Measured Power Consumption of the Elecraft K3/100

(To run QRP or QRO on Batteries?)

Les Gasser, W9XC

V. 1.2

When contemplating the prospect of operating portable with batteries, it's useful to have a clear idea of power consumption choices so you can optimize both signal effectiveness and operating time. Most rig specification sheets show power requirements at full tramsmit output. Sometimes receiver power consumption figures are listed as well. But it is a bit difficult to find power consumption figures at fine-grained intermediate output power levels.

On the Elecraft K3 it's very easy to change output power in small increments by simply twisting a front-panel knob.

Accordingly, I hooked up my K3/100 to an ammeter and measured its total transmit power consumption in CW mode, at a variety of output power level settings up to 50 watts. The results are reported below.

A couple of items are worthy of note:

Clifton Labs has reported on its measurements of the power efficiency of the K3 (i.e., RF output power for given DC input power). These are actual measurements of output power, not just the K3's own reported power settings that I was able to use. They also consider efficiency at a variety of different input voltage levels. This is useful when considering different types of power sources or drops in battery voltage with charge levels.

W1PNS, WA0ITP, and AB8XA have provided a very useful spreadsheet tool for computing battery capacity needs and expected battery usage time (see their "Battery Estimator Spreadsheet"). The figures below provide alot of useful information about the K3 that can be used in conjunction with that spreadsheet when planning portable battery powered (or otherwise power-limited) operations. K5DCM has adapted this calculator for online use on the web and it's available at the 4 States QRP Club site here.

Results

Receive Current: 1.12 A

K3 Power Setting vs Current Consumption

Table of Data: K3 Output Power Setting vs. Total Current Consumption (Transmit), on 40 Meters

Power Output Setting (Watts) Current Consumption (Amperes)
1W 2.5A
3W 3.0A
5W 3.3A
7W 3.6A
10W 4.17A
11W 4.3A
12W 4.3A
13W 8.75A
15W 9.2A
20W 10.1A
30W 11.9A
40W 13.25A
50W 14.5A