I'm building a musical instrument using thirty JF-0530B solenoids, rated 6VDC and 300mA. But I've discovered when I power them directly with 6VDC they draw ~1.5A, because they only have a resistance of ~4 Ω (they all do, except for three that appear to be shorted/bad).
(The values above are as measured with my multimeter, like so – just to make sure I didn't mess something up here.)
My concern is that I'm going to damage the MIDI decoder board, which switches the solenoids via ULN2803 chips (Darlington arrays with embedded flyback diodes) that are only rated up to 500mA per output.
The odd thing is, before discovering all this I tested the solenoids with the decoder – and not only does it work at 6VDC, it works at 12VDC when the solenoid pulls nearly 3A! (I just used the wrong supply.) Maybe I just got lucky here because the solenoids are only powered for a fraction of a second.
I'm not familiar with solenoids, but isn't 4 Ω a low resistance for a 300mA-rated solenoid? Did I get a bad batch or do I misunderstand how to use them? I'm trying to ask vendors for the resistance of the 12VDC version of this solenoid (which I'm thinking of using instead) but no success yet. I've seen this thread (among others) but that seems to have boiled down to misuse of equipment. Another forum suggested I was seeing inrush current, but this seems to apply only to AC solenoids.
Thanks in advance for any thoughts!