Battery recommendations for 1500W inverter

[syperk]

Does anyone have recommendations for a 12V battery setup that can power a 1500W inverter?

The background: my travel trailer is currently powered by two 6V golf cart batteries (Duracell SLIGC110 215Ah) connected in series. I recently installed a 1500W (3000W peak) pure sine wave inverter with the aim of being able to power my 1.35kW microwave while out in the woods. Unfortunately, when I turn on the microwave, the inverter trips out after a few seconds, and I'm pretty sure it's due to the low voltage protection (which shuts off the inverter when the battery voltage drops to 10.5V).

I've measured the voltage at the battery terminals while running the microwave, and the voltage does indeed drop to 10.5V, so it looks like the battery's internal resistance is just too high to supply the 120A or so that the inverter is drawing with the microwave running. I did an experiment with a smaller 100W load, and the battery voltage dropped by about 0.2V, indicating an internal resistance of approx 0.02 ohms. Is that high for a battery of this type? Does the battery just need replacing? Or do I need a fundamentally different battery setup? Any thoughts welcome!

[MEXICOWANDERER]

Specifications need to be READ people.

VOLTAGE
TIME

Affects ampere hours based percentage of discharge

Discharge a battery to 50% capacity using Two 2 Two 2 hours permitted discharge time

IS CALLED THE TWO HOUR RATE

HELLO PEUKERT

Compare this rate to the 2 hour rate, and it's like bragging "I own a car that tops out at 700 miles per six hours. Wuuuweee! 700 miles!

Compare that scale to a Concorde battery. This is good practice for people who wish to immerse themselves in numbers. Similar to an absurd advertisement 3,000 cranking amps at 60c with 1.350 acid.

Study the numbers, then run them through the Peukert machine.

Cycle Lifespan ratings have absolutely ZERO to do with ampere hour ratings at 20 hours. Remember the Battery Council International is owned managed and financed 100% by battery manufacturers.

Like the American Petroleum Institute.

Advertised cycle life graphs apply to telecom like conditions and not to long term discharges. ROUGHLY speaking the cycle life chart at 50% discharge would equal 37% discharged at the 20 hour rate.

[MEXICOWANDERER]

Custom Tailored Batteries For My Lifespan Requirement

Zinc Carbon

(sigh)

[Cydog15]

theoldwizard1 wrote:

time2roll wrote:
My 4x GC2 from Costco have done just fine driving the microwave.

There is your answer.

I don't know man. A lot of benefits to AGM. Even Lithium if you plan to live 10 years.

[ktmrfs]

theoldwizard1 wrote:
A couple of graphs from the Fullriver Battery web site. These were from their page on their Group 31 AGM battery, but the graphs are pretty close for ANY lead acid battery.

Discharging to less than 20% depth-of-discharge cuts the number of charge/discharge cycle by about 50%



This chart surprised me ! 80% state-of-charge is about 12.5V !

well, 75% DOD still gives over 500 cycles. way more than most any RV user will encounter before the batteries die from other causes.

BTW the cycle life is pretty close to what Trojan shows for t125 GC-2.

[pnichols]

theoldwizard1 wrote:
This chart surprised me ! 80% state-of-charge is about 12.5V !

Why?

Your answer may be related to an observation of mine:

My twin Group 31 Fullriver AGM RV batteries DO NOT show fully charged at-rest terminal voltages in the low 13.XX's range - like my Group 31 Yellow Top AGM Optima battery does. When fully charged, my Fullriver batteries always read only around ~12.8 volts after their post-recharge surface charge has dissipated.

At first I was concerned about this, but I finally accepted that probably not all AGM batteries have the same electro-chemical characteristics.

As I've mentioned many times, I went with Fullriver AGM batteries because of their advertised float voltage range being an exact match to my RV's stock Parallax converter's output voltage range. At the time, the closest Lifeline equivalent batteries had a required float voltage range around 13.2 volts and the Lifeline rep stated that long exposure to stock converter output voltages would over time degrade Lifeline AGM batteries.

As I mentioned earlier, the Fullriver batteries were priced only slightly less than the Lifeline batteries, so I figured that anything manufactured in China but priced only a little less than the best that were manufactured in America ... must be pretty good. Subsequent research and experience has so far confirmed that about Fullriver AGM batteries.

[theoldwizard1]

A couple of graphs from the Fullriver Battery web site. These were from their page on their Group 31 AGM battery, but the graphs are pretty close for ANY lead acid battery.

Discharging to less than 20% depth-of-discharge cuts the number of charge/discharge cycle by about 50%



This chart surprised me ! 80% state-of-charge is about 12.5V !

[2oldman]

pianotuna wrote:
The alternative is to have them in a heated space--but that means they would get to nearly -40 where I live. I'm certain that is not recommended.

Surely you don't mean your heated space is -40!

[BFL13]

syperk wrote:
Thanks again for all the details - lots of good stuff here. I did indeed install the GC-2's after reading that they were "best" for off the grid camping (we pretty much never stay at places with electrical hookups), but the relatively high internal resistance is an unexpected problem.

