AGM Battery Upgrade and Charger

[Minnewaska]

Both AGM and Gel batteries have very low self-discharge rates. 3% per month would be the very highest and you can experience as low as 1%. 2% is a safe bet.

Flooded batteries, I believe, self discharge at a rate well above 10% per month.

[PCP]

Originally Posted by blt2ski

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.

marty

Yes that could be a reason but AGM batteries are so much more expensive that I don't know if it is worth it just for that.

I have equipped my boat with AGM batteries and made a complete overall on the charging system and in my case the results were very good, but I have cruised nonstop for 3 months and during that time have been at only 6 marinas. I am not a big spender of energy and to have them charged at 80% It was enough the small time I run the engine in the morning before set sail and the small time after taking the sails out before set anchor (about or less than 1 hour a day).

I fully charged them on the times I have been in the marinas (more than a 24h charge) and in some passages where the engine was run for 7 or 8 hours, sometimes more. Never had them below 12.34V and most of the time the lower they get before being charged was 12.50. That small daily charge brought them to 12.80/12.90. if I remember correctly fully charged by the engine or the marina charger they get to 13.20 or 13.60? I cannot remember. Anyway, comparing with what I had in my previous boat, this set up is just wonderful.

Regards

Paulo

[dvuyxx]

One vendor at the Annapolis sailboat show said that a 5w solar trickle charger would fry an AGM due to overcharging. Another said I should use one.

Deka (the battery manufacturer) was at the show and agreed that I might need to change the shore charger, but mentioned using a solar charger.

Another solar panel dealer ironically said that my 14 ah load was pretty low and that I may not need a solar charger.

An alternator dealer said that I might need to replace my alternator with theirs.

Lastly, I met a couple in their early 80's, twice my age, that just finished sailing around the world for three years. And then I realized I really don't know anything.

[Stu Jackson]

A daily 14 ah load is nothing, really. You don't need AGMs for that sort of load.

For those considering AGMs, please be aware that they need complete charging on a regular basis. I still see little need to spend that extra $$ for them given the issues they have.

AGM Battery Issues (from Maine Sail)
AGM Batteries - Making The Choice - SailboatOwners.com

AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
Darn AGM Batteries - SailboatOwners.com

Your boat, your choice.

[dvuyxx]

If I put a 5 or 12v solar trickle on them, is there an inexpensive solar regulator that I can use with alligator clip panels?

[Stu Jackson]

1. A 5A panel is not even worth it. 11A should be considered a minimum to be able to deal with not only self discharge but charging during the week.

2. Solar controllers have been discussed sooooooooo much on boating forms on the web, including this one and at Cruisers & Sailing Forums, that it boggles the mind. I recommend you Google the topic and you'll have enough to read for thousands of years! Really. Here's an example: MPPT vs PWM Solar Regulators - Cruisers & Sailing Forums You could also Google solar regulators. There are many solar companies websites that include this information in great detail for boaters, like Morningstar.

[mitiempo]

Seems to be some confusion between amps and watts.

A 5 watt panel is a joke.

A 5 amp panel is about 80 to 90 watts.

[Maine Sail]

Originally Posted by mitiempo

Seems to be some confusion between amps and watts.

A 5 watt panel is a joke.

A 5 amp panel is about 80 to 90 watts.

Yeah 5 AMP output panel is nice. A 5 WATT panel, spend your quarters on gumballs. The gumballs will do about as much for "charging" as the 5W panel...

A 5 WATT panel is only capable of about 0.28 AMPS......

[hellosailor]

dv-
Find the specs from your battery charger, confirm that the "wet" settings are within the optimum voltage settings for your AGM batteries. AGM are very similar to wet in their requirements, but some chargers may be too crude or too hot to use with them. Rashly assuming that you will find your charger is suitable...

Then using a small solar panel to top them up on the mooring is also a good idea in any case and should extend battery life. A 5W panel is peanuts, it won't need a controller but won't do much. Basically it will keep a charged battery charged but not much more.

You've got maybe 200AH of batteries, let's say you run 'em down and moor the boat with them 30% down and expect that to be recharged in 5 days by your solar. Call it four days because of bad weather. Average, five or six hours of full rated power on sunny days. So you'd looking at maybe 25 hours of a panel's rated output, over the course of one week, to put in the missing 30% of 200AH. That would be roughly 60AH of panel output in 25 hours, or 2-3 amps of rated panel output. They're typically rated around 17 volts, pick your own min/max values and soething between a 30-60W panel should keep the batteries fat and happy. And at that power, yes, you'd need a controller. (Again, one that matches the optimal voltage charging points for your batteries.) For light use, a 25-30W panel might very well be all you want or need.

And coming out to the boat to see the batteries always fully topped up, even if there have been some gray days, can be a real pleasure. Having them FULLY topped up, really should extend their life, too. A good investment all around, considering the way battery prices keep going up.

[dvuyxx]

I'm looking for a 25W panel and a controller.