SSR, Heatsink and Thermal Grease Question

I have three of these Teledyne SD24R50 relays. All three of them have a slight curvature to the bottom mounting surface such that very little of it would make contact with a flat heat sink. This gap could be filled with relatively large amount of thermal grease.

Are these okay to use with so much grease? Is this gap too big?

I'll need to dissipate about 24 watts, these are 50A relays I should only draw about <15.

Hmm, you'll get some thermal transfer, but a big ol' glob of grease isn't actually very effective and will probably end up just making a mess. I'd do a thin layer on the heatsink like you would on a CPU heatsink and just screw it down snug, don't worry about the surface that is "floating". Or you could get an aluminum CPU shim and put it under just one side so it is tilted. None are idea solutions, but I'd just fly with it.

thekraken said:

I have three of these Teledyne SD24R50 relays. All three of them have a slight curvature to the bottom mounting surface such that very little of it would make contact with a flat heat sink. This gap could be filled with relatively large amount of thermal grease.

Are these okay to use with so much grease? Is this gap too big?

I'll need to dissipate about 24 watts, these are 50A relays I should only draw about <15.

Click to expand...

Thermal paste is actually really bad at transferring heat. It's better than air, which is why it's used, but too much can actually hurt your heat transfer. Certainly anything that's actually filling up a noticeable space would be too much. According to the drawing for that relay, they should be straight. Seems odd that you have 3 that are visibly curved. either way, SilverZero's solutions are probably the best options if you can't figure out a was to straighten the relays. Definitely do not just put a giant glob of thermal paste on anything ever. I would monitor the relay the first time you use it to make sure nothing out of the ordinary happens.

Should I lap it down?

It looks like the mounting locations are to low (or is it high?) to me. The gap between the SSR and the heat sink looks pretty consistent to me from the photo. Maybe try sanding in that area first then lap it all flat.

Have you checked to make sure the heatsinks are not out of flat?

If you go with heatsink compound, the best (and most $$) will be silver filled. Cheaper ones are usually something like zinc oxide filled. As said previously, you would want to use the least amount that would fill the gaps, and have minimal thickness at the contact points. You also want to make sure there are no voids in the film between SSR & HS. The best way to avoid voids is to apply a single "Hershey" kiss blob in the center of one of the compnents. Then press them together, with twisting if necessary, to push the compound out towards the edges, and get it as thin as possible. Other apply patterns have higher risk of voiding.

Brew on

Wrap some 100 grit sandpaper around the SSR and use it as a sanding block to lap a concave into the heat sink?

doug293cz said:

Have you checked to make sure the heatsinks are not out of flat?
...
"Hershey" kiss blob in the center of one of the compnents
...

Click to expand...

Yeah, I checked them against a reference glass surface.

A hershey's kiss worth is a lot more than I would have used, do they usually require that much?

Bobby_M said:

Wrap some 100 grit sandpaper around the SSR and use it as a sanding block to lap a concave into the heat sink?

Click to expand...

I thought about that but it would make it hard to replace the ssr if needed. It's been suggested that I flatten the ssr some on a belt sander then lap it, I may try that.

thekraken said:

Yeah, I checked them against a reference glass surface.

A hershey's kiss worth is a lot more than I would have used, do they usually require that much?

Click to expand...

Yeah, a full size kiss is too much. I only meant the approximate shape. I should have said about equivalent to 2 or 3 chocolate chips.

Brew on

Can you return them? I probably wouldn't bother with them either way, but your build, your choice.

jeffmeh said:

Can you return them? I probably wouldn't bother with them either way, but your build, your choice.

Click to expand...

I don't know. I bought them off of ebay per this thread. Something did (and still does, duh) seem fishy, my spidey sense is telling me that I might have trouble getting my money back. A lot of folks from that thread have recommended these...

thekraken said:

I don't know. I bought them off of ebay per this thread. Something did (and still does, duh) seem fishy, my spidey sense is telling me that I might have trouble getting my money back. A lot of folks from that thread have recommended these...

Click to expand...

How odd.... I bought one of those same ssrs from the same seller on ebay for $15 and I thought mine had a piece of black thermal tape on the backside already but I could be mistaken.... I used regular thermal grease and screwed it down to a $3 heatsink and have not had any issues.... I'm pretty sure there is a bunch of us using them with no issues? have to tried actually mounting them with thermal grease and using them? a lot of ssrs are warped in this fashion based upon the threads coming up about this...I havent seen anyone who mounted them correctly with grease to fill the gap say it actually caused failure...
these particular teledyne ssrs are over $100 a piece new so I think its worth trying them with thermal grease and checking to see if the heatsink is warming up from use...
these are the ones I bought a couple months ago....he has lowered the price I see since the thread you linked..

http://www.ebay.com/itm/TELEDYNE-SD24R50-280VAC-50A-SOLID-STATE-RELAY-NEW-/321634374868?

