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 > AGM Mystery Capacity Crash Below 75% SOC UPDATE

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MrWizard

Traveling

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Posted: 09/26/19 08:34pm Link  |  Quote  |  Print  |  Notify Moderator

A side note
I try to keep my batteries above 70%
At 50% I am not going to be running big inverter loads like MW or kettle or toaster

I'll run the generator or do without
Just because the standard is to not go below 50%
Doesn't mean doesn't mean go ahead and do 50% every camping night and do back to back heavy loads every them every morning

Even with my less intense loading and higher SOC, I charge them to full everyday
Unless there is something that prevents me from doing so


Radiate The Happy
....

Connected using Verizon and AT&T
1997 F53 Bounder 36s


MEXICOWANDERER

las peñas, michoacan, mexico

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Posted: 09/26/19 08:43pm Link  |  Quote  |  Print  |  Notify Moderator

There's an alternate way.
Add 300 watts of solar panels. Start gen in AM. Use for heavy loads and let panels charge from around 9:00 onward.

People who insist on 100% solar remind me of cruising sailboat skippers who won't move an inch without a breeze.

pianotuna

Regina, SK, Canada

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Posted: 09/26/19 08:45pm Link  |  Quote  |  Print  |  Notify Moderator

Hi BFL13,

Yes they care about gassing voltage, even though they are recombinate.

That said, so long as they don't vent voltage can be above the gassing number.


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.

BFL13

Victoria, BC

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Posted: 09/26/19 08:48pm Link  |  Quote  |  Print  |  Notify Moderator

Mr Wiz, it seems there is a good reason to be careful like that with this kind of battery.

Actually I have no proof it is because they are AGMs. It is just that this never happened doing the same thing with Wets.

I suppose someone going from T-105s doing what I do, would be in for a nasty surprise if he went to the T-105AGM thinking it is the same thing. I don't know.

I don't mind using the stove top instead of the kettle, but I refuse to give up the electric toaster! [emoticon]


1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
See Profile for House electronics set-up.

MEXICOWANDERER

las peñas, michoacan, mexico

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Posted: 09/27/19 01:14am Link  |  Quote  |  Print  |  Notify Moderator

Perfectly golden toast, mango preservatives, and Finca Renaldo toasted coffee beans. Yep, a toaster is important [emoticon]

Is this conversation about wet?
Regular AGM
Or telecom

Batteries?


nothing wrong with your memory BFL. Telecomm batteries charge slower than regular AGM batteries. They are at their best using the hundred hour rate.

landyacht318

Near a large body of salty water

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Posted: 09/27/19 01:52am Link  |  Quote  |  Print  |  Notify Moderator

Was it this thread that the topic of constant current loading was discussed?

This item claims to be a constant current device no matter the battery voltage.

[image]

If it works as described, one just needs the 77 degree water bath to achieve accurate capacity results.

https://www.ebay.com/itm/150W-200V-20A-C........0?hash=item23bdcbc3e4:g:6e8AAOSwZwxc8Iz1

BFL13

Victoria, BC

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Posted: 09/27/19 08:01am Link  |  Quote  |  Print  |  Notify Moderator

Here is some detail of the test I did at home to see if the two 100s did it too or was it just the 250. I see I ran the two 100s as a bank, so not individually as I reported earlier. Batteries were full at beginning according to 0.5/100 method the day before.

Method was use the full kettle with cold water till the kettle clicked off, boiling. Then dump the hot water, rinse with cold, and refill with cold for next run. Numbers from the Trimetric. I took turns so each had a little rest before its next run.

Runs in sequence for the 200 and 250 showing: before start voltage, initial voltage after start (the drop), and voltage when kettle clicked off, immediate bounce back voltage, and time of run. (Time variations probably due to different water temps at start)

Kettle 90 amps was 45% for the 200 as rated, and 36% of the 250. EDIT- when it happened earlier when camping, it was with the whole bank so 90 amps was then 20%.

Run 1.
200- 13.4, 12.4, 12.1, 12.9, 9 minutes
250- 13.0, 11.9, 11.9, 12.9, 8 minutes

Run 2
200- 13.0, 12.1, 12.0, 12.8, 9 minutes
250- 12.9, 11.9, 11.8, 12.8, 10 minutes\

Run 3
200- 12.9, 12.0, 11.8, 12.7, 8 minutes
250- 12.8, 11.8, 11.6, 12.5, 10 minutes

Run 4
200- 12.8, 11.7, rapid drop to 11.1, 3 minutes inverter quit 10.3v
250- 12.7, 11.6, rapid drop to 11.1, 4 minutes inverter quit 10.3v

Separated the two 100s and resting no loads --45 minutes later-- voltages : 250- 12.77, 100(1)- 12.76, 100(2)- 12.82

( 13.0 is full, 12.4 is 50%, 12.7 is about 75% resting.

Notes:
Run 4 initial voltage drop seemed ok, but then the running voltage drop fell right off

Run 3 showed first sign of trouble with the 250

Similar results for the 200 and 250 but with 45% vs 36% draws indicate the 250 is in worse shape than the two 100s? But they all did it whatever shape they are in.

