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  #21  
Old 10-01-2012
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Re: AGM Battery Upgrade and Charger

Paulo,

I'm still learning, too :-)

Reaching a full charge monthly would probably be OK, particularly as we're coming on to winter and cool temperatures.

In hot temperatures, it would be better to do it more frequently.

AGMs have a low self-discharge rate (I think Mastervolt claims about 3% per month) so can be left without charging current far longer than flooded batteries, but they DO need to be fully charged at reasonably short intervals.

In really cold weather they will self-discharge much less than in hot weather.

Bill
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  #22  
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Re: AGM Battery Upgrade and Charger

When on the hard, I have t-handles that fully disconnect the various battery banks, so there wouldn't be even a parasitic load. Both my Gels and AGMs will stay nearly at full charge for well over a month, and then lose very little. I usually plug in about every 6 weeks over the winter and top off and would be very comfortable going 2 months, if necessary.

My AGM genset start batt wasn't charged at all last winter. I thought I was going to swap it out as it was acting up. In the spring, I found a corroded connection. I put it back, charged it up and it was fine all season. It froze on the boat and wasn't charged for 5 months. Although, it was probably at full charge when disconnected last Fall.
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  #23  
Old 10-01-2012
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Re: AGM Battery Upgrade and Charger

Thanks guys.

That´s what I thought. I had said already to the guy on the shipyard that he doesn't need to charge the batteries every week, as he had propose to me, but that I would prefer a longer charging each month, but it is good to be sure

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Paulo
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  #24  
Old 10-02-2012
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Re: AGM Battery Upgrade and Charger

David,

Do not depend on your alternator running for 20 minutes to be anywhere near sufficient to charge you batteries. Even a 100 amp Electramaxx alternator at 70 degress will put only 80 amps per hour running our engine at normal cruising rpm ( 2700 ). So if it runs at that for 20 minutes I can only expect to put 27 amps back into the bank.

It is important to fingure out what you battery diet is for a day. On Haleakula chartplotter ( 3 amp/ hr), refrigeration 4 amp/ hr, lights (LED -1 amp/ hr, VHF 2 amps in standby ( 5 in transmition), radar 3 amps and other instruments. . Right there is 10-15 amps per hour and that doesnt include pumps etc. For a 6 hour sail thats conservatively 60 amps. Thats what registers on my Victron on an average when underway. At rest in anchorage usage is closer to 4-6 amps). Our diet per day we have calculated and measured is between 80 and 100 amps.

We fall into that categopry of being able to charge our 6- 6 volt ADM Lifeline house bank up to capacity of 720 ah because we usually only are out weekends and have a 40 amp Mastervolt 3 step charger at the dock. In addition our 100 samp alternater barley meets the requirements of the 20% of house bank rule. Alternators differ also in how much they generate in terms of amps vs the rpms of the engine. One reason we chose the electromaxx was its efficiency at lower rpms. Solar panels are in our future to help us when we cruiser for weeks at a time.

As Maine/ Btrays have mentioned AGM are not a choice for everyone and your whole system should be designed around them ( charging alternator, solar, shore power) to insure you can keep them as full as possible to increase their life.

Dave
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  #25  
Old 10-04-2012
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Re: AGM Battery Upgrade and Charger

Quote:
Originally Posted by chucklesR View Post
David,
Are you on the Magothy side of SP, or the Severn side?

I'm on the Magothy, right at the #2 / #16 and #MR triangle (where the river splits to Cockley, Old Man and Magothy river)
I'm on the Severn Side - north Round Bay.
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Re: AGM Battery Upgrade and Charger

So far this is what I have ... pretty low draw I think:

Endless Breeze 12v Fan 3.0
LED interior lights 0.5
Nav LED running lights forward 0.5
Stereo 1.0
Raymarine x-70 Autopilot 5.0
Garmin navigation GPSMAP 500series 1.0
Cockpit VHF Standby 1.0
Depthmeter 1.0
Speedometer 1.0

Total so far - 14.0 ah
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Re: AGM Battery Upgrade and Charger

No fridge?
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  #28  
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Re: AGM Battery Upgrade and Charger

Nope. Just the original icebox circa 1979.
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  #29  
Old 10-05-2012
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Re: AGM Battery Upgrade and Charger

Quote:
Originally Posted by dvuyxx View Post
So far this is what I have ... pretty low draw I think:

Endless Breeze 12v Fan 3.0
LED interior lights 0.5
Nav LED running lights forward 0.5
Stereo 1.0
Raymarine x-70 Autopilot 5.0
Garmin navigation GPSMAP 500series 1.0
Cockpit VHF Standby 1.0
Depthmeter 1.0
Speedometer 1.0

Total so far - 14.0 ah

Now you have to figure how many hours a day you run each of those.
You don't have anchor light listed, do you not anchor out?
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Re: AGM Battery Upgrade and Charger

Something not mentioned, I could be slightly off on the numbers. IIRC AGM and maybe gels lose 3% per month of power when not in use, where as lead will be 6%. Gels may be 6% too. For those on a mooring with out solar or other ways of keeping the batteries topped off when not in use, this too could be a reason to go with the AGM vs lead cell.

My 20amp truecharge IIRC has a place for AGM, GEL and flooded batteries. As Gel's take the least charge input vs lead with agm able to take the most.

With an older motor as the OP has, it would not surprise me if the alternator will need an upgrade. As mine from the mid 80's with a 20hp yanmar, a size 31 agm could take as much as 80-100% of its out put to charge it. So I stuck with a Lead cell. I was looking at a $500 alternator to upgrade etc too to go with at east one or two size 31's in my boat any how. I just went from a 24 to a 31. Gained enough for how I use my boat.

At the end, not sure there is a true right or wrong, only that you have the correct charging system for the type/style of battery and how big the pack is. This does take some number crunching.

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