Thanks for chiming in augiedoggy, I'm hoping to hear from more of us that have used this particular ssr. I'm curious how many really looked closely for flatness, if this is normal, and or if it's a non-issue. It's strange that all three I received had this same curvature. I've asked around other places and I'm told that this gap is rather significant, as much grease as that would take to fill would not be ideal for heat transfer.

I suppose I could just hook it up and try it but I'm not to that stage of the build yet.

thekraken said:

Thanks for chiming in augiedoggy, I'm hoping to hear from more of us that have used this particular ssr. I'm curious how many really looked for this, if this is normal, and or if it's a non-issue. It's strange that all three I received had this same curvature. I've asked around other places and I'm told that this gap is rather significant, as much grease as that would take to fill would not be ideal for heat transfer.

I suppose I could just hook it up and try it but I'm not to that stage of the build yet.

Click to expand...

makes me wonder if these were all factory seconds ?... I can tell you I've made 5 brews with mine so far and not a single issue. Keep in mind that many times the actual SSR circuit that generates the heat has a small surface area contact with that plate to begin with.. At least from what I've seen. You could always file them down with a file or grinding wheel.

augiedoggy said:

makes me wonder if these were all factory seconds ?

Click to expand...

Something is up, they are $150 relays being sold for $15. Either they are factory rejects, or they came from a box that fell off the back of a truck, or the authorized retailers are REALLY ripping people off.

*I'm not bad mouthing the seller at this point, I haven't actually used it yet and am not qualified to judge the product it self, no one else has voiced any problems with them. The seller is very generous with his sales and was fine to deal with. BUT how is it economically feasible to sell these items at a 90% discount.. If you ask politely he literally gives them away.

shimming it would be the easiest solution in my opinion. Well, apart from screwing it down tighter

I have a pile.of these around. I used 5 of them in my build. I didn't notice any problems with mounting them. I used them on extruded aluminum heatsink for all 5 of the ssrs. I'll check mine tomorrow and report back.

The ones in use have about 15 brews on them. Plenty of heat makes its way into the heatsink and into the atmosphere successfully pushing global warming right along.

Has anyone used these thermal conductive pads? I had never heard of them. Can they effectively transfer the heat I'll be generating to a heat sink, or are the ment for smaller applications? I'm figuring on needing to dissipate 24 watts.

http://www.amazon.com/dp/B00EQ23OQA/?tag=skimlinks_replacement-20

(edit) or these: http://www.amazon.com/dp/B00597UJC8/?tag=skimlinks_replacement-20

I've always understood the thinner the layer, the better the conduction. Those pads look relatively thick.

I recently purchased 4 of the SSRs. I checked mine and they are all flat or relatively flat. Nothing i would worry about on mine. Contrary to what some are saying i dont think they are stolen or factory seconds. My understanding is they are used and mine appear that way. There are some people who have access to decommissioned equipment coming from datacenters or something and they strip the parts before trashing it. I think maybe yours might have been mounted improperly in the equipment which warped it. To me that would make sense getting 3 in a row since they came from the same piece of equipment.

My personal opionion since you will be drawing just a fraction of the current rating, and not for extended time (1-2 hrs) you will probably be fine but i would send an email. He may just replace them too.

thekraken said:

Something is up, they are $150 relays being sold for $15. Either they are factory rejects, or they came from a box that fell off the back of a truck, or the authorized retailers are REALLY ripping people off.

*I'm not bad mouthing the seller at this point, I haven't actually used it yet and am not qualified to judge the product it self, no one else has voiced any problems with them. The seller is very generous with his sales and was fine to deal with. BUT how is it economically feasible to sell these items at a 90% discount.. If you ask politely he literally gives them away.

Click to expand...

well theres no doubt at 150 bucks normal price is a rip off... I cant possible see an ssr costing anywhere near that to manufacture. these are likely built in a limited production run or intended for customers like government use where sending more for something to use budget money is often praised...

thekraken said:

Has anyone used these thermal conductive pads? I had never heard of them. Can they effectively transfer the heat I'll be generating to a heat sink, or are the ment for smaller applications? I'm figuring on needing to dissipate 24 watts.

http://www.amazon.com/dp/B00EQ23OQA/?tag=skimlinks_replacement-20

(edit) or these: http://www.amazon.com/dp/B00597UJC8/?tag=skimlinks_replacement-20

Click to expand...

