AGM battery charging voltage anomalies

[frayedsheet]

I have what I believe to be a relatively standard and simple electrical setup on board yet most recent discussion here seems to be at a much higher level about more complex setups.

I have:

> Yanmar 3YM30
> Hitachi aftermarket 80Ah alternator
> 3 x 9 month old 80Ah AGM batteries (2 house, 1 starting)
> 20A shorepower charger

I also have what appears to be a smart charger. This pre dates my purchase of the boat some 3.5 years ago. I have yet to explore what it is and what it can do and have a feeling this could be the reason I am posting today.

I notice that the batteries do not seem to charge very quickly at all when under motor as compared to when connected to shorepower. The voltages I read while under motor are significantly lower then when charging via shorepower. One of the attached images details all voltage readings I took today from a combination of charge states. Could this be a smart charger issue?

Some other pictures attached might be of help if I have missed some key detail in the above explanation...

[atoll]

the charger voltages sound about right for AGM float voltages when fully charged 13.6-13.8v @25-30Celcius

AGM Charging : Technical Support Desk

sounds like your alternator is not putting out any power,or has a lower set point for AGMs

have you tried increasing the RPM on the engine,it may be the alternator is not getting enough rpm to excite the field current.

also you need to discharge the batteries a bit if you want to test charging ,no point in trying to check when they are fully charged

[john61ct]

Or get a big load going while testing.

Old school headlights, an electric appliance producing heat. . .

If you have ammeters, put one on the full battery, get the charge source going, then start turning up the load current.

When the battery starts being required to contribute amps, you've maxed out the charge source's production.

Volts should of course also be logged.

[Wotname]

Going by the data posted so far, it seems to me your alternator is not charging at all.

I'm unclear if your alternator still has it's internal regulator or has been modified to use an external regulator (the apparent smart charger might be an external regulator) but either way it should be delivering more volts than you have observed.

Can you post part / model numbers of the various components in the battery charging / combining / switching circuit?

[Amnesia II]

Six yrs ago when I picked up my Catalina 42 in California the first thing I did, (following Mainsail’s advice) was fit a high output alternator and smart charger in the stead of the Standard 80amp Hitachi, who’s primary job is to replace the power used to start the motor only, it’s power output reduces as the voltage increases. Check out Mainsail’s posts.

[smac999]

looks like your alternator is dead. as neither bank is getting any charge with engine running. either that or your battery isolator is bad. but that is unlikely.

if you continue to motor the boat without reaching shorepower, the motor will die and you will be stranded with no batteries.

you need to measure the voltage at the alternator output, (or isolator input). to confirm

also your 20a shore charger is a smart charger.

you are confusing terms.

that picture you posted is a battery isolator. used to split the alternator to both batteries. and has nothing do with smart charging.

[smac999]

Originally Posted by Amnesia II

Six yrs ago when I picked up my Catalina 42 in California the first thing I did, (following Mainsail’s advice) was fit a high output alternator and smart charger in the stead of the Standard 80amp Hitachi, who’s primary job is to replace the power used to start the motor only, it’s power output reduces as the voltage increases. Check out Mainsail’s posts.

with his tiny battery bank, the 80a alt is more then enough. once it works again.

[Uncle Bob]

Originally Posted by frayedsheet

I have what I believe to be a relatively standard and simple electrical setup on board yet most recent discussion here seems to be at a much higher level about more complex setups.

I have:

> Yanmar 3YM30
> Hitachi aftermarket 80Ah alternator
> 3 x 9 month old 80Ah AGM batteries (2 house, 1 starting)
> 20A shorepower charger

I also have what appears to be a smart charger. This pre dates my purchase of the boat some 3.5 years ago. I have yet to explore what it is and what it can do and have a feeling this could be the reason I am posting today.

I notice that the batteries do not seem to charge very quickly at all when under motor as compared to when connected to shorepower. The voltages I read while under motor are significantly lower then when charging via shorepower. One of the attached images details all voltage readings I took today from a combination of charge states. Could this be a smart charger issue?

Some other pictures attached might be of help if I have missed some key detail in the above explanation...

Hi, there appears to be a number of wires shown in your pics that have been "adjusted" with side cutters or capped, I think if it were me I would find a good auto or marine electrician to at least take a look at what you have and offer advice on how to proceed. I know that getting someone to the boat may be a little expensive at first glance however a successful outcome without the worries of have I done it correctly will be worth it in spades.

[Amnesia II]

Originally Posted by smac999

with his tiny battery bank, the 80a alt is more then enough. once it works again.

In my humble experience I do know that the Hitachi has it’s own internal regulation which limits output....the intention is to only recharge a starter battery and that I believe negates it from use to fully charge a house bank of 240amp/hr.

