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Mains power puzzle

Started by Phil Allison November 28, 2019
Hi to all my pals, 


on the bench I have a US made, bass instrument amplifier (Eden) in near new condition. It uses a 600VA toroidal tranny in the PSU.

The "T5A" 20mm AC fuse installed was blown and also a similar previous fuse, I'm told. Nothing wrong found with the amp when a new fuse was fitted.

However, repeated switch on testing shows max, peak inrush surges over 120 amps, either polarity.

But mysteriously, resistance readings at the IEC inlet are variable:

Eg:

DMM  =  83 ohms either way.

Analogue meter =  25 to 35 ohms, depending on polarity.

DC bench supply  =  0.5 A at 2 volts & 1A at 3V.

Any intelligent guesses ? 

Bet no-one gets it right. 


.....   Phil 
Phil Allison <pallison49@gmail.com> wrote in
news:d11d4b67-f5ff-42be-9367-c2714b830d16@googlegroups.com: 

> > Hi to all my pals, > > > on the bench I have a US made, bass instrument amplifier (Eden) in > near new condition. It uses a 600VA toroidal tranny in the PSU. > > The "T5A" 20mm AC fuse installed was blown and also a similar > previous fuse, I'm told. Nothing wrong found with the amp when a > new fuse was fitted. > > However, repeated switch on testing shows max, peak inrush surges > over 120 amps, either polarity. > > But mysteriously, resistance readings at the IEC inlet are > variable: > > Eg: > > DMM = 83 ohms either way. > > Analogue meter = 25 to 35 ohms, depending on polarity. > > DC bench supply = 0.5 A at 2 volts & 1A at 3V. > > Any intelligent guesses ? > > Bet no-one gets it right. > > > ..... Phil >
It has a shorted turn on a secondary or tertiary winding.
On Thursday, November 28, 2019 at 9:07:06 PM UTC-5, Phil Allison wrote:
> Hi to all my pals, > > Bet no-one gets it right.
The toroid has a big crack in it.
PM UTC+11, DecadentLinux...@decadence.org wrote:

----------------------------------------------


" Nothing wrong found with the amp when a new fuse was fitted. "


 mpm wrote:

------------

> > The toroid has a big crack in it. >
** Yeah, it does. Runs right round the core about 120 times. Strewth... .... Phil
mpm <mpmillard@aol.com> wrote in
news:cb37b506-0810-4413-921a-f91401924eaf@googlegroups.com: 

> On Thursday, November 28, 2019 at 9:07:06 PM UTC-5, Phil Allison > wrote: >> Hi to all my pals, >> >> Bet no-one gets it right. > > The toroid has a big crack in it.
He never said it had a ferrite core. But even if it did, being cracked would not hurt a 60 or 50 (or even 400) cycle power transformer one bit.
In article <d11d4b67-f5ff-42be-9367-c2714b830d16@googlegroups.com>,
 Phil Allison <pallison49@gmail.com> wrote:

> Hi to all my pals, > > > on the bench I have a US made, bass instrument amplifier (Eden) in near new > condition. It uses a 600VA toroidal tranny in the PSU. > > The "T5A" 20mm AC fuse installed was blown and also a similar previous fuse, > I'm told. Nothing wrong found with the amp when a new fuse was fitted. > > However, repeated switch on testing shows max, peak inrush surges over 120 > amps, either polarity. > > But mysteriously, resistance readings at the IEC inlet are variable: > > Eg: > > DMM = 83 ohms either way. > > Analogue meter = 25 to 35 ohms, depending on polarity. > > DC bench supply = 0.5 A at 2 volts & 1A at 3V. > > Any intelligent guesses ? > > Bet no-one gets it right.
Phil- I assume there is some marking that specifies a 5 Amp fuse is to be used. That sounds marginal for a 600 VA transformer at 120 VAC, but about right if you have over 200 VAC mains. When a power supply is first turned on, there is an in-rush of current as power supply capacitors charge. A normally blowing fuse may not always hold out long enough. Be sure you have the T5A a "slow blow" fuse. Your measurements do not make sense. Fred
Phil Allison <pallison49@gmail.com> wrote in news:4af515d1-9eb0-4ba8-
9826-aff5241c8b38@googlegroups.com:

> PM UTC+11, DecadentLinux...@decadence.org wrote: > > ---------------------------------------------- > > > " Nothing wrong found with the amp when a new fuse was fitted. " > >
You said 120 A inrush. That hardly qualifies as "nothing wrong".
DecadentLinux...@decadence.org wrote:

------------------------------------


> > > > You said 120 A inrush. > > That hardly qualifies as "nothing wrong". >
** Go tell the makers that - cos they have sold hundreds. I think pissed off users uprate the fuse to T8 or T10 amps to make it work. Remember, max inrush surges do not occur every time. ..... Phil
I'm just making stupid guesses, but I'll guess anyway just for giggles.

5A at 120VAC is 600VA, so that sounds about right.  That doesn't mean
the PS can source 600 watts at output, of course.

High inrush current might be OK, but might indicate a defective (or
missing) inrush thermistor, or abused thyristor or other EMI/surge
protection.

DMM and analog meter use low current/volts, the DC supply uses higher
volts, looks like effective resistance goes down as volts goes
up... semiconductor?  Is it reading the bridge rectifier as a resistor?

It would be interesting to see the amp ratings at 2V and 3V *AC* instead
of *DC*.