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Old 12-06-2016, 06:58 PM   #1
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AGM as genset start battery

Weird thing with my rarely used 7kva genset and it happens most every time we use it.

660cca start battery is charged, battery condition window has red and green indicating healthy state yet crank as much as you like and genset won't fire up.

If I disconnect it and reconnect to one of the 900 cca 12v start batts for the main diesel it fires up instantly.
Whats with that?

Simplistically it seems a bigger battery is the easy solution seeing how it starts on a bigger battery.

When I replaced the house battery bank 3 of the 6 220ah agm's the boat came with were deemed OK And they sit down there doing nothing.

What would be the ramifications of using one of these redundant batts as a start?
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Old 12-06-2016, 07:22 PM   #2
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this is Kohler generator ?

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Old 12-06-2016, 07:26 PM   #3
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Old 12-06-2016, 07:35 PM   #4
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ok

660CCA for 7Kva generator look plentyI assume your battery have problem (like one element cut inside) borrow a load tester for battery or buy one this is not expensive.

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Old 12-06-2016, 07:55 PM   #5
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I live on board on anchor and am not near a shop to buy a new battery or load tester.

I do have 3 x 220ah agm doing nothing down below which is why I am asking if one of those will suffice.
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Old 12-06-2016, 08:06 PM   #6
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I live on board on anchor and am not near a shop to buy a new battery or load tester.

I do have 3 x 220ah agm doing nothing down below which is why I am asking if one of those will suffice.
Normally yes but the problem with AGM that you need special charger or alternator to not kill them, like you know on floating model after full charge AGM need to be at 13,5V and normal alternator from you generator going to be at more that 14V and you going to kill them slowly
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Old 12-07-2016, 01:47 AM   #7
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Fair enough, so better off leaving it connected to one of the main engine starts for now and if genset needs to be ran up start it while main engine running.

Thanks.
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Old 12-07-2016, 02:44 AM   #8
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check what the battery voltage drops to while cranking (an analog meter works best for this). It could get too low for the genset to fire but will still crank.
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Old 12-07-2016, 07:13 AM   #9
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Normally yes but the problem with AGM that you need special charger or alternator to not kill them, like you know on floating model after full charge AGM need to be at 13,5V and normal alternator from you generator going to be at more that 14V and you going to kill them slowly
Operative word, "slowly". This problem is overstated in my experience. I ran AGM's on my sailboat with a 1980 era "dumb" alternator and got years of life out of them. The pair I ran down flat and then recharged three years ago are still going for the new owner. That said, overall cost will always be a lot more for AGM's. I had them on the sailboat because of very difficult access for maintenance and the risk of severe heeling in a sailboat. Now that we are trawler people, I have lead acid. 4D AGM's are expensive.
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Old 12-07-2016, 07:31 AM   #10
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Operative word, "slowly". This problem is overstated in my experience. I ran AGM's on my sailboat with a 1980 era "dumb" alternator and got years of life out of them. The pair I ran down flat and then recharged three years ago are still going for the new owner. That said, overall cost will always be a lot more for AGM's. I had them on the sailboat because of very difficult access for maintenance and the risk of severe heeling in a sailboat. Now that we are trawler people, I have lead acid. 4D AGM's are expensive.
Having done it both ways, I respectfully disagree!
AGM batteries that are treated to their manufacturers recommended charging regimen last far longer with higher voltage available at a given point of discharge.
The set of 2 4D Lifelines in our sailboat are now 7 years old and still had about 90% of their original capacity left this spring. They delivered unbelievable voltage under load and charged as easily/efficiently as they did when new.

The single 4D Lifeline battery in our Airstream trailer was subjected to the ridiculous charge regimen of the factory installed system for about 18 months before I understood just how poorly that battery was fairing in an annual capacity test. This battery had only about 75% of its original capacity left. It also charges more slowly now and has not got the voltage available that it had when new. This on a battery that was arguably better cared for in terms of state of discharge and how quickly it was brought back to full charge.

Since throwing the Airstream charger in the dump and replacing it with a proper 3 step, temperature charger the battery's condition has stabilized. It will obviously not give us the service that a battery that was treated properly for its entire life...what a shame!

The worst of this is that I knew better. I had my suspicions and called the manufacturer of the Airstream device and bought their story.

Just because your AGM battery is still in place and seeming working in spite of an abusive charge regemin doesn't mean that it has not been damaged.

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Old 12-07-2016, 08:00 AM   #11
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We've been using Optima AGM batteries on our generators for 20 years with good luck. I replaced the last one after 10 years. Could the battery lasted another few years with a smart charger? Maybe?

This is from the Optima web site for the Blue Top we have.



Battery Charger:
  • 13.8 to 15.0 volts, 10 amps maximum, approximately for six to twelve hours.
Cyclic Applications:
  • 14.7 volts, no current limit as long as battery temperature remains below 125F (51.7C). When current falls below one amp, finish with two-amp constant current for one hour for D34M and three-amp constant current for one hour for D27M and D31M.
Rapid Recharge:
  • Maximum voltage 15.6 volts (regulated), no current limit as long as battery temperature remains below 125F (51.7C). Charge until current drops below one amp.
Float Charge:
  • 13.2 to 13.8 volts, one amp maximum current, time indefinite (at lower voltage).
  • Strictly adhere to all limits.
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Old 12-07-2016, 08:54 AM   #12
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Back to Simi's problem -

His genset alternator and or related charging systems may not be able to boost battery voltage to point that safety switches or stop solenoid are energized.

