Replace the Fuse in the M5Stack SSR Unit

Replace the 2A SMD fuse in the M5Stack SSR Unit.

I'm building a heatplate project based on a 400W PTC heatplate which is supposed to have a max power of 1.8A (400W/220V) but the fuse in the SSR was dead (I don't know if it was dead on arrival or the heatplate blew it). As I spreading had soldering kit I thought I go about replacing the fuse.

This guide is written to accompany my Youtube video:

For this you will need the following:

• the SSR or other Unit with a blown fuse,
• Flux,
• Solder Wick,
• solder,
• SMD fuse,
• Soldering Iron,
• Tiny Allen/Hex key,
• Small flat blade screwdriver or spudger/guitar pick,
• Test meter.

How do I know it's the fuse?

Using a test meter set to resistance or continuity mode, place the test probes on each end of the fuse. If the fuse is working, there will be a small resistance, if its blown there will be a massive resistance.

Replacing the fuse.

First step is to open the SSR Unit. Undo the tiny Allen/Hex screw. Gently try opening the case but don't force it! the end closest to the screw terminals is held close by two small clips, you need to use the flat blade of the screwdriver or spudger tool to gently pry the case open. Once the case is open, you need to gently pry the two clips apart to release the PCB.

Place the case and the tiny screw to one side (or in the box the SSR came in).

On the left hand side of the PCB is a little white block that is the SMD fuse.

Apply so flux and fresh solder to each end of the fuse and then use solder wick to remove the solder. The old fuse should be released but if it doesn't (like in the video above) gently heat both ends and you should be able to remove the fuse with some tweezers.

Next apply a small amount of fresh solder to the pads and solder the new fuse in place.

Using the test meter again we can see that the resistance of the new part is low and if we activate the SSR you will see that the output terminal and input terminals now connect together.

While I could have put a bigger fuse in or even a slow blow fuse in the problem lies with the Mosfet is only related at a max of four amps.

In order to control a bigger current we will need to switch to the Single Phase AC SSR Unit which is made just for this type of job.

https://shop.m5stack.com/products/single-phase-ac-ssr-unit-cdg1-1da-10a?ref=pfpqkvphmgr

Unfortunately, I don't have one of these yet and so will have to wait to order one and add a part two to this guide.