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Topic: Choosing an SSR (Read 993 times) previous topic - next topic

retrolefty


Just a followup. This SSR showed up. It's a Kodak, PN 611490. I have duly searched for a datasheet and come up empty. The input resistance is about 891 ohms, so that's good news. But what I hadn't thought about was whether I need a big heat sink for the load. From the faceplate of my A/C unit, the load will be ~ 8A @230VAC. The MPJA page for it says,
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Opto-Isolated, "0" voltage turn-on, internal snubber
which tells me not much.

So, anyone have some experience or memory to draw on here?

@JimG. It's going to be inside an enclosure, but your point is well taken.


Most of those industrial SSR are pretty much the same. The input side is straight forward, an internal LED with built in series current limiting resistor. You can control it directly with a arduino digital output pin and a ground connection. The internal snubber part is actually good for you. Most SSR don't handle inductive loads well (fail to turn on, or fail to turn off) when driving inductive loads (like motors). Snubber circuits help deal with this kind of problems, however it kind of depends on the amount of induction and the specific value of the snubber components in your SSR. Worst case you may have to add external snubber components if needed.

As far as heatsink needed, yes you will. The maximum current ratings for SSR only apply if you can also keep the device below it's maximum operating temperature rating. Past experience I've has is that most SSR will 'drop' about 2vac across it's switching device, so at your 8 amp current load, that's 16 watts of heat dissipation that will surely overheat the SSR unless bolted down to a large enough heatsink using proper heatsink paste, etc.
So how big a heatsink? Probably larger then you wish, have room for, or have avalible on hand.  :D

floresta

I have been using similar units (that I bought used at a hamfest) to control my baseboard heaters for several decades.  The only heatsink is the 4" x 4" aluminum plate that I fabricated to mount them on and to cover the standard outlet box that they are mounted in. 

Don

justjed


As far as heatsink needed, yes you will. The maximum current ratings for SSR only apply if you can also keep the device below it's maximum operating temperature rating. Past experience I've has is that most SSR will 'drop' about 2vac across it's switching device, so at your 8 amp current load, that's 16 watts of heat dissipation that will surely overheat the SSR unless bolted down to a large enough heatsink using proper heatsink paste, etc.
So how big a heatsink? Probably larger then you wish, have room for, or have avalible on hand.  :D


Heh. Well, my motto is, 'Nothing exceeds like excess'. I'll grab a CPU heatsink at MicroCenter. And then maybe I'll lap the back plate of the SSR. And use heatsink compound.


I have been using similar units (that I bought used at a hamfest) to control my baseboard heaters for several decades.  The only heatsink is the 4" x 4" aluminum plate that I fabricated to mount them on and to cover the standard outlet box that they are mounted in. 

Don


That's an idea too. But, what would Tim Taylor do? :)
... it is poor civic hygiene to install technologies that could someday
facilitate a police state. -- Bruce Schneier

retrolefty

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That's an idea too. But, what would Tim Taylor do?


He would mount a freakin 10HP snow blower pointed right at that SSR.  ;)

floresta

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That's an idea too. But, what would Tim Taylor do?

I guess I am culturally deprived.

Don

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