[NLRS] The woes of 13.8 vdc

[W0ZQ@aol.com]

I need some help from you DC power guys.   Here is my problem.  For now, I'm 
using my FT100D for my IF rig on 10 GHz.   The FT100D is really an amazing 
radio for a HF/VHF guy like me, it really does a lot of stuff !   One thing that 
it does not excel in is power management.   For example, my 10 GHz transverter 
with 1 watt amp takes about 1 amp at 13.8 vdc but the FT100D, throttled back 
to just 2 watts of drive at 144 MHz still sucks about 6 to 7 amps or so on 
transmit.    Don't ask me why .... probably because of the broad band final 
section (hey, it does 1.8 to 440 MHz).   A fully charged battery like a deep cycle 
battery will provide about 12.5 or 12.6 vdc that drops to around 12.1 to 12.0 
vdc on transmit.     This gets worse as the battery is depleted.   The specs 
on the FT100d are 13.8vdc +/- 10%, or a range of 12.42 vdc to 15.18 vdc.   As 
you can see, even with a fully charged battery, I am already operating at or 
slightly below the bottom end of the VDC spec for the FT100d.

So, without going to another IF rig, here are some options.   I'm wondering 
if anyone else has tried these options and if so how it worked for them, or, if 
there are some other options.

1.  Add a single cell in series.   A single cell lead acid is about 2.1 vdc 
so this would make the fully charged voltage around 14.7 vdc which is within 
the upper spec of the FT100d of 15.2 vdc with about 0.5 vdc of headroom.   The 
cell would need to pass 6 or 7 amps when I transmitted.   Anyone have any ideas 
where one can find a single cell lead acid rechargable battery like this ?  
How about a seven cell lead acid deep cycle (one can ask) ?

2.  Go with a two battery system to provide18 vdc or 24 vdc and build a 
regulator to regulate at 13.8 vdc.    The regulator would need to pass around 8 
amps and need to dissipate about 80 watts when transmitting (8 amps x (24-14vdc)) 
.... a bit less if you use an 18 vdc system.   Anyone done this ?

3.   Go with a DC/DC converter of some type.   Some unregulated DC voltage 
in, a regulated 13.8vdc out.   Sounds kind of expensive and messy to me, 
especially when running portable.   Anyone have any experience with doing this ?   Is 
there anything commercial available.   

4.   Bite the bullet and get a different IF rig that uses current more 
appropriate for its output power and that has a higher tolerance DC voltage input 
range.    What are good candidates?   

73, Jon
W0ZQ


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