Hunting through the archives I did actually find a post from full_mosey saying that they successfully ran a 1000W inverter off a single 12V AGM battery so it seems like a pair of those should do the trick (confirmed by som eother posts above). It's a bit of a pricey upgrade for the ability to reheat my coffee in the microwave (or run my Nespresso machine once a day), but having sealed batteries would also be nice. We'll see!

And I know that a generator would solve all my issues, but I'm a bit philosophically opposed to getting one - that's why I have the solar panels on the roof!

Part of going AGM is to have an ammeter so you can tell when they are fully recharged. I use my Trimetric. AGMology is a whole other topic, but you have to follow their procedures. It is not like Flooded batts and an hydrometer.

[pnichols]

MEXICOWANDERER wrote:
.105" thick plates just beats the snot out of .060" plate for overall life. So does the ultrapremium grade of separator and especially envelope sealing that Concorde brags about. 50 amps draw per battery is no way connected to cold cranking performance. If the price per battery is within 50 dollars my vote goes solidly with the Lifeline.

Well ... maybe not too much snot:

1. Who/what has "only" .060" thick plates?

2. And who besides myself and my Fullrivers need advertised 13.5 to 13.8 volt float voltages in an expensive AGM because they think their 10 YO Parallax fixed voltage converter meets battery float requirements perfectly month after month?

[MEXICOWANDERER]

Just for drill, a pair of 800 cca AGM batteries would allow you to use your microwave every day to heat coffee and still allow reasonable hotel draw (no heater blower!) for several days autonomously.

Jeez I wasn't aware that the cost of Full River was anywhere near the Concorde Lifeline. So I have to retract my earlier recommendation of selecting Chinese Full River brand.

.105" thick plates just beats the snot out of .060" plate for overall life. So does the ultrapremium grade of separator and especially envelope sealing that Concorde brags about. 50 amps draw per battery is no way connected to cold cranking performance. If the price per battery is within 50 dollars my vote goes solidly with the Lifeline.

REMEMBER Peukert is not linear! When a calculated draw is only 10% of CCA, judging the suitability of a battery by sheer CCA is being ignorant (politely stated).

If there is substantial money savings involved then I would tend to favor the lower cost battery, but in a heads-up comparison something about choosing a Chinese battery grates on me. Like selecting a 2-row core radiator over a thicker 4 row core and saving $20.00

[syperk]

Thanks again for all the details - lots of good stuff here. I did indeed install the GC-2's after reading that they were "best" for off the grid camping (we pretty much never stay at places with electrical hookups), but the relatively high internal resistance is an unexpected problem.

Hunting through the archives I did actually find a post from full_mosey saying that they successfully ran a 1000W inverter off a single 12V AGM battery so it seems like a pair of those should do the trick (confirmed by som eother posts above). It's a bit of a pricey upgrade for the ability to reheat my coffee in the microwave (or run my Nespresso machine once a day), but having sealed batteries would also be nice. We'll see!

And I know that a generator would solve all my issues, but I'm a bit philosophically opposed to getting one - that's why I have the solar panels on the roof!

[BFL13]

I have measured several times that a typical microwave will pull more amps from a PSW inverter than from a MSW inverter, but take longer to heat up something. Where PSW wants 150a, MSW wants 125a is typical

I happen to have the ingredients for a fun bench test in the garage now, with two full 100AH marine/rv 27s in parallel, a MSW 3000w inverter, and "1000w" microwave.

I unplugged the float charger on the two batts, so their voltage was dropping slowly from 13.4 and turned on the inverter, plugged in the microwave with a cup of water in it, set the time for two minutes, and fired her up.

It ran with battery voltage falling fast till 11v and the inverter alarm went off, but it kept running. Can go to 10.5 it says. 1.2Kw at first but that fell too. It kept running with voltage about 10.8 and watts about 1Kw at the end when the two minutes was up.

Voltage bounced back to 12.5 and 12.6 after that, when I plugged the float charger back in.

Short, fat wiring of course.

[MEXICOWANDERER]

Inverter efficiency really enters into the picture. My Trace 4024 is a hog. But one day Jesus had to break up concrete steps with an impact 20-amp rated jack hammer. The tool stayed working for an hour. The fan in the inverter was howling and the job got done. I did not want to run the generator right after a tropical storm. Sadly some time that night the power was restored. I figure I lost somewhere around 35% efficiency in the transaction. The concrete steps had broken under the soft soil. 4" of gravel under the new steps cured that, along with 5-sack dry concrete mix and angle iron on the steps lips.

My microwave is the same, it chews up more amperage than with a PSW and food takes longer to cook. It's unbelievable. A 260 watt Weller soldering gun takes longer to heat up with the monster MSW than it does with a piddly SAMLEX 300 watt PSW inverter.

[time2roll]

MEXICOWANDERER wrote:
-There is your answer-

If you are a clone and use the microwave like he does. How long can it drive a microwave? That is...

The Rest Of The Story...

Coffee warmup 3 minutes

Marie Callander pot pie 5 minutes

Big bowl of frozen vegetables 8 minutes

(2) Russet potatoes 13 minutes

I think the longest continuous run was about 15 minutes. No issues with my 4x Costco GC2. Solar would have been minimal. 5.5' 4/0 wire on the 12v side.