cwaldner wrote:do you think anything blew?

yes

There is no derating curve for NO HEATSINK in the pdf.

i changed to the new ssr, thats really nice without the clicking sound. How hot should it get? after heating the machine from room temp it gets uncomfortably hot to touch, but i can still touch it. is that OK? at what temp should i get concerned?

Don't be concerned.
Keep a spare handy.

How did you end up mounting this? Did you use a heat sink? I'm thinking about adding one to my Alex as well and I'm looking for ideas.

Here's the derating curve for an OMRON G3NA-220B 20A SSR.



and for Crydom 25A



At 50°C, the load current should not exceed about 6A.

At the very minimum, the device should be attached to the chassis and bedded with a good thermal compound

@cafeike does that mean it wouldnt last?
Yes i used a heatsync thats close to the size of the relay. I mounted it about where old relay was

Something like the OMRON Y92B-A100 is adequate when mounted outside the chassis




After milling off the upper fins, the heatsink is about 100 x 100 x 35, several multiples of the SSR size.

Note that efficiency is reduced due to the fins down in a restricted area and the intervening SS machine base. Probably good for about 15A continuous. Thus far, it's lasted almost 6 years and at least that again is expected.

The heating element on my Alex draws 11.3A @ 115V so I used a Crouzet 84137011 wired similarly as described earlier in this thread and found a nice cool mounting spot under the reservoir (that was the coolest part of the machine I could find outside of the outer side of the skin). Secure it to the base of the machine remembering a bit of thermal paste.

The mass of a heat sink is generally more relevant to cooling ability than its material or design so even though SS looks terrible on paper as a heatsink, don't be afraid.

The machine's been on more or less continuously for a year with a loaded and covered warming tray (~8500 hours) without a problem.

What I have not done is measure the temperature of the relay.

Hopefully this data point will help your or someone else looking to do the same further down the line.

isr2kba wrote:The mass of a heat sink is generally more relevant to cooling ability than its material or design so even though SS looks terrible on paper as a heatsink, don't be afraid.

A 4kg wood block would work as well The efficiency of a heatsink is directly related to its ability to conduct heat. SS is far worse than aluminum.

Stainless steel [k~16] is about 1/3 as effective as steel [k~50] which is about 1/4 as effective as aluminum [k~200] in dissipating heat.

Very rough calculation for a Vibiemme Domobar Super :
pan where SSR mounted .25m x .15m x .0015m
Stainless thermal conductivity ~16
Steady state thermal resistance about .0025 K/W
Horizontal surface thermal radiance efficiency to still air about .1%
Bottom surface efficiency derating 50%

.0025 / .001 / 0.5 = 5 K/W - Borderline.
A steel pan with the same dimensions would have a thermal resistance of about 1.7 K/W, but paint could decrease the heat transfer to the air.

from SSR Heatsink Basics

isr2kba wrote: The machine's been on more or less continuously for a year with a loaded and covered warming tray (~8500 hours) without a problem.

Continuous operation is less stressful as the device is ON for only a few seconds every couple of minutes after it survives the initial heating.

Im not comfortable how hot it gets. Planing on putting a cpu heatsync thats about 3 times as big as the ssr. Any ideas where i could mount it? Where did you?