what capacitor for an a/c PCB

[paul_h]

Hi all.
I'm going above and beyond here to help a guy out.
I work in a/c where the usual tech just replaces the whole circuit boards if anything goes wrong. Thanks to sites like this I'm trying to learn electronics to get the things fixed on site and straight away, and at the same time save them some cash.
I met this awesome guy today, he's an 82 yo pensioner now, and used to be an electronics specialist himself.

boring background:
His background story is growing up in lithuania, learning electronics in hamburg germany before ww2, moving to australia working in radio and film. Then he started a current major home/car hifi chain here in perth australia which still is big today. But he sold it 30+ years ago when it was clear people wanted retail cheap new stuff, rather than using his knowledge to build/repair.
After selling that he spent 20 years working for the railways in the U.S. and canada, before coming back here to retire.

Anyway, my situation is here we get a lot of power surges, normally that means a blown fuse and varistor. But in this case the main capacitor had blown as well. It was a rubicon 100uF, 450V.
I'm trying to help this guy out and fix it cheaply, but I'm quite the amateur in electronics and don't know quite what this capacitor does. I assume it's to smooth it out prior to the recifier, but I can't even see it on the diagram.
Anyone good at tracking down a components purpose or what the decent replacement parts are, because I couldn't find an identicle part from my retailers either.

[kikkoman]

Re: what capacitor for an a/c PCB

Most probably it's C6 (right behind the bridge rectifier). Looks like someone else didn't strictly go with the specs before and used a lower value.
If you have access to the underside of the PCB, that should be quite easy to verify.

Replacing it with a cap with the intended 150µ (or even higher) won't hurt, and if you have lots of power surges as you say, you should stick with a 400 or 450V type.
I guess I don't have to say much about the brand....

[paul_h]

Re: what capacitor for an a/c PCB

Thanks, it makes sense that this capacitor is across the DC side of the bridge rectifier, so I guess thats the one.
Though I do wonder why theyv'e used a 100uF when their specs are 150uF.
I'll keep my eye out on any others I come across to see if they're all 100uF. Maybe they've changed from the specs on purpose for this country.
I guess it's another bunch of parts to buy out of my own pocket to carry around just so I can do this job. I might grab a few 4A 600V bridge rectifiers too.
Ordering parts like whole new PCBs takes 2-3 weeks, then it's a struggle to book them in again with new jobs coming in everyday that demand attention.
It costs too much capital to carry PCBs when there's so many models and they constantly change. But at the same time it sucks to tell people they've got to wait 3-4 weeks, and with this being summer and holiday season down here, the wait could be longer.
This is why I'm learning electronics and buying the parts out of my own pocket. To get the jobs done first time and not have to book them back in with a rip-off PCB change ($200-500) weeks later.

[starfury1]

Re: what capacitor for an a/c PCB

If that diagram is of the circuit you got
its a switcher psu of some type description and if the 100 uf 450 Volt cap blew.
I would go along with kikkoman its probably C6. (regardless of what the schematic says value wise)

As to why it maybe 100 uf rather the 150uf, the tolerance capacitance wise is like 50 % (if I remember correctly, might be 20%)

So its a wide margin...voltage wise it will have about *320V DC across it so you couldn't use a 315 Volt (ditto what he said above 450V in your case)

(*direct rectification of the mains voltage 1.414 X 230Vac nom, less Voltage drops across other components on the mains side, like diode drops etc)

A 100 or 150uf (or a bit more) 450V is what I would put it that position for mains in OZ,
WA use to have higher voltages in reality then east coast not sure if this still applies ...it was nominal 240VAC but we have now reduced to 230AC inline with the rest of the world that runs at that mains voltage.
(so maybe the regulation is tighter now, I don't know)

if mains transits are a problem I would possibly look into beefing up the components used in the front end and possibly more protection of some kind
I would use a 1000 PIV bridge myself

Here is a link to what I think is the right PDF for the controller IC IC8
TOP232~4

I would isolate the psu for testing under a load and use the lt bulb trick on first fire up

Have a good look around the posts here cause more or less the same procedures and basic functions apply to this psu as computer psu's.

