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 > Load test a bank of 6 AGM house batteries.

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Teeshot1939

Massachusetts

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Posted: 05/21/20 02:23pm Link  |  Quote  |  Print  |  Notify Moderator

My 10k genset won't crank fast enough to start unless I am running the main engine at the same time. I have 6 AGM house batties that operate the 120v generator starter. The battery boost button adds power from the house TO the chassis batteries and NOT the other way around so that doesn't help me. I need to load test the 6 AGM batteries. Do they have to be disconnected and tested individually? Never done a load test before. Please advise...thanks.

rgatijnet1

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Posted: 05/21/20 02:54pm Link  |  Quote  |  Print  |  Notify Moderator

Your boost switch CONNECTS all batteries together so I think it would help to crank your generator. I have always believed the only way to test a group of batteries is to disconnect them from each other. If tied together for the load test, you will usually find out the condition of the worst battery. By taking them individually you can find out if only one is bad. If you have more than one battery that tests weak, it is usually advised to replace all of the batteries.

Son of Norway

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Posted: 05/21/20 03:51pm Link  |  Quote  |  Print  |  Notify Moderator

If your genset won't crank w/ 6 AGM batteries you may have more than one problem. test the charge as they sit. To load test batteries, I have a set-up with an inverter and a small electric heater. I test the batteries individually. The inverter and heater draw about 13 amps from the battery. I let them run until the battery is down to 50% or 12.06 volts. Then I add up the amp hours and check the result against 50% of the batteries rated capacity. I replace a battery if it falls under 80%. Not a throughly scientific test, but it gives me a good idea of the amp hours a battery will give me during actual camping conditions.


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time2roll

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Posted: 05/21/20 04:14pm Link  |  Quote  |  Print  |  Notify Moderator

First just check the voltage is 12.6+ Check right on the battery terminals to verify this is not a wiring issue.

Yes? Check how much the voltage drops on the battery terminals when cranking the generator.

No? Charge the batteries. Minimum 14.4 volts on the batteries for 4 hours.


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wa8yxm

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Posted: 05/21/20 04:16pm Link  |  Quote  |  Print  |  Notify Moderator

Ok A series of questions. and the results
Your load tester is (I hope) a good 12 volt unit with adjustable load

If the AGM's are six volts paired. you test each pair as though it was a single 220 amp hour 12 volt. This means 660 amps most load testers max out around 400-500 so it's not the best test

If they are 12 volt.. Again you test each battery by itself.

WHY: the load tester can't pull enough current to test 'em all at once.

(Just got done doing that with mine a couple months ago by the way I can hit 450 amps but consider if it's still Green. it's Green.

* This post was edited 05/22/20 04:34pm by wa8yxm *


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Gjac

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Posted: 05/22/20 07:28am Link  |  Quote  |  Print  |  Notify Moderator

Auto parts stores will load test your batteries for free. How old are you batteries? After you fully charge your batteries what is the resting voltage reading? If less than 7 years or so I would suspect bad connections at the battery posts. Clean all the terminals first and see if that works. 6 AGM batteries even with reduced capacity should start turnover a genset.

dougrainer

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Posted: 05/22/20 08:37am Link  |  Quote  |  Print  |  Notify Moderator

AGM batteries CANNOT be load tested with a standard Load Tester. You must have a Load Tester that is designed for AGM batteries. You need to state how OLD the AGM's are. As another poster stated, when you engage the battery boost, it uses the COACH batteries to close the jump solenoid. When the engine is running, it uses a Ignition Chassis signal to jump the Chassis and Coach together at that Jump Solenoid. AGM batteries are great if taken care of. AND when they get old and worn out they will fail with no real warning. From your description of you problem, your AGM's are bad/worn out. You ALWAYS replace ALL batteries in a Battery bank. NEVER just replace any that test bad and leave the ones that test good/marginal, especially AGM batteries. If you have 6, I would bet they are 6 volt and not 12 volt. But, some Large Motorhomes have 12 volt AGM's. Especially since you state the larger 10k Genset. Doug

navigator2346

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Posted: 05/22/20 09:30am Link  |  Quote  |  Print  |  Notify Moderator

Double post

* This post was edited 05/22/20 10:12pm by navigator2346 *

navigator2346

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Posted: 05/22/20 09:33am Link  |  Quote  |  Print  |  Notify Moderator

"AGM batteries CANNOT be load tested with a standard Load Tester. You must have a Load Tester that is designed for AGM batteries."

What is the difference between a "standard" load tester and a "AGM" load tester. This is something ew to me. Seems a load is a load that doesn't know the difference between a AGM and wet cell

dougrainer

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Posted: 05/22/20 04:18pm Link  |  Quote  |  Print  |  Notify Moderator

navigator2346 wrote:

"AGM batteries CANNOT be load tested with a standard Load Tester. You must have a Load Tester that is designed for AGM batteries."

What is the difference between a "standard" load tester and a "AGM" load tester. This is something ew to me. Seems a load is a load that doesn't know the difference between a AGM and wet cell


I should have explained further. Most people think of a Load tester as a PILE that when the Tester is started, DRAWS a LOT of amps(Heats up the coil bank and glows orange). Those went out of style 20 years ago. Load Testers now are totally electronic. They
"electrically" TEST the Battery plates. So, AGM's require a specialized Load Tester. This is per Interstate Battery Corporation. Years ago we never purchased one because the Interstate model was around $1500 and Interstate would test them for us on their regular run to the Dealership. They have dropped a lot in price. AGM's are really easy to test without a Load tester. You slow charge them for a few days and then take voltage readings. A BAD or marginal AGM will not get over 12.5 volts. An older style Load tester WILL cause a tremendous drop in voltage on a bad AGM, but will not give an accurate test for a "good" AGM. It may signal BAD when the AGM is good. There are also "different" types of AGM's, that require specific testers to use. Those testers will usually test all various types of AGM's and Lead Acid. Doug

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