Electrical issue on brew day....

[passedpawn]

Crydom for the WIN! The used ones I have have lasted a very long time. 40amp SSRs on a 23amp circuit.

BTW, I've been to Fenton MO several times. Pretty small town.

 

[WolfgangVonFrankenStein]

My panel is pretty simple. I bought it from a guy on this forum, I didn't build it myself. Just a single PID.
I'll get some pics tonight for you guys to look at.
When I took the SSR off the heat sink, I did notice a lot of thermal grease. I wiped it off an applied the "old pea sized" amount.
The type of grease I used was a different color and consistency.
While running my auto tune, I noticed the heat sink was much warmer than it ever was before.

 

[augiedoggy]

During the auto tune process it flashes from "AT" to the temp current. Once the auto tune is complete it stops flashing. Right?

The auto tune stopped, it stopped flashing and the temp kept rising. I figured at 170 it was safe to give up on it.

you mentioned the output light on the pid started to flash on and off when setpoint was reached? if there is a led on the srr that should have been flashing too... even if it was flashing there is a v ery real chance the ssr has failed and is stuck in the on position as they often fail in that state. if the output light on the pid was in fact flashing then I suspect that was working correctly.

BTW if your using the fake knockoff fotek ssr clones like pictured above the chances of it being ssr failure are VERY good. those have a high failure rate as many of them are only made with an opto switch thats rated for 10a despite the stickers the factory throws on them with higher ratings. these ssrs sell in large quantities for as little as one half a cent! (on alibaba) I doubt the type of thermal grease played a part here myself.

I recommend a better ssr like the mager or berme branded ones (both made by MGR along with aubers branded ones.)

EDIT++ Sorry I somehow missed reading the whole second page of the thread until after commenting... glad to see you got it worked out, Crydom and opto22 ssrs are good too I have a bunch of them. realistically the ones I mentioned above also have about as good of a reliability rate though too, and are much less expensive.

 

[WolfgangVonFrankenStein]

Ok here are the pics.
Let me know if you have any questions or comments.

-Ron

 

[WolfgangVonFrankenStein]

One more

 

[Tobor_8thMan]

View media item 70236
View media item 70237

Appears, at least to me, in the photo some bare wire in the black wire are exposed. Possible arcing happened between these exposed wires and other things?

Remember too current runs on the outside of the wire. Current doesn't run thru the wire.

 

[golfindia]

That heat sink is big, but it sure is thin..... All the fins don't help much without some mass to absorb the heat to begin with.

I'd set a PC fan on top of it too.

 

[augiedoggy]

that really should be ok honestly.. the ssr looks to be an mgr made one but I have seen reports of them failing. its rare but it does happen.

 

[WolfgangVonFrankenStein]

@Tobor_8thMan, the pictures you referencing were after the mishap. I had some wires burn up, assuming it was due to a loose spade connection which spawned this thread. I posted some pictures last night of the current set up.

@golfindia , @augiedoggy , I was thinking of adding a fan. I mentioned earlier, I never felt the sink get hot in my previous batches. After replacing the SSR and thermal grease, it really warmed up during the auto-tune. I'll keep an eye one it.

The replacement SSR was purchased from Kai's website.
https://shop.theelectricbrewery.com/products/40-amp-ssr-12v-dc-input-240v-ac-output

 

[augiedoggy]

that replacement ssr appears to be an MGR made ssr.

 

[doug293cz]

...

Remember too current runs on the outside of the wire. Current doesn't run thru the wire.

Skin effect is usually only of concern for high frequencies, as the skin thickness decreases with decreasing frequency. There are many skin depth calculators on-line (here's one.) At 60 Hz the skin depth is a little less than 0.4", and the diameter of a 10AWG wire is a bit more than 0.1". Thus skin effect is irrelevant for brewing control panels (and lots of other things), so the current runs thru the entire cross section.

Brew on

 

[doug293cz]

That heat sink is big, but it sure is thin..... All the fins don't help much without some mass to absorb the heat to begin with.

I'd set a PC fan on top of it too.

The purpose of a heat sink is not to absorb heat, but rather to transfer heat from the source (SSR) to the air. In order to do this the base of the heat sink needs to conduct heat from the source to the fins. Thickness improves conduction laterally within the base, which improves heat conduction to the fins farther away from the heat source, but that really has nothing to do with the mass. For vertical heat conduction, a thin base is actually better.

