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Old 02-20-2020, 06:32 PM   #1
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City: Rock Island, IL
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How Do I Test a 3 Stage Battery Charger

Here is my situation. We are home for the winter in IL and the boat is winterized in her slip in TN. Our slip neighbors noticed the smoke alarm going off and when they went over to investigate noticed a sulphur smell. They checked the 8d batteries and found that the water had cooked out of the SB battery. Apparently, the port battery was ok. I had topped off the batteries with water when we winterized it in Dec. The only AC load turned on was the battery charger in case it needed to charge the batteries if the bilge pumps went off. There should not be any constant DC loads turned on. My first question is why would the smoke alarm go off in the salon? The batteries are in the aft lazarette. I should be able to test the cells in the battery to see if it is bad, but was wondering how I can test the 3 Stage Battery charger to make sure it is working properly. I'm not sure why it would cook the battery if no DC loads were applied and why this happened if supposedly the charger should have been in the float mode? To be safe I had the neighbor cut the power at the shore power pedestal so just hope the boat doesn't start sinking. Hope to get down to the boat next month. Thanks for any insights and your recommendations!!!

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Old 02-20-2020, 06:49 PM   #2
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If your charger is one of the newer multi step type and not a constant volt type does it have a display? If so it should tell you what charging phase it is in (bulk, Absorb, float, etc.). If no display the only way to really know is by testing the voltage for your specific battery type. You can find lots of information online.

If you don’t have a modern multi stage charger with an information display I would highly recommend one and with temperature sensor install on the battery.

You may also have just a bad battery. Sometimes it just happens that batteries fail internally and will keep asking the charger to keep charging. Again it’s all based on the battery’s internal voltage.

Until you get to the boat and do some voltage testing with a meter your just speculating.

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Old 02-20-2020, 06:59 PM   #3
City: San Francisco
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You would need a way to measure the voltage and charging amperage. Sounds like it was stuck in absorb phase too long, or perhaps the float voltage is too high. A more nefarious possibility is flakey shore power. Some less expensive 3 stage chargers have a fixed absorb time, say 6 hours. If shore power is blinking on and off, at every 'on' you will get 6 more hours. If it is blinking off quicker than that the charger is effectively stuck in absorb.
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Old 02-20-2020, 07:42 PM   #4
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Although it is possible that the battery charger has gone bad or that you had flakey shore power (although I don't see how that would cascade down to the battery) is much more likely the battery was bad. When batteries, particularly non deep cycle batteries like most 8Ds go bad because sulfate has collected in the bottom and bridges the plates, they draw lots of current and heat up. When they heat up they boill electrolyte out.

So first replace the battery. Preferably with a couple of 6V GC2 batteries connected in series. See the Misc section of the TF Library for a short treatise on this topic.

Then watch the voltage build up starting with the batteries half discharged. The voltage will rise from the low 13s or even the upper 12s to about 14.5 and then drop to its float voltage in the mid 13s.

If it does that the charger is doing its job.

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Old 02-20-2020, 08:29 PM   #5
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Since both batteries are not cooked, I would suspect the one battery that has gone dry. The fumes from the battery cooking probably drifted throughout the boat and set off the alarm.
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Old 02-21-2020, 07:03 AM   #6
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One of the most important things a "modern" battery charger can do is change its charge profile.

For plugged in long term storage 12.8 to 13.2 is as high a float voltage that should be set.

When cruising the normal higher set points will result in a faster charge.

An older batt going bad is not uncommon , sadly it overcharges itself , and usually boils out the second battery as well.

Its really low tech but a Battery Tender on each battery is one solution.
have no idea weather the cheapo China stuff works , but these do.
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Old 02-21-2020, 07:45 AM   #7
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City: Gloucester, MA
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Is it a Xantrex charger?

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