I fried my SSR........ HELP!!! - Page 1
Forum section: electronics / projects

author: jwilson
author_rank: Contributor
timestamp: January 24, 2020, 10:24:13 pm
content: Hey guys, I'm a newbie and really need some help.I'm trying to replace the old controls in a Paragon kiln and use a PID with 2 SSR's using 220v.Here's a list of the equipment I'm using:SSR - 2 x Inkbird Solid State Relay 40DA DC SSRPID - Auber Instruments PID TEMPERATURE CONTROLLER,W/ 30 RAMP / SOAK,SSR OUTPUTHere's how I wired everything and killed an SSR.....220V coming into the box and the white leg going to SSR #1 on terminal 2.The black leg of the 220V going to SSR #2 on terminal 2.I wired the SSR's in series going from SSR #1 I wired terminal 4 to terminal 4 on SSR #2.I wired SSR #1's terminal 3 to SSR #2's terminal 3.Then I ran a wire from SSR #2's terminal 4, negative, to terminal 8 on the PID.I ran a wire from SSR #2's terminal 3 to terminal 7 on the PID.I ran a wire from SSR #1's terminal 2 to to terminal 9 on the PID.I ran a wire from SSR #2's terminal 2 to a rocker switch and then to terminal 10 on the PID.I also hooked up the thermocouple to the PID via terminals 4 and 5.So, I was using terminal #1 on BOTH SSR's to go to the heating elements on the kiln.When I switched the PID on and the output light kicked on, the elements started to heat up and then SSR #2, with the black 220V wire going to it, started smoking and made a POP!!! It's dead.How should I wire this thing up??? This is killing me and I don't get it.Please help!!!!

author: duak
author_rank: Super Contributor
timestamp: January 24, 2020, 11:06:15 pm
content: Ouch!A few questions:1.) what is the element power rating or the rated current?2.) is the element isolated from ground? Please check with a meter.3.) has this kiln worked before, perhaps with a different controller?

author: james_s
author_rank: Super Contributor
timestamp: January 24, 2020, 11:21:32 pm
content: Are these cheap SSR's from China? I'm not familiar with that brand but they sure look like it. Keep in mind the specs on those are hugely exaggerated, I think you'd be lucky to reliably switch 15A with a "40A" SSR. Buy SSRs from a reputable company like Crydom, they will cost a lot more but you can rely on their specs to be honest. Also make sure you mount them on an adequate heatsink, if you are pushing 30-40A through SSRs they're going to get hot, they have a much higher dissipation than mechanical relays though they are superior for applications that do frequent cycling such as PID temperature controllers.You'll also probably want to have some sort of backup protection, see this for an example of what can happen when one of thee fails:https://hackaday.com/2018/08/24/fail-of-the-week-solid-state-relay-fails-spectacularly/When a SSR fails it usually fails closed, this can be a very bad situation when you are controlling a heating device. I would probably add an additional mechanical relay controlled by a thermal fuse.

author: james_s
author_rank: Super Contributor
timestamp: January 24, 2020, 11:39:59 pm
content: This is the sort of thing you want. You can either get a pair of single ones like this:https://www.digikey.com/product-detail/en/sensata-crydom/D2440/CC1071-ND/221764Or you can get a double one like this and only need one of them.https://www.digikey.com/product-detail/en/sensata-crydom/D2440D/CC1122-ND/221840

author: jwilson
author_rank: Contributor
timestamp: January 25, 2020, 12:33:12 am
content: Quote from: duak on January 24, 2020, 11:06:15 pm1. The element power rating is 30 Amps and 7200 Watts2. The element wasn't grounded.......That's probably the problem.3. The kiln did work before, but I'm a knife maker and need to hold precise temps in order to heat treat knives.Thanks for chiming in!!!

author: jwilson
author_rank: Contributor
timestamp: January 25, 2020, 12:35:52 am
content: Quote from: james_s on January 24, 2020, 11:21:32 pmThe SSR's are from China via Amazon. I probably should have purchased American made components.I do have an adequate heat sink and I used thermal paste on each one just to be safe.Thanks for the info!

