[RESOLVED] Modify a Fluke 8012A from 110v to 220v

[gkmaia]

Has anyone modified a fluke 8012a from 110v to 220v?

I am trying to source the 461723 transformer but obviously that is obsolete.

Is it possible (I mean likely) to based on the readings on TPs to then source a new transformer?

I am also getting confused with what the actual voltages coming out of both transformer secondaries.

[Ewald1963]

To me it seems all you have to do is to put switch S2 in the 220V position. The selection to switch between 110VAC and 220VAC is done at the secundary of the transformer. In the 110V position the two secundary windings are in series, in 220V position only one winding is used.

[Ewald1963]

S2 is not really a switch. On the Photo of the PCB it seems to be some solder pads only. Whats on the other side? Maybe you have to remove a solder bridge there and make another one?

[gkmaia]

S2 is only for when you have the battery pack option installed.

[gkmaia]

I suspect

In the 110V position the two secundary windings are in series, in 220V position only one winding is used.

Can you please elaborate that further?!

i imagine you suggest something like the image bellow.

[Twoflower]

From my understanding: No you can't do this change without replacing one of the transformers. For T2 you can change that using the S2 to change the input voltage. But T1 needs to be changed as it has not the option to change between 110V/220V.

For T1 you need to figure out wha's the secondary voltages and maybe you can find a pin compatible replacement or another way to mount it off the PCB and use wires.

A side-note: It very interesting that the switch 110V to 220V on T2 is on the secondary. Usually that's done on the primary.

[gkmaia]

Has anyone modified a fluke 8012a from 110v to 220v?

I am trying to source the 461723 transformer but obviously that is obsolete.

Is it possible (I mean likely) to based on the readings on TPs to then source a new transformer?

I am also getting confused with what the actual voltages coming out of both transformer secondaries.

If the primary has two windings and I put them in series I may manage to make the primary 220v. The problem is. I am not sure there are two windings, but seems logical to be. Second the whole thing is enclosed in silicone... that is turning out to be interesting.

[Shock]

It looks explained in the manual if you have the -01 option you get the switch, T2 etc as shown in the schematic, along with a procedure for selecting line voltage in the field. Says it also in the catalog.
https://people.ok.ubc.ca/jbobowsk/phys231/specs/Fluke%208012A.pdf

For the standard model it appears they came with two options with different voltages and 461509 (the one you show in the image) is the 110V-115V part.

So reading between the lines I don't think it can't be done just with the switch mod.  I'd suspect the transformer is not rated for both voltages (you would also need to halve the secondary). There is a fuse assembly part that seems rated for 110V-115V as well.

Mains voltage warning!

I would be tracing the circuit and figure out what is actually connected to where from the transformer secondary and then measuring any secondary AC voltages. But I also have a step down transformer and tend to buy only gear that can be easily converted this saves a bit of frustration.

[Chris56000]

Hi!

Looking at the circuit–extract provided, it isn't too difficult to work out what is needed for T1:–

For the VDD supply, the reservoir cap is only 220uF, implying a circuit current (for half–wave rectification) of about 50mA, so you're looking at a secondary of about 3.5V rms rated to supply 50mA, and for the +VA & –VA supplies, 9.5V rms rated at 100mA should do!

If you're good at, or know someone who is experienced at transformer rewinds, buy one of these cheap little 5W Chinese transformers, and get two secondaries wound on it, 3.5V @ 50mA and 9.5V at 100mA, alternatively, if you've got spare room in your meter, you can probably find a couple of those little pcb "block" transformers in Mouser that meet the specs suggested above, and mount them on a piece of "protoboard!"

Chris Williams

[gkmaia]

I think I will try a different approach and do not mess with the T1.

As you can see I have some space on the far left side of the board. So I just bought a 220-110 / 50w transformer and will pretty much wire the primary of T1 to the secondary 110 of the new transformer and the primary of the new transformer to the black/white socket and leave the earth where it is. So basically bring an external step down transformer inside the case.

Does it sound like a good plan? Any drawbacks?

[coromonadalix]

there wont be any problems if it is a transformer, not a 240 to 120v gimmick

[gkmaia]

there wont be any problems if it is a transformer, not a 240 to 120v gimmick

I think plugging it on 220 and checking if the secondary outputs a sine of 110 volts @ 50hz would be enough? Right?

[coromonadalix]

not so sure, some of the gimmick i saw they used a diode to chop half of the voltage sinusoidal voltage ........ you must have a real transformer nothing else.

[gkmaia]

I did a bit more work on that as I am exploring the idea of building my own transformer.

First image has chart with a test I did where I feed 1v @ 50hz on the primary and retrieved 13.3v and 10.5v on the secondary under a load resistor of 47k.
That is quite different from what you suggested as 3.5v and 9.5v. Also different from what the manual suggests for VDD as +2.9V and VA as +15v.

Second image shows a chart I build using standard calculation for main transformers. Core would be around 15mm by 15mm in size.
For the primary that would be 2000 turns @ 38AWG wire. Secondaries could be done with 260 and 205 turns of 28AWG wire.

Can you please give me some insight why my first image output does not match your output or manuals output?

And also if my estimate of 2000 turns of 38AWG on a 15mm size core sounds reasonable?

