POWER SUPPLY AMPERAGE VERSES POWER DRAW

[TonyV225]

Power supply amperage verses power draw is such a confusing topic when talking to a number of people. It seems everyone has a different answer or theory all my HF radio owners manuals say 20-22 amps for 100 watts of power now I know theres extra added for a little head room so were not taxing our power supply (beating the p!$$ out of the supply).

Where is the actual truth in this and its limits? I often see or look at amplifier specs like the texas star specs or comparison chart and it hardly seems accurate and underated as far as amp draw with there amplifiers. Where is the truth in this there are formulas or equations for this but whats really the most accurate and the correct way?

 

[W5LZ]

First, there are no really accurate ways of determining amplifier output power from knowing it's input power. That has to be established for the individual amplifier, or, for it's general type if all of them are made and tuned exactly the same. Not really much chance of that though, is there. You also have to figure in the amplifier's efficiency. A typical amplifier is only about 50% efficient, give or take a few percent. Some of that input power is used by the amplifier to make the transistors or tubes work. Some of it is 'eaten' in normal losses. And then there's some small percentage that's a 'fudge factor' to account for whatever else may be 'eating' some of that input power. Nothing is 100% efficient. So basically, the output is never going to be as much as the input. So, you can figure roughly half of the input power is sort of an average that you can expect as output power. If it ever approaches 75%, you know somebody is 'playing' with numbers, just isn't going to happen, sorry 'bout that.

Part of that 'playing' with numbers deals with how 'work' is figured with alternating current. 'Pep' has no meaning as far as 'work' power is concerned. That rms or average power thingy does. I'm a lousy teacher and definitely not a text book, I would suggest finding one to see what I'm saying (the text book!). That will 'handle' the input or power supply part of all this. Won't do much for the output side of the amplifier, things sort of change with that. How do you figure 'work' with RF? Good question, tell me when you find out.
- 'Doc


Don't you just hate answers like that? Me too.

 

[TonyV225]

Well you know for example I take my Texas Star 500 if running it on 10 meters the website for texas star says I believe 45 amps or so is the max draw for amperage.

I can tell you that is not enough because 52 amps isnt enough unless they are going by a 12 watt input SSB I just never took into consideration the fact brought up about the differences in tuning between these builders or manufactures.

 

[Moleculo]

You can use Ohm's law to get you pretty close: Amp Power Output (watts) / voltage used (13.8 V typcial car or power supply) / amp efficiency (figure 50% or 0.5) = current (amperage) draw of the linear amplifier

 

[BOOTY MONSTER]

if that 52 amp power supply is this pyramid its actually a 46 amp contious power supply .
Pyramid PS-52KX Power Supply

i have a 50 amp contious power supply on mine . its a audio authority i got when circuit city went out of business .
PS2.jpg picture by BOOTY-MONSTER - Photobucket
its output limit LED ever flickers in any way with my washington getting 500 watts out of my 500v . the export i had befor would swing the amp to 575 and sometimes the led would flicker , something like a lil 1/4 second every 4 or 5 seconds . i use an astatic meter which is accurate enough for me , i couldnt afford a meter that cost more than my radio and amp combined even if i wanted one . LOL .

 

[Captain Kilowatt]

Also don't forget that when talking about CB or "10m" amplifiers you need to pay absolutely no attention whatsoever to the power output versus current draw ratings given by the manufacturer.

 

[mackmobile43]

You can use Ohm's law to get you pretty close: Amp Power Output (watts) / voltage used (13.8 V typcial car or power supply) / amp efficiency (figure 50% or 0.5) = current (amperage) draw of the linear amplifier

Yes effieciency is the name of the game as class-c offers better but at what cost? signal quality is what and at class-ab or ab1 one could easily figure the effieciency rating to drop by 15 to 20% but even with that loss the input drive level drops also extending the life of the transistor involved.

