Michael Tope wrote:
> Okay, I see what you are getting at Steve. That makes sense,
> and in fact I should be able to see it if I put an oscope on the
> line. Perhaps I will do that sometime. BTW, FWIW when I run
> the L-7 off my Honda EU2000i generator, there is very little
> change in the RMS line voltage from no load to load (much
> better regulation than off the 110V outlet in the shack). I should
> run the oscope on the Honda sometime to see how good the
> "true sine" waveform looks when its powering the amplifier.
> That should be interesting.
My snapshot does help explain why amps can be really dreadful when run from
'building yard' generators. A 'proper' alternator has dc in the field to
produce a sinewave output. If the field current holds up under load (as it
probably will with an electronic regulator) then you get a low impedance
source. Cheap gennys usually have the field fed from the output, via a
saturating inductor (or something similar), so the output waveform is far
from a sinewave; they're fine driving a motor but the source impedance is
high just when you need it to be low for a capacitor input psu.
I think I've probably laboured my point long enough now - capacitor input
psus have peak currents that are much larger than most people realise. Don't
get me started on the consequences of (I^2 x R) when you consider Ipk ....
:-)
Steve
>
> 73 de Mike, W4EF...............................
>
> ----- Original Message -----
> From: "Steve Thompson" <g8gsq@ic24.net>
> To: "Michael Tope" <W4EF@dellroy.com>; <amps@contesting.com>
> Sent: Friday, December 03, 2004 10:41 AM
> Subject: Re: [Amps] Current draw at 110 volts for SB-200 and SB-1000
>
>
>> Michael Tope wrote:
>>> Steve,
>>>
>>> I was speaking of the case where I have a brick on the key (A0).
>>> When I measured the power factor of the amp in this mode a
>>> while back, it was something like 0.80. I would agree with you
>>> that line voltage drop would be hard to measure in intermittment
>>> CW or SSB service, but in A0 (brick on key), I think its pretty
>>> straightforward. Or am I missing something?
>>
>> The high current 'gulps' I meant are the ones every line half cycle,
>> not at syllabic rate. The line voltage your meter measures tends to
>> reflect a cycle to cycle average, and doesn't indicate what happens
>> during those few ms whereas the psu feels the full effect.
>>
>> An example (imprecise, so please don't shoot me down): If your amp is
>> pulling an average of, say, 10A from the line for something
>> approaching a kW input, the charge goes into the capacitors in a
>> space of maybe 2ms during the half cycle of 8.33ms. The average
>> current during those 2ms has to be 40A, with the peak being 50, 60
>> or even higher. That sets the voltage drop that the psu suffers
>> whereas your voltmeter and lights don't react so much to the short
>> term disturbance.
>>
>> Steve
>>
>>> ----- Original Message -----
>>> From: "Steve Thompson" <g8gsq@ic24.net>
>>> To: <amps@contesting.com>
>>> Sent: Friday, December 03, 2004 12:17 AM
>>> Subject: Re: [Amps] Current draw at 110 volts for SB-200 and SB-1000
>>>
>>>
>>>> Michael Tope wrote:
>>>>> I run my Drake L-7 off a 110V drop and it seems to do fine. I get
>>>>> about 1200 watts output with 100 watts of drive. Checking it just
>>>>> now, line voltage drops from 117.7 to 111.7 VAC when I go key down
>>>>> with maximum exciter drive (about 100 watts). There is a small,
>>>>> but perceptible dimming of the lights in the shack and hallway
>>>>> (the circuit in the hallway drops about 1.5 VAC when I key the
>>>>> amplifier).
>>>>
>>>> Part of the problem is that the current the amp pulls (or tries to
>>>> pull) is not like a resistive load but is taken in big gulps for a
>>>> short period. The peak current is many (typ 5-10) times the
>>>> 'average' you work out from the dc input. The drop from this tends
>>>> not to show to its full extent on ac voltage readings and dimming
>>>> lights, but does hit the ht in the amp.
>>>>
>>>> Steve
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|