Heat sinks on SSR's

[robots4joey]

I know this topic is brought up too many times a year... but I would really like some personalised advice.

The pics below show my SSR setup. (using parts for the parts coop) I am wanting to run these with no more than three strings of mini lights per outlet. (but definitely 3 on some of them)

It's crunch time and my first year, so I am really out of time, can I skip the heat sinks? I live in Wichita Kansas, so the highest temperature I'd expect for the season is about 65 F.(during the day)

If ya'll think that no heat sinks are ok for the show, can I turn all channels on while I'm setting up the display, or will that overheat the SSR's?

Thanks so much for the advice!

-Joey

[Mudsculpter]

I havn't put heat sinks on any of my SSRs.

[xmus]

Depending on who you ask, the answer is "up to 1 or 2 amps per channel without a heat sink is fine".

3 strings of lights, worst case, would get you to 1.5Amp so you are a bit marginal (Assuming 100' * 3 or 3 sets of net lights). You need to tally your current!

[robots4joey]

yes 1.5 amps is about my maximum...

Can I turn them all on for a half hour? or is that likely to overheat something?

[xmus]

yes 1.5 amps is about my maximum...

Can I turn them all on for a half hour? or is that likely to overheat something?

I personally would not run anything over 1 Amp continuously, I would get heat sinks at that point. But again, this is based on rumor and grass-roots info. Your mileage my vary. Do you have a way to measure the temp? Just try it with a wireless outdoor thermometer....

[mac_man_luke]

your using a metal case!

just use the case as a heat sink by bolting it on

[robots4joey]

your using a metal case!

just use the case as a heat sink by bolting it on

Yeah... that is what I originally intended to do... but the outlet strips I bought are very slim and I couldn't get the geometry to work out for me. (I spent many hours trying)

I figured out how to make it work, but I would have had to directly solder the opto's, (getting rid of the sockets) and I didn't really trust my solder skills back then...

I can still add a heat sink, it just won't be the case any more...

[xmus]

it just won't be the case any more...

But it defeats the purpose to not use the case...
If you use the case as a heat sink, you will use conductive heating to dissipate heat (Very efficient) , if you use an inside heat sink, you will use convective cooling (You will just be heating up the air within the case, and it is hard for the case to loose the heat through convection), which is inefficient. It would be best if you could come up with a heat sink design that could connect to the Triacs and bolt to the side of the case as well.


http://en.wikipedia.org/wiki/Heat_convection

[ben]

sorry to "interupt" here but I am using metal 4 socket cases for my SSR's could I take some 12 gauge wire and use a small bolt and put one on the case and one on the triac hole to dissapate the heat?

Ben

[robots4joey]

Precisely xmus!

I thought about that myself after we talked about heat transfer in my thermo 2 class : )

I was definitely going to mount the heat sink to the case, however I am probably going to skip heat sinks this year... I haven't even finished all of the SSR's yet.


-Thanks for the help!

[wjohn]

Run a test, put them on a test loop with the lights connected, and do a touch test after 30min (disconnecting the power)

100C + will burn your finger (you are warned) while 80-90C will feel like hot coffee cup.

I ran TRIACs with a couple of AMPs (at 12VAC) and they were hot to touch, but with a small alum strip heatsink, the temp dropped significantly.

So, even adding a small strip of alum material would be benifical.

[sandy]

Even adding a #4 or #6 screw and short 1/4" to 1/2" standoff to each triac will do wonders
Not much for the long term, but it adds quite a bit of thermal mass to the shorter bursts.

[NogginBoink]

Before doing any of this, ensure your TRIACs have isolated tabs! (Read the datasheet for the TRIAC you bought.) Some triacs actually have the 110V connected to the tab, which could get exciting real quick if you connected it to the metal housing of your power strip.

The datasheet will also give the thermal characteristics of the package and allow you to calculate how hot the package should get given a certain load current.

[Michael]

Flexable heat sink material?

Is there something that will efficiently conduct heat, but still be flexable like a large wire? The way I have my boards mounted in their case, it would be hard to use a fixed heatsink like a metal bar.

But I could easily bolt a wire to the group of 8 and snake it out the back of the case to a large metal block.

- Michael

[andyhough]

Would a fan like this one solve the problem? I found some 5v fans in an older netgear switch, and Fry's has 120v fans.

[robots4joey]

A fan seems a little over the top. but it would work... If you have room for a fan there should be room for a heat sink though....

on the wire idea.. I think we need to get xmus back in here with a take on that. I don't think it will work. think about how hot you can get a wire with a soldering iorn and how cool that wire is just an inch or two away. I would assume that it is just not conductive enough for it to transfer heat to a case. but I'll leave that up to the experts.

[NogginBoink]

I think a fan makes a cheap, available solution. Of course, a fan would be much more effective with a heatsink as well, but if you have the fan handy, it sure wouldn't hurt.

[xmus]

I think a fan makes a cheap, available solution. Of course, a fan would be much more effective with a heatsink as well, but if you have the fan handy, it sure wouldn't hurt.

Are these for outdoor use? If yes, don't use a fan, they won't take the moisture, and you wouldn't want holes in the case to allow for ventilation....


The wire idea.... At that point you are conducting heat through the wire. Copper wire is a good conductor of heat.... but you would lose some (no idea what percentage) to convection, which could work against you....(heat the enclosure up like an oven). I'm not fond of the wire idea personally, but it is just a gut feeling, no science behind it.

Couldn't you just make a new SSR board with your perf board and get the backs of the SSR's against the outside edge of the PCB? Then you could just bolt them right to the case? ("Just" redesign!)

[robots4joey]

That is what I wanted to do. Should have been easy. But those outlet strips I bought are so tight that it is a mashing act just to fit them in the case... I tried bending the tabs on the triacs in different angles, mounting them to the bottom of the case, and several other combinations..

It just won't work unless I modify the case. which also defeats the point of using them...

As for the wire idea, i guess it can't hurt right? I'll probably skip that though, I just don't have the time.

Thanks for all the help! it has been a really interesting discussion.

[robots4joey]

Oh, I see what you were saying... by moving the triacs back to the back of the board, I wouldn't have the 120VAC wires back there... (I'd put them right in front of them) I'll have to try that... it would definitely help, but I think it will still be a very difficult fit.

too bad I finished soldering them all last saturday.... I guess there's always next year.

More Lights! More Channels!

[Ronp]

I used the 6 outlet strips but didnt put the relays inside (no room) I drilled holes in the strip and ran one wire per ssr out the bottom then put the relays in a bigger case below the strip