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Old 9th Feb 2010, 7:15 pm   #142
David G4EBT
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Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,737
Default Re: The "Sussex" Homebrew Valve Tester.

Although I'm not building the Sussex, I am using a digital panel meter for another project I'm building, which looks identical to those used in the Sussex. The meter arrived today from China, and warns that you must not use a common earth for the measured power and the power supply to the meter.

To quote verbatim:

"Warning: The working power and the measured power can't use one power system together. When LCD meter uses DC working power, must use the isolated power suplly, can't be sharing the power for meter. Wworking power and meter power can't use common ground wire, otherwise meter will be burnt. The meter power must be 9 - 13.5V, if greater than, then be burn".

So there you go then - "no crash and burn = no common ground"!

Oddly, it also says "meter power AC/DC: No +/- differ".

I can understand that on AC, but it seems odd that it infers that even on DC, the power supply to the meter isn't sensitive to polarity. I haven't tried to pwer it up yet - the colour code of the wire doesn't give much of a clue - brown and red is meter power, orange and yellow is measured power.

The one I've bought is scaled 0 - 199.9V DC. (It's for a zenner diode tester project).

I know it's a bit off-topic from the Sussex, and haven't studied the circuit to see what the power supply arrangments are to the meters, but they obviously work OK as Mike has proven.

I guess these Far East meters are fairly generic - the type I've obtained is a "D69" - they come in a range of scales, up to 500V AC or DC, and up to 2 Amps. The last one I bought was a 500V one for the Capacitor Reformer project which featured in Bygones and the BVWS Bull.

I did squirt more than 500V into it, and - as our inscrutible friends advised, sure enough, it did "burn", so I sent for another and was more careful with that one!

Regards, and best of luck to the "Sussex Legionaires"!


David,
G4EBT
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