FAQ - Measuring fusor voltage part II - Hands-On

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Richard Hull
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FAQ - Measuring fusor voltage part II - Hands-On

Post by Richard Hull » Thu Sep 12, 2013 1:49 pm

Before reading this read part I at

viewtopic.php?f=29&t=4267&p=27105#p27105

This is a hands-on posting to show how to turn your digital meter of choice into a 20 kilovolt meter, setting it up for assembly of the High Voltage divider covered in part III, to follow.

This effort will lower the input Z of the meter to about 100k ohms. Again, if you chose the LED display you will need a 5volt DC power supply to make it work. If you picked the backlit LCD display you will need a 8-11 volt DC supply with 9 volts being ideal. Make sure that the polarities of your DC supply is hooked up properly to power the meter.

The meters shown here are from Marlin P. Jones and can be found at.....

http://www.mpja.com/Digital-Panel-Meters/products/52/

These are current part numbers as of Sept. 2013. Note* sales can end and meters go obsolete or be no longer available. Similar meters will always be around.

LED meter is part number 8054ME and is type PM129B $13.95
LCD is on super sale.... Part number is 11273ME type is a PM188BL and is currently only $4.95
The resistor kit is part number 12073-RS and is $1.00 each

This process will involve your removing a jumper and soldering two resistors onto the meter's circuit board of each meter type. You will receive a data sheet that can be misleading and in error regarding the resistor placement. NOTE the high value resistor with the multiple white bands must go to the pad pair that has one pad connected directly to the pad marked "Vin".

The images below help a bit. Please study them. (click on image to enlarge for extra detail)

After soldering the RA and RB resistors, you must hook up you power supply and make sure your meter comes on and goes to 00.0. Next, you must have a multi-meter of some sort, perferably a digital one. Take a battery, maybe a 1.5 volt or 9 volt, and connect it from Vin to its ground reference pad on the meter. Also, across this battery hook you multimeter. The two meters should read close. There is a small variable resistor (potentiometer) on the rear of your panel meter. Adjust this using a small screwdriver to where your panel meter is in general agreement with the multimeter. You panel meter is now an accurate 0-19.99 volt meter. You are ready to get busy with the assembly of the HV divider resistor chain to be discussed in some detail in part III.

Shameless advertising: Check the trading post in my store to see my offerings to those befuddled by all of this for outright purchase of a custom calibrated system for both voltage and current on a demo or real fusor.

Richard Hull
Attachments
1.JPG
Rear view of meters with divider kit to make 20 volt meter LED (top), LCD (bottom)
2.JPG
Front of meters LED (top), LCD (bottom)
3.JPG
RA and RB locations for adding 20 volt divider chain resistors
4.JPG
Resistors soldered in place to turn 0.1999 volt meter into 19.99 volt meter
5.JPG
P3 pads shorted with solder blob to turn on required decimal point
6.JPG
Final calibration of the LED display using Fluke multimeter to verify
7.JPG
Resistor divider installed on the LCD display
8.JPG
Final calibration of the backlit LCD display
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Boris Said
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Re: FAQ - Measuring fusor voltage part II - Hands-On

Post by Boris Said » Wed Mar 09, 2016 3:26 am

I can't seem to find the meter. Can someone please tell me what they used, or recommend a different one.

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Richard Hull
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Re: FAQ - Measuring fusor voltage part II - Hands-On

Post by Richard Hull » Wed Mar 09, 2016 3:05 pm

This post is three years old and these specific meters come and go. Marlin P. Jones still offers an LCD panel meter that is 200 millivolts and scalable for about $10.00 Any digital panel meter whether LCD or LED that is a stock 200 milivolt (0.2volt), meter will serve as all have areas on them for scaling resistors and most all come with a data sheet telling where to put the resistors and what values might be required.

LED meters are now much harder to find, as the world is pretty much an LCD place now. Too bad as LEDs were great.

Finally, you can easily, (in the United States), purchase an entire finished, fully ranged, DVM, (digital voltmeter), now for under $15.00! The need for a panel meter is just not there anymore with the influx of Chicom electronics. Harbor Freight, here in the U.S., offers full blown Chinese DVM's for under $8.00 each.

I have assembled 4 to these cheapo, crummy meters on a movable tilt rack and board as a Geiger counter development system allowing each meter to be plugged into a solderless bread board to look at circuit parameters, rather than struggle with just one meter, constantly changing ranges and farting with long meter cables and leads all over the bench top. (see images attached)

Actually, I obtained over 30 of these meters at no charge!!! FREE!!! Harbor Freight here had a habit of offering coupons for free items if you came into their store and bought one other item at the regular price. (you had to buy somethng to get the free item on the coupon) These meters appeared on numerous free coupons from 2013-2015. Their list price, in the store, was $8.00, but free is better. I would go in with the free coupon and buy a $1.79 screwdriver or a $2.00 pack of sandpaper and get the meter for free. Naturally, I would buy some very inexpensive item that I could, also, really use in my shop, home or lab.

Sadly, now Harbor Freight only offers them for free on special 3 day sales about every two months. So, now I am down to just 6 free meters per year! My best year was 2014 when I picked up 17 free meters!

By the way, have I mentioned how much I detest reflective only LCD displays? Still, free is free....Back lighted ones are marginally better.

Look about for cheap DVM's in your environment. They are there, believe me, unless you live in Chad or the Congo.

Richard Hull
Attachments
DSC00178.JPG
As you can see, the meters are conveniently mounted and all leads run to a pinned header going to a solderless breadboard
DSC00174.JPG
The GM development board is visible in the foreground. The meters can be set to useful ranges and pluged into various parts of the electronics in the project via simple jumpers without long meter leads all over the benchtop. Developed a lot of stuff this way and all the meters were free!!! Cool beans.....
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Richard Hull
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Re: FAQ - Measuring fusor voltage part II - Hands-On

Post by Richard Hull » Thu Mar 10, 2016 7:03 am

The net impedance of the DVM set to 200mv is generally the same as the 200mv digital panel meter. (100megohms) The whole thrust of this "part II" post is to turn your 200mv Digital panel meter into a 20 volt meter.

If you chose a DVM just put you meter on its 20 volt range and you are done. You have to read part I and part III of this three part FAQ, of course, to scale the high voltage to the resultant 20 volt meter. Part III is the tough part in getting your hands on the proper super high ohm resistor.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Bob Reite
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Re: FAQ - Measuring fusor voltage part II - Hands-On

Post by Bob Reite » Thu Mar 10, 2016 11:43 pm

As Richard said, the hardest part is getting the high value resistors that can stand the high voltage. I was lucky enough to have a high voltage probe from my TV set repair days, and I used the 600 megohm multiplier resistor from it for my fusor. If you have to buy new hvstuff.com has resistors rated at 25 KV. Buy three of the 200 megohm 25 KV 5% resistors they sell, hook them in series to get a 600 megohm resistor that will be good up to 75 KV. It will set you back $30.00 plus shipping.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.

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Richard Hull
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Re: FAQ - Measuring fusor voltage part II - Hands-On

Post by Richard Hull » Sun Mar 13, 2016 2:56 pm

I have posted an update on the base metering to reflect that a digital panel meter is not absolutely necessary. Bob has posted on a source for the needed HV resistors. Thanks Bob.

Please, if you can't add to the FAQ post informationally, post basic questions in the normal HV forum and just reference this FAQ.

FAQs are not for Q and A postings.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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