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Old 10-12-2019, 19:30   #1
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running the engine to charge the batteries

We recently purchased 2 Engel freezer/refrig 12V units. We may possibly need to run the diesel engine to charge the batteries. We have never had to do this as we have 3 solar panels. I'm thinking their total is of 300 watts. I have read that running the engine with no load is detrimental to the engine. If this is true how does one use the engine and engine driven generator to charge the batteries without causing damage to the engine.
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Old 10-12-2019, 19:46   #2
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Re: running the engine to charge the batteries

Short simple answer - find other ways to load the engine, based on the coolant temperature not getting hot enough.

More detailed, complex answer:

For the propulsion engine, get an alternator (or add one) that can load the engine properly, say 25-30%, and put an external VR on it to regulate the output properly

Make sure your battery bank is indeed depleted (say below 80%), large enough in Ah, and / or of a chemistry that will accept a high percentage of the maximum actual continuous electrical output, say 60-80%.
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Old 10-12-2019, 20:09   #3
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Re: running the engine to charge the batteries

Quote:
Originally Posted by tomlisasail View Post
We recently purchased 2 Engel freezer/refrig 12V units. We may possibly need to run the diesel engine to charge the batteries. We have never had to do this as we have 3 solar panels. I'm thinking their total is of 300 watts. I have read that running the engine with no load is detrimental to the engine. If this is true how does one use the engine and engine driven generator to charge the batteries without causing damage to the engine.
with 300 watts solar you may be fine what is your power usage ?
You really need to know how much power you are using before you really can go about feeding it .

As john suggests you may need / want a larger alternator.

Questions are
1) what is your power consumption?
2) what is your house bank ? Type and size of battery and ah capacity?
3) what boat?
4) what engine?
5) what size is your current alternator?
6 ) what is your expected boat usage ? ( weekends, passages, coastal, marinas, or anchor/ mooring ball)
7) generator?
8) onboard battery charger?
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Old 10-12-2019, 20:17   #4
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Re: running the engine to charge the batteries

Quote:
Originally Posted by newhaul View Post
with 300 watts solar you may be fine what is your power usage ?
You really need to know how much power you are using before you really can go about feeding it .

As john suggests you may need / want a larger alternator.

Questions are
1) what is your power consumption?
2) what is your house bank ? Type and size of battery and ah capacity?
3) what boat?
4) what engine?
5) what size is your current alternator?
6 ) what is your expected boat usage ? ( weekends, passages, coastal, marinas, or anchor/ mooring ball)
7) generator?
8) onboard battery charger?
9) How much sun do you get?
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Old 10-12-2019, 20:26   #5
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Re: running the engine to charge the batteries

By my quick reckoning, you 300W array will give you 300/ 12.7 (v) x 60% (efficiency) x 8 hours if you get that much quality sun. That about 110ah per day. My fridge and freezer (not dissimilar to Engel in terms of consumption) run at about 8 amps together, run maybe 50% of the time for 24 hours. That’s about 96ah consumed. So assuming you run nothing else electrical the fridges should be OK with the solar array.

These are very rough calcs but indicative of where you may be. Do your own calcs from specs you know and you’ll get it better than me.

But then, you never get by using nothing else electrical through a 24 hour cycle so you’re gonna have to run the donk at some point.
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Old 10-12-2019, 20:26   #6
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Re: running the engine to charge the batteries

If you do, run the engine first thing in the morning when the batteries are most depleted and will accept a good charge rate, then let the solar do its work for the rest of the day.
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Old 10-12-2019, 20:27   #7
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Re: running the engine to charge the batteries

The issues with running a diesel lightly loaded are far less serious than most sailors seem to think. It is one of those things that keeps getting repeated over and over, but with precious little actual data to support it.

Just as an example, my boat has a diesel generator. It spends most of it operating hours quite lightly loaded. It has 9,000 hours on its motor. and has good compression and runs as new.

It is true that your engine NEEDS to come up to operating temperature, but in my experience most diesels will do this with very little load if they have well designed cooling systems and working thermostats. Other than that, take good care of it, and it will work just fine.

When somebody tells you how terrible this is for your engine, ask then exactly HOW bad? If an engine runs lightly loaded will it last 1000 hours? 4000?
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Old 10-12-2019, 20:38   #8
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Re: running the engine to charge the batteries

It's not good to run a diesel at high rpm under a light load.
In the old days in commercial fishing, before generators were common in smaller boats, people ran a jack shaft. A shaft, bearing at each end,
along side the engine running at higher speed when cruising at slower speeds. Small pulley on the shaft and big pulley on the engine. Sometimes controlled by a clutch. Alternator running off the shaft or maybe a 2nd alternator.

