[Elecraft] [KPA500]KPA500 power cord question

Tue May 3 17:18:54 EDT 2011

> No. The KPA500 peak demand is less from your 120 volt outlet than
> most household vacuum cleaners or window air conditioners. And,
> unless you are running a full-carrier mode, the average demand by
> your KPA500 is far  below the peak.

While the average current requirement may be less that the typical
vacuum cleaner or window air conditioner, the peak current demand
*will* be significantly higher if the KPA-500 has a capacitor input
filter in the (analog) power supply.

What Ron refers to as "peak" is a long term (multi-cycle) peak
current and that is much less than the true instantaneous peak
current in a "linear" capacitor input filter power supply.
Depending on the conduction angle of the rectifier/capacitor circuit,
instantaneous peak currents use can be many times the average current 
requirement - and significantly higher than the multi-cycle peak
current one would read on an amp meter in the supply line.  It is
the instantaneous peak current use that drives losses in the supply
wiring and thus the effective source voltage regulation while it is
the longer term currents (and duty cycle) that impact heating.

Even with a relatively low power (average current < 10A), the peak
currents can easily exceed 50A unless the power supply includes
"power factor correction".  While this will not trip breakers or
even cause heating in the wiring because of the very short duration,
with even 0.5 Ohms of resistance in the power lines, connectors, etc.
50 A peak currents can result in significant "short term" (partial
cycle) voltage drops.

Reducing the voltage drop in the supply by half is *always* a good
idea.  Using 240V instead of 120V - particularly if it is already
available - is never a bad idea and certainly worth sacrificing an
inexpensive IEC cable by cutting off the 115V plug and replacing it
with the proper 240V/15A plug (often known as an "air conditioner"
plug after the old window air conditioners that required 220V/15A).

73,

    ... Joe, W4TV

On 5/3/2011 4:39 PM, Ron D'Eau Claire wrote:
> No. The KPA500 peak demand is less from your 120 volt outlet than most
> household vacuum cleaners or window air conditioners. And, unless you are
> running a full-carrier mode, the average demand by your KPA500 is far below
> the peak.
>
> Of course, you want to consider all the various stuff you have plugged into
> the circuit you are using for the KPA500. It is a significant load at full
> peak power. It wouldn't be a good idea to share the same circuit with a
> window air conditioner, for example.
>
> Ron AC7AC
>
> -----Original Message-----
>
> Hi Clyde,
>
> Can we boil this down a bit? Would a 220/240V input get me more power
> out of the KPA-500 (vs. a 20A 110V circuit, say)? A cleaner signal?
> Less input power consumed? Anything discernible?
>
>       ~iain / N6ML
>
>
> On Tue, May 3, 2011 at 7:21 PM, Clyde Washburn<k2ue at rochester.rr.com>
> wrote:
>> Currently the nominal voltages for most US power companies is 240/120V
> single phase, although in some areas 120/208V 3-phase is
>> common, with 120V outlets being served by any one phase, and 208V circuits
> being fed across any 2 phases.  Accordingly, most US
>> appliances either have specific performance ratings that differ slightly
> for 208V vs. 240V (resistive heaters and A/C compressors
>> are a common example), or have power supply taps to accommodate either
> (common in electronic equipment).
>>
>> The major advantage of 240V operation is improved voltage regulation:  the
> same circuit, fed with the same wire (such as a common
>> 20A 12 gauge circuit), will have the same resistance in either case.  But
> since the current is roughly half at 240V, the I*R drop
>> will be half, which will be 1/4 the relative amount compared to the
> doubled voltage.  You can see that unregulated supplies will
>> perform much better, if the current is high enough for line drop to be
> noticeable.
>>
>> US plugs and receptacles are rated for either 125V (max) or 250V (max),
> and are non-mating between voltages, for safety.  However
>> 20A receptacles of ether voltage will accept 15A plugs of the same
> voltage, so the ideal hamshack receptacle for a linear is a
>> 250V/20A receptacle wired to a 240V or 208V 20A circuit, which will also
> accept 15A 250V plugs, the smallest and most common type.
>> Since 20A wiring and circuit breakers cost very little more than 15A,
> there is little point in installing 15A circuits, unless it is
>> advantageous to use existing wiring in an house or building where new wire
> installation is difficult.  Please note that if you
>> convert an existing 120V wire run to 208 or 240V, you are obligated by
> code (and common sense) to remark the white (formerly
>> neutral) wire with red paint or tape at all points of access, to identify
> as a "hot" lead.  And receptacle ratings should never
>> exceed the rating of the circuit they are on:  never use a 20A receptacle
> on a 15A circuit.
>>
>> In the specific case of the KPA500, it requires 1000VA (volt-amperes), so
> that is 8.3A at 120V, 4.8A at 208V, or 4.2A at 240V.  8.3A
>> is not a particularly heavy load for a 20A circuit, but if it is a 15A
> circuit or is also loaded with all the other hamshack gear,
>> then either a separate 120V circuit for the linear, or preferably a 240V
> circuit is a good idea.
>>
>> _____________________
>> Clyde Washburn, K2UE
>> 82 Lasalle Pkwy
>> Victor, NY 14564-9610
>> 585-317-7006
>> k2ue at rochester.rr.com
>>
>> -----Original Message-----
>> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of iain macdonnell -
> N6ML
>> Sent: Tuesday, May 03, 2011 2:21 PM
>> To: K2GN
>> Cc: Elecraft - K3
>> Subject: Re: [Elecraft] [KPA500]KPA500 power cord question
>>
>> On Tue, May 3, 2011 at 5:59 PM, K2GN<k2gn at k2gn.com>  wrote:
>>> GA,
>>>
>>> I am in the process of rebuilding my shack and planning for the future.
>>>
>>> I will order a KPA500 and want to be ready for it power wise.
>>>
>>> I want to run it on 220V as it is available in a nearby panel.
>>>
>>> Question is:
>>>
>>> The manual states for 220V operation I would need an adaptor or new
>>> plug on the power cord.
>>>
>>> Is this a choice that I have as far as wall outlet and matching plug?
>>> If so, no problem, my electrician can fix it up.
>>>
>>> If it's some special, I need specs for it.
>>
>> I think that's left as an exercise for you ... find a heavy computer power
> cord, cut the plug off, and install one that matches your
>> outlet .. or install a matching pair that you like.
>>
>> I'd be interested to hear about benefits (if any) of running the
>> KPA-500 on 220V vs 110V (in the US)......
>>
>>     ~iain / N6ML
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