Re: [Amel Yacht Owners] Re: Does my ONAN need a new 12V charger?

Alex Ramseyer <alexramseyer@...>

Hi Bill,
thanks for your information.
I looked at IWW in St. Georges and catalogue and couldn't see the 1000 CCA starter battery there. Not sure that I will get it here in Grenada. The other reason I bought this battery was that before the boat had the same one built in. The former owner replaced it also in the Caribbean...
The next problem with batteries here in Grenada and other parts of the Caribbean is that the height of the battery compartment wouldn' allwo to install the (higher) american dimensions. The former owner changed the starter battery space, so I can at least have a higher battery there. But when I was looking for housing batteries in the U.S. earlier this year I found nothing. So I bought new housing batteries in St. Martin (Duracel AGM 12V 85A). They worked fine so far.
Yesterday I let the Volvo run for an hour and this morning I read 13,2V at the starter battery. Likelyhood increases that I have a problem with the 12V alternator on the ONAN.
A friend of mine will pass by with a battery load tester device tomorrow. Will know more by then..
Best regards, Alex

On Monday, November 20, 2017, 5:49:52 PM GMT-4, 'Bill & Judy Rouse' yahoogroups@... [amelyachtowners] wrote:



 is undersized. Why did you buy a Grp27? Your 54 came with a Grp31
 The Grp27 battery ​you bought is 840CCA. Deka makes a Grp 31 1000CCA battery.

Did you replace your other batteries?
Do you have the 4 cylinder Onan, or 3?

If you are reading battery voltage in the cockpit, you must be reading it on a Volvo output panel, which means that you have the entire suite of Volvo electronics, 2 computers and various sensors powered-up as well as the 12VDC exhaust fans running. I am guessing 6-10 amps at 12VDC draw on your starting battery. This is NOT a way to test resting voltage, nor is it the thing to do before starting the generator.

In my opinion, you undersized the starting battery. This is especially significant when we are talking about the generator. The length of 12VDC wire from the starting battery to the starter is almost 7 meters from battery to starting motor. If everything is perfect, the wire that Amel uses for this is adequate, but, with an undersized battery, I suspect NOT.

Continue testing the "resting voltage," but at the battery. Continue to look for resting voltage of less than 12.8 volts, then see if you can determine why. Turning ON your Volvo systems and energizing the fans will drop the voltage and drain the battery. You did not say whether you "prime" the Onan when starting. This is pressing and holding down before starting. This should not be necessary for you unless the Onan has not started in a while. If you do this before starting, you will drain the battery.

Hopefully, you will learn why the resting voltage got as low as 12.4 volts (basically discharged), and hopefully your battery is OK. However, I think you need to plan on replacing that Group 27 starting battery with the correct size. BTW, if after running the Onan only for 1-2 hours the resting voltage on the starting battery after turning OFF the Onan should be 12.8-12.9 VDC at the battery...if it is not, the little alternator on the Onan needs attention.

I have forgotten the output of that little alternator, but see to remember something like only 10 amps.

Good luck.


CW Bill Rouse
Admiral, Texas Navy
Commander Emeritus
Amel School
720 Winnie St
Galveston Island, TX 77550
+1(832) 380-4970

On Mon, Nov 20, 2017 at 3:01 PM, Alex Ramseyer alexramseyer@... [amelyachtowners] <amelyachtowners@...> wrote:

So these are the answers to Bill's questions:
1. I  read it from the display in the cockpit, which in the past showed the same numbers when I did it at the battery.
2. I went to IWW in St. Georges and the employee tested a battery in the shelf (they store them loaded), but I was stupid enought not to interfere when he took another battery from that same shelf when we went to the cashier.

4. This morning I saw 12,8V before starting and the genset started fine. But yesterday I had the main engine running for ca. 10 min after I discovered the starting problem.
5. I own no load tester, but I will get one from a friend and uncircle the problem....

Thanks for your advice,
AMEL54 #15

On Sunday, November 19, 2017, 1:23:39 PM GMT-4, greatketch@... [amelyachtowners] <amelyachtowners@yahoogroups. com> wrote:


It certainly looks like the alternator on the Onan is not charging the battery.

Lots of possible reasons... 

As with anything electrical, start with ALL the connections.  They are not always the most likely cause, but they are cheap and easy to fix, so it makes sense to test them first.  Since the problem started after a service on the generator, it is quite possible you bumped a wire and broke a connection somewhere.  Many times I have been working in the engine room and managed to bump the main power switch on the genset...  "Why won't this darn things start???"

Be sure to NEVER disconnect the alternator from the battery when it is running.  That will kill the diodes in very short order.

If it turns out the alternator is the source of the problem, it is almost certainly able to be rebuilt at a fr action of the cost of a new one.  That service is available all over.

Bill Kinney
sm160, Harmonie
Fort Lauderdale, FL

---In amelyachtowners@yahoogroups. com, wrote :

When the generator runs, I see 13,6V on the starter battery. When I turn the ignition key of the engine in the cockpit the current goes down to 13,2V (maybe because of the ventilator in engine room / generator is still running). When I start the main engine the current goes to 14,4V.

After servicing the ONAN and replacing the starter battery a short while ago, everything worked find for a while, but this morning the ONAN only started AFTER I started the main engine. The starter battery showed 12, 4 V initially. It showed 13,2 after I run the genset for 2h and then 12,8 anoher 2h later. All observations come from the little display in the cockpit.

So what is the conclusion of you fellow Amelians from this observations?

Thanks, Alex
SY NO STRESS in Grenada
AMEL54 #15


CW Bill Rouse
Admiral, Texas Navy
Commander Emeritus

Amel School
720 Winnie St
Galveston Island, TX 77550

+1(832) 380-4970

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