Multi-channel relays, why lower voltage in some relays?

Hi everyone,

I have been using Sainsmart 16-channel relay for controlling 12V device. The relay is not Solid state relay, so I expect some problems if I use the relay for a long time. However, I find a problem even in a relative new relay. So, this is the problem. All 15 relays outputs 12.5V when I supply power with 12V battery. BUT, only one relay outputs 11.5V, and this causes random behavior of 12V device (I use 12V solenoid valve. Sometimes it works, sometimes it's not).

Could you please explain why it happens, and what I can do for fixing or preventing?

BTW, I use the relay in a remote area for science experiment. So, sometimes, due to hardware or software errors, relays can be repeatedly operated (this is what happened yesterday).

Thank you very much.

You'll need to get the datasheet from Sainsmart and see what are the specifications for the relays. Nothing to do with Arduino.

Relays do not "output" anything, They switch contacts on and off.

You have either a faulty relay, or a faulty connection. It is not possible for us, not being able to physically inspect and test your equipment, to find such a fault. You need someone locally with that expertise to help you.

Do you have a kickback diode across the 12volt solenoid valve. Repeated arcing across the relay's opening contacts from the coil's back emf could burn/melt the relay contacts. Leo..