I come across these in plasma tvs I have repaired... they are effective but no where near as effective as thermal grease... thinner the better yess but the grease still does a great job of bridging the gap... I honestly think it would work find if you just used the grease. these are 50a units so they shouldnt generate a whole lot of heat with 22 or 18 amps anyway... are you planning on using both sides of the relay at the same time with a 50a service? if not this is really a non issue.

Aerobrew said:

I recently purchased 4 of the SSRs. I checked mine and they are all flat or relatively flat. Nothing i would worry about on mine. Contrary to what some are saying i dont think they are stolen or factory seconds. My understanding is they are used and mine appear that way. There are some people who have access to decommissioned equipment coming from datacenters or something and they strip the parts before trashing it. I think maybe yours might have been mounted improperly in the equipment which warped it. To me that would make sense getting 3 in a row since they came from the same piece of equipment.

My personal opionion since you will be drawing just a fraction of the current rating, and not for extended time (1-2 hrs) you will probably be fine but i would send an email. He may just replace them too.

Click to expand...

well considering the photo in the auction showed well over $100,000 in ssr relays if purchased at "retail" and this seller has been selling them for over a year on ebay it makes one wonder .... Still you could be right... maybe google updated their main data storage facility? but in that case the seller would be lying to us...
Its hard to imagine a business that would need to switch that many amps that many times for anything but who knows.... Like I said they could be government surplus or used government stock sold at auction which would explain the original cost... the seller implies they are new but missing original packaging and states so... And mine had no evidence of being used... no marks from mounting screws or thermal grease residue..

My strong suspicion is they were either left over discontinued items or factory seconds... in either case that doesnt make they any less useful for my needs and mine works better than my fotek units which have more leakage when off. and take up twice the space...

normally the price for one dual ssr of comparable quality is about $75 new...like the CRYDOM units...I have a quad control unit actually (crydom) but the only means to control them independantly is by removing the negative side of the control vsignal voltage and Im not sure thats how my pids can work with the ssr output.

Yeah, the auction states "Item condition:New other (see details) &#8220;Out of original packaging.&#8221;"

Y'all are right though, I only will be switching about 13 of the 50 amps it's rated for, maybe this is a non-issue (for me). Nonetheless, I'll try flattening one out just for piece of mind. UNLESS the consensus is that I don't need to?

... I suppose the thing to do is just mount one and watch the temps like a hawk the first time.

thekraken said:

Should I lap it down?

Click to expand...

First choice would be to return it. What you have is totally unacceptable, the vendor should understand. 2nd choice would be to lap it flat, it should sand easily seeing that it's a block of epoxy.

As others have noted, filling the gap with compound is not a solution. Heatsink compound is intended to fill the pores of the mating surfaces and should be applied very thinly. There are thermally conductive epoxies that would be a better choice for gap filling, but that would make the installation less.. uh.. flexible.

The questions I have though, are how much current are you going to switch with it and what is the duty cycle of the application and ambient temperature? The data sheet on that part says that without a heatsink you can run about 5 amps at 30°C ambient.

Edit: You posted while I was typing. At 13 amps I would want that sucker dead flat.

Dave C
EE

Maylar said:

2nd choice would be to lap it flat, it should sand easily seeing that it's a block of epoxy.

Click to expand...

Well, we will see how easy it is to flatten, the contact surface is steel.



Pretty rough finish too.

I just checked some of my spare relays. The metal part is nearly perfectly flat. I set it on a few level surfaces and also used the straightedge of a level. The plastic housing is slightly raised around the heat transfer backing by about 1mm.

Maylar said:

First choice would be to return it. What you have is totally unacceptable, the vendor should understand. 2nd choice would be to lap it flat, it should sand easily seeing that it's a block of epoxy.

As others have noted, filling the gap with compound is not a solution. Heatsink compound is intended to fill the pores of the mating surfaces and should be applied very thinly. There are thermally conductive epoxies that would be a better choice for gap filling, but that would make the installation less.. uh.. flexible.

The questions I have though, are how much current are you going to switch with it and what is the duty cycle of the application and ambient temperature? The data sheet on that part says that without a heatsink you can run about 5 amps at 30°C ambient.

Edit: You posted while I was typing. At 13 amps I would want that sucker dead flat.

Dave C
EE

Click to expand...

seriously? you are aware that these are $150 relays being sold on ebay for 1/10th the original price right? to say its totally unacceptable when many cheaper relays come with warped back plates like this all the time is a bit over over demanding IMHO.... its kind of like buying something at the goodwill and complaining its used..

And I disagree... at 13amps he will still have plenty of heat trasfer to the heatsink... more than enough agian my opinion.

thekraken said:

Well, we will see how easy it is to flatten, the contact surface is steel.

