Ah I wasn't using a preassembled jobbie but a true DIY affair with a home made coil as suggested a while back. Most reeds need around 20AT to operate so for a 500W load at mains voltage gives 2A or there abouts. So 20 or less turns for the current detection easy enough with some 1 or 1.5mm^2 enameled wire. Might have to be careful not to wind the coil to tight so as not to crack the enamel.
But it does have to handle the full operating current (and any startup transients) of the load.
MBQ
But will need to handle the full current of the load.
MBQ
Some people appear to be unaware that the custom-wound reed coil is acting as a current operated rather than a voltage operated relay. Just like an ammeter, it's wired in series with the load.
When I made mine, the reed was about 50mm long and I calculated that I'd need around 12 turns at the expected load.
I didn't use enamelled wire, but instead used PVC insulated wire of an appropriate cross section.
On further consideration, I think enamelled wire would have been OK as there will only be a small potential difference across it, but I didn't think of that at the time. I had the PVC wire already and there was plenty of room to wind it.
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