When Good Coils Go Bad

[Reloadron]

Attached is an image of a solenoid valve coil. This coil had a pretty short life of about maybe an hour. I recently designed a large control panel, part of which involves the control of many assorted valves. As we move towards a more safe work environment I try to use low DC voltage wherever possible. When I drew up the BOM (Bill of Materials) I called out 24 VDC coils for all solenoids. In order to leave the pipe fitters and welders some margin I stopped with the coil voltage being 24 VDC.

Note the fine print on the coil. Looks good right till we see the 60 Hz. People sometimes ask what will happen if we apply 24 VDC to a 24 VAC coil? I always answer with humor it will work fine for a little while then things get ugly. The attached image defines the ugly I speak of. This coil and another identical coil lasted about 30 min of continuous duty. Initially it ran intermittent duty during system test. Besides the two used for one application I found a few others that never had a chance to fry. The remainder were all correct so go figure.

Anyway it shows what happens when we apply 24 VDC to a coil rated for 24 VAC. Obviously the same would hold true for a relay coil.

Ron

 

[jpanhalt]

Well at least you don't have to pay a lot for shipping to Cleveland.

John

 

[Reloadron]

Good point John and funny.

Ron

 

[BrownOut]

That is ugly. Even uglier was when, in my haste, I installed a 24vac coil in a circuit for 240vac. It ran for about 10 sec then burst into flames!

 

[Reloadron]

That is ugly. Even uglier was when, in my haste, I installed a 24vac coil in a circuit for 240vac. It ran for about 10 sec then burst into flames!

Been there and done that too.

I generally photograph and save mistakes for awhile. Then I use them at safety meetings. That coil in the image I posted gave its all for the cause. I passed along to the guys at the subsequent meeting this is why we test and test a new massive system before we actually begin using it to test parts or product. There will always be a thermocouple or two with reversed polarity out of a few dozen or a delta pressure gauge connected baff ass backwards. The kid responsible was all sheepish but no big deal, I have smoked my share of stuff over a long career.

Ron

 

[duffy]

I designed a 128 valve controller for Mead Fluid Dynamics in Chicago that would operate valves at assorted voltages, both AC and DC. One of the things I did was to put a current check on each drive and match the valve against a table to an existing type before activating it. Never had this problem. nyah nyah nyah