the other meters to it...

[dnix71]

Inverters and mppt's have internal adjustments to make voltage and current true, but it's risky business to mess with internal trim pots. My two solar MPPT's both read true at rest but go way off when charging because the voltage reference is internal not at the input or output posts. My 2 HF power taps read wrong all the time because they haven't been adjusted for the rewiring done when the displays were replaced.
I just know how far they are off and mentally adjust for it.

If your prosine has gone off recently, you might call or email them and ask how much to have the unit checked and adjusted.

[velacreations]

well, that's the thing, I don't know that it is the inverter, because the charge controller matches it.

I guess I need to find an absolute voltage supply that I can calibrate to, and test them against each other.  Any ideas?

[dnix71]

A cheap multimeter may work sometimes measuring battery voltage and not at other times. The inverter is pulling pulses from the battery bank, remember a/c goes to zero twice a cycle. The real time battery voltage on a decent oscilloscope would look choppy.

If you can, turn the inverter off for a few seconds and read the battery bank voltage, then reboot and wait a minute and read again. Read with no load and read with a moderate load.

You could also adding a ceramic filtering capacitor in series with one multimeter lead and see if that changes the reading. Use a ceramic, not a polarized electrolytic.

All that said, 12.4v would be a ruined battery if that was resting for long. 12.8v sounds real, esp. since you said they are sealed. AGM's tend to rest a little higher than flooded batts.

[velacreations]

All that said, 12.4v would be a ruined battery if that was resting for long. 12.8v sounds real, esp. since you said they are sealed. AGM's tend to rest a little higher than flooded batts.

12.4 is ruined?  I would think that is about 50% discharged, but not ruined.

[DamonHD]

Leaving it sat around at anything like <= 50% DoD for any length of time => ruined, IMHO.

Rgds

Damon

[velacreations]

Leaving it sat around at anything like <= 50% DoD for any length of time => ruined, IMHO.

Rgds

Damon

like overnight?

[dnix71]

Taking a sealed lead battery to 12.4 on a regular basis makes for a short life. That's why you need to be sure of the voltage. 12.5 would be okay. I unplug loads to keep mine above 12.5 if it's overcast for a couple of days in a row.

[velacreations]

Taking a sealed lead battery to 12.4 on a regular basis makes for a short life. That's why you need to be sure of the voltage. 12.5 would be okay. I unplug loads to keep mine above 12.5 if it's overcast for a couple of days in a row.

Yeah, I understand taking them down that much and keeping there for extended periods is not good, but sitting at that level overnight is not a ruined battery, IMO.

I agree, though, I need to know the voltage for sure.

[DamonHD]

Overnight is probably OK once in a blue moon, but that's the lowest that I'd ever like to draw mine down to, even transiently.

Rgds

Damon