Charger for Yaseu FT290R Mark II with NiMH batteries??

Perhaps someone in the group will have a circuit for a regulated 12V charger.

If not, I would experiment, starting with something simple. Stick a 25-ohm resistor in series with the output of a 12V supply and see what happens.

If you want true constant-current charge, you'll need a higher voltage (25V, perhaps?). You might, for example, put the battery in the collector circuit of a power transistor and vary the base bias to get the charging current you want.

The voltage of 9 rechargeable cells is 10.8V. If you can't come up with a charger design that will prevent overcharging, the cells won't last long. I have AA to C cell adapters that adapt the AA cells to the same size as C cells, so that would be one option.

There are universal smart chargers that will charge battery packs from 4.8 to 10.8V in either NIMH or NICD. The ones I use are Powerizer brand, and have international 120/240VAC input, but the charge rate is manually set for 1A or 2A, which is likely too high of a rate for your 2500mAh AA cells. Some would consider a 1A rate suitable, but it depends upon the quality/grade of the cells. Powerizer may have some models of universal chargers with a 0.5A/1A rate.. or you could buy some full size C rechargeables, which would have more capacity than 2500mAh, and the universal 1A rate would likely be fine.

-- Cheers, WB .............

What is a Yaseu FT290R Mark II?

Eww. Wall-wart with a really thin-gauge secondary, I'd guess... built-in resistance limit.

My understanding is that NiMH cells really do *not* do well if overcharged (even at relatively low rates) - it's fairly important to cut off the charge when they hit 100%. Failing to do so, shortens their life considerably.

Doing this properly seems to require either a temperature sensor connected to the battery pack (or one of the cells) to detect the temperature rise at the full-charge point, or a NiMH-aware charge control circuit which can detect the "zero delta V" point where the battery's terminal voltage stops rising and begins to fall (a secondary effect of the temperature rise, I believe).

There are dedicated NiMH charge-control ICs available. You might want to see if you have enough room to pooge one (with the necessary support circuitry and temperature sensor) into the FT-290R in between the battery terminals and the "charger connection" point.

You maybe-could wire up a charge controller of this sort externally, and depend on zero-delta-V detection (and not have a temperature sensor) and/or a cutoff timer... but I'd expect poorer battery lifetime under these circumstances.

Using some sort of actively-regulated current source (maybe just an LM317 in current-source mode) rather than a resistor or a really lousy wall-wart would probably be sensible.

I'm starting to think the OP would be better off buying two sets of NiMH C cells and charging them outboard.

-- Jeff Liebermann snipped-for-privacy@cruzio.com