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Topic: How to test 8D AGMs (Read 1420 times) previous topic - next topic

How to test 8D AGMs

With all the talk of battery problems I thought I'd better finally get around to posting this...

While in Tucson this winter we were in the same campground as Scott & Carol. Scott & I & anyone else that would listen had some long discussions about his batteries. I told Scott about a very knowledgeable guy in town that had made some cables for me. We made a trip down to his shop and had a long discussion with Mike at General Power about the difficulty of testing large AGMs. He suggested we bring them in to test but the prospect of pulling almost 700lb of batteries from the coach and hauling them to the shop gave some pause. Scott asked if they could test at the coach. Mike said sure but he would have to charge for the techs time. Scott & Mike reached an agreement and the tech came out the next day.

The tech showed up with his tester. The tester & how it was used is what this post is really all about. See pics of the tester below.

The tester was impressive. It looked decidedly low tech and like it came out of a Flash Gordon movie... The tech said they don't make em' like this anymore. :) He also mentioned that the carbon pile in this tester sells for about $5k! The tester itself was pretty simple. A volt meter, a switch, and a amp meter on the front. A carbon pile and shunt in the back with 2 heavy duty cables with heavy duty battery clamps on the ends.

To test he disconnected each battery and then connected the battery cables. While watching the amp meter he pressed the switch to put the load on. He then used the screw crank on the end of the carbon pile to dial in the load. The tighter the carbon pile the higher the load. In the pictures you can see the gauge goes to 1000 amps! Not sure if the tester can really go that high but for Scott's batteries he took the load to between 550 and 600 amps and left it there for 2 minutes all the while watching the DC voltage. The voltage dropped to 12.2 almost immediately and stayed there. That was for the 2 "strong" batteries. The 2 "weak" batteries dropped into the low 11s over the 2 minute test. During the test the battery cables from the tester got almost too hot to hold and the carbon pile heated up. The tech waited about 20 minutes between each battery test for them to cool down.

The tech concluded from the testing that out of Scott's 4 batteries that the 2 weak batteries were drawing down the two strong batteries.

See Scott's thread about his decision to replace his batteries with 3 new Lifeline 8DAGMs.

Link to General Power Tucson: Wholesale Battery Store Tucson | General Power Batteries

Now let the serious discussion and wild speculation begin!

see ya
ken
The selected media item is not currently available.ken & dori hathaway & Big Agnes
🍺1992 U300 GrandVilla WTBI #4150 FOT FBP 2011
✨6V-92TA DDEC Parlor Coach 350HP Series 92
🏁2011 Nissan XTerra Pro-4X

Re: How to test 8D AGMs

Reply #1 –
Ken, that is how my battery tester works.
2003 U320 Battery Tray
I bought it on EBay, almost new, for a fraction of what new ones cost.  You hook it up to an 8D, crank up to load to three times the capacity of the battery, about 750 amps and press and hold the test button. Watch the amps and volts.  Normal test is less than two minutes.  Two minutes is a severe test.  But if they are showing weak after 15 seconds it is time to replace them. 

They are probably fine for a solar collector on your barn.  I use my old ones to run a 12 volt to 120 volt motor generator to run my electric chain saw out in the woods.  They last longer than I do.
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: How to test 8D AGMs

Reply #2 –
Mine only goes to 600 amps but will identify a bad battery. excuse the missing Y.
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: How to test 8D AGMs

Reply #3 –
I believe those type of testers are generally used to test start batteries with a short duration high amp load.  For a business owner this is probably the best way to test customers batteries (start or house) due to how fast it can be done.  As a battery owner (who has time on their side) one can test house batteries in a way that is closer to how they are used.

Here's the method I have used:
-Starting with the battery full charged (when less than 5 amps would feed into it), I connected it to a dedicated inverter with a programmable shutdown voltage (I think I set it to 12.2 volts which is about the 50% discharge voltage).
-I had a load (light bulbs) plugged into the inverter but had it pass through a mechanical vacation timer and set the time on the timer to 12:00.
- After starting the test I would measure the current (via the controller on the inverter).
-When the inverter shut down at the "low volts" setting I read the hours on the timer and multiplied it by the amps to give the Amp-Hours provided.  I then compared this to the manufacture's Amp-Hour ratings.

I did this on some "old" batteries a business owner/friend gave me that had sat on a shelf for an unknown time and were written off as bad.  They were 8D AGMs and after repeated testing and equalization I was able to recover much of their capacity (for a 50% discharge).  One was a Lifeline and it's still going strong after 8 years.  The other was a FullRiver that lasted about 4 years.

One thing I learned by doing this is how many "gray areas" there are with battery specs and testing.  Such as when to decide when the battery is "fully charged" or the discharge rate verse the AmpHours you can get (you get more AH with a slower discharge for the same cut-off voltage).  Some manufactures have gotten more detailed about the spec of their batteries by providing several time frames for a discharge rate.  While my method is somewhat crude, I do think it was fairly repeatable as a measure of improvement.

I know you are not supposed to equalize AGMs but I had nothing to loose and the inverter (RS-3000) had a temperature probe that I used hoping it would shut down the equalization process if the battery got hot.
So we don't go off on an "equalizing AGM" discussion tangent here's a recent thread on the subject: Equalizing AGM batteries
John Fitzgerald
1991 U300 (SAI) Side Aisle Island Bed 40'
Detroit 6V92 with Allison Retarder
Meridian (Boise), Idaho

Re: How to test 8D AGMs

Reply #4 –
Question,have 2 8d batteries and the shorter of the 2 sides are bulged out,pretty sure the batteries are shot but if they are buiging
does that mean they are bad?No date code marked.
96 U270 BUILD 4810
85 380SL
Drummonds TN.

