​VARIAC Stanley Meyers Application know how

 

the meyer circuits posted here so far, with the variac, were his bench top test equipment. to understand what he did, this is the most simple, setup. this unit was not for running a car, this unit is to understand what does what.

 

the 9xb was used with the variac. the 9xb is the gate. it all together was the 8xa circuit, complete 

meyer used a 5 amp powerstat

 

Notes 

max's 9xa can handle 5amp, stan used a 5amp varac. 
i got a 4amp variac.. coz i couldnt afford to pay for extra 2 amp. ( in my place they make variac starting from 4, 6, 8,10 ... amp). 

i choose a 3amp fuse to variac output.. fisrtly to protect the variac( cant afford another, if this goes down). i also have some spare 3 & 4 amps fuses to play around. 

target-- to find good production..

 

BUying used variacs 

check the brush to see if it is worn or blown out. a brush is easy fix, but common problem. you will see if its worn or chips missing

 

I am wondering if I should put insulate around the variac to ensure no spark jumps, electric shocks or interference in a confide space.

will be ok not to insulate the variac since you have the choke coil transformer insulated the way you do. It should be just fine the way you have it.

 

Example also See 9xa 8xa Treads for more infor on chokes and builds of desk top box 

 

Ok so I learned a new thing today.... 
Max you problem already told me about this but it is easy for me to forget as there is so may things to remember for me right now as i an't no expert in electronics... 
So i have these digital Amp/Volt meters right and to power them they need 5-12 Volts just to run the display... 
I want them to take a reading from the variac but it would keep blowing the RCD in Dads Lab which i am sure he was getting real happy with me about especially when he was on the computer LOL! 

The patent Circuit diagram shows an isolated ground veritable transformer. 
And i have just found out that my variac is not isolated from the case! 
So going back to the 8xa pictures from the estate... Stan's is not isolated either?!? 
Ok so i have a computer power supply that is grounded to the case runs my low voltage for the 9xa's and digital Amp/Volt meters and a variac that is not isolated. 
((TRIP)) goes the RCD! 

So to fix the problem I made the computer power supply isolated from the case now everything is floating it would seem. 
I understand you can buy an isolated ground transformer i can plug in before the variac so i may still do that if needed for safety later tho i suspect Stan never had one! 

I have not had time to run it yet but i think i have fixed the problem. 

In the back of my mind i am sure Max has said everything needs to be isolated ground. 
but if my veriac is not... and turns out to be not the same as Stan's I am not sure what to do?! 
maybe i should forget the digital meters altogether?!? 

you will need to isolate your scope from mains or you will not see the unipolar pulses coming out of the scr. And yes you will blow a fuse if you touch the ground clip of the probe up to the cell. It's a direct short to ground. In my video you'll see the isolated transformer. Their not cheap though. I got mine off of ebay for @ $100. 

 

cheap way 

take 2 microwave oven transformers, identicle ones.........cut the cores apart.........use the 2 primaries.........weld it back together...... 
presto..........cheapy isolation transformer...............Might get something like this... the old school ones are normally around 2000 - 3000VA

An isolation transformer is a linear transformer, often with symmetrical windings, which is used to decouple two circuits.  An isolation transformer lets an AC signal or power be taken from one device and fed into another device without electrically connecting the two circuits.  Isolation transformers block transmission of DC signals from one circuit to another, allowing AC signals to pass.  Isolation transformers also block interference caused by ground loops.


In electronics troubleshooting, an isolation transformer has a ratio of 1:1 which is used as a safety precaution (to eliminate the shock hazard for hot chassis device such as SMPS).  That means 240 VAC in and 240 VAC out.  You may also use the configuration such as two 240V:12V transformers connected in the below manner:

240V:12V (T1) and 12V back to 240V(T2).

Without the isolation transformer, exposed live metal in a device under test is at a hazardous voltage level relative to grounded objects such as an oscilloscope ground lead. That means that if you connect the oscilloscope ground to the primary side of the switch mode power supply (SMPS), it will cause the building to trip!  With the transformer, as there is no conductive connection between transformer secondary and earth (ground), there is no danger of touching a live part of the circuit while another part of the body is earthed (grounded).

If you are new in this field, do yourself a favour and get an isolation transformer. Remember, the power transformer must be rated to handle the power of any equipment connected to it.

Yes you can use it with your oscilloscope, but you need to check the secondary side of the isolation transformer. Check and see if the neutral leg of the secondary is tied to the earth ground pin of the power cord. A lot of the isolation transformers out there tie the secondary to ground. If there is a connection of the neutral leg to earth ground remove it. The ground coming in from the power cord will still be connected to the output side, but can't be tied to the output power of the secondary. 

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