Pot controlled ssr?

[01z28auto]

What are the ssr's for that are available with only a pot connected to them? I see no board on them,just the relay and a pot? Like this one.

http://www.emtechsolidstaterelay.com/ma ... _relay.htm

Hopefully the link works.

[Brucepts]

You will find some feedback in a post on here of what I found using one on my flowbench. If I find it or someone else does I'll post the link here. I picked one up from China to play with as a cheaper alternative to the one I sell now. Importing in volume from China might be an issue so I haven't pursued it just yet.

It was not recommended by the manufacturer to use in a motor application but I found it worked with no issues for the amount of time I had it on my flowbench. I used it to control 2 motors. Would like to give it a go on a full motor control bench. If I get some order down-time in the next week or two I might be re-wiring my flowbench to the new schematic. Or get my ass in gear and get building my second flowbench that's been sitting here in pieces for over a year now!

The POT was cheap!
It was less than 1 turn rotation
Had to supply a heat sink

I had the heat sinks already
I just got in this week some better POTS to try out

I think with a 10 turn pot (the SSR I have uses a 500K pot which is impossible to find a 10 turn model) these things would be a nice inexpensive setup for a DIY'er (sub $100?), would I use them on a flowbench being used everyday for hours on end? Probably not. They also will not work with the PID control add-on.

[01z28auto]

I've found this one. It says it's 75a which is well over what I plan to be at. I may buy one and try it. Is there any way my motors could be damaged if it's inadequate? Thanks Bruce.

http://m.ebay.com/itm?itemId=130662445830


I've also got lots of .125 aluminum plate to use for a heat sink. Is there a way to calculate how much area is needed?

[Brucepts]

That is the one I have

I used a cheap eBay heat sink that was rated for close to the 75amp rating. I was picking up heat sinks off eBay when I found them to use for my SSR builds so I have a good selection of sizes to play with.

No idea of the long term effects on the motors if one of these does not work correctly. Reason why I stress it should be for a DIY casual user and not a full-time shop flowbench.

A larger knob would make the pot easier to dial in the speed. The pot you get is knurled so it's not easy to fit a proper knob to it. I picked up some 1/4" solid shaft pots from Mouser to give it a go for testing.

I'm going to fit one of my 10 turn pots on it to also see what happens with a different rated pot. Maybe one of the electronic gurus will weigh in on this, that's not my specialty.

[01z28auto]

I'd probably buy one of these. It's the only place I've found one.

http://www.alltronics.com/cgi-bin/item/ ... 500K%2Dohm

[RACEPUMPER]

I bought some from the link above, didn't realise they were used till they turned up.
They are super industrial and quite large.
Jim

[Tony]

I've also got lots of .125 aluminum plate to use for a heat sink. Is there a way to calculate how much area is needed?

About two square inches of exposed plate per amp mounted vertically with free convective airrflow both sides would be about the absolute minimum. That will get quite hot, it will work, but cooler is always better.

If you can keep your finger on it, with the motors flat at out maximum, its probably o/k.
The cooler you can keep it, potentially the more long term reliable it is likely to be.
Best is to make the plate as large as you have space for.

[Hotz]

I've also got lots of .125 aluminum plate to use for a heat sink. Is there a way to calculate how much area is needed?

About two square inches of exposed plate per amp mounted vertically with free convective airrflow both sides would be about the absolute minimum. That will get quite hot, it will work, but cooler is always better.

If you can keep your finger on it, with the motors flat at out maximum, its probably o/k.
The cooler you can keep it, potentially the more long term reliable it is likely to be.
Best is to make the plate as large as you have space for.

Tony as always great explanation ...
thank you.

[RACEPUMPER]

Sorry to make you repeat yourself Tony,
With a 15 amp draw, a 6" x 5" plate spaced 1" off the mdf wall is the minimum size? Assuming adequate air circulation.
My next build is small size and budget, so space will be tight in the electrics area.

Jim

[Tony]

With a 15 amp draw, a 6" x 5" plate spaced 1" off the mdf wall is the minimum size?
Assuming adequate air circulation.

That would be a very reasonable starting point in still air with natural air convection.
It will run quite warm, because it needs to get a bit hot, before it can start to dissipate heat into the surroundings.
Bigger is always better.