I suspect, like the OP, that the original issue was the excessive thickness of the thermal paste, and perhaps its quality as well. The fact that the heat sink is getting warmer with the new, thinner paste indicates that more heat is being conducted from the SSR to the heat sink, which is a good thing. OP should be fine with the new configuration.

Brew on

 

[golfindia]

The purpose of a heat sink is not to absorb heat, but rather to transfer heat from the source (SSR) to the air. In order to do this the base of the heat sink needs to conduct heat from the source to the fins. Thickness improves conduction laterally within the base, which improves heat conduction to the fins farther away from the heat source, but that really has nothing to do with the mass. For vertical heat conduction, a thin base is actually better.

I suspect, like the OP, that the original issue was the excessive thickness of the thermal paste, and perhaps its quality as well. The fact that the heat sink is getting warmer with the new, thinner paste indicates that more heat is being conducted from the SSR to the heat sink, which is a good thing. OP should be fine with the new configuration.

Brew on

Um, no.

Because, physics. Its a combination of the two thermodynamic principles. Thermal mass and radiation. Pretty simple equations. I use Al chill blocks for TIG all the time. No "fins". I guarantee the heat sink in that photo is cold at the edges and 160F in the middle. Useless.

Screw your SSR to a beer can. I really don't care. I'm just pointing out facts, boss.

In the mean time one or two people will just keep whining about "fake chinese SSRs blowing up".

 

[passedpawn]

I agree with Doug. Surface area and thermal conductivity are the important parameters here, and mass really isn't after the first minute.

Get on Digikey and search thermal heat sink, then sort by thermal resistance. Take a look at what the best (lowest thermal resistance) heat sinks look like.

Fun with science:

Thermal resistance is a sweet number that lets you figure out exactly how much rise in temperature you'll get when you push an amount of power (Watts) into it. Just add up all the thermal resistances, and multiply by the power being dissipated and you'll get the temperature rise.

Example: When I bought my heat sinks 10 years ago, I got the lowest thermal resistance ones on Digikey ( This one ). Its thermal resistivity (sink to ambient) is 0.7°C/W. The thermal resistivity of the SSR is 0.8°C/W. I'd add the thermal resistance of the paste, but it depends on thickness and that's something I don't really know, so I'll ignore it (might be significant, but what can do). Total thermal resistivity is then 0.7 + 0.8 = 1.5°C/W. The total watts is amps (rms) * voltage drop of SSR (see datasheet). My Crydom D2425 is 1.15V. So I'm dissipating 1.15V* 23A= 26.4W. Then my total temperature rise will be 1.5°C/W * 26.4W = ~ 40°C. That's about 100F above ambient. My heat sink is going to get hot.

 

[passedpawn]

Also agree about paste. It should be extremely thin. It only needs to fill the non-planar gaps between the heat sink and the SSR. I used Arctic Silver 5 which I already had for a computer application.

 

[doug293cz]

Um, no.

Because, physics. Its a combination of the two thermodynamic principles. Thermal mass and radiation. Pretty simple equations. I use Al chill blocks for TIG all the time. No "fins". I guarantee the heat sink in that photo is cold at the edges and 160F in the middle. Useless.

Screw your SSR to a beer can. I really don't care. I'm just pointing out facts, boss.

In the mean time one or two people will just keep whining about "fake chinese SSRs blowing up".

Ok, first my credentials. Before my retirement, I was a Senior Engineer at a major electronics manufacturing firm. My responsibilities were electronic packaging. Thermal management (getting rid of the heat generated by active components) is one of the major functions of, and concerns with, packaging electronics. I have some real expertise here.

Thermal flow systems are often modeled as electrical networks. In a steady state flow situation, the only components in the model that matter are the resistors. A thermal mass is modeled as a capacitor, the higher the thermal mas, the higher the capacitance. A capacitor can collect and store charge in a transient situation, but once it is charged to full capacity, then it cannot absorb any more charge. A thermal mass behaves the same way. It can absorb heat until it's temperature is the same as the source, and at that point it ceases to do anything, except hold the heat it already has. It's the resistors (thermal resistances) in the network that determine how fast the charge (heat) flows from one place to another. The faster the heat flows away from the source, the cooler the source stays. The capacitor (thermal mass) can increase the time it takes to reach equilibrium (and keep the source cooler until equilibrium is reached), but it cannot change the charge (temp) at equilibrium. Thus it is not thermal mass that is important for situations with continuous heat generation, but rather the rate at which heat can be removed once steady state is reached.

