Convoluted charging, alternator issues

[Minggat]

I will try to be concise here.

Optima starter battery. Brand new. At this point, the alternator is only charging that battery. Dedicated MPPT also feeds that battery.
It settles down to 13.2 volts after the sun goes down and the surface charge dissipates. Optima says 13-13.1. I’m now kicking about the extra tenth.

After the sun comes up, the MPPT settles in float charging that battery at 13.8.

All good so far.

When I fire up the engine, the alternator trys packing more in at 14.8 volts. High, but marginally high.

I would be happy if the alternator recognized that the battery was already full, but I would excuse that high voltage for a while. So far, I have only teen tolerant for 15 minutes. I am looking for the charge voltage to drop down to 13.8.

Does the regulator on my alternator have a problem?

I pulled it off today to have it bench tested. The rebuild shop here in Lihue is out of business. Auto parts stores just couldn’t adapt to my non-automotive connection.

I put it back on, and ran it a bit. I noticed that the tachometer is now unreliable at high idle. Very stable at low idle. Possible indication of bad regulator?

Would this be a good reason to buy an external regulator?

Leece Neville 90 amp alternator.

Thanks

[goboatingnow]

If this is a stock alternator , it’s set very high indeed , most car alternators are set for 13.8.

Is it an OEM part or an after market fitment ?

[Minggat]

Not a stock alternator on my old Perkins.
Prestolite- Leece Neville are built for industrial equipment. Also common on busses.

Yes. Target is 13.8 volts float. Higher for bulk. The problem is getting it to drop down to float voltage.

It’s common for charging systems to start out high and settle into float. I’m asking is 15 minutes is a little long for that to happen. I have not run the engine longer than 15 minutes with the new Optima starter battery. The alternator may have been packing the previous Odyssey batteries that high. Not sure.

Because I am maintaining everything with solar, I really am tempted to not have an alternator in my system.

I did purchase a DC/DC charger to take advantage of the alternator as a supplemental charger for my lithium house batteries, but I haven’t installed it yet.

I don’t want to stray here, but the only time that the alternator would be utilized is while running the engine on night passages. Even then, maybe hard to justify.

But since I do have an alternator, good idea to utilize it.

I’m just trying to make sure that having it isn’t counterproductive.

[cal40john]

If I understand correctly you have an internal regulator. All the internal regulators I'm familiar with are not 3 stage. Once the battery is charged enough that the setpoint voltage of the regulator is reached, the regulator limits current as necessary to maintain that voltage. The setpoint is typically around 14.2 - 14.5 volts. It will hold that voltage until the engine is shutdown.

14.8 is high.

[goboatingnow]

Just to confirm , unless you have a three stage regulator , alternators don’t “ start high “. They start at the regulator voltage and they should never exceed that if they are the only charge source running. Nor will the voltage be dropped down by the alternator.

Bus alternators are often set higher to handle large recharging loads , but 14.8 is too high , 14.2 would be more normal for bus and high demand alternators.

Note in bulk charging the voltage will typically be at its lowest , rising as the battery reaches the absorption point.

[Minggat]

Thanks guys.

From what I’m hearing, it sounds like I might be happier to have no alternator.
While I’m not so happy to be stuck at the dock, I have not been plugged in. My power demands are easily handled by my solar.

Changing over to lithium and now have a dedicated AGM start battery with its dedicated MPPT to deal with non-use battery maintenance has me feeling like I have made a couple of good choices.

Along those lines, would I not be doing myself a favor to have an alternator that only put out 13.8?

I’m thinking that anything higher than that would just shorten the battery life.

My power demands at night on passage with the radar and other electronics running is the only unknown.

[Boatyarddog]

Originally Posted by Minggat

Thanks guys.

From what I’m hearing, it sounds like I might be happier to have no alternator.
While I’m not so happy to be stuck at the dock, I have not been plugged in. My power demands are easily handled by my solar.

Changing over to lithium and now have a dedicated AGM start battery with its dedicated MPPT to deal with non-use battery maintenance has me feeling like I have made a couple of good choices.

Along those lines, would I not be doing myself a favor to have an alternator that only put out 13.8?

I’m thinking that anything higher than that would just shorten the battery life.

My power demands at night on passage with the radar and other electronics running is the only unknown.

Is the optima, a FL, AGM?
You'll be adding a DC to DC charger and a Lithium Battery?
Does the DC Charger your installing have a Selection for charging protocol?
Otherwise, there maybe some problems.
Boatyarddog

[d design]

Dont worry about it its fine. Put a switch on the regulator ignition if you dont want it running for long periods.

[smac999]

Unless you have an external regulator. No alt will drop to float.

Millions of cars drive all day long at 14.4v. Don’t worry about over charging a start battery.

[donradcliffe]

I agree with d design. It may be as simple as turning off the ignition switch, depending on how your boat is wired.

Long term, you should consider switching to external regulation to prevent times you forget you have switched the alternator off.

[Minggat]

Originally Posted by Boatyarddog

Is the optima, a FL, AGM?
You'll be adding a DC to DC charger and a Lithium Battery?
Does the DC Charger your installing have a Selection for charging protocol?
Otherwise, there maybe some problems.
Boatyarddog

Optima is AGM. Dedicated MPPT keeps it topped up, so adding the existing alternator was not a requirement.

Battleborn lithium house bank on dedicated MPPT. Also doing just great on solar. Battleborn supplied the Victron smart isolated DC/DC charger. The isolated part takes care of the potential problem you mention.

The batteries and MPPTs have happy for weeks.
Remember, that my original concern included have an alternator in the system at all. Once I did fire the engine and saw that high voltage, the can of worms was opened. Now that I have been able to adjust the voltage, done deal.

I have not yet installed the DC/DC charger. I will hold off until I see how my night passages power consumption goes.

Just because I can add the alternator into the system doesn’t mean that it’s required. At the same time, it‘s already there.

It was the counterproductive high voltage that got all the keystrokes out of me.