Of Generators and Batteries

[Fly-by-Night CC]

Oh great and all-knowing men among men, wordy, worldly and wise. Please bestow upon me your deep knowledge, your passing proficiency, sense of the common and not so much common. I humbly ask for guidance...

A friend, really my wife's manager, has a cabin, in the woods, near St. Helens. No electricity and runs the cabin off a Honda generator hooked up to 4 auto-style batteries, on a plywood shelf, connected in series. The generator, below the plywood shelf, is run through an inverter to charge the batteries - when they're full, the generator is turned off, switches are switched and the needed electric comes from the batteries.

Problem is that the batteries, on the plywood shelf, don't seem to hold a charge as they did a couple years ago when he bought the cabin, in the woods. His father-in-law, uncle, neighbor, or grocery checkout clerk told him that one battery might be dead and sucking the juice from the others.

Last summer when he loaned us the cabin, in the woods near St. Helens, I checked and filled the cells with distilled water, and cleaned and tightened all cable connections. Seemed as though we were still running the generator, under the plywood shelf, a lot - considering that practically all of the house is run off propane except for a TV/VCR and a few lights which are religiously turned off when not needed.

We're headed up there for a week and the friend asked my wife if I might know how to check the batteries on the plywood shelf. Bless her heart, she said that I would indeed, probably, know how to test the batteries on the plywood shelf. Having a digital multi-tester at the ready, I am turning to you for guidance and awaiting further instruction.

How to test for a faulty battery? What type of replacement battery would be best for this use? What winterizing steps to help ensure long battery life?

Thank you, oh wordy, worldly and wise ones.

[David D]

Well, that lets me out, but ...

Here's one link that might be useful:

[Norman D. Crow]

Owen, are you sure this isn't a troll????? However . . .

Buy a battery hydrometer, check the cells for specific gravity. This is the best way, other than having a "resistor pile" to load test each battery. You say series connection, so you're using 48VDC to power the cabin, right? Possible to have a bad cell or two hindering things. Are you sure you don't mean they charge the batteries with generator, then the batteries run through an inverter to supply 110VAC for the cabin?

With your digital meter, you can come close by putting one lead on a post, then put a piece of wire on the other lead, remove the caps and dip the wire in the acid in the cell. Just far enough in to get the voltage, don't touch the plates! Voltage should progressively increase 2VDC with each progressive cell. Find one that doesn't, it's a bad cell.

Replacement? I would suggest a marine style "deep cycle", as they can take being drained very low & recharged better than a regular auto type.

Winterizing, make sure they are fully charged and cover them any time the cabin won't be in use for a while.

[Wilson Lamb]

Yep, the Harbor Freight battery tester is a good thiing to have anyway. It contains a big resistor to apply a test load. It doesn't tell the whole story, but is a good start to find the bad ones.

Making the voltage readings, even across each battery, after they are half or so run down will tell you more about which is the weakest.

My guess is that they are all in fairly bad shape and you'll end up buying a new set. Considering the cost of a vacation home, $250-300 probably isn't a big deal. Maybe some of the guests could pitch in on them.

I'd probably just buy the best marine battery WalMart has. Otherwise you are into special stuff and doing some research.

Care is important. It's a good idea to run them down pretty far occasionally...keeps them in more uniform condition. Also leave them fully charged when not in use.

Wally gives a good guarantee, especially on their best batteries, so keep the paperwork. I've actually received free replacements during the initial guarantee period. They didn't even check the old ones!

[Leon]

Snip

1. It does not matter if a modern battery sits on plywood or concrete. Modern batteries have plastic cases and this works much better than the wood and tar batteries of years ago that would discharge on a concrete surface.
2. If a battery does have a shorted out cell it can discharge itself and those connected to it rather quickly.

If you can check the cells individually, use a battery hydeoneter to look for consistancy in each cell. A reading that is far higher or lower will indicate a bad battery. Low readings on all cells ususlly only indicate a discharged battery. If you have a volt meter you should have 2.2 bolts per cell when the battery is fully charged and has a surface charge from not being used at immediatley after full recharge. After putting a load on the batteries for 10 minutes or so this surface charge should be gone and the battery voltage reading should be that of the battery spec. If the battery shows below 11 volts you probably have a shorted out cell. Be sure to check batteries individually and disconected from the others. Also, these batteries should be of the marine/motor home variety. If you are using regular automotive batteries they will fail in a short period of time. Automotive batteries are designed to give out lots of energy in short bursts and not be run down to a dead state. OTOH marine/motor home batteries are designed to provide a consistant LOW demand and can be safely run down to total didcharge with out harm to the battery. Typically these batteries have caps for maintence on each cell although this is not a guarantee that it is a marine/hotor home style battery.

