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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #11  
Old 11-01-2010
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From what I have been reading lately in support of designing and installing a new electrical system in an old boat, the AGM batteries are far more sensitive to overcharging than the wet cell batteries are. I can't remember if the limit is 14.4 volts or 14.1 volts but if you go over the limit of this charging voltage on an AGM battery you severely limit its life. My references for this information are Nigel Calder's Boatowner's Mechanical and Electrical Manual and Don Casey's Sailboat Electrics Simplified. They say that having an excellent voltage regulator is essential with AGM batteries.
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Old 11-01-2010
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"the AGM batteries are far more sensitive to overcharging than the wet cell batteries are. "
Strike "AGM" and insert "sealed" and you've got a larger truth. AGM batteries are "sealed valve regulated" batteries, meaning that as with any "sealed" battery, if you cook off some of the electrolyte there's no way to replace it. Since they are "starved electrolyte" design to begin with, using the minimum amount of electrolyte between plates, there's not much to spare.
With a conventional wet battery, you can top up the electrolyte to compensate for any that is boiled off by overcharging. So you can routinely abuse them & correct the abuse.
But with AGM, or even a "maintenance free sealed" wet cell, that's just not possible. Something all the sealed batteries have in common, not just AGMs.

Of course if you really wanted to, you could drill a hole, break the seal, and top up the electrolyte. I suppose somewhere out there, someone has tried that kludge. In theory it would work perfectly well, as long as you remember to plug the hole afterwards.
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Old 11-03-2010
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I too have a large AGM bank (2 8D's-490 ah's) comparred to the Balmar alternator(100 amps) and understand the concern about stressing that alternator. I assume that the external Balmar regulator ARS-5 with temperature sensor would limit concerns about burning out the alternator when those AGM's are near depleted. Is that assumption valid??
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Old 11-03-2010
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Quote:
Originally Posted by lancelot9898 View Post
...I assume that the external Balmar regulator ARS-5 with temperature sensor would limit concerns about burning out the alternator when those AGM's are near depleted. Is that assumption valid??
Pretty much right on.

The regulator simply decides on bulk, absorption and float based on a timing algorithm built into the regulator and the voltages at the battery (if you wire it so) or to the back of the alternator.

The controlling factor of output is the ACCEPTANCE of the batteries.

AGMs will accept far more than wet cells.

I would urge you to install either an alternator temperature sensor or a Small Engine Mode switch on your regulator to avoid overheating your alternator.

Rea this and also the links within the topic: Alternator Output Management with External Regulators [Small Engine Mode]
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Old 11-04-2010
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Thanks Stu for the link. I am careful about depleting or even using the second 8d AGM battery so in effect the most amperage that I've taken out of the bank is 50% of the 245 amps or around 120 amps. Also I'm not sure if the regulator has the small engine mode switch and the remote temperature sensor is located at the battery instead of at the regulator. Another factor is that I let the engine idle for maybe 20 minutes or more as I bring up the anchor with a manual windless. At idle speed there should also be less amperage coming from the alternator and gives the 490 a/h battery bank more time to recover. I would think that the design of a 100 amp Balmar alternator would be such that it would not burn out at the high end of its output.
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Old 11-04-2010
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Quote:
Originally Posted by lancelot9898 View Post
Thanks Stu for the link. I am careful about depleting or even using the second 8d AGM battery so in effect the most amperage that I've taken out of the bank is 50% of the 245 amps or around 120 amps.
This can shorten the life of the battery bank. You are significantly better off to run one large bank rather than two smaller ones. Separating the two banks of 12V batts only serves to more deeply discharge each "bank" or individual battery, and thus shorten it's life. The deeper the discharges, the shorter the life. The shallower the discharge, the longer the life. The bigger the bank the less discharge at the same Ah's drawn down.