[rgleason]

I have a new unused Hitachi Alt 80a taken off our new engine. Internally regulated. Depending on where you are it can be made available, however you really should get a better alt with external regulation and alt and batt temp sensors for more effective charging.

[gonesail]

your alternator is not charging but it looks to be in excellent condition. i would suspect the voltage regulator is at fault. but then again you need to discharge the batteries before the test. it could be the regulator thinks the batteries are full. you could also check to see if the regulator is attempting to activate the alternator. still if you installed a new intelligent voltage regulator you could better program it to handle the AGM batteries.

[Pete7]

Originally Posted by rgleason

I have a new unused Hitachi Alt 80a taken off our new engine. Internally regulated. Depending on where you are it can be made available, however you really should get a better alt with external regulation and alt and batt temp sensors for more effective charging.

He could, but it might be more effective to just add an external regulator to the existing alternator like one of these, once the existing alternator is fixed.

https://sterling-power.com/collectio...tor-regulators

I think the point SMAC99 is making is that the existing alternator is more than capable of supplying all the power a pair of 80AH AGM batteries can take. Putting a bigger alternator in won't change that. I have a 60A alternator supplying 2 x 110AH FLA batteries. The maximum we see is about 42A going into the batteries because that is all they will absorb. There might be some gain from raising the voltage with a Sterling Alternator charger but fitting a much larger alternator will be a waste. There is Mainesail article which high lights this.

Pete

[frayedsheet]

Hi all, thanks very much for your super thoughtful responses. To answer some queries:

I was able to read 14.3V on the alternator itself – it’s just not getting anywhere near this downstream of the RCE electronic battery isolator which I now understand is how power is distributed to the two separate banks. I also now understand that my hitachi alternator does have an internal regulator. Regarding field current, the engine was at least 1500 rpm. When I get to about 1400rpm the battery light on the Yanmar panel no longer illuminates. I am assuming this is when the field current is excited.

I do appreciate the batteries should have been discharged some more first, but this is just where they happened to be at when I had the time to do this initial test. If I need to test further ill discharge and also try to add more load.

I did not replace the alternator myself in 2016, rather I had an electrician do it and also had him take a good look over the boat. (The cut wires in one of the pics have been that way long before all was working well and I think they relate to the HF radio install). Lucky for me he is very very helpful and was happy to take my call to discuss this little problem too. He believes the RCE electronic battery isolator needs an additional connection back to the alternator and that it is the likely issue. I plan to chase this down before investigating further. I will report back soon!

[john61ct]

Originally Posted by frayedsheet

Regarding field current, the engine was at least 1500 rpm. When I get to about 1400rpm the battery light on the Yanmar panel no longer illuminates. I am assuming this is when the field current is excited.

I do appreciate the batteries should have been discharged some more first, but this is just where they happened to be at when I had the time to do this initial test. If I need to test further ill discharge and also try to add more load.

Either / or, same (required) effect.

But both are required for a more complete test.
A load you can explicitly vary lets you see - as current demanded increases - the point when power starts to be drawn **from** the bank, as opposed to getting pushed **into** it.

And rpm well over 2200 would be more realistic, depending on your pulley ratio.

[Stu Jackson]

Hitachi/Yanmar Alternators: (by Maine Sail)

Some alternators though, such as those made by Hitachi and found on Yanmar diesels, are dumber than a pound of beetle poop. Actually, to the alternator, they are pretty smart but to your batteries and the speed of charging they are flat out stupid. Why?

Hitachi alts with dumb regulators, and some others, limit voltage but also reduce voltage based on alternator temperature. This is a self protective feature installed in the internal dumb regulator to prevent the alternator from cooking itself. Remember voltage is the pressure that allows more current to flow. So, if we reduce the absorption voltage, then we also reduce the current the alternator is supplying.. The battery simply will not accept the same current at 13.4V that it did at 14.4V and as a result the alternator will run cooler. What do you suppose this does to your batteries over time.......?

The problem is that when cold you will get 14.3V to 14.4V out of the Hitachi but as the alternator heats up the dumb regulator begins to reduce the CV/voltage limit based on the alternators internal temperature. It is not uncommon to find a Hitachi alternator at 13.4V when hot. This is REALLY, REALLY DUMB....

If you have a dumb regulator, and notice the voltage dropping, it is likely a temp compensated dumb regulator. Get rid of it or plan to buy new batteries more often.

If you have a temp compensated alternator or a Hitachi alternator on a Yanmar you really are in dire need of external regulation if deep cycling a larger battery bank.

This is from:

http://forums.sbo.sailboatowners.com...d.php?t=125392

and these, too:

http://www.cruisersforum.com/forums/...on-125843.html


http://www.cruisersforum.com/forums/...or-142083.html