vvega
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All good , if it wasn’t for the article you wrote I would still be sitting here annoyed at an amp that was sub par at best . I appreciate that you put it out there and it’s work like that that keeps diy alive and out there . Its appreciated I guess all I’m trying to do with the testing is show the reasons behind why you did spec the ceramic insulators in the first place . But for me missing that detail and using silicon , something that would have failed at even 500v , I wouldn’t have damaged my amp and had to repair it. The testing so far has shown that a steel bolt with ceramic is good enough in fact it’s as good as a synthetic bolt and mica if not better.
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JimL saying the purpose is contrariness actually a pretty offensive thing to say to an engineer . Its just an adventure in building some electronics , I didn’t decide to build the circuit just to be a dick about it , i started doing it because I wanted better sound , i started testing because I made a mistake , a potentially harmful one and I’d like to not make that mistake again . Im still quite grateful to the fellow because it was his article that set me on this path and Kevin’s support that got me through it . ps I’ve started acquiring parts to build a carbon ... so this should be interesting
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I don’t agree , when someone tells me on the internet that the specs are wrong on a part ... then why shouldn’t you test those specs . And if you have something against testing when hv is concerned well , that’s just silly. as an engineer I spend a lot of time testing to failure because that’s how we keep opinions in check over facts . Fact is mica is thinner and at the same thickness has very similar thermal barrier property’s . So a thinner insulator less thermal resistance . Whats wrong with looking for efficiency or better design From the testing I’ve done so far you shouldn’t have any issues with this combo . It would seam you can use mica with synthetic fastenings or ceramic with steel . I don’t use grease in testing because .. it eventually dries out and it’s dialetric property’s change so the test wouldn’t give a result that would account for that . im actually looking forward to trying different compounds to see how much if any extra insulative effect they give . this is just a blog of my personal little project , if it’s upsetting people they should probably just unsubscribe .
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Do you want to send me that part ? Give me a pm and well sort it ... it’s not avalible here as far as I can tell
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I have a ceramic washer and steel screws and the messy paste , can test that combo .
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In this case its an arc , a direct short , however the meter does measure leakage ... you will get voltage leakage before you get an arc . You select a voltage and it will give you a resistance value ... you then work out from there using I=VR to determine the current ... Type of Equipment Maximum Leakage Current Class I 0.75mA for hand held devices 3.5mA for other devices Class II 0.25mA Class III No hazardous voltages Both gave an open circuit test @1000v with the meter with nylon , the ceramic gave resistance value @ 1000v with the steel bolt and the mica gave an arc fail . The silicon gave an arc fail @ 1000v with both the nylon and steel bolt What i have done is a modified HiPot test .. i have tested well above the required insulation as a longevity test, however 220v is normally tested @ 1400v for a pass ... so 440v would require 2800v for a pass ... none of the options currently selected could pass that test .. but both the mica and ceramic give a definite 1000v pass with 0 leakage at all . http://carelabz.com/what-leakage-current-testing-measuring-how-leakage-current-testing-measuring-done/
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- stax
- kevin gilmore
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Did the testing with the ceramic insulators with a steel bolt .. 500v ...pass 1000v ... fail with a nylon bolt .... 500v... pass 1000v .. pass 2500v ... fail so same results as the mica with the nylon ... i don't doubt that there is a point between 1000 and 2500 that the ceramic would pass at a higher voltage but my tester doesn't have a mode between .. ill look at creating something to do that later .. but for now it would seem the issue is the steel bolts and not the insulation thickness or type of material . well between the mica and the ceramic . the sil is thinner again and the airgap becomes the problem , still waiting on the ceramic bolts .. but i'm imagining they will give the same results as the nylon .
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because testing it showed ... I don’t have too . But hey I already have the ceramic bolts and pads coming , so I’ll do a test when they arrive and see how much better they are as well as a thermal test to see how much worse they are at transmitting heat , Because ceramic is not just a electrical insulator ... its a thermal one too as is Mica . whats wrong with good engineering and testing ?
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So i got my insulation tester today . i have videos of the failures ill upload later but .... steel bolt , silicon pad and the plastic bolt insulators 500v - Fail 1000v - fail with visible arc 2500v - fail with visible and audible arc The arc when front the fet plate .. through the plastic to the bolt .. from the bolt .. through the plastic to the sink. so ... that combo .. failed at every stage the mica plastic/rubbery collets and nylon bolt combo 500v - pass 1000v - pass 2500v - fail 5000v -fail In this case the arc went from the fet , around the mica at the bolt hole and directly to the heatsink . Ill try the silcon pad and nylon bolt tomorrow , But given that the silicon is thinner than the mica and the air gap is the failure point it will fail earlier than the mica . i will post the pictures and a couple videos of the failure tomorrow , the nylon was quite interesting because its clear so you can see the arc happening through the bolt .
