Proportional Output SSR, 480V 1

[RyreInc]

I'm looking for some options for a proportional output SSR that can power 480V heaters, up to 6A. Ideally it would be able to power 120V heaters as well, be driven by a 4-20mA current, and be DIN rail mountable. There seems to be very little out there, even disregarding my preferences; either that or I'm using the wrong search terms...

So far I have found Carlo Gavazzi's offerings, which is the closest to what I want except the voltage range is not quite large enough; and Crydom's selection, which is not so close since all of their proportional output options need a separate DIN rail mount and possibly a heat sink, plus the voltage range is even smaller than CV's. I am also aware of Advanced Energy's power controllers but these are a bit expensive, and have an even narrower range than either of the aforementioned.

What else is out there?

 

[itsmoked]

Personally I would NEVER use Carlo Gavazzi anything. I've had to suffer thru some of the crap they produce.

You should not be looking for an SSR you should be looking for a "phase angle controller" to do what you want. You will see MANY offerings and you can wiki up your understanding of them.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MatthewDB]

Crydom makes what you're looking for.

http://www.crydom.com/en/products/control-relays/mcpc-series/

I've used the 10V input models on 240 and 480V. It requires an external 8-32V DC power supply. They are really easy to use. They are range limited; the 480V model minimum AC voltage is 300V, so you'll have to use one model for your 120V heaters and another for 480V.

If your heater is three phase, you need to be able to break the delta connection of the elements and put each SSR on a phase to phase connection with one resistor. If you try leaving the heater connected in delta, the phase angle timing circuit will be messed up.

 

[ScottyUK]

Rather than go into exotic controllers can you use a transformer to handle the 120V heaters? If they're only 120V then they presumably are quite small. Most phase angle controllers will handle the little bit of inductance due to the transformer without problem. The waveform will be awful but heaters don't care and small transformers are usually quite tolerant. Be careful if there any assymmetry in the output because that can create a DC level which will cause problems with the transformer.

 

[RyreInc]

Hmm, we use Carlo Gavazzi SSRs pretty extensively (almost) without issue. We have had one or two times where a relay was DOA, and one instance I can recall where a unit failed after put into operation. But we have used hundreds over the years.

"Phase angle controller" does deliver more results but I haven't found anything that isn't huge and expensive. These seem to be geared to larger loads. I did find one option from Control Concepts that covers the voltage range I'm looking for but the thing is almost 5" wide!

Matthew, I had looked at those but as you mention the voltage range is pretty narrow. The relevant specs aren't as good as Carlo Gavazzi's anyways.

Scotty, I like your idea the best so far. I had been considering this myself; however a transformer would cost a large fraction of the SSR itself, so it may end up being as cost effective to just get two sets of relays--certainly the wiring will be more straightforward. Still, something to consider, and a safer option than my other idea:

Another idea I had was to put a 480:240V transformer on the input side (or even omit this) and then limit the max duty of the SSR so that the RMS voltage does not exceed 120V. I have been advised against this by the heater manufacture, but I am not too concerned--it may degrade the lifespan of the heater, or I could mis-program the control signal and blow the heater up, but this is just a test machine for internal use so the risk of embarrassment is low.

 

[jraef]

Carlo Gavazzi doesn't actually make much, most of the stuff they sell is brand labeled from someone else. In the case of their SSRs, they are actually Celduc.

As Keith said, the problem may be your search term. "SSR" is the sort of generic term for a solid state RELAY. If what you want is a POWER CONTROLLER, it can be made USING an SSR as the power device, but the continuous firing of the SSR is the critical part, not the SSR itself. It's kind of like saying you want to buy a new car and are searching for one using the term "internal combustion engine". The term you want to search for is "SCR Power Controller".

A phase angle controller is one TYPE of SCR Power Controller, and that's the type you need if you want to use a transformer. A Phase Angle controller fires on each sine wave, but controls the voltage by only turning on for a portion of each sine wave by delaying the turn-on point of the SCRs (the phase angle). That works fine for inductive loads like transformers and motors, and of course resistive loads, But there is a significant amount of line noise created in firing like that, so it can be problematic with other sensitive loads on the same circuit. The other major type is a Proportional Time Base Zero Cross controller. Instead of turning on for a portion of every sine wave, it turns on all the way, but for a proportional NUMBER of sine waves corresponding to the average voltage you want to attain. So for example if you want 50% power, it turns on every other sine wave. If you want 20% power, it turns on for 2, off for 3. This works out just fine for resistive heating elements. The advantage is that by turning on only at the zero-cross points, there is little to no electrical noise. The bad part is, inductive loads like transformers don't operate well with this.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[RyreInc]

Thanks jraef, sounds like I may want to seek a Celduc distributor!

Thanks for the primer as well. The Carlo Gavazzi proportional output SSR, which I have now ordered, will do each of the control methods you describe and more.

There does appear to be a gray area where "proportional output" SSRs and "power controllers" overlap, and really they are nearly the same thing. However I get some mutually exclusive results when searching for either of those terms...

BTW we ended up going with 120V SSRs, since that will be the initial focus for this test machine.