Running the engine to charge batteries - gear for load or no gear?

[double u]

...the caveat "you might drag your anchor" is absolutely ridulous though! If a normally-sized sailboat auxiliary drags your anchor when reversing at say 1500rpm, what are 25, 30kn of wind going to do?

[team karst]

Originally Posted by double u

...the caveat "you might drag your anchor" is absolutely ridulous though! If a normally-sized sailboat auxiliary drags your anchor when reversing at say 1500rpm, what are 25, 30kn of wind going to do?

May wear out the hull bottom. [emoji33]

But seriously folks:

I would tend to favor a large frame alternator on the existing motor. Why not?? Higher loading, shorter run time, no storage issues.

[double u]

the biggest problem that I see with charging your batts with the engine is the charging curve of lead-based batteries (wet, gel & AGM): the last 5-10% of charge take a long time to be absorbed

[PineyWoodsPete]

Originally Posted by team karst

May wear out the hull bottom. [emoji33]

But seriously folks:

I would tend to favor a large frame alternator on the existing motor. Why not?? Higher loading, shorter run time, no storage issues.

The biggest challenge to alternators is the heat buildup from putting high amps into depleted banks. A directed blower with cooler bilge air intake could help prevent failure, or even fire in a large frame alt.

[EngineerRetired]

So you pull into any rest stop in the country at night and see, 50 - 100 Big rig Diesels running. Trust me, they are not in gear. Keep in mind, these engines go a million miles.

[goboatingnow]

Originally Posted by EngineerRetired

So you pull into any rest stop in the country at night and see, 50 - 100 Big rig Diesels running. Trust me, they are not in gear. Keep in mind, these engines go a million miles.

I’ve explained that these engines get subjected to heavy loading over a wide range of throttle settings the next day. That prevents bore glazing. Boat engines are not used the same way.

[skipperpete]

I’m not a true believer in the “Glazed bores” story. I’ve seen a fair number of glazed up engines and as a routine overhaul procedure, de glazed quite a few but I’m still not able to definitely say that low load running causes glazed cylinders. I spent an uncomfortably long time working on generators and a lot of them ran at 750 or 1500 rpm with almost no load until a demand was made and bore glazing was not an issue. I was involved with one installation where a constant precise frequency was needed so the standby generator engine was motored on phase and frequency by the alternator it had to drive and a change of 2Hz would trip the rack and it was instantly able to provide full load. It did this 24 hours a day for 8 years and was replaced by a more modern system. Still running and still putting out good PV cards when it went out of service.
It’s not very difficult to deglaze an engine if it does actually happen... Caterpillar once sold a deglazing powder that you dusted into the intakes at high idle... widely suspected of being the abrasive “Bon Ami”

[EngineerRetired]

Originally Posted by goboatingnow

I’ve explained that these engines get subjected to heavy loading over a wide range of throttle settings the next day. That prevents bore glazing. Boat engines are not used the same way.

So long hours of my chore tractor (with a 3 cyl. Yanmar) running at around 1000 RPM driving a genny / welder with little load (maybe 5% duty cycle) will cause glazing in the engine? Sorry, I've rebuilt too many of them to agree with that.


I don't think most people realize just how tough and dependable the small Yanmars are. There really is a reason John Deere stopped manufacturing their own and buy them from Yanmar. I typically see 6,000 to 8,000 hours on them before needing a rebuild. Many run at PTO Speed (3600 RPM) 90% of the time. Others hardly get above 1000 RPM.

[EngineerRetired]

Originally Posted by skipperpete

I’m not a true believer in the “Glazed bores” story. I’ve seen a fair number of glazed up engines and as a routine overhaul procedure, de glazed quite a few but I’m still not able to definitely say that low load running causes glazed cylinders. I spent an uncomfortably long time working on generators and a lot of them ran at 750 or 1500 rpm with almost no load until a demand was made and bore glazing was not an issue. I was involved with one installation where a constant precise frequency was needed so the standby generator engine was motored on phase and frequency by the alternator it had to drive and a change of 2Hz would trip the rack and it was instantly able to provide full load. It did this 24 hours a day for 8 years and was replaced by a more modern system. Still running and still putting out good PV cards when it went out of service.
It’s not very difficult to deglaze an engine if it does actually happen... Caterpillar once sold a deglazing powder that you dusted into the intakes at high idle... widely suspected of being the abrasive “Bon Ami”Attachment 242312

Agreed. See my post on running a genny / welder (PTO). Any time I have seen glazing there was a cooling issue and /or horrible fuel.

[Exile]

Originally Posted by EngineerRetired

Agreed. See my post on running a genny / welder (PTO). Any time I have seen glazing there was a cooling issue and /or horrible fuel.

What about the oft-cited problem of carbon build-up from running light loads? Is there any utility then of the equally oft-cited recommendation (from marine diesel mechanics it seems) to periodically run the engine WOT for a few minutes to clear the cabin deposits?

[Wotname]

Originally Posted by Exile

What about the oft-cited problem of carbon build-up from running light loads? Is there any utility then of the equally oft-cited recommendation (from marine diesel mechanics it seems) to periodically run the engine WOT for a few minutes to clear the cabin deposits?

And not just by marine diesel mechanics but also by an engine manufacturer (Yanmar). One would like to think Yanmar has some idea about what is the best way to operate their engines.

[Exile]

Originally Posted by Wotname

And not just by marine diesel mechanics but also by an engine manufacturer (Yanmar). One would like to think Yanmar has some idea about what is the best way to operate their engines.

I was hoping you'd chime in. I thought (maybe incorrectly) that these recommendations had more to do with turbocharged engines (like many Yanmars) not gunking up with carbon deposits.

[valhalla360]

Originally Posted by EngineerRetired

So long hours of my chore tractor (with a 3 cyl. Yanmar) running at around 1000 RPM driving a genny / welder with little load (maybe 5% duty cycle) will cause glazing in the engine? Sorry, I've rebuilt too many of them to agree with that.


I don't think most people realize just how tough and dependable the small Yanmars are. There really is a reason John Deere stopped manufacturing their own and buy them from Yanmar. I typically see 6,000 to 8,000 hours on them before needing a rebuild. Many run at PTO Speed (3600 RPM) 90% of the time. Others hardly get above 1000 RPM.

I think you are missing the point. Sure they may spend 5-6hr at light load but it's rare to just leave the tractor parked in one place never to be moved or otherwise loaded.

Even 10% of the time at heavier loads suggests a few hours per week at higher loading to get things up to temp and burn off any deposits.

Where concerns with cruising boat motors come into play is when people anchor for months never using the engine for anything beyond charging the batteries. It's becoming less common with the proliferation of cheap solar but historically it was a fairly common use pattern among anchor out liveaboards.

[Wotname]

Originally Posted by Exile

I was hoping you'd chime in. I thought (maybe incorrectly) that these recommendations had more to do with turbocharged engines (like many Yanmars) not gunking up with carbon deposits.

I can't speak to turbo's as I have had almost zero experience of them but for most (all?) of the others, Yanmar makes a point of detailing (in black and white) when and how "to race" the engine at WOT after every few hours of light loading.

[EngineerRetired]

Low rpms with a light load *may* be an issue, I have never seen it but anything is possible. With that said, putting the engine in gear at a low rpm to load it simply defies everything I know of diesels.