good morning YouTube this is the isolated variable AC power supply put together a little over a year
ago and I added this AC panel meter and I did a couple videos on those and overall I've been
pretty happy with this setup there's a couple of things though that I'd like to fix one is right
here that there's a residual current and power reading and those vary with the voltage if I go
up to around 120 volts yeah the power jumps up to like six tenths of a watt you've got about
40 milliamps current and as you go down and the current drops to 30 and the power drops to 0.4
watts and then the other problem is if you keep going down in voltage that happens it freezes up
around 60 volts and then at some point it shuts off there's actually two different causes of
those problems so one of the problems not really a problem it's just this particular meter uses a
current transformer and I chose that because I put the current transformer inside the power supply
here and I just ran the wire that goes to this a built-in ammeter through the current transformer
in that way I'm able to sense the current without having to modify any of the wiring inside the
power supply however that current transformer is rated for up to 100 amps and we're trying to
read down to 10 milliamps so that's like a 10,000 to one range and so this least significant digit
here is pretty much noise you know it's not going to read very accurately and then that
reflects into the power I imagine this current transformer is just picking up stray magnetic
fields inside of this and this this particular power supply has got a big very on this side and
then a big isolation transformer on this side so there's a lot of magnetic fields running
around and that's what that current transformer is sensing the other problem is this meter runs
off of the voltage that it's measuring and it's only rated down to 80 volts it seems to work down
to about 60 there's two different fixes so one is I'm going to swap this meter which is the PZ II
M 0 6 1 which is the hundred amp with the current transformer I'm gonna swap it out for one of these
meters which is the you can see that there it's the PZ II M 0 to 1 which is a 0 to 20 amp meter
and it has a built in current shunt instead of the current transformer so I'm hoping that by
using a lower range meter Ike 20 amps is more than enough because this power supply only puts out 7
amps maximum so a 20 amp meter will be a lot more in range and I'm hoping with the current
shunt which is just a low value resistor that this least significant digit here will be a lot
more accurate and then the other thing I want to do is inside of this meter I want to repower the
meter by adding a wire off of this input capacitor which is the capacitive dropper power supply for
this device so I want to take that input power and run it from a separate non variable voltage
so I'm going to be adding a 5th wire over here so I'll have the 4 cents wires voltage sense the
current cents on the outside and then there'll be a 5th wire that will actually power this unit
I will show you that in a bit I've got to get this taken down off my bench open it up and then see
if I can find the best place to cut this wire because I'm gonna have to cut and tap into the
wire running to the ammeter which feeds the two outlets and then I've got to find a good place to
get the 120 volt constant voltage out and then get this meter out of here and then I'll have
to get this meter modified and so I'll show you how to modify this meter to give it an external
power supply so to speak and then we'll see if we can get that put back in here and I don't want to
modify this meter until I see what's inside of this power supply because I need to figure out
how long of a wire to a out on here because I'd rather just come right out of here have a
wire that's long enough to run inside the gear next step we'll shut this down get it off the
bench and take a look inside there again and see what we're looking at so we'll catch you later