SteveTheShadow wrote: ↑Sat Mar 03, 2018 10:59 am
I'm watching this with interest.
I've had a basket full of bits for mine since Thursday but have not hit the checkout button yet.
I'll, of course, be building to class 1 specs so that I can play with £1500 mains leads.
Oh damn it . No foo mains cable experiments for me then Just some run of the mill shite
Dr Bunsen Honeydew wrote: ↑Sat Mar 03, 2018 11:07 am
Forget classII you don't have to comply as you are not selling. I am worried plastic will not give you strong proper contact to the heatsink, These are not like TO 3 you don't have two bolts to bolt down you only have one.
Thanks for your input Doc. I have lots of other bolts but they have to be long to get through the transistor, sil pad, 6mm aluminum and have enough thread to get a non slip washer and nut on.
Ok, i dont have to comply with class II but i want them to be safe. How much pressure will the transistors take from tightening before they are damaged?
Ok, i dont have to comply with class II but i want them to be safe. How much pressure will the transistors take from tightening before they are damaged?
I normally tap the heatsink so don't need long screws. The parts look like TO247, they are much easier to mount than TO220 as they have a insulating land around the mounting hole. Depending on the sil pads, you want them to be tight, but not too tight, the sil pad will flow to fill the gap. Worth a larger washer on the top of the device to spread the load though. 8-10 kgf·cm is recommended, but unless you have a torque screwdriver that’s not much help. But don't obsess over it.
Ok, i dont have to comply with class II but i want them to be safe. How much pressure will the transistors take from tightening before they are damaged?
Stu
Feck nose I glue them.
I would too but they may be moving to different heat sinks along the way. Maybe in the final build.
Lurcher300b wrote: ↑Sat Mar 03, 2018 11:49 am
I normally tap the heatsink so don't need long screws. The parts look like TO247, they are much easier to mount than TO220 as they have a insulating land around the mounting hole. Depending on the sil pads, you want them to be tight, but not too tight, the sil pad will flow to fill the gap. Worth a larger washer on the top of the device to spread the load though. 8-10 kgf·cm is recommended, but unless you have a torque screwdriver that’s not much help. But don't obsess over it.
Thanks for your input Nick. Yes they have insulation around the hole. I have a torque wrench but that means using hex bolts that will take a socket. Have plenty of washers and can tap the holes i have already done. I drilled 3mm holes and the transistors will take 4mm bolts so i have the option.
Can the bolt material affect the transistors performance ? Les W swears by stainless rather than ordinary steel.
Stu
Last edited by karatestu on Sat Mar 03, 2018 12:05 pm, edited 1 time in total.
The big advantage I can see over stainless is its less likely to corrode against the alu and stronger, anything else I would put in the foo camp. Overtightened is probably worst that under.
There's firmly tight, and breaking tight which I had to wean off post Linn days Stainless steel into the aluminium means the ally with strip first if you overdo it I think, but if you've ever fitted cooling sink assemblies to computer CPU's, I don't think they're ever clamped so tightly and some are under sprung plastic clips, yet the heat-sink paste-compound is usually flexible enough to spread and form a perfectly good lasting bond for years. As long as the fixing bolts aren't going to loosen off, that should be enough (with Allen bolts I always use the short end of the key as a lever now, NEVER the long-arm as I used to in the bad old days ).
Hanging on in quiet desperation is the English way...The time has gone, The song is over, Thought I'd something more to say...
Lurcher300b wrote: ↑Sat Mar 03, 2018 1:07 pm
As I say, don't obsess over it.
Obsess is my middle name I usually end up over engineering things and to heck with what it looks like
_D_S_J_R_ wrote: ↑Sat Mar 03, 2018 1:13 pm
There's firmly tight, and breaking tight which I had to wean off post Linn days Stainless steel into the aluminium means the ally with strip first if you overdo it I think, but if you've ever fitted cooling sink assemblies to computer CPU's, I don't think they're ever clamped so tightly and some are under sprung plastic clips, yet the heat-sink paste-compound is usually flexible enough to spread and form a perfectly good lasting bond for years. As long as the fixing bolts aren't going to loosen off, that should be enough (with Allen bolts I always use the short end of the key as a lever now, NEVER the long-arm as I used to in the bad old days ).
Linn tight is just fricking ridiculous.
I always use a very small amount of heat transfer paste (snot) It is only to fill and tiny voids between the two surfaces. I am of the opinion that too much snot would be a bad thing.
karatestu wrote: ↑Sat Mar 03, 2018 1:45 pm
I always use a very small amount of heat transfer paste (snot) It is only to fill and tiny voids between the two surfaces. I am of the opinion that too much snot would be a bad thing.
. No foo mains cable experiments for me then 
Stainless steel into the aluminium means the ally with strip first if you overdo it I think, but if you've ever fitted cooling sink assemblies to computer CPU's, I don't think they're ever clamped so tightly and some are under sprung plastic clips, yet the heat-sink paste-compound is usually flexible enough to spread and form a perfectly good lasting bond for years. As long as the fixing bolts aren't going to loosen off, that should be enough (with Allen bolts I always use the short end of the key as a lever now, NEVER the long-arm as I used to in the bad old days 
