KPA800/1500 Power Question

[Jim Harris-4]

Well, just to complain a little the KPA800 was not
shown to the regular attendees at the Elecraft booth
at Dayton.  Darn, really wanted to eyeball it!!  I
hope my money is as good as that of the next guy.  I
was even considering how to squeeze it into my budget.

Now my real question.  Does anyone know what the AC
power requirements are for both models.  I'm bringing
more power into my shack this summer and it would be
great to know what power is required.  I've heard a
figure of 70+ percent efficiency but my thinking is
closer to 40-50 percent.

Thanks and have a great day!

Jim, AB0UK
K2 #4787


               
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[Vic K2VCO]

Jim Harris wrote:

> Now my real question.  Does anyone know what the AC
> power requirements are for both models.  I'm bringing
> more power into my shack this summer and it would be
> great to know what power is required.  

I don't know the actual power requirements, Jim, but I would expect
overall efficiency of around 50%, taking into account the power supply
and amplifier efficiency.  However, if you are installing ANY high power
amplifier, it's generally thought that a 20-amp 240V circuit is
appropriate.  This is probably more than you will need for a KPA800,
which would probably work fine with 15 or perhaps even 10 amp service at
240V, but (depending on the length of the line to your service entrance)
it probably means no. 12 wire, which is not a big deal.  An electrician
can tell you what you need to do to meet code in terms of wire size,
type of conduit, type of receptacles, etc.

What I did was install 20 amp breakers and use no. 10 wire to ensure the
minimum voltage drop under load.  I brought out 4 wires:  two hots, one
neutral, and one ground.  The neutral is ONLY connected to the ground at
the service entrance, noplace else.  Most amplifiers only need the two
hot leads and ground (there are exceptions).  I use the hot-to-neutral
connections to provide two 120v circuits for other shack equipment.

I would not run a 1KW amp on a 120v line if I could avoid it, due to the
greater voltage drop that would be incurred.  I understand that the
KPA800 is capable of 1000w or more output on CW (it's limited to 800w on
SSB due to increased IMD at higher power levels).

--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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[Bill Coleman-2]

On May 26, 2005, at 11:16 AM, Jim Harris wrote:

> Now my real question.  Does anyone know what the AC
> power requirements are for both models.  I'm bringing
> more power into my shack this summer and it would be
> great to know what power is required.

While I have no idea exactly what power level is required, typical  
amplifiers require enough power to be worthy of a 240v circuit. A 15-
amp 240v circuit should provide more than enough AC power to run just  
about any amplifier.

A typical 15-amp 120v circuit is only good for 1800 watts. The KPA800  
would need to have an overall efficiency of 44%, and the KPA1500  
would need 83%. The latter is not likely, and the former seriously in  
doubt.

I've had two shacks in two different houses. While I've never owned  
an amplifier, I've always wired in a 15-amp 240 volt circuit for just  
this purpose -- in case I decide to get an amp one day....

Bill Coleman, AA4LR, PP-ASEL        Mail: [hidden email]
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901

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[Bill Coleman-2]

On May 26, 2005, at 12:33 PM, Vic Rosenthal wrote:
>
> I don't know the actual power requirements, Jim, but I would expect  
> overall efficiency of around 50%, taking into account the power  
> supply and amplifier efficiency.  However, if you are installing  
> ANY high power amplifier, it's generally thought that a 20-amp 240V  
> circuit is appropriate.

15-amp service is probably sufficient.

>   This is probably more than you will need for a KPA800, which  
> would probably work fine with 15 or perhaps even 10 amp service at  
> 240V, but (depending on the length of the line to your service  
> entrance) it probably means no. 12 wire, which is not a big deal.  
> An electrician can tell you what you need to do to meet code in  
> terms of wire size, type of conduit, type of receptacles, etc.

NEC requires 12-2 for a 20 amp circuit, 14-2 for a 15 amp circuit.

> What I did was install 20 amp breakers and use no. 10 wire to  
> ensure the minimum voltage drop under load.  I brought out 4  
> wires:  two hots, one neutral, and one ground.

Why would you need a neutral? On a 240v circuit, there's only three  
connections - both hot sides and ground.

>   The neutral is ONLY connected to the ground at the service  
> entrance, noplace else.  Most amplifiers only need the two hot  
> leads and ground (there are exceptions).  I use the hot-to-neutral  
> connections to provide two 120v circuits for other shack equipment.

I would not do this. I would run a single 240 volt circuit for the  
amp. If you need other circuits, you can run a separate 120 volt runs  
for them. You really shouldn't have offset neutral runs away from the  
panel like that. I'm pretty sure that's not to code. (Consider what  
would happen if the neutral line from the panel to your 120v circuits  
should open in that case)

In my current basement shack (which I wired myself), I have two  
separate 120v (14-2) circuits feeding a total of 10 outlets (with  
GFI), a separate 240v (14-2) circuit for the (future) amp, and a  
forth circuit that feeds the lighting (which is shared with another  
room). (Its generally good practice to run lighting and outlet  
circuits separately)

> I would not run a 1KW amp on a 120v line if I could avoid it, due  
> to the greater voltage drop that would be incurred.  I understand  
> that the KPA800 is capable of 1000w or more output on CW (it's  
> limited to 800w on SSB due to increased IMD at higher power levels).

Agreed. A 15-amp 240v circuit should do it, or you can go to 20-amps.  
(It is sometimes easier to find a 20-amp dual-gang breaker than a 15-
amp. Size the breaker according to the wiring used)

Bill Coleman, AA4LR, PP-ASEL        Mail: [hidden email]
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901

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[N2EY]

In a message dated 5/26/05 12:38:05 PM Eastern Daylight Time, [hidden email]
writes:


> , it's generally thought that a 20-amp 240V circuit is
> appropriate.  This is probably more than you will need for a KPA800,
> which would probably work fine with 15 or perhaps even 10 amp service at
> 240V, but (depending on the length of the line to your service entrance)
> it probably means no. 12 wire, which is not a big deal.  

General rule for house wiring:

#14 for up to 15 amps
#12 for up to 20 amps
#10 for up to 30 amps

You can use heavier wire for less drop. The cost of the wire is usually
insignificant compared to the cost of installing it.

---

Many amplifiers have a dual-primary transformer whose windings can be
connected in series for 240 and in parallel for 120. If you ever use one of these, do
NOT connect the neutral to the point where the two windings are connected in
series - just connect the outer ends.

73 de Jim, N2EY
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