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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel > Charging batteries with engine while sailing
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Thread: Charging batteries with engine while sailing Reply to Thread
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Topic Review (Newest First)
12-06-2012 02:01 AM
chef2sail
Re: Charging batteries with engine while sailing

73Mmorgan,

One of the most important tools is a good battery, charge meter whoich will give you the info you are talking about. The Victron meter is a rwaosnably priced starter here.

BMV-600S and BMV-602S - Victron Energy
12-06-2012 12:20 AM
hellosailor
Re: Charging batteries with engine while sailing

Simplify? Sure, buy a battery management system that tracks and records the number of amphours or watthours that go in or out of the batteries.

Or use your ammeter, note the amperage that is going into the batteries 9assuming they're charging) every 5 minutes over the course of any hour. Then average it out. The charging rate should tail off as the alternator heats up, the batteries heat up, the charge comes up closer to full.
12-05-2012 11:57 PM
73Morgan
Re: Charging batteries with engine while sailing

Quote:
Originally Posted by hellosailor View Post
"Also, when you know the Amp Hour of the battery and the Amp charge capacity of your alternator how do you calculate how much charge you are getting per hour. "
You can calculate what you MIGHT be getting but you need an ammeter or battery monitor system to actually MEASURE what you are getting.
The difference between teh two will be based on the battery's acceptance rate, which will vary based on the condition of the battery, temperature, etc. as well as how much power the alternator is putting out, and typically they may cut back by 1/4-1/3 of capacity once they have been running really hot. Then there's what the regulator is programmed to do.
So while you can estimate the charge rate you might be getting, you need an ammeter to actually measure it to be sure. (Which also will tell you if there are problems, like battery sulphating, that you haven't been aware of.)
I do have an amp meter as part of the Inverter/charging system which displays the charge rate when on shore power or generator. That is part of what I am trying to get a better understanding of. I know there a lot of variables but is ther a way to simplify this stuf. Or, as I am not doing much sailing at this time being in the NE region, I wouldent even mind a complicated formula.
12-05-2012 11:35 PM
hellosailor
Re: Charging batteries with engine while sailing

"Also, when you know the Amp Hour of the battery and the Amp charge capacity of your alternator how do you calculate how much charge you are getting per hour. "
You can calculate what you MIGHT be getting but you need an ammeter or battery monitor system to actually MEASURE what you are getting.
The difference between teh two will be based on the battery's acceptance rate, which will vary based on the condition of the battery, temperature, etc. as well as how much power the alternator is putting out, and typically they may cut back by 1/4-1/3 of capacity once they have been running really hot. Then there's what the regulator is programmed to do.
So while you can estimate the charge rate you might be getting, you need an ammeter to actually measure it to be sure. (Which also will tell you if there are problems, like battery sulphating, that you haven't been aware of.)
12-05-2012 11:28 PM
73Morgan
Re: Charging batteries with engine while sailing

This is why I love this site, there is no limit on how much you can learn about any subject. Great posts. Very informative, great tips. Here is my question at this point, it may be remedial, but before I can maintain the batteries I need to grasp some fundamentals. How do you know when your battery has 0% charge, is that when it is totally dead or is that at some other point? So, when % charge is discussed what is the starting point? Also, when you know the Amp Hour of the battery and the Amp charge capacity of your alternator how do you calculate how much charge you are getting per hour.
12-05-2012 01:31 PM
hellosailor
Re: Charging batteries with engine while sailing

Brian-
" Yanmar requires that if sailing with the engine OFF (not running) the transmission shifter must be in the neutral position or internal damage to the gear or sail-drive will result. "
This is one of those memos that has to be kept in context, because Yanmar's statement is extremely limited in what it addresses. They are ONLY discussing what to do if you are sailing with the engine off. Their statement makes no comment on what you should do if you are sailing with the engine on for charging (not propulsion) purposes. The concept of sailing with the engine on but not in gear may seem odd--but that's normal for racers who are allowed to charge their batteries but not use the engine for propulsion.

I was going to ask why folks are referring to the gear position on Yanmar's as if they all used the same Yanmar transmission, but as you brought up, there ARE different transmissions and IIRC the Hurth lives in a world of it's own wrt fluids and use. I'm sure the instructions for what is proper have to vary with the different transmissions Yanmar must have used over the years.

Ditto with alternators, every installation will be different and the only thing I'd bet on is that most "stock" installations are not as efficient as the ones where folks have paid a professional to install something better. Some time ago we had to (had to) replace an oddball alternator that apparently wasn't stock but had been installed when the PO had to put in someplace for a replacement and that was what someone had on hand. After looking at the options we went with a modern (ha, 1970's design, but newer than the oddball Motorola with a Marchal regulator) Delcotron and a custom alternator pulley, sized to match up the rpm ranges. Literally cut the charging time in half, simply because that alternator had a much wider rpm range and that allowed for a much better pulley match. Offhand, I think we sized it up for 80-90% output at idle speed and still only hit about 2/3 of the maximum continuous speed rating under wide open throttle.