author: jwilson
author_rank: Contributor
timestamp: January 25, 2020, 12:38:14 am
content: My main question is this.Should I connect one leg of the 220 to the SSR and one leg to the element?Or, do both legs of the 220 go to both SSR's? One leg to each.I'm confused.Thank you all for chiming in and giving me some direction!

author: ignator
author_rank: Regular Contributor
timestamp: January 25, 2020, 02:02:47 am
content: I have a 3KW radiant heater that is wired similar to your initial wiring. Mains power L1 through one SSR (then connect its terminal to the heater), and mains power L2 through the other SSR (and then connected to the other heater lead). This is correct to have the SSR's connected this way.Now, cheap China SSR can be fake and use a name brand, Fotek being one that is the most common to counterfeit (from what I see and buy). They do not have the Triacs of correct capable max current, nor are they connected properly to the heat sink back plate of the SSR.I used to see a guy on eBay that had a fake selling listing to warn people about the Fotek's he got. He had photos of the inside showing bad parts and assembly practices.This really looks like you connected it correctly, but the SSRs are junk to start with for what your trying to do.I also had one of the SSRs fail last year after using this for over 5 years. I replaced it with a Crydon. And yes mine are 40amp SSRs, but I paid ~$5 each for them from China.

author: ConKbot
author_rank: Super Contributor
timestamp: January 25, 2020, 05:23:37 am
content: A 30A heater will draw over 30A during warm-up until the element itself is at temperature. They have a positive temperature coefficient, similar to a lightbulb, just nowhere as severe. I'd suspect overly optimistic ratings from the manufacturer is what is the problem. As far as I can tell, the hookup looks fine.But the choice of wire for supplying 240V to the PID controller looks dubious. If that's speaker wire, it absolutely needs to change to something meant for mains. If that's lamp cord, it's a bit sketchy, but probably fine as long as that compartment doesn't get too warm inside it when the kiln is on.I'd also echo the suggestion for a crydom relay (not from ebay or Amazon resellers) it won't be super cheap, but if the SSRs fail short while your doing a final temper, it will waste a bunch of your time when it turns out you accidentally annealed the knife. Determine if future time savings is worth the cost to you. The two relays in series mitigates this some, but if you're not monitoring for a failed relay, you won't notice the first one failing.

author: duak
author_rank: Super Contributor
timestamp: January 25, 2020, 05:31:49 am
content: Jwilson, here's what I think:1.) the SSRs are probably NFG. Last I checked, Crydom or other quality SSRs are quite a bit more expensive2.) If the element has a metal case or tube, that can be grounded but you definitely do not want the resistance wire to connect or even slightly conduct to ground. Check this out!3.) as wired, two SSRs in series is a good idea in case one fails.4.) you are dealing with 30 amps here and anything smaller than 10 AWG conductors is marginal if not hazardous.5.) each SSR is running at about 75% of capacity and will dissipate about 15-20 W. You seem to have a galvanized sheet steel enclosure probably about 0.030" thick. IMHO, this is nowhere near good enough as steel is not a good conductor of heat as is aluminum. It's just too thin to carry much heat away. I've used a rule of thumb of at least 1 square inch of 1/8" thick aluminum sheet for heat sinking. Where to put it is another question.

author: jwilson
author_rank: Contributor
timestamp: January 25, 2020, 02:34:08 pm
content: Quote from: duak on January 25, 2020, 05:31:49 amBear with me here, so I do not want to ground the heating element?The heating element is just coiled wire with 2 ends. I have 4 elements in total. Here's what I did.Since I have 8 leads total, I wired 4 wires together for a + lead and 4 wires together for a - lead.Should I ground the "-" leads to the chassis?When I blew the SSR, I had power going to each set of leads and it blew the SSR.I figured my mistake was that I didn't ground half of the leads.What do you think?THANK YOU!!!!!

author: jwilson
author_rank: Contributor
timestamp: January 25, 2020, 02:36:17 pm
content: Quote from: duak on January 25, 2020, 05:31:49 amOh, and to address #5, you can't see it well in the pictures, but each SSR is connected to a heat sink per SSR. The heat sinks are aluminum and about 2"x2"x2" tall.Thanks again!