A good genset guy like Ski would be able to source the issue and recommend fix.
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Old 12-07-2016, 10:12 AM   #13
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I was considering replacing my FLA genset batt with AGM. Have had excellent batt life from AGM's used as starters in my diesel truck. I've been under the impression that smarter regulation makes quite a difference for a house bank, and do have that in my 26-footer. Wouldn't my NL genset batt be treated much the same at my truck batts?
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Old 12-07-2016, 10:42 AM   #14
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Measure volts on batt terminals while cranking. Don't know that gennie but could be volts going too low on crank for some sort of relay to latch or fuel solenoid to pull in. Some fuel solenoids are external and you can give it a shove.

AGM can be harmed by some gennies primitive "motorcycle" type DC charging regulator. Measure volts an hour after running and see if it is appropriate for the AGM.

Some folks, including me, disable the charging circuit on the gennie and let the AC powered charger do the job. Batteries much happier with careful charging.
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Old 12-07-2016, 01:23 PM   #15
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I have AGMs that are charged using a Balmer Duo-charger set with their "AGM" setting. I haven't owned the boat that long but the start battery seems to have been working well for a number of years. I replaced the sealed LA genset start battery last spring with an AGM, again using a Duo-Charger so we will see how it performs over the next 5-6 years.
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Old 12-07-2016, 09:45 PM   #16
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Measure volts on batt terminals while cranking. Don't know that gennie but could be volts going too low on crank for some sort of relay to latch or fuel solenoid to pull in. Some fuel solenoids are external and you can give it a shove.

AGM can be harmed by some gennies primitive "motorcycle" type DC charging regulator. Measure volts an hour after running and see if it is appropriate for the AGM.

Some folks, including me, disable the charging circuit on the gennie and let the AC powered charger do the job. Batteries much happier with careful charging.

When posts say check battery voltage between the two terminals on the start battery, while someone is turning the generator over, what you are looking for is to confirm your reading at least 10.5 VDC. Anything lower than that indicates your battery has a bad connection or one or more cells are damaged and replacement is the only answer.
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Old 12-07-2016, 10:02 PM   #17
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What size batt is recommended? Onan recommend a 6D/135ah for my little 6.5kw with 3cyl Kubota, seemed overkill when I replaced it, but I did anyway, using a sealed LA panel,which I gave a dedicated 25w regulated solar panel.
I reckon you have a battery issue, especially as it starts fine off the 220ah.
Does it have to do a preheat, as well as start it? As I remember, you very rarely use the genset, so does the batt get fed at all meantime?
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Old 12-08-2016, 04:46 AM   #18
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Weird thing with my rarely used 7kva genset and it happens most every time we use it.

660cca start battery is charged, battery condition window has red and green indicating healthy state yet crank as much as you like and genset won't fire up.

If I disconnect it and reconnect to one of the 900 cca 12v start batts for the main diesel it fires up instantly.
Whats with that?

Simplistically it seems a bigger battery is the easy solution seeing how it starts on a bigger battery.

When I replaced the house battery bank 3 of the 6 220ah agm's the boat came with were deemed OK And they sit down there doing nothing.

What would be the ramifications of using one of these redundant batts as a start?
Seems like swopping the battery fixes the problem? Kind of obvious then its the power available to the starter that is the problem??
Can you identify a cranking speed difference between the batteries?? By this I mean does it spin faster on the bigger battery?? If yes it is the original battery either at fault or it is not getting charged up enough.
Maybe nothing wrong with the battery, its just not charged up and the bigger battery does the job not because it is bigger but because it is charged......
Indicators only give you a rough guide to charge state.

If it was mine I woud investigate the charging aspect first. If this proves ok then I would stick on the alternative "spare" AGM, do you care if it gets spoiled (in time)?? Sounds like it is just ballast?? anyway??
If I was worried about "spoiling" my old AGM then a new cranking battery is next on the list. Small money for a battery big enough for a gen set.
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Old 12-08-2016, 06:58 AM   #19
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Back to Simi's problem -

His genset alternator and or related charging systems may not be able to boost battery voltage to point that safety switches or stop solenoid are energized.
BINGO! I think you may have solved my gen set mystery. The ONAN MTJE on the boat we bought in September started fine for a few days after we took delivery. Ever since, we have to push the stop solenoid up just after turning on the start switch. Big pain as I have to open up the sound shield and crawl into the engine room.

The generator starts almost instantly and there seems to be plenty of cranking power so I didn't think about the AGM battery. I've checked everything else I could without taking the electronics box apart.

Battery voltage could be slightly low, possibly due to damage from the 70's era charging system. Plenty of amps but some relay or control in the starting / auto shutdown circuit (always troublsome on these units) is looking for a specific voltage threshold and and not switching on the signal to energize the stop solenoid. Once the engines starts running, there is plenty of voltage and the solenoid stays up.

I wish we hadn't just left the boat for a month so I could check this but I'll put a new battery in as soon as we return. Wet Cell for sure.
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Old 12-09-2016, 02:29 AM   #20
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Seems it was a combo of a few things.
There is a very slight weep of diesel, I suspect from hard, clear with weave, fuel line going into the engine.
Hence, when I crank and crank and crank I get no start as pressure has dropped.
Later, when I try again, battery may be lacking, but fresh battery and now, a diesel system up to pressure gets a result.

I put the smaller start battery on a seperate charger for a while and now it starts and as was suggested by others, there is no other charge on the battery apart from what it gets when running.

Fix the fuel issue and periodically connect the charger and all should be good.
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