AGM Adventures- Update

Updated 31 Jan 17

Initial results. I will re-test the AGM after it does one deep cycle to confirm these results.

EDIT completed 6 Oct

Test was to put the test battery as the only battery running the 5er, and whole house with the inverter to run a kettle and then a toaster, measuring initial voltage sag and noting the amps draw.

The AGM is brand new out of the box

http://www.hespv.ca/hesproductspecs/HES/Stark_Battery_TD_ENG.pdf

Out of the box voltage was 12.82. Dated July this year (I think) did an initial charge and left overnight voltage today 12.89 very slowly still going down--can't wait, do the tests!

Used the Trimetric which is only to one decimal point, so that can throw things off some, but anyway, this is how it came out.

First the AGM showed 12.9 on the Trimetric, turned on inverter and bam, voltage dropped to 12.6 with a 1.1 amp draw (no inverter load yet) voltage still falling fast got to 12.2 !!! so turned on toaster voltage dropped to 11.2, turned off toaster, voltage bounced right back to 12.6 with inverter still on.

Seems the battery needed a kick? Waited for things to settle, still 12.6v so ran kettle. Voltage 10.9 with 93.4 amps draw. Unplugged kettle, voltage right back to 12.6 inverter off 12.7 !

Anyway results seem to be ( new 100AH AGM)
A. Toaster- 1 volt sag with 75 amps draw
B Kettle= 1.7 volt sag with 93 amps draw

However, something funny might be going on with the battery not up to speed yet, so will try again after taking it down to 50% and recharging. Not sure when that will get done.

Meanwhile, for comparison I did the same test with one 5 yr old T-1275 that spent its first 2 years in a golf cart then I have been working it hard off and on but also trying to take care of it for the last three years. SGs are all in the green, capacity tested recently as about 135AH out of 150AH rated. Battery full going into the test.

A. Toaster- 1.2v sag with 71 amps draw
B. Kettle- 1.5v sag with 93 amps draw

With my usual 6 battery bank in the 5er (two T-1275s and four 6s)I got

A. Toaster- 0.5 volt sag with 66 amp draw
B. Kettle- 0.6 volt sag with 84 amp draw.

I don't know why the same inverter with the same loads has different (fewer) amps draw from the 6 battery bank. Most of the wiring is the same.

(I will not be able to report when amps begin to taper with the AGM vs a Wet like PT wanted to know, because I have to use my Vector charger which has its own taper time. I would need two of these AGMs to use my charger that could show that for PT due to the 27a charging limit on the one.)

I don't know what is normal for a brand new AGM not been cycled yet, so I will do a deep cycle and then see what it behaves like after that.

2oldman
Explorer II
Oct 05, 2016
BFL13 wrote:
I don't know why the same inverter with the same loads has different (fewer) amps draw from the 6 battery bank. Most of the wiring is the same.

I don't know what is normal for a brand new AGM not been cycled yet, so I will do a deep cycle and then see what it behaves like after that.
Because the 6v bank has a smaller voltage drop.

I doubt any cycling is going to make much difference. That's a big load to put on a single battery. I'm sure a LiFePo wouldn't drop voltage at all!
landyacht318
Explorer
Oct 05, 2016
Yeeehawwww

Nothing like actual data.

Weird how it dropped to 12.1v under just the initial inverter parasitic load.

My Northstar agm was definitely weird before I cycled deep it and hit it with 25 amps recharge.
MEXICOWANDERER
Explorer
Oct 05, 2016
Fully charged static, the 31 Lifeline that owns me, will drop from 12.79 to 12.77 with a 3-amp Bi-PAP load. With an LED 30-watt load added it drops to 12.66

What you are doing is invaluable. Later on, when a question of capacity arises the trends and tendencies you record today can be compared to suspicious activity later on. If in fact the slump has noticeably increased do a conditioning charge followed by a capacity test.

NOTE: As a general trend the more an AGM plays the part of a high CCA starting battery the less slump a person shall see. I love the idea of a heavy AGM with less than stellar CCA but with superior capacity.
landyacht318
Explorer
Oct 05, 2016
I just tried a quickie test with my ~65% charged Northstar AGM and an 11 amp Milwaukee 5540 polisher with variable speed finger trigger on my 800 watt MSW inverter.

Slowly ramping up speed to maximum 2800 rpm over 5 seconds with tool unloaded, was 33.8 amps out of battery and battery voltage dropped to 12.3v and held there for 10 more seconds until I released trigger. But the battery monitor takes voltage readings from a shared buss a few feet from battery terminals over 4awg.

Need to find a bigger load and start with a full battery to be a comparable test to BFLs battery and really put the voltmeter on battery terminals directly.

Passing clouds + other loads like fans fridge and laptop and TV, battery after test reading 12.8v and +1.3 amps into battery. Reading 28AH from full. Not getting to full today on solar.

