Makita Charger

Go buy a new charger. It has the smarts to figure out what kind of battery you have and properly charge it. Charging it on an nicad charger will probably damage the Nimh battery beyond repair.

--Dale

How does a charger tell a regular NiCad from a regular NiMH until it charges it for some time and sees the voltage depress (or just flatten out) or the temperature go up?

The NiMH battery has the same physical dimensions as the NICAD >

By "refuses to work" what do you mean? Does it not charge at all, or is the charge rate too high/low? Try:

for a good rundown on the type of charger you need. Probably a p/n PST-5830-8 will work? There's also a lot of information on the same site about charge/discharge rates etc. (usual disclaimer - I have no interest in the company). A "trickle" charger can be easily built from a junked walwart with a dropping resistor to limit the charging current to what you need. Not too sophisticated, but will do the job if you watch the amount of time you leave it plugged in (i.e. don't leave it on charge for weeks at a time :-) Hope this helps. If not, drop me a line (delete the obvious) - I've made several inexpensive (read "cheap") chargers for small NiMH batteries to replace original NiCad packs. Haggis.

You can build a constant current charger with one transistor and a few extra components if you have a suitable DC wall wart. Really not much more expensive than the resistor and much better.

--
*A bartender is just a pharmacist with a limited inventory.

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Be glad it somehow refused to charge. Never attempt to charge a NiMH battery with a NiCd charger! People have burned down their houses this way.

I can't see how it would. Thats the difference between a NiCd and an NiMH charger. A NiCd charger may not detect when a NiMH battery is full and continue rapid charging. The excess charge will turn into heat, destroying the battery and possibly anything surrounding it.

A "smart enough" charger could distinguish between a Ni-Cad and a NiMH battery by looking at the voltage and charging current profile over time in a test session, and "knowing" how many cells were in the battery. Most chargers however are set up to charge based on a specific cell chemistry and "looking" at the rate of change of voltage over time to decide if a cell is charged.

Fast chargers must take many more factors into consideration, temperature being one, in order to charge a cell or battery quickly without distroying it.

Dorian

What puzzles me is how that Makita charger knows right away when NiMHs are connected to it. I've read of only one other case like that, for a Norelco shaver where the user replaced the 500 mAH cells with something like 1000 mAH cells, but they were charge only up to 500 mAH. I.e., the charger didn't run twice as long with the higher-capacity cells.

I've got a charger which knows how many cells and what type without any operator input.

--
  

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

It can tell the difference between NiCD and NiMH? I wonder how it does that? The charging profiles are nearly identical.

--
Regards,
  Bob Monsen

"A man who dares to waste one hour of time has not discovered the
value of life"
 -- Charles Darwin

--
*If vegetable oil comes from vegetables, where does baby oil come from? *

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

In addition to

has lots of info about battery charging, including graphs showing charge state verses temperature and voltage for NiCads and NiMHs, and some of their chips can handle both types, I think by measuring the rate of temperature rise. They also give out free samples.

I'm certainly no expert, but I've noticed that many battery packs have several contact pads. Several meaning as many as 5. Some of these "extra" contacts may carry info about battery internal temp. But others could be simple one/zero info to tell the charger about battery type or charge profile.

Just a thought.

Bill Jeffrey ~~~~~~~~~~~~~~~~~~~~~~`

larry moe 'n curly wrote:

High capacity (of same physical size) and old cells have high internal resistance..