# Running diesel to Charge Batteries



## LarryandSusanMacDonald (Apr 3, 2005)

This has probably been talked about, but I'm too lazy to look it up. 

Today, we started the diesel engine again to charge up the batteries. Saltwater Suzi (an order of magnitude smarter than I) softly asked, "I thought we bought the Honda Generator to do that."

I answered, "It's a hassle and makes too much noise."

She countered, "I thought you told me that it wasn't good for the diesel to run it just to charge the batteries."

I pondered a response that wasn't going to get me into a lot of hot water, and failing same said, "I've heard that, too. But I can't imagine why."

And I can't. So I ask, is it so and if so why? Not too technical please, I can't afford to risk spraining my brain again. (Had a thought the other day and it laid me up for hours.)

As usual, thanks in advance for your input.


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## deniseO30 (Nov 27, 2006)

Now if you had even 10watts of solar the batteries would stay topped off. so there's a 3rd option . giggles


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## priscilla (Mar 20, 2000)

The engine is just happy to be running....it likes a little load and your alternator provides that.


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## GeorgeB (Dec 30, 2004)

You have a Morgan 41? What size is your engine and how big is your alternator? I imagine that your engine is somewhere around 50 horse? A 120 amp alternator is barely going to put a load on the engine. Over time, you run the risk of the exhaust elbow "coking up" with un burnt hydrocarbons because there isn't sufficient pressure to blow them out. They build up over time, restricting the exhaust flow, resulting in higher pressures and temperatures. Ultimately causing elbow cracking or burn-through. Diesels are happiest running WOT. Is your alternator an externally regulated one?


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## JohnRPollard (Mar 26, 2007)

LarryandSusanMacDonald said:


> "I thought we bought the Honda Generator to do that."


For that kind of money, you could have avoided all the noise and hassle and bought a few linear miles of extension cord.


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## BarryL (Aug 21, 2003)

Hello,

Engines, especially older engines, do not like to idle. The engine does not get hot enough to burn off impurities in the oil. The fuel injection is not designed to be very accurate at idle, so the fuel burn is not complete and the exhaust will be sooty. This leads to build up in the exhaust system.

In short, diesels like to be run at cruising RPM and not idle speed. IMHO, if you need to run the engine to charge batts, put the boat in gear. That will put more load on the engine.

Barry


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## LarryandSusanMacDonald (Apr 3, 2005)

Denise:

I guess I didn't mention that we are live-aboard cruisers. 10 watts is akin to spitting in the ocean. We've got computer, microwave, coffeemaker, TV, etc. all the comforts of home.

Priscilla,
<o> </o>
I like your answer best (for my purposes, at least, it keeps me out of trouble with Suzi)

GeorgeB.

Westerbeke 55B (about 4 years old 853 hours) with 170amp alternator, set to 100 amp output max with Link 2000r. We run at about 1400 rpm when charging batts - it runs about the same temp (~180) when we are moving the boat as when just charging batteries.

John,

Got it used - 2000 watt for only $500. I am the _Frugal Mariner_, you know!

So am I O.K. here? Can I run the diesel or should I go with Mr. Noisy?


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## SteveInMD (May 11, 2007)

Here's a short article on the subject...

Bore glazing


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## JohnRPollard (Mar 26, 2007)

LarryandSusanMacDonald said:


> John,
> 
> Got it used - 2000 watt for only $500. I am the _Frugal Mariner_, you know!


Yeah, but the extension cords are so much quieter. And they can double as spare standing rigging in a pinch.


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## negrini (Apr 2, 2008)

Barry, me too were educated on this, including specialists observating same advice. Steve, I had red this article before, wich corroborate to people like Nigel Calder. What I couldn't explain is in a heavy traffic city like here, people spend (an average) 3 hours per day in traffic, mostly iddling the engines, but diesel cars/van/truck are still very reputable for longevity and reliability. I can understand the efficiency math (running a big beast to power tinny 500W to your DC system), where oversized generators are wasting more fuel per Watt, if compared to smaller unities) but cannot understand why marine diesels wear faster if iddling, copared to automtive diesels iddling. Should marine learn a thing or two from automotive industry ?


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## SteveInMD (May 11, 2007)

Actually "marine diesels" are diesels from other lines of work that have marine add-ons to them.

Cars and trucks idle for a while, but then are loaded up when you drive. Treat your marine diesel the same way and you'll be fine.

A 170 amp alternator is plenty of load by itself, in my opinion.


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## priscilla (Mar 20, 2000)

Priscilla has a 150A alternator on a Westerbeke 63, When that alternator kicks in you can hear the rpms take the load. Diesel gensets run constantly at 1800 rpm's with or without loads......Still, I agree with the others, it would be better to take her out for a powerboat run.


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## Omatako (Sep 14, 2003)

Spend another few dollars D) and put a water maker pump and a dive compressor on at the same time. Then your engine load will be OK and you'll be making water and charging your bottles at the same time (if you don't have any bottles, charge other people a few bucks to do theirs, pays for your diesel).

