6V battery problems

[captainkf]

Here's one for you Sharkey (and of course all others)


I have 8 6v batteries for the house system and 2 8D's for the starting system. I know some might think this is a bit overkill. They cost me nothing though, so I thought why not? I tested them all before putting them in. They were not perfect but they held a reasonable amount of charge. Well, things have changed. They are not able to hold a whole lot anymore but I don't want to junk them. I have read about people emptying them, flushing with distilled h20, they refilling and charging. Being such beefy batteries I have read they can handle it. I have topped them up, I use a very nice 3 stage charger (I have a 4 stage also, which hasn't helped much), they are clean, I use 1/0 welding cable with soldered (sp ) ends. I think my electrical system is solid.

Power control center. Ac breaker, perko dc power source selector, tripp 750 watt pure sine inverter, motomaster 1200 watt inverter.

http://www.skoolie.net/gallery/v/Skooli ... 1.JPG.html

You can view the batteries here. This is the pic after installation. They haven't changed asthetically.

http://www.skoolie.net/gallery/v/Skooli ... 7.JPG.html

Am I doing somthing wrong? Is it possible that one pair might be shot taking out the rest? How do I test for this?

So many questions, I hope someone (or many) has the expertise to assist.

I look forward to your creative reply's as per usual.

-Richard

[Sharkey]

Well, you didn't tell us which set you're having problems with, but I'm going to assume that it's the house batteries.

In any case, series/parallel connecting unmatched sets of batteries is less than desirable. Unless ALL of the batteries are the same age/make/type, have experienced the same charge/discharge cycles, and had the same maintenance, then you are asking for trouble. It only takes one cell (not battery, 2 volt cell) to cause the whole thing to get crappy fast. In the case of unmatched batteries, you end up with the strong ones charging the weak ones during idle periods, and the weakest ones doing nothing under load.

As batteries age, they lose capacity, even without catastrophic failures. Usually this is due to sulfation, which is the growing and hardening of sulfur crystals on the plates. There is no effective method to reverse sulfation. The other "wear-out" mode for batteries is the loss of active plate area due to normal erosion of the lead material.

Flushing the batteries will only help of you are experiencing higher than normal self-discharge rates due to the chaff that falls off the plates building up a layer in the bottom of the battery that reaches the bottom of the plates, causing a conductive path to discharge the cell(s). More often than not, attempting to flush will stir up the sediment and lodge it between the plates somewhere, resulting in shorted cells.

Changing the electrolyte probably won't help, especially in the long run. Pouring new electrolyte into a tired battery will perk it up in the short term due to the greater concentration of sulfuric acid in the electrolyte, but this stronger acid will cause the ageing process of the battery to accelerate, causing it to completely fail sooner.

If you must continue to use worn out batteries, weed out the weakest of them and send them to the recycler. Running with a set of fewer batteries that hold a charge as long or longer is better than limping along on old worn out ones.

There's nothing like a nice fresh set of batteries. Lots of available current, loads of ampere-hour capacity, and high charge/discharge efficiency. Face it, eventually, you'll need to buy new batteries, and if you wait, they'll cost even more than they do now!

I ran into this on my EV Rabbit. In the end, I decided it was nuts to be hauling around 1,000 pounds of old batteries that would only drive the car as far as 200 pounds of fresh batteries. And yep, a set of T-105's for that car run about $1,200. And yep, the set I put in some years back is worn out and needs replacing again. Ouch.

[captainkf]

Yes, I know it is not optimal to mix old batteries together. However the price (free) was too good to pass up. Yes it is the house bank that is lacking. After being charged the resting voltage drops to 12.8. The battery guy I deal with said that is reasonable for older 6v's. I will replace mabye next year, I just don't have the $ right now as we are moving and I am switching jobs. Good times!

I have never cycled them below 11.2 volts, could this be a problem? They still hold enough juice to carry us through 4 days of boondocking, so they do for now.

I appreciate the heads up about replacing the electrolyte in them.

What do you think is the best diagnostic tool for finding a pooched battery?
Electorlyte tester, multimeter or load tester?

I load tested all these before installing these before using them. Finding an inexpensive load tester that can test 6v has been a challenge.

Thanks.

-Richard

[Sharkey]

I have never cycled them below 11.2 volts, could this be a problem? They still hold enough juice to carry us through 4 days of boondocking, so they do for now.