One of the 100s might be in better shape than the other based on the 45 minute bounce back voltages.

* This post was edited 09/27/19 08:20am by BFL13 *

BFL13

Victoria, BC

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Posted: 09/28/19 01:05pm Link  |  Quote  |  Print  |  Notify Moderator

Interesting results from a mix of 27s with AGMs!

Tried out the mixed bank in a backyard test to see if it was ok to go camping with and not have to come home early.

I have no idea what the bank is in AH with the strange way the AGMs act now, but I chose to run the bank down at 25.5 amps because that is the max using all the lights. 30 amps would be for 600AH, eg. I have 650 as rated total, but can't get that with the "broken" AGMs.

Loaded voltage started at about 12.7 and after five hours it was 12.1, with 127AH drawn. If this were a normal 20 hr rate draw down, the 12.1 loaded would be about right for being at 75% SOC (as seen on previous tests) and the five hours is right. SG of the 27s was 1.265 (was 1.275 at start)

Turned off all lights , no load, immediate bounce back 12.45 so ran a kettle test. 90 amps starting at 12.4-drop to 11.7, was 11.5 when kettle clicked off, bounce back 12.3.

Back to the 25 amps of lights test 12.1 loaded another two hours and voltage 11.9, SG of 27s is 1.200ish (which is 50% SOC)

Wanted to see if it could still do the kettle, and it did, holding at 11.3 before click off-- no crash.

Looking dubious at only 7 hours (instead of 10) to get to 50%, and AH 216, so is "full" only 432? Seems very low.

Disconnected all batteries to take individual bounce back voltages, where 12.4 would be 50% of AGMs and 12.2 for the 27s.

After one hour, the two 27s were at 12.17 and 12.21 so really at 50% confirmed by matching SG numbers.

The two 100AH AGMs (tested in April at 90) were 12.78 for one and 12.69 the other. The 250 was 12.59.

So the AGMs were letting the 27s do the work! But without the 27s added in, no kettle.

So the AGMs were about 75% (by voltage--could be anything actually) while the 27s were at 50% at the end of the test run. Still plenty of camping AH left to go in the AGMs, but the 27s are at 50. If I went further I would still be fine for running things, but the 27s would be taken down below 50 to unknown level.

Puzzle. I need a way to disconnect the 27s and continue (but without high amp draws) just on the AGMs. But how to tell when the 27s are at 50 using the whole bank, unless I take SGs? (No thanks).

I still have the switches where the two AGM 100s can be separated from the 250 so I can recharge them separately, and now that means I can have the 27s and the shaky 250 in one set and the two not as shaky 100s in the other.

One approach might be to start camping with only the 27s and 250 and wait till voltage indicates the 27s are at 50%, then switch so all draws are from the two full 100s, but no high draws allowed. That would give longer till a generator recharge is needed, and keep the 27s above 50%. Total time would be less than using the whole bank at once (Peukert), but gets more out of whatever the AGMs have in them for low amp draws like the furnace and usual RV loads.

Not ideal, but we could probably get by like that until I get new batteries eventually. Have to go camping and find out, now it looks like it ought to work.

full_mosey

Oklahoma

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Posted: 09/28/19 02:31pm Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

I have always used the same voltage vs SOC at all ambient temperatures. Is that proper?

The AGM loses 15% capacity at freezing vs at rating temp of 77F, so is it still 13.0v when full? BUT at freezing temp, your charging rate of 14.8 is now supposed to be adjusted upwards to 15.2 volts to compensate for the cold. Voltage going opposite directions there maybe.
...


Hi BFL13;

In support of temp-comp charging, I offer link.

I also believe the electrolysis(bubbling/gassing) that is sought after by FLA users, is a waste of charging energy for AGMs, as there is no requirement to stir the electrolyte .I know AGMs are recombinant, but IMHO, that is a recovery process in the event of gassing.

A temp-comp charger should automatically charge faster/cheaper while avoiding electrolosis.

I have looked at the annual temp variance for BC. Your temps are influenced by the Pacific Ocean and do not vary widely like they do in Oklahoma, USA. I need temp-comp. My battery temps can vary 10C inside of 24hrs. I have graphs that show daily charge Volts decreasing automatically while charging is in progress. No set and forget knob twisting will do that.

HTH;
John

BFL13

Victoria, BC

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Posted: 09/28/19 02:48pm Link  |  Quote  |  Print  |  Notify Moderator

I do in fact adjust the charging voltage for temperature, so that when camping in February and ambient is 35F, I will set 15.2 instead of 14.7 as in July. The adjustable voltage PowerMax "LK" line of converters lets you do that manually.

My old VEC1093DBD portable charger has built in temperature comp and you can see it working when it operates at higher or lower voltages.
Neither compensates for battery internal temperature though, just ambient.

The AGM guides insist upon temp comp. If you set the spec 14.4 (for 77F) in February at 35F, you will be undercharging the AGM, with no way to see the SG failing to rise to the right amount.

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