Pretty rough finish too.

Click to expand...

Bummer. I think a flat mill file might be a start. But it sux that the quality of the part is so poor that you're forced to do that. I'd avoid that vendor in the future.

thekraken said:

Well, we will see how easy it is to flatten, the contact surface is steel.

Pretty rough finish too.

Click to expand...

you only have to take a tiny bit of material away by the screw mount cutouts... you could use a hand file

Maylar said:

Bummer. I think a flat mill file might be a start. But it sux that the quality of the part is so poor that you're forced to do that. I'd avoid that vendor in the future.

Click to expand...

lol As the OP has said he hasnt even contacted the seller to notify him of the problem or ask for a replacement yet and many of us who have bought and used these have noticed no issues, In fact no one has commented at all about any issue with functionality..everyone who has contacted the seller has said he has been more than accommodating. Way to jump the gun though... let hang the guy without even telling him why!

Wow talk about making a mountain out of a molehill...

augiedoggy said:

seriously? you are aware that these are $150 relays being sold on ebay for 1/10th the original price right? to say its totally unacceptable when many cheaper relays come with warped back plates like this all the time is a bit over over demanding IMHO.... its kind of like buying something at the goodwill and complaining its used..

And I disagree... at 13amps he will still have plenty of heat trasfer to the heatsink... more than enough agian my opinion.

Click to expand...

I wasn't aware that the parts are bargain basement. So, no, I wouldn't expect a Chinese clone at 1/10th the price to be perfect. And I wouldn't count on them being capable of published specs either. All the more reason to have intimate contact with the heatsink.

We don't know that these are clones. But they were acquired relatively cheaply, I'll give them a fighting chance.

I may have taken your original post out of context. My replies stem from being an EE and having designed power supplies for a living. On principle I would want the mating surface to be flat. Being an anal sort of fellow, I'd probably be takin' out the file...

But if others have used the same parts in the same application without issues, maybe it's a moot point.

Mouser does indeed show that device as being $150 each. Ouch.

Yeah, many others have used them without any complaints. I wondered how many inspected them specifically for flatness, and maybe I'm worrying about nothing. Several pros that I've spoken to, including yourself, have said that gap is unacceptable. I'll try and grind one flat and see what happens.

I really appreciate everyone's input.

Maylar said:

I wasn't aware that the parts are bargain basement. So, no, I wouldn't expect a Chinese clone at 1/10th the price to be perfect. And I wouldn't count on them being capable of published specs either. All the more reason to have intimate contact with the heatsink.

Click to expand...

They are not clones... They are supposedly new but have no packaging which suggests factory second or discontinued...

Ok this inspired me to dig out some spares I have for future builds or from changes to my setup... the two cheap fotek clones I have both have warped base plates.. one is still mounted to the heat sink and you can see the thermal grease filling the gap... these were recently removed from my panel and replaced with the Teledyne to save space for another ssr that was used for a rims... keep in mind these were mounted to $3 heat sinks and have over 30 brew sessions driving 4500w elements with no issues... one is a 25a the other a 40a... the third is actually a Teledyne quad ssr (Sq24d25) made in france that I bought for $15 used... notice the black thermal pad glued to the uneven base with the raised section? this small area is designed to handle dissipating 100amps worth of heat! the baseplate on these teledynes is flush instead of extruded like my quad relay... maybe thats the defect?
I strongly believe this is a non issue for you and a 15a or even 22amp load for that matter... PS I find it funny that my knock off foteks say made in Taiwan but clearly have "HK" stamped into the baseplate....

Thanks for looking into that augiedoggy, good info.

It's interesting that the big 'ol quad relay simply uses a thermal pad. To clarify, you have been using that quad relay with that thermal pad or that's one of your backups?

thekraken said:

Thanks for looking into that augiedoggy, good info.

It's interesting that the big 'ol quad relay simply uses a thermal pad. To clarify, you have been using that quad relay with that thermal pad or that's one of your backups?

Click to expand...

its a backup... because it only has one + and four negative pins to control each relay Im not sure I can get it to work with my pid configuration and honestly havent investigated it much since I haven't needed it... the foteks I used for a year...

thekraken said:

Well, we will see how easy it is to flatten, the contact surface is steel.

Pretty rough finish too.

Click to expand...

How did you determine that the base plate (which is also intended to be a heat spreader) is steel? Is it magnetic? Steel has lousy thermal conductivity, so is a very poor choice to use as a heat spreader. I worked for over thirty years in electronic component packaging, and don't remember any instances of steel used for a heat spreader (but we didn't build SSR's.)

Brew on