Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Calculate transceiver amp draw  (Read 2199 times)
KC8MTV
Member

Posts: 2


WWW

Ignore
« on: October 18, 2017, 06:32:30 AM »

When I see radio specs such as the Yaesu FT-857D that say:
Power Requirements:
DC 13.8V ±10 %, Negative Ground
Current Consumption:
Receive (Squelched): 0.55A,
Receive (Max. Audio): 1A
Transmit: 22A (@ 100W RF output)

How is the 22A calculated, what is the formula?
Logged
M0GVZ
Member

Posts: 339




Ignore
« Reply #1 on: October 18, 2017, 06:53:40 AM »

There is no formula. You cannot use P/V=I applying it to the transmitted power from the PA because the PA is not the only part of the radio and it is also not operating at the voltage of the input.

It is calculated by them putting it on a test bench, transmitting into a dummy load at max power and measuring the current drain.
Logged
SWMAN
Member

Posts: 1066




Ignore
« Reply #2 on: October 18, 2017, 08:12:12 AM »

 My TS 570 says the same ratings but never ever goes up to the listed 22 amp current draw. Even on FM or CW key down at 100 watts into a dummy load it shows about 17 or 18 amps.
Logged
G8JNJ
Member

Posts: 655


WWW

Ignore
« Reply #3 on: October 18, 2017, 08:50:49 AM »

Hi,

The current draw depends upon the supply voltage and the overall transceiver efficiency, which varies from band to band. The main factors being the power amplifier efficiency and the load it is feeding.

The manufacturers will generally give a worst case figure, but you need to allow some margin if you are choosing a power supply to use with it.

Some transceivers also draw a high inrush current for a fraction of a second when first powered up, this can sometimes be problematic with some brands of power supply, causing the PSU over current trip to operate.

If your transceiver is drawing much less current than the manufacturers specification, it could be that the fuses in the DC power leads are not making good contact and have a significant voltage drop across them. This may result in the transceiver producing less than the specified RF output.

Regards,

Martin - G8JNJ



Logged
KC4ZGP
Member

Posts: 1637




Ignore
« Reply #4 on: October 18, 2017, 02:00:37 PM »


Transceiver amperes draw.

Simple. Put an ammeter in series at the D.C. power supply connection. As you do different things
with the transceiver, you'll see the amperage go up and go down. Even increasing the audio will
draw more current.

But, most handheld ammeters have a 10 ampere capability. Exceed that and fuse blows. If you
place ammeters in parallel, add each reading for total current drawn.

Kraus
Logged
K0UA
Member

Posts: 1339




Ignore
« Reply #5 on: October 18, 2017, 02:06:51 PM »

Most 100 watt class transcievr seem to suck up almost 4 amps of current before you say your first word in SSB mode .  Part of it is low level stages but a large part of it is final bias current.  This is why 100 watt class rigs are not very efficient when turned down to 5 watts.  That 45+ watts of input power is used at 5 watts or a hundred. QRP rigs that top out at 5 watts are much more efficient because thier bias current is measured in milliamps not amps.
Logged
K4JJL
Member

Posts: 814




Ignore
« Reply #6 on: October 18, 2017, 02:46:12 PM »

You just figured out the difference between input power vs. output power.  Output is roughly 50-70% of input due to inefficiencies (heat generation).
Logged
WA3SKN
Member

Posts: 6490




Ignore
« Reply #7 on: October 21, 2017, 03:37:02 PM »

They probably just measured it.
73s.

-Mike.
Logged
KE2KB
Member

Posts: 633




Ignore
« Reply #8 on: October 21, 2017, 05:04:55 PM »

Don't have an ammeter that can measure 20+ amps?
Get a 0.05 ohm 20 Watt resistor and put it in series with the DC power lead. Measure the voltage across the resistor and do the math.
Now let's see if one can actually buy a 0.05 ohm 20 watt resistor... checking Mouser... yes, you can.
Go here: https://www.mouser.com/Search/Refine.aspx?Keyword=0.05+ohm+power+resistor
Maybe one of the 50 micro-ohm resistors would be better. With the .05 ohm you get a 1V drop @ 20A. That could be too much for the rig, but I don't think so - especially if you set the output of your supply to 13.5V.
Use the 50 micro ohm and @ 20A you get 20mV. That's a nice shunt.
These resistors aren't expensive. Under $20 each.
Here's another shunt at Mouser: https://www.mouser.com/ProductDetail/Murata/3020-01096-0/?qs=%2fha2pyFaduiOXo9Pw6E53GmhwkfS3l%252beuVrKFnez3pVRBsGkSXs2gw%3d%3d
Logged
K6AER
Member

Posts: 4663




Ignore
« Reply #9 on: October 21, 2017, 05:23:33 PM »

The transceiver will draw 4-6 amps wither it puts out 1 watt of 100 watts just for operational overhead. Then the output amplifier and driver will ramp up amperage depending on the output power. Their is no formula for this for it depends on the design of the radio. Most HF transceivers will draw 18 to 22 amps for 100 watts out. The higher the supply voltage the lower the current draw.
Logged
KC4ZGP
Member

Posts: 1637




Ignore
« Reply #10 on: October 22, 2017, 05:33:15 AM »



Ron and Wendy Whiner here.

What's a resistor?

Do the math?



Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!