Radiation is one way that heat can be removed, and can be the dominating mechanism in some situations. With a finned heat sink, convection is most often the dominant mechanism for heat removal, especially so when a fan is used. Fins are used to improve heat transfer with convection, as they are almost useless for improving radiative heat transfer. (The physics of this is complex, so I won't go into it here.)

In OP's case, in the original configuration, the heat sink remained cool during operation, but after remounting a new SSR on the same heat sink, the heat sink now heats up during operation. This indicates that the problem was with heat flow from the SSR to the heat sink (the thermal interface between SSR and HS was the largest thermal resistance in the system.) I agree that the heat sink will be hotter at the source of the heat and cooler at the periphery, but then this will always be the case, no matter what the geometry of the heat sink.

As far a low quality SSR's, there are published teardowns of Fotek SSR's that found 10A TRIAC's inside a 25A rated SSR. The problem with some SSR's is real.

I see @passedpawn types faster than I do. The thermal resistances he mentions are derived from the electrical models I discussed, and actual measurements of components under specific operating conditions.

Brew on

 

[augiedoggy]

Um, no.

Because, physics.

I seem to remember brundog using that exact line on you a few weeks ago.
Tell you what I'll just keep doing my thing by "whining" and warning people of the garbage ssrs and you just keep talking down to all of us simple folks when we are wrong

BTW OP I have a panel I made a few years ago that uses a non anodized version of that same heatsink mounted on a plastic enclosure with an SSVR AND a 25a ssr for controlling both the bk and HLT mounted to it .. no overheating issues. That why I mentioned I think your setup should not have failed.. I also have no idea how much paste was between your ssr and sink either. and I now that I think about it there was another case of the ssr failing from too much paste about 6 months ago here.

 

[golfindia]

I seem to remember brundog using that exact line on you a few weeks ago.
Tell you what I'll just keep doing my thing by "whining" and warning people of the garbage ssrs and you just keep talking down to all of us simple folks when we are wrong

BTW OP I have a panel I made a few years ago that uses a non anodized version of that same heatsink mounted on a plastic enclosure with an SSVR AND a 25a ssr for controlling both the bk and HLT mounted to it .. no overheating issues. That why I mentioned I think your setup should not have failed.. I also have no idea how much paste was between your ssr and sink either. and I now that I think about it there was another case of the ssr failing from too much paste about 6 months ago here.

Zinger. You got me bud....

Like I said do whatever you want, I don't care. I've never blown anything up or melted any SSRs while using electricity to brew beer, so I'm all set.

This sub forum never ceases to disappoint. From ludicrous to ridiculous and everything in between. You guys can keep nitpicking the $hit out of everything and I'll try even harder to resist my urge to reply.

 

[processhead]

I'll throw in. With a heat sink, mass, no matter how large, only absorbs/conducts heat from a source like an SSR until it reaches equilibrium with the source.
At that point, you are depending on transfer of the heat energy to the air to lower or maintain the temperature to some safe level. The greater the surface area of the heat sink, the more effective it is in transferring heat to the air, whether that be by conduction, convection or radiation.

 

[Tobor_8thMan]

I'll throw in. With a heat sink, mass, no matter how large, only absorbs/conducts heat from a source like an SSR until it reaches equilibrium with the source.
At that point, you are depending on transfer of the heat energy to the air to lower or maintain the temperature to some safe level. The greater the surface area of the heat sink, the more effective it is in transferring heat to the air, whether that be by conduction, convection or radiation.

Well put!

 

[Ninoid]

I have twice had a problem with electrical contacts on the heater when making beer. Both times my heater stopped working when the wort started to boil. Both times I had no choice but to put all the hop on the hopstand and make the beer different than I imagined. That beer drank, just like everything else. You do not have to worry about it, but adjust to the situation.