Good Sam Club Open Roads Forum: AGM Mystery Capacity Crash Below 75% SOC UPDATE
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 > AGM Mystery Capacity Crash Below 75% SOC UPDATE

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BFL13

Victoria, BC

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Posted: 09/23/19 02:06pm Link  |  Quote  |  Print  |  Notify Moderator

The link in the OP has the 8D that first acted up. Seems it is more of a "standby use" than a "cycle use" battery as it has turned out. The specs don't really say. I thought it would be a good deep cycler, which it seemed to be at first. If I take it out of the RV it will go in the garage as the standby power with inverter we use for short time power failures we get here sometimes in the winter. The two 27DCs have been doing that. So not a total loss.

The two AGM 100AH ones are supposed to be actual deep cycle. Three years old now and used hard but not mistreated especially. I got them to go in the truck camper where I had to have them inside and Wets would not work, what their fumes. (Did have Wets there at first and they set off the LP alarm when being charged)

I keep having mixed battery banks over the years what with one thing and another. Never had four new batts all the same and just stayed with that.

I suppose the free, used T-1275s I got that lasted five years makes up for these AGMs not lasting, so I can't complain about costs really.

I am thinking of going back to cheap 27DCs that will last a couple years at least, now that I have learned how to get them properly charged up after doing 50-90s. Had a lot of trouble with them last time I tried 27DCs, but Mex has since described how to do it. Also now I have chargers that will do that process.

I don't have to keep the batts inside the MH, so I could go back to Wets ok for fumes. We'll see.

Probably no sense paying big bucks for batts that don't last me any longer than the cheap ones, even with all the proper care routines I do. Boo hoo, it sucks to be me, etc. [emoticon]


1991 Oakland 28DB Class C
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CA Traveler

The Western States

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Posted: 09/24/19 08:01am Link  |  Quote  |  Print  |  Notify Moderator

How do telecomms hold up when deep cycled? Aren't they designed for limited deep cycling? ie Limited cycling and very large charge rates in case the disruption occurs again in a short time?


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pianotuna

Regina, SK, Canada

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Posted: 09/24/19 08:33am Link  |  Quote  |  Print  |  Notify Moderator

Hi CA Traveller,

I believe they are a thin plate design on the Negative and a thick plate on the Positive. I purchased mine "used" not new. They were less expensive than flooded deep cycle. I paid less than one dollar Cdn per amp-hour of capacity.

https://www.jstor.org/stable/softtechaltetech.26.25?seq=1#page_scan_tab_contents

To read the full article (written in 1987) you must register online for free. I think I'm going to adore this site.

* This post was edited 09/24/19 09:02am by pianotuna *


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

MrWizard

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Posted: 09/24/19 11:41am Link  |  Quote  |  Print  |  Notify Moderator

I installed AGM telcom/server batteries in the previous MH a DP,
Capable of 500w per cell AKA 3000 watts per battery until discharged, about 10 minutes, but would be totally discharged, but this is Tested what it could stand spec for when new, Not recommend design use
And was very happy even after several years of use
But I did not do back to back electric kettle water boiling
Or run the A/C

I think your use pattern, has created a physical/ molecular barrier in the plates , that cañnot carry/pass the amount of current you want to use

Just like any other lead battery, you need enough Total capacity, that max power use does not exceed designed power use per cell
If you want long life trouble free use
If not enough storage space for that
Then you have to expect, replacement when performance drops below need

* This post was last edited 09/24/19 12:01pm by MrWizard *   View edit history


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BFL13

Victoria, BC

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Posted: 09/24/19 12:38pm Link  |  Quote  |  Print  |  Notify Moderator

I have been doing 50-90s with my various 400AH ish battery banks over the years without any real trouble until now, using the inverter to run MW, kettle, and toaster as desired.

The usual battery advice is to keep draws and charging under 25% of capacity.

MW at 125amps is 125/450 = 28%
Kettle at 90 amps is 90/450 = 20%
Toaster at 70 amps is 15.5%

The only problem in the past has been voltage drop to keep the inverter from shutting down. I typically have about a 0.8v drop from whatever the bank's voltage is at the time.

The goal is to be able to run the toaster once for three minutes in the morning of a recharge day, when at 50% SOC or 12.1 volts. That makes it drop to say 11.3, and you hope the toast is done before it sinks to 11 and sets off the inverter alarm.

So with various banks of mixed 6s and 27s, 6s and T-1275s, AGMs and 6s and T-1275s, nothing like this ever happened.

I think it is very weird that these AGMs could still do all that until recently as described in the OP. They can still do it as long as they are above 75% SOC (according to voltage being above 12.7ish)

I don't know what the bank capacity is anymore. They can do the 20 hr rate for a long time, down lower than 75% SOC. But they have no capacity at the higher rates once voltage gets to about 12.7.

Peukert went on strike! Mex explains that somehow I did damage these AGMs, but doing the same things to my previous batteries did not do anything like this. So whatever I am doing "wrong" , all I need to do probably is go back to using Wet deep cycles that can "take" whatever I am doing.

Meanwhile, I will see how far I can get by adding a couple of Wet 27DCs to this AGM bank since I have them handy. If it doesn't work, or when it stops working well enough, whatever, then it is obvious what the next step must be.

pianotuna

Regina, SK, Canada

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Posted: 09/24/19 01:05pm Link  |  Quote  |  Print  |  Notify Moderator

BFL13,

I wonder if the thicker positive plates are causing the same sort of effect that happens on six volt jars?

MEXICOWANDERER

las peñas, michoacan, mexico

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Posted: 09/24/19 01:10pm Link  |  Quote  |  Print  |  Notify Moderator

Heat within the grid. Why have heavy expensive grids when a calculated design says an X design would do the job.

BFL13

Victoria, BC

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Posted: 09/24/19 01:12pm Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

BFL13,

I wonder if the thicker positive plates are causing the same sort of effect that happens on six volt jars?


You lost me there PT! Please explain what you mean.

landyacht318

Near a large body of salty water

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Posted: 09/24/19 01:27pm Link  |  Quote  |  Print  |  Notify Moderator

China's cheapest agms have their time and place.

You've found their limitations in actual use with tools knowledge and observational focus that few ever bother with.


Agms on automotive forums seem to be viewed as magical upgrades that are immune to anything a human can do to them. Marketer's sense more profit, More bonuses and more shiny objects obtainable for their significant others who are enraptured by such things and judge everything and everybody by them.

Cheap as possible agms made in usa now can compete with China's cheapestfree shipping online agms in autoparts stores nationwide, and will proudly state deep cycle on their stickers too.
The deka intimidator agm tested horribly in actual deep cycle use, although east penn can certainly make top quality if the profit motive is there. It is not.

Any battery can be marketed for deep cycle use. Whether it is built for actual deep cycle use is apparently now irrellevant, if it gets in the way of max profit.


Many batteries that are 'still going strong' according to their owners, would likely also jump off a cliff if subjected to your high occassional loads below 75%soc
But ignorance is indeed bliss,for a while anyway.
Then it's finger point city.

time2roll

Southern California

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Posted: 09/24/19 02:18pm Link  |  Quote  |  Print  |  Notify Moderator

Sam Spade wrote:

BFL13 wrote:

Looks like a new battery set early next year. ( Which is ok)
IF.....you would run those high draw appliances off of the generator instead of complicating the issue with an inverter...you would be a LOT less likely to have problems like this.

Just sayin.....
+1 or use propane for coffee, cocoa, toast, waffles, hash browns, poached eggs, pancakes, bacon and the rest.

If money is easy start pricing lithium. It will be the last battery you buy.


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