author: calzap
author_rank: Frequent Contributor
timestamp: January 25, 2020, 04:05:29 pm
content: I agree that quality brand SSRs are the way to go. However, if the controller is slapped on the side of or anywhere near the kiln, passive cooling may not be enough. Advise fan-cooled heat sinks. And if possible, don't attach the controller to the kiln or place it above it.My one experience with an Auber controller (for a smoker) was not good.And, minor point, your power voltage is almost certainly 240 VAC, not 220 VACMike in California

author: james_s
author_rank: Super Contributor
timestamp: January 25, 2020, 04:47:14 pm
content: For chassis wiring you can get away with #14 wire though I don't think I'd go smaller than #12. The ampacity is considerably higher than for power transmission where the length is greater and it may be enclosed within walls or covered by insulation.https://www.powerstream.com/Wire_Size.htm

author: DBecker
author_rank: Frequent Contributor
timestamp: January 25, 2020, 06:58:50 pm
content: Quote from: james_s on January 25, 2020, 04:47:14 pmThat is correct: chassis wiring suspended in free air has much higher ampacity than supply wiring that is likely thermally insulated and bundled with other current-carrying conductors.But for one-off prototypes and projects you can afford to be much more conservative and use thicker wire. That will compensate for inconsistent connections and act as additional heat sinking.I agree with the other posters: eBay SSRs are often rated more like fuses than components. The stated current is where they very likely will fail, not a continuous operating current. A Chinese "40A" SSR is OK for 10 amps, but (generalizing here) unsuitable for 20 amps.If you want reliable operation at a low price, use a single SSR to operate a 40 amp dual circuit contactor. Most will operate continuously at their rated current, survive surges and overloads if they aren't make- or break-current, and will survive hot conditions. Their main down-sides are size, slight noise, and a floor on power use.

author: dmills
author_rank: Super Contributor
timestamp: January 25, 2020, 07:21:30 pm
content: What does that PID controller output on its control terminals? For SSRs it should be dc of a modest number of volts, not mains!No you should NOT earth ether end of the heating element! That you suggest this says you probably want to find someone who understands US style split phase wiring.There should be a modestly rated fuse or circuit breaker separating the control power from the heavy current, otherwise a fault in the PID controller could cause many, many amps to flow thru its supply wiring, which would be bad.SSRs are not usable as isolation, so given you need a separate isolation switch to make touching the elements safe, you may as well just use one 240V rated SSR instead of two, and leave one end of the load connected to one leg of the supply, this saves you half the heat load in the control box as each SSR will drop around a volt, so at 30A will be burning off 30W as heat.

author: floobydust
author_rank: Super Contributor
timestamp: January 25, 2020, 07:49:14 pm
content: I drew a circuit and realized you may have wired the heating elements wrong. How many ohms are they each, or as a quad? Originally they have might been wired in pairs, as 120V elements each? This could overcurrent the SSR.I have a few issues with safety, the galvanized enclosure and kiln must both be grounded.Why are you using cheapola PVC speaker wire when this enclosure sure looks like it gets very hot. The indicator lamps have high temp wire so I'm worried the whole thing will melt.Can you touch the heating elements (when the kiln is cold) ? Usually this is the case, when putting stuff in or out of the kiln. Using SSR's (instead of a contactor) there can be an electrocution hazard due to the SSR's leakage current putting stray voltage at the heating elements, despite the SSR's being off. You'll need to measure ACV at the heater when the controller is off, to make sure.

author: DBecker
author_rank: Frequent Contributor
timestamp: January 25, 2020, 07:52:55 pm
content: Quote from: dmills on January 25, 2020, 07:21:30 pmMost SSRs are rated for and suitable for line isolation. Internally they use an opto-triac. Most types have excellent isolation at very low cost, with the circuit board layout generally being the weak point rather than the component.A kiln will have incompletely shrouded heating elements, so both sides of the supply will need to be switched, likely including a safety switch on the lid hinge.

author: james_s
author_rank: Super Contributor
timestamp: January 25, 2020, 07:55:19 pm
content: Almost all of those low cost Chinese SSRs will have a 10A triac in them regardless of what the label says. There is no need to explore other options until this part is taken care of, if you look at the bottom of the SSR and see the end of a screw that is a dead giveaway that internally it contains a standard TO220 triac instead of a proper design with the die bonded to the plate. there is no way that a 10A triac is going to control a 30A heating element without burning up, that is your problem.

