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Art24:
I was wondering if I could connect a few inputs of a 16 channel-relay for 230V and other ones for 15V? I am working on a project where I want to control 4 big lightbulbs and 6 small lights with one arduino. I don't want to use a lot of seperate relays. Is it even possible to use a 230V relay for 15V?
If it's rated for 230V, there'll be no problem using it for a smaller voltage.
Be aware that relays have one rating for AC and a lower one for DC. The ones you linked to are OK up to 250V AC or 30V DC.
Side note: I always get a bit twitchy when people who don't know these basics tell the forum they're planning a mains-voltage project, so please please please be careful.
The relay contacts are electrically isolated from the coil and the relays are isolated from each other so everything will be fine as long as it's wired correctly.
I don't want to use a lot of seperate relays.
That board has 16 separate relays.
Similar relay boards have had problems with relay ratings.
“4 big lightbulbs” does not give us much information.
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● 16-channel relay interface board, each one needs 15 - 25mA driver current
How many is "a few"? The relay coils need 75 mA each as well, is your 5V power supply adequate?