 

[Moleculo]

A class AB transistor amp is maybe 50% efficient (probably a little less), which is why I used that number. Class C will be higher/more efficient; I've seen figures thrown around as much as 65%, but I'm not sure about that. To figure out the current draw you have to input at least a rough plug efficiency number to the formula to get close. Remember, efficiency is just a measure of how much of the consumed input power is wasted as heat and other things. It says very little, if not anything about how well the amplifier actually works.

 

[W5LZ]

Don't get too obsessed with amplifier efficiency, it's just not that big of a deal. It's about as important as the efficiency of a top/middle/bottom loaded antenna. Sure, there's some difference, but it's never going to amount to much. Nothing wrong with wanting higher efficiency, but there are practical limits. Quantifying those limits in dollars is an individual thing. If you live long enough, I think you will find that having the most absolutest bestest most efficient thingy in the world only lasts for maybe a second or two. And thinking back over all that effort, you'll wonder if it was ever worth the trouble. I'll bet I can tell you what your answer will be too! A better bet would be that you'll never believe me, so why bother?
- 'Doc

 

[TonyV225]

I was looking at power suplies there are so many unregulated but frankly that $h!+ point blank scares me . However I did find a Lambda 13 volt 200 Amp supply with digital meters for $350.00 shipped until the guy p!$$ed in my cake and icecream and told me that the supply was strictly a 220Volt.

does anyone make a 150 - 200 amp supply thats regulated?

 

[Captain Kilowatt]

A class AB transistor amp is maybe 50% efficient (probably a little less), which is why I used that number. Class C will be higher/more efficient; I've seen figures thrown around as much as 65%, but I'm not sure about that. To figure out the current draw you have to input at least a rough plug efficiency number to the formula to get close. Remember, efficiency is just a measure of how much of the consumed input power is wasted as heat and other things. It says very little, if not anything about how well the amplifier actually works.

I had two differant tube type broadcast transmitters,one AM and the other FM, that both ran the finals in class C.(The AM transmitter was plate modulated by a pair of tubes running class B audio service) The best efficiency I could get out of the Harris FM transmitter using a 4CX5000A was 52% with a new tube. The Gates AM transmitter with a pair of 833C's in the finals ran about 72% efficiency. For class C, 65-70% is quite realistic if properly designed.

 

[bob85]

you would assume class c is more efficient, it should be,
i found my ampower 2x2879 to be much less efficient than any of my 2 or 4pill class ab amps including my old yaesu fl110,
maybe they are better on keydown voltages but on 14volts it has very poor efficiency,
if all you have is a 30 amp power supply then a rmitaly 2x1446 or 4x1446 will make more power on the wattmeter and a stronger signal on air,
the am400 uses the same component values/ferrite/turns ratio as other davemade clones.

 

[dudmuck]

does anyone make a 150 - 200 amp supply thats regulated?

Its possible to build, but its just not practical.
Linear supplies weigh on the order of one pound per amp. and thats probably on the light side.
For alternative there is a switching power supply, but then your talking major $$ if you dont want RFI hash everywhere.

This is why tube amplifiers are used for base amps. because the transformer is stepping up voltage instead of the other way.

The 13.8v pills are at a major disadvantage because of the high current involved. The 2nd disadvantage is the impedance transformation from an ohm or less on the collector to get to 50 ohms.

 

[TonyV225]

I dont understand how these unregulated supplies work or how it doesnt burn up what your running on it. I never thought about this deeply until I got this amplifier but it is brand new so selling or trading shouldnt be a problem.

I was just saying in my Texas Star 1600 Post that I should just sell this Amplifier and get another Amateur tube Amplifier this is more of a headache than its worth Im starting to think :w00t:

 

[BOOTY MONSTER]

you could daisy chain several power supplies or use one that can be used as a battery charger (IOTA) with a battery or two to get higher amp capacity .

IOTA Engineering DLS Series AC/DC Power Converters and Battery Chargers for 12VDC Systems

Iota Regulated Battery Chargers