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Old 14-09-2010, 16:58   #1
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Troubled Trojans

“Namo” is equipped with four Trojan 6V AGM’s in the house bank and they appear to have died a mysterious death since the boat was built two years ago. Wired in two pairs to provide a total of 400 ah at 12 volts, they instead only now deliver 40 ah before the voltage drops below 11V. The boat spends 95% of its time at the dock where the batteries are charged by a Mastervolt Combi charger. If one cuts AC power at the dock or takes the boat out for a sail, the normal draw from the fridge and lights and/or navigation system (about 10 amps) will now exhaust the Trojans in about 4 hours. I have isolated the battery pairs and found that there is no bad battery – they appear equally weak. No idea why this is but my best theories so far are:
· High Float Charge: The charger keeps them at a float voltage of 14.0V. This seems high to me but appears reasonable given the Trojan specs. of 2.35 – 2.45 V/Cell (14.1 – 14.7V for six cells).
· Occasional Heavy Loads: The Mastervolt Combi (inverter/charger) will automatically jump into inverter mode if shore power is lost. Since we live aboard in a cool climate, there is usually an electric heater load of about 1,200 watts on the boat and I have observed the batteries having to respond to a 120 amp load when the shore power fails (I switch the inverter off manually when this happens).
Anyone seen a similar problem?
Thanks.
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Old 14-09-2010, 17:03   #2
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I don't want to blame the whole thing on AGMs, but there's a general consensus that AGM's work really well in the brochure.
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Old 14-09-2010, 17:09   #3
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I got rid of mine after two years. An expensive lesson. When cruising they seldom get charged right up, usually get back up to 85% and I understand this is not the best thing with AGM's. I now have Trojans, flooded 12v.
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Old 14-09-2010, 17:39   #4
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I would hazard a guess that you either have at least one dead cell or your batteries have sulfated and need to be equalized. That is if they can be equalized. Check with Trojan to see if this is possible and what their procedure is. Some AGM's can withstand the equalization process.
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Old 14-09-2010, 18:28   #5
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FWIW, I would agree that the batteries are probably badly sulfated.

Lead acid batteries (including AGMs, gels, flooded) lose their capacity to accept, store, and deliver energy through several mechanisms, including:

1. buildup of PBSO4 crystals on the plates;
2. boiling off and/or evaporation of the electrolyte;
3. physical damage to the plates through erosion, buckling, corrosion;
4. shorting of the plates thru buildup of precipitates beneath the plates;
5. contamination of the electrolyte; and
6. stratification of the electrolyte;

AGMs and gels are less susceptible to some of these causes than are flooded batteries.

Trojan says that you should never equalize AGM or gel batteries. The equalization process is useful with flooded batteries to knock loose lead sulfate matter off the plates, but what to do with AGMs?

You said, "I have isolated the battery pairs and found that there is no bad battery – they appear equally weak." How did you test that?

Exercising batteries is often very helpful in restoring capacity. Often when cruising after a long stint at dockside, you'll see voltages lower than expected sooner than expected, but after a few deep discharge and recharge cycles you'll see "normal" voltages reappear, and the batteries seem to have "recovered". Have you noticed that with your AGMs?

Before pronouncing them dead, I'd exercise them vigorously a few times, and I'd even try a "soft" equalization cycle or two to see if any capacity is regained.

BTW, the AGM bank you have should be able to deliver 120A for a short while without damage. Nevertheless,
I'd turn off the automatic inverter switchover when the shorepower fails. One slipup -- like if you're away from the boat when the power fails -- and you could flatten your batteries completely, which surely isn't good for them.

Let us know how it turns out, OK?

Bill
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Old 15-09-2010, 21:40   #6
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To elaborate on Bill's excellent points: one of the absolutely worst things you can do to lead acid batteries is to float them for extended periods of time. Lead acid batteries include flooded, gels and AGMs. Lead acid batteries will give the longest service life if they are used...and not abused. The conditions you describe are textbook sulfation.

Follow Bill's recommendation regarding "soft equalizing" as you have nothing to lose. BE CAREFUL and understand what equalization is about before proceeding. Very destructive results can occur if it is not done correctly.

Charlie

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Old 16-09-2010, 14:45   #7
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Thank you for all your thoughts on this. For these batteries to have failed in two years of while mainly (and unfortunately) sitting at the dock, I suspect there is some other factor at play besides the possible unsuitability of AGMs for cruising.

I have been looking for a fault in the charging profile of the Mastervolt Combi charger but it looks good as do the profiles of the Balmar regulator and the Blue Sky solar controllers. My last suspect is the rapid discharge of the batteries to 10V when a shore power failure occurs as the Mastervolt will automatically switch to inverter mode if it doesn’t see shorepower A/C. Since this may have happened only 3 or 4 times at most (we live aboard), it still doesn’t explain it. I just disabled this automatic switchover feature though.