Re: How to test 8D AGMs

Reply #5 –
Quote from: John44 –
Question,have 2 8d batteries and the shorter of the 2 sides are bulged out,pretty sure the batteries are shot but if they are buiging
does that mean they are bad?No date code marked.
Either the battery has plates that are badly sulphated or perhaps overheated and the plates buckled from too high voltage/charging rate.
Try charging at a low rate for a couple of days.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: How to test 8D AGMs

Reply #6 –
Quote from: JohnFitz –
I believe those type of testers are generally used to test start batteries with a short duration high amp load.  For a business owner this is probably the best way to test customers batteries (start or house) due to how fast it can be done.  As a battery owner (who has time on their side) one can test house batteries in a way that is closer to how they are used.

Here's the method I have used:
-Starting with the battery full charged (when less than 5 amps would feed into it), I connected it to a dedicated inverter with a programmable shutdown voltage (I think I set it to 12.2 volts which is about the 50% discharge voltage).
-I had a load (light bulbs) plugged into the inverter but had it pass through a mechanical vacation timer and set the time on the timer to 12:00.
- After starting the test I would measure the current (via the controller on the inverter).
-When the inverter shut down at the "low volts" setting I read the hours on the timer and multiplied it by the amps to give the Amp-Hours provided.  I then compared this to the manufacture's Amp-Hour ratings.

I did this on some "old" batteries a business owner/friend gave me that had sat on a shelf for an unknown time and were written off as bad.  They were 8D AGMs and after repeated testing and equalization I was able to recover much of their capacity (for a 50% discharge).  One was a Lifeline and it's still going strong after 8 years.  The other was a FullRiver that lasted about 4 years.

One thing I learned by doing this is how many "gray areas" there are with battery specs and testing.  Such as when to decide when the battery is "fully charged" or the discharge rate verse the AmpHours you can get (you get more AH with a slower discharge for the same cut-off voltage).  Some manufactures have gotten more detailed about the spec of their batteries by providing several time frames for a discharge rate.  While my method is somewhat crude, I do think it was fairly repeatable as a measure of improvement.

I know you are not supposed to equalize AGMs but I had nothing to loose and the inverter (RS-3000) had a temperature probe that I used hoping it would shut down the equalization process if the battery got hot.
So we don't go off on an "equalizing AGM" discussion tangent here's a recent thread on the subject: Equalizing AGM batteries
Read reply # 8 straight from Lifeline on your link.
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: How to test 8D AGMs

Reply #7 –
A carbon pile battery tester is fast and convenient but I do not have one, so here are two alternate methods.

I determine the health of my deep cycle batteries by using a ten hour (or less), 10 amp, four step test. Step one: measure voltage (initial voltage) after leaving battery disconnected overnight, Step two: Attach an ammeter with two headlight bulbs (5 amps each), measure amps every hour and keep track of number of hours. Step three: disconnect bulbs/ammeter, then measure voltage (finish voltage) after leaving overnight. Step four: calculate used amp hours and compare to battery capacity charts.

I will also check the health of a deep cycle battery by disconnecting it for 3 hours after it has been fully solar charged during the day, then measuring voltage (this is the start voltage). Reconnect battery and use it as normal until ready for bed, then disconnect battery after noting amp hours used. In the morning, note the voltage before reconnecting (this is the finish voltage). Calculate voltage drop and determine % discharge from battery tables, then compare % discharge to noted amphours used to determine amphour capacity of battery. Note: this procedure is possible because I have an amphour meter on each battery, so three batteries and three amphour meters.
Wyatt
96 U320 40 WTFE, build 4943
84 Toyota Supra towd
2015 Jeep Wrangler towd
Victoria, BC, Canada

Re: How to test 8D AGMs

Reply #8 –
I test my batteries with an OTC 3167 Sabre battery tester. I had a boat with 10 Lifeline AGM batteries. I would post a link but I don't know how. This tester is available at Amazon and other retailers for about $450.00.. It is different than the testers talked about but it works.
Larry and Terry
Ex 2004 U270 36'

Re: How to test 8D AGMs

Reply #9 –
John44 in Reply#4 regarding bulging sides:
Bulging sides on a battery, while not desired, does not mean the battery is definitely no good.
Typically, 8D AGM batteries with bulging sides have been rapidly charged when hot.
Too hot may be caused by a 120 degree day, or batteries in an enclosed compartment, or fast charging.
Charging causes heating while releasing gas (hydrogen and oxygen). A sealed battery does not need water because the hydrogen and oxygen gases recombine back into water, unless charging too fast such that the pressure building inside the battery causes gasses to vent through a control valve (so battery does not explode).  This pressure with hot (and soft) plastic sides, causes the case to bulge and stay bulged after cooling.
Use a desulphator for a few weeks or Equalize the battery for a couple hours while monitoring for heat build up. Then determine battery capacity using one of the methods described previously.
Wyatt
96 U320 40 WTFE, build 4943
84 Toyota Supra towd
2015 Jeep Wrangler towd
Victoria, BC, Canada

Re: How to test 8D AGMs

Reply #10 –
Wyatt, Thanks for the alternative battery test idea.  I don't haul my big battery tester with me.
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN