i'm on a roll... the kgsshv

[Earspeakers]

4A is needed? Good to know, I throw 3A in builds by default. 

 

Also are you testing the power supply by itself, unconnected to the amp boards? 

[Kerry]

I might be stating something that you already know, but make sure it is a slow-blow fuse.

[spritzer]

The fuse rating for torodial has very little to do with the actual current draw of the circuit.  The inrush current is the problem that needs to be accounted for. 

[mwl168]

Thanks all for your responses.

I am in US hence working with 110v AC. The 3.15A fuse is a slow blow. I chose it based on information I collected reading the thread.

I was testing the PSU alone without load.

Don't have 4A fuse but do have 5A ones. I thought about trying the 5A fuse soon after I blew the 3.15A but hesitated because I worry if there was something wrong with the PSU the 5A fuse may allow catastrophic damage to take place.

Just got home from driving around town looking for a variac. Search was in vein - did not realize many stores are closed for Easter and Home Depot, which is open, did not carry one. I am surprised no one I asked, including the Home Depot guy, know what a variac is, let alone owning one.

The reason I skipped the variac test is because the one I managed to borrow was defective and I was hopping to get this test done this weekend to verify if the PCB is correct. May just bite the bullet and buy the one I found on Amazon that's rated at 3A.

Edit: To be sure, the fuse is Digikey part # 507-1251-ND. MFG P/N says " 5ST 3.15 -R".

Edited April 5, 2015 by mwl168

[spritzer]

Just try the 5A one.  It should only blow the fuse if something is shorted on the board.  I've seen all manner of KGSSHV psu failures but never a full short. 

[mwl168]

Tried the 5A fuse. Upon flipping the switch, the two thermistor started smoking, no output voltage registered. Shut down, visually inspected everything and noticed the transformer was warm to the touch and the STTH802FP rectifiers were very hot to the touch. Measured the rectifiers and the two on the back for the - rail were shorted.

Did I make a dumb and ignorant mistake ordering the wrong rectifiers? STTH802FP (Mouser part # 511-STTH802FP) is rated at 8A continuous forward current but only 200V reverse voltage.

I have ordered two extra STTH802FP. I also have many uninsulated HFA2TB60PBF and HFA08TB60 at home but decided to be safe and ordered the insulated part.

I assume the reverse voltage of the rectifier needs to be above the 400 v + working voltage. Is 600v reverse voltage rating safe to use?

Thanks!

Edit: A further thought; this may explain why the PSU seemed fine when being fed 15v secondaries but failed when fed the 350v secondaries. I wonder if any further damage was done other than the toasted rectifiers. I visually inspected the PSU but did not see any obvious problem like charred resistors or cracked transistors. I am guessing those rectifiers were fried on my first attempt with the 3.15A fuse. On the second try with the 5A fuse and, presumed fied rectifiers, the 680uf capacitor did not appear to be charged at all.

Another question, how do I check if the thermistors are OK?

Edited April 5, 2015 by mwl168

[kevin gilmore]

you are supposed to use 1kv diodes!

[Pars]

I also avoid ST Micro parts like the plaque. Had some negative regulators from them that didn't work right. National and On Semi parts worked just fine.

 

Diodes I like Fairchild personally, depends on the individual rectifier diode I am looking for.

[mwl168]

Thanks Kevin and Pars.

I assume by 1kv diodes you mean diode rectifiers with 1kv reverse voltage rating?

Would 600v diodes work?

Edited April 5, 2015 by mwl168

[mypasswordis]

Why not just get the STTH512 like it says on the PCB silkscreen? Or the STTH1210 that I'm using now which I think was part of a previous BOM, or anything similar (STTH812, etc).

[johnwmclean]

Would 600v diodes work?

 

The recommended part (STTH512FP) is rated 1200V, so you’re like, you know, halfway there... 

 

I’ve had no problems using ST Micro diodes, their regulators I wouldn’t know.

[mwl168]

Thanks guys. Point taken. Will order the correct part tonight.

It came back to me now how I ordered those incorrect diodes. The screen says STTH512FB ( should be STTH512FP ) which is not found at Mouser. I then proceeded to find insulated TO220 rectifIer diode and picked the one with high current rating but did not know the need to spec for high reverse voltage rating. I learnt something today.

