Fake SSR Burned Up

[JeremyAgost]

So my DC-DC solid state relay and 24V power supply arrived today. I went with the suggestions I've seen elsewhere on this forum, the Meanwell PSU and the Sunkee 25A DC-DC SSR (http://www.amazon.com/Sunkee-Solid-SSR- ... 00CI4HBCQ/). I hooked it up as shown in the image, V+ on the PSU going to the (+) on the output end of the SSR, (-) on the SSR output going to (+) on the Onyx, V- on the PSU going to (-) on the Onyx. And of course Bed (+) and (-) going to (+) and (-) on the SSR input, respectively. So I turn on the RAMBO and the external PSU and dial up the Bed temp. Within a minute it's getting close to 100ºC but I'm smelling the fiery death of electronics and sure enough the SSR's plastic case is beginning to melt. That's when I realize that the label on this particular SSR is NOT the same as the rating/picture on the one from Amazon! Different ratings and the stickers show different polarity... WTF!!! I google a little and immediately find someone else explaining they had a similar burnout and they suspected someone was shipping knockoff components or some such. Any thoughts? How about somewhere I can get the SSR I actually ordered?

[img]http://i.imgur.com/Bja3XbP.jpg[/img]

[Tinyhead]

You really should have had that thing on a heat sink of some kind. They generate quite a bit of heat.

I'm no expert, but just looking at the unit, it appears it should be up to the task. Current rating was high enough and everything. It really looks like the only difference in the one you received and the one in the picture is that it's capable of a higher switching voltage. It might have just been a revision on that particular model and the polarity is different... but I suppose it's possible it was a knock-off.

I would wager that the unit simply got too hot from lack of cooling.

http://www.amazon.com/Heatsink-Heat-Sol ... r+heatsink

[nitewatchman]

This seems to be a common problem with this package of the SSR's. They generate enough heat from internal resistance that they MUST be mounted to a substantial panel or a fairly large heat sink.

I would not rule out the possibility of a knock-off but a heat sink is a necessity. I haven't used one of these on my printer but we do use them in simple machine controls where fast switching is desirable. They can get pretty warm.

nitewatchman

[JeremyAgost]

I ordered from a different vendor so we'll see. I also got a heat sink, although I'm not convinced it would've made any difference in this case. This unit burned up in 30 seconds max. Not to mention the fact that the labeling on this one is totally different than any online photos I can find of the component I supposedly ordered makes it beyond suspect. The label on the one I have doesn't even match photos of the SSR-25 DD H, which should be the "real" model that operates at that 24-220VDC range.

[Hansen]

If I measure the resistance of my heat bed, I get around 0.8 ohms. This means that at 12 V it will consume 15 amps. Had I increased the voltage to 24 V, it would have been 30 amps! This would be a bit above the maximum ratings of your relay.

[guanu]

If I measure the resistance of my heat bed, I get around 0.8 ohms. This means that at 12 V it will consume 15 amps. Had I increased the voltage to 24 V, it would have been 30 amps! This would be a bit above the maximum ratings of your relay.

yup, but with the voltage drop from the psu, it drops to 11v, so that keeps it in range for the 15A fuse, brings it to 13.75A, and as it heats up, the resistance rises, so it stays safe.. also at temp you hit the pid, which makes the componants stay cooler.. its that initial heatup that is the big draw

Guanu

[Jimustanguitar]

I've also heard that using PID control is a bit fast for these relays and can contribute to the heat. The advice I was given was to change the heater circuit to "bang bang" in the firmware to keep the SSR cooler. This operates the heater in slower on/off clicks instead of the rapid flutter from a PID control.

[JeremyAgost]

Ugh. Perhaps the power draw overloaded it as well. Well this was the wrong V range anyway. I ordered a 5-60V output SSR and I plan to bring the output voltage of the PSU down to 19V. That'll keep it under the 25A load rating.

EDIT:
On a related note, is there any reason I can't get power for a 40mm 12V fan by siphoning off the RAMBo's input for the heated bed? Since that rail is now just supplying current to regulate the SSR I figure its the least loaded on the board now.

[JeremyAgost]

So the new "real" SSR and dialing down the PSU to 19V has worked wonders. My bed heats up nice and quick now. I also attached a heatsink and a little 12V fan to the relay as well as changed the heating algorithm to BangBang. It stays pretty cool. Thanks for the advice!

