I got a silver eagle 200 linear, and was wondering how big of a power supply i would need to run this on high power. Thanks to anyone that can help
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amp help
- Thread starter bluestallion
- Start date
Ohms law.
200w / 12vdc = 16.666666 amps
For safety, you'd probably want a 20 amp power supply.
I'd actually go past that, and recommend a 25 or 30 amp power supply, so you've got room for tinkering / expansion.
That would work if the amp was 100% efficient. Typical efficiency is around 50-55% with 60% being absolute best case so figure 200w/12 volts X 55%= 30 amps peak for 200 watts output.
guess my 18amp power supply aint gonna be big enough.:blink: saw a 36amp power supply on ebay. guess gonna have to spend some money:redface:
Thanks for adding efficiency to the mix. Double the amperage you THINK you'll need is always a safe bet too!
You should check yours too... Wait, you didn't do any?
What doesn't add up?
200w/12 volts= 16.67 amps
16.67 amps X 55% eff.= 30.3 amps. Sounds right to me. My 100 watt radio requires about +/- 16 amps on average.
Remember that multiplying by 55% efficiency is actually dividing by 0.55.
Toll_Free
Well-Known Member
You almost got it right.
Ohms law, then add 30-40 percent on top to account for inefficiencies in the amplifier.
Figure 15-20A per transistor.
OR, another way to do it is before you do ohms law, take your Pout, multiply it by 1.5, then do your ohms law, and you'll have a real INPUT power rating.
--Toll_Free
--Toll_Free
... and then if you're smart, you'll add on another 10 - 20% to keep from being just barely adequate. Then you get into how power supplies are typically advertised. The usual quoted amp rating is for surges, not for continuous service (ICS and CCS ratings). Ask what the CCS rating is, that's the one you need to pay attention to.
It never hurts to have more than you need, and will always hurt to have less than you need. This really is one of those things where 'bigger is better' fits.
- 'Doc
It never hurts to have more than you need, and will always hurt to have less than you need. This really is one of those things where 'bigger is better' fits.
- 'Doc
Toll_Free
Well-Known Member
Toll_Free
Well-Known Member
The 20 amps per transistor rule of thumb will certainly insure you purchase a big enough power supply. This rule really only applies to single ended RF stages where each 120 watt transistor may draw 20 to 25 amps max for a 2SC2879. The situation is quite different in most amps where you have pairs of transistors operating in push pull. In a push pull bank of two 2SC2879 transistors it is not possible for it to draw 40 amps because only one transistor is actually working at any given time (excluding slight bias current if any). In fact if you reach over 25 amps on a push pull pair of these transistors one is almost certain to fail. Most HF radios that used a pair of 2SC2879 were only fused at 25 amps. About 5 amps for the radio and drivers with 20 amps for the pair of finals.