Yes, that is the problem, but not in the way you think it is. At 11.2 volts, a 12 volt battery is discharged ~way~ past the optimal 50% depth-of-discharge. As you probably know, each time you take them to a low state of charge, you shave time off their useful life. Lead acid batteries do not benefit from deep discharges, in fact, it hurts them badly.

What do you think is the best diagnostic tool for finding a pooched battery? Electorlyte tester, multimeter or load tester?

All three, but the hydrometer (a good one, temperature compensated, not the little colored beads in an eyedropper, but a full-scaled scientific-type) is the only one of the three that can isolate your problem down to a specific cell in a 6 volt battery of three cells.

A load tester (at least the type that are used in automotive applications) is only an approximation of actual capacity, and really is only useful when comparing batteries to each other. It would allow you to find out which are your weakest batteries, but not much more than that. An actual load test involves applying a steady-state load of a known value, and counting the time until a benchmark voltage is attained. Most batteries are rated as 8-hour capacity, so a 180 ampere-hour battery would be load tested at a steady 22.5 amperes and left to discharge at that rate until the terminal voltage read 10 volts (really, really dead). It's kind of a destructive method of determining capacity.

Battery terminal voltage is proportional to battery health, but isn't 100% effective in determining capacity. One battery may have more capacity than another, but at a lower terminal voltage.

How often are you giving them equalizing charges? If you are discharging them deeply, you should be overcharging them at least once a month. In your case, I would isolate the pairs of batteries into four 12 volt packs and then charge the heck out them individually for 6-8 hours, making sure that the terminal voltage gets up to 15 volts during the entire time. This will agitate the electrolyte, insure that each cell is fully charged, and dissolve any soft sulfur deposits on the plates. The cells will boil like mad during this time, so be aware that you will probably have a clean-up job afterwards. It helps to loosen the caps and set them on the opening a little cockeyed to allow the gas to escape, but keep most of the liquid that pops to the surface inside the battery. You will be making lots of hydrogen gas, so have plenty of ventilation going to prevent explosions. Much better to do all this outside the bus.

Most "automatic" battery chargers will never allow the terminal voltage to reach 15 volts, so you'll need something that doesn't have an internal regulator. An old fashioned gas station "brute force" charger is what you want. Remember that during this time, you'll be watching terminal voltage, not charge current. Apply whatever it takes to get the voltage up to 15 volts and ignore the current.

If they need water, only add it ~after~ they are fully charged (in the normal manner), and be sure to check the level after equalizing, as it tends to boil off a lot of water.

Also remember that battery efficiency is affected by temperature. In the winter, terminal voltage will be depressed, and capacity will be lower.

The best way to know what the capacity of your batteries is comes in the form of an ampere-hour gauge that is connected as part of your metering on a day-to-day basis. Your batteries would have a capacity of 720 ampere-hours if they were fresh, meaning you should be able to pull 360 ampere-hours out of them before hitting the 50% DOD point. That's approximately 4,300 watt hours, which is a significant amount of power. With an installed AH meter, you could look at your 4 days of use and get an idea what the true capacity of your bank is.

Anyway, more stuff to think about...

[captainkf]

Thanks for the thoughtful reply. I may wait until sping before taking you up on your suggestion of the big 15 volt charge. I have 3 chargers, and all are "intelligent" chargers, however I do have access in the spring to a simpler machine.

They have only gotten that low once. Usually when I use the bus they only get down to 12.1 as I don't like to run down the batteries too much. If I need more power I switch it to the 8d's.

Thanks for the info. I am sure I will comment more after I have processed the info more.

-Richard

[Sharkey]

OK, but remember, the longer you wait, the more solid the sulfur deposits become and the less likely they will be to become dissolved by the equalizing charge.

There are a variety of "pulse charge" anti-sulfation devices which claim to reverse crystalized sulfur deposits. Their manufacturers claims are still unproven and many in the battery industry doubt their effectiveness. I own one (it was given to me), and I use it frequently when charging. The general consensus is that they don't hurt anything and might help, but maybe not.

[captainkf]

I ran an equalizing charge the other night and that did help. I have heard of people doing this upwards of once a week with good results, assuming full time use. We are heading to BC tommorrow in the bus, where it will stay for a month until we move out. I'll charge it up and leave her. Have a great Christmas all!

-Richard