[Amps] How do you - powering a SS amp with a capacitor?

[chas]

ok, Vic
I have learned a lot from this discussion and  I am glad we got into it as 
there is a lot of interest in it among the newbies and those who are barely 
QRO literate, as it were.  I believe that a 1 or 2 farad cap would be useful 
only to supplement low capacity batteries and that the money spent on same 
would probably be better invested in another pair of golf cart batteries - 
with these two packs wired appropriately, we would have double the capacity 
of one battery of the matched set of 4 and double the voltage of two of these 
batteries.  so, the problem becomes one of needing to talk with intellipower 
and find out if that 9280 can charge all that lead <G>.
otoh, a cap would be useful if the discharge rate is low and slow to allow it 
to charge up during a low duty cycle.

thanks again... don't want to kill this as I am always ready to learn more if 
anyone has more sources of articles. or discussion. I was told a year or so 
ago, to go to an audio store and get an education on the linear amp power 
supply system and that is still apparently, good advice.

I will contact progressivedyn by telephone tomorrow and see what my 
limitations are isfa the number of batteries which can be charged.

I would still like to see a PP presentation of an installation of a Cube/SS 
amp both in mobile and in base station.  Finally - I am sure that I will be 
coming back to the fine folks here in the future for more advice.  I am an 
old retired man who has played with HF over the years but never with QRO 
until the last couple of years.

73
chas, k5dam


Vic K2VCO wrote:
> On 8/9/2010 10:50 AM, chas wrote:
> 
> The capacitors are available up to 1 to 5 farads. Initially they charge 
> in a very short time, depending on the resistance of the wire between 
> the power supply and the capacitor (which should be right at the amp). A 
> capacitor like that looks almost like a dead short when it's discharged, 
> so the cable can't be too fat (too low resistance) or it might keep a 
> switching supply from turning on.
> 
> When you are operating normal ssb or cw even if the peak power is 90A, 
> the amp is only drawing this much on voice peaks or when the key is 
> down. This is called a "duty cycle" of less than 100%. So the capacitor 
> can charge between syllables or keyed elements and then supply power on 
> the peaks. In effect it evens out the demand of the amplifier, so maybe 
> you would only need a 22 amp supply. The supply would be 'working' 100% 
> of the time that you were transmitting, because it would either be 
> supplying power to the amp or charging the capacitor. When you are in 
> receive mode, of course, the cap would stay charged and not draw any 
> current.
> 
> For example, the duty cycle of CW is about 50%. So if you had an 
> amplifier that needs 100A key-down, then you could theoretically get by 
> with a capacitor and a 50A supply -- as long as you didn't hold the key 
> down for more than a second or two.
> 
> The SSB duty cycle ranges from about 35% with no compression to 60% or 
> more with heavy compression.
> 
> But note that if you were transmitting FM, RTTY, PSK or AM the power 
> demand is continuous. The duty cycle is 100%. So in this case the 
> capacitor wouldn't help because it would have no time to charge up.
> 
> You can't replace a battery with a capacitor of this size because it 
> could only supply 90A for maybe half a second (that's a lot of current). 
> But it could make it possible to use a smaller power source and smaller 
> cables.
> 
> If you are interested in doing this, the place to go is one that builds 
> custom audio amps for vehicles. An SSB linear has very similar 
> power-demand characteristics to an audio amplifier.
> 
>>
>> Vic, what is the recharge time on the capacitors? is there a measuring
>> meter for a tell tale?
>>
>> Not sure what the discusion about 22A power supplies was about... the
>> Cube requires a min of 40a and a max of 90A.
>>
>> and yes, I am really looking forward to attaching #4 to the front panel
>> of the Cube... there is space for lugs not to exceed a MAX of .5" in
>> width. otherwise, it it off to a vise and a file <G>.
>>
>> thanks for your input. I am sure I will be hitting on you more in the
>> future.
>>
>> 73
>>
>> chas, k5dam
> 
> 


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chasm at texas.net   k5dam  Houston, TX

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