FIMER X 1600 Resistor help?

[Tonyg64]

Well, all parts arrived Thurs from Mouser and fitted new parts and.... nothing. Got the light bulb soldered where the resistor would go in anticipation too . So I get 240 ac in, rectifier showing 300ish DC out. The 12v side doesnt seem to be alive so when powered off if I put 14v from a power supply to the relay it clicks and the power led lights up and the fan runs.

Looking at one of the transformer coils (presume its a DC one), there are 2 wires coming from the windings and go to the board labelled "aux +" and "aux -" and I'm now suspecting these may be feed out to the board and then to the small 12v regulator (7812). So I need to check those wires whilst powered on in case the 12v side is dead.

When I used power supply to check I touched either side of the 12v reg and the fan ran slower/quicker so the reg appears to be fine. Heres hoping for a better day today

Cheers

Tony

 

[DavidL]

Well done for getting so far and good luck.

Just a quick note to save you possibly barking up the wrong tree - transformers don't work with DC - they require the input to have a frequency to induce current in the output windings.

Is it possible that transformer you've found is straight to mains voltage as part of a PSU for the low voltage parts of the board (and that's goosed?)

 

[Tonyg64]

Ah ok thats good to know. I wonder what the aux + and - are for then. The + has a trace connected to the 7812 reg and from there to the relay so maybe the relay is taking low V AC?. The 2 windings from the transformer have continuity, can I do more to check this?

Cheers

Tony

 

[DavidL]

Ok, that's interesting - is there any rectification with the reg?
Have you got a picture perchance (and/or does it have a label/markings), and do you know what the other windings are connected to?
(Sorry if I missed that before)
I'm guessing it's either mains or the IGBT (or whatever they are!!) pre-rectified output?

Isn't it fun making a schematic from the boards (!)

 

[Tonyg64]

Sorry the + does not connect to the relay +, my bad. The neg does thou (or is common)
I'll post a pic of the transformer in a min.

 

[Tonyg64]

Hers the transformer. Note the extra coil hanging off the side. Not sure what that does. The ends of each wire all have nearly zero ohms so it seems ok but I dont know how to test them really.
The small brownish looking wires feel like single strand and are the aux + and - . After probing around I can't find a link to anything else from the aux + wire. Both the aux wires also have near zero resistance (to each other). There is also a current sense transformer nearby (TA-116100) but I dont really know if I can test in circuit either.

And yes its great fun making schematic from the boards!

Cheers

Tony

 

[Tonyg64]

Sorry David I never answered the reg question, I dont think it can rectify its a normal 7812 albeit a surface mount one not through board but using ext power supply I can see the difference in the fan speed so its working with DC at that point. I can't find the source of the 12v though to energise the relay (may be 16v reg'd down to 12 of course)

 

[Tonyg64]

 

[DavidL]

Again, impressive work so far

Am I seeing that correctly - the transformer is a power transformer - and has four heavy-ish connections to the board and then two flying leads (so a primary, secondary and auxiliary i.e. another secondary, rather than tapped)??

If so, I'd hazard a guess that the 3 sets of numbers might indicate the relationship between these windings, but this doesn't entirely tie up with what appears to be UTK's present day numbering system.

Also, my numbering theory isn't too sound as while the heavy secondary might then be close ratio (especially if you've found the bus is now 300v, near to that hoped), it's not clear why the auxiliary is still quite a high ratio (if we want it down at 12-24v)
Sorry, not too helpful, just thinking out loud.

Can you determine:
Does the primary go to the mains supply as suspected?
If so, does the heavy secondary go to rectification for the power transistors (as if so, presumably the heavy bit of the transformer is working!)?
Can you follow the path of both aux wires on your board to try to see if they go to either a single rectifier or a pair/four diodes?

I noticed quite a lot of rectifier diodes near the IGBTs and drive transformer, but they look quite heavy and are presumably part of the drive circuitry for them.

If you're happy to work live, perhaps the easiest way to test it in circuit, if you can *safely* is to measure AC voltage on the primary, secondary and auxiliary, when operational.

Please only do this if you're confident you can get access without putting yourself in danger, as per Eddie's warnings. You're there and can judge for yourself.

To be honest though, if you can path trace the heavy primary/secondary, there would be value to measuring the aux only, which might present easier access!

