outboards charging agm batteries

aweigh again

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A couple of years ago I switched from wet cell lead acid batteries to agm type because I have my batteries mounted under the deck. Even though there are two vents leading to outside air, I thought that there would be less gassing of hazardous fumes, so I was all over the idea. During the 1st year of use, The Yamaha voltage regulator started putting out 17 volts, so I replaced it,but even with the new regulator ,it was still putting out 15.2 volts. I ran it like that all last season, but both batteries tested bad when I charged them a few weeks ago. I just put new new agms in and have not run with them yet, but I feel like I am probably going to cook another set of batteries within 2 years. I dont have AC at my slip, so the outboard alternator is what I rely on during the season for charging. I might go for a battery monitor and a solar panel with a suitable charge profile, but still think there is trouble with the high charge voltage. any one else using agms with their outboards?
 

Genius

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that's high for wet lead acid also which for all purposes really is the same as AGM. Need to get that voltage regulator fixed. IDK, external voltage regulator? I don't know outboards.
 

tsharac

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I fried an outboard voltage regulator when I left a cheap 12v 5 watt solar trickle charger on my battery for a few months. After a few months on the solar trickle charger, my outboard voltage was 18 volts when running, so I figured the voltage rectifier went bad. The solar panel put out 5 watts, but was at 22 volts in direct sun. I won't use another trickle charger like that again. Since replacing the rectifier in 2015? the problem hasn't returned. I use a lead acid battery.
 

tsharac

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You're charging at 15.2 volts, while it should charge at 15.0 volts - is that within the margin of error?


F115_voltage.png
 

tsharac

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If you don't have AC power at your slip, your batteries may be going flat between boat trips and your outboard is overcharging to compensate.

What's the resting charge of the battery with the engine off? If less than 12.8 volts, the outboard might be overcharging to compensate, but if the battery is 12.8 - 13.1 volts at rest, it's likely overcharging or the outboard is sensing lower voltage than exists at the battery.

It's possible the problem of the failing voltage rectifier is unrelated to the failure of the batteries and that the batteries are failing due to lack of charge while at the slip.
 

c1steve

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Most AGM batteries are sensitive to higher voltages. At 60 degrees F., max voltage would be 14.5 volts, at 80 deg., max voltage should be 14.3. Float voltages should be 1.0 volts lower.

If you cannot change the regulated voltage in some way, best to use regular batteries that have sealed tops. AGMs use cadmium for the alloy, not antimony. This makes them physically much stronger, and they can handle super high amperages, but need lower voltages.

Charger settings for AGM batteries
 

captjohn

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I worked on someone's boat a few years ago, outboard engine, AMG batteries, problems with them. I knew it was the charging voltage, but the battery manufacturer insisted the batteries were fine. Charging voltage was too high as far as I was concerned. I never finished the project, but I was going to try installing a diode in line with the output from the alternator, to drop the voltage. But never got a chance to see if it worked.
 

aweigh again

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I worked on someone's boat a few years ago, outboard engine, AMG batteries, problems with them. I knew it was the charging voltage, but the battery manufacturer insisted the batteries were fine. Charging voltage was too high as far as I was concerned. I never finished the project, but I was going to try installing a diode in line with the output from the alternator, to drop the voltage. But never got a chance to see if it worked.
dropping .6 volt across a diode would work.
 

Brooksie

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AGM's require a different charging regimen than your Yahama can provide, it's regimen is for lead/acid/flooded cells and not a very sophisticated one at that. I think it would be easier and cheaper to find a way to vent your battery area if gassing really worries you,
 

aweigh again

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AGM's require a different charging regimen than your Yahama can provide, it's regimen is for lead/acid/flooded cells and not a very sophisticated one at that. I think it would be easier and cheaper to find a way to vent your battery area if gassing really worries you,
I brought the new agms back today and exchanged them for wet cell lead acid ones. The straw that broke the camel's back was this morning when i went to plug the stator harness back into the voltage regulator,and the plastic electrical connector more or less crumbled in my hand from excessive heat that its seen. 450 bucks for an oem stator coil , because yamaha won't sell you a 20 dollar connector.
 

