Low battery voltage when using microwave

[Captain8]

My victron inverter sometimes gets low voltage error and will even shut off if I'm using my microwave/oven on battery. All 4 gc2 batteries are only a few months old. Is this normal or anything I can do other than switching to lithium?

[litzdog911]

Which Victron Inverter?
What are the batteries' state-of-charge?
Is the Victron properly configured for those batteries?

[TacomaJoe]

Low voltage at the inverter can have a number of causes. Voltage drop: wire too small for high load of microwave, poor connection along the line, or low battery voltage to start with.

How are the batteries being re-charged? It takes a long slow charge to get them to full capacity.

[Captain8]

Quattro 12v 5000w also have cerboGX and everything else. This happens often and the batteries are at various state of charges including fully charged. Whenever I pull over 1000w my battery voltages drop like crazy. Got error for 10.92 and even 9.25v and batteries were 90+ full.

I don't think it's an inverter issue but either the batteries or wiring. Also I'm not certain if the voltage is read at the inverter or by the smartshunt/actually battery terminals

[Unplanned Tourist]

Get bigger cables if the voltage is dropping, or move the inverter closer to the batteries. It's a very common problem with the heavy draw.

[Captain8]

How many amps/watts should 4 GC2 batteries in a series/parallel be able to comfortably handle without large voltage drop?

Inverter is 5ft including a main disconnect and fuse block.

[Unplanned Tourist]

Originally Posted by Captain8

How many amps/watts should 4 GC2 batteries in a series/parallel be able to comfortably handle without large voltage drop?

Inverter is 5ft including a main disconnect and fuse block.

A simple test is to put your voltmeter leads on the positive and negative terminals of your inverter and turn on your microwave. Then do the same only right at your batteries. This will give you an idea of the voltage drop in the cables.

4 GC2 batteries should run your microwave no problem for a few minutes. 1500 watts is a fairly normal draw for it, so that's around 120 plus 10% efficiency loss, so 130+ amp draw. How many amp-hours capacity do you have?

[Persistent]

Lots of good advice posted above. Generally I would expect 4 gulf cart batteries to power a microwave until the battery state of charge drops to 50%.

Lead acid battery voltage drops for multiple reasons.
State of charge changes static voltage. 12.7 volts static is 100% fully charged. 11.3 is 10% SoC.
The higher the current out, the lower the voltage will drop. Each design of lead acid battery has a different, but similar discharge voltage profile.
Batteries with fewer thicker plates drop voltage quicker.
Smaller gauge 12 volt supply wire to the inverter drops voltage quicker.
Longer runs of 12 volt supply wire drop voltage quicker.
Corroded or loose supply wire (both positive and negative) drops voltage.

The inverter may have a low voltage cutoff of 11.5 volts.
If static voltage is 12.0 volts (50% SoC) a voltage drop under load of 0.5 volts will trip the low voltage protection.
If static voltage is 12.7 volts (100% SoC) a voltage drop of 1.2 volts is required to trip the low voltage cutoff.

A microwave requires a lot of power. That requires high 12 volt current to the inverter. All of the above causes can combine to trip the low voltage protection. The inverter may draw 150 amps to power a 120 watt microwave.

AGM batteries generally have more thinner plates. They support high current better. Flooded cell gulf cart batteries generally have few but thicker plates.

[SJ-Chris]

Originally Posted by Unplanned Tourist

A simple test is to put your voltmeter leads on the positive and negative terminals of your inverter and turn on your microwave. Then do the same only right at your batteries. This will give you an idea of the voltage drop in the cables.

4 GC2 batteries should run your microwave no problem for a few minutes. 1500 watts is a fairly normal draw for it, so that's around 120 plus 10% efficiency loss, so 130+ amp draw. How many amp-hours capacity do you have?

YES....do the above test. Sounds like your batteries are good, so unless you have a loose connection somewhere it seems like the wires from your batteries to your inverter are too small. Much too small (for the ~130 amps being drawn by your microwave).



Do you know what size wire you are using between your batteries and your inverter? Let us know.


Here is a website where you can calculate voltage drop for different types of wires, draw, and length.


https://www.calculator.net/voltage-drop-calculator.html


Good news: If this is the problem, then you just need thicker wires to solve your problem. Tip: If you want thicker wires, you can add another pos and neg wire in parallel to what you have. They don't need to be the same size either. In fact, it sounds like your wires might be grossly undersized (because you mentioned fully charged batteries resulting in low voltage at inverter).


Test you can try: If you have a set of heavy duty jumper cables, you can connect them from your battery to your inverter (keeping your existing wires connected from battery to inverter) and try running your microwave. If it helped, then insufficient wire gauge is likely the problem.


CAUTION: Any time you are messing with batteries, jumper cables, etc you need to be very careful to not create a short.


Let us know what you find out.


-Chris

[SJ-Chris]

Originally Posted by Persistent

A microwave requires a lot of power. That requires high 12 volt current to the inverter. All of the above causes can combine to trip the low voltage protection. The inverter may draw 150 amps to power a 120 watt microwave.

AGM batteries generally have more thinner plates. They support high current better. Flooded cell gulf cart batteries generally have few but thicker plates.

Good info in your post.


Slight correction: I believe you meant "1200 watt" microwave.

[Captain8]

Great advice. Im not sure of the gauge cables but they seem very thick maybe 0 gauge I'll confirm though.

I believe my Victron has voltage monitors sensors at the batteries and inverter (either inverter or smartshunt) I'll check where it's monitoring.

I'm having another voltage issue as it appears my alternator isn't charging my house batteries anymore and even the starter batteries are low voltage while driving. Not sure if bad alternator or whars going on.

My original question still remains. If the batteries are at a 100% soc then what percent voltage drop at the batteries is acceptable when running a 1500w draw for 1/5 minutes?

[Persistent]

Originally Posted by Captain8

Great advice. Im not sure of the gauge cables but they seem very thick maybe 0 gauge I'll confirm though.

I believe my Victron has voltage monitors sensors at the batteries and inverter (either inverter or smartshunt) I'll check where it's monitoring.

I'm having another voltage issue as it appears my alternator isn't charging my house batteries anymore and even the starter batteries are low voltage while driving. Not sure if bad alternator or whars going on.

My original question still remains. If the batteries are at a 100% soc then what percent voltage drop at the batteries is acceptable when running a 1500w draw for 1/5 minutes?

If the voltage at the 12 volt input to the inverter drops below the preset cutoff, the inverter will trip "off". Acceptable voltage drop keeps the voltage above cutoff.

[pasdad1]

You probably need to adjust your LBCO low battery cutoff voltage lower.

I have 8 six volt lifeline AGM batteries, in excellent condition, and I have mine set at 10.7v

Remember when batteries have to supply huge current demands, voltage goes down, way down, temporarily…..it recovers back to over 12.5v when current demand is stopped.

All battery wiring tying the bank together is 0000 gauge.
Inverter wiring is factory and I believe is 00 gauge

I see over 170 amps on inverter readout while running microwave.

[Captain8]

What do you see your voltage at when you're running it?