But just to look at it, without numbers and specs and models? There's no telling wtf is going on in the engine room.

Of course the big trick today is asking ANY vendor for technical information, and getting them to respond ON POINT instead of with some boilerplate about liability and authorized persons only. No doubt Yanmar will fire the distributor who leaked that memo. (sigh)
12-05-2012 12:54 PM
chef2sail
Re: Charging batteries with engine while sailing

Every brand of alternator has a different charging curve vs rpm so there is no steadfast rule here. One of the reasons when I upgraded my system I went with Electromaxx ( per Mainesails recommendation) over Balmar was the charging curve of the Electromaxx in the lower RPM curve as well as the cooling properties of the Electromaxx due to their being hand wound vs Balmar machine wound..

http://www.electromaax.com/wp-conten...s-brochure.pdf

http://www.google.com/url?sa=t&rct=j...Myy2P2UpTG5o8A
12-05-2012 11:53 AM
PCP
Re: Charging batteries with engine while sailing

Quote:
Originally Posted by hellosailor View Post
...
Then there's the idea of running the engine at low speed to charge the batteries. WRONG! Let's say the engine has an idle speed around 800 rpm and a cruising speed around 2600 rpm. If the alternator was properly matched up (pulley size & output curve) then the alternator will not be putting out signficant power at low rpms. At 1000 rpm it may be putting out 20-25 of the rated power, at 2000 spm it may be closer to 85% of the rated power. (Numbers drawn from a hat but good enough for examples.)

You need to know how the system has been designed, or have an ammeter in circuit to see what the alternator is putting out, because they are usually designed to put out something near rated power at something near typical cruising rpm, and all you are doing at lower rpm is wasting fuel.

Part of this is cheap and sloppy design (who notices?) and part of this is money, because an alternator that can put out full power at low rpms costs more. And an alternator that can put out full power at low rpms while also not burning out at sustained high rpms (i.e. trying to claw off a lee shore for eight hours) is more expensive again.
I had done that in my new set up and the performance of the new alternator and new setup was measured with different RPM. I have not here the list but I found out that probably the most efficient relation between charging and fuel consumption was between 1350 and 1500RPM and that about 2000/2150RPM the max charge was obtained. The cruising speed on my boat is 2400/2600RPM and the engine max RPM are 3600. Of course all systems are different but this can give a general idea. The alternator has 120A and is not a particularly good one but all the rest is maximized, I mean I have a good regulator and a bank charge distributor.

Regards

Paulo
12-05-2012 11:33 AM
PCP
Re: .

Quote:
Originally Posted by Maine Sail View Post
Wow, this tread is a prime example of why people like me replace sooooo many batteries on boats.

10 minutes does squat for charging a house bank of batteries.... This is simple math & physics.. Ten minutes run time won't even burn off start up condensation in the motor. Here in the cold waters of Maine 10 minutes won't even bring most diesels up to operating temp.

Flooded batteries take 10+ hours to charge to full even with a large charge source because of battery acceptance rates as the bank hits absorption voltage.

A 400Ah bank at 50% state of charge needs roughly 240Ah's returned to it to be full due to charge inefficiency.

With a 100A alternator it will really put out about 80A so roughly 1.3Ah per minute at 80A. Easy math shows that 1.3Ah X 10 minutes is about 13.3Ah returned to the battery or just 5.5% of the energy need to charge this bank to full....

5.5% is a long way from a "decent charge", in 10 minutes....10 minutes of run with a 100A alt on a 400Ah bank barely gets you from 50% SOC to 53% SOC when charge inefficiencies are taken into account..

Also keep in mind that just because a "charger" has gone through bulk, absorption and is into float in 2.5 - 3 hours also means little other than the charger is poorly programmed for the bank you are charging. When a charger comes out of bulk quickly all it usually means is that your batteries are already toast and sulfated enough to build a surface charge.
,,,

When charging via alternator it is wishful thinking that you'll ever get anywhere close to full unless you spend 10+ hours running the motor like a trawler would.

This is why experienced cruisers use the "cruisers rule" and cycle the bank between 50% SOC and 80-85% SOC. Trying to charge much above 85% SOC is simply a waste of fuel due to declining battery acceptance...

..
To complete that good explanation one question: Assuming (like you did) a 100A alternator putting out about 80A with a 400Ah bank how much time would the engine have to be running to go from 50% to 80% and 85% charge on the Bank?

About one hour and a half for a 80% charge? And if so it is better to let it fall to 50% before charging an hour and a half or just let it go to 65% and charge it for 45 minutes? What is more efficient regarding charging and what is better for the battery life?

Regards

Paulo
12-05-2012 04:59 AM
chef2sail
Re: Charging batteries with engine while sailing

I apoligize for my mistake...I think the Kanzaki transmissions are ok to run while in neutral when the engine is not running. Its the Hurth zr which is not.

I have always sailed with it in reverse because i dont like it spinning or the rumbling noise and worried about the tyranmission being properly lubed.. Apparently I should only sail with it in neutral.

Live and learn
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