Any Tech's here use Solid state relays?

[Oldman2]

I just bought a couple from Amazon to control an 8amp AC motor load with 12 volts DC signal input.


I bought 25 Amp ones but when testing under AC load I find the heat sink is measuring 70 V AC in respect to ground. Which means of course that unless I isolate the sink from ground I end up tripping the 240v mains supply.


Surely this isn't normal?

[tehguy]

Have you actually tripped an RCD by using this, or are you just theorising that's what would happen due to the presence of voltage on the heat sink? If the latter, have you confirmed that the heat sink is offering a low impedence connection to the AC circuit and it's not just some voltage appearing through induction/capacitance, and in fact cannot provide any meaningful current to make it dangerous?

I found this online which suggests it may not be as uncommon as you'd think: https://www.celduc-relais.com/en/how...sr-assemblies/

[Oldman2]

Thanks for the reply, I originally mounted the ssr with the heat sink grounded on the machines control panel which is earthed. As soon as the ssr output is switched on the control 20amp mcb would trip (Less than 1 second) It was the ssr causing this as I removed it and isolated the sink from ground and then the motor ran as intended. A clamp meter showed normal run amps of 8 amps although the start current will have been at least 3 times that for a very small period.
While the ssr is switched on the heat sink is reading an increasing with time ac voltage from 10v to 70v after 20mins on.
I did try a second ssr isolated from ground and that was the same, They were Fotek 25amp with 3 to 32v dc in and 24 to 380v ac out.
I have now decided to give these a miss and go back to the good old reliable relays so tomorrow an octal 8 pin relay & base will be installed, I will have to parallel up the 10amp relay contacts to deal with the inrush current on startup, but its the devil you know.