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Charging Batteries

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Captmorgan
Navigator

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USA
220 Posts

Initially Posted - 07/22/2019 : 20:32:02

I have a tohatsu 9.8 4 stroke outboard. Yesterday my batteries died due to no charging. I got back in after a great sail but have to fix this.

Now, I know I probably need new ones its been 3 yrs. Whats the best way. Can they charge from an outboard set up with some additional components,or,do you have to purchsse a charger that works when your plugged in at dock. How about solar charging?

Let me know how you do it. Thanks

"The Gal-Way" 1985 SR/SK Barnegat Bay, NJ

Enjoy Sailing =) Be Safe

Happy Sailing - John

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SKS
Navigator

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USA
161 Posts

Response Posted - 07/22/2019 : 21:00:18

I take it the outboard doesn't charge the batteries ?
If you have access to shore power, charge up the batteries while you're at the dock.
You can buy a charger that will charge two batteries at the same time.
I have one on my boat.
I assume they're deep cycle marine batteries.
Nevertheless, keeping the batteries charged will also help them last longer.

"Lady E" 1986 Catalina 25: Fin Keel, Standard Rig, Inboard M12 Diesel, Sail No. 5339
Sailing out of Norwalk Cove Marina, Connecticut

Edited by - SKS on 07/22/2019 21:01:27

Lee Panza
Captain

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USA
465 Posts

Response Posted - 07/22/2019 : 22:22:11

quote:
Originally posted by Captmorgan

...my batteries died due to no charging.

That outboard has an alternator that can help replace the loss due to starting as well as any other electrical use (and self-discharge), but you need to run it much longer than you might think in order to do so. Or else you need an additional source of charging power.

The maximum output from that alternator is 6 amps. Normally you can expect less than that, considering the various inefficiencies in the system, and even a little less at idle. Let's figure 5A as a working number (even that could be high). The amount of effective recharging is under 100% of the input power: that means you have even less than 5A actually going into your batteries.

Battery capacity is figured in amp-hours (AH): so-many amperes for so-many hours (multiply one by the other). A lead-acid battery can survive a lot more than 3 years if it is kept well-charged, but its life expectancy drops radically if it is deeply discharged and/or not fully recharged. Prevailing recommendations seem to be to not discharge more than 50% of capacity, and then to fully recharge. A pair (you used the plural) of Group 27 batteries (for example) might have a capacity (at a standardized discharge duration rate of 20 hours) of 110 x 2 = 220 AH. Even 50% of that capacity is 110 AH, which would require running that 5A alternator for 22 continuous hours to bring those batteries back from 50% to 100% (this is an over-simplification, but it illustrates that your outboard motor probably wasn't effectively recharging your batteries, even though you might have thought it was).

In order to keep your batteries fully charged you need an additional source of electrons.

Some people keep an AC charger running when they are hooked-up to dock power. Others use a solar panel (even just a small 5A panel can provide a lot of total power when it runs every day, and even on fairly cloudy days they can put out a surprisingly high amount of their rated power).

Other than providing enough power, perhaps a bigger concern is providing too much power. A continuous supply of recharging can actually do more harm than good by over-charging. This causes the batteries to "boil-off" the water in the electrolyte, causing the levels in the battery cells to drop. A "smart" battery charger is supposed to minimize this, and a controller on a solar installation is supposed to do the same, but it's important to periodically check the electrolyte levels anyway and keep them topped-off by adding distilled water.

A good hydrometer would be worth many times its cost in postponing battery replacement by allowing you to monitor your battery condition. It will allow you to maintain your batteries over time, and it can help you to know when replacement is becoming necessary if your batteries are not coming back to full-charge.

You can extend the life of your new batteries by providing an additional source of charging power and by regularly checking their condition (once a lead-acid battery is over-discharged it will never come fully back to life). It can get a lot more complicated than you probably would like, but the bottom line is almost any source will help. And if you regularly check your batteries you can probably avoid an embarrassing situation like the other day for may years to come.

There's an enormous amount of information available online about maintaining healthy batteries, and it's likely that you aren't interested in doing much research. But by regularly checking your batteries, and with minimal routine maintenance, you can extend their life greatly.

I consider stored electrical power to be about as important as fuel and fresh water, not only to be able to get that motor started in an emergency but to be able to use the radio to call for help. It's easy to take battery power for granted until it's not there when you need it. Your experience the other day should be a wake-up call.

Of course, it would also be advisable to check whether there's an electrical drain that you're not aware of.

The trouble with a destination - any destination, really - is that it interrupts The Journey.

Lee Panza
SR/SK #2134
San Francisco Bay
(Brisbane, CA)

OLarryR
Master Marine Consultant

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USA
3367 Posts

Response Posted - 07/23/2019 : 14:11:12

A solar panel 14"x20", 20 watts would be sufficient to keep 2 batteries charged utilizing light loads weekly such as fish finder and nav lights for a few hours, twice a week. A 20"x20", 30 watt would provide add load use such as cabin lights and a boom box once, maybe twice a week. You can calculate load use and figure on at least 4-5 days of 6 hour/day solar charging at 60-70% max amp rating of the panel for a conservative max load use. For real world charging rate - My 20 watt panel, ideally puts out 1.2 amps, that is when new and perfect (and full) sun orientation. But, on the average, my panels provide .6-.8 amps during mid-day all sun and that has been the story since....2006. But it charges for longer than 6 hours a day, just that it begins charging around .2 amps and gradually increases until sun is overhead and then decreases in charging rate....so, just figure a minimum of 6 hrs/day for 4-5 days a week at 60-70% max charging rate for an estimate. Your charging will probably be greater but also depends on how many average full sun verses overcast days you have in your region.

Flooded batteries each discharge about .4 amps/day in the summer and .25amps/day in the winter. AGMs and Gel batteries discharge less per day. Use that in your weekly load calcs to determine appropriate solar panel capacity. A 20 or 30 watt panel would also require a controller to ensure you do not cook the batteries when batteries are fully charged. My website has photos and details of the install. Below is link to the solar panel info.

http://catalina25.homestead.com/SolarVentPanel.html

Larry
'89 Robin's Nest#5820, Potomac River/Quantico, Va
http://catalina25.homestead.com/olarryr.html

Edited by - OLarryR on 07/23/2019 14:25:00

Captmorgan
Navigator

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USA
220 Posts

Response Posted - 07/24/2019 : 20:56:29

Awesome thanks for the help