A friend and I are busy with parallel projects to do the same on both our boats. We plan on putting the watermaker and dive compressor on electro-magnetic clutches so that they can be switched on and off as required.


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## GeorgeB (Dec 30, 2004)

Wow, how big are your battery banks? I thought I had a "grown up" system of 35 HP driving a 120 Amp alternator feeding a 720 Amp house bank. I guess it goes without saying you guys have a double pulley system. Another thought. Even with a 150 Amp alt, you are generating only a fraction of the amps at dle speed than you would be if you were up to "operating" RPMs on the engine. My comment about the exhaust elbow is from painful first hand experience where I coked mine up. Your temp sensor measures heat in the cooling system and not the heat build up in the exhaust elbow due to restricted flow. I first noticed the problem it with a very minor increase in fuel consumption, then by a persistent black smudge on my gelcote around my exhaust port. One of my friends ignored the symptoms and burned a hole through the elbow while motoring up from Southern California - he had a very expensive tow into Monterey.


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## NaviGsr (Sep 17, 2009)

I drive a diesel car and I've been told by mechanics that the main danger from idling in traffic a lot is that the timing chain tensioner will not keep working to correct the tension of the timing chain. When the engine is under load, the tensioner works properly. Big diesel trucks idle a lot, but timing chain adjustments are part of their regular service intervals. I doubt idling a marine diesel once in a while will hurt it as long as you keep an eye on the temp. Buildup should just be blown off once you are running under load.


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## xort (Aug 4, 2006)

Idling the engine will usually get the coolant water up to temp and the thermostat will cycle at around 170d. But that isn't really hot enough. One of the issues can be moisture or condensation inside the engine. I try to make sure my oil temps get up over 200d frequently. How can you check for that? Buy a temp gun. This is a small pistol grip like device that points a laser beam and measures temps where the beam hits. Very good for looking for hot spots on the engine. I read all the injectors, the exhaust manifold, the transmission, the stuffing box and the oil filter. The temp guage will read 170 but the oil can get to about 205 when fully up to temp.

Before replacing the packing on the stuffing box, the temps were reading about 20d over seawater. Now it's reading about 2 to 4d above seawater. There's a lot that can be monitored with a temp gun.


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## Omatako (Sep 14, 2003)

xort said:


> Idling the engine will usually get the coolant water up to temp and the thermostat will cycle at around 170d. But that isn't really hot enough. One of the issues can be moisture or condensation inside the engine. I try to make sure my oil temps get up over 200d frequently. How can you check for that? Buy a temp gun. This is a small pistol grip like device that points a laser beam and measures temps where the beam hits. Very good for looking for hot spots on the engine. I read all the injectors, the exhaust manifold, the transmission, the stuffing box and the oil filter. The temp guage will read 170 but the oil can get to about 205 when fully up to temp.
> 
> Before replacing the packing on the stuffing box, the temps were reading about 20d over seawater. Now it's reading about 2 to 4d above seawater. There's a lot that can be monitored with a temp gun.


Gee some folks worry about amazing stuff!! I never even thought about oil temperature before. And now the stuffing box as well. Oh my, what am I going to do?!?!?? 

Sailing for me has always been a sport/pastime - I'm not about to turn it into a science. There is enough paranoia in the world without adding all this stuff to it.

Not a critcism, just an observation - measure whatever you feel is necessary.


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## captbillc (Jul 31, 2008)

SteveInMD====everyone should read that article. it plainly states that running a diesel only to charge the batteries is not enough load on the engine & will eventually shorten its life. as a retired cummins diesel technician i agree with the article. i never use my engine that way.


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## Valiente (Jun 16, 2006)

I've installed four big solar panels, and will install a wind genny, and already have a Honda 2000 precisely to avoid this situation, which in my understanding is bad news for diesels for the reasons cited. If your frugality doesn't allow buying a separate genset, then buy ear plugs or a thick piece of rubber mat for the Honda 2000, or schedule "power runs" at 2,400 RPM out to sea and back until the required amps have been pushed into the batteries.

We are happy to make amps from the diesel while motoring, but I've spent a fair number of dollars to have a quiet boat at anchor. The Honda 2000 is meant a) to avoid inversion for power tools, b) to charge the anchor windlass battery to full power when the echo charger from the main bank isn't doing it or I anticipate heavy use, and c) as a tertiary charging source (after solar/wind and alternator) should all else fail.

You must have a super-insulated engine bay if the sound of a Honda 2000 on deck bugs you and the sound of a 1,400 RPM diesel doesn't.


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## negrini (Apr 2, 2008)

Guys, I just wanted to know why iddling "marine diesel" will shorten its life, and a automotive diesel accept it whithout complains. I don't want to conclude that iddling cause cancer ....


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## bobmcgov (Jul 19, 2007)

Another consideration is engine life. Rebuilding or replacing your diesel inboard will ding you upwards of $8000. Even if we work on the assumption that running it underloaded or at idle is no harder on it than running at W.O.T., you are still spooling life off the hours meter. Shortening time between oil changes, filter cleanings, risking the engine not being there when you need it for driving the boat. Even tho keeping gasoline on board is nasty and they don't always provide the nicest power, a modern portable is better than running the main powerplant if just charging batteries. If it croaks, you toss it overboard & buy another. Cheaper than cutting 5 yrs off your inboard.

