Rex C100 PID

[dikman]

My spare PID arrived today, a Rex C100, and I just learnt a bit more about PIDs! This one said it was rated to 400*C, but I thought that what they read was dependent on the rating of the thermocouple used. Not so! This one will only read to 400*C, no more (as this is 750*F it's not too much of an issue, but at least I know next time to look more carefully at the rating). It's also a relay output, but that's not a problem. While it's rated to 7 amps @240v, I have grave reservations about those figures. I intend to remove the relay from inside and connect the two coil wire connections to the output terminals, so that I can measure the current/voltage that it uses. My idea is to simply use those connections to drive a heavier duty (external) relay directly from the PID - I just need 12v @ 30 mA (with my luck the internal relay will only be 5v!).

One other interesting thing I've noticed - I have a Rex and an XMT PID, both purchased via Hong Kong, and both are labelled Made in Japan.

[6bg6ga]

The same thing I have been telling people. The relay inside the PID while having a printed rating on the side of it for 7A when you look at the contacts they are smaller than a 3A relay contact. My suggestion is this... leave the internal relay where it is and simply use the internal relay to control a larger external relay. I would suggest using a wall wart's secondary voltage and run that thru the internal relay to operate the external relay. I know its a little more trouble to do this but it will live for a lifetime of use. Just my .02

[jsizemore]

My PID has relay output. I added a SSR with a 90-280VAC contol circuit. It's rated for 25 amps. When I checked the current draw on the line wiring it's 6.94 amps. idec solid state relay rssan-25a.
I got it off ebay for $20. More expensive than dc control circuit SSR but cheaper than buying a new PID.

[sackot]

I'm fairly sure the PID I'm using (an Ebay cheapo) is a Rex 100 or clone. It came set up to max out at 400c, but I found some detailed programming instructions somewhere online and discovered that I could change the maximum to a higher value. It took a bit of fiddling, of the "hold two buttons down for 5 seconds, then scroll down to setting 7 and set it to 0110" sort. This is not guaranteed to apply to your model, the options depend on the exact full model number. I found, for example, that mine could not be set to read degrees F, even though the programming setting was present.

I pulled out the relay and bridged across it to the outputs, then connected those to an SSR.

Now I mean to buy another for my lubesizer.

[dikman]

I've just removed the relay from the PC board and connected the coil points on the board to two of the relay screw connections on the PID. I then hooked up the relay and measured the current drain - 32 mA. I then replaced it with a better relay (rated at 250v/5A) and current drain was 42 mA, so I don't see any problems with using the PID to drive this relay directly. Although this other relay is rated at 5A, this is probably slightly conservative judging by the size of the contacts! If I connect both sets of make contacts in parallel this should be perfectly adequate for my pot.

If I decide to use a relay and not an SSR. Then again, at this stage I only intend to use this second PID as a glorified thermometer to monitor the smelting pot (cheaper than buying a conventional thermometer).

These cheap REX C100's do come as an SSR output, but they're not that common on ebay (they probably just do what I did, leave out the relay and put in two jumpers to bypass it). They also only read *C and only read up to 400*C (750*F), but for the price they're perfectly adequate as a basic PID.

sackot, I've also found some more detailed instructions (although they still seem to assume one has more knowledge of these things that one actually does) and I did wonder about whether the limit could be changed. Knowing that you've done so, I'll try and decipher the instructions - again! Thanks for that.

[leadman]

I have been buying the REX100 set up for an SSR and they seem to work fine. I did buy 3 package deals with PID, SSR, and Thermocouple together from the same seller. Got 1 pid for SSR and 2 for Relay. When I contacted the seller he said all 3 should have been for relay. I asked him why he was selling an SSR as part of the package if it won't work with the relay pid, no answer but he did replace the 2 pids marked for relay.
I originally bought 40a SSRs but the package deals had 25a and I also bought a couple other 25a SSRs separate. So far 3 have failed and 2 are starting to go. Could be a bad batch and the seller replaced them but I am going to stick with the 40a SSR.
My son gave me a scrap strobe generator box yesterday and it had some nice components in it. A 25a SSR, a 110v electric fan, a large breaker and 2 huge capacitors about the size of a can of Red Bull!

[dikman]

Sackot, you're a champ! A bit more digging around and I found that one can indeed change the max. read temperature.
1. Turn it on (always a good start)
2. Hold the Set button and the left arrow button down
3. Will display COD (for code) in top line, enter 0001 in second line and press Set
4. There are several parameters under this setting, the first one is SLH (high limit setting for Set-Value (SV))
5. The instructions I have show the K input type as 0 to 1372*C, so I entered 1372
6. Either hold Set and left arrow to exit, or wait approx 1 minute and it will return to the main display.
(Note: the next parameter is SLL - low value limit - make sure this is set to 0).

