UK Source for Ventilation Grille / Mesh?

[thermionic]

Hi,

Can anyone direct me to a source in the UK (or EU if not) that sells fine mesh, i.e. the type you see on valve amps? Ideally it'd be quite fine, but also fairly rigid (i.e. not the 'cloth' mesh that comes on a reel). It'd needed for a PSU that I've built in a sealed box. It's not quite so hot as to go to the extent of fitting a fan, but I'm worried it'll get hotter than I'd like in the summer months. If I leave the top off the enclosure it runs cool. If I cut out the middle of the alloy top and fit mesh, hopefully this should give it all the ventilation it needs.

Thanks in advance.

 

[JohnRoberts]

It's called expanded metal.. that might help your search

JR

 

[ruffrecords]

http://www.wiremesh.co.uk/buy-wire-mesh/brass

Cheers

Ian

 

[thermionic]

Thanks, John + Ian.

Have spoken to the firm who supplied the case and they say they've got a CNC programme to drill 3mm holes in the lid, which would make an alternative to the mesh. Trouble is, the holes, although only 3mm, are likely to let a lot of carp in - so the PSU would need 'dusting' off every few months (which it'll probably do with the mesh...hmmm).

Out of interest, at the risk of going OT in my own thread, going on the basis that no one can get their fingers in there, how hot would you run a 317 / 337 VReg combination? I've seen 7800 Regs run for decades at over 100-deg C, but that shouldn't endorse the concept... The PCBs have brown scorch markings... I'm thinking that 65-C in winter will equate to 80-ish in summer, which is a little borderline for my liking...

 

[JohnRoberts]

Cooler is always better...

I have seen solder joints on 3 terminal regulators that ran too hot for too long degrade and fail (looked like dull overheated solder joints from leaving the iron on it too long) .

The old regulators still worked but the solder joint integrity didn't survive.

JR

 

[zebra50]

Hi Justin,

Can you clamp the regulators to the case and use the whole enclosure as a heat sink?

Stewart

 

[thermionic]

Hi Stewart,

Thought about that one. It has a total of 8 LM3** VRegs in it, organised as 4 x -ve and 4 x +ve. One option is to keep them seated on the PCB and fashion a fairly complex alloy bracket to attach to all of them, which connects to a larger heatsink. This is doable, but the machining costs would be prohibitive.

Option 2 would be to fit flying leads to the Vregs, seat them on the alloy case panels, which in turn clamp tightly to a large external heatsink. The downside of this is a) it's messy with the flying leads - and b) I'm told LM3** Vregs prefer to be mounted on the PCB with the minimum of resistance / inductance between them and ancillary components. Oscillation can result, supposedly.

I've just done a test, comparing Vreg temps with lid on / off. With lid off, I'd say they're 'comfortable' - probably around 35 C. Lid on makes a massive difference and a couple of them are getting up to around 65 C. In the summer this will likely be 80+

If I ventilate the lid to the absolute maximum, hopefully this should result in temps nearer what they'd be with the lid off, right?

John's suggestion that the solder joint integrity is compromised before component failure sounds believable to me.

I did think about installing a fan... But the insinuation if you fit one is that the PSU is prone to heat issues, wouldn't you say?

 

[okgb]

I have a bunch of smaller  [ 1 x 3 " ] plastic ones you [ or anyone ] are welcome to for postage
although I'm in Canada

 

[thermionic]

That's very kind of you, Greg - thanks!

Alas, I've just ordered a machining firm to make my lid look like a pepper pot. Hopefully it'll do the job!

 

[Gold]

Wire mesh is also called wire cloth on this side of the pond. You can get it in pretty much any wire gauge and any spacing you want.