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Author Topic: External Fuses For The Kenwood TH-235A HT  (Read 577 times)
N3BQA
Member

Posts: 9




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« on: July 24, 2006, 10:47:57 PM »

1. This ht on high pwr draws 1.3A at 13.8 vdc. What would  
   the appropriate amperage be for the two fuses leading  
   from the pos & neg terminals of a regulated 13.8 pwr
   supply to the above ht? Should one consider a surge  
   factor in the above estimation?

2. Should i remove or leave the six AA cells connected to
   this ht when using the external pwr supply?    
   

       
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W3LK
Member

Posts: 5644




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« Reply #1 on: July 25, 2006, 12:50:08 PM »

<< What would the appropriate amperage be for the two fuses leading
from the pos & neg terminals of a regulated 13.8 pwr
supply to the above ht? >>

Since the HT draws 1.3A on high power, then use 1.5A. If that blows on transmit, then 1.75 or 2A.

<<Should one consider a surge factor in the above estimation? >>

No, there is no "surge"

<<2. Should i remove or leave the six AA cells connected to
this ht when using the external pwr supply? >>

Depends on the HT. If there is a separate 13.8v input, you can probably leave them in. I would think the owner's manual would address both of these issues.

I'm just surprised an Extra class ham can't figure out fuse sizes when he already knows the maximum curerent draw.

73,

Lon - W3LK
Baltimore, Maryland
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
KB1LKR
Member

Posts: 1899




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« Reply #2 on: July 25, 2006, 06:17:06 PM »

In general, assuming the fuse is not at elevated temperatures (say 60-120°C) , but near 25° (77°F), one would choose a value at least 33% over the full load current (i.e. the fuse is derated 25% or operated at less than 75% of its rating) For a 1.3 A draw 1.3*1.33=1.73A so 2 Amp fuse, the next larger standard value, would be chosen to prevent nuisance blowing, yet provide short circuit protection. A 1.5 Amp fuse, on the other hand, may fail from time to time, w/o offering any real improvement in short circuit protection.  

At elevated temperature, say 100°C the fuse would be derated slightly, say 10%, so your 2Amp fuse at 100°C would behave as a 2*0.90= 1.9A fuse at room temperature; since this is still above 1.73A the 2A fuse would still be okay for you application.

For more info see: Bussmann, Littelfuse or Schurter's web pages and tech notes.
 
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WB6DGN
Member

Posts: 582




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« Reply #3 on: March 10, 2009, 09:30:16 PM »

KB1LKR,
OH, DARN!  I was going to ask W3LK to give us a few words on the derating of fuses with voltage and temperature.  Perhaps he would have also thrown in a comment or two on the time constants of the various types of fuses at their rated current and steps above/below!  I bet he could have told us a thing or two (he usually does!)  Now we're going to have to go to another site and look them up ourselves!  ShuckyDarn!
Tom DGN
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KE4DRN
Member

Posts: 3710




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« Reply #4 on: March 11, 2009, 05:18:31 PM »

hi Tom,

he is too busy posting about the other ham who
wants to build a tube amp,
even though the ham is only a tech class.

http://www.eham.net/forums/HomeBrew/6162

Or this one where he says he can't help

http://www.eham.net/forums/Misc/9183

and then some.


73 james

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W3LK
Member

Posts: 5644




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« Reply #5 on: March 11, 2009, 06:55:34 PM »

<< http://www.eham.net/forums/Misc/9183>>

And you're bitching because I wished him good luck with his project?

73,

Lon - W3LK
Naugatuck, Connecticut
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
KE4DRN
Member

Posts: 3710




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« Reply #6 on: March 11, 2009, 08:21:38 PM »

Hi Lon,

No, not at all !

Seems you check the license class of the
person asking the questions or just put them
down for asking the question!

If you're at the hamfest or meeting I know
you would not do that, am I right ?

If another guy says he likes your mobile
antenna setup, do you ask him if he is an Extra ?

Sort of like in some communist countries,

"Your Papers" !

BTW, I'm building an experimental aircraft but I
have no plans to fly it or obtain a pilots license!

73 james



Lon wrote....

I'm just surprised an Extra class ham can't figure out fuse sizes when he already knows the maximum curerent draw.

Lon wrote...

With all due respect, as a Technician, you have no SSB or RTTY privileges on 40m and you have a 200w power out limit on everything below 6 meters.

Are you planning to upgrade your license class?

Lon wrote...

I can't help, but god luck with the project.

Lon wrote...

From your profile:

"almost 270 DXCC confirmed on 11metres"

DXCC doesn't recognize 11m contacts.

Lon wrote...

I fail to see what one thing has to do with the other.

Maybe getting out of ham radio is a good thing. It will give you time to work on your grammar and other English-related skills. Smiley
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