impedance meter to test car battery

The latter.

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Thanks,

Also when a car battery can no longer provide enough CCA to reliably start the car but is in otherwise "good condition", are there any disadvantages to putting a supercapacitor in parallel with the battery rather than replacing the battery with a new one?

cheers, Jamie

why bother? just get new one

I've actually seen that video (good youtuber), ironically his first sentence gives the answer to your question! (lead acid batteries are a waste of money)

cheers, Jamie

How much is a supercapacitor that will have a useful capacity at that voltage?

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Under $40US on ebay (see above link)

cheers, Jamie

:

ry

oltage?

Not sure how the battery and supercap will interact. On discharge, the cap will supply current at a decreasing voltage, so the battery won't supply m uch current until the voltage starts to drop. As the battery voltage start s to drop the battery will drain down. Once the cranking stops and the alt ernator starts to charge, the cap will still be at a low voltage and will s uck up all the current. Do you know if the electronics in the alternator w ill prevent damage by charging a very high current into a low voltage? Wil l the current be limited? Will the alternator not try to raise the voltage immediately? I don't really know how the electronics in the alternator is designed.

Regardless, I don't see the point. A new battery isn't $100. I get mine a t Costco for more like $70, which is more than $40, but not enough to make me want to try to make this work.

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Impedance isn't a very useful measure for a couple-second surge into the nonlinear* range of operation. What frequency was the impedance measured at? Around 1Hz would seem to be more relevant.

*Actually I don't think it's so much nonlinear at low voltages, but it is for similarly high voltages, so it seems worth noting. That is, you can discharge a battery with say 200A at -3V change, but you sure as hell can't charge at +3V and 200A.

On a slightly less related subject, I've had good results floating car batteries. Once most of the charge is done, remaining charge current drops very slowly, like at 13.6V it might be down to 500mA after a day, 300mA after two days, etc. The further down it goes, the stronger the start.

Tim

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"Jamie M"  wrote in message  
news:qubftk$uds$1@gioia.aioe.org... 
> Hi, 
> 
> For a 12V lead acid car battery, at 12.6V and a 
> measured internal impedance of 9mOhms, is that enough 
> info to accurately estimate the CCA of the battery, or should 
> a battery load tester be used? 
> 
> cheers, 
> Jamie

te:

ly

tery

a

voltage?

ap will supply current at a decreasing voltage, so the battery won't supply much current until the voltage starts to drop. As the battery voltage sta rts to drop the battery will drain down. Once the cranking stops and the a lternator starts to charge, the cap will still be at a low voltage and will suck up all the current. Do you know if the electronics in the alternator will prevent damage by charging a very high current into a low voltage? W ill the current be limited? Will the alternator not try to raise the volta ge immediately? I don't really know how the electronics in the alternator is designed.

at Costco for more like $70, which is more than $40, but not enough to mak e me want to try to make this work.

Price depends on the size of that battery. Larger batteries for SUVs, for example, are over $100. But that doesn't change the rest, which I agree with. A battery should last 5+ years. It's a small expense in owning a vehicle. Many places even install them for free. I would not be looking at screwing around with band-aids that could have an undesirable effect on other parts of the system.

You seem to have forgotten that altenators are current sources, incapable of producing more than the rated current.

--
  Jasen.

rote:

ably

y

attery

t

re a

at voltage?

cap will supply current at a decreasing voltage, so the battery won't supp ly much current until the voltage starts to drop. As the battery voltage s tarts to drop the battery will drain down. Once the cranking stops and the alternator starts to charge, the cap will still be at a low voltage and wi ll suck up all the current. Do you know if the electronics in the alternat or will prevent damage by charging a very high current into a low voltage? Will the current be limited? Will the alternator not try to raise the vol tage immediately? I don't really know how the electronics in the alternato r is designed.

ne at Costco for more like $70, which is more than $40, but not enough to m ake me want to try to make this work.

So your SUV takes a larger battery than my V8, full size pickup???

Sure, you can pay more, or you can pay less for the same battery. Costco h as a good price, but not as good as it used to be. One I bought had a 9 ye ar warranty, pro-rated of course, but only after 3 years of replacement. I think someone lost a lot of money on that and the warranty is a lot short er now.

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If it is a current source, then it can be equated to a voltage source with a high value series resistor. What would the open circuit voltage be? What would the short circuit current be?

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  Rick C. 

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It's seems like it is rare to get 5 years here in North Florida. More than 3 years less than 5 years.

One does NOT measure battery _impedance_; one _can_ derive internal resistance and thus CCA. Standard is to use an 0.01 ohm resistor (120A load) with a voltmeter; voltage must be greater than 10V (100A load) after ten seconds.

Both gel (sealed) and standard batteries, if good, will easily pass this test.

Say what? The current would then decline rapidly with any applied load. That isn't a current source.

Ok, if you say so Always Wrong.

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  Rick C. 

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And what exactly was that about? A current source most definitely does not look anything like a voltage source with a high value resistor is series. It's not clear exactly what the poster who said alternators are a current source meant. If he meant they behave similar to an ideal current source, that's wrong too. They look more like a voltage source, with the alternator/VR trying to maintain a constant voltage. A current source puts out a fixed current, regardless of the voltage or load.

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Do you need a LMGTFY link, Always Wrong? Try "Norton equivalent". This i s the real problem with Always Wrong. Anyone can be wrong, but it takes a special person to be wrong and refuse to admit they are wrong when they onl y need to look it up and learn something. I'm guessing you know or knew th is and had a brain cramp. Now you have dug in your heels and are refusing to acknowledge that you need to learn or relearn something.

I know in the "old days" the generators/alternators would try to maintain a constant voltage output. But that's actually not ideal for batteries. I don't know if they have improved any or not. Certainly it would not be har d to do. I don't know if the alternator protects itself in event of an ove rload which would be likely if a huge supercap is drained down to 6 volts a s the engine cranks. Then when the engine starts and spins up the alternat or tries to drive 13 volts into a hugely capacitive load at 6 volts. Actua lly, in this case a current source would be preferred.

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  Rick C. 

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You are mistaken. Please get an elementary textbook on basic electronic theory and look up de Thevenin's and Norton's theorems.

--

-TV