[KX3] LiPol battery pack and KX3 - voltage vs output

[Thomas Horsten]

Hi,

I have my fully loaded KX3 on order and have some questions about the power
supply. I've operated with my FT-817 powered from an 8Ah LiPol battery
pack, which has 3 LiPol cells in series and gives from about 12.5V when
full down to about 9.5V when fully drained.

The FT-817 gives just about full output power throughout the range,
dropping the output slightly as the voltage gets below ~10.5V.

Given that the KX3 can operate from 8 1.2V NiMH cells, I am guessing that
it will be fine with using my LiPol pack as an external power source. But
how efficient will it be? What output power can I expect to see at the
different voltages?

73, Thomas M0TRN
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[wayne burdick]

Thomas Horsten wrote:

> I have my fully loaded KX3 on order and have some questions about  
> the power
> supply. I've operated with my FT-817 powered from an 8Ah LiPol battery
> pack, which has 3 LiPol cells in series and gives from about 12.5V  
> when
> full down to about 9.5V when fully drained.
>
> The FT-817 gives just about full output power throughout the range,
> dropping the output slightly as the voltage gets below ~10.5V.
>
> Given that the KX3 can operate from 8 1.2V NiMH cells, I am guessing  
> that
> it will be fine with using my LiPol pack as an external power  
> source. But
> how efficient will it be? What output power can I expect to see at the
> different voltages?

The KX3 can put out up to 12 W. At this power level we recommend using  
a 13-14 V power supply.

On some bands the KX3 will put out 10 W with a supply voltage as low  
as 11 V. This is ideal for use with gel-cells and car or motorcycle  
batteries.

Below 11 V, the max power setting is 5.0 W, where the KX3  
automatically switches the PA to a mode that's more efficient at low  
voltage/low power. On most bands, 5 W is possible with a 9.6-V supply,  
e.g. 8 internal NiMH cells.

73,
Wayne
N6KR


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[Thomas Horsten]

On 12 January 2012 17:02, Wayne Burdick <[hidden email]> wrote:

> The KX3 can put out up to 12 W. At this power level we recommend using a
> 13-14 V power supply.
>
> On some bands the KX3 will put out 10 W with a supply voltage as low as 11
> V. This is ideal for use with gel-cells and car or motorcycle batteries.
>
> Below 11 V, the max power setting is 5.0 W, where the KX3 automatically
> switches the PA to a mode that's more efficient at low voltage/low power.
> On most bands, 5 W is possible with a 9.6-V supply, e.g. 8 internal NiMH
> cells.
>

Thanks for that info Wayne, basically the TX performance will be on par
with or better than the FT-817 with the Li-Pol cell (much better when it's
fully charged).

That said, does anyone on the list know of a circuit that could step up the
voltage of the 12V LiPol cell to a regulated clean 13.8V supply? It would
be great to be able to put out the full power continuously. I guess an
inverter and switched mode supply could be used but that would be far
overkill, does anyone know of any chips e.g. available from Farnell that
could be used in such a box? The LiPol should easily be able to deliver the
amps needed even when partially discharged, and the supply would have other
uses too.

73, Thomas
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[wayne burdick]

Thomas Horsten wrote:


> Thanks for that info Wayne, basically the TX performance will be on  
> par with or better than the FT-817 with the Li-Pol cell (much better  
> when it's fully charged).

And of course the KX3's current drain in receive mode is far lower.  
With backlight off it's as low as ~120 mA. Your batteries should last  
a lot longer.


> That said, does anyone on the list know of a circuit that could step  
> up the voltage of the 12V LiPol cell to a regulated clean 13.8V  
> supply?

It would definitely have to be very clean, which probably means not  
just well-regulated but also shielded. Switching regulators can be  
notoriously noisy on both RX and TX.

Wayne
N6KR


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[Phillip Nichols-2]

My 817 has an RX drain of 450mA on RX and 250 Squelched... This is only
useful in CW mode and lets me listen for Strong stations. Or listen on a
quiet frequency for a planned QSO if the prop is good. It really applies
though on 2M. And since all of these will apply on the KX3....

Can you tell us Wayne, what the Squelched current Drain is
approximately; with Backlight off?

Thanks for all the time and work you guys have done. I have heard
nothing but good about your company and will enjoy being another "happy
camper"!

73/Phillip/N8AYE
-.  ---..  .-  -.--  .


    Wayne Burdick said the following on 1/12/2012 3:22 PM:

    And of course the KX3's current drain in receive mode is far lower.  
    With backlight off it's as low as ~120 mA. Your batteries should last  
    a lot longer.
     

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[Mike Morrow-3]

>> That said, does anyone on the list know of a circuit that could step  
>> up the voltage of the 12V LiPol cell to a regulated clean 13.8V  
>> supply?
>
>It would definitely have to be very clean, which probably means not  
>just well-regulated but also shielded. Switching regulators can be  
>notoriously noisy on both RX and TX.