For example let's look at a 450 Ah bank: Taking 150 Ah's out of half of it, or a 225 Ah bank, puts you at a 33% state of charge on that bank. If you left the two 225 Ah batteries together and then drew 150Ah's off it. 450 Ah's - 150 Ah's = 67% SOC. Your batteries will last significantly longer when only drawn down to 67% SOC vs. 33% SOC. You are using the SAME Ah's in each situation but the batteries will last a LOT longer the less you draw them down.

If you don't have a reserve battery then a group 24, 27 or 31 12V would be great and you could permanently combine the 2 12V batts for one 490 Ah bank and add a group 24 starter batt.

Quote:
Originally Posted by lancelot9898 View Post
At idle speed there should also be less amperage coming from the alternator and gives the 490 a/h battery bank more time to recover. I would think that the design of a 100 amp Balmar alternator would be such that it would not burn out at the high end of its output.
This all depends upon your specific alternators curves and your engine to alternator pulley ratio. It may put out full amperage at 1000 RPM engine speed. The ARS-5 does have an optional alternator temperature sensor you can install. It will cut back the field output when an over temp is sensed.

Any alt that is asked for full output for hours on end will eventually cook. Alternator temp sensors on gel, TPPL or AGM batteries are critically importan and can also be important on large banks of wet cells where bulk charge acceptance can exceed the alts capabilities..

This is the stator off a 125A HO alternator that was connected to a 450 Ah bank of AGM batteries. This alt worked flawlessly for over ten years with the same size bank of wet cells. It was cooked in less than a few weeks with the new AGM bank. It had no temp sensing. Those windings are supposed to have a coating on them but the alt got so hot it literally burned it completely off.
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Maine, it's been a number of years since I've installed the ARS-5, but I'll likely add that alternator temperature sensor if it's not already there. Also we've not been anchoring out that much, but if that changes going to one large bank is best for the reasons noted. Also having a seperate starting battery such as a group 31 instead of keeping the one 8D in reserve would be good and more economical too by extending the life of the 8D's. (not to mention my back and moving the 180 pounds around)
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The alt temp sensor is a simple switch, as I discussed in those links. It could very well be (I don't know for sure) that the battery temperature sensor is the same thing on your ARS-5. If it is, then simply add that toggle switch in line (series) with the batt temp sensor wire, and you can check it out easily for the cost of a toggle switch and a bit of wire and connectors.
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The Balmar website has been effectively messed up, and says it's Under Construction! Why, for the life of me, manufacturers who have good websites with important information continue to mess with them and make them less worthwhile is beyond me.

Editorial over, I'll write to Balmar.

Anyways...the ARS-5 information that's still left, after they took off the manuals (so much for Editorial over!!!), says that the ARS-5 has BOTH battery and temperature sensors. You should be able to easily install the Small Engine Mode as I've described it. I'll check my downloaded ARS-5 manual to confirm and get back to you.
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Turns out I never downloaded the ARS-5, but I do have the ARS-4, which has the alternator temp sensors. It appears, then, that the ARS-5 has BOTH batt and alt sensors, so you should be able to do so.

Again, how you use it is important. As Maine Sail cautioned, the AGMs will accept far higher input amps than wet cells, so regardless of how you configure your banks, X amps out requiring charging of X amps back in, is gonna require a higher alternator output at engine startup, unless you use the Amp Manager (a royal pain) or the Small Engine Mode.

Another factor is that I let the engine idle for maybe 20 minutes or more as I bring up the anchor with a manual windless. At idle speed there should also be less amperage coming from the alternator and gives the 490 a/h battery bank more time to recover. I would think that the design of a 100 amp Balmar alternator would be such that it would not burn out at the high end of its output.

That's not necessarily true, because your alternator won't be putting much back at idle speed, even with your manual windlass, and 20 minutes is not a long time to "refill" a night's load when on the hook if you have a fridge. So when you eventually get up to cruising speed, you'll experience what I wrote about in the Hot Alternator link. Think about it. The Small Engine Mode as I've discussed it is right up your alley.
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Last edited by Stu Jackson; 11-04-2010 at 03:11 PM.
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