PID using a relay

[dikman]

No argument from me, 6bg. I'm familiar with those PC mount relays, and there's no way I'd run the main feed through the internal relay contacts, I'd only use it for switching an external relay (with decent contacts on it). I've been talking about those "ice cube" type relays, btw, I have a couple (Siemens) that are rated at 240v/10A. In the "old days", when components were manufactured in the US, UK, Germany, Japan - even here in Oz - their ratings were generally conservative. These days I wouldn't consider many of the components coming out of China to be rated on the conservative side. There are some factories there that do make good stuff, but there are many where the only concern is to make it/sell it as cheap as possible (and they're often somewhat "loose" when describing their products' capabilities, I've noticed).

Anyhow, I figure that even if a 25A SSR is over-rated by 25%, that still leaves me with a hefty margin if only switching 3-4A. Thanks for your input, it's been most useful.

[el34]

If relays were better for this application than SSRs, we'd all be buying relays.

[6bg6ga]

If relays were better for this application than SSRs, we'd all be buying relays.

Start from the beginning and read this thread over again. No one is saying relays are better. What has been discussed are the pros and cons of both.

[Dale in Louisiana]

It will be cheaper.

But why do you want a "small transformer and bridge rectifier"??? by the time you get that in there you might as well use the SSR.

The controllers are available with relays in them that handle 10A, more than enough for your pot.

Or are you going to buy an SSR output controller to run an External relay?
Or worse an internal relay controller to run an external relay?

( I put the last line in a PM to you.)

You don't NEED a small transformer and rectifier IF your controller's contact outputs are rated for your power supply.

I do this all the time in an industrial environment. I use a wide variety of relays suitable for load currents of anywhere from fractions of an amp to HUNDREDS of amps and voltages from 5 vDC to 5 kV. (Okay, that last one is called a medium voltage contactor, but it operates at 120 vAC).

Choose your relay based on load current and voltage. You want something that will switch ten amps at 120 VAC. These are common as mud. And you want one with coil voltage at 120 vAC. Again, common as mud.

In industrial applications with which I work daily, solid state relays are not common electromechanical relays are.

And one thing I didn't see mentioned about a possible plus for the electromechanical relay is that you can normally hear it pick up and drop out, so you know your controller is working.

dale in Louisiana
(this week it was 771 kW at 480 volts. Like working on a watch)

[el34]

Start from the beginning and read this thread over again. No one is saying relays are better. What has been discussed are the pros and cons of both.

You're totally right, no argument here. I'm also an EE and understand the pros/cons, all I meant to do was point out the obvious.

[dikman]

Dale, hearing a relay dropping in/out had occurred to me, I just didn't bother mentioning it (I wondered if anyone else would). I too grew up around relays, although not of the capacity you work with! There is something "re-assuring" about hearing a relay operating .

The reason I mentioned the internal transformer to drive an external relay is because none of the PID's I've been looking at are rated higher than 3A via the internal relay contacts. I could probably replace the internal relay with a higher rated one, but
a) I can't be bothered and
b) I'd rather not have 230v switching within the PID

If it decided to go belly-up, for whatever reason, it quite possibly would render the PID itself unusable. Much better to have that sort of switching, whether by relay or SSR, external to the PID. Easier to get to, and if the switching died it shouldn't affect the PID.

Actually, el, even if relays were better I suspect that most would still use SSR's, as Frozone pointed out they are more convenient to use and simplify the circuitry (which also makes things slightly safer, particularly for those who aren't too conversant with electrics/electronics - something I think you will probably understand).

[6bg6ga]

Good points

I personally like hearing a relay drop in and out. I would guess that 99.9% of the people don't like or don't understand relays. When faced with having a PID on hand with no control voltage output in order to run a SSR I am perfectly at home using a external relay and using the internal relay to switch it. I'm not comfortable using 230volts and having it switch via the internal relay. My pictures of the MYPIN's internal relay contact points do show the relay isn't a 10A/250volt relay. The relay points are less that 1/2 the size of a trusted relay that is rated at 7A. So you be your own judge on this. The SSR's are easy for the child at heart and don't require any thought and this is why Frozone makes money selling his little kit. His kit works, no one has to come up with a box and the wiring has been done.