There is no practical value to ten watts of output, compared to five.
Why turn battery energy into heat in the voltage converter?

73,
Mike / KK5F


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[David Christ]

I'm not an EE so maybe someone who is can answer my question.  A
boost circuit certainly cannot have 100% efficiency, but how
efficient would it be?  Some of the energy in the battery will be
consumed by the boost circuit and not available to the radio.  So
then how does one evaluate whether using a boost circuit will get you
more operating time or not?  I presume it must have something to do
with the flatness of the battery's discharge curve and also whether
you need more than 5 watts.

David K0LUM

At 7:40 PM +0000 1/12/12, Thomas Horsten wrote:

>
>
>That said, does anyone on the list know of a circuit that could step up the
>voltage of the 12V LiPol cell to a regulated clean 13.8V supply? It would
>be great to be able to put out the full power continuously. I guess an
>inverter and switched mode supply could be used but that would be far
>overkill, does anyone know of any chips e.g. available from Farnell that
>could be used in such a box? The LiPol should easily be able to deliver the
>amps needed even when partially discharged, and the supply would have other
>uses too.
>
>73, Thomas

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[John Huggins, kx4o]

Being a switching circuit topology, boost circuits' efficiencies can well
exceed 50% and often 80%.  Some are in the nineties.  You can think of
them as a constant power circuit which will tend to consume more current
as the voltage drops to deliver the same power to the load.  What this
means to your battery life is hard to say.  Lithiums can maintain a decent
current till the voltage dives off the cliff so your idea has merit.

However, the boost circuit is a switching circuit and generates a ton of
noise that requires special care in design to reduce.  It's not impossible
to achieve, but not easy.

For simplicity's sake, you are likely to be better off adding one more
cell in series and using a linear low dropout (LDO) regulator to ensure
the voltage never exceeds 15V or whatever Elecraft says is the practical
max.  As the battery voltage lowers below 15V+headroom the voltage will
track downwards with a small loss.  LDOs sometimes misbehave (oscillate)
at the point where the Vheadroom drops below regulation, but the lower
loss is usually worth it.

Lots of choices exist including just living with the 3 cell voltage.  The
switcher is likely too noisy.  The LDO allows for max voltage longer.  A
plain old linear regulator with 2V+ headroom might work too, but you are
wasting a bit more power.

John, kx4o

> I'm not an EE so maybe someone who is can answer my question.  A
> boost circuit certainly cannot have 100% efficiency, but how
> efficient would it be?  Some of the energy in the battery will be
> consumed by the boost circuit and not available to the radio.  So
> then how does one evaluate whether using a boost circuit will get you
> more operating time or not?  I presume it must have something to do
> with the flatness of the battery's discharge curve and also whether
> you need more than 5 watts.
>
> David K0LUM
>

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[wayne burdick]

John Huggins, kx4o wrote:


> For simplicity's sake, you are likely to be better off adding one more
> cell in series and using a linear low dropout (LDO) regulator to  
> ensure
> the voltage never exceeds 15V or whatever Elecraft says is the  
> practical
> max.

This is a possibility, as long as the regulator appears "transparent"  
to the supply when the supply voltage drops below the regulator's  
threshold.

Wayne
N6KR

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[wayne burdick]

Mike Morrow wrote:

> There is no practical value to ten watts of output, compared to five.
> Why turn battery energy into heat in the voltage converter?

When a band is *open*, 5 watts can usually do the job, IMHO. But a lot  
of operation takes place right at the noise floor, and the extra 3 dB  
can really help at such times.

Wayne


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[Thomas Horsten]

On 12 January 2012 23:59, Wayne Burdick <[hidden email]> wrote:

> Mike Morrow wrote:
>
> > There is no practical value to ten watts of output, compared to five.
> > Why turn battery energy into heat in the voltage converter?
>
> When a band is *open*, 5 watts can usually do the job, IMHO. But a lot
> of operation takes place right at the noise floor, and the extra 3 dB
> can really help at such times.
>
>

Exactly what I was going to say - when conditions are sub-optimal you want
to squeeze out every single decibel you can, whether from repositioning the
antenna, using more compression (for SSB), or cranking up the power. When I
was operating in Denmark with my FT-817 last week there were quite a few
stations that could barely copy me and sent "QRZ?" and "AGN?", I'm sure if
I'd had another 3dB I could have worked some of them. Also the remote
operator may have local QRM or urban noise and a less sensitive receiver,
which again makes QRP ops harder even if the band is open.

73, Thomas
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[wayne burdick]

12 W is nearly an S-unit stronger than 5 W.

Those who knew me in my NorCal QRP heyday, when 2 watts was full  
power, may be chuckling a bit. But hey -- if the goal is to  
communicate, at times a bit more power is justified. And as 12-W-
capable rigs go, the KX3 is about as frugal as it gets.

