replacing batteries in Norelco shaver

Darmok wrote in news: snipped-for-privacy@4ax.com:

NiMH cells have a more complicated charge requirement than NiCd. Unless you plan on designing a new charger,you should only replace with NiCd cells similar to what you removed.

Hi...

I'm in Canada, where Norelco is called Phillips, and I have one (though there are so many models)

The heads-up I'd offer is to measure the cells carefully before you get it too far apart at an inconvenient time... mine has one of the sub-C variations, which is physically just a little shorter than a AA. Shorter enough that you can't get it in and still put it back together :)

Take care.

Ken

I replaced the NiCads with new NicCads. No problems after about a year. Don't remember for sure what size they were but I think they were sub-C.

Bill K7NOM

Jim, could you be more specific? Not to hijack anyone's thread, but we recently replaced a 3.6V NiCd cordless phone battery pack (600mAh) with 1300mAh NiMH's, and plan to use the phone's base (150mV input) to recharge it. If we're careful to time the recharges properly, what other complications could there be?

TomS: The main complication would be very short battery life. electricitym ' ' '

Use nicads with solder tabs. Get then at a hobby shop that supports Radio Control models.

Have changed mine several times no problems.

Hugh

"Tom S" wrote in news:GKuPe.1770$ snipped-for-privacy@newsread1.news.pas.earthlink.net:

I hope you mean "mA".

Well,your cells usually still have a partial charge of unknown amount,and thus charging for the "standard time" will overcharge the cells. A proper charger will monitor the charge voltage and look for the small V drop as the cells reach full charge,regardless of the original charge left on the cells,maximizing cell life.

That's why they are "smart" chargers. And from what I've read,you can leave the pack on the charger even after it is fully charged. No "forgetting" and overcharging.

Yes i have . I have an older 3 head shaver and removed the 2 old AA batterys and soldered in 2 ordinary Hi-MH AA cells about a year or so ago and the thing has worked just fine , it does not overheat or act funny in any way .

Call up a norelco shaver repair place. I don't remember the number, but I do remember being amazed at how low their battery prices were. I'd just been thru the hassle of replacing cells and would have just bought them from Norelco had I realized they were affordable. YMMV mike

Thanks for all the input .. very helpful indeed!

Bill, KB8EB

Charging in only 20 minutes is a 3C charge rate ie, three times the cell mAh capacity. Shaver NiCads would be in the 500m-1000Ah range. NiMh 2000-2600mAh AAs can handle that 1500-2000mA charge rate but must not go over full charge or will be destroyed.

The question is: is that a timed 20 minutes or a "smart" 20 minutes? If timed and one starts with fully discharged cells then all is well. NiMh have no memory effect so can be charged and dicharged from-to any level But, if a smart charger is used, it may not properly detect the NiMh charge state and keep charging past fully charged.

For say, 1500mAh cells, that would take about one hour however so manul timing would suffice. Monitoring the cell temperature is a good idea. Some heating while charging is normal for NiMh but after full charge is reached it quickly ruins the cells.

H. Dziardziel wrote in news: snipped-for-privacy@4ax.com:

According to what I've read here and there,cell temperature is NOT a good way to detect full charge for NiMH cells. For NiCd,its OK. By the time the temp changes the NiMH cell is overcharged.

I have one (Norelco repair facility) here locally -- still repair very old models and parts are very inexpensive (sometime cheaper than the department store batteries).

gb

A typo, "1500mAh cells" should read "1500mA."

My post was poorly worded thanks. My "monitoring the cell temperature" along with "some heating" was to imply hand sensing as a very simple check of what's going on in the cells if they have charged for more than 20 minutes or from an unknown charge state..

The assumption was the shaver does not use temperature sensing except for catastrophic shutoff and if a smart 20 minute charger it is of course designed for NiCad characteristics so may not ever shut off.

Unlike NiCads, NiMh are exothermic while charging so will get warm, especially at this rather high charge rate.. Once fully charged however the temperature (T) rises sharply after the very small voltage drop that indicate full charge . The problem is this short delay and the electronics and packaging usually getting warm along with ambient variations. So, as you say, it's not usually used since difficult to detect reliably.

NiCads, being endothermic are more reliably temperature end of charge detected since the T change is sharper. In either case, _hot_ cells indicate overcharging

Regards..

Well, I did as someone suggested, and "Googled" for "Norelco battery replacements". I found a place that carries replacements for almost all versions of the Norelco shavers. When I looked up my model number (4845XL) it showed them as a pair of AA NiMH batteries! When I looked at the actual cells in the shaver, they were a pair of 600mah Ni-Cds. So, since I have a lot of NiMH cells around (for digital cameras and hobby use), I decided to solder in a couple of them and see what happens.

