No! Never. That's called "overfusing".

A fuse is supposed to be the weak link that fails when there is a problem in order to protect all the other components behind it. It is a ceiling for the current being drawn on that particular circuit. If the draw is too high for that particular circuit, it can damage things, so the idea is that the fuse will blow before damage occurs.

I keep at least 5 (but usually 10) of each fuse on hand. I also have a few different push button circuit breakers for diagnosing a fuse that keeps blowing (so that I don't keep wasting fuses).

Fuses blow for all sorts of reasons. Sometimes because the amperage draw is too high. Sometimes just because the fuse is flawed in some way. Usually, if a fuse blows without any prior history of blowing, just replace it and see what happens. If it doesn't blow, there might not even be a problem. If it does blow a second time, then it's time to investigate further.

Assuming things are wired and fused properly(read this http://home.kpn.nl/p.koch3/Inkochnito_Bridge_Board.pdf ), if that fuse blows immediately on power up. The bridge rectifier is shorted.

Take your DMM. Set it to diode test.

Red lead on bridge negative lug (i know it seems backwards) and probe the AC lugs (wavy lines). You should see 0.4v to 0.6v. If 0.00 is shown, that is why the fuse is blowing.

Repeat procedure for other half of the bridge. Set the black lead on positive lug. Red lead probe the AC lugs. Again. 0.4v to 0.6v.

If the bridge is OK but the fuse is blowing, you have some kind of wiring issue i'd assume. The 2.5a slow blow fuse on the power board is much lower rated value, it will blow if something on the rectified side is shorted/pulling to much current.

I wonder if these could be useful in our hobby?

ebay.com link: 20pcs RUEF300 30V 3A UF300 PPTC PolySwitch Resettable Fuse

They have other values, I might try some and solder them across a blown fuse.

When you installed the fuse, did the fuse blow the first time you powered the machine on? Or did the fuse blow after a few games/days?

Depending on how much metal has attached itself to the inside of the fuse (i.e. how black the glass is or not) can tell you if it was a violent short circuit blow, or a mild over current blow.

I think the biggest issue would be that you want total isolation in HV applications when a component fails. Current leakage can occur when a PPTC goes into high resistance on a failure. That current leakage could then potentially damage other areas. Probably best to just have a clean break with a traditional fuse.

These might work in the lower voltage areas though. I still would feel a little nervous trying it out though. I like the idea of a clean break.

These are good for sealed up low voltage modern electronics that were designed with their use in mind, like computer components running on USB or something. I couldn't see using these ending well in a pin. Although I've never used these in any designs, so maybe someone that has experience with these can chime in.

I have no idea. But it is easy to measure anything under 10a with a multimeter yourself to see what the load is while idle and while under stress. Although, it is usually best to do this on a game that is known to be operating correctly.

I had to measure and specify a new fuse value for an obscure game that was obviously overfused from the factory on the solenoid circuit. The result of the factory spec was that locked coils would not blow a fuse since it was rated too high, which would have caused damage if the coil was left on like that for too long.

I purchased a couple of these fuse circuit breakers from Bob Roberts for my arcades. They work great for identifying problems without going through a box of fuses.

http://www.therealbobroberts.net/cirbreaker.html

cirbreaker_(resized).jpg

I've taken the fuse value from the advise on Clay's guide (now gone) to add an 8A SB fuse in front of the bridge rectifiers.
Since this is a Black Knight it could use a higher fuse value.
The schematics for the Power Supply calls for a 20A fuse for the flippers en magnets!!!
This is WAY higher than the 8A SB.
Maybe with some trial and error we can conclude that a higher value would be needed with Black Knight.
Just be sure that all coils are good and working properly before you put in a higher fuse on the Bridge Board.
I think you can easy put in a 10A or 12A fuse.
The coils are only pulsed for a short time and the fuse gets time to cool down.
Don't worry about the rectifiers, they can handle put to 30A.
Each magnet is fused by an 8A fuse (see schematics).
I'm not sure about the flippers though.
They might have a fuse under the playfield, but if there isn't a fuse, there is only the 20A fuse on the power supply.
Maybe adding a seperate fuse for the flippers would be a good idea.

This might very well be the case.
If you activate both magnets AND hold in the flipper buttons, that would most likely cause the fuse to blow!

The dimming of the led is normal.
When there is a power draw, the voltage drops a bit and thus dimming the led.

Thanks for putting your trust in my Bridge Board.

Peter
www.inkochnito.nl

Did this ever get resolved? Considering adding one of those to my Black Knight.

Thanks
Tim

I never got any word back.
Go ahead and install my Bridge Board.
You can't go wroung, only safer.
If you run into trouble, just let me know.

Peter
www.inkochnito.nl