Alternator Overcharging Batteries?

[Stillwater1]

Last week I installed new house and start batteries on my (new to me) 1979 Watkins 27. The wiring is still in need of some serious sorting out, as it is a tangle and nothing is labeled, but I was moving from a marina slip to a mooring and needed to also install some solar, which I also did, 2 days ago.

Yesterday was the day to move her. I had checked my electrical systems after finishing the installs and so I knew everything was working as it was supposed to, including that the alternator was in fact charging the starter battery. Who knows why but at the end of a long day I did not check to see if it was charging the house batteries as well.

We ended up needing to motor for about 2 hours of the 5 hour trip, and it occurred to me to check charging status again. I had installed the Balmar SmartGuage which provides SOC and Voltage reading on the house bank, and voltage on the starter battery. The MPPT charge controller connects the solar panel to only the house bank, and it also gives me SOC and voltage for the house bank.

The house bank is at 100% SOC and is receiving a float charge of 13.2 volts when we leave the dock and stays there for 3 hours under sail. The start battery is at 12.55 volts. Then we start the diesel and the Balmar and the charge controller both show the house bank and the start battery at 14.0 volts, I assume this is indicating they both are being charged by the alternator, but then it occurs to me:

Am I overcharging my house bank (2 DuraCell 215Ah 6volt GC2's) which will shorten their lifespan?

Advice please.

Bob

[rom]

Originally Posted by Stillwater1

The MPPT charge controller connects the solar panel to only the house bank, and it also gives me SOC and voltage for the house bank.

Sorry I am not qualified to answer your question, I am just curious about that MPPT that gives you a SOC ... The only time it would theoretically be able to do that is when reaching absorption and that would not even be accurate. Which brand is it ?

[Stillwater1]

Renogy is the brand and the model is Rover 20 amp

https://smile.amazon.com/dp/B01MRWTA...ing=UTF8&psc=1

[rom]

Originally Posted by Stillwater1

Renogy is the brand and the model is Rover 20 amp

https://smile.amazon.com/dp/B01MRWTA...ing=UTF8&psc=1

OK got it, page 14 of the manual:"NOTE:The Battery Capacity (SOC%) is an estimation based on the charging voltage." I can only think of scenarios where this would lead to plain wrong results, I would not trust that.

Anyway, your question reminds of another thread where someone recently said that his batteries could handle 14.2V float, as per manufacturer recommendations. You might first check what your battery manufacturer says.

[kenbo]

Those Duracell GC2's are East Penn batteries and their absorption voltage is 14.4 to 14.7. If your charging system is set to 14.0 they will be chronically undercharged. Your going to have to get under the hood of your charging system to make sure they all dance together.

[Colin A]

I guess the key question is how is the alternator setup for regulation. Most stock alternators just put out a set voltage then cut back when the alternator heats up.

Maine sail has a good article on it
Automotive Alternators vs. Deep Cycle Batteries Photo Gallery by Compass Marine How To at pbase.com

[hellosailor]

Alternators don't care about voltage. Regulators do that. And whether they are integral or external, the regulator has a battery voltage sense lead which it uses to read the battery voltage. (It can use the charge output lead if the electronics are sophisticated enough, but that's rarely done.)

Note that says "battery voltage sense" singular. One battery. Once you have two batteries or banks, and the ability to switch or charge them separately, someone has to either hoodwink the regulator and give it some mythical kludge, or switch the sense lead to each battery bank as they are switched. And, there's no way to accommodate two different brands or types of batteries, or integrate other charging sources, and still have it all done accurately. So...If you really want to "do it right"...there's no simple answer.

You'd have to detail all the equipment and then try to work out a solution that integrates it all, or at least, minimizes the insults to the battery.