Out of circuit, you'd expect to see low ohm values on each winding, but each winding should have no continuity to the others.

Sorry, rambly and not overly helpful from me

 

[Tonyg64]

Thanks David, I'll have a look today with it live and see what I get from the windings. I dont remember checking continuity between different windings so i'll check that first.

Tony

 

[Tonyg64]

Could someone explain this relay please? If I connect external 12v to pins A1 and A2, the relay clicks and power goes to the power light and the fan runs (unit not plugged into wall at that point). Could it be the other contacts take in higher voltage from the board and then supply the lower DC to make the contacts work? I need to confirm if the relay is operating properly and what pins should see Voltage. Heres a link to the relay http://www.farnell.com/datasheets/2790229.pdf (40.61 series is us)

Cheers

Tony

 

[DavidL]

Hi Tony,

From that datasheet, it's apparently a simple single pole, double throw (changeover) relay.
without coil power, it looks like:
terms 11/21 are connected to 12/22
with coil power, it looks like:
terms 11/21 are connected to 14/24

The coil expects DC on that one, whereas the switched terminals are rated to 250V/16A AC.

Does that help?

Best wishes,
-David

 

[DavidL]

Sorry to add - so to test from below at the bunch of 6 pins, you should see whatever voltage is at the middle 2 pins move from the adjacent pair (NC) on the side nearest the coil pins, to the adjacent pair (NO) on the other side (furthest from coil pins) when coil power is applied.

At first glance, it's not clear if the pin out is shown top down or bottom up on the datasheet, but you can figure this out by looking to see which way the contact strip is at rest - from the pic - I *think* the pinout is topdown - so when the coil is powered, it switches middle to the pins nearest us in the photo you've shown. I *think*

The NC set of terminals may just be used as fixing pins on the PCB if the relay's just being an on/off control.

edited to add - double sorry if I've just taught grandma to suck eggs, and you weren't asking how that relay works

 

[Tonyg64]

Thanks David yes that backs up what I was thinking. Unpowered, the middle 4 pins 11,12,21,22 have continuity. Powering A1/A2 switches the contact so 11,14,21,24 have continuity. So in an actual power on test we would expect voltage to go to A1 A2 ? This doesnt happen. Its only when I put external power source to the relay it clicks and I get life in the fan and power light. This makes me wonder if the power should come from the UTK TA transformer I put a pic of earlier? . As I try to get the path in my head it gets more tricky when surface mount parts so the trace isnt always visible. I did wonder if it was either the transformer or the relay at fault I'd buy them and try before I throw the towel in .

Cheers

Tony

 

[Tonyg64]

David what is odd about the relay is that where the visible contact is (and coil) its at the other end compared to the schematic.

 

[Tonyg64]

Where Ive put + and - is the dc input that makes the fan work etc. The opposite end (top in the pic) is where the contact is.

Cheers

Tony

 

[Tonyg64]

http://www.utkcomponent.com/en/current-sense-transformers

Could this transformer be the unit that drops the high voltage DC down to a level where the 7812 voltage reg can do its thing for powering up? I woke up thinking of it . (furlough madness). I'll try and check it in circuit today.

Cheers

Tony

 

[Seadog]

Current sense transformers are exactly what they say they are. They sense the current flowing in a circuit. They have no other function. And, once again, transformers and DC are not compatible. Transformers only work with AC.

 

[Tonyg64]

Ok thanks, once the current has been "sensed" what does the transformer do with it?

Cheers

Tony

 

[DavidL]

Hi Tony

Much like any other transformer, a sensing transformer uses current in one winding to induce current in another.
However with a sense transformer, unlike most power transformers, the ratio is 1:>1, so it's designed to increase the voltage - i.e. crucially reducing the current carried (i.e. P = IV and transformers can't create energy!)
You can then measure voltage drop across a known resistance value (possibly with amplification) and a known voltage ratio to determine the current in the primary.

The key difference between this and a simple shunt resistor to do much the same is a) the voltage is manipulated upward to minimise the work the resistor must do, and b) that the sensing circuit is galvanically isolated from the measured circuit (i.e. no shared ground so no noise on the - likely sensitive - measurement end.)

There's a couple of good circuit design PDFs on the likes of mouser etc for sense transformers (none of which I can find on first search!), but yes, in short, they're there to facilitate electrically separate current sensing.

Best wishes
David