[Chris56000]

 :HI!

The +2.9V Vdd is referenced to 0V chassis earth as is the –2.1V Vss supply, so the required supply is about 5V between the two!

Allowing for the regulation percentage of minature transformers, if you calculate turns for 3.5V and add a couple extra this will give a bit over 5V between the +Vdd and –Vss lines!

Likewise, you've got two half–wave diodes off the secondary feeding the +Va and -Va lines, again, allowing for transformer percentage regulation, a 10V nominal r.m.s. secondary run off–load will give close to the +15V and –15V given in the voltage table!

Chris Williams

[macboy]

I would worry about transformer saturation due to the change in line frequency. If the transformer saturates, then it may run hot and fail.
The original transformer is specified for up to 132 V at 60 Hz (and as low as 90 V). The flux density within the transformer per half cycle is proportional to voltage and inversely proportional to frequency (or proportional to cycle time which is 1/f). So, to avoid saturating the transformer, do not run it at higher than 132*(50/60)= 110 V at 50 Hz.  Your step down transformer is probably simply 2:1, so at 220 V in, it should be 110 V out, but what is your line voltage? 220 V? or 240 V? Is the line voltage even higher in your location? Don't exceed 110 V actual (not nominal) on the transformer. Actually, I'd recommend shooting lower, like 100 V. That gives you about +- 10% room (between 90 and 110 V) to account for variations in the line. That will mean using a transformer that is not 2:1 ratio. Measure your line voltage and determine the actual (not nominal) secondary voltage based on the transformer specs and/or measurements. Of course the transformer may have enough margin to work perfectly well enough, but it is good to at least anticipate such a problem.

[gkmaia]

:HI!

The +2.9V Vdd is referenced to 0V chassis earth as is the –2.1V Vss supply, so the required supply is about 5V between the two!

Allowing for the regulation percentage of minature transformers, if you calculate turns for 3.5V and add a couple extra this will give a bit over 5V between the +Vdd and –Vss lines!

Likewise, you've got two half–wave diodes off the secondary feeding the +Va and -Va lines, again, allowing for transformer percentage regulation, a 10V nominal r.m.s. secondary run off–load will give close to the +15V and –15V given in the voltage table!

Chris Williams

:HI!

The +2.9V Vdd is referenced to 0V chassis earth as is the –2.1V Vss supply, so the required supply is about 5V between the two!

Allowing for the regulation percentage of minature transformers, if you calculate turns for 3.5V and add a couple extra this will give a bit over 5V between the +Vdd and –Vss lines!

Likewise, you've got two half–wave diodes off the secondary feeding the +Va and -Va lines, again, allowing for transformer percentage regulation, a 10V nominal r.m.s. secondary run off–load will give close to the +15V and –15V given in the voltage table!

Chris Williams

I’ve dome some experiments trying to understand reproduce what you said above and see these things happening in practice. I do have questions. I am very curious about this transformer.

Primary
11 v mains input @50hz

Secondary white (pin7-9)
Transformer AC output off load: 3.5v
Transformer AC output under load: 3.3v
Rectified DC output +VA: +15.7v (matches the manual)
Rectified DC output -VA:  -15.7v (matches the manual)

Secondary green (pin 10-12)
Transformer AC output off load: 2.2v
Transformer AC output under load: 2.0v
Rectified DC output +VDD: +10.5v (manual +2.9v)
Rectified DC output -VSS:  0.0v (manual -6.5v)

 I would like to ask you if you could explain in more detail and maybe show some calculations on how the diodes could output +15v out of a 3.5v source.

Also your suggestion of a secondary of 3.5v for pins 7-9 seems spot on. But the suggestion of 9.5v for pins 10-12 does not seem to align with my experiments. Could you please give me some insight on why they do not match?

[gkmaia]

Here is the final result of the idea of including a 220/110 second transformer inside the fluke.

Did print on 3D a little support for the transformer. It outputs 119v which is in range and it is also phased the same way the old wires were.

[bd139]

Nice so you used a dual tap 110/220 transformer as an autotransformer and fed mains into the old transformer with it? If so, neat hack 

[gkmaia]

Nice so you used a dual tap 110/220 transformer as an autotransformer and fed mains into the old transformer with it? If so, neat hack 

Yes, that is pretty much what I did. Was impossible to source the original 220v one.

Also, not really excited about wiring a new transformer. Probably will do in the future that as another exercise.

[coromonadalix]

 

[gkmaia]

AND when I first tested it by adding 220 to the input, guess what my output was???

Was 400 something volts!!! They mounted the transformer as a step up... WTF... imagine someone plugging this to run a 110v device?

[emptech]

It's been a while since you posted, hope you were able to solve your issue with the voltage change.  I'm trying to find a diagram of the circuit.  I see you got a screen capture of part of the power supply, I would like to find a diagram of the battery circuit.  Your's shows part of it, I need more details to the right of your diagram.

Thanks in advance -   Jim

[wolfy007]

Hmm, funny, was just doing this myself on a fluke 8050A, using some 240>120v 5W transformers I found on aliexpress. Did a few tests, they seem ok, set it up so I can switch between 120v and 240v.
PS: yes I am also putting a fuse in, just waiting on fuse holder bits to arrive (and some capacitors).