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Recharging a Nicad Battery(10 posts)

Recharging a Nicad Batterypmf1
Nov 6, 2001 9:36 AM
I'm on my second Niterider system. The first I had was a Classic dual beam that lasted about 4 years. It started losing life and I bought a single beam 16 watt Nicad system. I always question how to charge these. The Niterider literature says
1. Never let it completely discharge (I did this once or twice with my old system)
2. Never over charge it. They say 16 hours is the max re-charge time and it should feel warm when charged.

My question is since it runs 2.5 hours on a charge, can I simply recharge it after say 1.5 hours of run time, or should I run it down and then recharge it. I know lead acid batteries are this way, but do nicads have a "memory" too? The manual says you can "top it off" with an hour or two charge if its been sitting for a week or so.

Any advice?
re: Recharging a Nicad Batteryjs5280
Nov 6, 2001 11:26 AM
I've heard lots of conflicting views on this but here's my take in layman's terms. I read that if you let a battery pack completely discharge, you risk the polarity will reverse in one of the cells (talk to the guys/gals w/ horn-rimmed glasses and pocket protectors for an explination). Battery packs are usually made up of multiple cells so if you had 6 cells and one reverses, you only have capacity of 5 now. There is a way to re-reverse a cell(quick charging I think) though, not sure how it is done. This is true for both new and older battery designs.

Now the second problem you hear about is memory. That is charging a partially discharged battery. The theory is that if you discharge and recharge (say your normal ride is 1 hour) you risk losing that capacity because of this memory effect. Makes sense, kind of like wearing a hole into something from overuse. I've heard though that this was a bigger problem w/ older batteries, but new technology has lessened, but not totally eliminated this effect. The greater danger seems to be the reversed polarity to me. As far as preventing memory loss, I think if you careful to not discharge to the same level everytime, you're going to minimize that loss.

Lastly, on over charging. I use a outlet timer, same as you use when your go on vacation and wants the lights to turn on at a certain time. Just make sure it doesn't cycle on/off/on/off. On my timer, you have a peg that turns it off, and a different one to turn it on. I manually set the timer on, and then set the OFF peg for my charge time. That way, it trips off, and there is no ON peg to start the process again and overcharge the battery. Works great and is very cheap compared to buying systems w/ intelligent chargers. Hope this helps!
re: Recharging a Nicad Batterypmf1
Nov 6, 2001 11:32 AM
I do use one of those light timers with one peg removed. I still wonder if running it down and recharging is the best way to go. My night time commute has a pretty fixed length. Do Nicads have memory problems???
Yes, NiCads have memory issues. Check out this site. . .js5280
Nov 6, 2001 2:51 PM
Found one of the better pages I looked at earlier. Lots of stuff if you put "NiCad memory" into Yahoo. RC modelers are big on rechargable batteries. . .
Reversing one cell is like losing two ...Humma Hah
Nov 6, 2001 7:01 PM
... the one that reverse charges not only loses its voltage, it subtracts from the others.

The timer idea is great -- I'm using it on my new NiMH battery in case I forget to unplug it when it has been on the prescribed time.
The definitive way to do it ...Humma Hah
Nov 6, 2001 6:59 PM
... I've been long plagued by flaky nicads, and am now doing some nicad work professionally. One of the guys where I work is a real expert in the field, a world-class RC modeler, and has done many of the spectacular plane and helicopter model crashes for recent movies.

His advice, discharge each cell independently to about 1 volt. Once at that point, the cell's voltage drops like a rock.

The problem with discharging all together to full discharge is that one cell goes first, and the others reverse charge it, which is very damaging, may even make the weak cell explode.

Larry tests each cell independently to verify its capacity, and puts together matched sets. These can then be charged and discharged together, occasionally pulling the set apart for full discharge to avoid memory.

Charge nicads until they start to get warm. That is fully charged. Don't charge beyond that.

Larry says Sanyo makes the best nicads.
The definitive way to do it ...Bruno S
Nov 6, 2001 9:39 PM
RC racing car companies buy thousands of batteries. They test all of them and keep the best to built matched battery packs for their pro teams. The average batteries get sold to the public. It seem that once in a while you get a battery with a very high capacity and sets of those ones is what they look for.
Now I'm giving myself advice ...pmf1
Nov 7, 2001 4:43 AM
Should have gone ther ein the first place. Yep, Sheldon Brown. He claims the memory thing for a nicad is a myth. He also says the biggest problem with commercial lights are not the batteries, but the lousy rechargers. Apparently, one can build a better one. I'm going to look into this.
Rechargers...Bruno S
Nov 7, 2001 3:18 PM
Try a RC model shop. The type of rechargers used in RC are very sofisticated. They should not be too expensive but a custom connection to your battery pack is needed. The RC shop may help with that.
Crappy cheap and crappy expensive chargers ...Humma Hah
Nov 7, 2001 6:13 PM
... yeah, the dumb "wall warts" typically used are terrible, particularly if you leave them plugged in and over-charge the batteries.

However, at work we have a very sophisticated Christie battery charger, cost $6000. It just let us down. Swore up and down it was charging the batteries but it was not.

I ended up just hooking the batteries up to a constant-current power supply, charging at C/10 (one tenth the amp-hour rating) until the battery started to get warm, and that works.

That's the real key. Charge til they get a little warm, then stop. Once a month, run a nicad stack until it starts to dim.

Memory is NOT a myth, but is more often a function of overcharging than underuse.