I have several Motorola Talkabout radios. In some of them the NiCad batteries won't take a charge anymore. I see new compatable batteries that are NiMH. Do they require a different kind of charger? The charging station is basically a AC adaptor going into a plastic base that the radios sit in. Inside the circuitry is just a couple of diodes, some resistors and 2 LEDs. Will i need new chargers or can I use the old ones without blowing anything up?
Is there some reason you don't want to disclose the model number of the radio and the battery pack number? Numbers are amazingly useful.
That's normal for a Motorola charger. Many of them lack the intelligence to prevent overcharging. If the battery pack gets hot, it's too late.
Yes, although many will claim that they can be charged in the same charger. Actually, that's true as both types can be charged in the same device. However, such a charger would not know when to stop charging, which is the key to protecting your batteries. The mechanism is different for different chemistry batteries. If your unspecified model Talkabout uses removable individual cells, there are plenty of external NiMH chargers that can handle them, usually two or four at a time. If you go that route, I strongly suggest you look into low self-discharge NiMH batteries (i.e. Eneloop). One problem is that quick charging is not a good idea with these.
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Ok, that's a brain dead minimalist battery killer designed to sell replacement batteries. However, don't throw it away. You can build a proper NiMH charger and build it into the base. Some ideas: Lots of reference designs supplies with controller IC's such as: If it doesn't have a controller IC, or uses overheated for EOC (end of charge) detection, forget it.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
FYI, this guy has assembled eneloop battery packs. The look like they still have the buttons on them but thats a minor draw back.
Cheers
Sorry. The Nicad radio is a T5320 with a MOT-4002 High Cappcity(sic) Battery. 800mAh. The other (it took some looking to find the model number) is a SX780R with a KEBT-072-C 700 mAh NiMH.
Just found an upgrade kit for Motorolas on Amazon. Includes batteries with proper contact configuration for my models.
Good find, but I suspect you may have a problem. The charger looks exactly like the one I have for NiCd batteries for my Talkabout radios (including the insert). For all I know, they may be the same, with maybe a series resistor value changed for NiMH rates. Without an intelligent EOC (end-o-charge) detection circuit, you're going to kill NiMH batteries in the same manner as NiCd. Incidentaly, NiMH batteries are more sensitive to overcharging than NiCd.
There's also no indication that the NiMH batteries supplied are LSD (low self discharge) types, such as Eneloop. I just hate grabbing a radio, only to find that the battery is dead.
Typical self discharge rates for common rechargeable cells: LiIon 2% to 3% per month Lead-Acid 4% to 6% per month NiCd 15% to 20% per month NiMH 30% per month That's at 25C. It doubles for every 10C increase in temperature. If you keep the radio in a hot car, you'll have a dead battery in short order with NiMH. You could just leave the radio in the charger, but there you run the risk of overcharging.
The solution is to use LSD NiMH batteries which self-discharge at about 2-3%/month. Ever since I switched to Eneloop batteries for my cameras and radios, they're always ready to go, not dead and requiring a panic recharge.
So, what I recommend is that you buy some Eneloop cells. Looks like the T5320 take 3ea AA batteries, which might be a problem in an external charger that takes 2 or 4 cells. You may need to charge it in your existing NiCd charger and just reduce the charging current to safe levels or build a proper NiMH charger into the base.
Personally, I prefer a "balance charger" as favored by the RC (radio control) crowd. The charger monitors each individual cell and tried to balance the charge so that no cell hogs all the current and ends up overheated. I've modified electric power tools to use this system with good results. However, that primarily for LiIon batteries. The charger I use does claim to charge NiMH cells. I've never tried balance charging with NiMH and the manual is of little help. I'll test or ask when I have time. This might be overkill, but it's nice having a charger that works with everything:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Good point. They do look the same. Still, they are on order and I will let you all know what I get. I still have some time before I need the radios and can still find a LSD type charger (or build one myself) Thanks again.
Ideally, yes. But, most of those Talkabout radios take three AA (or AAA) cells as an alternate to the 'official' rechargeable, so you can switch to any AA NiMH charger and cells.
There are some chargers that only charge cells in pairs; if you have TWO Talkabouts, that can work, but if you have an odd number, it's gonna be a problem.
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