Marine/motor home style. Do not mix with automotive style batteries.

Do not let them freeze and keep them DRY and charged with a trickle charger.

[Larry Jaques]

On Sun, 13 Mar 2005 23:18:41 -0800, the inscrutable Fly-by-Night CC spake:

Batteries wear out. Chances are very high that they all need replacement. Check the solar electric stores for tips.

Ain't gonna cut it. Take a hydrometer to check the individual cells after charging. That might show you a bad cell, ruling out a battery right away.

Carefully. (Sorry, couldn't resist.)

You'll need to charge the batteries with the generator then test them with a load tester, Owie. Got a friend at a gas station (or slight chance: rental yard) where you can borrow one? If the batteries are more than 4 years old, don't worry about going to all that trouble Just have them replace them. When I was researching solar a few years ago (just after moving up here; off-grid folks go through batteries like terlit papah), I read up a bit on batteries. Newer styles last anywhere from 4 to 10 years, max, depending upon the percentage of discharge each time. The higher the discharge rate and lower the discharge level before recharging, the quicker they die. I'm betting that those batteries are worn out in that environment.

David's William Darden link has good info. Here are more:

magazine articles, check your lib (Wow, half my bookmarks are dead already!)

Marine/solar deep-cycle @ $100-200 a pop.

House them in a warmer environment, like a basement. Keep them charged even when the owners are not there. (solar trickle)

Thanks are unnecessary. Send mass quantities of cash instead. ;)

[Larry Jaques]

Here's another good source of info, Owie.

[Thomas Kendrick]

Oops, I was tempted to suggest a trickle charger as well. The only way that will work is to remove these batteries from the cabin and take them to a location where full-time power is available. If the generator isn't running, there's no power in the cabin.

Try to find a friend in the area of the cabin who will keep these units warm, dry and charged so hauling them back and forth to your home is not required.

[Andrew V]

snip

You might post this to alt.energy.homepower or google for it. I remember lots of battery maintenance posts, just not the specifics.

Enjoy

Andrew V

[Wes Stewart]

[snip]

Really? How?

Actually to acertain charge condition, the battery should remain unloaded for 24 hours before measuring the voltage.

This is a topic that's been beaten to death in rec.outdoors.rv-travel.

Recommended reading:

of this is self-serving but it is probably the most comprehensive site around that deals with the subject.

[Don Dando]

If I were confronted with the task, I go to the local car parts house any purchase a battery hydrometer.

Don Dando

[DJ Delorie]

If it were me, I'd take the batteries home, charge them each up on the AC charger, and bring them to Autozone. They have equipment for checking batteries that beats a simple home battery tester.

You can test a battery's remaining capacity by charging it with an AC charger and them hooking it up to a light bulb (like an old headlight). If you know the watts of the light, you can calculate the watt-hours the battery is capable of storing.

Batteries should always be tested separately.

Replace these batteries with deep cycle batteries, not regular car batteries.

[Roy Smith]

First off, for this kind of use, you don't want "auto-style batteries", you want deep-cycle batteries. You will find these in a store that sells to the marine or RV markets.

A regular car battery is designed to produce large bursts of current to crank the starter motor, and then immediately get recharged and be kept topped off. This kind of battery has many thin plates to give lots of surface area, so it can generate the high current burst. The problem is that if you repeatedly run it all the way down then charge it back up (like you're doing), you will quickly ruin the plates.

A "deep cycle" battery looks similar on the outside, but inside has a fewer number of thicker plates. It cannot produce the same high-current surge a car starting battery can, but it is designed to handle many cycles of being deeply discharged and then recharged. If your friend really is using regular car batteries, that could be part of the problem.

If it's not holding a charge, it's faulty :-). Somebody else suggested a hygrometer, which will measure charge level indirectly by measuring the density of the electrolyte (water-acid mixture) in the battery.

If the 4 batteries are in series, I'd go armed with 4 voltmeters (you can get them plenty cheap at Radio Shack). Hook one up to each battery, charge up the whole bank to full charge, and watch the voltages as you use power. If one is dropping significantly faster than the others, that's your problem. You could just use a single meeter, but 4 is simplier (and increases the geek factor).

Deep cycle (see above).

Make sure the battery is fully charged and kept topped off. A dead battery will freeze, which will probably destroy it. Make sure the outside of the battery is clean; crud accumulating on the outside of the case can form a conductive path between the terminals leading to discharge. A battery will self-discharge slowly anyway, hence the need to keep it topped off. Sounds like a good application for some solar cells; they won't provide enough power to run the whole place, but will do fine to keep things topped off over the winter with no load.

