Re: What size fuse?

micky

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Mar 29, 2019, 9:14:14 AM3/29/19

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To recap for the scientists: What size fuse to use in a 22V microwave:

In alt.home.repair, on Thu, 28 Mar 2019 19:07:29 -0500, Dean Hoffman
<dh0...@windstream.net> wrote:

>On 3/28/19 7:00 PM, hub...@ccanoemail.ca wrote:
>>
>>>>
>>>> 12a
>>>
>>> Okay. I'll look for 12 amps, I'm glad I asked.
>>> But I may have to settle for 10.
>>>
>>
>> Yep - the problem that caused the 12 amp to blow
>> has surely cleared itself up by now - so a 10 amp is perfect !
>> .. or not. >> John T.
>>
> I suspect that was tongue in cheek. If not, fuses fail just
>like everything else involving humans. I've changed a lot of them over the years
>without having to do anything else.

LOL. I wasn't living here when it broke; I don't know what they did to
it.

By the same token, I'm leaving and I wanted to either put in the right
fuse or leave a note inside the case for the new owner (my roommate
already bought a replacement and they plan to put this one in the lobby
for someone to take.)

The second store I called had it, even 12 amps, not just 10, but as I
expected, only fast-blow. The original was ceramic.

I thought all ceramic fuses were slo-blo, but this one is embossed
F12H250 and some webpages say that F means fast-blow????
"The types of fuses include long-time-lag or super-time-lag (TT),
fast-acting fuses (FF), quick-blow fuses (F) and slow-blow or time-lag
fuses (T)"
https://www.hunker.com/13418825/difference-between-ceramic-glass-fuses

Nothing I read decribes why a microwave should need ceramic or slow-blo
(in the power part, not the high voltage part).

One page says " Glass has a low rupturing point, such as 15 amperes."

That's fine since it's a 12 amp fuse, and the normal usage is about 7
amps.

" If a high voltage comes down the electrical line, the fuse element
will melt.

Are there really surges that come down the line that increase the
amperage for normally 7 to over 12?

"The tiny glass fuses are great for small items that don't draw a heavy
amount of current and blow on a regular basis. They don't perform well
outdoors and can shatter when placed in high temperatures due to its low
thermal stability."

Microwave is not used outdoors or at high temperatures.

From before
According to the label on the back "The input is 1400 watts, but it's a
220 volt device, so that's less than 7amps normally. So, 10, right?
Unless F12 in F12H250 at the top means 12 amps? " And the home.repair
people told me it did, but the web says F means fast-blow.

It's a Crystal, model wp900AP23, but no schematic could I find on the
web and the one taped inside just shows fuse, no details.

Look165

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Mar 29, 2019, 9:37:07 AM3/29/19

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I've seen no fuse in mine.

Consider the protection is outside and 16A is enough.

Phil Allison

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Mar 29, 2019, 5:30:14 PM3/29/19

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micky wrote:

>
> I thought all ceramic fuses were slo-blo, but this one is embossed
> F12H250 and some webpages say that F means fast-blow????
>

** Ceramic fuses come in all types, fast, medium and slo- blow as well as HRC.

HRC = High Rupture Current and are found in some uW ovens.

>
> Nothing I read decribes why a microwave should need ceramic or slow-blo
> (in the power part, not the high voltage part).
>

** Ceramic fuses are specified as they do not shatter when heavily overloaded.
Slow blow is needed to cope with inrush surges from the transformer, if there is one.

> " If a high voltage comes down the electrical line, the fuse element
> will melt.
>

** Absurd.

> From before
> According to the label on the back "The input is 1400 watts, but it's a
> 220 volt device, so that's less than 7amps normally. So, 10, right?
> Unless F12 in F12H250 at the top means 12 amps? " And the home.repair
> people told me it did, but the web says F means fast-blow.
>

** Single plated wire "F? fuses are in fact rather slow and tolerate brief surges of say 5 times their rating.

.... Phil

Phil Allison

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Mar 29, 2019, 5:48:14 PM3/29/19

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Phil Allison wrote:

*Correction:

** Single strand, plated wire "F" fuses of 10 amp raring or more are in fact rather slow and tolerate brief surges of say 5 times their rating.

