Flash! Bang!

I was using my old Bosch PST-50E 'electronic' jigsaw yesterday, and I noticed the handle seemed rather warm. Then there was a flash and a bang from inside, but the saw carried on as if nothing had happened. No trips gone, no fuses blown (13A in the plug, probably way too high, it's only 350W), variable speed still OK, no obvious RFI. So what happened? I suspect a capacitor popped, but where, I don't know. I don't particularly want to open it up to find out, as it still seems to be working OK and I might not be able to re-assemble it. It doesn't get much use, so I'm not in a hurry to replace it, and being plastic and so-say double-insulated, with no earth wire, it should be safe enough to handle.
Any thoughts?
--

Chris

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Chris Hogg wrote:

Yes it will be the failure of the shunt capacitor across the mains input. Dramatic at the time, yes but no real issue and no need to replace it either.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It could be the suppressor capacitor across the mains, it'll not affect the working of the jigsaw at all if it's not there. They are 'X' rated (I think that's it) for direct connection across 240v AC and they're supposed to fail safely. If this is what happened I don't think it failed all *that* safely! :-)
--
Chris Green
·

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yes, wotesaid.
Some even fail benignly, aka "self-healing". The are a metallic layer on plastic film, wrapped around. A local short-circuit due to overload causes an arc which locally burns off the metal, leaving a pinhole with a non-metallized circle around it.
So it goes bang, emits magic smoke, and continues working fine afterwards with slightly reduced capacitance.
In fitting a new capacitor its probably best to get a spare, not a generic part, because they caps tend to be wedged into place and need to have the "right" shape for that. Waiting to replace it should be fine (until it happens again, causes radio interference, warms up, smells, emits sparks, goes off and joins the Foreign Legion, ...)
Thomas Prufer
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 17 May 2018 12:18:20 +0200, Thomas Prufer wrote:

I'd have finished that with "and joins the choir invisible...". :-)
I had a similar experience a month or two back. I was sat at this very desktop computer late one evening when I heard a very loud and distinct bang of a major catastrophic HT component failure in an SMPSU. The strange thing was that nothing seemed to be in the least bit effected (and I had a few candidates plugged in and powered up in my 'Den').
My best guess for "The Event" was that it could only have been an X rated filter cap that had gone bang (self healing or not[1]) and, quite possibly the one in the ATX PSU of my desktop computer (or maybe the one in the ITX PSU in my Gateway 2000 desktop NAS4Free server box). Since I'd only heard and not seen or smelt any other evidence, I just shrugged and carried on, placing my trust in the non end user serviceable fast blow fuses inside of metal cased smpsus to protect me from the risk of a fatal conflagration, as if nothing had happened[2].
[1] Quite frankly, in the complete and utter absence of *any* failed devices, I simply CBA to waste time trying to track down a blown filter cap. Whether it had self healed was a matter of total indifference to me. The important consideration in this case being that everything was still functioning with literally no sign of 'magic smoke emission' nor any unusual smell to suggest any further trouble brewing.
[2] Such an "Event" could have happened before whilst the 'Den' wasn't being occupied. Such a scenario, "If a mains filter capacitor arcs over internally and there's no one there to hear it, does it make a noise?", reminds me of the other, rather more prosaic, 'Chestnut',"If a tree falls in a forest... yada, yada, yada..." which begs the question, "Why worry?". :-)
--
Johnny B Good

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 17/05/2018 09:46, Chris Hogg wrote:

Have you counted all your fingers ?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Well, if its got suppression capacitors then you may feel its not giving rfi, but it probably is. Normally the switch and handle are not that bad to get at. The thing to watch is the springs in the trigger if its the speed control as well. You need to do the final cover removal under a plastic bag, so anything that shoots out is caught. Chances are its one of maybe three capacitors which has gone leaky and has been a bit of a drama queen, and blown open circuit.Note, change all of them! I've not forgotten my rectifier diode cheapskate repair of a video which meant I had to change all four in the end as they died one after the other! Brian
--
----- -
This newsgroup posting comes to you directly from...
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks for the replies. I'll just ignore it then.
--

Chris

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 17 May 2018 09:46:32 +0100, Chris Hogg wrote:

Had similar with my Bosch SDS drill the other day. Except that the drill stopped, opened it up, (well designed no ping fuckits), and found supression capacitor across the mains had ruptured it's casing and the coiled up ali/plastic core damaged and exposed. Removed it, reset the MCB, drill worked fine. Have have since replaced it with a proper spare part from Miles Tool and Machinery Centre.
I guess if I'd just reset the MCB it may have just worked but I wouldn't have known about the state of that capicitor...
--
Cheers
Dave.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.