Of Generators and Batteries

[Leon]

That depends on which cell is shorted as to what voltage will be remaining. Not always will a battery with 1 shorted cell show 10 volts. I'll admit that it has probably been 20 years since I have done any battery testing. Given that, When I tested for a short, I would connect a lead to 1 battery terminal, I do not recall which, and another lead/probe would go down into the water in the cell. If the first cell was good the volt meter would indicate about 2 volts. With the probe in the next good cell the voltage would be about 4 volts. If the third cell was bad/ shorted out, the voltage would remain at about four bolts for the remaining cells and or if another lead was connected to the other terminal.

And I need to correct a statement that I made earlier. The second battery connected up parallel will also be run down by the bad battery. Having retired from the automotive industry and worked for Oldsmobile for 10 years I saw this often. One day the engins starte fine, the next morning, only a click from the starter solenoid. Oldsmobile always recomended replacing both batteries if one battery was bad as the second battery could often be recharged but would seldom hold up after having been discharged so sompletely. Oldsmobile/ Delco ate many batteries under warranty on cars equiped with dielel engines.

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[Roy Smith]

How is that possible? A car battery is just 6 lead-acid cells in series, that happen to share a common case. Each cell has a potential of a little over 2 volts. The schematic looks like this (assuming I haven't gotten the anode and cathode symbols bass ackwards):

• | | | | | | - ------||-----||-----||-----||-----||-----||------ | | | | | |

Since each cell produces 2 volts, the end-to-end potential is 12 volts. If you short out a single cell:

• | | | | | | - ------||--*---||--*--||-----||-----||-----||------ | | | | | | | | | | +-------+

You're left with 5 2-volt cells in series, giving you 10 volts. It doesn't matter which cell shorted, you're still left with 5 2-volt cells in series. 2+0+2+2+2+2 is the same as 2+2+0+2+2+2.

Anybody who designs a system with two voltage sources in parallel or two current sources in series deserves what they get.

[no(SPAM)vasys]

One of the things you have to watch out for in a set up like the one your friend is using is if the batteries are deep discharged you stand a chance of "cell reversal". With lead-acid batteries no cell should be allowed to discharge below 1.75 volts. See:

[Leon]

Many years have passed,, ;~( and I undoubatably have use the wrong termonology. Seeing was believing with the old style battery tester and my memory of the end result is probably inaccurate. That said however since a battery by definieion is more than one, and or several of any one thing, a battery of cells make up a higher voltage storage unit commonly called a battery. A D cell is technically not a battery but 2 D cells are a battery. I guess to help understand what I am trying to convey, cells in a series contribute to a higher voltage. If one of the cells in a series no longer allows current to pass through the voltage stops increasing at that point. I think similarly with cheap Christmas tree lights wired in a series if a bulb does not work the whole string quits working. If you terminate the strings of lights before the bulb that does not work and close the circuit the lights before the non working light will again light up. A bad cell will have a detremental effect on the remaining cells.

I totally agree but I suspect at that time a battery with enough cranking amps would have been too large to fit in one spot under a crowded hood. 2 smaller batteries could be more easily located. IIRC the combined CCA's were around 1500. The smaller V6 260 ci diesel used in the front wheel drive vehicles used a single larger battery rated at over 1200 CCA. The whole Olds diesel scenario had many weak points. Further, RV's use multiple batteries set up parallel for lighting and water pumps. When one went bad they all seemed to go bad. I was able to make some of them last a little longer by disconnecting them from each other during storage. Then only 1 would usually go bad at a time. I would check the voltage of each one before reconnecting.

[Wilson Lamb]

Yeah, I meant to mention golf cart batteries. But paralleling is bad, as mentioned, because of dragging each other down. Series is better also because the higher voltage means less current is needed to the appliances and to an inverter. Less current means less voltage drop and smaller connectors and wire.

I'd bet that a good inverter on 48, 72, or 96 volts input and 120VAC output will give superior performance, long term, UNLESS it is way oversize. At near full load, they can be in the 90% efficiency range. Ideally, one could use multiple inverters, so that each runs something that puts it at near full load.

