AGMs and Inverter Alarm Voltage

[BFL13]

In another thread I mentioned:

"50% might be the limit anyway, since the real lower limit is whether you can still run your electric toaster in the morning without setting off the inverter's low voltage alarm.

With only a pair of 6s that might be at 75% SOC and with four 6s, 50% SOC. Or if you want, you can make your set-up so it would not alarm till lower than 50%, if your RV's size and layout will allow for that.

(Assumes no running the gen or any engine to "support" the voltage for that inverter time)"

AGMs have an advantage with that, because they have higher voltages per SOC than Wets. (I just tried my new bank of AGMs for voltage drop when running the microwave with the big MSW inverter and realized this.)

(A few years ago member full mosey reported that he could get away with two AGMs instead of having four 6s, which was good if you have a small RV and can only carry two batteries, but want a big inverter)

Running 125 amps on a full AGM bank of 450AH, with surface charge removed, I got initial drop of 0.6 volts with my particular wiring etc. That initial drop is a constant, so if the inverter will alarm at 11 volts, and I will lose 0.3 volts while the appliance is running, I would need 11.9 volts going in.

The trick is 11.9v might be 40% SOC with Wets, but is more like 15% SOC with my AGMs, where 12.4v is 50%. (Trojan L16 AGM 6s are 12.2v for 50%, so it varies by brand, etc.) The inverter doesn't know what kind of batteries I have- it still alarms at 11 volts.

That means I could run my AGM battery bank down way lower than I could with the Flooded batteries, and I could still use the electric toaster! 🙂

Previously, I had two battery banks to avoid that issue, where the "house" bank could be run down without getting too low to run the inverter.

The inverter had its own battery bank which could be kept above the inverter's voltage needs by judicious usage, no matter how much the furnace was on that night.

I was worried going to one bank would lose that advantage, but it turns out that with AGMs it is not a problem.

Of course AGMs are low resistance themselves, which helps with the degree of voltage drop, along with the usual proper wiring, but that is not the same thing as the voltage per/SOC thing I am talking about here.

[BFL13]

time2roll wrote:
Alarm is annoying but would not cause me to stop. Low voltage cut-off is the important point to note. And yes AGM might hang in a bit longer. However at that point I would wish I had just started a bit sooner with propane.

The idea is that at 6am while you are making toast, your park neighbours will hear that alarm, the dogs will start barking, and chaos will ensue. Otherwise later in the day the noise doesn't matter and you can keep going till the job is done as long as the inverter stays above its shut-off voltage.

---Full Mosey is the man when it comes to AGMs as far as I am concerned! Got me onto it eventually. 🙂

[full_mosey]

BFL13 wrote:

...
(A few years ago member full mosey reported that he could get away with two AGMs instead of having four 6s, which was good if you have a small RV and can only carry two batteries, but want a big inverter)
...

That was back in Jan 2014 where I had bought the Magnum MMS1012 1000W/50A inverter charger while at Quartzite. I only had the one Deka 8a24M, a 79AH AGM that was 5yo. Overnight the battery had run two Dometic CF35 fridge freezers. I ran 26 minutes in the AM making coffee and running the microwave until the LVD shutoff. Each device ran at ~700W.

Last year for a capacity test I wanted to draw 2KWh from the bank of two used 135AH Eaton Powerware batteries that were telco pulls.
It took a 5000BTU AC 4.5 hours to reach 2KWh.

HTH;
John

[time2roll]

Alarm is annoying but would not cause me to stop. Low voltage cut-off is the important point to note. And yes AGM might hang in a bit longer. However at that point I would wish I had just started a bit sooner with propane.

[pianotuna]

Foreman Grill is GREAT for garlic toast, too. Especially after cooking a steak.

I've upgraded to a Bella now--it came with four sets of removable plates some of which are dual sided. It can also be opened enough so it can act as a griddle for doing pancakes.

It works well on the inverter, too.

[BFL13]

MEXICOWANDERER wrote:
The George Foreman grille makes excellent toast with minimum wattage, four slices.

Interesting! 🙂

https://en.wikipedia.org/wiki/George_Foreman_Grill

[MEXICOWANDERER]

The George Foreman grille makes excellent toast with minimum wattage, four slices.