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  #1  
Old 07-06-2008
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yet another battery question

Hey everyone,

I've been following battery based threads here for a while as I worked on my own challenge.

I've added a fishfinder and GPS (Garmin 440) to my 25' O'day and the fishfinder has a voltmeter built into it so I'm able to monitor my system's charge for the first time.

After a few sails this year and a few electric starts of my outboard my battery quickly dropped from 12.8v to 12.2. I ran my motor for a good thirty minutes on a light wind day to charge it up but only saw it gradually raise to 12.4/12.5.

I purchased a smart-charger 3 stage charger based on forum recommendations and it safely and quickly charged my 1 year old class 24 (70 amp/hour) multi-purpose wet-cell battery up to full charge again.

This weekend we went out and I monitored the battery as one start of the 15 hp Evinrude O/B motor dropped the charge again from 12.8v to 12.5.

Is that normal? Is my battery toast? Under-rated for the job?

I am planning my first week long trip on the boat and I feel like I should get this worked out prior to departure... my manual pull-start died recently and the electric start would be my only route during this trip. (writing this has prompted me to call to get the pull-start repaired prior to departure as well... better safe than sorry)

Anyway, I was planning on adding a second battery and switch this week as well, but I'm not sure if I should ditch this battery entirely and go with two specific types - starter/house, instead of this "multi-purpose" that seems to have about three engine starts in it.


Thanks, as always these forums and their archives are my main and most reliable source of education.

-Mike
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Old 07-06-2008
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Mike, Small outboard motors really don't have much in the way of alternators on them. I did a quick search for "15 HP Evinrude specifications" and "15 HP Evinrude alternator output" and, near as I can tell, those motors came with either 3A or 6A alternators. Either way: Not much.

This thread: Evinrude Charging Current - Moderated Discussion Areas on another site, contains a post that tells how you may be able to find out what alternator your motor has.

According to the user's manual for your Garmin 440: It can draw up to 15W max. That'd be 1.25A at 12VDC - either about 1/2 or 1/4 of what your alternator is capable of putting out on a good day. If you're running any other electronics, such as radio, depth finder or knotmeter, that would even-further deplete charging current available for the battery.

Jim
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Charging

Consider taking a small portable generator so you can run your smart charger if needed while away from sure power.
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Old 07-06-2008
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Jim has it exactly right. If you have the larger 6amp alternator you are only supplying 3 amphours in a half hour of run time and your Garmin will delpete that in one hour. Then you have starting loads and perhaps lights and other instruments to further deplete the battery. You need a second house battery of deep cycle type, a charging system and a battery switch. You can keep the current battery in place until it gives up the ghost but you need to fully charge it and perhaps do an EQ on it to restore maximum performance.
Get a three stage charger that is rated around 20% of your house battery's amp hour rating. (i.e. 20 amp charger for a 100ah house battery (group 30).
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Nice thanks guys.

I was at Sam's Club today so I snagged a marine starting battery ($50.00). I'm going to make the current multi-purpose the house battery until it dies. I'm also going to pull it and fully charge it again. I'll go with the Blue Sea 2nd battery kit that ArtbyJody posted installation information on and I'll be at two batteries with the switch and charger controller. My smart charger from WM is a 15/10/2 so it should suffice for these group 24 batteries.

I'm also going to get my pull starter fixed as it seems starting load is my real drainer... and I don't mind pull starting at all. I hope it's not a pricey repair but I think it's enough of a pain that I won't attempt it myself.

Sounds like maybe next year it's some type of passive charging system like solar or wind, but for those price-tags I might just save the money in the "next boat fund". I love this 32 year old 25 foot boat but I'm going to outgrow it in the next few years.

Appreciate the responses, I'll post follow-ups if I learn more along the way.

-M
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Last edited by Birdface; 07-06-2008 at 05:18 PM.
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Old 07-06-2008
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Also, the 12.8 Volts you're seeing is surface charge on the plates, and not the real voltage of the plates. If you would leave the batteries sitting for a day with no load and no charge on them, you'd see that the actual voltage of the battery, when fully charged, was more like 12.6-12.7 volts, and that the drop isn't a great as you're thinking.

BTW, SEMIJim is being optimistic about the 3 amp-hours supplied by the alternator. If your batteries are nearly fully charged, they may not even accept that much charging from the alternator, as the charge acceptance rate drops as the batteries approach being fully charged. If the batteries were at 50% charge, they'd probably take in the 3 amp hours he mentions, but if you're just leaving the dock and they've been charged the whole time and at full..... you're probably effectively getting less than an amp-hour or two from the alternator during half-hour of motoring.
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Okay,

So part of this is me just relaxing and letting the batteries cycle to 50% charge and then observing recharge via alternator.

Thanks guys.

Now isolating my starting load to this starting battery I have a feeling my issues will be a thing of the past.

-M
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Yup...as long as you just charge your new house bank from the plug in charger, your outboard should be able to keep your starting battery in good shape. Good luck with it all!
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I went out with the PO today just to show him my three years of refurb. (He was all smiles)

During the trip we flooded the outboard, it happens often to this 15HP Evinrude.

Regardless, it took a good 10-20 attempts to clear and start and I ended up at 12.4v after the event. (down from 12.6)

I decided to pull the older house battery (which took that beating) and run it through a full 3 stage charge and equalization.

Even though I'm adding the switch and starting battery I'll update this post to let you know how the older house held out for the trip.

I'll be off forums for a while, leaving for the first leg of our trip on Saturday with high tide. Hope you guys all enjoy the sailing for the next week and a half, I'll send an email update from mid-trip if I find internet.

-Mike
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