.... Phil

tabb...@gmail.com

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Mar 29, 2019, 7:46:03 PM3/29/19

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If it's F12H250 then you need to fit a 12A F12H250 of the same size & construction type. Fuses are more of a big deal in nukes than other appliances. Don't cut corners on them.

NT

Lucifer

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Mar 30, 2019, 5:58:59 AM3/30/19

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On Fri, 29 Mar 2019 16:14:10 +0300, micky <NONONO...@bigfoot.com>
wrote:

>To recap for the scientists: What size fuse to use in a 22V microwave:

The size would be 6 mm if there was such a thing as a 22 volt
microwave.

Lucifer

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Mar 30, 2019, 6:01:00 AM3/30/19

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On Fri, 29 Mar 2019 14:37:03 +0100, Look165 <loo...@numericable.fr>
wrote:

>I've seen no fuse in mine.
>
>Consider the protection is outside and 16A is enough.

https://en.wikipedia.org/wiki/Usenet_quoting

Lucifer

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Mar 30, 2019, 6:04:18 AM3/30/19

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On Fri, 29 Mar 2019 14:30:10 -0700 (PDT), Phil Allison
<palli...@gmail.com> wrote:

> micky wrote:
>
>
>>
>> I thought all ceramic fuses were slo-blo, but this one is embossed
>> F12H250 and some webpages say that F means fast-blow????
>>
>
>** Ceramic fuses come in all types, fast, medium and slo- blow as well as HRC.
>
> HRC = High Rupture Current and are found in some uW ovens.

I had a 5 volt UPS from a Data General mini computer which had
a 200 amp HRC fuse.

Martin Gregorie

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Mar 30, 2019, 8:02:22 AM3/30/19

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On Sat, 30 Mar 2019 21:04:14 +1100, Lucifer wrote:

> I had a 5 volt UPS from a Data General mini computer which had a 200 amp
> HRC fuse.
>

Unsurprising: old computers ate power.

The CPU of 1902S mainframe I was sysadmin for in 1972 was entirely solid
state (discrete transistors) and with 32 kWords (96kB equivalent) of
ferrite core memory. That CPU used 20KW. Add in 6 tape decks, two disk
drives, printer, cardreader and a comms multiplexor and the system
consumed 40 KW when fully up and running - typical for kit in that era.

--
Martin | martin at
Gregorie | gregorie dot org

Stephen Wolstenholme

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Mar 30, 2019, 9:28:42 AM3/30/19

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I never worked on 1902S but I worked on System 4 and the largest
2900's. The current demands were very high but generally low voltage
so some engineers would work on live power supplies. Mending the 3
phase mains primary supply in the middle of the night could be
dangerous. The secondary output was much lower voltage but high
current. We kept an adjustable spanner that had been dropped onto the
5.6V DC supply. It was to remind some engineers of the power involved.
The spanner had blown like a fuse. I can't remember the current limit
but it was huge!

Steve

--
http://www.npsnn.com

Martin Gregorie

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Mar 30, 2019, 10:57:55 AM3/30/19

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No System 4 for me - only 1900, 2903 (the 2900 DFC in a different orange
box running microcode to emulate a 1900), and a fair bit of time at the
BBC writing systems for their 2900s.

Somebody working in the computer room managed to drop a short crowbar
into the BBC UPS when it had its covers off, but caught it before it did
any damage - and then had to stand there holding it while the pair of
2960s were shut down and the UPS turned off. Were you there, by any
chance?

Stephen Wolstenholme

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Mar 31, 2019, 6:49:49 AM3/31/19

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On Sat, 30 Mar 2019 14:57:53 +0000 (UTC), Martin Gregorie

I never worked on a BBC site. Most of my work was around Manchester. I
started on a LEO3 at the town hall. Then System 4 on shifts at Norweb,
NW Gas, TSB and a few other places during the night. Night calls were
often a long way from Manchester. I once got a call at about 01:00 to
drive to Bristol. When I got to Bristol the site was closed so I drove
back to Manchester. That's about 350 miles for expenses plus 7 hours
overtime at double time. That was quite a lot of money but I would
have preferred to stay in bed.

Steve

--
http://www.npsnn.com