10/2 amp battery charger

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On 5/3/15 3:45 AM, sms wrote:

A battery that has just been on a charger or come in from driving may well read 13.8 volts, but it will settle down over a period of hours. A brief load helps it settle faster.
The article points out that it's hard to know the best voltage for an automobile regulator. They all seem to be temperature compensated these days, providing more voltage for a cooler battery. That helps.
A battery used for for a couple of 10-minute drives a day would probably last longer with more charging voltage. A battery on the interstate 10 hours a day would probably last longer with less voltage. How can a car manufacturer predict your driving habits?
I once owned a charger with a switch for conventional or maintenance-free batteries. The maintenance-free does better with more charging voltage.
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On Sunday, May 3, 2015 at 4:44:08 AM UTC-4, J Burns wrote:

Exactly. A fully charged batter is around the 12.6V that you state. When it's being charged or right after it's been charged, then it will be temporarily higher, but that higher level is temporary and not necessary for it to be fully charged. To bleed off that excess, you can just put on the headlights for a minute, then measure the voltage.

BMW has a solution. Their new cars now have some sophisticated charging/monitoring system that closely controls the battery. A real nice feature of this for the consumer is that if you replace the battery, you have to go to the dealer to have the new battery registered into the car computer. I'm sure this is really about making those batteries work better and not making money for the stealerships, by leading you to them to buy their batteries, right?
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On 5/3/15 9:51 AM, trader_4 wrote:

I like that! I haven't even been able to find out if my Walmart battery is low-maintenance or maintenance-free. The cell caps can be removed, but that doesn't prove it's not maintenance-free.
I'm very curious about the specifics because after charging, it may take 48 hours to come down to a "proper" voltage.
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wrote:

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
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On 5/3/15 4:45 PM, snipped-for-privacy@snyder.on.ca wrote:

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.
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wrote:

Normal battery SG for up to 25C is 1280. 1240 is common for tropical use. 1290 to 1300 works best for arctic use.
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On 5/3/15 5:58 PM, snipped-for-privacy@snyder.on.ca wrote:

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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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?
--
Tekkie *Please post a follow-up*

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wrote:

In the aircraft world they are referred to as a 14 volt system, with 12 cell battery systems referred to as 28 volt.
As for the chargers - a "decent"charger limits the charge current as well as the voltage, so a 2 amp charger will not put out over 2 amps into the battery for trickle charging and will limit the voltage to 14.4 so it will never boil a battery dry.. Most chargers out there fall short of "decent" but there are more and more "microprocessor controlled" 3 stage chargers on the market for approaching an affordable price.
Some will test the battery for shorted cells, indicate the failure, and refuse to charge a defective battery.
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On 5/3/15 9:06 AM, snipped-for-privacy@snyder.on.ca wrote:

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.
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wrote:

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.
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wrote:

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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