I imagine that's because automobile systems were developed to power a starter from a battery, and, in the days of generators, you could be down to 12 volts on the road.
Aircraft electrical systems were designed primarily to power equipment aloft, without much variation in engine speed.
Actually, with any battery I've tested. I've never had a problem sucking up enough electrolyte or having bubbles get in the way. The floating part of the hydrometer has a semi-spherical bottom, and if there were bubbles, they would go right past the floating part and up to the surface of the electrolyte.
How could they not be? There was nothing adhering to the floating part. What else could cause a bad reading?
How?. What hygrometer changes its reading so quickly it can distinguish one cell from another? And why would the condition of the cell aftect the humidity above the cell?
I'm dubious, but it doesn't matter this time. He had hoped to take the battery with him so I started charging right away.
Do i have another load, other than his car or my car, which I don't want to bother? A lot of things could have done. My question was "What does it mean to be a 2 amp charger if it charges at 7 amps? " I don't see how any of this would have helped to answer that question.
But you were not here. Thanks anyhow.
Neither does mine. Two of you seem to have gotten the impression that my ammeter had two scales, but I don't know where you got that impression.
Thanks for the info.
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The only "maintenance free" battery is one you cannot maintain. If you can remove the caps it is possible to maintain the battery - so it will be a "low maintenance" battery by definition.
It's called a "surface charge". After charging a battery to a full charge, the voltage will often be higher than the "chemically dependent" charge - the voltage predicted by the chemical reaction - but with a light load the "surface charge " will dissappear and the true battery voltage will be evident.
The true voltage will vary depending on the acid strength used in the battery - batteried for cold climates generally start with a higher SG than batteries for a warm climate because to reduce self discharge in hot climates they start out with a lower SG. This means the battery sold for use in the Kalahari desert will have a lower voltage than a battery sold for use in Ottawa, Ankorage, or Nunavit
And the avionics need to be designed to function optimally at the prevailing operating voltage. Something designed with a 12 volt maximum voltage wouldn't last long at 14 - and in the aircraft world they are nothing if not precise when it comes to specs.
Automobile owners, if told their system was a 14 volt system, would be all bent out of shape to find the resting state voltage to be only
12.6.
I must have used the wrong word. What's the one that measures humility? Until 1959, the best batteries were at Humble service stations. A battery that's all puffed up could explode.
You said the battery was dead. If a 2-amp charger was charging at 7 amps, one possibility was that the battery was dead because of shorted cells. A DMM would have told you. it would also have told you if it was really charging at 7 amps.
That's what we need, a humility meter. Really. I can think of lots of uses.
But I never had any doubt that 7 amps, or between 6 and 8 amps, were going into it. A lot more than 2 amps. I could that tell just by the high number of hydrogen bubbles surfacing in each cell.
When I use the thing again, I'll check the voltages at the 2 and 10 amp settings.
Lately I've read that maintenance-free means a calcium alloy on both plates, and the cells may be accessible, maybe to check specific gravity.
I've read 4 hours or maybe 8. My battery will hold its "surface charge" a lot longer. An AGM will do that, but mine's not AGM.
I read about that in an Exide manual given to me in the 1970s. It didn't say how much the voltage or SG might vary.
I'm interested, and dadburnit, you've talked me into buying a hydrometer to hang beside my hygrometer.
Wikipedia says stratification happens in normal use if you don't fully charge a battery. The bottoms of plates sulfate and the tops corrode. I want to check that with a hydrometer. Watch me drip acid on my pants!
There's a curb in front of my house. Maybe I should make a habit of driving over it to keep my battery stirred up. I won't know until I buy a hydrometer... unless of course I could borrow one...
Normal battery SG for up to 25C is 1280.
1240 is common for tropical use. 1290 to 1300 works best for arctic use.trader_4 posted for all of us...
Many car makers have this now. There is an article in "QST" magazine about them and electrically installing ham radios properly. It's not just connecting a wire to the positive... Both positive and negative sides must be fused. I wonder how many alarm / radio shops know this?
Thanks. I have a spreadsheet from batteryfaq.org. It's in fahrenheit.
80F is close to 25C. It says the SG at 80F for sb/sb or sb/ca (low maintenance) is 1.265. I wonder how widely their figure applies.One article about stratification says the watery mix at the top causes corrosion and the concentrated mix at the bottom causes sulphation. Another article says it's the other way around. It sounds as if a certain SG is a happy medium between corrosion and sulphation. I wonder if it varies with temperature. I wonder if it varies with plate composition.
If batteries were really, really simple, maybe some day I could understand!
I've read that the way to tell if a battery is really charged is to see when the SG stops rising. As it's sampled at the top, that means it's fully mixed.
Darn, I'm going to end up dripping acid on my pants!
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