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Old 02-28-2016, 09:50 PM   #1
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Question Why excess acid on top of bow thruster battery ?

1700 amp 12 volt D size as I recall, two of them, maintained by ProMariner ProSport 20 charger. Batteries less then 2 years old, mounted just a foot or so behind the bow thruster tube. All state of charge lights check ok on charger.

Puddle of acid found on top of one battery, perhaps 4" circle. Checked the cell in the middle of it, has plenty of acid still.

Could this have happened from something so mundane as rough seas at the dock ? Would make no sense if so however, seeing as it made it from Florida to SC without a leak like that.

So, gotta be either that, combined with cell cap seal deterioating (seemed ok though) or something strange with charger overheating that battery, right ?

(and yes it was acid not a rain leak...I dipped finger in and touched a tiny bit to my tongue...yikes)
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Old 02-28-2016, 10:27 PM   #2
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you should check the charging voltage. I suspect it's too hot, and boiling off the battery acid.
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Old 02-29-2016, 12:30 AM   #3
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That would be my guess as well. Possibly a bad cell in the battery as well?
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Old 02-29-2016, 06:17 AM   #4
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Yes, sounds like it is being boiled out by the charger. This is often not the charger that is the problem though. It can be caused by one of the batteries connected to the charger having a shorted or weak cell. I would turn charger off for a few hours and then measure battery voltage, should be about 12.4 volts. Then hit thruster (assuming the batteries are for the thruster) for 5 seconds or so. Check voltage again and if it is down by more than two tenths of a volt I would suspect battery replacement is due. In my experience overcharging is most of the time caused by a defective cell.
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Old 02-29-2016, 06:46 AM   #5
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A fully charged bat that is just resting should be 12.8 or near that , 12.4 is nearly dead , .
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Old 02-29-2016, 07:34 AM   #6
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Good catch FF. Typing to early in the morning. Check of the battery would be a good thing to do in this situation though......
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Old 02-29-2016, 08:30 AM   #7
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I'd check the specific gravity of each cell.

These are approximate and not correcting for temperature. I would look to see if one or two cell's are much lower than the rest.

STATE OF CHARGE
SPECIFIC GRAVITY/VOLTAGE
100% 1.265 12.62(6.3)
90% 1.251 12.54
80% 1.236 12.45
75% 1.225 12.40(6.2)
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Old 02-29-2016, 08:32 AM   #8
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The problem with two batteries in parallel is that if one cell gets weak the other battery will dump large currents into it causing boiling, overheating and venting.
Disconnect the batts from each other and use a hydrometer to measure each cell.
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Old 02-29-2016, 10:22 AM   #9
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Quote:
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A fully charged bat that is just resting should be 12.8 or near that , 12.4 is nearly dead , .
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Old 02-29-2016, 11:15 AM   #10
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I have Water Miser battery caps on my house bank that prevents this type of water loss. I've been pleased with the results over the past 5 years. I'll be switching these caps to my new house bank when this one gets replaced.



Water Miser Battery Vent Caps
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Old 03-01-2016, 07:01 AM   #11
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If the thruster batt is near the operating unit the chance is that it gess discharged more than the other batts in the circuit 30-40 ft away.

When the use is over those other batts will want to bring the voltages up to the same level.

So instead of having a 20A batt charger , you may be providing 200-400 amps of charge , for a short period of time.
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Old 03-01-2016, 07:40 AM   #12
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If the thruster batt is near the operating unit the chance is that it guess discharged more than the other batts in the circuit 30-40 ft away.

When the use is over those other batts will want to bring the voltages up to the same level.

So instead of having a 20A batt charger , you may be providing 200-400 amps of charge , for a short period of time.
What you're saying is the thruster battery/batteries are parallel to the house batteries and they charge up the thruster batteries? If that is the case, the wire gauge between the two banks should be equal to the combined amperage of the largest bank since they are in effect, one battery bank.

If they are combined, then the thruster batteries won't be as discharged with the use of the thruster, and won't generate the high recharge currents since all the batteries would be nearly equally discharged during thruster use.

A better design is a battery isolator between the house bank and the thruster batteries, so you only discharge the thruster batteries, and recharge them at a reasonable rate. That way, the wire between the isolator and thruster can be much smaller.
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Old 03-01-2016, 10:12 AM   #13
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"What you're saying is the thruster battery/batteries are parallel to the house batteries and they charge up the thruster batteries? If that is the case, the wire gauge between the two banks should be equal to the combined amperage of the largest bank since they are in effect, one battery bank. "

Yes , but most folks do not use very large wiring from the house to the thruster , so the voltage seen by the thruster batt is diminished by the thin wiring,and distance.

