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dinac

Running HOT BED with SSRelay - fail

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Ok, i ended all, my Solid state relay came, connected, but after 5 mins relay is so damn hot that it started to melt lol

my IR temerature thermometer said over 150 degreed Celsius on relay :shock:

where is the catch ?

SSR is SSR25DD , 25 Amps

Heated bed drawn only 8 Amps

th_IMG_20130513_222338_zps9de8d28f.jpg

th_IMG_20130513_222023_zps66ed1624.jpg

 

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most SSR are made to switch a AC load, and will fail/die miserably if you use them for switching a DC load.

looking at your pictures, it seems to be a (rare) DC SSR. did you mix up the payload with the control side? control is 3/4, while payload (HBP) is 1/2.

 

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Pin 2 also needs to be at a higher voltage than pin1 so Pin2 needs to go to + power, or pin 1 needs to go to ground and the other pin would go to the HB.

There is a small chance that you didn't damage the part. Small.

By the way, did the HB warm up at all?

 

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it was connected like this :

th_images_zps69b6d8bf.jpg

HBed was warmed up to 80 oC for cca 8 mins, then i realised that something is smelling :)

After that i turn off all, checked all, and tried again, but BED is getting only 3 V@ 2 amps

so SSR is obviously not working any more LOL

 

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Pin 2 also needs to be at a higher voltage than pin1 so Pin2 needs to go to + power, or pin 1 needs to go to ground and the other pin would go to the HB.

There is a small chance that you didn't damage the part. Small.

By the way, did the HB warm up at all?

 

OK, I wired again all like you said above bolded : and it is working again :)

it is heating bed, but with only 9,6 V and it draws 7,2A

Output from Power supply is 12,50V

-relay is eating 3Volts :)

Dont know what is going on :)

I will try to heat to 100 oC, maybe SSR will blow up forever

EDIT: working LED on relay stoped working, but relay is still operational, but it is heating like hell :twisted:

 

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Some need a heatsink which are massive. I gave up with the SSR route because the ones I found were way to big to fit undet the machine base with the heatsink fitted. I went for a kit on Ebay which includes the heated bed, thermocouple, controller and power supply for less than £100. In my view it was not worth the hassel in going for the built in version. OK, I cant control it from software, but at least it requires no surgery on the Ultimaker and i know it will work

Paul

 

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I know for heatsink, but it is designed for 25 A, i tought that this 8-9 A will be nothing fot it.

It is connected now with mechanical relay....

But i have another Q - in Marlin, is there any code that for controling when it start heating and stop heating .

If set let say temp= 100 oC

why not heat to 102, then turn off relay- till it reach 98 oC and then again turn on relay.

Insted of - when reach 100,xy it shout down relay, and on 99,9 it turn on again ...

many clicks for controlling temp it is not neccesery to be exact 100oC...

 

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I don't think so. But the default bed control method is PID meaning it turns the heater on and off 10 times per second - so when it thinks it is at the right temp it turns it on at a certain duty cycle.

To disable that feature you want to disable bed PID mode (enable bang-bang mode). Like this in configuration.h:

//#define PIDTEMPBED

 

The "//" disables PID mode.

 

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I know this is a real old thread, but i just wanted to note this: The SSR in question (the one in the pictures) is a cheap knock off (counterfeit) model. There is NO way in hell that it can support the 25A rating. The power transistor inside is not even in the vicinity of the bottom heatsink, so there is no way for the heat to escape. Useless crap!

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This is why SSRs are just plain bad :)

If you have a soldering iron, you could take a look at my Heated bed MosFET relay hack.

This one can handle more than 10A without needing a heatsink. Why? Because it uses a high performance MosFET in contrary to the cheap stuff they put in these SSRs.

Also, my hack lacks any kind of safeties. But as you can see on your part, these don't work anyways :D

If you use the hack, just make sure you wire it up EXACTLY like shown in the schematics. You put your SSR in the positive path (between 12V and the heatbed), and not the negative path (between the heatbed and GND). You should always put the switch / relay / SSR in the negative path if possible.

A MosFET like in my hack will not work in the positive path, while other parts might work fine.

/edit:

Lol, I only read "May 13"...

/edit2:

By the way, this Fotek relay is pretty much the same circuit as my hack. Just with cheap-ass components...

Edited by Guest

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I know for heatsink, but it is designed  for 25 A, i tought that this 8-9 A  will be nothing fot it.

It is connected now with mechanical relay....

But i have another Q - in Marlin, is there any code that for controling when it start heating and stop heating .

If set let say temp= 100 oC

why not heat to 102, then turn off relay- till it reach 98 oC and then again turn on relay.

Insted of - when reach 100,xy it shout down relay, and on 99,9 it turn on again ...

many clicks for controlling temp it is not neccesery to be exact 100oC...

If you switch the bed to bang-bang mode, there is indeed some settings for when to turn the bed on and off like you mention... Its in configuration.h and called something like "bed hysteresis" I believe

Edited by Guest

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