Bingo! It will now read higher than 400*C. But you're right about changing it to F, while the instructions show the setting as SL2, under the COD 0000 parameters, it appears to have been disabled as nothing I changed had any effect.

Centigrade is fine for me, however, as being able to change the higher setting is more important. I reckon that at $12 it's excellent value for a PID.

Leadman, if you happen to open up one of your SSR PID's (hint, hint) I'm very curious to know if they're different inside or if they simply leave out the relay and put in a couple of jumpers.

[leadman]

dikman, if I can get it apart without damaging it I may do it.
I am building 2 more and am moving the SSR from the bottom of the box to the back wall and installing a heat sink on the outside. Don't know if this is really necessary as I never recorded a temperature over 105 degrees on the bottom of the box under the SSR. The strobe generator I disassembled had a 120 degree thermostat to turn on the fan mounted near the SSR.

[dikman]

Thanks leadman, they're easy to open. On one side, at the front, is a clip (3 sides are plain). I gently pushed the clip in with a small screwdriver and then just levered the front away. It will feel a bit tight, but that's because the pc board makes contact at the back via a series of spring contacts that push against pads at the back of the board. Which, by the way, raises an interesting point for those who say using dissimilar metals on the probe connections causes additional small voltages which can affect the reading .

I guess when you're running at those temps, while it shouldn't be a problem, it's always nice to err on the side of caution.

[hermans]

dikman, I have ripped out those contacts from the body side of the casing and soldered my wires directly onto the PCB, thus eliminating the possibility of any bad contacts which could cause you many problems later on.

[dikman]

That would certainly eliminate any contact problems! Personally, I don't see it as a problem as there appears to be a fair bit of tension in those spring contacts.

[dikman]

I've resurrected this thread, rather than carry on with discussions about this PID on the other Lee pot thread.
The settings to control the output type are under the SL6 parameter. The default setting on mine is 0001, which is Reverse PID action (no idea what that means) and Time proportional output (M, V, G), where M = Relay, V = Voltage pulse and G = Trigger (for driving a Triac). So it seems to me that regardless of whether it's a relay output or an SSR the same MVG setting is used, as there is no way to select any of them individually, which would mean that the only difference inside is the lack of a relay.

I'm a bit confused, as I would have thought Direct action, rather than Reverse, would have been the default but unfortunately I don't understand the significance of the terms with regard to PID action. Hopefully someone can enlighten me.

[10x]

Detailed video on removing the internal relay and soldering in jumpers for an SSR.

[stanley2]

Leadman, if you happen to open up one of your SSR PID's (hint, hint) I'm very curious to know if they're different inside or if they simply leave out the relay and put in a couple of jumpers.

Hope this pic help, mine has a couple of resistors instead of the relay.

[6bg6ga]

Cannot see the traces but if you have a meter its easy to find the ground and the +. Measure the voltage and using ohms law install a resistor to limit current and lower the output to say 5 volts.

[stanley2]

What you are saying is that if I change the resistors I may be able to get 12 volts?

In my set up I have a fan that is 12v

[6bg6ga]

What you are saying is that if I change the resistors I may be able to get 12 volts?

In my set up I have a fan that is 12v

If you had a PID that had a 12 volt relay in it there would be 12 volts all right. The 12 volt supply inside the PID probably wouldn't have the current capability to run your 12 volt fan if that is what you had in mind.

[el34]

Cannot see the traces but if you have a meter its easy to find the ground and the +. Measure the voltage and using ohms law install a resistor to limit current and lower the output to say 5 volts.

You'd have to hook up 110vac, watch where you're touching.

If you had a PID that had a 12 volt relay in it there would be 12 volts all right. The 12 volt supply inside the PID probably wouldn't have the current capability to run your 12 volt fan if that is what you had in mind.

I agree, that fan probably wants 100mA or more. Curious- what would be the reason to get 5v? If it's to connect an SSR the input voltage can handle 12v, possibly considerably more, 3v-32v is a common SSR input specification.

[6bg6ga]

You'd have to hook up 110vac, watch where you're touching.



I agree, that fan probably wants 100mA or more. Curious- what would be the reason to get 5v? If it's to connect an SSR the input voltage can handle 12v, possibly considerably more, 3v-32v is a common SSR input specification.

Yes, it goes without saying that your going to have to plug it in(supply 110 from outlet).

The five volts is a common output voltage from PIDs and yes anything from about 3-32volts DC will work. Won't hurt to drop it down with a resistor and add some current limiting as a safety factor.

[el34]

Mypin controllers output 24V, Aubers output 12. My guess is that they were designed to provide nominal current for typical SSRs.

I may have misunderstood the suggestion to measure voltage, I thought you meant probing around on the pcb with no case and didn't picture how the ac would be connected to the terminal pads. And that it might be easy to stumble onto the ac by surprise.