Charging my batteries while under way

[Jeff B]

I just purchased my first sailboat; 78' Hunter 25My outboard has a alternator and the wiring which is terminated at the back of the cockpit. In my limited knowledge, the way I'm charging the batteries now is, while on shore power I plug in a battery charger and insert the cigarette lighter type adapter at the panel and turn the battery switch to "both"I've seen chargers and inverters online and am not sure what/how to do.1. Is this the correct way to charge while on shore power?2. What do I need to do and/or hook up to charge while under outboard power using the leads provided?Thanks in advance for any info or helpJeff B.s/v Midnight Fox

 

[Landsend]

Two ways...

First for shore charging...buy a dedicated marine battery charger, if you have two batteries get one that will charge two battery banks at the same time and hook the leads directly to the battery terminals. This charger can be small 5 to 10 amps will do fine, but make sure it's automatic. That means it will taper down the charge as the batteries become full.Second hook the leads of your outboard to you starter battery terminals. Or you could hook them as follows...the ground terminal from the outboard to the negative side of the batteries and the red wire from the out board to the common terminal of your battery switch. With the output from your outboard connected your battery switch you can direct which battery you decide needs charging. However, ALWAYS make sure that the battery switch isn't in the off position as you will damage the alternator on the outboard. And NEVER switch battery selector positions while the motor is running as this will also damage the alternator.

 

[Bill Roosa]

What is your situation?

Depending on your usage and battery bank size you may not need to charge underway.If your usage of electrical power is low (25' boat I can't imagine it is that high) and your battery bank(s) have sufficient capacity you may only need to recharge while at the dock.The amount of charging you are going to get from an outboard is probably only 5-10 amps so there is not really much production capacity here.What kind of sailing do you do? Worst case it. If you occasionally go on week long trips and use that as your longest time between recharges.What kinds of electrical loads are you running and how often and how long?Example: a 100 AH (Amp-Hours) bank will reliably give you 50 AH of electricity. If all you run is an anchor light drawing 2 amps and running from 1800 to 0600 (12 hours) per day then the math looks like thisStarting capacity 50 AHusage 2 amps X 12 hours = 24 AH per daydays till you use 50 AH is 50/24= 2.1 daysIf you are just going out Friday, staying over night, staying out all day and night Saturday, and then returning to your slip on Sunday you don't need to recharge while under way.If you get 10 amps from the outboard and motor 3 hours that is something less than 30 AH due to charging losses. Lets say 25 AH or basically your usage for the day. You could go on like that till the fuel ran our but you would have to motor 3 hours every day.A better solution than running the motor may be just get a bigger (or another) battery or a solar panel. There are really too many variables to guess to give you a definitive answer.

 

[Jeff B]

Day sailing mostly................

.......with a few overnighters planned. Usage will be VHF, Marine stereo, misc displays, (knot meter, etc.) and a few basic 60 watt lamps and a color plotter, (soon I hope).I have one large battery, (car sized) under the cockpit and another smaller one in storage next to battery switch panel. Sorry to sound so uneducated about types. So, you think that 2 standard sized batteries with full charges would give me enough juice for a weekender. Its sound as if the charging off the outboard is very minimal and will only be relevant if under outboard for a extended period of time.In addition, while I have the marine charger plugged in and am charging at the dock, do i switch the selector on the battery switch to both? Does that open the connection to charge both simultaneously?Thanks,Jeff

 

[Fred Ficarra]

Jeff, you've met several of our resident experts

already. But be sure to do this; get a book about the subject and study it.We can recommend several. These forums really aren't designed to take the reader from 'novice' to 'expert', in a matter of hours. We're at our best with specific questions or procedures. Welcome to sailing!

 

[Bill Roosa]