73,
Wayne
N6KR

On Jan 12, 2012, at 4:41 PM, Thomas Horsten wrote:

> On 12 January 2012 23:59, Wayne Burdick <[hidden email]> wrote:
> Mike Morrow wrote:
>
> > There is no practical value to ten watts of output, compared to  
> five.
> > Why turn battery energy into heat in the voltage converter?
>
> When a band is *open*, 5 watts can usually do the job, IMHO. But a lot
> of operation takes place right at the noise floor, and the extra 3 dB
> can really help at such times.
>
>
> Exactly what I was going to say - when conditions are sub-optimal  
> you want to squeeze out every single decibel you can, whether from  
> repositioning the antenna, using more compression (for SSB), or  
> cranking up the power. When I was operating in Denmark with my  
> FT-817 last week there were quite a few stations that could barely  
> copy me and sent "QRZ?" and "AGN?", I'm sure if I'd had another 3dB  
> I could have worked some of them. Also the remote operator may have  
> local QRM or urban noise and a less sensitive receiver, which again  
> makes QRP ops harder even if the band is open.
>
> 73, Thomas
>

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[Bruce Beford-2]

It's a slippery slope, Wayne... 8-)
72,
Bruce, N1RX

> Wayne, N6KR wrote:
> 12 W is nearly an S-unit stronger than 5 W.

>Those who knew me in my NorCal QRP heyday, when 2 watts was full  
> power, may be chuckling a bit. But hey -- if the goal is to  
> communicate, at times a bit more power is justified.


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[Mike Morrow-3]

> 12 W is nearly an S-unit stronger than 5 W.

Well, it's 3.8 dB vs. the 6 dB an S-unit requires, so if 60 percent
is **almost** as good as 100 percent I guess the quoted statement is
true.

I've played this radio game too, since the mid-1960s, and you can't BS a
BS'er!  I've learned enough to know that you'll never get wealthy if
someone gives you a dollar every time 10 or 12 watts make a go/no-go
difference compared to 5 watts, except in terms of battery depletion.
Now there, that's where you will see a very practical (but undesirable)
effect. :-)  Especially if you're going to waste battery energy as heat
in a voltage converter.

YMMV, but I really doubt it.

Now that said, a voltage converter designed to maintain 13.8 vdc output as
the battery terminal voltage drops can be very useful when operating some
solid-state rigs without latching relays from a battery not under charge.
The limiting devices in, say, an old TS-430S are the PA output filter board
band-switching relays.  They are not latching relays, and they require about
11.5 volts to remain firmly closed when energized.  Below 11.5 volts, the
rest of the radio works, but various relays start to drop out.  That's a
non-problem with Elecraft latching relay designs, so that removes any real
technical basis for maintaining 13.8 vdc to the KX3 or other K-rigs.

In battery-powered operation, it's battery energy that is always critical,
not the transmitter output power level.

73,
Mike / KK5F
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[wayne burdick]

Mike wrote:

>> 12 W is nearly an S-unit stronger than 5 W.
>
> Well, it's 3.8 dB vs. the 6 dB an S-unit requires

6 dB is the IARU recommendation, but when we were trying to decide  
what level to use, we consulted various references and looked at lots  
of receivers. They were all over the map--between 3 and 6 dB--so we  
used 5.

That said, I admit to putting a certain spin on it to make my point.  
There's a first time for everything :)

73,
Wayne
N6KR


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[Eugene Balinski]

Will there be a release (soon) of mechanical drawings of
the KX3 showing size and location of mounting holes and/or
other bracket attachment points ?  

Would like to prepare in advance.

Also, will there be an interface from the 100 PA to the
KPA-500 ?

73

Gene K1NR

(KX3 on order)

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[Dick]

I order a couple of 14.8v battery packs that are used with RC cars. High capacity, light weight.

[Dick]

I ordered a couple of 14.8gel velas. vdc RC car racing battery packs. Very light compared to
gel cells.

[Dick]

I ran into a problem running the KX3 on 14.8vdc Li-ion packs after charging.  The initial voltage exceeded 16 volts, the KX3 reported it and then shut down. The solution was a simple one. I put two 50v, 3A diodes in series with the positive lead.  I also added a center off - spdt switch to bypass one or both diodes as the voltage dropped after operating for awhile.

[Alan Bloom]

A more elegant way to do it would be a low drop-out regulator.  Maybe
something like this:

http://search.digikey.com/us/en/products/MIC29302WT/576-1124-ND/771593

Alan N1AL

On Mon, 2012-05-07 at 16:48 -0700, Dick wrote:

> I ran into a problem running the KX3 on 14.8vdc Li-ion packs after charging.
> The initial voltage exceeded 16 volts, the KX3 reported it and then shut
> down. The solution was a simple one. I put two 50v, 3A diodes in series with
> the positive lead.  I also added a center off - spdt switch to bypass one or
> both diodes as the voltage dropped after operating for awhile.
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/KX3-LiPol-battery-pack-and-KX3-voltage-vs-output-tp7180886p7537289.html
> Sent from the Elecraft mailing list archive at Nabble.com.
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