Myth Busters....Chapter 2

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frizbeedog

frizbeedog

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My old man used to keep batteries in the refrigerator, and like a lemming, I've always done the same.

What gives?

Good for batteries, or not?.......and why?
 
Since we are talking bout batteries how bout the myth that if you don't run nicads down they will develop memory. When in fact by doing that you are ruining them!
 
wawireguy said:
Since we are talking bout batteries how bout the myth that if you don't run nicads down they will develop memory. When in fact by doing that you are ruining them!
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Ok, I'm all ears. Can you explain that last part more?

...if you run them down, you ruin them?
 
frizbeedog said:
Ok, I'm all ears. Can you explain that last part more?

...if you run them down, you ruin them?
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Thats what I heard too Nicads can't be run down to null........otherwise they're not worth a damn.
 
wawireguy said:
Since we are talking bout batteries how bout the myth that if you don't run nicads down they will develop memory. When in fact by doing that you are ruining them!
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Can't speak for sealed Nicads but if I rememeber correctly vented nicads can be run down to 0.0 VDC. I'll look at literature Monday.

From the garden of knowledge WIKIPEDIA. http://en.wikipedia.org/wiki/Nickel-cadmium_battery

The batteries are more difficult to damage than other batteries, tolerating deep discharge for long periods. In fact, NiCd batteries in long-term storage are typically stored fully discharged. This is in contrast, for example, to lithium ion batteries, which are highly volatile and will be permanently damaged if discharged below a minimum voltage. In addition, NiCd batteries typically last longer, in terms of number of charge/discharge cycles, than other rechargeable batteries, and have faster charge and discharge rates than lead-acid batteries, with minimal loss of capacity even at high discharge rates.
 
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http://www.greenbatteries.com/batterymyths.html


Putting batteries in the freezer or refrigerator doesn't necessarily prolong their life
Alkaline batteries stored at "room temperature" self discharge at a rate of less than two percent per year. So normally refrigerating or freezing them will only help maintain their charge by a tiny amount. Hardly worth the effort of chilling them. However, if alkaline batteries are stored at higher temperatures they will start to lose capacity much quicker. At 85 degrees F they only lose about 5% per year, but at 100 degrees they lose 25% per year. So if you live in a very hot climate or are storing your batteries in a very hot location, it may be worthwhile for you to store your alkaline batteries in a refrigerator instead.
NiMH and NiCd batteries self discharge at a MUCH faster rate than alkaline batteries. In fact, at "room temperature" (about 70 degrees F) NiMH and NiCD batteries will self discharge a few percent PER DAY. Storing them at lower temperatures will slow their self discharge rate dramatically. NiMH batteries stored at freezing will retain over 90% of their charge for full month. So it might make sense to store them in a freezer. If you do, it's best to bring them back to room temperature before using them. Even if you don't freeze your NiMH batteries after charging them, you should store them in a cool place to minimize their self discharge.
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Normally the difference between a 'battery' and a 'cell' is someone being pedantic. However when discussing deep discharge of NiCd and NiMH batteries, the distinction is quite important.

It is entirely safe to discharge a NiCd or NiMH _cell_ down to 0.0V. However _reverse charging_ such a cell will damage it.

If you discharge a _battery_ of such cells, then you run a serious risk of reverse charging some of the cells. In a battery, you will almost always have one cell that discharges _first_, meaning that the voltage of this cell drops to 0.0V. If you continue to discharge the _battery_ then the discharged cell will get charged in reverse, likely damaging it.

-Jon
 
i was watching the nasa channel the other day and they were interviewing a smart guy about more work they're going to do on the hubble telescope; updating instruments, new technology, etc. . .

Anyway, he said they were going to replace the batteries with a set that was "built years ago", and I'm almost certain he said they've been keeping them in "cold storage"; the lifespan of the batteries once installed was another 10-15 years.

Like I said, they were interviewing a smart guy. Maybe I didn't hear him correctly.
 
benaround said:
jon,

So on cordless tools, it would not be a good idea to drain the battery before

recharge.
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Depends ,..you may want to do a google for your battery and charger and see what they say about it


.... If a NiCd battery is repeatedly charged after it has only been partially discharged it will develop a lower voltage and a lower capacity. Fortunately, this effect is reversible by conditioning NiCds. Conditioning is simply fully discharging the battery (down to about 1.0 V per cell) after charging it. If a full discharge followed by a charge cycle is done several times, a battery suffering from voltage depletion (voltage depression, memory effect, or whatever you would like to call it) should be restored back to its normal voltage and capacity.
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M.D., I agree with the source that you quoted that voltage depression is both real and corrected by discharge. However I want to emphasize the part about 'fully discharging the battery down to 1.0V per cell'.

A NiCd or NiMH battery hot off the charger will be about 1.3-1.4V per cell, will do most of its discharge at 1.2V per cell, and is fully discharged at about 0.9-1.0V per cell. If you have a tool with an 18V battery pack, it is 'fully discharged' at 15V. There is some risk here; at 15V for a 15 cell battery, you _may_ have cell reversal if one of the cells was particularly weak.

The hard part is achieving this state of discharge without having proper tools for the job. 'Voltage depression' is only a problem if the battery protection circuitry in the load detects the voltage depression point and confuses it with 'fully discharged'. If your application keeps shutting down to 'protect the battery' then you can't use your application to properly discharge the battery. If you use something like a resistor as the load, then you run the risk of over-discharge. If your application will properly discharge the battery to 1.0V per cell, then you won't see the voltage depression as a problem; the little bit of voltage depression will just show up as slightly reduced capacity until condition the battery.

When I am manually running batteries for competition use, I recommend conditioning by first overcharging the battery at a slow rate (C/50-C/30) to equalize all the cells in the battery, and then doing a discharge/recharge cycle to get rid of any voltage depression. The equalizing charge will do a bit of heat damage to the cells, but far less than having one reverse.

-Jon
 
brantmacga said:
Anyway, he said they were going to replace the batteries with a set that was "built years ago", and I'm almost certain he said they've been keeping them in "cold storage"; the lifespan of the batteries once installed was another 10-15 years
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Spacecraft don't use the more common battery types. For instance, my brother-in-law was telling me about some lithium-hydrogen cells he had designed for a project. Said you could tell the charge level by the gas pressure in the box- 900 psi was full, 500psi was discharged. I'm not putting one of those in my car. There were some others designed to operate at over 150 degC.
 
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