Convert fluke transformer from 110 to 220 - should modify primary or secondary?

[gkmaia]

I finally got courage to modify my fluke transformer from 110 to 220.

I have two ways to go and would like to hear from you which one you believe is best.

First I thought about double the primary turns. I would then reduce the wire diameter to maintain the copper area. But the wire is already too thin and I believe there wont be space in the coil former for that many turns.

Second option would be to reduce secondary turns in half, then double the wire diameter to maintain similar copper area. As the secondary coil former still has plenty space any modification there will be fine.

I just want to know. If that is fine to go ahead and modify just the secondary.

[exe]

You have to modify primary as there is simply not enough turns to work from  230 V +10%/−6% (assuming you are in AU and information here is correct: https://en.wikipedia.org/wiki/Mains_electricity#Voltage_levels).

[ArthurDent]

If you try to power a 110 volt transformer primary from 220 you will either instantly blow a fuse in the instrument or destroy the transformer- don't even try it. Doubling the input voltage on the primary will saturate the core and cause the current drawn to increase greatly so it won't matter what you do to the secondary.

Most older Fluke instruments are designed with split primaries so they can be configured to run on either mains voltage. Have you checked the back for switches or checked the manual to see if there are internal jumpers to already do this? List the model number here and maybe someone has knowledge of this instrument.

If it has only a 110 volt primary the easiest way would be to buy a 110 to 220 autotransformer that you can find on eBay and many other places. A small one could be in the $25 range. Just make sure it can handle the wattage of the Fluke instrument.

[m3vuv]

just my two pence worth,i recently brought an old heath computor osscilloscope,that was for 110 volt,all i did was buy a small converter from ebay and mounted it inside the case,works fine,was only about £4 too,simple solution that works well and is neat.!

[Electro Detective]

My six winds worth is if you do buy one of those magic box cheap n suss converters, pull it apart and check and secure EVERYTHING top to bottom, TWICE!!!

because hungry and sleep deprived great grandparents and 12 year old kids aren't exactly the best assemblers or soldering wizards

Yes, these OS transformers are that bad, been there/done that/NEVER AGAIN! 
and pray the toy output sockets don't crumble to muesli
and or the internal pins mangle and short out on first insertion... 


FWIW I'll only convert with an 240-120 isolation transformer with real output sockets and appropriate fusing. 
Works out cheaper and better than upgrading and redesigning those death box OS transformers 

EMMV 

[themadhippy]

One little gotcha thats often overlooked is not only the voltage different,but also the frequency of the mains supply.This may affect motors if   there AC,also if the clock signal is derived from the mains supply its going to be slightly out. 

[gkmaia]

I appreciate all the tips guys. The whole exercise is about trying and learning how to change a transformer. Core calculation. Turns per volt. Etc...

I do have other flukes DMM I can use on the bench.

I posted on the beginners session and got a transformer lesson from Jwillis. 

https://www.eevblog.com/forum/beginners/ei375-steel-laminate-primary-transformer-calculation/msg2594667/#msg2594667

[james_s]

If that's what you want then design and build a stepdown transformer from scratch. It's not that hard, you can buy cores and bobbins and everything else you need. If you try to modify the Fluke transformer you will probably destroy it. They are not made to be disassembled.

[gkmaia]

It is already disassembled, laminate removed and cleaned. 100% intact. No damage.

Bobbin is ready for rewiring and laminate is ready for varnishing.

Just needed the calculations for the primary. But so far that has been all sorted out.

I have another fluke that is running with a step down transformer I built inside it. I already know how to do it so there is not much fun doing the same again.

I am adamant I want to modify the original transformer and see what I get out of it. If it ruins it I am ok with it.

[Assafl]

If you remove (unwind) the primary windings, you’ll still have to figure out the number of turns for 220 (or 110 x 2). To do that you’ll need to know the secondary number of turns.

I can think of one way to do this: I assume you measured or know the secondary voltage - so wind 20 or so windings and put the output voltage (AC - duh) on the secondary. The voltage on the 20 turns will get you N:20 ratio so you’ll know N. At that point calculate how many windings will be necessary for 220v.

[gkmaia]

Is has been sorted. Fluke probably went by the book for a EI375 1.5T 0.0001 mm2 core with 25turns/v @ 60HZ or 30turns/v @ 50HZ. It is just a matter of unwinding the primary and finding out if they winded it for 50 or 60hz and do the calculations for the 375 core to sustain 235V at 50Hz.

[m3vuv]

meant to add that i removed the transformer from its plastic case and used it so all the connections etc were my own,there were issues if i remember on pulling it apart,think one of the 240v input wires was just tack soldered on if i remember!