author: floobydust
author_rank: Super Contributor
timestamp: January 25, 2020, 08:07:48 pm
content: Quote from: DBecker on January 25, 2020, 07:52:55 pmIt's not the isolation I'm talking about, it's the leakage currents from the triac and snubber that are significant in any SSR. They flow mA's when off and that's enough to keep a floating load hazardous live.I think OP should have a Neutral wire in there and the heaters may be all be 120V elements. Have to check the kiln's make and model to see how it was originally wired.

author: jwilson
author_rank: Contributor
timestamp: January 25, 2020, 08:14:58 pm
content: Quote from: floobydust on January 25, 2020, 07:49:14 pmFor the elements, they are 8 ohms.Here's a link to the elementshttps://www.paragonweb.com/ELA82.cfmI changed out the speaker wire........ I now realize that was a horrible idea. I'm using 16 ga primary wire to run power from the SSR to the PID.I haven't tried to touch the elements when they are live. Due to my mistakes, I can't now until I wire it up properly.I wish I could pay one of you guys to come over and help me wire this thing up!!!!! I'm in Fayetteville, AR.Anyone close?

author: jwilson
author_rank: Contributor
timestamp: January 25, 2020, 08:18:59 pm
content: Quote from: floobydust on January 25, 2020, 07:49:14 pmFLOOBYDUST, I can't thank you enough for the schematic!!!! I have a new SSR coming tomorrow and I'm going to leave well enough alone until I get it and then wire according to your schematic.Thank you so much!

author: jwilson
author_rank: Contributor
timestamp: January 25, 2020, 08:25:22 pm
content: Quote from: floobydust on January 25, 2020, 07:49:14 pmOne more question, your schematic includes everything I need, but how about the AC lines going to terminals 9 and 10?Here the PID I'm using:https://www.auberins.com/images/Manual/SYL-2352P%20Manual.pdfThanks again.

author: floobydust
author_rank: Super Contributor
timestamp: January 25, 2020, 08:26:00 pm
content: WAIT - that's a schematic based on your picture, what you wired up. Not how it should be- I'd have to think about it. The heaters surely aren't all in parallel! Groan.Inkbird 40A SSR reviews are pretty funny on Amazon. They seem to smoke and melt."Got two of these in succession, both caught fire filling the air with acrid smoke! First one, than the second one a few months later as well. Too late for Amazon refund.""Melted on first use, despite heat sink. Unable to brew beer until I get it replaced, this is the second 40A Inkbird SSR to go bad on me, 0 for 2.""This SSR should have been over powered for the setup I put it into but it failed about 15 minutes after being turned on. The system was drawing 6.3 amps @ 238v when it popped and failed. The 10 amp inline fuse didn’t have a chance to protect this 40 amp switch..."

author: jwilson
author_rank: Contributor
timestamp: January 25, 2020, 08:35:15 pm
content: Quote from: floobydust on January 25, 2020, 08:26:00 pmDOH.... I thought your schematic was how it SHOULD be wired up.Definitely time to invest in better SSR's.........How should the elements be wired?There are four in total, with 2 leads on each.I am attaching a pic of what the element arrangement looks like.I can't thank you enough for all your help!!!I owe you lots and lots of beers!!!

author: jwilson
author_rank: Contributor
timestamp: January 25, 2020, 08:36:44 pm
content: Also, the lines drawn on the kiln represent the two leads for each element. 8 pairs, 4 leads total.

author: jwilson
author_rank: Contributor
timestamp: January 25, 2020, 08:38:41 pm
content: Is this a suitable relay?https://www.automationdirect.com/adc/shopping/catalog/relays_-z-_timers/solid_state_relays/panel_mount_relays,_hockey_puck_style,10a_-_75a_(ad-ssr6_series)/ad-ssr640-ac-480a?gclid=CjwKCAiA66_xBRBhEiwAhrMuLYSIR0jvmlq4Jov-z3gH_w68Pn-nENwTheYSLJqrflV9q_HEu2M5WRoCIPUQAvD_BwE

