Negative voltage at SSR out triggering relay when not at SV

[dderemer]

I need to Keep a small chamber at 40C with a SSR connected to 48v dc fans. (I am burning in equipement 12hrs)

The internal relays worked fine and hold 40c plus/minus 1 degree, but they cycle very freqently and I don't think they would last long.
I installed a 50A dc ssr and cannot get it to function properly.
The ssr output starts at -2.5v at room temp. When the temp hits SV (40c) the volage goes to +9v
The -2 volts is keeping the relay on which means the relay is always on.


2 Questions.
How do I make the ssr output work off/on at SV?
How do I eliminate the ssr output from putting out voltage when not at or close to SV?

[Tech_Marco]

SSR won't be off completely even when it getting closed to the 'SV'
It will send out a 'pulse' to the SSR with either higher rate or less. When the temperature is far from the SV, the output signal look like "DC" at about 8~9V. When temperature getting very closed or even at SV, it send puse voltage in a few seconds or could be once a minute.

SSR won't turn on wht negative signal. I'll say "impossible". The SSR is drving by a LED and a LED never turn On when appying it negative.


Marco

[richiem]

I would add that you should be sure that the SSR is connected with the correct polarity -- the + output of the controller goes to the + input of the SSR. Same with the - out and in. If these are reversed, you'll get strange results.