Specially designed NiMH chargers?

Are there any chargers actually designed for NiMH AAs?

Most chargers I've seen (actually all) charge both NiCd and NiMH and use negative delta to terminate the charge. Of course this works fine for NiCds but NiMH's have a much smaller drop thus being much harder to detect.

Is there a charger out there with some sort of temperature sensor?

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Someguy:
Are there any chargers actually designed for NiMH AAs?

Most chargers I've seen (actually all) charge both NiCd and NiMH and use negative delta to terminate the charge. Of course this works fine for NiCds but NiMH's have a much smaller drop thus being much harder to detect.

Is there a charger out there with some sort of temperature sensor?<HR></BLOCKQUOTE>

I can only speak for the Ncd/Nimh Saitek/CCrane combo charger.

The reason I'm posting is becos I've noticed on both of those chargers something really interesting to me.

As you mentioned, a Hydride cell is harder for the charger to detect as fully charged. This is evidenced by the chargers (only with Nimh cells), that the charger will stay in "top-off" mode occasionally (reduced current as shown on the voltmeter) for quite a while compared to a similar capacity Nicad.

IMO-owners of these two very similar chargers should note:

My solution for this problem turns out to be very simple:
I simply open and re-close the door of the unit...-which will start the whole sequence of charge all over again, but the unit will then rapidly cycle through the soft start->main charge->top-off->finish/trickle modes to completion-usually in less than 10min

-This little trick seems to work for me with these units every single time, -when the unit gets a little confused about when a charge should have been finished.

I use the famous MAHA MH-C204F...I charge both NiCads and NiMh in it (I have some old NiCads that still work in my discman, its like the LED flashlight of Discmans, it runs FOREVER on 2 AAs but anyway) and I believe it uses different charging techniques for both types, but I could be dead wrong. Don't know if it has a temp sensor but it seems to do a nice job of charging them...Even has a refresh feature...

You also have to remember that NiCds and NiMH both have different trickle charge rate requirements for the same amp hour capacity.

A charger designed to charge NiCds which requires a higher C Rate trickle charge (partly due to the self-discharge characteristics of NiCd) may well be enough to damage NiMH batteries.

Dan

I also really like the 204. When I bought it I had been using some older 1200 cells and they weren't holding up at all. I put them in the 204 for fun and low and behold they are useable again in my digital camera. I went from about 10 shots to about 40 on the same batteries. Granted the 1800 I am using now run about 100 shots, but it is amazing what a good charger can do.

I've heard a lot of good things about Maha chargers but they are pretty expensive to get here.

mr. glow, it sounds like your charger isn't designed for NiMH. Take a look at the first couple of paragraphs at: http://www.powerstream.com/nimh.htm

but it is amazing what a good charger can do.For sure! I've been charging NiMHs with two rather old chargers and the batteries tend to get warm which I've been told isn't good for the batteries.

Thats why I'm doing a little research before getting another. Don't want to end with with another lemon!

You might want to try the RayOVac PS4 charger. For $30 it includes 2 1600mA AA cells. I have the Quest Q2 charger and I can say that the PS4 is much better. I was having some problems with the Q2 sensing the lower delta voltage dips in charging completely discharged NiMH. The PS4 has no problems with this. These are single cell chargers, which I like, as it charges each cell to it's max. They switch to trickle charge after their fast charge cycle. You can just leave the batteries in the charger.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Someguy:

mr. glow, it sounds like your charger isn't designed for NiMH. Take a look at the first couple of paragraphs at:
but it is amazing what a good charger can do.For sure! I've been charging NiMHs with two rather old chargers and the batteries tend to get warm which I've been told isn't good for the batteries.
Thats why I'm doing a little research before getting another. Don't want to end with with another lemon!<HR></BLOCKQUOTE>
My Nimh cells never get more than slightly warm with my chargers.

Also, I've been using both of these units very successfully for over 2 years without any problems-except that minor problem I noted. Also, the manuals do definitely recommend Nimhs or it wouldn't be emblazoned on the lid and case of the charger....
-For my uses, this has been the best charger $40. can buy-I'm sure there are better ones (I've seen as high as $200.U.S.)-but I'm still mighty happy with the ones I use.

The recommendations from what several people who work with NiMH cells are:

* The charger should be of a new NiMH smart style and not one that is several years old. Many of the older units were not designed to handle the new ultra high capacity NiMHs.

* It is best to have the charger monitor the individual single cell rather than requiring more than one cell to charge.

* It should be a fast smart charger (no more than several hours), with a trickle charge mode after reaching full charge. It is OK to have the batteries get hot, but should cool down on the trickle charge mode.

From what was said, NiMHs charges better if there is a high inrush of current. But, NiMHs do not like overcharging and this causes the most fails with rechargeable batteries. Since this is a smart charger, it will sense the slight dip in voltage when the individual cell tops off. There is some sort of lowering of internal resistance to cause this effect. This will signal the charger to switch from full to trickle charge mode.

Old chargers do not have enough current to create this high inrush and therefore will never bring the NiMH cells even close to 100% charge. It is claimed that NiMHs are not good collectors of energy, if the charge current rate is low.