The first thing I noticed was that, for the first time in years, the RED charge LED came on (for a few minutes) as well as the GREEN LED. It then proceeded to charge for about 20 minutes, then the GREEN LED began flashing, and I knew charging had stopped. The case of the shaver felt warm, but not as warm as when there were Ni-Cds in there. I've been using it now for a couple days, and it has plenty of zip, and sounds real good (by the pitch of the motor). BTW, I assume that there is some kind of "smart charging" going on, as if I were to plug it in after only a couple days, it would shut off (green LED blinking) after only a few minutes. Maybe its voltage based?

I guess I'll know how well, this works after some time has expired, but for now, it appears to be working well. BTW, I have 2 Norelco shavers, and this is the older of the 2. I use one until it runs down, then grab the other one, and put the exhausted one on charge.

Thanks again ..

Bill, KB8EB

| The main complication would be very short battery life.

As you hinted at, that depends on the charger.

Most cheap rechargable appliances have a slow charger that charge the battery at around C/10. If you replace 600 mAh AA NiCds with 2400 mAh AA NiMH cells, the charger will work just fine, except that it's now charging at a C/40 rate -- which is slow enough that the incresaed self discharge of the NiMH cells will become an issue, but it'll probably work just fine. (It might not ever fully charge the batteries though. But it should be OK anyways.)

You really only have to worry about the charger if it 1) only charges for X hours, which would mean that it won't fully charge the new, larger battery unless you unplug it and plug it back in after X hours, or 2) is a fast peak-detecting charger, as NiMH cells have a similar peak to NiCds, but it's smaller.

In my experience, most cheap devices that have NiCd or NiMH cells have slow chargers that will work fine with either. Only the higher quality ones have things that actually detect when the battery is actually fully charged -- things like better power tools and the like. (And of course, anything with LiPo cells. Overcharging them is bad. But LiPo cells don't fit within the `NiCd or NiMH' classification I mentioned earlier.)

| Most cheap rechargable appliances have a slow charger that charge the | battery at around C/10.

Of course, since the original poster says it charges the batteries in

It would be best to replace those batteries with similar batteries.

Modern NiMH cells will tolerate overcharge almost as well as NiCd cells, but they don't like being charged at over 1C rates, except for the sub-C cells which can go a bit higher, probably 2C.

As another poster suggested, if they're sub-C cells, get them at a hobby store that sells R/C stuff. You can buy them online too easily enough --

Places like Batteries Plus probably have what you need too, but their prices are generally quite high.

| On 27 Aug 2005 05:04:45 GMT, Jim Yanik wrote: | | >> For say, 1500mAh cells | | A typo, "1500mAh cells" should read "1500mA."

Are you sure? 1500 mAh seems right to me. You're talking about the capacity of the cell itself, not the discharge rate, right?

Capacity is given in mAh. Charge/Discharge rates in mA.

| Unlike NiCads, NiMh are exothermic while charging so will get | warm, especially at this rather high charge rate..

NiCds get warm during charging too. Just not as warm, due to their generally lower internal resistance.

| Once fully charged however the temperature (T) rises sharply after | the very small voltage drop that indicate full charge.

Same with NiCd and NiMH cells -- it's just that with NiMH cells, the voltage drop is smaller.

| NiCads, being endothermic are more reliably temperature end of | charge detected since the T change is sharper. In either case, | _hot_ cells indicate overcharging

Endothermic? No way.

Apparantly there is an endothermic component to the chemical charging process (and I see references to that in many places) but the current going through the internal resistance will generate heat as well, and from what I've seen, the overall temperature _increases_ as you charge, even for NiCds, during the entire charge cycle, even when you're not charging at an extremely high rate. (Of course, if you're charging at a low rate, any temperature changes are hard to detect, at least until the cell is fully charged, where it becomes much easier as all energy is going into heat, not just some.)

Perhaps at low charge rates the endothermic component is slightly stronger than the exothermic heating, but if you're charging a NiCd battery in 20 minutes -- at a 3C rate -- no way. It's going to get warm.

The 1500mA was an estimated 3C charge rate for the original NiCads, hence the following words "..that would take about one hour.." (to begin to fully charge the new high capacity NiMh etc).

Well, I do believe that strikes a note but thanks for the reminder to be more alert. Sigh.

Yes.and it's significant but I don't claim to understand the electrochemical.theory behind it,. Good NiCads stay pretty cool even at high rates. By the way, Li-ion are also somewhat endothermic until nearly fully charged.

I'm warming to your point. Regards.