acceptance charging rate AGM batteries

pianotuna wrote:
Hi Niner,

How do you know they don't like high discharge rates? i.e. what are the symptoms you are seeing to make you believe that?

NinerBikes wrote:
They also do NOT like being taxed with high discharge rates, either. I try to keep the draw down to nothing more than 10 amps... try to take my showers in the morning when the sun is beating on the solar panel and the voltage is up a bit, let the solar panel make the electricity to run the water pump at a higher voltage and lower amperage draw.

I have a ham radio that at 100w will draw at 23 amps. The Telecom battery does NOT like that, so I usually limit my watts to 75 or 80w Tx. Listening Rx is a whole another matter, 2 to 3 amps listening or idling.

These are my observations, YMMV this is what works for me on 2 to 4 week camping trips dry camping.

Stop and think about the chemistry involved. If you can recharge at 21 amps, and there is some energy lost in possible heat generation, then you are effectively saying the chemistry with VERY thick lead acid plates might actually take 18 or 19 amp per hour.

With that magical number of 18 or 19 amps, how do you expect the chemistry to allow you to discharge it at a faster rate than it will recharge? It flat out just won't. You'll try, but you'll see the voltage drop quickly. That's not good for the radio, the Transmit finals, or the chemistry of the battery or longevity either.... I don't know, it just seems like common sense to me? Blowing Tx finals is a very, very expensive lesson on a ham radio. I've no intention of trying to blue smoke a Yaesu FT-991 on a boon docking trip.

Hi Naio,

They used to weld by shorting out batteries. It was not so good for the batteries. Plates warp if you exceed their output capacity and it sure doesn't take long (as you found out the hard way).

Basically, you may have inadvertently "welded" the inside of the battery.

Naio wrote:
When I damaged a battery by pulling 2c from it for a second, I don't think it was because I drained the battery.

ok i'll confuse the issue a little
What do you mean by 'c'
batteries have an AmpHrs capacity
often called C20
which is total capacity from full charge to depleted, normally a cell voltage below 1.7 or approx 10.42 for the whole battery
a battery with a c20 rating of 100ampHrs
a c/5 charge or discharge is 20amps

so to me 2C means a discharge rate of 200amps
a 45ampHr gel discharged at 2c would be putting out 90amps

is this what you mean Naio ?

this type of load for more time than what is need to crank and start an engine is very bad for the battery

the most load i have seen on these (5) new batteries
was while using the MW to warm up a cup of coffee
got to go find the post, but im thinking it was 154 amps, just under 31 amps per battery
they are rated for more than that
and that has only been a couple of times
my next MW will be a lower power unit

when someone is talking about the MW or coffee maker or Nuwave cooker
loads, the load PER battery is the important item, not what ever the total load is, the total load is only NEEDED to derive the Load PER battery

IIRC the specs on mine said 496 watts per cell
thats over 200amps for something like 45 minutes to depletion
the 8hr capacity is 135amphrs thats 16+amps for 480 minutes
31 amps for 2 minutes is almost nothing

overnight load PC qnd lights and 6fans until 11:30 pm
then 3fans fridge etc until 7am
total overnight usage 154 ampHrs, SOC at 7am 78.6%, 14 amp load at 7am
voltage reading 12.54v

How do you know, Mex? Did you actually TRY pouring in some Bactine?

If Bactine doesn't help, bourbon might.

Overamped plates BURN. They warp and scorch. Try as I might, Bactine does not seem to remedy the owie.

pianotuna wrote:
Naio,

It makes a large difference to the total available capacity. Low watts for double the time may use 1/3 less energy--depending on the battery bank capacity.

I get that; that's the Peukart part. I am asking about a different thing.

When I damaged a battery by pulling 2c from it for a second, I don't think it was because I drained the battery.

Maybe it is due to what Mex describes above (IIUC), the draw causing too big a drop in voltage?

Naio,

It makes a large difference to the total available capacity. Low watts for double the time may use 1/3 less energy--depending on the battery bank capacity.

pianotuna wrote:
Hi Naio,

Peukert says lower wattage is always better than higher wattage, given the same efficiency in the devices being powered.

Sure. Thhat's why I have the halfpint. But since we were talking about how AGMs will tolerate a much bigger load for a few seconds than they will for 10 minutes, I wonder if the diff between 5 minutes and 10 matters.

Folks in stores think I'm nutty as a fruit cake as I test their devices with my kill-a-watt meter to see which brand is lower wattage.

LOL :)

Hi Naio,

Peukert says lower wattage is always better than higher wattage, given the same efficiency in the devices being powered.

Folks in stores think I'm nutty as a fruit cake as I test their devices with my kill-a-watt meter to see which brand is lower wattage.

pianotuna wrote:
Hi Naio,

Yes, I do run the microwave from the inverter/battery bank.

But it represents a load of 160 amps and I have four twelve volt jars. So the load per cell is 40 amps. From a capacity point of view I have 556 amp-hours. So I'm loading at 28% of capacity when I use the microwave. Or c/3.5.

Run times tend to be short. For example, lunch today was a left over boneless pork chop sandwich heated in the microwave for 44 seconds (actually two 22 second runs). Two nights ago I had popcorn. Run time of 2 minutes and 22 seconds.

My biggest use, so far, was in June when I was being a "power pole princess" at an inadequately wired campground (is there any other kind?) I was forcing the Magnum into doing not just load support but voltage support. That meant drawing 64 amps from the battery bank for several hours. The numbers say 16 amps per cell. Or C/8.8.

I should never have to do voltage support now that I have the autoformer, and it will be automatic.

Naio wrote:

pianotuna wrote:
The worst load is the 1591 watt microwave.

Do you actually use that on the batteries?

That's cool! Did not realise I would be able to run mine, when I get my 4 big jars into service.

Are longer runtimes at lower wattage better or worse? I have a halfpint (nominally 600watt but have not tested it) and a larger one. Wondering which I should bring with me when I greturn to the batteries. The halfpint takes about twice as long to heat food, as one would expect. 8-10 minutes vs. 4-5, for a frozen stew.