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That is literally exactly what the both and collet i used looked like just a tiny little dot instead of a weld mark (i got those on the chassis wall ) . There was just a dot on the screw and a little bit of melted plastic . I originally though I had got some swarf stuck between the pad and the fet and that caused it .. but all evidence says otherwise. Its a interesting failure because the arc would have had to go to the bolt and then back to the heat sink so thats a lot of point energy to initiate the arc . because the bolt itself is electrically isolated the heat sink as well . So physics wise the distance between the edge of the conductive materials ( heatsink and fet itself) is smaller than the distance to the bolt and back through the plastic . so i guess what im saying ... is because pad had a hole in it it didn't arc to the bolt the damage to that is a side effect of the ionization it jumped around the insulator through the hole thus the pad was the issue it its design leaving that air gap through the hole . However the thickness of the mica is almost identical to the silicon pad i used so it should have done the same thing .... EXCEPT the hole is much smaller and the collet doesn't pass through the mica one .. instead i lapped the back of the fet and the collet to the same height and the collet face sealed on the mica .. making the air gap distance non existent thus no arc path besides through the actual mica panel itself . The reality is that if your insulator has a hole for the collet to pass through you still have that air gap issue its just less because you have increased the air gap itself . the solution it would seam would to have a pad with an integral sleeve that passes up through the fet so that the air gap is eliminated. Or just put a dialetric in there to arrest it .. however dialectics dry out and stop working over time . Ill take some pictures of the difference im talking about Its a really interesting failure
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I’ve been looking for where it happened for the last hour and it looks like I had the exact same issue , the screws , one has a mark on it that looks like an arc mark (there is no reason for it to have a white mark on it otherwise it’s brand spanky plating ). The collets I used in the first instance were just thin plastic as well . I guess the reason I’m asking was just simply if the pad is rated for 1kv and the 10n90s for 900v the fet should fail before the insulation does , also mica is a little better at thermal Transfer than silicon and a lot better than ceramic , so my thoughts were that that was an important consideration , I’ll do some readings before I change of fet temps vs heatsink pre staturation and post saturation to see exactly what that variance will be in mica vs ceramic . It is a totally mute point because I’m changing them , but I always like to know why rated componants can’t do even do 380v in this case and be rated to 1000v , it would Seem in this case it’s simply the steel bolts , I’m also way more excited about the ceramic bolts than I should be , but they should be way superior in clamp force to peek without variation to heat something that nylon is just aweful at reguardless if it’s variant . Ok so bias line resisters , not an issue I will add them , you say required with the sr007/009 , what makes the different and what is there function ? I’m asking so when I do the edit above I can add a reasoning for them , I really hate writing anything in a report with a just cause type of reasoning. It also helps me understand what is going on there electrically I’m pretty excited about the next project , and this has and still is giving me lots of good foundations to apply to that . also heat pipes , I really wanna work out a way to use heat pipes
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1) already ordered and I’ll look again , I am going to ask thou , the mica I got is rated to 1kv , the voltage is only 580v the ceramic to 27kv , is it a concern it’s going to break down over time ? , the first ones I used were silicone and I couldn’t find any arc marks however I did tests resistance from tab to heatsink before installation on the first instance . However there was clearly an issue . 2) yes , you asked for 2 ? Watt Kevin had me fit .25 watt , I’ll have to check that , but I’ll correct it , was just a typo. 3) ohhhhhh ok I’ll have a look to see if it’s there when I pull it down today to rotate the assembly , I did ask Kevin if I fitted anything to the bias line , What’s it’s function ? Or is it similar to the reason Kevin had me fit the much lower wattage 5.1k resisters ? 4) I did it at 20v , I though i had put a picture up of that , ill edit that in !!! ... nope it was already there ...are you meaning less than 20v ? Or should I add that the setting voltage range be 5-30 ? Because I did test that afterwards and it worked all the way through . Thank you did I mention my first post ever at doing this so it might be a bit shit , but the adjustments are appreciated, I did it from a mixture of the forum posts and the article ( I bought that edition btw to support the work ) it’s very much appreciated
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well then , will change and order , Ive used mica before up to 1kv ( I'm not going to lie Kevin did say go ceramic ) but will order and replace , already have the peek screws ordered because unhappy with nylon at this temp . the heatsink is 43 deg c ATM and hasnt changed for the last 24 hours of continuous use however did you drill the PCB to mount ? or just use an epoxy ? will move it asap because ... good engineering is just the right way to do things . cheers for the corrections update , Ceramic To-220 insulators ordered and also ceramic m3x12 capscrews and nuts , Ill compare them with the peek ones when they arrive .