I'd say no

With what you have told me I (the great Roosack)(letter to the forehead please) would say you have the following:I'm going to SWAG that a normal day sailing day is 14 hoursVHF with a 10%/90% transmit/receive ratio that draws 3 amps transmitting and 1 amp receiving or (3 X 0.1) + (1 X 0.9) = 1.2 amps "average" draw or 1.2 AH each hour of use.Marine Stereo running 14 hours/day and drawing 1.5 amps average or 1.5 AH each hour of use.Nav instruments drawing a total of 1 amp and running 14 hours a day or 1 AH each hour of use.60 watt lamps????? That is a really big lamp for a small boat but OK 60 watts / 12.6 volts = 4.8 amps draw or 4.8 AH each hour of use. You will probably not be leaving the nights on all night so I'll guess at 4 hours over all use each day.Color Plotter's drawaround 3 amps or 3 AH each hour of use. I imagine you will only use it 12 hours each daySumming up we get VHF + stereo + instruments + lights + plotter(1.2 A X 14 H) + (1.5 AH X 14 H) + (1.0 A X 14 H) + ( 4.8 A X 4 H) + (3 A X 12 H)16.8 AH + 21.0 AH + 14 AH + 36 AH = 99.8 AH every 14 hour day of sailing.That is the consumption side of the house, the storage side is a car sized batt of maybe 50 AH max capacity and a tractor batt of 25 AH max capacity.Since you don't want to fry the batts we only take 50% of the max or 25 and 12.5 AH for a total of 37.5 AH. That means you will be able to take 37.5 AH out of them before you should recharge.The break down point is when you consume 37.5 AH at a 99.8 AH/day rate or37.5 AH /99.8 AH/day = 0.375 days or 9 hours.When you add a under way charging system you have to go to a per hour consumption scheme to do the calculations. Using the same numbers above but for only 1 hour you get: 99.8 AH / 14 Hours = 7.1 Amps consumption continuous. IF you are getting more than 7.1 amps from somewhere then as long as that source is operating you can forget the batteries. The source will supply the current for the boat consumption. If you go below 7.1 then the difference in amps is the amount the batteries have to supply. Since this is an "hourly" rate is is also the AH rateSo a 5 amp alternator will be "loosing ground" at the rate of 7.1-5.0=2.1 AH each hour the engine is on.Since you want to "sail" for 14 hours and only have 37.5 AH to do it on you have to produce 99.8 AH/14 hours - 37.5 AH storage = 62.3 AH every 14 hours. An alternator putting out 5 amps will have to run 62.3/5=12.5 hours to do that.Another way to look at it is what amps do I have to produce for some period to "stay afloat" electricaly? If you only wanted to motor for 2 hours then you would need to produce 62.3 AH in 2 hours or 62.3/2= 31.2 amps continous for the entire 2 hours.As you can see this gets envolved even for the simpelest situations. The math is not hard but it is teidous which is why I made a spread sheet that does it for me. Then you can play with usage schedules - storage - production schedules without going too crazy. email me at roosaw@verizon.net for a copy.Roosack says buy a bigger battery bank. Like 200 AH. Put them low in the boat and enjoy a stiffer boat.You are correct when you select "Both" to charge the batteries. No doubt the cig lighter is wired through the selector switch so you can select which battery runs the lighter and which batteries the lighter charges.

 

[Fred Ficarra]

Whew!

Ya just gotta love Bill!

 

[John Nantz]

Bill - Your're AWSOME !

I have to agree with Fred. That's a really helpful write-up!

 

[Jeff B]

Great info..

Wow, that is some awesome info by all. Thank You.Now I just have to read it all over a few times to let it all soak in. Jeff

 

[Bill Roosa]

The spreadsheet is free

But not ready for prime time. I'm was geeky systems engineer in another life so I can use it as I understand the math behind it. If you have a basic understanding of how to calculate the average AH usage for a device like a VHF radio or autopilot AND understand how to conduct an analysis based on a scenario (at sea, at anchor, in a storm worst case.....) then you should not have much trouble using it. It comes with an instructions.If you can't spell AH then you are going to need my help. Help is available for free. Just be aware, you gets what yous pay for.I built the thing for two reasons. 1) I wanted to determine what combination of alternator-solar-wind-genset was the most cost effective and 2) I wanted to see if changing when I consumed-produced electricity could be managed so as to reduce the generating requirements.What I found for my set up (pretty typical IMHO) is that except for that snug anchorage that is sheltered from the wind a wind generator is the most bang for the buck IF you consider turning on the engine a bad thing. I also found that the time you consume and produce your electricity can lower your requirements on the production side.

 

[Bill Roosa]

Hay Rick!!

I'm in the market for one of those gals you have in your post picture. I assume that one is taken, does she have a sister?

 

[Landsend]

Now that you have more info than you need...

Here's a bit more...If you have your battery switch in the "both" position, the least charged battery will charge first until it reaches the potential of the other battery then they will charge at almost the same rate.I never asked...Is your outboard an electric start? Also you could change some of your cabin lights and running lights to led's which use a lot less current?Good luck.

 

[Rick9619]

Bill, I would be suprised based on...

your keyword "engineer", that your spreadsheet isnt a great tool for us. Im an aero "science" major and if you read my bio, you'll see im more comfortable around the cockpit of our passion. I did some simple math and then went caveman. Just wired up four 6 volters in parallel/series and have 440 amp hours. I put a digital volt monitor on the group, so when the voltage drops below 12.56 roughly, I fire up the 100 amp balmar and commence rejuicing them. Our typical draw on the hook or can at night during extended cocktail hours is 27 amps, and that includes the 600 watt amp . I believe your comment about the wind generator but just dont find that pleasing to the eye on our 336 that only does a "crossing" to Catalina, or the Channel Islands. Otherwise she is just cruising around the bay. I was thinking about a solar panel though.And that one up the mast is one of a kind. She has no fear of heights or a squall at night. She would rather have a great boat than a big house. Im lucky. I found her skiing a black diamond run at Squaw Valley. Go figure.Cheers

 

[Bill Roosa]

Story of my life

All the good ones are taken.I'm hip to your wind generators are an eye-sore issue. The truth is an alternator is the cheapest by far means of meeting your electrical needs. But then you are tied to running the engine once a day or so. Different strokes for different folks.