author: floobydust
author_rank: Super Contributor
timestamp: January 25, 2020, 10:35:57 pm
content: Paragon kiln model A82 wiring,the manufacturer states"Neutral is essential"so I'm wondering about the power cord missing that. It should have 4-prongs.So I updated the wiring diagram to match the manufacturer's wiring - having the heater's top mid-point connected to neutral.If you wired all four heaters in parallel it would overload the SSR's. They are wired in pairs.The Kiln companies are using mechanical contactors, I couldn't see any SSR's likely because they do make a lot of heat.I'm worried about how hot this enclosure gets sitting on the side of the kiln. You need high-temp wire.The Automation Direct SSR is the wrong one, it wants 90-280VAC input but the PID controller's output is 12VDC to the SSR's.AD-SSR6T40-DC-480Alooked right.edit: forgotCheck your thermocouple polarity with a magnet, the more magnetic (iron) wire is (+). Red is almost always (-) it's counterintuitive.Also make sure the one you have can take the heat- kilns get really hot. Type-J is good to only 750°C and would burn out. Kilns are usually type-K 1300°C/2372°F max. It should be yellow/red (K), not a white/red wire (J) like you have.

author: jwilson
author_rank: Contributor
timestamp: January 25, 2020, 11:10:54 pm
content: Quote from: floobydust on January 25, 2020, 10:35:57 pmYou're amazing and I can't thank you enough for all your help!!!You just potentially saved a house fireMy 240 volt outlet only has 3 prongs. It sounds like I need to replace it to a 4 prong/wire receptacle.Also, thanks for the update on the SSR. I will pickup a couple of the model you recommended.I am using a type K thermocouple. That's probably the only part I got right about all of this!Thank you again for all your help!!!

author: Nusa
author_rank: Super Contributor
timestamp: January 25, 2020, 11:25:16 pm
content: "Neutral is essential" makes sense. The likely original configuration with two 4-way rotary switches was manual operation with OFF/LOW/MED/HIGH. As I understand it, LOW turned on one element at 120V. MED turned on both elements at 120V, and HIGH put them in parallel at 240V. And the other rotary switch controlled the other two elements in the other heating zone. If you've still got the original switches, you could confirm how they operate if you wanted.You may discover that you actually need two zone control to get even heat, especially if you have longer blades to temper. But if you get this working, that should be an easy upgrade.

author: DBecker
author_rank: Frequent Contributor
timestamp: January 26, 2020, 12:37:10 am
content: Quote from: floobydust on January 25, 2020, 08:07:48 pmAh, yes, you are correct. I was considering the isolation to the control panel. SSRs are often not suitable for load isolation e.g. with a potentially exposed heating coil when one end isn't permanently at ground potential (grounded neutral connection, not the safety ground). The common, inexpensive design is a 'definite purpose contactor'. Using a small SSR to switch power to the contactor coil is a good approach.

author: jwilson
author_rank: Contributor
timestamp: January 26, 2020, 08:28:54 pm
content: Quote from: floobydust on January 25, 2020, 10:35:57 pmGREAT NEWS!!!! THE KILN WORKS!!!But....... there's one small problem.When I plug in the kiln, it heats up WITHOUT any input from the PID.I plugged it in after wiring to your newest diagram and it just heats up!The PID does not control the coils. I think the SSR is just completing the circuit for power to go to the coils and the PID has no control of when power goes to the coils.I tested this by turning, via the toggle switch, the PID off and waiting for several minutes and the coils still heat up.I then unplugged the kiln and waited for 5 minutes so all the power would drain out of the system and the coils would cool down, from red hot.I then plugged the cord back in and everything heats right back up.I will tell you that I just tested the kiln with my original 3 wire/prong cord and outlet.I connected the neutral from all the coils to the green ground wire from the plug.Is that why it comes on by itself?Should I get another receptacle and plug with 4 wires?Thank you for all your help!!!

author: james_s
author_rank: Super Contributor
timestamp: January 26, 2020, 08:39:57 pm
content: Are you sure the SSRs have not failed? A common failure mode that is less spectacular than you saw with your drastically under-rated SSRs is to fail shorted so the load is always powered. You can test this easily enough, disconnect the control side of the SSR and no current should pass through the load side.

