bridge rectifier blows fuse when negative is grounded.

Thread Starter

616223

Joined Nov 15, 2023
4
I have a small bridge rectifier on a high pressure washer that feeds 24 VDC to the clutch coil for the high pressure pump. It started blowing fuses and I found that whenever I grounded the negative wire of the rectifier, The fuse blows immediately. It has always been grounded, since the negative side of the coil is the metal case of the clutch, Which is mounted directly to the metal frame of the power washer unit. Any help appreciated. Thanks, Steve Wiese.
 

Dodgydave

Joined Jun 22, 2012
11,241
Sounds like the bridge is being shorted out, or taking the AC to ground. Can you post any pictures of the circuit board or electronics?
 

Thread Starter

616223

Joined Nov 15, 2023
4
I will try and post pictures tomorrow. The rectifier is just one of those square type, about 1.25" square. On the two input terminals is the 24 AC input, and the negative and positive termials. No circuit board in this installation. I meaures (-) 16 VDC from the negative terminal to ground. Fuse blows instantly when I touch the negative terminal to ground.
 

BobTPH

Joined Jun 5, 2013
8,664
You cannot connect one of the * and - outputs of a bridge rectifier to either of the inputs. So if one if the inputs is grounded, you have created a short.
 

Thread Starter

616223

Joined Nov 15, 2023
4
None of the inputs to the bridge are connected to or touching any of the two output terminals. The input to the bridge is 24 AC from a control transformer. This has been running fine for several years. It just started blowing fuses. No changes in wiring have been made. The only thing on the output of the bridge is the clutch coil ,With the positive output from the bridge connected to the coil wire , And the negative output of the bridge connected to the metal clutch housing which is connected to the grounded metal enclosure of the washer unit. I currently have the D.C. clutch connected to a regulated 24 D.C. power supply, And it works fine. It draws 1.6 amps D.C. Why does the bridge blow fuses when I connect the negative to ground where it has always been ?
 

Thread Starter

616223

Joined Nov 15, 2023
4
okay remove all wires from the bridge rectifier, and check the bridge for shorts on a multimeter using diode function,
I checked the bridge and it checks out fine. I also tested a new bridge, Tested good on the diode function also,and it blows fuses too. I would normally suspect that the clutch coil could be shorted,But I never get as far as hooking up the positive wire from the bridge because hooking up the negative blows the fuse right away. Quite the mystery since this has been in operation for several years.I might just leave the 24 VDC power supply in place and use it. I would still like to figure out what the actual problem is though,since I am the plant electrician and I do not like to leave problems uncorrected.
 

Dodgydave

Joined Jun 22, 2012
11,241
I checked the bridge and it checks out fine. I also tested a new bridge, Tested good on the diode function also,and it blows fuses too. I would normally suspect that the clutch coil could be shorted,But I never get as far as hooking up the positive wire from the bridge because hooking up the negative blows the fuse right away. Quite the mystery since this has been in operation for several years.I might just leave the 24 VDC power supply in place and use it. I would still like to figure out what the actual problem is though,since I am the plant electrician and I do not like to leave problems uncorrected.

Okay so does the fuse blow without any load on the bridge rectifier, check the transformer output for shorts to earth .( no power applied)
 
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