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Old 27-04-2008, 14:28   #1
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AGM and Wet Cell Together

When I bought my boat, she had two batteries charged by a common MARINCO/GUEST 6 amp charger.

One battery is a AGM West Marine 810 MCA/ 580 CCA 92AH @ 200hr.

The other battery is a Trojan wet cell 770 MCA / 630 CCA 79AH @ 5 hr.

I tested the batteries this weekend -- both are good. Trojan is near the top of the hydro test thing. AGM is 13.67 698CCA. Meter says "good"

I am redoing the electrical.

I want to have three batteries (maybe 4). I have calculated my peak load and I am pretty sure two house and one starter will be ok.

The Guest charger has blown once already (after 2 yrs of service). My electrician said it was likely the repeated back kick from the fridge that caused the blow out (fridge draws 15amps when it kicks on, then settles into a 10amp draw). I replaced the charger with the same exact one since I could rewire the new wires to the exact same positions. Otherwise, I would have been lost.

My electrician says to go with wet cell. She says they are more accessible across the world as you sail. BUT, she says, whatever you do, all batteries have to be the same. AND this post is not about which style batt is best!!

I do not want to give up one perfectly good battery.

1. Can I buy another wet cell and use the two wet cells for the house bank and use the AGM as a started battery? Or conversely, use two agms for the house and the wet cell for the starter?

2. If I mix batteries as above, could I not use something like the XC Multi-Chemistry Battery Charger West Marine: XC Multi-Chemistry Battery Chargers Product Display?

3. I have a Perkins 4108. I am thinking of adding a Balmar alternator. Given the configuration above (3 battteries 2+1) would it be a good idea to use one?

4. I am going to add an inverter, but the installation will likely have to wait a few months ($ outlay). Does the inverter have to be installed at the same time?

Thanks

Michael
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Old 28-04-2008, 08:19   #2
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Knock knock.... Hello??
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Old 28-04-2008, 10:04   #3
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I have two 4D batteries, and no separate starting battery. The batts are wired to be usable as individual banks or as one single. I always use them as a single bank. I also beat the crap out of my batteries, often running them down to an indicated 25% (11.8v) and I have never had any problem starting my 35hp Universal diesel in that advanced state of discharge. I really don't get the need for separate starting batteries if all you have is a relatively small diesel. I want every spare amp hour I can get my hands on wired directly into my house bank.

I switched from wet cell to AGM and I do not recommend them. AGM batteries are fragile and need to be babied, they are not intended for harsh marine live-aboard use. For example they should never be discharged below 50% and should always be recharged to 100%. Yeah right - I'll make sure to run my generator for 6 hours every 12 just to be sure I stay within those margins... Lifeline no longer recommends the use of their AGM batteries in yachts.
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Old 28-04-2008, 10:17   #4
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PS: Oops... I realized I went off on a rant there and never addressed your questions. She's right, don't mix battery types, or battery sizes. If I were you I'd pack as many wet cell amp hours as I could into a single bank which would double as your engine starter. I'd leave the AGM battery on the dock, it adds weight, takes up space, adds complexity (you'll need an alternator that can charge AGM, plus a shore power charger for it especially), and of course it'll add expense to get it all wired up right.

I rely on a car jump starter box for the emergency situation where the house has run down to 0.
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Old 28-04-2008, 10:53   #5
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Ok, that helps. I had thought a special charger would allow me to keep both, but it is clear to just make a choice, listen up, and pass on the AGM. Silly question I know.... but just to make absolutely sure: When you say "single bank of batterries" you mean all batteries are wired together; however, do they all have to be in immediate proximity to each other? Or can two pairs be on either side of an engine compartment?


Thanks

M
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Old 28-04-2008, 11:44   #6
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Michael,

You can put them anywhere you want to, as long as you size the cables correctly.
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Old 28-04-2008, 11:57   #7
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AGM and Wet Cell Together

Michael:

It's true that you can find wet cell batteries all around the world. You will need to change them often.
It's also true that a properly used AGM battery bank can last more than 10 years. So you probably will be back at home when need to replace them.

It's a good advice from your electrician to avoid mixing battery types.
They requiere different charging voltages. So you will need different charging devices (alternators, solar panels, wind generators) for each battery type or you will destroy most of them.

An alternative is an intelligent charger as the one here:
http://www.balmar.net/page20-Duocharge.html

Anyway, it will be wise to slow down a bit and design a good marine electrical system for your boat before starting to spend money.
There are many good books on the subject (I'm sure many people in this forum can suggest you the best ones you can find in your side of the world)

Meanwhile you can have a look at this document:
http://www.outbackmarine.com.au/Pdf/...ystem.book.pdf

It's important to be clear defining your goals beforehand (daysailing, coastal cruising, deep sea global circunavigation, ....) and then after designing your system, stay with the design even if you implement it partially in steps.

