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Old 23-06-2011, 08:31   #1
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Voltage drop under load, amps read 99% ??

I have three Power-Tech Gel batteries each 200amp, 12V batteries of which one tested 90% under a lead test done months ago, the others tested 100%. The yard at that time told me to continue to use it and monitor it.

Now I am about to take the suspected one out and see what happens to the voltage.

After running the Generator or engine the battery meter reads 12.45 (loading under 14.2), it remains there until I switch on the fridge or invert, or anything else that takes a bit of load. The voltage meter drops quickly, in a matter of 4 hours, to 11.3 or lower.

Any suggestions what to do other than taking this one out and check if this is the culprit. If so, should I replace all three batteries?
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Old 23-06-2011, 08:48   #2
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Re: Voltage drop under load, amps read 99% ??

The easy thing is just to disconnect that on questionable battery and see what happens If it is bad it will affect the other two
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Old 23-06-2011, 09:02   #3
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Re: Voltage drop under load, amps read 99% ??

I am no fan of gel cell house batteries and I don't know of any 200 AH, 12V batteries other than maybe 4Ds or 8Ds. And FWIW the "load test" that your yard performed was probably a starting current test, which says nothing about how the batteries hold and release their charge in house battery use.

As Motion said, remove the battery and see what happens. It may have one or more bad cells which are taking down the others.

For a real load test, hook up some kind of DC load, maybe a bank of lights or something. Their amp draw should be 1/20 of the real amphour rating. Then measure how long it takes to go down to about 10 V which is totally discharged. The actual capacity is current times actual hours to discharge.

Then buy golf cart batteries to replace your gel cells.
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Old 23-06-2011, 09:04   #4
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Re: Voltage drop under load, amps read 99% ??

I agree about removing the suspect battery and see what happens, but if your taking a trip it would be better to replace it. Remember it could be an appliance drawing the system down. To check the appliances run an amp check on each.

Good Luck,
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Old 23-06-2011, 09:11   #5
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Re: Voltage drop under load, amps read 99% ??

Electrically isolate the battery from the others and test it. No need to pull it until you have confirmed its condition.
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Old 26-06-2011, 07:11   #6
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Re: Voltage drop under load, amps read 99% ??

Thanks for a the help. I said they were Gel but the label reads Lead batteries, 198ah, 8A4DM, 14.6V at 68F. My regulator maxes at 14.1 so this might be wrongly set. We tested all of three of them and they are all loosing Voltage. The batteries are not accepting enough amps while they are probably not full. I therefore suspect they are done. Bummer, because that is a nice price tag. I will now have to shop for three new ones. I would like to buy the same dimensions as I have (POWERTEC 8A4DM) so does anybody have a strong suggestion as to which I should buy. Many thanks.
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Old 26-06-2011, 07:16   #7
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Re: Voltage drop under load, amps read 99% ??

Try discharging down to about 10.5 - 10.8 volts and then charging them fully. You may have to get your regulator up to 14.6 volts to do this (maybe even higher if you can get it set higher). It may help extend the life of the batteries.

However if they are badly sulfated you are probably out of luck.
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Old 26-06-2011, 07:52   #8
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Re: Voltage drop under load, amps read 99% ??

Be careful of the voltage if these are Gel batteries and follow the manufacturers specs.
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Old 26-06-2011, 08:04   #9
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Re: Voltage drop under load, amps read 99% ??

I am on a soapbox about this: I don't believe that any flooded cell batteries other than golf cart batteries are true deep cycle. Most are starting batteries that have a sticker slapped on that says "deep cycle" or worse a sign on the rack that says deep cycle but nothing on the battery (Sam's Club). There are a few exceptions- Rolls being one, but none that you are going to find at WM, NAPA stores, Costco or Sams.

If you don't see an amphour rating on the battery and only a starting spec, like MCA, you can be sure that it is not deep cycle.

Buy 6V golf cart batteries. You know for sure that they are designed from the ground up as deep cycle and if anyone tries to pull a fast one, the returns from the golf cart users will quickly put them out of business. Wire them in series/parallel to get the amphours you need. Two golf carts wired in series provide 220 amphours at 12V.

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Old 26-06-2011, 08:23   #10
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Re: Voltage drop under load, amps read 99% ??

Doing a search on the web site doesn't produce a product match, using the 8A4DM product number. Maybe an email directly to the manufacturer in China will produce more information on the battery for you. Shenzhen Worldstar Powertech Co., Ltd. - batteries, chargers, controllers

Perhaps there is another number on the battery, something starting with JP or LJP?
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Old 26-06-2011, 08:28   #11
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Old 26-06-2011, 14:50   #12
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Re: Voltage drop under load, amps read 99% ??

VVD,
Since none of us are on-board with you, it's difficult to give precise answers.....(the more/better info you give, the more/better answers you get)

But using just what you wrote, here are some things that may help you....

