I read in several places that while NiMH have no memory effect, brand new batteries usually need a break-in to get to a full charging state -- a couple of cycles of discharging (to about 1V) and slow charging (i.e. not using a fast charger even if it is a smart charger); I've even seen it written on the package of one brand of NiMH batteries I bought. (However, I find that I cannot discharge them fast even if I short + to -, because these batteries have a very large output resistance.) Can anyone comment on this break-in thing? Is it really necessary? Can it be shortened?
Hmm, according to this, it's true. Reading this whole battery book, what a mess. And apparently fuel cells will not be able to replace batteries in many applications.
Maybe when the ITER spinoffs begin operation in thirty years we'll have enough energy to spare to put the inefficient antimatter production in large scale, and then we'll finally have a perfect portable power source (I think currently the maximum achieved efficiency is much less than 1% of energy converted to antimatter in accelerator experiments). 😀
Maybe when the ITER spinoffs begin operation in thirty years we'll have enough energy to spare to put the inefficient antimatter production in large scale, and then we'll finally have a perfect portable power source (I think currently the maximum achieved efficiency is much less than 1% of energy converted to antimatter in accelerator experiments). 😀
I think that shorting positive to ground is discharging them "fast", at least, as fast as they will go on their own.
I had a NiMH charger that would do fast discharge, and charging at different rates. It ran a fan during discharge, but I don't know if it was applying any sort of negative potential or just shorting it through some sort of shunt.
As far as whether or not it's necessary- that's a matter of performance. Are the batteries performing as well as you would like? If not, what's wrong with them? There's still some improvement to be had with the best lithium batteries; though there is some overlap between weight/energy and volume/energy ratios for good NiMH and bad Li-Ion batteries.
Joe
I had a NiMH charger that would do fast discharge, and charging at different rates. It ran a fan during discharge, but I don't know if it was applying any sort of negative potential or just shorting it through some sort of shunt.
As far as whether or not it's necessary- that's a matter of performance. Are the batteries performing as well as you would like? If not, what's wrong with them? There's still some improvement to be had with the best lithium batteries; though there is some overlap between weight/energy and volume/energy ratios for good NiMH and bad Li-Ion batteries.
Joe
I f I understood correctly, shorting batteries to discharge them is not a good idea!
This site is has plenty of helpful 'care and feeding' information about all manner of cell chemistries:
http://www.batteryuniversity.com/index.htm
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This site is has plenty of helpful 'care and feeding' information about all manner of cell chemistries:
http://www.batteryuniversity.com/index.htm
Setmenu
I have worked as a battery engineer for the last 5 years for a cell phone comapny and have done quite a bit of testing on NiMH and Lithium Ion batteries. For NiMH you generally see a rise in capacity over the first 5-10 full cycles of use, but the rise is on the order of 3-5%. So basically you don't gain much. Second, I certainly wouldn't short any battery to do a fast discharge, the cell impedance of a NiMH battery is on the order of 50milliohms or so, so by shorting it you will be getting many Amps, and those cells are generally not designed for currents higher than 1C rate or 2.3A in the case of the AA size. Too much current, especially a constant current will cause heat buildup and gas to form inside the cell and damages the cell.
The things you want to do to prolong your NiMH batteries is to not let them overcharge, the common method of charge termination of -dV/dt overcharges the cells by 5-10% depending on the detection threshold, anything more than that just heats up the cell and deteriorates the performance. Don't store NiMH in a discharged state, the self discharge will continue to drain the battery until they are useless.
The things you want to do to prolong your NiMH batteries is to not let them overcharge, the common method of charge termination of -dV/dt overcharges the cells by 5-10% depending on the detection threshold, anything more than that just heats up the cell and deteriorates the performance. Don't store NiMH in a discharged state, the self discharge will continue to drain the battery until they are useless.
Jc2, thanks for saying something that's actually informative 🙂
And shame on me for not pointing out the hazard of shorting a battery- I really do know better 🙁
(from now on, I'll try not to post before coffee)
And shame on me for not pointing out the hazard of shorting a battery- I really do know better 🙁
(from now on, I'll try not to post before coffee)
Prune said:
The simplest thing I can think of is to just select a suitable load
resistor , and discharge the cell/pack at the rate recommended by the cell manufacturer.
Usually the data sheets seem to consider a cell voltage of 1-1.1 v
fully discharged.
Depending on how many cells your pack contains you may be able
to find more economic conditioning charger sold for radio control
model applications.
That said, if you intend to use nimh cells for a number of applications purchasing a good one will pay off eventually by
keeping your cells in top condition.
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Is discharging them even a good idea? From jc2's post it certainly seems that storing them this way is bad.
The easy solution as used for RC cars is to use a bulb for discharging, simply keep an eye on when the light goes dim. Headlight bulbs seem to serve well for the purpose.
You can quick charge them with no disadvantage. After something like 5 cycles the cells will perfom to their max, depending what brand.
Magura 🙂
You can quick charge them with no disadvantage. After something like 5 cycles the cells will perfom to their max, depending what brand.
