# Specific 3D Printers, Scanners, & Hardware > RepRap Format Printer Forum > MakerFarm Forum >  SSR keeps melting.

## tsteever

I have upgraded the relay on my printer to a SSR following the guide posted here. For some reason I have gone through 3 relays. They keep melting on the 12v load side.

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## fred_dot_u

Do you have the SSR mounted to a heat sink or other metal surface to conduct away the excess heat?

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## tsteever

Yes I do. It is melting the terminals were power being supplied by my power supply.

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## fred_dot_u

If it's melting on the power supply side, that's the supply side, not the load side as stated in your first post. Important distinction!

Are you using crimp type connectors on those wires, or are the wires wrapped around the terminal screws or under the terminal clamp plates?

A photo of the damaged device would be helpful.

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## kd7eir

A photo and the specs/model number of the relay that you are using would be very helpful in figuring this out.

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## tsteever

> If it's melting on the power supply side, that's the supply side, not the load side as stated in your first post. Important distinction!
> 
> Are you using crimp type connectors on those wires, or are the wires wrapped around the terminal screws or under the terminal clamp plates?
> 
> A photo of the damaged device would be helpful.



I am using 12 gauge wire and just using bare wires into the screw terminals. it is melting on the side the power supply is attached to, not the side my control board is attached to. I have used the Omron and a different SSR with no long term luck.
IMG_6139.jpgIMG_6138.jpgIMG_6141.jpgIMG_6142.jpg

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## printbus

I couldn't tell from the photos - what seems to get the hottest (i.e., where is the worst damage)? Is it where the wire wraps around the screw or where the terminal attaches to the circuit board inside the relay?

Damage from heat means there's a high resistance at that spot for the current being carried.  Some general thoughts (which may or may not apply to your case, and some of which have brought on counter-arguments in past threads) - 

* Make sure the wire gauge is adequate for the current.
* Make sure no strands are nicked or cut off when stripping the wire. Missing or damaged strands won't carry their share of the current. 
* Make sure there is NO wire insulation under the screw terminal - wire strands only. Tightening the terminal on the insulation can leave the wire strands somewhat loose. 
* Make sure all strands are under the wire capture part of the terminal. Strands not captured can't carry their share of the current. 
* Always retighten screw terminals periodically. 
* Solder creeps with pressure.  Don't tin stranded wire being used with a screw terminal.
* Don't let wires flex at fixed terminals with use.  Doing so can eventually lead to metal fatigue at the terminal, leading to higher resistance.  Doing so also puts a bit of push-pull action on the terminal; over thousands of movements this can then lead to the solder connection degrading with time.  Strain relief the wire somehow away from the terminal so the flex occurs somewhere other than at the fixed terminal. 
* In an application where wires flex constantly with use, consider using high-strand silicone insulated wire like that often used in RC hobby stuff
* Where I worked, the assembly techs were not allowed to attach stranded wires directly to screw terminals.  Stranded wire always had to terminate with a lug, crimp pin, or whatever that could then be properly grabbed by the screw terminal.

IMO, the majority of issues people have had with the OEM MakerFarm heat bed relays  were caused by wires flexing at the relay every time the heat bed  moved.

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## Roxy

Those Fortec SSR's you get on eBay are usually counterfeit.   They work...  But not at the current they are rated at.    You need to go with a much higher current rating than what you are really doing if you use 'Fortec' SSR's.

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## gah

I second the last posters comments about reliability.  You are absorbing 12V and up to the power supplies max amperage into the device.  I have a Fotek DC-DC with a 30A rating that has been running for 2 years since I burned up the originally supplied relay.  Suggest Amazon rather than E-Bay - more accountability from the supplier if you do see a failure.

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## voltatek

Use a current measurement device (ampmeter) to see how much current is travelling through the Solid State Relay. That will help you determine the relay size needed.

And, if you don't want to burn your house down, I strongly suggest to use a circuit breaker to protect your wiring and relay. See your local electrical code.

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## kd7eir

An excellent post with critical safety recommendations.





> Use a current measurement device (ampmeter) to see how much current is travelling through the Solid State Relay. That will help you determine the relay size needed.
> 
> And, if you don't want to burn your house down, I strongly suggest to use a circuit breaker to protect your wiring and relay. See your local electrical code.

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## Jhlewis10

Going to piggy back on this thread, the terminals on my included relay board melted.  I want to order a new one but what about those two small wires on the original that went to D8?

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## printbus

> Going to piggy back on this thread, the terminals on my included relay board melted.  I want to order a new one but what about those two small wires on the original that went to D8?


What is it that you want to know?  The small wires are what controls the relay, using the D8 output of RAMPS or equivalent.  A replacement relay board from MakerFarm comes with those small wires pre-attached. 

If you are going to replace the relay board with something other than a MakerFarm board, you'd run wires from whatever the control pins are on the new relay or SSR to those same D8 terminals.

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## Jhlewis10

Makerfarm has been sold out of their relays for months.   

The SSR I see online look like they only have 4 pins out, vs 4 on the Makerfarm relay with 2 additional control wires on the board.  

So I double up the 4 wires on one side for the bed and Pwr supply and use the other side for the control wires?

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## printbus

> ...The SSR I see online look like they only have 4 pins out, vs 4 on the Makerfarm relay with 2 additional control wires on the board.  
> 
> So I double up the 4 wires on one side for the bed and Pwr supply and use the other side for the control wires?


Ah, OK.  The SSR will have two switched contacts and two control pins.  The MakerFarm relay board as two terminals that are switched through the relay, the two small wires that are the control pins, and two additional terminals that are just shorted together.  To move from a MakerFarm relay board to a SSR, one wire from your power supply to the bed would pass through the SSR, and the other wire from the power supply would go directly to the bed, without passing through the SSR.  Edit: and RAMPS D8 would connect to the control pins on the SSR (watch the polarity).

I assume only one of the two terminal blocks was damaged on your relay board.  If so, which one and how bad is the circuit board? If the board isn't in bad shape and the damaged terminal block does not have traces going to the relay, just splice those two wires together.  If the damage is at the terminal block with traces going to the relay, you could consider unsoldering both terminal blocks and reinstalling the good one at the location with traces going to the relay.  Then the other two wires would be just spliced together.

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## printbus

Searching the MakerFarm subforum for threads containing "SSR wiring" will provide some threads where replacement with an SSR has been discussed.  If you want more generic info on the relay wiring, this old thread of mine might help - Clarifying i3/i3v heat bed and heat bed relay wiring

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## Jhlewis10

Two of the connectors were melted, I removed both and direct soldered everything back in place, but during reinstall I cracked one of the solders joints due to it being brittle, and me being crappy at soldering.  

So I am ordering an SSR, heatsink, and silicone covered 12 awg wire and starting over.  

Thanks for the tips, I will post a mock up when I get it.

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## printbus

Hopefully you purchased an SSR that can switch DC loads.  An SSR for AC loads won't work with a DC power supply.  Also note that you'll have to pay attention to the polarity of the control lines for the SSR. That didn't matter with the relay coil on the MakerFarm relay board but it does on the optical input stage of the SSR.

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