Hope this helps you, and you acomplish your goals.

Regards,

Juan Josť
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Old 28-04-2008, 14:31   #8
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Quote:
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... Lifeline no longer recommends the use of their AGM batteries in yachts.
Where did you get this info? Can you point to any statement online by Lifeline? They sure still push them at boat shows.

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Old 28-04-2008, 14:45   #9
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Well, MV, you can mix any kind of batteries you want AS LONG AS THE CHARGING PROFILES ARE IDENTICAL. Or substantially similar.

Every battery maker will tell you pretty much the same thing. If the batteries have different charging characteristics (different acceptance/discharge rates, different float/bulk/absorption charging voltages) then they CANNOT be properly charged from one same charger at the same time.

You may get away that for a while--but you will be either undercharging or overcharging one battery or the other, with a net loss of cycles from it, and possible damage to the other battery. AGM and wet cell batteries used to have substantially different voltages, many are quite similar now--but you are better off deciding which type you want, and making up a new bank of the new kind (and you don't mix old/vs/new cells for the same reasons thast you don't mix different types) and using the odd battery up as a dedicated and isolated starting battery. Since the AZGM cell can be left alone for long periods (i.e. 6 months) without charging and without harm, I'd use the wet cell as my starting battery, buy a new bank of house batteries, and stick the single old AGM cell someplace out of the way. Pull it out and recharge it every 3-6 months, and when that old wet cell dies, replace it with the AGM, which should still be good.

Juan-
It seems that Balmar either forgot to pay their blls or went belly-up, their domain responds as "not valid" today.
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Old 28-04-2008, 18:12   #10
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Paul L: Hmmm, I guess I was wrong, Lifeline is certainly still marketing a marine AGM line of batteries - oops, my bad. HOWEVER consider the following from Lifeline's AGM charging instructions: "For maximum battery life, a battery must be recharged to 100% capacity. Recharging less than 100% may result in premature battery failure. Lifeline batteries are not covered under warranty if they are not recharged properly."

This is a big problem for us guys at anchor because it takes many hours to charge a batt up to 100% due to the fact that modern chargers tail off the charge as the battery fills. So while my batteries might hit 90% charge in 2hrs it might take another 2 to finally hit 100%. Obviously it doesn't make sense for me to run my generator for a couple extra hours just so a finicky battery can be coddled up to 100%.

Oh, and of course the 100% charge requirement is completely incompatible with a wind generator.
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Old 28-04-2008, 20:06   #11
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Hubec,
I understand the issues of not being practical to get a full charge after each use in a cruising scenario. If you look deeper onto Lifelines site you will also see they now have equalization directions for the AGMs. I have less of a problem with the slow failures that should occur with not fully charging, as this also affects wet cell batteries, although perhaps to a lesser extent. What bothers me about going to AGMs for the house bank are the number anecdotal reports of premature failures in situations with healthy charging regimes. Basically unexplained failures after a year or so.

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Old 28-04-2008, 21:17   #12
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Quote:
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Oh, and of course the 100% charge requirement is completely incompatible with a wind generator.
Could you please explain this to me?

I thought wind and solar could take care of that pretty well.
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Old 28-04-2008, 21:21   #13
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Quote:
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.....

3. I have a Perkins 4108. I am thinking of adding a Balmar alternator. Given the configuration above (3 battteries 2+1) would it be a good idea to use one?

4. I am going to add an inverter, but the installation will likely have to wait a few months ($ outlay). Does the inverter have to be installed at the same time?

Thanks

Michael
I don't know the answers to those questions Michael. Maybe someone who has posted on the thread here could give #3 and #4 a shot? The posters here certainly seem knowledgeable!

Good luck!


Michael
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Old 28-04-2008, 23:09   #14
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Paul; I'm aware of the equalization procedure - in fact it's explained on the page I linked last post. Lifeline seems to discourage the regular use of equalization so I suspect it may also be harmful to the batteries. Maybe you can only do it so many times? I definitely plan to do it this summer while the boat's on the hard. Now I just have to figure out a way to feed a constant 15.5v to my batts for 8 hours !?

Therapy; The problem with wind is that it's both powerful and unreliable, one minute it could be pumping 200 amps into your batteries, the next... nothing. Obviously this is a pretty big conflict with Lifeline stating that your warranty is void if you don't bring your batteries to 100% on every charge cycle. Keep in mind that the boat is still drawing power while this is going on, so the batteries are actually flopping between charge and discharge. Before my wind generator quit for good my batteries would continuously float between 50% and 85% depending on the wind and how power hungry I was that day. Clearly this type of use (which I think is normal for most cruisers) is far outside the scope that Lifeline sets out in their warranty.
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Old 29-04-2008, 06:03   #15
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Lots of good information about using different types of batteries in parallel
available on the KatieKat site. Check the link below.


KatieKat 2004 Cruise Chapter Six
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