These batteries were functionally dead, yet on a volt meter showed they were fine. I wasn't until we put a load tester on them that were saw their true state. We further tested each battery with a hydrometer and both showed 'replace'. What I don't understand is how can a battery show it is fully charged when looking at the volts and yet be dead? Is it the 'amps' that are dead? Is there an instrument that I can hook up to a battery and have it show me how many amps it has? Such as a battery is rated as having 400 cranking amps at 32 degrees F. I want to know how many amps are in a particular battery. Can this be done? Thanks, Ed
2007-10-29 11:42:53 · 11 answers · asked by Ed 1 in Cars & Transportation ➔ Maintenance & Repairs
Yes as you suspected there were no amps to work with.
Any good voltmeter will have a selector switch to show amps my fluke multimeter does
2007-10-29 11:46:09 · answer #1 · answered by ? 2 · 0⤊ 1⤋
A volt meter is a high impedance so it wont load the battery down, hence the high reading. The only way to test the battery with a voltmeter is to read the voltage while applying a load.
That's okay if you're testing dry cells, you just connect it a to a lamp or put a resistor across it. It's harder to do it with a lead acid battery. The best way is test it with a hydrometer, you can change the acid (that's a bit drastic) and of course you could charge it up over night and test it with the hydrometer again. You can only go by the specs as to what the battery is capable of delivering. Sorry.
2007-10-29 18:56:02 · answer #2 · answered by Andrew 4 · 0⤊ 0⤋
The batteries had a static reading of 13.8 volts, but when you put a load on them, the voltage dropped drastically and the motor would not turn.
They do make test equipment to check batteries under load. This will let you know whether the battery is good or not.
The plates inside the batteries could be covered with sulphate and not making contact and will not carry current internally.
So you are looking for a battery load tester.
Forget about the Fluke vom since it can't handle the current normally unless you would have an extra adapter.
good luck.
2007-10-29 18:53:20 · answer #3 · answered by Fordman 7 · 0⤊ 0⤋
The key is something called "internal resistance". There are various failure modes of lead-acid batteries, and one such is called sulfation: the plates become encrusted with lead sulfate in such a manner that charging won't break it down into the original lead and lead oxide. This can leave the active area of the plates too small to be able to supply much current; it acts as if a resistor were in series with the battery. The resistance isn't enough to discourage a voltmeter, because these draw very little current, but it could easily be enough to discourage an electric motor. Connect the voltmeter to the battery, and then connect the motor in addition, and watch the indicated voltage take a dive. The solution is, of course, new batteries.
2007-10-29 18:51:50 · answer #4 · answered by Anonymous · 0⤊ 0⤋
There are battery charger/testers that do show the actual amperage before and after the charge. They are referred to as conductive battery testers.
It is fairly common to see a bad battery that shows 12 volts. This is normally a result of sulfated plates in the battery. The potential is there, just not the current. Once the plates become sulfated, no chemical reaction takes place, thus you are only reading a surface charge on the voltmeter.
2007-10-29 18:51:22 · answer #5 · answered by Anonymous · 0⤊ 0⤋
The only way to correctly test a battery is under load. A battery which is nearly expired may well show full voltage in a no load condition. In order to measure the current the battery must be under load. An Ammeter is placed in series with the load to measure the amperage supplied by the battery.
2007-10-29 18:53:50 · answer #6 · answered by mustanger 7 · 0⤊ 0⤋
The internal resistance of the battery has become fairly high, which is why you can't pull much current out of it. Think of a resistor inside the battery - it's value is now quite high.
An ordinary DVM won't tell you (DO NOT use one set to 'DC current' in an attempt to measure the current that the battery can deliver, as you will either most probably blow a fuse in the meter, or possibly burn it out.)
Batteries don't have amps in them, but I think there is a thing a bit like a DVM that you may be able to buy from your local car parts store that will give you an idea of the condition of your (car?) battery.
2007-10-29 18:53:26 · answer #7 · answered by Here there and everywhere 5 · 0⤊ 0⤋
if the battery has 12 volt with no load,the voltage will drop the more you put a load on it,you need the volts to hold.
2007-10-29 18:52:20 · answer #8 · answered by tugboat 4 · 0⤊ 0⤋
with out amps the voltage is Miss leading.IT says you have 13.8 volts.but no amps to push them.
2007-10-29 18:52:40 · answer #9 · answered by Anonymous · 0⤊ 0⤋
You may need to add water to your battery.
2007-10-29 18:46:58 · answer #10 · answered by Anonymous · 0⤊ 0⤋