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  #1  
Old 08-14-2008
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Red face Alternator Voltage regulation

Hey all,

I'm brand new here and I've got an alternator/regulator problem/question...

I've got a small internally regulated alternator on my 12 hp Westerbeke. Now, my boat is rigged for offshore sailing and I've got 3 105AH AGM's. I've got a good shoreside charger that charges them 3 stage like supposed to. But with the internally regulated alternator, I get 14.XX to the batteries which is way too high. I'd like to know if there's anything I can do to limit the voltage to the batteries while motoring. Just turning the radar, SSB, VHF etc doesn't do it. I have experience with AGM's and know they're sensitive to overcharging. Here's what happened. I got my boat all ready and rigged for the single handed transpac but ran out of money so didn't go. That's why I'm looking to build some sort of voltage limiter diode thingy. If not, I'll have to save and get a new alternator and external regulator and on and on.

Much thanks in advance and sorry to ramble,

Rich
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Old 08-14-2008
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I believe you can use an external voltage regulator on your current alternator. They're not all that expensive. Balmar makes a unit that retails for about $260 or so. It would help if you said what alternator you currently have.
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Old 08-14-2008
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Attaching an external regulator to an internally regulated alternator requires some modifications to the alternator. I recall finding some "how to" instructions on disabling internal regulated alternators on the Ample Power or similar website. An external regulator would be a lot safer than adding some sort of resistance in the wire between the alternator output and your battery (which would also knock back the voltage)
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Welcome aboard Rich,

Hay guys, I thought regulators put out 14 volts. Or is there something wrong with my boat and cars?
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Rich,

You may be just fine.

Trojan recommends a charging voltage of 2.35V to 2.45V per cell for their AGM batteries (14.1 to 14.7 volts for a 12V battery). This is for the last 20% of the charge cycle, i.e., when the state of charge of the battery is above 80%. These recommendations are for 77 degrees F.

Note that batteries can be damaged both by undercharging and by overcharging. Typically, batteries on sailboats tend to be undercharged much or most of the time.

To see what your alternator w/internal regulator is REALLY doing, get yourself a good multimeter and measure the voltage AT THE BATTERY while the engine is running. That will tell you what voltage is actually getting to the batteries.

Do this when the batteries are fully charged, almost charged, and pretty depleted to see how "smart" the internal regulator is. If you don't like what you see, then consider modifying your alternator and adding an external smart regulator.

Bill
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Most "12" volt regulators put out 14.3-14.4 under full power, and many AGM batteries have been optimized to work with that same voltage.

Rich, without knowing exactly what the charging specs are for your batteries, and what the exact alternator output is, it is hard to guess what might be a good solution.

An external regulator with adjustable charging profiles can certainly do the job (at a price) and it is a more effective way to charge, as well. You'll still need to know exactly how the maker prefers your batteries to be charged. Some of them give out voltages (for absorbtion/bulk/float) but when pressed, they'll tell you vey different numbers based on both voltage AND amperage limits. Since you are matching an entire system--try to get the best information they have.
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Rich...what brand are your AGM's?
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I posted a response to everyone on Saturday but I don't see it here. I wonder if that happens from time to time? Let me try and hit the high points. The 3 stage works like this - 1st stage bulk - max current supplied to batteries. This is limited by the wiring and batteries. The voltage is not important but not more than 15.5 and about 14.2-14.4. Stage 2 acceptance voltage is monitored and current is varied. Voltage is kept about 14.2-14.4. Stage 2 occurs when the batteries are 80% charged. Stage 3 float - This occurs after batteries are fully charged and is to minimize gassing, keep the charge up and to prolong battery life. About 13.2 volts. This is for AGM batteries. Gel and wet cells are different and are selected by switches on external regulator. I think I mentioned that I have an AC 3 stage charger but whenever I head out, the alternator is putting out 14.57. I could actually live with that TEMPORARILY if I could switch the batteries on and off line because 14.57 isn't that high if the batteries aren't charged.
Saildog, I llooked at Balmar but I need to speak with a live person. Thanks.
Btrayfors, About the 14.1-14.7 volts, correct until the battery is fully charged. That's when you gotta float or overcharge and shorten life.
Camaraderie, My batteries are Lifeline.
Hellosailor, I've got the numbers that I need. I've got a digital meter that I put below in the bulkhead that's hooked to the batteries. I checked it with my fluke and it's right on.
A bit more info. I used to be on this board from 1997 to 2003 with a bigger boat. The systems were already put in when she was commissioned. That's why I'm a boob but this is great experience for me.

Thanks again everybody for taking the time to respond.
Rich
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Rich-
"1st stage bulk - max current supplied to batteries. This is limited by the wiring and batteries. The voltage is not important but not "
I spent some quality time asking questions to a couple of battery mfr techs about charging in this past year. Each seems to contribute one more nugget. Each said, specifically, that during the bulk phase BOTH amperage and voltage have specific maximums, and that exceeding either one can damage the battery. They go hand and hand, and as a practical matter of keeping things simple enough for the mass market consumer, the mfrs only give you the one figure (voltage) and tell you not to exceed that. HOWEVER, there is a much wider range of both voltage and amperage and it really is a matter of not exceeding some combinations of the two.

In that one specific case, the AGM mfr told me 13.5-14.4 volts at no more than 10 amps, for a 75AH rated deep cycle battery. So even at a conservative 13.5V, if I supplied a 15A charge I could damage the battery.

OK, you have 14.57 and want to cut that down probably to 14.3-14.4, right? Buy an isolator, any isolator, and wire up one diode to your alternator output. It should reduce peak voltage by possibly 0.7V at high current rates, to a more typical 0.3V at lower current rates. (Or, browser some component houses, you can find specific high-power diodes with specific 0.3V drops, sometimes under $10 at surplus houses.)

OR, you may be able to trick the alternator even more simply. Assuming (rashly!) that it has a sense lead, where is that sense lead conected to? If it is conected at the batteries, you can temporarily disconect it there, and bring it back closer to the alternator--even to the alternator output post directly. Some "one wire" alternator installations are actually designed that way. What happens now is that the sense lead is reading "full" output, but the cables to the batteries are providing some drop, often 0.3V or thereabouts. So the alternator folds back a little sooner than what the batteries are really getting--compensating for the extra voltage you're seeing.

It is possible that someone, sometime, set the rig up "a little hot" in order to overcome cable losses in the system. You know the saying? "It seemed like a good idea at the time." ?
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"In that one specific case, the AGM mfr told me 13.5-14.4 volts at no more than 10 amps, for a 75AH rated deep cycle battery. So even at a conservative 13.5V, if I supplied a 15A charge I could damage the battery."

I don't believe it. Somebody gave you a bum steer!

One of the features of AGM batteries is that they may be recharged much faster than flooded batteries.

Specifically, the Lifeline website states the following in respect to their AGM marine batteries:

Quote
Faster recharge; no current limitations with voltage regulated recharging.

Unquote.

In other words, you don't really have to worry about how much amperage is being pumped into the battery, so long as you limit the voltage.

Lifeline recommended charging voltages are:

Bulk................14.2-14.4
Acceptance.....14.2-14.4
Float...............13.2
Long-term float.13.0

Equalization......15.5 for 8 hours, voltage regulated

Bill
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