[Elecraft] K3 - small power supply 110-240VAC
Joe Subich, W4TV
lists at subich.com
Wed Aug 18 16:49:42 EDT 2010
> That's interesting. I have a RM 70 that has been turned on for
> over 15 years with no problems and a RS-35 for 10 years w/o a
> problem. Rock Solid.
The RM-35 (linear) supply is my absolute favorite for powering
a 100 W 13.8V transceiver. If it is an older unit with the captive
cord, I would recommend removing the MOV that is connected from
line to Neutral and the bypass capacitor connected from neutral to
ground. The capacitor does not appear to be rated for line voltage
and the MOV is in circuit even when the supply is turned off. Both
of those concern me as matters of safety.
73,
... Joe, W4TV
On 8/18/2010 12:55 PM, Phil LaMarche wrote:
>
> That's interesting. I have a RM 70 that has been turned on for over 15
> years with no problems and a RS-35 for 10 years w/o a problem. Rock Solid.
>
> Phil
>
>
> Philip LaMarche
>
> LaMarche Enterprises, Inc
> Phil at LaMarcheEnterprises.com
> www.LaMarcheEnterprises.com
>
> 727-944-3226
> 727-937-8834 Fax
> 727-510-5038 Cell
>
> www.w9dvm.com
>
> K3 #1605
>
> CCA 98-00827
> CRA 1701
> W9DVM
>
>
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of george fritkin
> Sent: Wednesday, August 18, 2010 12:45 PM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 - small power supply 110-240VAC
>
> I have several of the MFJ-4125 supplies and several of the ASTRON 20 and 35
> amp models. The only ones I have trouble with have been the ASTRONs.
> Random failures even when not under load. Go figure. MFJs....rock solid.
> George, W6GF
>
>
>
>
> --- On Wed, 8/18/10, K4IA at aol.com<K4IA at aol.com> wrote:
>
> From: K4IA at aol.com<K4IA at aol.com>
> Subject: Re: [Elecraft] K3 - small power supply 110-240VAC
> To:
> Date: Wednesday, August 18, 2010, 9:37 AM
>
> I've used the Gamma on PSK at 30 watts and CW at 100w and no one complained
> (I realize that only means no one complained). I may have been pushing the
> envelope but the Gamma met my needs for a small lightweight portable
> supply. I wouldn't use it full time in the shack when there are other more
> robust choices.
>
> Buck
> k4ia
> K3 #101
>
> In a message dated 8/18/2010 11:57:34 A.M. Eastern Daylight Time,
> lists at subich.com writes:
>
>> *Gamma Research further hedges their rating by adding a footnote to
>> their spex that "Output power should be limited to 25 or 300 watts
>> during tune-up or other prolonged key-down operation." At
>> 13.8 VDC that means the supply should not be expected to provide more
>> than 2A continuous!
>
> With a less than 50% DC to RF efficiency for most solid state rigs
> (K3 is 36% based on 20A @13.8V for 100 W output), 25 or 30 Watts output
> would be close to 5 Amps @ 13.8V assuming 40% efficiency.
>
> 73,
>
> ... Joe, W4TV
>
>
> On 8/18/2010 11:39 AM, Ron D'Eau Claire wrote:
>> Quite true Joe, and that's why it's important to note how the supply
>> is rated.
>>
>> If you're talking about the Gamma HPS1a, it's rated at only 5 amps
>> continuous* and they do not offer an ICAS rating. Instead they say it
> will
>> handle 22 amps peak at 25% duty/sec., which I interpret to mean no
>> more
> than
>> 22 amps for up to 250 milliseconds during any 1 second interval.
>> Clearly that's useless for supplying anything but SSB voice
>> modulation, and I'd
> be
>> concerned with using it with any degree of compression at that. I'd
>> never expect it to support RTTY or FM with the K3 above 10 watts RF
>> output
> where
>> the current demand exceeds the 5 amp rating of the HPS1a.
>>
>> By comparison the MFJ-4125 with its 22A continuous, 25 A peak rating
> should
>> allow you to put a brick on the key at 100 watts with *most* K3s
>> feeding
> a
>> low SWR. K3's can be well with in factory spec's and show a variation
>> in current demand of a few amps at 100W RF out from rig to rig and
>> band to
> band
>> and, of course, the SWR has a big effect on the current needed.
>>
>> As I noted, with my K3 if I were to run a 100% duty cycle mode like
>> RTTY
> or
>> FM and planned to transmit more than 5 minutes at a time, I might
>> dial
> back
>> the RF output power 1 or 2 dB to keep the Astron 20A within its CCS
> rating.
>>
>> Ron AC7AC
>>
>> *Gamma Research further hedges their rating by adding a footnote to
>> their spex that "Output power should be limited to 25 or 30 watts
>> during
> tune-up
>> or other prolonged key-down operation." At 13.8 VDC that means the
>> supply should not be expected to provide more than 2A continuous!
>>
>> -----Original Message-----
>> > I run my K3 from an Astron 20A with no problems at all. The 20A
>> > is rated at 20A Intermittent Commercial and Amateur Service
>> (ICAS)
>> > and 16A continuous commercial service (CCS).
>>
>> Ah, but there is a significant difference in the rating between a
>> linear supply (your Astron RS-20) and a switching supply like the
>> MFJ-4125 or similar. The Astron is rated for average current and
>> duty cycle ... it can almost certainly provide more than 20A on short
>> peaks ... the 20A rating is based on heating of the transformer and
>> regulator transistors.
>>
>> A switching supply is generally rated for CCS with peak current
>> rating based on the energy storage in the capacitors (how much
>> current can be drawn before the output drops too low) and the average
>> current based on the capacity of the switching circuit to keep the
>> capacitor charged (current rating of the inductor, transformer, and
>> switching devices).
>>
>> A prime example of the peak/average issue is the Gamma supply.
>> It does not even tolerate full power CW well at slow speeds and falls
>> apart completely at 100 W (even 50 W) RTTY because of the
>> "continuous" current limitations.
>>
>> The K3 is quite happy with a 25A peak / 20-22A continuous switching
>> supply. Since a linear supply generally has sufficient energy
>> storage in the filter cap because of the need to work with a much
>> lower ripple voltage than a switcher, a "20A" linear supply can
>> usually supply the same brief 25A peaks (dynamic load) within the
>> heating limits of 20A (average) ICAS service depending on the design
>> of the regulator (current limiting).
>>
>> 73,
>>
>> ... Joe, W4TV
>>
>>
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