The Shop > Electronics & IC Programing
I need someone to ID a doohickey.
websterz:
I recently replaced the DC motor control on my home-brew mini mill power-feed with the 30 amp module pictured below. The controller runs a 14.4 volt cordless drill motor utilizing a 12 volt 6 amp battery charger for the power supply. I reverse polarity with a heavy duty DPDT toggle switch. The old controller was only rated for 5 amps and eventually the traces on the board gave out. It was just a proof of concept fix, and since it worked reasonably well I changed out for the heavier controller which I felt would have more than enough cojones for the intended purpose. I installed the board, wired everything up and did a few dry runs with my multi-meter in place of the motor. Everything looked good, and ran quite well when I finished assembling it. I was running the table to the left under power to line up for a cut when the doohickey circled in pink popped like a firecracker. Scared the crap out of me! I cut the power and pulled the cover off and had doohickey guts all over the controller...looked like firecracker paper. I am no electronics whiz but I guess the doohickey overloaded? At any rate the board was in a fully sealed aluminum enclosure, mounted on brass PCB stand-offs with fiber insulating washers. I blew out the enclosure before I installed the board to make sure there was no swarf in it, and covered the ventilation holes with fiberglass window screen to keep the chips out. Cooling is supplied via a 12 volt muffin fan drawing air though the enclosure and venting through the side of the motor housing, again covered with screen. Here's where I get confused. Even with the dookickey guts blown out, and a couple of tabs sticking up where the doohickey USED to be, the controller still runs just fine, both directions, nothing seemingly affected by the pop. Any ideas why? Do I need to replace the doohickey? Do I even NEED it?
John Hill:
Yes, you should replace the doohicky, the designers were careful not to put anything surplus in there.
The doohicky is a capacitor and it will have it value clearly written on the side. It will be easy to find a replacement at any electrical/electronics parts store or repair shop and it will not cost more than a cup of coffee. Just take note of which way it goes on the board, that black strip is the key.
John
websterz:
--- Quote from: John Hill on September 14, 2009, 11:26:56 PM ---Yes, you should replace the doohicky, the designers were careful not to put anything surplus in there.
The doohicky is a capacitor and it will have it value clearly written on the side. It will be easy to find a replacement at any electrical/electronics parts store or repair shop and it will not cost more than a cup of coffee. Just take note of which way it goes on the board, that black strip is the key.
John
--- End quote ---
Well, the side of the capacitor is now shrapnel. Guess I need to locate a schematic for the board, huh? Soooo...why does the controller still work? And any idea why the cap popped? The board is rated for 12-30 VDC and my power supply doesn't exceed 12. In fact it may be a tad lower than 12. Surely that couldn't cause it? The ammeter on the charger showed about a 2 amp draw so I know it wasn't an issue with the current.
websterz:
Okay, found a schematic and it shows a 35 volt 47 microfarad capacitor. Guess I'll hit radio Shack tomorrow and grab a replacement. Actually I think I'll look through my vast PCB collection first and see if I can't get lucky and find one I can recycle. Damn I'm cheap! :lol:
websterz:
This is the one I need, right?
http://www.radioshack.com/product/index.jsp?productId=2102512
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