Charging batteries with engine

[jalmberg]

While at anchor, I occasionally have to recharge our 400 amp-hour deep cycle battery bank with the diesel engine equipped with a Bosch 14v/90amp alternator. Normally our solar panels do the recharging.

Generally, I run the engine at 1000-1200 rpm.

My questions: is this really bad for the engine? What rpm should I be using?

The engine is a Mercedes OM 616 diesel, used in many light trucks.

Thanks in advance for any advice.

[sailorboy1]

I do it sometimes, but don’t think I run mine as fast (I slowly bring the pm up till he amps into the batteries stops going up). My engine manual says if you run at low load for long periods to rev it to max a few times once in a while. I do this also every few hours when I’m motoring.

In other words I don’t think it is bad for the engine

[gRider]

generally speaking running diesel engines under low loads is bad for diesel engines. I try to minimize idle time on mine. If I needed to recharge my batteries and solar wasn't enough and I didn't have shore power, Id use my portable gas generator to power the on board charger. Idling the diesel to recharge batteries would be the last option Id consider.

Originally Posted by jalmberg

While at anchor, I occasionally have to recharge our 400 amp-hour deep cycle battery bank with the diesel engine equipped with a Bosch 14v/90amp alternator. Normally our solar panels do the recharging.

Generally, I run the engine at 1000-1200 rpm.

My questions: is this really bad for the engine? What rpm should I be using?

The engine is a Mercedes OM 616 diesel, used in many light trucks.

Thanks in advance for any advice.

[a64pilot]

It's not going to kill it, although doing so for days on end isn't good.
Google Diesel slobbering or Diesel stacking for some good explanations. It's a common issue with standby generators that are often run to exercise them, but are not often put under a load.
A little Honda generator can be a good thing to have.
Especially if your running an internally regulated alternator, the Honda powering your shore power charger will do a much better job and your not putting hours on the high dollar Diesel

[roland stockham]

It's not the revs it is the temp. If the engine is up to normal operating temp then it will do no harm. Older diesels can run cold at low loads and that causes glazing of the cylinders. Also if you have a turbo you need to periodically run the engine up to a load/speed that gets it spinning. I gather they can cease up if the engine is run for long periods without the turbo kicking in. I think that is around 60-80%. Most of the time it sits there doing nothing on a sailboat.

[DEAN2140]

For what its worth, whenever I charter the standard advice for charging the batteries is to run the engine @ 1500 RPM. I agree that in general you shouldn't run the engine without load for long periods but if the alternative is a dead battery...........

[waterman46]

I assume you do have a smart regulator on that alternator, if not, it is good to minimize the charge time. And my smart regulator needed to be re-programmed from factory values so it wouldn't just go to float charge after 30 min, which was the default.

The diesel underloading is not too bad when you first start charging a discharged battery, but as the battery charges it will always draw less and less current, even if your smart regulator/alternator is programmed to keep the voltage at the bulk charge voltage.

So as the battery approaches full charge and you see the battery charging current decrease, you could activate 12V loads on the boat like refrigeration or watermaker, or if you have an invertor, run a small 120V cabin heater, rice cooker or other other 120V appliance on your boat, to increase alternator and engine loading.

To do all this correctly you need to have a battery current and voltage monitor and if you have an Amp-Hour meter, that's best to quickly approximate your battery state of charge.

[StuM]

Originally Posted by waterman46

The diesel underloading is not too bad when you first start charging a discharged battery, but as the battery charges it will always draw less and less current, even if your smart regulator/alternator is programmed to keep the voltage at the bulk charge voltage.

That depends on your alternator and engine.


Assume an 80 Amp alternator on a 40HP engine (not an unusual combination).


80Amp @ 12V nominal = 960W = 1.3HP. Call it around 2HP to allow for actual output voltage and inefficiencies. That's severe underloading at full output.

[roverhi]

Don't do it with a GM series Yanmar or you'll carbon up the water injection elbow. Best to run at 1500rpm or so in gear. The 2GM in my new to me boat had less than 200 hours on the engine when I bought it. Unfortunately because of the PO's poor health and subsequent death with title issues, the engine was periodically run at idle just to keep the oil circulated for at least 2 years and probably double that. I moved the boat a few miles and a couple of short motors of not more than 5 hours total. Discovered the mixing elbow was blocked as I was attempting to leave on a 400 mile delivery to its new home port.

Other diesels may do fine. Had a friend who worked in logging in Canada. He said they started the diesels in all their equipment in November and didn't shut them off till April. In the sub zero weather the diesels were such a bear to start it was easier to just keep them running, most of the time at idle.

[Wotname]

Originally Posted by jalmberg

While at anchor, I occasionally have to recharge our 400 amp-hour deep cycle battery bank with the diesel engine equipped with a Bosch 14v/90amp alternator. Normally our solar panels do the recharging.

Generally, I run the engine at 1000-1200 rpm.

My questions: is this really bad for the engine? What rpm should I be using?

The engine is a Mercedes OM 616 diesel, used in many light trucks.

Thanks in advance for any advice.

Originally Posted by roverhi

Don't do it with a GM series Yanmar or you'll carbon up the water injection elbow. Best to run at 1500rpm or so in gear. The 2GM in my new to me boat had less than 200 hours on the engine when I bought it. Unfortunately because of the PO's poor health and subsequent death with title issues, the engine was periodically run at idle just to keep the oil circulated for at least 2 years and probably double that. I moved the boat a few miles and a couple of short motors of not more than 5 hours total. Discovered the mixing elbow was blocked as I was attempting to leave on a 400 mile delivery to its new home port.

Other diesels may do fine. Had a friend who worked in logging in Canada. He said they started the diesels in all their equipment in November and didn't shut them off till April. In the sub zero weather the diesels were such a bear to start it was easier to just keep them running, most of the time at idle.

I alway run the engine in gear if battery charging; if at anchor then reverse is best

Keeps some load on the engine.

[FionaJC]

Originally Posted by Wotname

I alway run the engine in gear if battery charging; if at anchor then reverse is best Keeps some load on the engine.

I try not to charge the battery alone, I do run the engine under load forward and reverse occasionally when attached to the pontoon but I worry about putting that HP into my warps for long periods.
Should I worry?

[rgleason]

We have a 3YM30 installed in 2015. On a mooring or anchor we will put the engine in reverse and have to run at 1500 to 1600 rpm the get enough amps/volts to charge in bulk. The alternator is an old Balmar 90-65, with a new stator. The pulley is 2.7" with a ratio of about 1:1.9. We will run the engine for 2 hrs sometimes but will vary the speed by 200 rpm. When shutting down we accelerate to 3000 several times as per yanmar manual. However I don't like doing this, running engine to charge. Bigger solar to top off the batts would be better or a good charger with shore power. At the docks I have run the engine in forward and reverse with good cleats and lines, up to 1800rpm and in shorter periods up to 2400.

[Wotname]

Originally Posted by FionaJC

I try not to charge the battery alone, I do run the engine under load forward and reverse occasionally when attached to the pontoon but I worry about putting that HP into my warps for long periods.
Should I worry?

Only if you have seriously undersized warps!
Or a humungous engine

[waterman46]

Originally Posted by FionaJC

I try not to charge the battery alone, I do run the engine under load forward and reverse occasionally when attached to the pontoon but I worry about putting that HP into my warps for long periods.
Should I worry?

That's a good practice. Don't worry about the docking line warps. Your boat can put only a small amout of strain on them for a relatively short time and its a constant tension, so there is very little wear or chafe. The cyclic tension and relaxation they undergo every day from boat wakes, wind and surge is much worse.