Obviously there are lots of tradeoffs, but the 12V appliances/electronics are great. Having multiple 12V batteries that can be switched in as needed would be a good way too handle the TV load.

Then again, there's a lot to be said for peace and quiet! Buy some books! Wilson

[Greg O]

Digital voltmeter AND a hydrometer. I have yet to have a hydrometer fail me for testing lead acid batteries, unless the battery is sealed! Greg

[max]

They make inexpensive solar chargers for autos. You can get a few and hook them up. max

[Too_Many_Tools]

Very interesting thread

Does anyone have links as to what and where to buy 12v appliances?

I am new to the world of camping and will be setting up a cabin off grid later this year.

Any suggestions are appreciated.

Thanks

TMT

[no(SPAM)vasys]

[Leon]

The most abundant places would probably be RV dealers. But, they are going to come with a premium price tag.

[Wilson Lamb]

More efficiency talk:

For something that isn't on long, like a blender or microwave, efficiency isn't all that big a deal, so an inverter for that stuff is fine. The same inverter will carry small tools, like drills and sanders.

For radio, a car radio and some good speakers is a fine choice.

For TV, if it has to be big, then an inverter just big enough to carry it will be best.

2KW is a big generator. You should be taking a few hours for a full charge. Say you run 50V at 15A, that's only 750W. There are some small water heaters at about 1-1.5KW, so you could heat enough water for a shower or two at the same time. Larger generators are gas hogs, especially when not heavily loaded.

[Patriarch]

"Wilson Lamb" wrote in news:pYCZd.4702$ [e-mail]:

I'm not disagreeing with all of this, as my limited real-world experience is several decades old.

I'm curious, however, about why one would consider an electric water heater, off-grid? It seems that burning a fossil fuel to make electricity to make resistance heat for water HAS to be less efficient than applying that burning fossil fuel directly to the water tank. Or so I would think.

In a vacation home, one could consider a wood fired water heater, no?

Patriarch, who loves these electrical, educational threads, generally from a distance.

[Teamcasa]

"Wilson Lamb" Snip

Snip

A 2KW generator is not a very big generator at all. One of my Honda's is a

2000W is small, quiet and efficient.

My other one is 5500W, water cooled, quiet and will run my entire house with kids for 10 hours on 3 gals of fuel.

OP said the cabin had most appliances on propane so I don't think an electric water heater is much of an option.

Dave

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[Wilson Lamb]

[Patriarch]

Charles Krug wrote in news:ZvXZd.142020$ [e-mail]:

Got any free plans?

[Charles Krug]

Nope. But I bet Joat does.

[Patriarch]

Charles Krug wrote in news:qZZZd.142445$Th1.83863 @bgtnsc04-news.ops.worldnet.att.net:

YOU send him the email. ;-)

[Fly-by-Night CC]

Wow, 40 messages and even some divergance to plasma torches... Did I mention that you guys are not only worldly and wise but WORDY?

Thank you all for the hydrometer suggestion. Given the "maintenance free" batteries of the last decade or more, I'd pretty much forgotten about hydrometer testing.

I've passed along the replies that I thought the cabin owner could use. I'm going to recommend that I bring back the batteries after our stay and he can then have them load tested - and likely replaced. I'll also recommend that he replace the 4 with 6 or 8 deep-cycle batts. Plus hook up some sort of solar trickle charger for the periods between visits. (Not sure how effective they may be as the cabin is well surrounded by tall trees - plus the often cloudy/rainy October to April up here.)

Thanks again - I knew I'd get good feedback from you old farts. Age wise over youthful beauty, no?

[Fly-by-Night CC]

I had to include that and similar wood references, dear Leon, as I didn't want to be accused of posting an off-topic message. ;)

[Norman D. Crow]

Well, you know the saying about "If you can't dazzle them with brilliance, then baffle them with . . . ". You get both ends of the spectrum here, Owen. Sorry about the "troll" remark, but it sounded *almost* like one.