Like I pointed out this thread is not to deceide which is better as we certainly don't need 3000 members each telling that they like their SSR. Who gives a rats ear? The point is that questions were asked if anyone had used a relay and these questions have been answered.

Both the relay and the SSR will work fine............................

[Frozone]

Well, you do realize that you're going to be sending 230V into the PID anyway.

"Frozone pointed out they are more convenient to use and simplify the circuitry"
And actually, I pointed out the Opposite, The internal relay is the simplest of the options to wire.

[6bg6ga]

If we can trust the specifications of the MYPIN PID it is rated 90-260v AC/DC input voltage.


The internal relay however is another story and its ratings cannot be trusted. I believe the poster had misgivings when trusting the internal relay to switch the 220-240 v AC line voltage.

In examining the relay myself I found its contacts 1/2 the size of a 7A Japaneese relay that I happen to stock. Which makes it more in line to be a 3A relay not a 10A one.

[dikman]

Ok, you're correct, Frozone, in that from a purely practical aspect using the internal relay is the simplest method (assuming that the relay has sufficient rating). My apologies for mis-quoting you. However, being able to do it in theory is one thing, actually doing it in practice is another issue entirely. I have learnt, over the years, to be very cautious about building ccts. using 230v AC mains, and switching it inside the PID, via a tiny PC mount relay of questionable rating is not what I (at least) consider good practice. Besides, other than the Mypin every other PID I've looked at has the relay rated at 3A, which is clearly not enough.

230v going into the PID to operate it is one thing, but as 6bg said, switching 230v via the internal relay is something I'm just not comfortable with.

So, a cheap 25A SSR is on it's way, as is a (non-Mypin) PID - about 1/2 the price of a Mypin - along with a 1000C K-probe. All up, about $30. As I've mentioned, it's not something that I need, but after all this talk about them I've just got to build one!!!
I can't help myself......

[6bg6ga]

Mr. Frozone,

In response to the PM you sent me. Please have someone read post #20 to you and you will see that I do indeed have the correct rating on your MYPIN PID. That would be 10A/125vac, 5A/250vac.

Please do not send me any more vulgar PM"S.

[Frozone]

......Besides, other than the Mypin every other PID I've looked at has the relay rated at 3A, which is clearly not enough........as is a (non-Mypin) PID - about 1/2 the price of a Mypin............

Well the Auber units are rated 10A@120V/5A@250V but if you don't like the Mypin price then you won't like that cost!
Where did you find a 48mm square controller for $12? Mypins run under $25.

I think You have made the right choice, as far as the SSR, in this application they are a good choice (actually in Most if not all apps).
Just be sure that low priced unit is capable of all you need, read the specs carefully.

I certainly understand wanting one - the darn things are addictive!

[dikman]

It's an XMT800 (just over Aus $20). The Mypins were a bit under Aus $40 (out of Hong Kong, even dearer in Oz!), if I saw one for $25 I would have grabbed it! I went slightly cross-eyed reading specs. The XMT's are also available with bigger displays, for not much more money, but the smaller size should make a neater package overall. All these bits are generally cheaper out of China, but shipping from there is a lot slower than from HK.

If you want cheap, how about a Rex-C100 for Aus$13? (from HK, cheapest I've seen yet, only problem is they're relay output).
Or a package deal - Rex-C100, 40A SSR and 400*C probe for Aus $19 ex-HK? Of course, I'm not sure how the SSR is supposed to work with relay o/p, and the probe is a short screw-mount type. But for that price I'm sorely tempted just to have a play with it.
http://www.ebay.com.au/itm/100-240V-...item1c3b043366

Edit: I just looked at the manual for the Rex-C100, and it seems that they may do a model with SSR o/p. Only way to find out is to try and work out the code for the model no.