[Lew Hodgett]

Could ramble on for hours about "house banks" of batteries, it is a major topic of discussion among cruising sailors, but will try to be brief.

Chances are pretty good the existing automotive batteries are at end of life and need replacement.

A hydrometer is needed to do basic battery health investigation.

Use T-105, 6V, golf cart batteries as replacements, basically a 200 AH unit designed specifically for this purpose, wired in series and parallel as req'd.

When it comes to batteries in a house bank, they are like clamps to a wood worker, you can't have too many.

In this application, I'd probably use at least 8, T-105 units.

SFWIW, I will be putting 16 of them on my boat to provide a 12 VDC house bank.

Your description of the system is confusing.

1) Is the cabin electrical system being operated at 120 VAC, being fed by the batteries and an inverter? 2) Are the batteries being charged at 12 VDC from the Honda generator?

BTW, to extend the life of the batteries, recharge more frequently.

Maximum discharge of a bank is 50%, but if you do that, you sacrifice life.

HTH

Lew

[Teamcasa]

"Fly-by-Night CC" Snip

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Assumptions: The batteries power an inverter to provide AC to the lights and TV/VCR. The batteries are old - +2 years. Small Honda generator 2000 watts or less.

Recommendations: The use of an inverter to provide AC is a poor use of battery resources. Suggest the owner get a new, larger generator. The new generators are more efficient and significantly quieter. Or Replace the lamps in the cabin with RV style fluorescent 12V lamps. Replace the TV/VCR with 12V style as well. Replace the batteries with RV/Boat batteries (deep cycle). Keep from freezing. / Disconnect all cables when not in use for long periods. Most important - Keep then clean and dry!

Many of the other suggestions for testing are good. Forget the hydrometer however, a load test is the best method. If they are a newer, car type batteries you won't be able to access the individual cells anyway

Dave

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[Leon]

Yeah, A battery is simply a serieries of cells and adding another battery simply adds another series of cells. A fully charged 12 volt battery will have a voltage of 13.2 volts. With a slight load for a few minutes the voltage goes down to 12 volts. A shorted cell works the same on the battery as leaving the head lights on with the motor not running. Basically a battery with a shorted cell will run itself down. Other batteries connected in the series will also run down through that short. With automotive type batteries there are some times 2 batteries under the hood when the car has a diesel engine. Late 70's and early 80's Oldsmobiles with diesel engines had

2 batteries. Almost with out fail if one battery went bad the other battery would go bad as a result of being run down to a dead state. Automotive batteries do not hold up long when fully discharged repeatedly.

This is true if you do not have the right type of testing equipment. A fresh charged battery will have that surface charge that I mentioned earlier and will reflect 2.2 volts per cell totaling 13.2 volts. Better HD battery testers can draw a load on the fresh charged battery for a few seconds to remove that surface charge and the voltage on the battery will drop to just at or just over 12 volts. The condition of the battery can then be checked successfully.

[Dave Hall]

On Mon, 14 Mar 2005 13:14:33 GMT, "Leon" SNIP

In the described environment which does not have electricity to run a trickle charger you may want to check around for a solar based "battery tender". Assuming the cabin is not too deeply in the woods and gets sun at least to the roof you could probably set one up rather inexpensively that would be sufficient to keep the batteries topped off as long as you give them a good charge with the generator before leaving between visits. Of course a good snow on an unheated roof................

Dave Hall

[Leon]

Oh, to go a bit farther as to how a cell shorts out, If you have ever seen in side the battery you have lead plates separated by insulators. The insulators can crack or break from excess cold or heat and eventually allow the plates to come in contact with each other. That causes the short.

[John]

Best way is to put a load on each battery in turn (sperated from each other) and monitor time vs voltage. I would put at least a

200-300watt load on (12 v light bulbs work great for loads when testing batteries)

Lead Acid batteries typically have about a 100x charge/discharge to

500x charge/discharge lifespan, depending on how deeply they are discharged before recharging. Might be a better idea to double or tripple the # of batteries so that the same usage will NOT drain them as much as now, and keep an eye on the voltage and base the recharges based on those measured voltages

Also, lead acid batteries do best if they are left >> Oh great and all-knowing men among men, wordy, worldly and wise >

[Wes Stewart]

Baloney. Look at a 12V (nominal) battery in isolation. It is comprised of 6 cells connected in series (aiding). If one cell shorts (i.e. provides zero volts) the series connection yields ~10 V. There is no mechanism resulting from this that affects the remaining 5 cells in the slightest. Period. End of story. There is no additional discharge path. Unloaded, the battery sits there providing 10V.

One or more of them with shorted cells *will not* affect the others.

This situation had the two batteries in parallel. A shorted cell in one will cause the second to discharge to the 10V (nominal) level.