Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

[sam_sam_sam]

I have hacked this meter so that it can be with

Variac 10A AC Power Auto Transformer 0-130 VAC w/ Meter,1000W Voltage Regulator

( I have seen on You Tube where people have put digital meters on a Variac but all the one I seen they have where the volt meter can not read the voltage below about 80 volts I did not mine to work this way )

Which is something I going to buy soon

How I figured out where the voltage input was I had decided to replace all the caps on the board top board with all the caps remove and high powered light it fairly easy to trace where the traces go

So I traced wear all the input power went and found all you have to do is remove a surface mount diode ( M7 )

and replace it with a 1N4007 and on the side of the diode that has the line is where you put the wire so you can measure the line voltage of the Variac out put

[stj]

Re: Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

that variac looks a hell of a lot better than the last set of foto's

[redwire]

Re: Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

Here is a better PCB pic (version with on-board CT) showing the voltage-sense rectifier diode.

For my variac, I did the same but used the $1 mini-panel meters, the 22mm ones. It is easy to separate the power and voltage-sense.

[sam_sam_sam]

Re: Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

I want to change the input voltage from 80 volts AC to 24 volts AC
I know I have to change the input capacitor but to what value

How do calculated this value

Thanks to anyone that can help

[redwire]

Re: Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

What is the brown film capacitor's value?
To go from 120VAC power to 24VAC, that is 1/5 so it would get upsized 5X. Assuming it's say 2.2uF 250VAC, to 10uF 100V.

It's almost where you could just use a resistor dropper instead of a capacitive dropper. Short out that cap and replace the big 100R with say 270R 3W to get the same power supply current.
But I'm not sure how current the panel meter uses, with backlight LED and LCD display+MCU. Guessing around 5V at 15mA.

[stj]

Re: Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

it would be better to use a rectifier and micro switching regulator for 24v

[sam_sam_sam]

Re: Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

Powering from the rectifier at about 7 volts gives about 20 milliamperes
So my guess is that it runs at five volts

[stj]

Re: Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

i already suspected that because it has a microcontroller.

[sam_sam_sam]

Re: Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

UpDate on running this meter module on 24 volts AC

The main capacitor was 330nf I replaced with a 1.5uf cap and now it will work down to 12 volts it might go lower than that but it might not read the voltage and current right

I did have to adjust the pot controls a little bit for it to read right it was reading a little bit high

[sam_sam_sam]

Re: Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

What is the brown film capacitor's value?
To go from 120VAC power to 24VAC, that is 1/5 so it would get upsized 5X. Assuming it's say 2.2uF 250VAC, to 10uF 100V.

It's almost where you could just use a resistor dropper instead of a capacitive dropper. Short out that cap and replace the big 100R with say 270R 3W to get the same power supply current.
But I'm not sure how current the panel meter uses, with backlight LED and LCD display+MCU. Guessing around 5V at 15mA.

Your calculation 1/5 was right on

330nf I put in a 1.5uf

[sam_sam_sam]

Re: Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

UpDate

Did a burn in test over night and the meter module still working this morning
I now know that that this will work

[sam_sam_sam]

Re: Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

UpDate

This is with the volt meter module modified installed in the Variac 20 amp
as you can see it reads the voltage the same as the Radio Shack volt meter does

Now the voltage scale on Variac is way off it shows 105 volts which is better to show low than high

I am only going to use the scale for a ruff estimate of what voltage could be on the output side

Very pleased with the way it turned out

Here is the main ( but not the only) reason for buying this Variac is that sometimes I buy LED modules and do not have a power supply to power them

This brings me to this question

I would like to have a bridge rectifier with a capacitor and fuse

To have a dc power supply

What else should I use,do to make this setup as safe as possible

One note

With the control knob turn all the way to the right the voltage is 151 volts AC


One other question I have is what other uses does a Variac have please give examples

Thanks

[stj]

Re: Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

one thing worth pointing out is the output voltage will probably change a bit with different loads.
so trust your meter and not any printed scale around the control knob.

[redwire]

Re: Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

You can add a rectifier/filter cap/bleeder resistor etc. and make an adjustable DC output- but it is dangerous.

A variac is an autotransformer, so it does not provide isolation from mains.

If line and neutral are flipped anywhere, the variac's (common) output would be hazardous live with respect to earth ground, even if set to zero volts output.

You would need an isolation transformer to ensure the variac's output is safe.

[sam_sam_sam]

Re: Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

You would need an isolation transformer to ensure the variac's output is safe.

Would this isolation transformer work for me

[redwire]

Re: Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

I think you could make an adjustable DC power supply with the variac using Triad N-51X looks good for a smaller isolation transformer, 0.3A output max. so a fuse for it would be good.

[japlytic]

Re: Digital AC100-300V BLUE LCD DISPLAY PANEL VOLT/AMP meter WITH SPLIT 0-100A CT

On my unit, I used a digital voltmeter display which has a minimum voltage of 60 VAC, but the display was just visible down to 30 VAC - this would be unreasonably low, since the connected appliance would not function at all!