Degaussing circuit for a rebuilt ali express chassis.

Adrianlamande

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OK a bit of history first. I am restoring a terrible Chinese Storm City Cab I got for free As part of the process I rebuilt an aliexpress chassis (cab and chassis build documented on AP). Once they are unreliable-afide they are not too bad. They take a bit of time to warm up but the picture is pretty good.

Having done that I was thinking about building a degaussing pcb for them as they are missing anywhere to plug your coil. I initially posted on AP my idea and then thought I would replicate it here as I may get more input. Here goes...

AC live to an NO relay, AC neutral to one pin on the degaussing coil.
The other NO relay goes to a PTC thermistor. The other side of the PCT goes to the other side of the degaussing coil.
The AC goes to a AC to 12v DC converter.
12v DC from the converter goes to a 555 timer, with pin 2 of the timer connecting to momentary switch. Pin 5 is tied to gnd with an 0.01uf cap.pins 6 & 7 are tied together, pin 7 is tied to VCC with a 270ohm resistor, 10uf cap between pin 6 and GND.
Output of the 555 (pin 3) goes to a 1k ohm resistor which then goes to the base of a 2n2222 transistor. Emitter of the transistor to gnd. Collector to 1 side of the relay coii other end of the relay coil to 12v DC with a 1n4007 diode across the relay coil (cathode to the 12vdc side).
Pressing the switch activates the 555, the 555s output in turn activates the transistor which energises the relay allowing 120VAC or 250VAC to flow through the degaussing coil via the PTC. As current flows the initial high PTC current is reduced gradually. After 3 secs the 555 shuts off deactivating the relay.

Is the theory sound. Does that work? I have never built or had to build one of these before.
 
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Something like this maybe? I am really working on not alot of actual fact and bits and pieces of what I have seen and managed to figure out. Excuse the rough diagram.
 

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Just copy how one is done from any other monitor. They're all very similar. Relays are not used, as the PTC just chokes off the current itself. Here's the one from a k4600.

Are you sure the chassis you have doesn't already have one? Maybe it doesn't have the same kind of plug. But if there's a PTC anywhere on it, it might already have a circuit on board.

1748530841566.png
 
Yeah 100% sure it dosen't have one, no PTC, when it turned up it had terrible caps, a wire wond resistor and transistor that got way too hot and 2A rectifier diodes on a 2A fused circuit, diode roulette. I changed all that out. The relay and 555 were there so it could work with a button press as well as on start up and so the PTC only had current when degaussing, but it looks and sounds like that's not much of an issue. Thanks
 
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The PTC you want to use (Amphenol CL-21) is not the right type as it's for circuit protection. There are several categories of PTCs depending on their purpose and degaussing PTCs are just one of them. Needless to say they're not made anymore so you won't find any on Digikey, Mouser, etc. Read here:

http://info.incomp.hu/NETPDF/Q63100.pdf
 
The PTC you want to use (Amphenol CL-21) is not the right type as it's for circuit protection. There are several categories of PTCs depending on their purpose and degaussing PTCs are just one of them. Needless to say they're not made anymore so you won't find any on Digikey, Mouser, etc. Read here:

http://info.incomp.hu/NETPDF/Q63100.pdf
Yes that's one of the problems, however the CL-21 appears to have the right resistance qualities to mimic a degaussing PTC. Also one of the reasons for relaying the circuit so it dosen't have constant current. The idea was to create something open source out of readly available parts. That may not be possible, hence the checking. Thanks for the link that's great
 
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