[john61ct]

If you **need** your Alt to contribute a lot of charging power **and** your House bank is expensive and fussy, either

spend heaps converting to something like an MC-614 external regulator, maybe go for large-frame alt that can sustain rated output, or

use a quality batt2batt DC-DC charger like Sterling or ProMariner

[Stu Jackson]

Originally Posted by Colin A

1. I guess the key question is how is the alternator setup for regulation.

2. Most stock alternators just put out a set voltage then cut back when the alternator heats up.

3. Maine sail has a good article on it
Automotive Alternators vs. Deep Cycle Batteries Photo Gallery by Compass Marine How To at pbase.com

1. Yes, good question.

2. Colin, as far as I know, ONLY Hitachi alternators are built that way with internal regulation. These come with Yanmar engines. Universals used Motorolas, which did not have built-in temp sensing on their internal regulators. "Most stock alternators" do NOT do that. Just to clarify for newbies.

3. Yes, he has a wealth of info on his website, including his long discussion about Hitachi alternators.

[kenbo]

Originally Posted by Stu Jackson

1. Yes, good question.

2. Colin, as far as I know, ONLY Hitachi alternators are built that way with internal regulation. These come with Yanmar engines. Universals used Motorolas, which did not have built-in temp sensing on their internal regulators. "Most stock alternators" do NOT do that. Just to clarify for newbies.

3. Yes, he has a wealth of info on his website, including his long discussion about Hitachi alternators.

Sorry, statement #2 is incorrect. Most internally regulated Delco, Paris Rhone and Valeo alternators as well as Hitachi have temperature compensation. I believe the point that Maine Sail was making in regards to Hitachi alternators is that their temperature compensation factor was higher than most and at high temps could make the Vset too low to adequately charge the battery.

[john61ct]

I read "built that way" as referring to the full "just put out a set voltage then cut back when the alternator heats up" in #2, rather than temp compensation / protection in general

[Colin A]

Originally Posted by kenbo

Sorry, statement #2 is incorrect. Most internally regulated Delco, Paris Rhone and Valeo alternators as well as Hitachi have temperature compensation. I believe the point that Maine Sail was making in regards to Hitachi alternators is that their temperature compensation factor was higher than most and at high temps could make the Vset too low to adequately charge the battery.

I was wondering about that I'm no expert but I knew I had run into other alternators that react the same way (or similar cutting power on hot days or long runs) as the Yanmar ones. You also run into the ones that simply regulate at a set voltage with no real failsafe.

[Colin A]

Originally Posted by hellosailor

Alternators don't care about voltage. Regulators do that. And whether they are integral or external, the regulator has a battery voltage sense lead which it uses to read the battery voltage. (It can use the charge output lead if the electronics are sophisticated enough, but that's rarely done.)

Note that says "battery voltage sense" singular. One battery. Once you have two batteries or banks, and the ability to switch or charge them separately, someone has to either hoodwink the regulator and give it some mythical kludge, or switch the sense lead to each battery bank as they are switched. And, there's no way to accommodate two different brands or types of batteries, or integrate other charging sources, and still have it all done accurately. So...If you really want to "do it right"...there's no simple answer.

You'd have to detail all the equipment and then try to work out a solution that integrates it all, or at least, minimizes the insults to the battery.

You are correct on the voltage regulator but most engines now a days seem to be internally regulated.

[Stu Jackson]

Originally Posted by kenbo

Sorry, statement #2 is incorrect. Most internally regulated Delco, Paris Rhone and Valeo alternators as well as Hitachi have temperature compensation. I believe the point that Maine Sail was making in regards to Hitachi alternators is that their temperature compensation factor was higher than most and at high temps could make the Vset too low to adequately charge the battery.

Thanks for that input, much appreciated. Very true conclusion.

[sailinglegend]

Originally Posted by kenbo

Sorry, statement #2 is incorrect. Most internally regulated Delco, Paris Rhone and Valeo alternators as well as Hitachi have temperature compensation.....

My expensive hot rated Balmar 6 series alternator has temperature compensation so after half an hour is down from 14.4v to below 14 volts.

It's set up on a two-way switch so if the external regulator fails you switch to the internal regulator.