HTH Cheers


Just on you situation ...yeah getting replacement PCB's is expensive and a pain...you might want to see if you can stock pile a few refurb and tested pcb units for yourself So you can do a pcb swap out for the comfort of customers or offer them the option of a new or refurb unit but that I suppose depends on how you do business

I agree, telling someone they got to wait 3 weeks....they are not going to be happy

[paul_h]

Re: what capacitor for an a/c PCB

yeah, the lowest I've seen our mains in 237Vac, a lot of places have 250vac mains, most still have 240vac on average, we haven't dropped to the standard.
In a way I'm glad, there would be more problems with a 230V supply here, when there's some dodgy electricians running an undersized cable 20m so there's already a 10Vac drop.
I already do a fair bit of refurbishment for older stuff, this is my first inverter a/c electronics repair. Most inverters are still under 5 y/o, so still under warranty and I don't have to worry about them so much, hence I don't have any spares or parts scavenged. When repairs are done in warranty, all defective boards must be sent back to the manufacturer, or you don't get paid anything.
So I've got no inverter boards to look at or scavenge from.

Because of the voltage rating of this cap, and what kikkoman said, that's when I realised that c6 must be the blown cap myself, because of where it is.
This being an inverter system, the mains would be recified at 320Vdc to power the whole system.
But as said previously I don't get to look at any busted or new PCBs, so I can't actually double check.
Thanks for your help in this thread and the PSU thread BTW.

As far as the time they have to wait, it sucks and I don;t feel right doing it, but it's a symptom of living in WA.
In these type of non warranty jobs they are charged $125-$150 for the priviledge of the callout, only to be told they have to Wait Awhile. Then 2-4 weeks later we come back and charge them some huge mark up for a whole new PCB.
It even annoys me, I have ordered parts for friends, and even I have been waiting 3+ weeks for parts from my own company, so the parts problem is not on our end.

[starfury1]

Re: what capacitor for an a/c PCB

Humm yeah your right that sucks... with regards to the PCB supply situation

I think we worked out somewhere that the guide lines for the 230VAC would allow enough
(think its plus 10% minus 6% but dont quote me)
you can be at 240VAC and its still with in tolerance...NOMINAL 230AC

from what I understood WA (long time ago now) was liable to be towards 260VAC
but thats only what I was told...and maybe this was due to the size of the place
population and distance of distribution.

no worries glad to help when I can...and alway hoping I got it right

Cheers

[paul_h]

Re: what capacitor for an a/c PCB

Nah, never even seen 260V in my 15years in the trade covering the whole s/w corner.
It's getting lower in general due to increased housing developments and old blocks being sub divided.
It's pretty much bang on 240v everywhere, a few places have 250v if it's low building concentration in the area, ie semi rural, or industrial/commercial which is always close to the transformers.
A few places have 230v if a few blocks had been demolished and three units put up every 500m^2.
But I've been to heaps of houses where there's 240V at the circuit breaker, but 225v by the time it reaches the a/c 20m away on undersized cable. That's enough to chew through the soft starters we use, so I'm glad we err on the higher side of mains voltage than the australian standard.
edit: went to a nice one the other day, a/c powering a underground cellar at the back and underneath the house, 2.5mm^2 powered everything in the cellar (light's GPOs, a/c controller) The a/c controller ran 1.5mm^2 cable to the 6kw a/c.
This unit constantly burn't out soft starter capacitors, but ran fine when tested in the workshop. I get called there and see the crap power supply, and see the 1.5mm^2 cable actually get hot, with the compressor failing to start and blowing the 16A fuse. All that just because it only had 217V by the time it reached the compressor.

[starfury1]

Re: what capacitor for an a/c PCB

coming to think of it that might have been something to do with the UK (260V)

Anyway bottom line was its was liable on average to be higher in WA was my understanding from what I read or was told...long time ago
(as you say in your case a good thing)

Yeah I suppose its not so much the running current as in the initial startup when most current is drawn causing the larger voltage drop across the line.

Still those that wire...well lest wise sparks should know this and use the right size copper. In this case at 6 KW I would think it should be about 3mm square. (or a bit more)
My understanding was 2.5 mm is considered standard for GPO's (power points)
lights 1.0mm or now I think 1.5mm square is used
(they did I remember de-rate it, cable size/current...I think ?)

In fact I would have thought it illegal to run something on under size cables but suppose thats another issue.
(I suppose sometimes the *AC installers just hang it off the pre existing line of an old lower Rated AC...still not the right thing to do ....*used loosely as I suppose there are cowboys out there)

I am not a spark so don't really know

but if you told me you wanted to hang something going to pull up to 6 KW
I "wouldn't be" reaching for 1.5mm square twin & Earth...something for a stove would be more the go.

Cheers mate, all

[starfury1]

Re: what capacitor for an a/c PCB

I should add, there also the DIYers as well and customers that don't want to pay to have a new line run (again were that stands legally no idea)