Magura 🙂
richie00boy said:
Nimh work best and last longest when topped up rather than deep discharged for every cycle.
A sporadic deep discharge reverses changes in the cell that
would cause permanent impairment to performance if omitted.
Check the link I posted for a more/better detailed explanation.
When 'manually' discharging a cell it is always a good idea to monitor the voltage to prevent it going to low and damaging the cell.
Observing a lamp might not be the best way to do this, unless
one is familiar with the light output at a given voltage that is
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I was talking about discharge/charge cycles to prime brand new batteries. Also, the link I posted says they should be trickle charged the first time after very long storage or when brand new (though normally fast charging should be used to avoid making the cadmium crystals get too large).
Prune said:
Well same still applies about obtaining a good charger.
I agree about the trickle charging for first time.
Sometimes a very deeply discharged pack can take few
cycles to reach full potential.
Regarding storage, some battery packs I have received seem
to be well below recommended cell voltages when I receive them
before I give them their first charge.
Some nominal 9.6v packs arrive at anything between 2.6-9.4v.
I would guess the former voltage packs/cells have been stored for some time.
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Again, I don't really see the point of needing to charge and discharge the batteries to prime them. Just use them normally and you'll be set after 5 or so cycles, you probably wouldn't even notice the difference between the first and the 5th use. Discharging a battery won't hurt anything as long as you don't discharge them too deeply, or store them ddeeply discharged, I wasn't too clear on this before. By storage I mean for a couple weeks or more, and discharged I mean by less than 1V/cell. If the batteries were discharged fully and you weren't going to use them for a while I would put them on a charge for 30 minutes or so to get them about 25-50% charged and then take them off. Heck if you want to you can store them in your fridge to slow down the self discharge somewhat.
Trickle charging is a good idea on deeply discharged batteries, new batteries might be discharged quite deeply by them time you get them so it wouldn't hurt to do that. However you don't have to worry about Cadmium crystals in your batteries since you have Nickel Metal Hydride and not Nickel Cadmium.
One thing about the batteryuniversity site, while I agree with Mr. Buchmann on many things and his site has very useful information and the rest of the web has mostly misinformation about battery care and use, don't forget he is in the business of selling battery chargers and conditioners. I have tested many different charging and conditioning algorithms from Cadex and other companies, both implementing them on my own test equipment and doing comparisons between batteries charged on special equipment and normal charging/discharging. In most cases there was little to no difference in overall battery capacity or cycle life, nothing that you would even notice in use. In the other cases the "improved" algorithms actually decreased capacity. Summary you don't need a 125$ Cadex conditioner to get the most from your batteries. If you want to build your own charger I could probably help to pick out the main ICs you'd need to do a good job at charging them correctly, and you can just discharge them with normal use.
Trickle charging is a good idea on deeply discharged batteries, new batteries might be discharged quite deeply by them time you get them so it wouldn't hurt to do that. However you don't have to worry about Cadmium crystals in your batteries since you have Nickel Metal Hydride and not Nickel Cadmium.
One thing about the batteryuniversity site, while I agree with Mr. Buchmann on many things and his site has very useful information and the rest of the web has mostly misinformation about battery care and use, don't forget he is in the business of selling battery chargers and conditioners. I have tested many different charging and conditioning algorithms from Cadex and other companies, both implementing them on my own test equipment and doing comparisons between batteries charged on special equipment and normal charging/discharging. In most cases there was little to no difference in overall battery capacity or cycle life, nothing that you would even notice in use. In the other cases the "improved" algorithms actually decreased capacity. Summary you don't need a 125$ Cadex conditioner to get the most from your batteries. If you want to build your own charger I could probably help to pick out the main ICs you'd need to do a good job at charging them correctly, and you can just discharge them with normal use.
I used to race 1/10 electric RC buggies and I'm thinking about getting back into it. I used to make my own chargers and used to just charge at constant current about 3.5-4.0 amps, until -dv/dt was reached. Can anybody offer advice on whether constant current charging is any good for NiCad and NiMh? NiMh weren't around when I last raced so I want to know if 1) I will be ruining my old batteries and 2) will ruin new ones.
I have been using constant current chargers for both NiMh and NiCd cells for racing, no problem. Just watch the teperature rise, but I guess that should not be news to you.
Magura 🙂
Magura 🙂
How can you distinguish the difference between a fast or slow charger? In other words, how long must it be able to charge for before you would class it as a slow charger?
Have you got a slow charge circuit for Ni-MH batteries (AA,AAA)
that you could post?
I have been able to find many circuits for fast chargers.
I was thinking of building this circuit
http://www.geocities.com/iecmaster/circuits_ps/cir_ps016.html
which uses the Max712 chip. My motivation being that the manufacturers really do send out samples.
Any comments?
Have you got a slow charge circuit for Ni-MH batteries (AA,AAA)
that you could post?
I have been able to find many circuits for fast chargers.
I was thinking of building this circuit
http://www.geocities.com/iecmaster/circuits_ps/cir_ps016.html
which uses the Max712 chip. My motivation being that the manufacturers really do send out samples.
Any comments?
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