How do you measure how much power a battery still has?
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old4570
Flashlight Enthusiast
What is the current draw ? So if you have some idea of current draw and run time , you should then have a reasonable idea .
:tinfoil:
:tinfoil:
Mr Happy
Flashlight Enthusiast
If it is a NiMH rechargeable battery, the short answer is you cannot reliably know.
If you become familiar with the particular brand of battery you have and take lots of voltage measurements, you will find there is some correlation between voltage and remaining charge. But this varies between batteries and is hard to generalize.
Another common recommendation is to note the amount of time used. If you know a given light will run for one hour on a full charge, for example, then if you use the light for half an hour you know the batteries have about half their capacity remaining.
If you become familiar with the particular brand of battery you have and take lots of voltage measurements, you will find there is some correlation between voltage and remaining charge. But this varies between batteries and is hard to generalize.
Another common recommendation is to note the amount of time used. If you know a given light will run for one hour on a full charge, for example, then if you use the light for half an hour you know the batteries have about half their capacity remaining.
Mr Happy
Flashlight Enthusiast
There isn't a tester that will give a reliable state of charge indication for NiMH batteries, so it isn't worth spending money on even a cheap one.
The best bet is to know when you last charged the battery and to know how much you have used it since then.
As mentioned by Mr Happy, there is a correlation between voltage and remaining capacity. This correlation works for alkaline batteries and li-ion batteries due to a larger and "less gradual" drop in the battery voltage. This than characteristic can be calibrated to the remaining capacity and the commonly available "good/bad testers" are designed to be used with alkalines.
Somewhat like how certain long distance runners slow down as energy runs down. In the case of NiMh, the "runner" would maintain the "same" speed (i.e. voltage) and then suddenly just stop when he ran out of energy reserves. It would be impossible to figure out how much energy was left in the NiMh runner just based on his speed. This has been referred to as the "flat discharge curve" characterized by a very low voltage slope.
PeAK
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TakeTheActive
Enlightened
It's like driving my Dad's 1963 Chevy BelAir Station Wagon with the broken gas gauge. You:
- Know how many gallons, GAL, the gas tank holds
- Know how many miles-to-the-gallon, MPG, the old Chevy gets
- Write down the mileage reading from the odometer each time you buy gas (you FILL the tank!)
The *ONLY* way to know exactly how many gallons are left is to drain the gas tank and measure it. That's what a Charger/Analyzer 'Discharge Cycle' does.
alright thanks guys. i think i will just charge up the batts every 2 months
Ruri,
The remaining capacity that you seek leaves you in the company of current and budding electric car manufacturers. For an interesting perspective on this read this article by Mr. Buchmann of Cadex.
My take on the article is that it is offers some fresh commentary mixed in with a bit of marketing panache("40 million transactions")...this coming from someone with a background in electrical engineering. The simple model, though attactive, may not be appropriate for the question at hand...
PeAK
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the only problem with this approach is that regular non-LSD NiMH have a fairly large hole in the tank leaking out electrons all over the floor.
try this.
http://www.nickhill.co.uk/nimh-capacity-tester.html
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