[6bg6ga]

dikman

At this time your supposed to drop down on one knee and purchase Frozones complete PID package. After all he is the only one that knows absolutely everything about PIDs and electronics.

How dare you even think of purchasing Aubor or anything off ebay for that matter.

[el34]

dikman

At this time your supposed to drop down on one knee and purchase Frozones complete PID package. After all he is the only one that knows absolutely everything about PIDs and electronics.

How dare you even think of purchasing Aubor or anything off ebay for that matter.

So dikman, you're the original owner of the post. I'm hoping you got some good stuff out of it! Whichever way you go, I'll bet you'll enjoy it, you seemed excited about it.

Bill

[dikman]

Ahh, 6bg, there's no doubt about it, you're a very funny man . If that's the case then I've failed miserably. Although I've built kits in the past, I usually make my own PC boards, where possible, buy what components I don't have (and I've accumulated a lot of stuff over the years) and build things myself.
As for ebay, it's been a godsend for those of us living in Oz. We've been ripped off for years when it comes to buying things and ebay is now starting to level the playing field somewhat.

Bill, yep, it's been a good thread. Lots of info, and it's helped me get a better grasp on something I knew nothing about - PID's, and what makes them tick. I have no qualms about using a relay (heck, the early automatic telephone exchanges I built/worked on were basically nothing but relays and relay switches - just an awful lot of them!). In fact, that's what I intended doing until I realised that at 230v the pot's using half the current that most of you guys were talking about, so an el cheapo SSR is all I need, and will probably barely get warm. Anything heavier and I would have given serious thought to using relays.

Excited isn't quite the word I'd use. I just enjoy building/making stuff for my hobbies, and this is simply an excuse to build something new, along with the challenge of getting it working. (I'm now thinking that the cheap Rex unit, along with a suitable probe, might make a reasonable high-temp thermometer to use when melting scrap. No need to worry about switching anything, simply read the temp. Cheaper than buying a lead thermometer, too).

And that's one of the things I like about shooting black powder (besides the noise and smoke ), it's been a great excuse to make all sorts of things.

It's called FUN!

[el34]

You seem like a good guy and I sure hope you post about your project if/when you pull the trigger!
I'm still predicting the SSR will warm up nicely with that 15A current.

[dikman]

Ummm, 15A? Where did you get that from? The pot only draws just under 4A, so a 25A SSR should barely get warm, I reckon.

I'm using a housing that was used for switching computer video monitors. It's only just big enough for the bits, according to my figuring, so should be nice and compact. I ripped out the innards and made a couple of aluminium panels for the front/rear (to cover the holes). The 230v outlet is fitted to the rear, along with a 230v power cord using a grommet clamp. I've decided not to cut out the PID hole until I actually have it (just in case!), then all I need to fit is a power switch and a grommet for the probe cable. Emails indicate that everything has been shipped, so should take about 2 weeks to get here.

As for being a "good guy", some might say that but I'm sure there are others who will disagree .

[6bg6ga]

dikman,

I'm glad you liked my attempt at humor. I hope you got some useful information from this thread. Ebay is a good source of parts as we both know.

I learned something also... Frozone thru his PM to me has told me that I know exactly nothing about electronics and this is good information. Please disreguard all information that I have posted because Frozone says I'm incorrect. After learning this I will have no other recource but to give up my hobby of playing with valves and audio. I am also considering giving up my day job because I deal in electronics/audio/repair of large format audio systems. I am hoping that Frozone might like to school me thru this as I surely will need his experience the next time l open up one of say 15-20 racks of electronic equipment and look for the problem.

[el34]

Ummm, 15A? Where did you get that from? The pot only draws just under 4A, so a 25A SSR should barely get warm, I reckon.

Yikes! My flu-infected brain crisscrossed your build with another post. That one has 3 heating elements, 5A each in parallel. Sorry about that!