OutBack Inverter Shut Off

S_Ali

Currently testing a continuous 700W load on a 12V system, with the PV's off. The battery bank consists of 4 AGM batteries and is 780Ah total (NOTE: batteries are 6V, connected in parallel and series to give us a 12V system). All components are from Outback Power and we have the MATE3. The Battery Cut in and Cut Out voltages have been set at 12.5V and 11.6V. Before conducting the test, we fully charged the batteries, according to the FlexNet (blinking green means 100% SOC);We did not check the voltage across the system initially. The inverter does shut off once it reaches 11.7 but the MATE3 tells us the state of charge is above 70%. Is there a battery chart that show what the battery voltage should be at various State of Charges?

It could be a multitude of problems, but I think it's the following 1). The FLEXNet does not accurately tell us the batteries SOC or 2) There is some fault in the batteries themselves. We will recharge the batteries and once the FLEXNet indicates the batteries SOC is 100%, we will check the voltage across. Hopefully, this will help.

If you can think of something else it could be, I would appreciate the help!

westbranch

The cutoff V is under load, and your check of the SoC is, most likely, after the disconnecr  is done...  is that a correct description of your order?

Photowhit

A couple of things to check. Are you assessing your battery bank size correctly? 4 6 volt batteries would be 390 amp hours each for a 12 volt battery bank that is 2x2 - 6 volt batteries to be 780 at 12 volts. I don't know of any 390ah 6volt AGM batteries, though I'm sure there out there.

The next thing I would worry about is the wire sizing. One of the reasons that higher voltages are recommended at such a large size. Loads as large as 700watts will be drawing more than 60 amps from a 12 volt battery bank and if your bank is 780 amps you are reducing the effective size of your battery bank as most batteries are rated based on a 20 hour discharge, that is 1/13th of the size of the battery bank.

At such a high discharge rate you will have voltage sag. Yes there are basic voltage State of Charge (SOC) levels for lead acid batteries. These are based on batteries at rest for a few hours. Shutting down at 11.6-7 with a substantial load could well be at 70% SOC. I suspect after a couple -3 hours the voltage rebound on the batteries to a higher level.

Link to Battery FAQ's lots of good information here!

http://www.solar-electric.com/deep-cycle-battery-faq.html/#Battery Charging

S_Ali

Photowhit:

Yes, this system utilizes 4, 6V Crown 6CRV 390Ah batteries. We are using 2/0 wire to connect the battery bank to the DC Disconnect, then the same to the inverter. I understand there is a voltage sag when there is a load of 700W, however, when we intitally loaded the system, the voltage went down to 12.1V, which is quite a significant drop, as the table below shows.

We know from our calculations that 700W will rarely, if ever, be loaded all at once. The purpose of our testing is to see if the MATE3 would tell the inverter to cut-off when the SOC of the batteries reached 50% and cut in when the SOC reached at least 80%.

vtmaps

The flexnet DC is notorious for giving wrong SOC.   It's not the flexnet's fault that when fed garbage data it puts out garbage results.  There are many many settings that you must enter.   If you give the flexnet incorrect data, it gives incorrect results.

One of the more common mistakes is to power it up when the batteries are at less than 100% SOC.  Poke around on the Outback's forum and you will find plenty to read about it.

One of the problems you have is that there is no easy way to know the SOC of your AGM batteries when you turn on the flexnet.  Also, as batteries age or sulfate their capacity decreases.  If you don't tell the flexnet what your battery's TRUE capacity is, it can't give you a reliable SOC. 

Your AGM batteries, being AGMs, should have fairly low internal resistance, which means there should be very little voltage sag.   Excessive voltage sag implies high internal resistance. The most common cause of premature high internal resistance is sulfation caused by chronic undercharging.

I have written a bit on this forum about how shunt-based battery monitors (such as the flexnet) work.

--vtMaps

Photowhit

S_Ali Said; "We are using 2/0 wire to connect the battery bank to the DC Disconnect, then the same to the inverter."

There is more involved than wire size, how far is your wiring in total?

While AGMs are much better about voltage sag, at 700watts you are effectively pulling nearly 1/10th of the battery capacity per hour.

Blackcherry04

As was said with the FNdc. Charge the system and Check the SG level of all cells, EQ if necessary. Once your satisfied that your at 100% capacity, unplug and re-plug ( lights will go out ) the FNdc from the Mate and you'll reset the SOC counter.

The Charge Efficiency number is really hard to set, they say 94% and 80% is a better place to start. Basically the thing is a pain to deal with.