tsharac

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Thank you for sharing your expensive lesson with the rest of us. I was surprised to see that Yamaha voltage chart showing 15.0 voltage is normal charging.
 

south shore

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I ran into a pin hooker about 2 years ago had a fairly new Suzuki outboard he puts on a lot of hours and had changed in the 4th season to AGMs about mid season he was having all sorts of issues that was keeping him at the dock. miscellaneous parts were installed which didn't change things. he was ready to go for a new engine and one day the Suzuki rep was there and he gave him an ear full. The rep went down to his boat and looked around and told him to get rid of the AGMs that they screw up charging system I believe he had to go for a new rectifier and put in 2 new interstate marine wet cells and problem solved.
 

Brooksie

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I brought the new agms back today and exchanged them for wet cell lead acid ones. The straw that broke the camel's back was this morning when i went to plug the stator harness back into the voltage regulator,and the plastic electrical connector more or less crumbled in my hand from excessive heat that its seen. 450 bucks for an oem stator coil , because yamaha won't sell you a 20 dollar connector.
They won't sell you the injector connectors either and want you to buy the whole harness. However they are easily available on ebay $6. each including freight. Bet your stator connector is too
 

aweigh again

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I ran into a pin hooker about 2 years ago had a fairly new Suzuki outboard he puts on a lot of hours and had changed in the 4th season to AGMs about mid season he was having all sorts of issues that was keeping him at the dock. miscellaneous parts were installed which didn't change things. he was ready to go for a new engine and one day the Suzuki rep was there and he gave him an ear full. The rep went down to his boat and looked around and told him to get rid of the AGMs that they screw up charging system I believe he had to go for a new rectifier and put in 2 new interstate marine wet cells and problem solved.
very interesting, I talked to Yamaha customer service today, and was told that the charging system on the 2021 models has been redesigned to be more AGM friendly. He also said that a AGM is ok to use on older engines ,but may require more charging maintenance.
 

novivin

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I have a 2015 F115 Yamaha OB. Two AGM Group 31 batteries and a Blue Seas ACR and switch system. It has been fine for three years this way. Batteries fine. Trailered boat with weekly use. I never charge during season, voltage meter always reads outboard charging while running at 14.2 volts. Maintains batteries at 12.4 volts between uses.
I must have a different version of Yamaha’s charging system? Or:
I never use a solar panel to charge. I have been warned about those by others. Most don’t have voltage regulation I think. Guy that really researched it told me you can fry batteries easy with them.
 

aweigh again

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Thats interesting, I too have installed the blue seas ACR and switch, the only difference is i am using 2 group 24 baterries. I think i am getting in trouble when running my livewell pump for hours at a time. I typically leave my engine run at idle so i dont run my batteries way down . i may not be making enough electricity to compensate and really heating up the rectifier, plus you have a much greater storage capacity with the group 31s than i do with 24s.
 

novivin

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I am thinking it might be exactly what you just mentioned, battery size. The amperage from the engine might be enough to pump those volts up too high on smaller batteries. I am no physicist or engineer, but my observations of marine DC systems are that getting your volt meter out and actually checking the performance of anything what you install in the system is very important. The reason I have the 31’s is I use an electradyne hauler heavily seasonally to haul dredges for scallops. That is a idle speed - 1400 rpm game mostly so charging is minimal but I always see 14.2 volts while fishing that way. Coincidentally, I was charging the batteries to continue my season prep yesterday and I noticed the 10 amp setting on my cheap 17 year old black and decker battery charger was pumping the batteries with 15.2 volts!!! So, I switched to 2 amp setting and it came down. I sometimes have had to bump to 10 amp for a short time to get the ACR to close (reach 13.8 volts plus on start battery) and allow current to flow to my house battery, charging it simultaneously. I use 2 amp charge when using this charger the few to four times each year I use it to maintain the banks.
 
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