Cambridge Fuse Question

[Brian Iten]

I am in the process of renewing my instrument panel
and want to install a fuse or breaker on the panel
for my 302 and model 20. I have looked in the appropriate
manuals for the proper fuse size but can not find anything.
Can anyone help me with this?
Thanks
Brian
MB1

[cernauta]

Brian Iten > wrote:

>. I have looked in the appropriate
>manuals for the proper fuse size but can not find anything.
>Can anyone help me with this?

Hi,

1 Amp is usually fine, and easily available.

Aldo Cernezzi

[Greg Arnold]

cernauta wrote:
> Brian Iten > wrote:
>
>
>>. I have looked in the appropriate
>>manuals for the proper fuse size but can not find anything.
>>Can anyone help me with this?
>
>
> Hi,
>
> 1 Amp is usually fine, and easily available.
>
> Aldo Cernezzi

The 302 manual says the instrument uses 900 mA when hooked to an Ipaq
with backlight on, so a 1 amp fuse might be a bit small.

[Paul Remde]

Hi,

Make sure it is a "Slow Blow" fuse.

1 A for the GPS-NAV and 2 A for the 302 would be a good start.

Paul Remde

"Greg Arnold" > wrote in message
news:oFfCd.38262$8e5.14139@fed1read07...
> cernauta wrote:
>> Brian Iten > wrote:
>>
>>
>>>. I have looked in the appropriate
>>>manuals for the proper fuse size but can not find anything.
>>>Can anyone help me with this?
>>
>>
>> Hi,
>>
>> 1 Amp is usually fine, and easily available.
>>
>> Aldo Cernezzi
>
> The 302 manual says the instrument uses 900 mA when hooked to an Ipaq with
> backlight on, so a 1 amp fuse might be a bit small.

[Greg Arnold]

Why "slow blow"? I am pretty sure my gliders always came with "fast
blow" fuses.


Paul Remde wrote:
> Hi,
>
> Make sure it is a "Slow Blow" fuse.
>
> 1 A for the GPS-NAV and 2 A for the 302 would be a good start.
>
> Paul Remde
>
> "Greg Arnold" > wrote in message
> news:oFfCd.38262$8e5.14139@fed1read07...
>
>>cernauta wrote:
>>
>>> Brian Iten > wrote:
>>>
>>>
>>>
>>>>. I have looked in the appropriate
>>>>manuals for the proper fuse size but can not find anything.
>>>>Can anyone help me with this?
>>>
>>>
>>>Hi,
>>>
>>>1 Amp is usually fine, and easily available.
>>>
>>>Aldo Cernezzi
>>
>>The 302 manual says the instrument uses 900 mA when hooked to an Ipaq with
>>backlight on, so a 1 amp fuse might be a bit small.
>
>
>

[Paul Remde]

Hi Greg,

I can't say I'm an expert on fuses. I use slow blow fuses because they will
blow plenty fast if there is a short circuit and they allow for a short
period of higher current flow. That is nice because the GPS-NAV and 302
have internal capacitors (I believe) to help ride through very short power
losses such as when switching between 2 glider batteries (a very nice
feature not found in many soaring instruments). The capacitors cause the
units to have a slightly high inrush current when power is first applied.

That is my 2 cents. Can anyone express agreement or concern with my
suggestion?

Thanks,

Paul Remde
Cumulus Soaring, Inc.
http://www.cumulus-soaring.com

"Greg Arnold" > wrote in message
news:WbjCd.38296$8e5.30997@fed1read07...
> Why "slow blow"? I am pretty sure my gliders always came with "fast blow"
> fuses.
>
>
> Paul Remde wrote:
>> Hi,
>>
>> Make sure it is a "Slow Blow" fuse.
>>
>> 1 A for the GPS-NAV and 2 A for the 302 would be a good start.
>>
>> Paul Remde
>>
>> "Greg Arnold" > wrote in message
>> news:oFfCd.38262$8e5.14139@fed1read07...
>>
>>>cernauta wrote:
>>>
>>>> Brian Iten > wrote:
>>>>
>>>>
>>>>
>>>>>. I have looked in the appropriate
>>>>>manuals for the proper fuse size but can not find anything.
>>>>>Can anyone help me with this?
>>>>
>>>>
>>>>Hi,
>>>>
>>>>1 Amp is usually fine, and easily available.
>>>>
>>>>Aldo Cernezzi
>>>
>>>The 302 manual says the instrument uses 900 mA when hooked to an Ipaq
>>>with backlight on, so a 1 amp fuse might be a bit small.
>>
>>

[Don Hammer]

>>>. I have looked in the appropriate
>>>manuals for the proper fuse size but can not find anything.
>>>Can anyone help me with this?


