How Does This Weller Nicad Charger Work?

Your answer is great thankyou. David

I bought this iron on ebay a few months ago very cheap due to it being faulty. I assumed it would have a dead nicad but in fact the nicad was fine and the problem was that the switch was implemented in a basic way using a piece of spring metal that is pressed against a metal post and this contact had some oxide which a bit of sandpaper removed and the iron sprang to life.

Cheap product, cheap electronics and cheap charger design results in a charging circuit that is not ideal for the battery chemistry and that ultimately reduces the battery life.

It is not the ideal solution you may have expected but it is cheap and it does work, which is why it is commonly used.

My dad has small rotary tool (like a Dremel brand) that just had a small DC transformer and a battery with NO charging electronics, just a direct connection to a fullwave bridge. The battery was there for providing extra torque to keep the transformer size and cost down. Needless to say it did not last for more than a few years, but for the price.........

Weller has been known for using its earlier brand reputation for making cheap products.

Gajanan Phadte

I did not know that about Weller. A few manufacturers do that. I had a Teac mp3 player which was in the bin not long after I bought it.

I suppose if the rotary tool keeps going past its warranty period the maker might not care. The soldering iron works well despite being about 13 years old and having a nicad battery and I think its original selling price was about 90 U.K. pounds which seems quite a bit.

No that sounds about right. I have had no relilability issues with Weller products except the soldering iron I snapped in half (but that was my fault).

Another cheap simple trick sometimes done with a constant voltage battery charging approach is a thermal resettable chemical fuse attached electrically in series with the battery and mechanically attached to the battery. (I do not see one but it might be buried under the white plastic.) When the battery is fully discharged and charging starts an initial full voltage gets applied and the fuse self heats until it "opens". In this open condition a trickle current continues to flow into the battery. As the battery charges up the voltage drop across the fuse drops. When the fuse and battery cools sufficiently the fuse closes. This resetting fuse will also protect a fully charged battery from the occasional short circuit.

Weller Soldering Irons and stations has a variety of systems but the picture shows a simple full-wave rectifier (Bridge rectifier), Transformer is so designed that its 2xPrimary windings are 2x110V and connected in parallel for 110V supply and in series to work on 220V systems.

I would have thought that the single diode means half wave rectifier?

Yes. Single diod rectier is ½ wave rectifier.

Transformer design can limit the current to an acceptable level. In this case there is a series resistor doing that. The current doesn't need to be constant, just less that the maximum. As the battery charges up, the voltage increases, and the current drops.

Panasonic about NiMH charging (NiMH)

... !found this! (NiMH)

Ni-Cd ??? is more sensitive to overloading (overheating)

i just tested stuff yesterday about ... constant current src.-'s (low limits)

it's just 2 clicks away

click google [rechargeable batteries 1.2V comparison Ni-MH Cd-Ni Li-ion]

click http://michaelbluejay.com/batteries/rechargeable.html

http://www.angelfire.com/electronic/hayles/charge1.html

this is what i kept on mind however