1) I believe the "Power Tech 8A4DM's" are 4D-sized AGM batteries (Absorbed-Glass-Mat, lead-acid batteries), private labled for "Power Tech", by East Penn / Deka....

http://www.dekabatteries.com/assets/base/0151.pdf

http://www.dekabatteries.com/assets/base/1081.pdf

http://www.dekabatteries.com/assets/base/0139.pdf

AGM Deep Cycle Battery

Solar Energy, Premium Quality Compact Fluorescent Bulbs, Energy-Saving Devices - Deka 8A4DM, 12V/198AH AGM Sealed Battery

Marine Batteries and Boat Batteries - Gel Batteries, Gel Cell Batteries and Dominator - AGM and AGM Batteries



2) I agree with the others here, it sounds like you batteries are toast....
If they were flooded lead-acid, as opposed to the East Penn AGM's, you'd have a prayer of salvaging them, but not much of one....

Make your battery choices on what will work best for YOUR application (how YOU are using your batteries, as well as how you are chargingb them, etc.....and in general where, when, how, etc. you're sailing/cruising/voyaging....)
And, while the size/shape of the batteries does matter (heck, they've got to fit in your boat!), please make sure that this is placed much further down the list of criteria, than the above....



3) While I'm not on a soapbox about it, djmarchand does make a good point about many sailors/cruisers being mislead by the labels on batteries (as well as many other things marine-related)......

True deep-cycle batteries, whether flooded, gel, or agm, have different plate thicknesses, materials and construction that "normal" / "multi-purpose" batteries.....

Perhaps reading over a recent thread here will be of help....
Rolls versus AGM Batteries

Here's just a small part of that discussion.....
Quote:
Further info on deep-cycle battery positive plate thickness...
(from some battery engineering websites...)

[ Plate thickness (of the Positive plate) matters because of a factor called "positive grid corrosion". This ranks among the top 3 reasons for battery failure. The positive (+) plate is what gets eaten away gradually over time, so eventually there is nothing left - it all falls to the bottom as sediment. Thicker plates are directly related to longer life, so other things being equal, the battery with the thickest plates will last the longest. The negative plate in batteries expands somewhat during discharge, which is why nearly all batteries have separators, such as glass mat or paper, that can be compressed.
Automotive batteries typically have plates about .040" (4/100") thick, while forklift batteries may have plates more than 1/4" (.265" for example in larger Rolls-Surrette) thick - almost 7 times as thick as auto batteries.
The typical golf cart will have plates that are around .07 to .11" thick.
The Concorde AGM's are .115", The Rolls-Surrette L-16 type (CH460) is .150", and the US Battery and Trojan L-16 types are .090". The Crown L-16HC size has .22" thick plates. While plate thickness is not the only factor in how many deep cycles a battery can take before it dies, it is the most important one.

Most industrial (fork lift) deep-cycle batteries use Lead-Antimony plates rather than the Lead-Calcium used in AGM or gelled deep-cycle batteries and in automotive starting batteries. The Antimony increases plate life and strength, but increases gassing and water loss. This is why most industrial batteries have to be checked often for water level if you do not have Hydrocaps.]


4) My "advice" (such as it is, with the limited data I have to go on), is:
a) determine what caused the battery problems BEFORE you buy new batteries....
b) decide on how your battery usage and charging can be optimized...(add more solar, etc...)
c) choose your new batteries based on YOUR application, as descrided above....you may find flooded batteries better suit your needs, or you may find agm's will work for you (as long as you know how to treat them...)
d) repair/change your battery charging system to match your usage patterns AND to match your new battery choice....



5) As for what batteries to recommend.....that depends on YOUR application, so MY recommendations might not mean much .....(my favs are Rolls/Surettes 2-volt cells, or L-16 sized 6-volts, or their Big Red 8D's....or Trojan L-16sized 6-volts, or T-145's....etc.)



I do hope this helps....


John
s/v Annie Laurie
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Old 26-06-2011, 15:26   #13
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Re: Voltage drop under load, amps read 99% ??

As Ka4wja indicates - your batteries are AGM - size 4D batteries. See: AGM Deep Cycle Battery

- - So any "4D" form size battery will fit into where you have these batteries.

- - Whether you want to continue with AGM style batteries or replace them with standard - "liquid acid" batteries, is your decision. You can buy "Truck/Heavy Duty" 4D batteries for a fraction of the cost of an AGM battery.
- - AGM batteries - if you want any reasonable life out of them - require careful attention to monitoring and charging and an assortment of "smart" regulators and other battery charging and monitoring equipment. Unless you are planning on cruising areas for a long time were access to replacement batteries is very difficult, you can get better "bang for the buck" out of the simple deep cycle (heavy duty) liquid lead acid batteries.
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Old 26-06-2011, 16:35   #14
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Re: Voltage drop under load, amps read 99% ??

It appears you are looking at the frig & there could be a problem there. The range of cut in & out can be adjusted on the compressor to suit more the range of deep cycle batteries by selecting a different range by resistor changes. Most are setup expecting an automotive application. The house batteries without charge could be expected to cycle to about 11.2v as the lower point.

Regards Bill
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Old 27-06-2011, 23:35   #15
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Re: Voltage drop under load, amps read 99% ??

Hope not to hijack this thread but I'm reading with interest the discussion on voltage drop and I'm wondering are there tables for acceptable levels of voltage drop?

I have a similar though a less severe problem with voltage drop where my battery monitor may read 80% but even under moderate loads the voltage can drop significantly setting off alarms on my boat.

Without doing a capacity test is there anyway to diagnose by reading voltage drops alone?
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