Seem to remember from A&P school that a fuse is there to protect the
wire and not the component. If you know the current draw of the
component, AC43.13-2 will help you with wire size needed and the
recommended fuse size for that wire. On the same note, your
instructions probably call for a particular wire size. Use the fuse
recommended for that size wire.

I'm on the road, or I'd look it up for you. Anyone else have a copy
of the AC?


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[Tony Verhulst]

> Seem to remember from A&P school that a fuse is there to protect the
> wire and not the component.

this is certainly true in an automobile because the cost of replacing
the wiring may be much more than the cost of replacing the component. In
sailplanes, the wiring is trivial to replace and I choose to protect the
expensive component instead.

Tony V.

[Eric Greenwell]

Tony Verhulst wrote:
>
>> Seem to remember from A&P school that a fuse is there to protect the
>> wire and not the component.
>
>
> this is certainly true in an automobile because the cost of replacing
> the wiring may be much more than the cost of replacing the component. In
> sailplanes, the wiring is trivial to replace and I choose to protect the
> expensive component instead.

When you protect the wiring, you are protecting the "expensive
component" - the glider! A wire fire is always exciting, as the smoke
creeps out around the edges of the panel... But practically speaking, a
fuse that protects the 302 will also protect the wiring, unless you are
using _much_ smaller wire than normal. I vaguely recall that the 302 has
an internal self-resetting fuse - a call to Gary K at Cambridge would
discover the truth.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

[m pautz]

Greg Arnold wrote:
> Why "slow blow"? I am pretty sure my gliders always came with "fast
> blow" fuses.
>
>
> Paul Remde wrote:
>
>> Hi,
>>
>> Make sure it is a "Slow Blow" fuse.
>>
>> 1 A for the GPS-NAV and 2 A for the 302 would be a good start.
>>
>> Paul Remde
>>
>> "Greg Arnold" > wrote in message
>> news:oFfCd.38262$8e5.14139@fed1read07...
>>
>>> cernauta wrote:
>>>
>>>> Brian Iten > wrote:
>>>>
>>>>
>>>>
>>>>> . I have looked in the appropriate
>>>>> manuals for the proper fuse size but can not find anything.
>>>>> Can anyone help me with this?
>>>>
>>>>
>>>>
>>>> Hi,
>>>>
>>>> 1 Amp is usually fine, and easily available.
>>>>
>>>> Aldo Cernezzi
>>>
>>>
>>> The 302 manual says the instrument uses 900 mA when hooked to an Ipaq
>>> with backlight on, so a 1 amp fuse might be a bit small.
>>
>>
>>
>>


Slow blow is usually used for motors, where the initial current flow
greatly exceeds normal operation. For electronics, the general rule is
a fast blow fuse. All electronic equipment have capacitors in the power
supply that cause a greater inrush. I am not sure if the extra size
of the capacitors of the 302 would cause an inrush current excessive
enought to warrent the need of the slow blow. Maybe someone else can
provide some emperical test results. The general rule for the size of a
fuse is twice the normal current flow.

The purpose of a fuse is to keep the wire from burning if there is a
short. A fuse doesn't do a whole lot for protecting the equipment. If
there is an internal short in the equipment, the damage to the equipment
has already been done. The equipment fuse simply protects the internal
wiring, or circuitry that leads the the failed component.

That is why wiring fuses, or breaker panels are at the power source.
There should be a fuse right at the battery. The fuse wouldn't help if
the battery is behind the seat, and the first fuse is behind the panel.
With that arrangement, a frayed wire at the panel would create a fire
between the battery and the panel. This main fuse, located at the
battery, is sized for the gauge of wire that leads from the battery to
the distribution panel. The distribution panel breakers should be sized
to the wire that leads to each piece of equipment. It is ok to make
that fuse smaller than the wire size dictates, and size the fuse based
on the current draw of the equpment.