AVO VC-1 Any details on its technology ?

[Mooly]

I was wondering if anyone knew anything of the design of these voltage convertors. I have never even seen one of these mythical beasts and have never even been able to turn up even a picture of one.

A couple of things interest me,

1. As the device simply connects to the 1.5 volt cell does the device therefore run all the time, 24/7 ?

2. If it does run all the time then what impact on the 1.5 volt cell life is there ?

3. Anyone know what the technology used was ? I'm guessing it used some kind of L/C boost convertor rather than a capacitive charge pump or multiplier but I really have no idea on that.

Generating a stable 15 volts from 1.5 volts is do able but to do it at a very low quiescent current is another matter entirely hence me wondering if the device runs constantly.

[Leon Crampin]

As far as I'm aware the converter is designed to turn on when it sees a current draw - ie when Ohms x 100 is selected. I'm not familiar with the circuit but it could be very simple.

A stack of 5 CR2032 or similar lithium disk cells will power one of these meters for ages and is very stable. Taped into a stack and fitted with a spacer, no modifications are required to the meter.

If you find or derive the circuit of the voltage converter it would be interesting to see it.

Leon.

[Mooly]

Thanks Leon. I think lithiums as you mention probably are the best solution... I just love the idea of the electronic solution though.

Been having a bit of a play using what I had in the junkbox. Managed to get 15 volts at 2ma quiescent current draw (using a small audio matching transformer). That's not good enough though.

Be great to see a circuit of the original (or photo) and I bet it is simple too, maybe using a custom wound component.

[neonlamp]

SUrely there is someone with a VC-1 they can find out the circuit from?
A simple flyback converter could easily generate the voltage needed (see my 150V circuits for the INS extension under "Avo Add-ons"). It would only need a single transistor, but the flyback transformer might use an energy recovery winding (probably not though as it isn't too efficient at 1.5V) but may need a 15V Zener in that case.

A small ferrite core converter would do.

I'm intrigued as to how it switched on when current is taken...

[neonlamp]

Mooly01 ...

2 mA should be enough. On ohms x 10k there is a 177k resistor in series with a 51k, across which the unknown is measured via the pots.
So the maximum current needed is only 85 uA worst case. Or did you mean only 2 mA input from the 1.5V? Even then if it has a half decent efficiency it should only draw 1..2 mA from the 1.5V cell.

[Mooly]

It was 2 milliamps drawn from the 1.5 volt cell... so probably around 4 to 6 months life.

I do think the VC-1's secret will be a custom transformer/coil.

In the meantime I have done the Lithium battery trick...

[neonlamp]

Options, anyone?
To save power, the inverter should turn on only when the high ohms range is selected. So did the inverter work by a current (very tiny) passing through the unit when a high value resistor is connected? (probably not) Or did it have a separate switch? (probably not). Or did it free-run as Mooly01 suggests? It might do IF the unit could turn off when the voltage was high. It should have been possible to build a unit which generated 15V continuously - but with only a (leaky?) electrolytic to run it should take less than 0.1 mA (ideally) I think, so would not have burdened the D cell too much....

pmm - any ideas?
Thanks

[Barnmead]

I have just been given an AVO8 mk4 with one of these and a very leaky 1.5 volt cell. It was connected directly to the cell with wires rather than the flexible printed circuit conductors which are intended to slip between the cell and the meter contact springs. It would always be in circuit and drawing some current.

With a new 1.5 volt cell my unit drew 330 microamps on no load , the unit is rated at 90 microamps max at 15 volts according to its label.

I have opened it up for you see that it has 3 transistors one inductor and sundry components. See the pictures attached

[Dekatron]

Here are some teaser photos of what's to come!

I have just finished the third prototype (the one with the white sides in the photo below - the first prototype is green, the second black and the third white) of the reverse engineered AVO VC1 and I am working on an article which will contain a lot of information on how the AVO VC1 works and how to build one yourself - it will however take some more time to write all of the text for the build-it-yourself chapter.

All of the prototypes work as they should but I have had to trim the size of the converter as the AVO 8 multimeters didn't accommodate the maximum size specified for the BLR121 battery, so my first prototype was 0.8mm too large for some AVO 8s. The third prototype was just made to test an idea I had on making a jigsaw design of the PCBs so that the positive and negative sides were slotted so that they only fit on one side.

There article will probably be published in a magazine as I have been asked to do so by a few people, and also partly because it is large due to the build-it-yourself chapter takes up most of the article and it is stuffed with photos for all steps, including how to wind the transformer yourself. However most magazines might think it is too large for them too, so we'll have to see what happens.

/Martin

[Mooly]

That is very nice work indeed Very impressive.

[threeseven]

My reaction too!
Will the circuit boards be available Martin?

[mark pirate]

Very nice work, they look very professional
I have over a dozen Avo's that would benefit from such a device.

Mark

[Dekatron]

Thanks all for the kind words!

There is an issue with copyright on the AVO VC1 so I am not sure what Megger would say. I have contacted them several times but not heard from them yet. So I am not sure about how to do with PCBs and such yet.

Any ideas anyone?

/Martin

[threeseven]

Personally I wouldn't be concerned with patent, Megger don't support the old analogue meters anymore and any patent would have long ago expired.
As long as it isn't called an Avo VC-1 in commercial information I just don't see they could have any objection, particularly as they haven't responded to your attempts to contact them on the matter.