I think they have been exercised quite a bit recently so I may give equalization a try next even though Trojan warns against it. Any suggestions on how to perform a “soft” equalization?
Thanks again,
Ian
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Old 16-09-2010, 15:07   #8
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Doesnt your Mastervolt Combi have a desulphation shock charge to cleanse the plates occasionally?
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Old 16-09-2010, 15:17   #9
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Anjou: The Mastervolt Combi does have an equalization mode with an OFF-ON-OFF pulse charge. I'm just a little worried that since equalization is not recommended for these batteries, it may do more harm than good. Ian
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Old 16-09-2010, 15:33   #10
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Anjou: The Mastervolt Combi does have an equalization mode with an OFF-ON-OFF pulse charge. I'm just a little worried that since equalization is not recommended for these batteries, it may do more harm than good. Ian
Ian,

How much harm can you do to batteries which have lost upwards of 90% of their capacity?

The chief problem when equalizing gels and agms is the danger of boiling off the electrolyte, which isn't replaceable. The pulsing charge used in the Mastervolt's equalization process might be just the ticket for avoiding the overheating problem.

In any case, I'd watch them carefully for any signs of overheating or venting or other abnormal condition.

Re: a rapid discharge to 10V, if you do that a few times you could certainly harm the batteries. Lead-acid batteries are at effectively zero charge when their voltage falls to 10.5. None of the three types likes to be fully discharged, especially not at a high rate.

Since you live aboard, when it comes time to replace these batteries you might routinely "exercise" the new ones by turning the battery charger off every other day, or to some other convenient regime. Let them draw down 20-25% of capacity (i.e., 75-80% remaining charge) before fully charging them again.

And, unless you're wedded to AGM technology you might consider going with quality flooded batteries. T-105's will last 4-6 years on average; the Rolls/Surettes will go 10-15 years. Both will take much more punishment that gels or agms, and you can put your equalization mode to use on the Mastercharge :-)

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Old 16-09-2010, 15:37   #11
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Bill: You asked how I determined that all four batteries were equally week. I simply disconnected two batteries and found that they discharged in half the time as with all four connected. I then repeated this with the other two and came up with same discharge time. Logically if only one battery in a pair had a bad cell or something, I would have seen a difference in capacity between the two pairs.

I'm still mystified about what's going on here.
Ian
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Old 16-09-2010, 18:21   #12
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Bill: You asked how I determined that all four batteries were equally week. I simply disconnected two batteries and found that they discharged in half the time as with all four connected. I then repeated this with the other two and came up with same discharge time. Logically if only one battery in a pair had a bad cell or something, I would have seen a difference in capacity between the two pairs.

I'm still mystified about what's going on here.
Ian
Yeah, some things just aren't know-able :-)

The best way to check the capacity of batteries is to fully charge them, then put a known, constant load on them calculated to discharge them to 10.5V in a 20-hour period. For example, a 200AH (@ the 20-hour rate) battery should be able to sustain a 10 amp load for 20 hours. In reality, it will be something less than this. How much less, by experiment, will tell you the real capacity of the battery.

There are other testing methods, but none as accurate as this. I built a little tester consisiting of 12V incandescent light bulbs that I could switch into the load as desired, and a DC ammeter to measure the actual load. Also measured the voltage at many intervals during the discharge. Additionally, I had a "Watts Up" device in-line with the load which measured actual energy delivered by the battery, and several other parameters.

Here is the result for one pair of T-105 flooded batteries, and two pairs of gelled golf-cart batteries. The gelled batteries were then 11 years old, having spent their first 10 years in service on a sailboat. The T-105s were about half that age.

As you can easily see, one of the gelled pairs and the T-105 pair have both lost considerable capacity, while the other gelled pair went more than 15 hours before reaching 10.5V and isn't in bad shape at all for an 11-year old battery pair!

Click image for larger version

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I have a sophisticated battery tester (Midtronics MDX-650) which uses internal battery conductance/resistance to estimate capacity. It's meant for CCA and CA measurements rather than 20-hour deep cycle measurements, but it works pretty well in the latter role. It is a quick and easy method of estimating battery capacity, particularly useful for comparisons between batteries and those made with the same batteries over time. But, it costs $600. Maybe you could locate someone in your area who might have one.

Absent these two methods of battery capacity testing, you're really flying blind.

Bill
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Old 17-09-2010, 14:43   #13
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Thanks Bill, I appreciate your info on this. I do know of someone who has an AGM battery tester in the marina so will follow up on that although I think he will confirm that the Trojan's have died a premature death. I was hoping that my next batteries would be Lithium but they are still pretty expensive at 3X AGM. If I stay with Pb-acid, the Rolls/Surrette will probably be the way I go.
Regards,
Ian
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Old 27-09-2010, 00:07   #14
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Trojan has advised that the problem is due to the batteries being overcharged on the float part of the charge cycle causing the electrolite to evaporate and reducing the usable plate surface.

The Mastervolt Combi charger/inverter unit's standard profile for AGM batteries provides a 13.8V float voltage however, my unit is a little hotter at 14.0V. Trojan suggested a float voltage of 13.5V for their AGMs. I wish this info was more visible on their website. One needs to get a special cable from Mastervolt to connect a PC in order to tune the voltage (and other features). Anyway, new batteries for me.

By the way the Mastervolt Combi unit was just cited in the "Gear of the Year" section of this month's (September) Practical Sailor. I'm sure it is a quality piece of gear from Holland but one should check and confirm the default voltage settings.
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Old 27-09-2010, 01:23   #15
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Thanks for the tip Namoian
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