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KPA100 Temp/Fan

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Jim Stoneback

KPA100 Temp/Fan

I searched the archives and didn't find anything on this, but from what I've
read, I think I may have a problem with my KPA100. When operating CW the
fan turns on high during every transmission and the heat sink gets hot to
the touch. I'm a ragchewer so my transmissions do run to several minutes
and, regardless of power setting, the fan will kick on high after several
minutes of transmitting. Fan is set to 'nor'. Sending speed ranges from
15-20 wpm. Ambient temperature in the shack is around 74F. The fan has
never kicked up to high when on SSB but I don't operate fone much, and
generally don't talk for very long when I do. The K2/100 (recent build, sn
6194, KPA100 Version F1.10) operates well in all other respects. Does
anyone have an idea what may be wrong?

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Andrew Moore-3

Re: KPA100 Temp/Fan

> When operating CW the
> fan turns on high during every transmission and the heat sink gets hot to
> the touch. I'm a ragchewer so my transmissions do run to several minutes
> and, regardless of power setting, the fan will kick on high after several
> minutes of transmitting.
...
> Does anyone have an idea what may be wrong?

I think this is normal. I had the same experience and asked about it
and in the end realized that's how it behaves. It's the primary
reason I went back to the QRP cover. Fan is just too noisy and comes
on too often. It also failed to turn off by itself after going back
into RX mode -- it took a deliberate keying event to, apparently,
force the firmware to re-evaluate the temp and disable the fan (which
of course causes a transmission and confuses the op on the other
end!). Where or not that part was normal I don't know, but it's the
way mine behaved (on two different KPA100's). I don't know which
firmware it had so don't know if that's been addressed in a newer
version.

If I remember correctly, the amp is most efficient at about 75 watts,
so operating there might help cut down the heat and delay the fan
turn-on.

You might also look into other cooling methods -- larger, slower fan;
remote fan with custom duct work; active cooling; etc.

--Andrew, NV1B
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Don Wilhelm-4

Re: KPA100 Temp/Fan

In reply to this post by Jim Stoneback

Jim,

The fan does go on and off by sensing the temperature of the heat sink
(Q3 is the sensing element).
The temperature that the fan transition occurs is fixed, but will
operate at that fixed temperature only if CAL TPA is set correctly. CAL
TPA must be set to the actual temperature of the heat sink, and that is
easily done by allowing the KPA100 to cool (an hour or more) to the
ambient temperature and setting the parameter to match the ambient
temperature (in degrees C).

If you think the fan is coming on too soon, you might try running the
fan at the Hi/Lo setting rather than normal - the fan is not very noisy
at low speed. Another solution is to add a muffin fan on top of the
heat sink to draw air away from it - the means of keeping the fan in
place can vary - if the KPA100 is not tilted, it will likely just sit
there unaided, but if tilted, some fastening device may be required.
You can see Tom Hammond's implementation at www.n0ss.net. The speed of
an external 12 volt DC fan (salvaged from a defunct PC) can be slowed by
inserting a series resistor.

73,
Don W3FPR

Jim Stoneback wrote:

> I searched the archives and didn't find anything on this, but from
> what I've read, I think I may have a problem with my KPA100. When
> operating CW the fan turns on high during every transmission and the
> heat sink gets hot to the touch. I'm a ragchewer so my transmissions
> do run to several minutes and, regardless of power setting, the fan
> will kick on high after several minutes of transmitting. Fan is set
> to 'nor'. Sending speed ranges from 15-20 wpm. Ambient temperature
> in the shack is around 74F. The fan has never kicked up to high when
> on SSB but I don't operate fone much, and generally don't talk for
> very long when I do. The K2/100 (recent build, sn 6194, KPA100
> Version F1.10) operates well in all other respects. Does anyone have
> an idea what may be wrong?
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
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> Elecraft web page: http://www.elecraft.com
>
>

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Jay Schwisow

Re: KPA100 Temp/Fan

In reply to this post by Jim Stoneback

Jim,

I run alot of CW contests and with constant CQing/exchanges you could
fry an egg on the heatsink. The existing cooling cannot keep up with
the heat generated. It looks a bit Frankenstein but I mounted (with
double back tape) a 12 volt 2.5" muffin fan on top of the heat sink. It
runs cool as a cucumber now. This is now standard operating procedure
for contests I run at 100w.

Jay - KT5E

Jim Stoneback wrote:

Jim Stoneback

Re: KPA100 Temp/Fan

In reply to this post by Jim Stoneback

Wow! Thanks for all your replies. I think I'll take the advice offered by
several responders and set the fan for 'hi/lo' and stop worrying. I can
live with the noise using headphones much of the time anyway. Just thought
it was odd. Next time I open the rig up, I'll recheck the bias to the
finals - just to be sure.

73,

Jim

Jim Stoneback wrote:

AC7AC

RE: KPA100 Temp/Fan

In reply to this post by Jay Schwisow

CONTENTS DELETED

The author has deleted this message.

David Woolley (E.L)

Re: KPA100 Temp/Fan

In reply to this post by Andrew Moore-3

Andrew Moore wrote:

> into RX mode -- it took a deliberate keying event to, apparently,
> force the firmware to re-evaluate the temp and disable the fan (which
> of course causes a transmission and confuses the op on the other

I suspect this is because the AuxBus and peripheral microcontrollers are
shut down in receive mode to prevent the pickup of digital noise.

--
David Woolley
Emails are not formal business letters, whatever businesses may want.
RFC1855 says there should be an address here, but, in a world of spam,
that is no longer good advice, as archive address hiding may not work.
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