Heated relay overheating

sorry wrong thread - deleted

Edited 1 time(s). Last edit at 12/22/2016 06:57PM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

well that burned another relay, but this time it burned out in the open position, so the bed kept heating to max temp and then shutdown. So going to order an SSR and heatsink, can someone suggest a decent one that isnt to expensive. If this fails Im just getting another printer, It shouldn't take a month to figure what is probably a simple fix that were just not seeing

Try connecting a 1000pF 400v capacitor across the relay terminals

It's a shame we couldn't work out why this is happening as I've been using a mechanical relay for a year or so with no issues. Let us know which ssr you get and how hot it gets.

Edited 1 time(s). Last edit at 01/04/2017 02:47PM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

I suppose if the PSU voltage is low, then the holding force inside the relay will be low. This will mean a higher resistance joint between the contacts, leading to burnout.

I set my PSU voltage to around 14 volts, it gives the bed a bit more oomph without getting too high for the electronics. Most automotive relays are designed for 13.8 volts or thereabouts, as that's the normal voltage when the car is running.

Edited 1 time(s). Last edit at 01/02/2017 08:35PM by nebbian.

For SSR recommendations, see [duet3d.com]. Although that page is written for Duet electronics, the SSR choice does not depend on the electronics.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I mean if you are popping so many over-rated relays so quickly there is probably an underlying issue. Either you have a loose connection somewhere or a length of cable section is too long or has a break in it. The wires shouldn't get warmer when you move them, they shouldn't really be warm ever. IMO it sounds like there's a very small air-gap somewhere promoting excessive arcing when the relay breaks.

If you can, take some pictures of the relay setup and the burned contacts. The damage will either show more overheating or arc damage dependent on the issue and will rule out a lot.

If you do get an SSR, don't get a Fotek one, some are legit most are not. I have had a lot of luck buying unbranded relays and getting more decent brands like CNHF arriving. A 25a relay should do as long as it's switched at 50% duty cycle. Switching an SSR at any rate can increase it's current handling capacity while equally reducing it's heat output up to 4 times. You shouldn't even need a heatsink.

Here is a pic of how relay melts, its always on that side
ok I have taken your advice. I've shortened wires to minimum clearence for bed movement and checked connections all are tight now
here are photos
before


and after


and that may be most of the problem, running a print now and relay is warn to touch and wires arnt warm at all, will let ya know

That looks to me like it might have been a poor crimp on the spade connector that connects to the relay. ie not a relay problem at all.

Also, please put a cover over your exposed terminals on your power supply. It would be easy for a piece of metal, or a stray finger, to touch the exposed live terminals. DIY isn't worth dying for.

In case someone is looking in getting a Fotek SSR, beware there are knock offs or clones that are not good.
[www.ul.com]

better off with one where you can access the Mosfet and put a heatsink on it, but according to this this guy
[www.youmagine.com]
his design does not get hot.