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Old 03-16-2015, 08:42 AM   #1
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Generator Battery

My start, house and bow thruster batteries are charged by a xantrex tc 40 multistage battery charger. My generator battery is only charged when the generator is running. A friend of mine has suggested that I run a 2 AWG wire from my house battery to a perko #9601 battery switch and than to my generator battery. I would only have it turned on when plugged into shore power. All comments are welcomed. Thank you
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Old 03-16-2015, 09:31 AM   #2
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A $65 battery combiner from Yandina will do the same thing automatically- Combiner 100 Sheet and will also combine your engine's alternator output to the genset starting battery when it is running.

David
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Old 03-16-2015, 10:08 AM   #3
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You could run the genset more often, good for both the genset and the battery.

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Old 03-16-2015, 10:20 AM   #4
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96...

Does your gen batty have an on/off switch?

If so - you might consider replacing it w/ a off-1-2-all switch. and doing the same cross connection you mentioned. I have a similar situation and have the new switch to be installed this spring (same mtg /bolt holes and needs one jumper to be added. This will allow a great deal of manually selected flexibility - charge gen batty from alt while running, from batty charger, also allows using start / house batty to start gen or gen batty to start main engine.

David's suggestion above will do the charging automatically.

FYI - if you choose to go the combiner route...
There is a Reference Mat'l thread in this sub-forum Article: Battery Isolators & Combiners that includes a Link To The Sailing Today Article This outlines the many different options for combiners along w/ some +/-.
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Old 03-16-2015, 10:28 AM   #5
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No need to tie them together. Do you run the gen at least once per month? When the gen bat is near the end of its life, it will let you will know by cranking slower and just replace it.
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Old 03-16-2015, 11:23 AM   #6
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2 boats and 20 plus years and I have never had a shore battery charger hooked up to the gen battery. It has always been fine like that.
If I ever have a problem I have a set of jumper cables aboard.
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Old 03-16-2015, 11:26 AM   #7
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I just tied my gennie to the main engine start batt. No gennie batt at all. Works fine.
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Old 03-16-2015, 12:01 PM   #8
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Originally Posted by jleonard View Post
2 boats and 20 plus years and I have never had a shore battery charger hooked up to the gen battery. It has always been fine like that.
If I ever have a problem I have a set of jumper cables aboard.
Same here. KISS.
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Old 03-16-2015, 01:06 PM   #9
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2 boats and 20 plus years and I have never had a shore battery charger hooked up to the gen battery. It has always been fine like that.
Some marine gensets (NextGen and others) do not have a DC alternator to charge its starting battery. They rely on the shore power charger to keep the genset battery charged while they are running. And since they often use a 12V fuel pump the battery will continue to run down if not charged externally.

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Old 03-16-2015, 01:15 PM   #10
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Originally Posted by djmarchand View Post
Some marine gensets (NextGen and others) do not have a DC alternator to charge its starting battery. They rely on the shore power charger to keep the genset battery charged while they are running. And since they often use a 12V fuel pump the battery will continue to run down if not charged externally.

David
That is true on the little ones. And some of the larger gens have very crude voltage control on their charging systems, which are hard on batts. I've seen them run steady state at 15v and batt bubbling away. I often disconnect those provided the batt is connected to the boat charger. Onan MDKx, MDJx, NL 5-6kw, etc. Similar to motorcycle chargers. Gens that have car alternators generally have ok volt control, those I leave alone.

If in doubt, let gen run for a few hours then put a DVM on the terminals. Above 14.2 and batt is not happy long term.
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Old 03-16-2015, 06:50 PM   #11
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Thank you all for your comments. I asked this because we keep it in North Carolina for the winter and when we go back north for a few weeks it just nice to know that the generator battery is getting a charge when we are away. I do run the generator often when we are down here. I also am getting this for free and its easy.
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Old 03-16-2015, 07:46 PM   #12
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I would not do away with a genset battery, your genset is back up if the main engine start batt dies.
My solution was a small solar panel, connected via a regulator, to service the genset batt. 20-25 watts is enough to maintain the batt. Batteries kept full should not sulphate, last longer, and start better.
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Old 03-16-2015, 07:54 PM   #13
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I would not do away with a genset battery, your genset is back up if the main engine start batt dies.
My solution was a small solar panel, connected via a regulator, to service the genset batt. 20-25 watts is enough to maintain the batt. Batteries kept full should not sulphate, last longer, and start better.
On my rig, with the gen and main sharing a batt, my backup is my house batt that can be put on line with a switch. My second backup is to manually carry my thruster batt from bow back to the ER and hook it up to genny, then start it and charge the rest.

So each boat's DC system has to be analyzed as a system. I'm confident in mine, but gen and main sharing is not always a good idea. Gots to look at the system in total.

It's a good mental exercise to look at the system and go item one by one and ask what if this dies... What will I do to get a start or keep running.

And as someone posted above, carrying a set of jumper cables is not a bad idea.
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Old 03-17-2015, 12:29 PM   #14
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And as someone posted above, carrying a set of jumper cables is not a bad idea.
And I have 25 foot long cables! Ski, you wouldn't have to carry your battery!
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Old 03-17-2015, 12:53 PM   #15
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I would leave it like it is as long as you understand how every thing works and know what your options/backups are.
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Old 03-17-2015, 02:56 PM   #16
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I would keep the system as it is. Depending on what type of battery and the temperature it is normally stored at, it will keep a high enough charge to start you generator anywhere from 2 to 8 months. Lead acid batteries @ 75 degrees F, lose about 5%/month. As the temperature goes up the time gets shorter though. Optima say their batteries can sit for 8-12 months but suggest testing monthly and should be recharged at 12.4 VDC.
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Old 03-17-2015, 03:00 PM   #17
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I would keep the system as it is. Depending on what type of battery and the temperature it is normally stored at, it will keep a high enough charge to start you generator anywhere from 2 to 8 months. Lead acid batteries @ 75 degrees F, lose about 5%/month. As the temperature goes up the time gets shorter though. Optima say their batteries can sit for 8-12 months but suggest testing monthly and should be recharged at 12.4 VDC.
I leave my gen battery over the winter in the boat. The last time it gets charged is when I run fresh water to flush it before getting hauled out.
When I start the gen in the spring the battery has plenty to start it up.
When the battery is 5 (or 6) years old it gets replaced.
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