[cambo3d]

you should also check the spec sheet, to make sure that rating listed is with or without a heatsink. some state that in order to use the full current a heatsink is required. otherwise usable current that the relay can handle drops dramatically.. 10amps even 7 amps..at most with out a heatsink.. futek ssrs aren't worth purchasing, ive had a couple bad out of the box. Hit and miss on quality also.

the other thing, with using bang bang, is that your bed won't maintain a constant heat temp.. it will fluctuate vs using pid which is more steady.. if you your using bang bang in your setup.. you don't need an ssr.. just use a standard 30amp automotive relay..

[JeremyAgost]

Interestingly in BangBang mode it seems to switch the bed power on and off quite rapidly. The bed does maintain the set temperature just fine. Maybe my firmware is wonky and it's still really in PID loop mode.

[Jimustanguitar]

Interestingly in BangBang mode it seems to switch the bed power on and off quite rapidly. The bed does maintain the set temperature just fine. Maybe my firmware is wonky and it's still really in PID loop mode.

Bang bang mode would click on and off like the thermostat on your furnace, it reaches a temp and turns off, drops to another temp and turns on. PID would try to figure out a frequency (maybe a hundreds of pulses per second?) that would maintain a constant temperature.

[mhackney]

I wanted to see if anyone had a followup on this thread. I had my Fotek melt down tonight after a couple of weeks of smooth running. I got mine from Amazon and it is identical to the photo in the first post on this thread. SSR-25 DD 5-60VDC out 3-32VDC in.

It got extremely hot and started sparking. I immediately shut down. I was running in PID mode and like I said, it has been working fine for a few weeks and barely warm to the touch without a heat sink. Now I am gun-shy. I need an SSR or relay to run my Onyx at 24V from the Azteeg X3 Pro, I can't go back to 10 minute warm ups!

[JeremyAgost]

Well this item is the second relay I got and it's been working fine for a while now. The one I received even matches the picture/description . I also attached a heatsink with a small 12V fan. Even with the solid state relay I'm running the bed in BangBang mode because it's gentler than PID and it doesn't seem to cause any noticeable fluctuation in the bed temp. Oh and I adjusted my PSU to 19V for load safety.

[mhackney]

That is the EXACT item I got. I actually bought 2 of them but now I'm concerned about running the 2nd one. I didn't have a heatsink but frankly, I don't see that having made much of a difference. I run my machine A LOT so for the last few weeks with this device it was perfectly fine and barely got warm. Something happened last night that caused a melt down.

[Jimustanguitar]

I bought the SSR-40-DD just to be sure that it could hack the amperage. Put mine on a heatsink (with thermal grease) that a different Fotek SSR came on (the one Inventables sells).

Mounted nicely behind the side panel of my Max, pics later. Haven't actually used it though Stay tuned for that part.

[626Pilot]

I'm confused. I got a 10-amp SSR, thinking that because the RAMBo uses a 5A fuse for the heated bed, it would work. Is that really not enough? I have no problem getting a bigger one, just don't want to waste money on it.

[teoman]

Rambo is rated at 30V and 10A. Why are we not trusting it?

I remember reading it here but i cannot recall now.

[626Pilot]

My Azteeg X5's bed heat stopped working. Zero volts across the terminals with the heat cranked. I'd rather pay ten or twenty bucks than deal with this ever again. Printers without bed heat SUCK!

[critical_limit]

I bought the SSR-40-DD just to be sure that it could hack the amperage. Put mine on a heatsink (with thermal grease) that a different Fotek SSR came on (the one Inventables sells).

Mounted nicely behind the side panel of my Max, pics later. Haven't actually used it though Stay tuned for that part.

my first Fotek with 40A rated burned also in less than one minute. Ordered a second one which is working fine with PID. But even on a heatsink its at 70C when its working. Only 26amps drawing and its rated to 40Amps. Due to the fast switching on PID its getting hot. That was on the Rambo Board.

Now I'm on Smoothieware and can reduce frequency of PID Controlling. SSR is now 38C after 2h of printing.

[teoman]

You can mod the pid frequency on arduinos. 100hz was minimum if i remember correctly.

[critical_limit]

You can mod the pid frequency on arduinos. 100hz was minimum if i remember correctly.

Where can I change the Frequency on the Repetier firmware? I was going true the configuration.h but havent seen anything about the frequency.

thanx
Dirk

[626Pilot]

Dang, that's a good idea! A frequency of 1Hz should be fine for keeping the bed on temp. It has so much thermal mass.

[Gr8Scott]

I have a larger capacity version of this that is mounted directly to a pentium II heat sink and fan via two self tapping screws. Works like a charm for me every time.

[teoman]

Give me a couple of hours guys and i will find the code.