The thruster batt supplys more voltage during the run which can be a very high amp draw,running it down as the wiring is too thin for big amperage to help keep it up..

However when the thruster is off , the higher V house can use the existing wiring for a higher than usual charge rate.

A number 4 or 6 wiring will not usually do the job.
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Old 03-01-2016, 10:22 AM   #14
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I much prefer AGMs for inside cabin applications like thrusters. Wet cells in the ER only.
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Old 03-01-2016, 10:23 AM   #15
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In that case the wire should have a fuse to the capacity of the wire, lest it become an electrical heating element and cause a fire when the house batteries try to dump too much amperage into the thruster batteries. Better to have them isolated. IMHO
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Old 03-23-2016, 10:28 AM   #16
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Yes, sounds like it is being boiled out by the charger. This is often not the charger that is the problem though. It can be caused by one of the batteries connected to the charger having a shorted or weak cell. I would turn charger off for a few hours and then measure battery voltage, should be about 12.4 volts. Then hit thruster (assuming the batteries are for the thruster) for 5 seconds or so. Check voltage again and if it is down by more than two tenths of a volt I would suspect battery replacement is due. In my experience overcharging is most of the time caused by a defective cell.
Just a note that I keep forgetting to check the battery voltages but will try soon. There are two 8D batteries with West Marine stickers, less than two years old as I recall. The bow thruster system is it's own separate system....the two batteries, a dedicated charger for just those two batteries....wires going to the port/starboard joystick and the charger from one of the ac circuit breakers. Charger to the batteries, batteries to bow thruster control.

In feeling the cases there is no excess heat and there seems to be plenty of water in the cell at the puddle. I'm wondering if previous owner didn't overfill that cell. Anyhoo, will check voltages soon as I can remember (not on the boat that often this time of year)

Guess I need some Arm and Hammer to neutralize the acid before wiping it up, huh..
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Old 03-24-2016, 01:53 PM   #17
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Overfilling of one of the cells when topping off the water level can also cause this.

Do the checks as described to ensure the one battery is in good shape.
But take a good hard look at your water topping off procedures.
I quit filling to the ring at the bottom of the filler hole because charging would drive off a mist. I tried to maintain a good level without the water touching that ring and the problem disappeared.
May not be your cause but if the batteries and the charger appear to be good then review your topping off procedure.
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Old 03-24-2016, 02:08 PM   #18
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Overfilling of one of the cells when topping off the water level can also cause this.
May not be your cause but if the batteries and the charger appear to be good then review your topping off procedure.

This was my first thought. Over charging will boil off the water normally resulting in too little water. Never top off the water on a discharged battery, wait until it's fully charged and don't over fill, but never let the plates become exposed.
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Old 03-25-2016, 05:18 PM   #19
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I would tend to vote for an overfilled cell that just burped out some acid or a bad cell. A 20A charger would have a hard time overcharging a 1700AH bank unless it was REALLY bad.

Some checking with a meter both during charge and after rest and a specific gravity test on all cells should shed light on this.

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Old 03-25-2016, 05:59 PM   #20
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Quote:
Originally Posted by Dune View Post
1700 amp 12 volt D size as I recall, two of them, maintained by ProMariner ProSport 20 charger. Batteries less then 2 years old, mounted just a foot or so behind the bow thruster tube. All state of charge lights check ok on charger.

Puddle of acid found on top of one battery, perhaps 4" circle. Checked the cell in the middle of it, has plenty of acid still.

Could this have happened from something so mundane as rough seas at the dock ? Would make no sense if so however, seeing as it made it from Florida to SC without a leak like that.

So, gotta be either that, combined with cell cap seal deterioating (seemed ok though) or something strange with charger overheating that battery, right ?

(and yes it was acid not a rain leak...I dipped finger in and touched a tiny bit to my tongue...yikes)
Are these two 8D 1700 MCA batteries? Big difference from 1700 Amp Hour bank. It is unlikely that the Pro Mariner 20 would over charge two 8Ds unless there is a charger malfunction.
Check the cells with a battery hydrometer (<$20 at an auto parts store). Each cell should be pretty much equal. A bad cell specific gravity will read much lower than the others and will drag the battery voltage down to the 12.4-12.5 range with the other cells good.
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