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Reply to "Wiring Question on a 2203B/2403B/6403B tender"

That was perfect, I understand now. The hookup you described and the schematic you provided are EXACTLY how I tried my first attempt. Using jumper leads, I hooked everything up the same as shown in the schematic. When I touched the last jumper to provide "hot" power from the A terminal on my ZW, I got quite a blue flash, and a large amount of deflection in the bimetal strip. My human side got the better of me and I just had to try it again, with the same result - another blue flash, and an audible hum emitting from the ZW - I knew that I was drawing far too much current. 

As you can see in my pic, the remaining amount of insulation on the bimetal strip is half or less, while the number of turns of nichrome are about 1/3 the number of turns shown in your pic. Checking the cold resistance, it's about 2 ohms, which means at the 12v setting I was using, it was sucking down 6 amps, or about 72 watts! Clearly there's a missing hunk of nichrome wire, and it's a show stopper for this unit. I will be giving Dennis Walden a call tomorrow.

So wiring the remaining nichrome heater wire in series with the bell solenoid is required in this case to limit the current flow - but at the same time, it is robbing the solenoid of the power needed to give the bell a good kick - clearly a compromise solution.

There are two remaining mysteries, the first being the instruction sheet where it says the lamp is being used as a regulator - my impression is that the lamp is wired to HOT and GND, and that certainly wouldn't be a regulator circuit.

The other remaining mystery is where the nichrome wire is supposed to be attached at the contact end of the bimetal strip. Looking at your pic, it almost appears as though they have done what I ended up doing which was to solder the wire directly to the strip. But I really can't quite see that in the pic. Interestingly, before I soldered my wire, there was absolutely no sign of any previous soldering on that end of the strip - that is why I assumed the nichrome wire must have been somehow crimped under the actual contact rivet. That said, this whole paragraph is a moot point if I will be buying one from Dennis  

One last comment on grounding, whenever a truck has a mounting post on it with a horseshoe or E clip securing the truck to the frame, I always solder a ground wire to the outer edge of a new E clip, then attach that wire to the car frame - you will never have a ground issue with that in place!

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