Battery Analyzer

[crpntr133]

Bingo, that is why just a voltmeter for the most part tells you nothing.

Also watch out for some of the newer batteries since they need to be cycled (charge/dishcarge) a few times for a truly full charge to be taken. They can also discharge a fare amount by just sitting for a few months

 

[Hoosier]

Ok.... You must have a fancy charger.

Mine is from here... It won't give any info except an individual LED light (green/red).

If you don't mind, I have a question about NIMH battery.

It this kind of battery also requried to be fully charged and discharged three times before actually using it?

 

[Charlie99]

In other words, technically all battery tester is just a voltage meter..

Since the voltage of the cells change with temperature, you need to either test them only when at room temp, or add in temperature correction.

In real life, the problem is that a battery tester that only looks at the voltage of many cells in series will usually overestimate the charge left. This is because there will be one cell that is weaker than the others, and it will be discharged first and then go through that very rapid end-of-charge voltage drop. When you measure just the combined voltage of multiple cells in series, you won't detect that one cell shows significantly lower than full charge, while the others are near full. This is a big problem once you get past 4 cells in series.

With alkaline batteries, there is a signficant increase in the internal resistance as you discharge them. This means that for a given current draw, the less life left in an alkaline battery, the bigger then change there is between load and no load voltage. This effect is present in NiMH, but not nearly as great -- in other words, doing a loaded voltage test of a NiMH gives a slightly more accurate indication of charge left, but it's only a tiny bit better than looking at no load voltage.

In real life, simply looking at the no load voltage of each cell gives you a reasonable indication of charge. Cheap digital voltmeters from some place like Radio Shack work pretty good.

Charlie Allen

 

[jeraldjcook]

It this kind of battery also requried to be fully charged and discharged three times before actually using it?

NiMH batteries are usually already conditioned when you purchase them, they just need to be charged. Notice I said usually. Even if they aren't properly conditioned, they should still hold a charge, i.e., 1.4v, but won't be at 100% capacity,i.e., the full 2500 mAh. If you have a charger that will cycle/condition the batteries I do it, but if you don't it's no big deal.

I'll mention that there is a new type of NiMH battery out. One version is the Sanyo Eneloop that the pdf is from, Rayovac makes one called the "Hybrid", and UniRoss makes the Hybrio. Standard NiMH can self-discharge at a rate of 1-2% per day while these new batteries retain 85% of their charge after 1 year. These new batteries shouldn't need to be conditioned/cycled.

 

[jeraldjcook]

In real life, simply looking at the no load voltage of each cell gives you a reasonable indication of charge. Cheap digital voltmeters from some place like Radio Shack work pretty good.

That's assuming the batteries are good. I have a handful of dead NiMH batteries that are fully discharged after 100mAh. To a voltmeter they look fine, but you'll only get 5 photos out of them.

 

[Charlie99]

Are we talking life or charge left? If charge left you really need some type of load on them. If not the voltage may read, say 14V. But as soon as you put a load on it, it may slip to nothing. I use to race R/C cars and we used a capacitor and a volt meter until we could afford the good chargers.

What you are describing is a failed battery pack, not a partially discharged one. If you were to rip open the pack and check the individual cells, you would most likely find that there is one cell with extraordinarily high internal resistance. The typical cause is that it has slighly lower capacity than the other cells, and was reverse charged (by the other cells) during a deep discharge of the battery pack. This will destroy that weak cell after just a couple of cycles like that.

The specific failure mode is that reverse charging causes the electrolyte to be electrolyzed to gas, which then vents out of the battery. With less than the needed electrolyte, the battery now has lower capacity and will be reverse charged the next time the 14V pack is discharged. Loss of electrolyte also leads to high internal resistance --- just like in a car battery, if you don't have the liquid, you don't have any path for current to flow inside the battery.

 

[Charlie99]

That's assuming the batteries are good. I have a handful of dead NiMH batteries that are fully discharged after 100mAh. To a voltmeter they look fine, but you'll only get 5 photos out of them.

Right. Let's say that you use 4 cells in your strobe. It runs out much quicker than you expect. Open the thing up, and check the batteries. The culprit will be obvious when you check the voltage of each of the 4 cells.

Checking the relative cell voltages near the end of discharge is a very sensitive way of weeding out the weak cells.

 

[jeraldjcook]

The typical cause is that it has slighly lower capacity than the other cells, and was reverse charged (by the other cells) during a deep discharge of the battery pack. This will destroy that weak cell after just a couple of cycles like that.

Yup, there is a reason manufactures say to take the batteries out of electronics you are going to use for a while. I learned why the hard way. My battery knowledge has increased exponentially since getting into r/c. I ruined quite a few batteries by overcharging them in cheap timer chargers and leaving them a too high a tickle charge for way too long. More isn't always better.

 

[crpntr133]

What you are describing is a failed battery pack, not a partially discharged one. If you were to rip open the pack and check the individual cells, you would most likely find that there is one cell with extraordinarily high internal resistance. The typical cause is that it has slighly lower capacity than the other cells, and was reverse charged (by the other cells) during a deep discharge of the battery pack. This will destroy that weak cell after just a couple of cycles like that.

The specific failure mode is that reverse charging causes the electrolyte to be electrolyzed to gas, which then vents out of the battery. With less than the needed electrolyte, the battery now has lower capacity and will be reverse charged the next time the 14V pack is discharged. Loss of electrolyte also leads to high internal resistance --- just like in a car battery, if you don't have the liquid, you don't have any path for current to flow inside the battery.

But by a voltmeter the pack may seem charged and good. So as mentioned before a simple voltmeter to see if the battery pack is any good won't work.

 

[Puffer Fish]

The tester sold by Thomas:

http://thomasdistributing.com/shop/zts-minimbt9r-battery-testerbrincludes-free-deluxe-protective-carrying-case-p-564.html?SP_id=&osCsid=e2e2b36ca6f4f0bf1108af091093aefd

Is reasonably priced and works very well... sadly, the lead acid version is fairly pricy

I have used almost all of the batteries they sell, and The 2700 mh AA sanyo, is by far and away my favorite..

Note: The only batteries I have ever had actually break were the 2900's.. lasted less than a year.

Without using an actual load tester, there is no way to know.