Power calcs and simple charging mod

[m0bmn]

HI all

 

I have just about finished upgrading my K1 now (4 band module and backlight)

The current drain is about 65-75mA ,depending on volume setting about 70mA
for normal listening.

 

I have fitted 2400mA cells that just fit .

 

I have checked the current drain at 4 watts from these cells and it seems
about 1000mA (1Amp)

 

So I have worked the following out but would just like a check done

 

Irx = 60

Itx=1000

Tx duty cycle 50% (since CW)

 

Ratio tx/rx  25%

 

So in one hour I would be in tx mode for 15mins drawing 1000mA but since
it’s at 50% duty that’s 500mA for 15mins

Which works out to 250mA for 30 mins or 125mA for 1 hr

 

Plus the rx drain of say 70mA so that’s 70mA/Hrs

 

Total drain then is 125+70=195mA/Hr

 

Since I have 2400mA/Hr cells that’s 2400/195=12.3Hrs use

 

That just seems at lot of use at 25% tx/rx ratio and with 4 watts output
power but it seems right to me., anyone confirm ?

 

One more little mod I have done to the K1 (which I know I will be shot down
in flames for !)

 

I wanted the cells in the K1 to be kept topped up ready for action so I
found a pin on the on/off switch that only gives 12volts out when the switch
is in the OFF position

>From this pin I took a feed to the cells via a 1amp diode and series
resistor to limit the current to about 25mA on a fully charged pack and
about 50-60mA on a flat pack.

This only supplies charge to the cells when the k1 is connected to external
power and turned off ,so if using the K1 in the field off a gel pack or

 the like it does don’t add extra drain to the pack when the radio is turned
on , when the radio is turned off if you want to save any drain to the pack
just unplug it!

It works for me.

 

All the best

Paul

M0BMN

 

 


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[John Lonigro]

Paul:  Here's the way I'd figure it out:

Transmit current = 1000 ma
Receive current = 70 ma
Xmit duty cycle = 12.5% (25% transmit x 50% duty cycle while transmitting)
Average current drawn = 0.875 x 70 ma + 0.125 x 1000 ma = 186.25 ma.

Using a 2400 ma hr battery, you'd think you could get 2400/186.25  or
12.9 hours from that battery.  However, I think you'll find you'll get
less than that in practice.  I'm not familiar with the K1, but
transmitters usually draw more current as the supply voltage drops,
assuming the power out stays constant.  Also, the battery is rated at
2400 ma hr, only if it is discharged over 20 hours.  This means you
should be able to draw 120 ma from it for 20 hours.  But you couldn't
drawn 1 amp for 2.4 hours.  My guess is that you could use the K1 for at
least 8 and maybe 10 hours at that duty cycle.  That's still a long
time.  I'm sure my fist would get tired way before the battery died.  If
you took a break or your transmit duty cycle wasn't really 25%, you
could get close to the 12 hours.

73's,

John AA0VE


Paul Webb wrote:

>HI all
>
>The current drain is about 65-75mA ,depending on volume setting about 70mA
>for normal listening.
>
>
>
>I have fitted 2400mA cells that just fit .
>
>
>
>I have checked the current drain at 4 watts from these cells and it seems
>about 1000mA (1Amp)
>
>
>
>So I have worked the following out but would just like a check done
>
>
>
>Irx = 60
>
>Itx=1000
>
>Tx duty cycle 50% (since CW)
>
>
>
>Ratio tx/rx  25%
>
>
>
>So in one hour I would be in tx mode for 15mins drawing 1000mA but since
>it’s at 50% duty that’s 500mA for 15mins
>
>Which works out to 250mA for 30 mins or 125mA for 1 hr
>
>
>
>Plus the rx drain of say 70mA so that’s 70mA/Hrs
>
>
>
>Total drain then is 125+70=195mA/Hr
>
>
>
>Since I have 2400mA/Hr cells that’s 2400/195=12.3Hrs use
>
>
>
>That just seems at lot of use at 25% tx/rx ratio and with 4 watts output
>power but it seems right to me., anyone confirm ?
>
>  
>

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