I'll refrain from plugging up this thread with a different battery's results from here on out unless requested otherwise.
BFL13
Explorer II
Oct 05, 2016
Yes, the more results the better.

I wonder if the off the shelf battery was stratified but showing ok oc voltage, so it dropped voltage under a small load. ?

I forgot to say the reason for the test was to confirm full mosey's claim that you could get away with using one or two AGMs to supply the inverter instead of several flooded batts due to the small voltage sag under loads with AGMs. (To still stay above inverter low voltage cut off)

If so, it would make AGMs the choice when you have a small RV with battery space or weight limitations.

I got the one AGM for the Truck Camper with that I'm mind, and am now testing. It is all full mosey and PT's fault, nothing to do with me! :)

I have no plans to run such high amp loads on my one AGM in real life, but was hoping it would hold up in a pinch. We'll see. Whatever it can do, I need the AGM instead of a Flooded batt where it is mounted inside the TC. The flooded batts set off the LP alarm with their fumes. :(
landyacht318
Explorer
Oct 05, 2016
Not sure how an AGM stratifies.

Mex once typed the high amperage recharges helped force the migration of electrolyte through the glass matting and into the plates, which makes it seem that stratification of resting AGMs by gravity or just temperatures, is not likely to occur.

I rarely subject my single AGM to high inverter loads, but this subject interests me.

As far as PT's request for charge acceptance of AGMS.

Well here is some testing and data on a lifeline gpl-31t( same battery as Mex's lifeline)

http://www.pbase.com/mainecruising/effect_of_charge_rate_on_agm_battery

How it relates to PT's tellycom jars is unknown to me.

This is a good one too:

http://www.pbase.com/mainecruising/voltage_vs_soc_lifline_battery
BFL13
Explorer II
Oct 05, 2016
The tech support guy for the UPG AGM121 battery outfit said that AGMs will indeed stratify if left on a long float. That gets fixed when they are cycled again. He said you don't need to give them a boost every month like with flooded batts on a float, but once a year was enough.

He warned against overcharging them such as equalizing in case they vent. You can't just replace the water like with flooded. He liked the pulse method of reconditioning instead. 14.8 stop 14.8 stop 14.8 stop is how he described the pulse method that pulse chargers do. One is the CTEK 7002 he mentioned.

I don't know how Mr Wizard gets away with zapping his AGMs with 15.4 volts for a few minutes when they get a little sulfated from several incomplete cycles in a row. (What I call "progressive capacity loss" same as with flooded batts) I guess the key is the short duration he does it.
pianotuna
Nomad III
Oct 05, 2016
The initial drop may have just been the capacitors in the inverter getting filled up. I'm sure most of us have seen a spark when connecting to an inverter--even when it is turned off.

Did you happen to "shoot" the temperature of the battery bank before and after the testing?
BFL13
Explorer II
Oct 06, 2016
No I didn't take any temps, sorry. My IR gizmo is not much for pin-pointing. It is good for the back of a solar panel or whatever.

Good thought about the inverter caps. Yes I am used to the big spark. I don't know if that would explain it or just a slow initial chemical reaction in the new and possibly stratified batt. Anyway, the voltage came back.

Ok, so finished running the batt down and ready to recharge, I drew it down with 15 amps (20 hr rate is 5 amps) and waited till the Trimetric said it was down 50AH.

Interesting thing is at 50AH down and the 15a draw, voltage at the batt was 11.72. When I do my usual 20hr rate tests on my Flooded batts, voltage is 11.6 at 50% before bouncing back to 12.1

That suggests this AGM does hold its voltage higher under load.

After 30 minutes voltage came back to 12.04 and stopped rising. So that means I overshot 50% by some amount. Peukert says that will happen. Also new batt might not be up to rating yet--needs more cycles. Both most likely.

According to the spec sheet linked above, I might be at 35-40% SOC hard to say. Doesn't matter, idea is to get a deep cycle done, so now on with the recharge. Unfortunately I can't record the AH restored with the Vector since it is not part of the 5er set-up with the Tri. Idea is to get the batt to "full" and try the load tests again.
landyacht318
Explorer
Oct 06, 2016
In the past I have taken My NS down to 50% at much higher than 4.5 amps of the 20 Hr rate. Voltage rebounded to 12.32v while still under a 0.2 amp load.

NOrthstar PDF sheet indicates 50% OCV is 12.11v

I bet your battery performs better after the recharge.

Do watch the temp rise when feeding it the vector. The IR gun is accurate enough. I was surprised at the temp rise on mine@ 40 amps initial, but mine has some reflectix on it as it is exposed to engine/exhaust heat.

I will be removing the reflectix on the battery and make a simpler shield to deflect engine heat and that radiated from exhaust and Cat.

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