The reason I asked about using the 600 v diodes is simply because I have like 80 of them on hand and can replace them tonight and continue with my testing without further delay. I was impatient to wait 4 - 5 days to have Mouser order delivered to me and, on top of that, pay $5 shipping for $10 worth of parts.

Thanks all again for your help!

[Pars]

I've never used their diodes, but just avoid their regulators.

 

This is one I might think about using, unless someone sees something that doesn't meet the parameters required here.

 

512-RHRP30120

[mwl168]

So I am a bit paranoid now after my mess-up with the diodes. I have a part spec question on the amp board KGSSHVAMPV16MINI.

I could not find 175K 1/2W resistor for R14 and R29. I used 1/4W, 174K Xicon instead (Mouser part# 271-174K-RC). Is this OK? Or do I need to find 1/2W resistors for these positions?

I am using ixtp01n100d for CCS, so not populating R10 and R11 which are also 175k.

Thanks!

[johnwmclean]

Pars the spec looks good but the new smaller boards require an insulated package.

 

Michael take a look at the schematic, you need a 500mW in those positions, also the voltage with the Xicon 271s is only 250V.

 

[Pars]

Yeah, probably a little big current wise as well. They do make 8A also IIRC, but if you need an insulated package, then I guess the parts you guys have identified are the ones to go with.

 

As for > .25W resistors, Mouser does stock Dale RN65 in a 178K, .5W, 350V.

 

I couldn't find the schematic for that particular PSU either, but I only looked briefly.

[mwl168]

Thanks John. Glad I checked.

I am sorry, I am not knowledge enough to know what spec parts are needed by reading the schematic. IIRC, Kevin's original KGSS article mentioned that some resistors can be 1/4W rated. But these resistors appear to be part of the CCS, I figure I better check.

I cannot find 1/2W 174K or 175K resistor in stock at Mouser. So I am going to order Vishay CMF60 1/2W 348K resistors and parallel two to get the desired resistance to be safe. Vishay CMF60 is rated at 500V.

[mwl168]

Thanks Pars.

I was typing my response while you posted your response. I will check out those RN65 178K resistors.

[spritzer]

RN65 resistors won't work, they are huge.  The RN numbering is milspec so a 1/8W resistors is actually 1/4W, 1/4W is actually 1/2W and so on. 

 

Here is the diode, use it:

 

511-STTH512FP

 

This is the resistor you want:

 

71-RN60D1743F

[mwl168]

Thanks Birgir! 

[Pars]

I was thinking RN60s also, but for some reason they weren't coming up in my search on Mouser. I should have directly looked for them.

 

Also, I have a couple of RN65s and they aren't that huge that with creative lead bending they couldn't work. Though I suppose at these voltages, you don't want to give anything an excuse to arc

[spritzer]

It's been a while since I bought some but the RN65's are almost twice the length so yeah, creative lead bending would be needed.    It's a 1W part though so utter overkill with so many 1/2W units available. 

[mwl168]

I think I have a minor success to report on my kgsshvpsminifinalstn9360 PSU build.

After replacing the rectifier diodes with the correct STTH512FP parts, using my freshly arrived variac, I powered up the PSU successfully, and I measured -406V, +408V and bias voltage 560V (from test point) after about 15 minutes. These are the correct numbers I was expecting based on my setup. I did not notice any smoke, spark or abnormal temperature during this brief testing. The +/- output voltage was very stable, varying around 1V from start up till the end of the 15-min testing period. The bias voltage raised about 10V during the same time.

I do not have the equipment to measure noise and such but I hope this is enough evidence that the PSU board is fine. If so, this is good news for the GB participants who have received this board.

I have some work to do to complete the amp boards (kgsshvampv16mini) and start testing them.

Please let me know if there are additional testing I should and can run with my Fluke 112 meter to make sure the PSU is functioning as designed.

Many thanks again to all that came to my rescue with my problem.

P.S. A word of caution for safety - the bias voltage sustained much longer than the +/- outputs after powering down the PSU. When the output voltage dropped to below 1V after a couple of minutes the bias voltage still measured well over 100V!!!

Edited April 10, 2015 by mwl168

[nopants]

test it under load, some sinked resistor

[mwl168]

I have a 1000ohm ceramic resistor I use to bleed out the large smoothing capacitor in the past for other projects. Is it safe to use for this purpose? I assume I wire it across the ground and either the + or - out?

Thanks!