That way the engine could run near idle and charge the batteries.
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Old 10-12-2019, 20:54   #9
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Re: running the engine to charge the batteries

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Originally Posted by tomlisasail View Post
If this is true how does one use the engine and engine driven generator to charge the batteries without causing damage to the engine.
by moving the boat...

and keep in mind an engine at idle is not going to charge much either, it needs to be at ~1500rpm . so if you don't move the boat, it needs to be reved up.

add more solar if you need it.
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Old 10-12-2019, 21:02   #10
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Re: running the engine to charge the batteries

You could always run the engine in reverse to add a load. Don't know how Necessary it is to run engine with a load other than the alternator. We used our engine almost exclusively for battery charging for a couple years cruising. Ran the engine at about 1500 rpm putting on more than 500 hours. We were very low energy users with no refrigeration, oil lamps and incandescent running lights our biggest electrical drain. Ran the engine about once a week for 3-5 hours. Almost exclusively used the engine for getting in and out of harbors. We sold the boat to a couple who took the boat to SoPac twice still with no other charging capability but the engine before it died. Don’t know the final hours but it was close to 20 years old.
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Old 10-12-2019, 21:03   #11
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Re: running the engine to charge the batteries

Quote:
Originally Posted by tomlisasail View Post
We recently purchased 2 Engel freezer/refrig 12V units. We may possibly need to run the diesel engine to charge the batteries. We have never had to do this as we have 3 solar panels. I'm thinking their total is of 300 watts. I have read that running the engine with no load is detrimental to the engine. If this is true how does one use the engine and engine driven generator to charge the batteries without causing damage to the engine.
Quote:
Originally Posted by smac999 View Post
by moving the boat...

and keep in mind an engine at idle is not going to charge much either, it needs to be at ~1500rpm . so if you don't move the boat, it needs to be reved up.

add more solar if you need it.
Or by not moving the boat, just pop it into gear and run the engine in forward or reverse if tied to the dock or just in reverse if anchored or on a mooring. Helps keep the prop clean at the same time.

Charging achieved.
Engine loaded.
Prop cleaned.
Win / win /win
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Old 10-12-2019, 21:04   #12
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Re: running the engine to charge the batteries

I see Roverhi was one minute faster
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Old 11-12-2019, 05:21   #13
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Re: running the engine to charge the batteries

Quote:
Originally Posted by billknny View Post
... It is true that your engine NEEDS to come up to operating temperature ...
Indeed. That's the underlying potential problem.
As long as your engine runs long & hard enough to come up to temp., it'll be OK.
Notwithstanding, that's a very inefficient/dirty way to charge.
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Old 11-12-2019, 06:03   #14
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Re: running the engine to charge the batteries

Quote:
Originally Posted by tomlisasail View Post
We recently purchased 2 Engel freezer/refrig 12V units. We may possibly need to run the diesel engine to charge the batteries. We have never had to do this as we have 3 solar panels. I'm thinking their total is of 300 watts. I have read that running the engine with no load is detrimental to the engine. If this is true how does one use the engine and engine driven generator to charge the batteries without causing damage to the engine.
I spent my first years with a single 290w panel. So I can tell you that you will have to supplement charging with something.

You can run the engine to do it and the engine will be just fine. You just run it long enough to fully heat up the engine, but that shouldn’t be a problem as you will run for an hour at least anyway. At the end you should run the rpms up to 3000+ a few times to blow it out. (This question has been asked here lots of times if you want to save time and run a search)

It’s right in the Yanmar operational manual.

Btw for most economic operation charging this way run engine in morning so batteries will accept max amps and when the amps start dropping switch to just solar. You may not get 100% charged each day, just note when you do so you can decide how often you are gong to go between full charges. Cruisers operated like this for years before solar got inexpensive.
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Old 11-12-2019, 06:13   #15
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running the engine to charge the batteries

Itís not going to kill it, but an engine should come up to operating temp even now and again, now here Iím defining operating temp as cylinder head temp, that helps it burn off deposits and keeps things clean and is what is behind Yanmars recommendation of blowing it out every once and awhile.
I think the most harm is done at an idle, go ahead and bump that idle up to 1000 or 1200 RPM, your alternator will charge more too.
Best example I can think of to show how idling a Diesel wonít kill it is to think of Diesel trucks that used to idle all night, it never bothered them.
But remember after idling all night, they got out on the road and ran at cruise RPM and load too.
US ARMY did a study years ago to determine the harm of low load Diesel engine running and came up with it would cause slobbering etc, but seemed to do little actual harm, jus made a mess.

However what your considering is really better accomplished with a Honda, do you really want to put all those hours on your real expensive engine, when you could do the job better with a Honda and save the expensive motor for the job it was intended for?
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