author: floobydust
author_rank: Super Contributor
timestamp: January 26, 2020, 08:57:57 pm
content: It takes any SSR ON to give power to the heating coils. If the PID controller is off, the SSR LED's would be off too.With Neutral connected, one shorted SSR will give 120V to a pair of heaters which might be what you are experiencing.Get out your ohmmeter and check the SSR's are not shorted. Or you mains wiring is wrong, for L1, L2, N, GND. I would not use the green ground wire for a temporary neutral, that can be scary unless you are sure that is correct and there are no ground faults between any heating elements/SSR case to the kiln or controller box chassis.

author: jwilson
author_rank: Contributor
timestamp: January 26, 2020, 09:34:43 pm
content: Quote from: floobydust on January 26, 2020, 08:57:57 pmOk, I took the panel off to see what's happening with the SSR's when plugged in.When I plug the kiln in, the coils power up and start heating and the PID is off AND the lights on the SSR's, both, are off.My wiring has to be off.I'm testing with the 3 wire 240v plug and outlet.Sounds like I need to get a 4 wire plug, cord and outlet so I can hook the two pairs of the heating elements to neutral as opposed to the ground wire that is connected to the chassis.Does that sound right?

author: WattsThat
author_rank: Frequent Contributor
timestamp: January 27, 2020, 05:30:43 am
content: You don’t need a neutral but the elements do need to be wired correctly.You have (4) elements that are 8 ohms each. In order to have 7200 watts, you’ll need to:1) Wire two elements in series, making two 16 ohm elements.2) Wire the two 16 ohm elements in parallel so that you end up with an 8 ohm element.That will be a 30 amp load at 240 volts, no neutral wire required. Changing out the 3 wire plug for a 4 wire only provides for a proper 120 volt control voltage which your modified kiln does not use (or need).Personally, I would use mechanical relays and increase the cycle time of the controller to 30 seconds. The operating temps required versus the watt density means that turning on an element for a 30 seconds doesn’t raise the temperature by a degree, it takes several minutes to do that. Solid state relays almost always fail shorted and that results in a run away, not good with a kiln. That’s why they use mechanical controls. You could use two 20 amp contactors wired in parallel. If you’re going to stick with solid state, use four contactors, two for each 16 ohm pair to lower the amps and add some safety margin.Proper high temperature wire is fiberglass braid over Teflon with the copper wire and all lugs being nickel plated. Anything else just oxidizes and fails at those temperatures. The right stuff is pricey and not available from the usual sources, the kiln manufacturers are probably the easiest place to source it.My wife’s L&L kiln is controlled by their own custom PID unit that operates two mechanical contractors, one element on is low, both on is high. When the PID is within the proportional band, it use low heat, high when out, typically at startup.

author: james_s
author_rank: Super Contributor
timestamp: January 27, 2020, 07:39:45 am
content: That's a really good point, a lot of those PID controllers can have the cycle time turned way down and for a kiln there's really no reason to have the precision you can get by rapidly cycling. At the very least you'd want a separate mechanical contactor with an over-temp cutout or a circuit to monitor the SSR to ensure that the output is not live when the control has it shut off.

author: jwilson
author_rank: Contributor
timestamp: January 28, 2020, 11:43:07 pm
content: Quote from: WattsThat on January 27, 2020, 05:30:43 amIT WORKS!!!!!!!!!!! I did what you said and wired the elements in series and then in parallel and disconnected the ground and it works!!!!!!!!!!!YOU SIR ARE A GENIUS!!!THANK YOU!

author: WattsThat
author_rank: Frequent Contributor
timestamp: January 30, 2020, 12:40:38 am
content: I’m no genius but I understand that words can sometimes work when pictures don’t.Now, the fun begins - tuning the PID. Hopefully the controllers auto-tuning algorithm works well enough for your application.At the risk of repeating myself, I’ll mention again that you should increase the controller cycle time as the 2 second default value is extremely short and is likely to result in the inability to maintain a stable final temperature. 10 to 20 seconds is more realistic with such a large thermal mass like a kiln.You’ll need to test the range of final temperatures you’ll be using to insure there is little to no overshoot of the target (setpoint) value, that’s what the tuning is all about - reaching setpoint as fast as possible without overshooting.