BTW, a guy in Avalon ran a little blue Yamaha genset on his foredeck, similar to the enclosed Hondas. He was moored about 6 feet away and we could barely hear it. Very impressed!


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## T37Chef (Oct 9, 2006)

Can anyone explain all the semi trucks you see idling along the highways...I assume its not bad for their engines? or is it?

BTW, I was talking to a boat neighbor today who used to drive a semi, you know those trucks take about 40 qt of oil??? WOW.


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## hellosailor (Apr 11, 2006)

" Not too technical please, I can't afford to risk spraining my brain again."
OK. Bottom line? 

Listen to She Who Must be Obeyed. Use the genset, not the engine. Nothing else matters.

And in this case, she's correct anyhow.


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## BarryL (Aug 21, 2003)

*modern vs old diesel engines*



T37Chef said:


> Can anyone explain all the semi trucks you see idling along the highways...I assume its not bad for their engines? or is it?
> 
> BTW, I was talking to a boat neighbor today who used to drive a semi, you know those trucks take about 40 qt of oil??? WOW.


Hello,

There is a WORLD of difference between the typical marine diesel engine, built in the 80's and the engines in semi trucks. The Universal M25 in my 1986 O'day 35 has ZERO electronics. No computers, sensors, actuators, etc. It is a very simple mechanical device that is designed to operate in a relatively narrow RPM range - basically around 70-80% of Wide Open Throttle (WOT). At idle, the fuel injection is not optimum, and combustion is not nearly as complete at cruising RPM.

Modern diesel engines, especially trucks but also new marine diesels, are full of computers and sensors. There are throttle position sensors, crankshaft position sensors, etc. The computers and sensors allow for good combustion across the entire rev range.

Modern diesels are catching up, mainly for larger boats with high HP engines.

Barry


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## Valiente (Jun 16, 2006)

BarryL said:


> Modern diesels are catching up, mainly for larger boats with high HP engines.
> 
> Barry


True, but it's still the wrong tool (big diesel) for the job (turning an alternator belt). Gensets are designed differently than propulsion diesels for this reason. Even if it did no more harm to the diesel than to add hours (which some would say is harm enough), the cost in amps per litre is higher than with a gas genset and that's higher than a diesel genset.

You can compensate somewhat by having bigger alternators or twinned smaller ones, but then you have the issue of a heavier shearing load on the crankshaft, or the limitations of the battery banks to accept the greater number of amps.


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## LarryandSusanMacDonald (Apr 3, 2005)

> " Not too technical please, I can't afford to risk spraining my brain again."
> OK. Bottom line?
> 
> Listen to She Who Must be Obeyed. Use the genset, not the engine. Nothing else matters.
> ...


Hello Sailor summed it up perfectly - and almost all seemed in agreement. And I thank all of you for your input. So, I'll run the noisy genset, _most _of the time. When the weather's bad, of I'm feeling particularly larthargic, I'll run the diesel. (Lethargy is its own reward.)

But if you're at anchor and a green stripped Morgan Out Island with an extremely handsome, albeit elderly, salty looking curmudgeon of a Captain fires up a noisy genset, well, I don't want to hear any complaints. Remember, you told me to.

Thanks again, all. I've got to go now, and figure out why my engine is overheating.:hammer (That's me on the left and a personification of my boat on the right.)


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## JohnRPollard (Mar 26, 2007)

LarryandSusanMacDonald said:


> ...So, I'll run the noisy genset, _most _of the time. When the weather's bad, of I'm feeling particularly larthargic, I'll run the diesel. (Lethargy is its own reward.)


Okay, now that the thread has run its course, this is where I come in for my obligatory public safety announcement and mention that portable gas gensets are not approved by ABYC nor the U.S. Coast Guard for use aboard recreational vessels due to the hazard of CO poisoning.

So Larry, if you're feeling "lethargic", turn off that gas genset and make sure your CO detectors are operational.


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## Bene505 (Jul 31, 2008)

CO detectors are available at any hardware store and are cheap. The battery probably lasts 6 months too. I have one mounted in the salon. It's cheap defense. I'll probably move it farther from the hatch.

Regards,
Brad


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## LarryandSusanMacDonald (Apr 3, 2005)

Good points John and Bene505, I've got the genset running it's out on the back deck and the wind is piping about 15-20 with gusts to 30. I don't thimk I hove two werry abut co so i''l jes sav my money idgh jjid mdl nnhgd nkls ekkeb bh sl
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mnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn


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## JohnRPollard (Mar 26, 2007)

LarryandSusanMacDonald said:


> Good points John and Bene505, I've got the genset running it's out on the back deck and the wind is piping about 15-20 with gusts to 30. I don't thimk I hove two werry abut co so i''l jes sav my money idgh jjid mdl nnhgd nkls ekkeb bh sl
> kjhgfoui
> gdiu
> bf
> ...


Feeling lethargic, are we?


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