AGM Battery Charateristics?

54d18 · February 2018

I have a line on some new batteries, Ritar RA12-100 for use in my small off grid
system. The spec sheet is attached.

I have never used AGM's before, and am curious as to controller setup.
Basically, I am not sure what the cutoff for bulk or absorption charge is.
When setting up for FLA I had to enter the setpoint for charge current
to switch to Float mode, and a max time value.

Thanks,

T

Estragon · February 2018

These appear to be designed for standby (float) service in a UPS-type application, and may not handle deep-cycling for long. That said, they can sometimes be had for cheap.

You may have to experiment a bit with end amps to terminate absorb - typically it's ~1-2% of 20hr capacity, and a timeout of 3-4hrs or so.

Temperature compensation (preferably using a sensor attached to battery) is important, especially with AGMs. Too high voltage can make them vent gas, potentially ruining them.

westbranch · February 2018

Based on the table in that doc you should start charging, when new, at ~ 14.6 V ( cycle service) and if not enough increase at 0.1V increments.. Float at 13.6V -13.8V... and as previously stat above End Amps at 1% to 2% of capacity...
You want a good Charge controller that will allow these values to be adjusted EASILY as you learn about your new batteries.

I am not familiar with this brand, and ,as far as I have experienced, the higher the price and length of pro-rated warranty period (7 years is average AGM warranty ) , the better the product...

Raj174 · February 2018

I agree with @Estragon, these are designed for UPS/float service. I have a friend using similar batteries for about 4 months now. The spec sheet does state an equalization and cycle service charge rate of 14.6 to 14.8V, but I suggest something more conservative by setting absorb at 14.2 to 14.4V because you want to charge, not equalize.
Hopefully your charge controller can be configured with these settings. Since these are really not made for deep cycling you may only get 150 to 200 cycles out of them.

Rick

westbranch · February 2018

here is a very informative document from the maker of my AGMs or more properly named Valve Regulated Lead Acid batteries.... it has a good description about FLAs , AGMs and how to charge AGMs... I reread it on about a yearly basis to refresh my foggy brain.... http://www.cdtechno.com/pdf/ref/41_2128_0212.pdf

Note some of the AGM makers do not use the term " FRESHENING Charge" when they should as AGMs can NOT be EQUALIZED! due to their very nature, they are sealed and you can not add water if the valve vents O2 and Hydrogen. A not enough to freshening charge gets the voltage up but not high enough to cause venting..

Happy reading

Raj174 · February 2018

Yep, looks well worth the read. Thanks westbranch

westbranch · February 2018

Here is a whole page of VRLA documents if you have a few hours

http://www.cdtechno.com/resource/support_doc.html

54d18 · February 2018

Wow, as usual, a lot of very good info.
It would appear that these may not be what I am after in the way of battery storage,
I'll likely replace my old ones with FLA's like I had before.

Thanks everyone...

westbranch · February 2018

If the price is really good compared to retail, don't be scared off, there is lots to learn...

Estragon · February 2018

I agree with @westbranch - telcos etc sometimes swap them out based just on time in service, and they can sometimes be had for a bit over scrap value. In a standby application, they HAVE to work. The cost of replacing batteries in that application is less than routine load testing, and the implicit cost of risk of failure, so they get replaced.

They aren't ideal for deep cycling, but for the right price might make sense (assuming it isn't a giant PITA to install/remove them when they have to be replaced). At the right price, just sell any duds for scrap value and use the good ones until they're scrap too.

54d18 · February 2018

These were supposedly new, not sure where the individual got them, likely from a UPS,
and price was close to half of retail.

My old FLA's were 225AH 6v, and lasted me 13 years, they were configured for 12v,
and were likely not cared for the best for the first few years of their life as I didn't have
an MPPT controller at the beginning.

mcgivor · February 2018

54d18 said:

These were supposedly new, not sure where the individual got them, likely from a UPS,
and price was close to half of retail.

My old FLA's were 225AH 6v, and lasted me 13 years, they were configured for 12v,
and were likely not cared for the best for the first few years of their life as I didn't have
an MPPT controller at the beginning.

FLA are generally way more forgiving than AGM, it doesn't really matter wether they are charged with PWM or MPPT, get the settings wrong with either, problems will be the result. AGM are better suited to installations where maintenance cannot be performed regularly, but this doesn't mean they are maintenance free, complacency can result in unexpected issues. If checking the electrolyte level plus adding a little water now and again is too much of a chore then go for it, but these regular checks provide the opportunity to take meter readings across batteries, terminals and feed conductors all of which can avoid the proverbial Jack in the Box problems, if one depends on a system for daily life, it's a small price to pay to perform regular maintenance.

Raj174 · February 2018

@54d18

I would not use a percentage of the manufacturers retail price as a point of value. I would estimate 20 to 25% of the cost to replace your current FLA bank. At this price they might be worth the considerably shorter life span, but your call.

Rick

Estragon · February 2018

Personally, I wouldn't pay much over local scrap value, but as Rick says, your call.

AGM Battery Charateristics?

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