I confirmed this when I first got my Quest Q2 charger. I had an older Radio Shack NiMH and Panasonic charger that I used to charge several different 1600mA NiMHs. Since one being an overnight and the other being a 6 hour charger, I left the batteries in the chargers for 3 days. I tested them on my digital camera with full load and got about 15 minutes. They also got less than an hour of really bright light with my PT Surge. This didn't change much no matter which charger I used.

I then charged the same NiMH cells with the Quest Q2 and removed them immediately after signaling a full charge. In the digital camera, the same batteries now last about 40 minutes. The PT Surge now has about 3 hours of really bright light.

But, as I mentioned earlier, the $30 RayOVac PS4 is my new favorite NiMH charger. Also, their NiMH cells are really great and cheap at WalMart.

Cells CAN get quite hot in the MAHA but from what I have read, but aparently not too hot because the cells keep working great and overheating/overcharging will kill cells faster than anything else (Well, ok using them will kill them, but I meant for good )

It takes 2 batts to charge which CAN be a problem if one is much more dead than the other but this is solved by using your batteris in pairs, I.E. my FRS radios use 3 AA batteries so I have my cells labeled AA, BB, CC, etc etc so I will use AAB and then BCC and so on. I always take the pair that was split up (In the case above B) and refresh them.


The funny thing is that NiMh cells are probably the most indestructiable of all the rechargable technologies out there yet we obsess about them the most. I have an old cell phone I took from my brother when he got a newer one (GSM so we jsut changed SIM cards) he charged the battery every day even though it could go much longer than that, now I have it and even after 2 or 3 years of daily charging like that (He never allowed it to discharge) the battery works like the day it was new, now the phone itself on the other hand...

My MAHA charger was something like $35 on eBay with 8 1600mAh NEXCell batteries.

Like Saaby said, heating of the NiMH is normal when charging. It can get quite hot, but it seems that the cells are quite durable. NiMHs do not like deep discharges and anything less than 0.9 volts on the cell, you may not be able to charge them.

I just recharge my less used batteries once every month and they seem to be holding up OK. I heard that this is true with the new NiCads. What a lot of people are finding out that deep discharging of most rechargeable batteries are not a good thing. The reconditioning cycles that are available on several battery chargers are designed to not let the batteries discharge much below 1 volt.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>You might want to try the RayOVac PS4 charger.<HR></BLOCKQUOTE>Yeah they do look interesting but the only place I can find them is from a big electronics chain and they are selling it for US$45!

My only worry is the 1 hour charge time. I keep hearing that slow charging prolongs the life of the battery (and ensures a fuller charger) but I can't verify this anywhere!

Otherwise the single cell charging capability is tempting. The Nomad only takes 1 AA at a time.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>* It should be a fast smart charger (no more than several hours), with a trickle charge mode after reaching full charge. It is OK to have the batteries get hot, but should cool down on the trickle charge mode.<HR></BLOCKQUOTE>Its a confusing world out there. See the link above. They mention that if the batteries actually get hot, damage has already occured.

(GSM so we jsut changed SIM cards)On a completely different topic, how many of you guys have GSM phones? Is CDMA that huge in the US?

Actually, GSM is somewhat rare here, I think 2 providers use it (Voicestream and Cingulair) and the rest use...other technologies (I think AT&T uses CDMA but I think Sprint uses somethign different so I don't know...)

I think GSM is great though, if not for anythign else for the fact that you could have a different phone every day of the week if you wanted...

Someguy,

I have been using the new Energizer Compact Charger mod. CHM4AA to charge Nexcell 1800's and older stock.

They trickle charge AA/AAA and 9V and work on a 15 hr timer from when the units witches on.The lady in Cust. Service told me that these were specifically made for the new Energizer AA 1700's. It also charges NiCd's but you have to manually remove them after 6 hours.

Sorry, no idea on cost or availabilbity as I received mine as a replacement from Energizer.

BTW, yes it does run slightly warm.

Someguy; I checked the link and if you read towards the bottom where they describe their ideal charger, it states to charge with a full inrush of current (equal to the battery's rating) for about 1.5 hours (being monitored by heat produced). This describes the RayOVac PS4 pretty much, but I think they are using negative delta voltage.

They also mention that the heat monitoring should shut-off the fast charge at 45C degrees. This is the about the same as very hot water from a household water heater. Therefore, they claim that it is moderate heat is OK for the battery.

I think they are not recommending the fast charge to be something like several minutes and having the cell get so hot that you cannot touch them.

At a very slow charge rate, the batteries may be cooler, but I don't think you will like the charge capacity being held by the battery. I picked up my PS4 at the WalMart here in Hawaii for $30.

Thanks for your opinions guys. I've just bought myself one of those Grandcell chargers so I'll try out rechargable alkalines for all the low drain stuff.

Still the PS4 (Playstation 4?) does look pretty good. I'll look around and see if I can get a better price (or find a dT/dt charger).

[EDIT]
Just peeked at Ray-o-vac's FAQ and it looks like the unit does have a temp sensor. While it may not use it terminate charging by monitoring dT/dt, it will shut itself down to prevent overheating.

Well then, the PS4 it is!