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Grab-and-Go, pwr for Satalitte and ECOM use

Jul 10th 2013, 00:00


Joined: Apr 8th 2013, 00:09
Total Topics: 0
Total Posts: 0
BY physical limitations (as a human) I have taken older radio gear / equiptment and putting them to use in alterantive ways. I HAVE a Yeasu FT-7100 Dual Bander in my truck that is now is re-mounted into a 'grab-and-go" suitcase. I started my 'Project' by providing power with a 5 cell 12VDC battery pack rated at 4.5 amp/hrs. Basic electricity tells me that in a fully CHARGED case I couldn't and wouldn't want to draw more than about 4 Amps! (that is assuming a 3-4 amp dead key, and 100mA listening - on LOW power. with the radio) Given a 80% listening / 20% transmit ratio lies well within a 2 hour operating limit. What I am finding in practice is even a 'dead key' without modulation will kill the voltage and lead to a garbled transmission. My first assumtion is to add an additional 'pack' rated at 4.5 A/h in parellel with the first to increase not only amp draw, but battery life as well. While these small NiMH battery packs work well for remote airplanes and the like, they seem unsuitable for High draw applications. Seems (in my mind) that it would be best to leave the "grab-and-go" package intact - ie: small batteries for set-up, recieving, then port out the MAIN power cableing to either a cig plug (or powerpole connector) to something like a Marine U1 battery that could susstain amp draw over a longer period and still accept an amperage peak while keyed. It seems I am throwing my money at a problem (small battery packs) while what I should be doing is investing in a HIGH A/hr, marine battery! Once that is done, my electrical curcuits become a little more complex as I know from experience, marine 'type' batteries discharge explosive gases and are also prown to overheating from re-charging. I am also a sailboat owner and KNOW if you re-charge or even discharge (rapidly) even Gel-cells, you create an extreemly volitile environment, with cells reaching max. temp in a hurry and in combination with dicharge gases, try and light a cigarette! BOOM!
Anyone who (in my opinion) builds a battery pack without temp and /or gas monitoring is asking for trouble! Ask to see my scars from an airplane battery explosion on a business class jet while working as an aircraft mech.

The point in all of this dribble is I am asking for help in putting together a design for my FT (Yeasu) that is safe portable and reliable without a major cost of construction.

My ultimate goal is to use the FT as a satellite tracker / EMCOM station IN THE FIELD. While sat passes rarely last more than 10 minutes, sustained operations is not a must, but would also go hand-in-hand with EMCOM.

Hope for some help and advice as I KNOW we have many very talented people out there!


Jul 10th 2013, 12:12


Super Moderator

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

I've used 8AH Gates Cyclon (an early spiral wound AGM battery) cells to power my 25W 2M SSB/CW/FM portable radio with excellent results for many years--even though they were surplus pulls. I used a homebrew UC3906 based three state charging circuit to keep them charged.

I found that 25W was plenty from a good mountaintop location. Operating at the beach and trying to work inland 200 miles was another story--I ended up mounting a roof rack on the sedan and putting a 4 element beam on a 5 ft mast--so the antenna was 9 feet above ground. This worked OK, though it helped when I switched in a brick amplifier, powered by a car battery.
Zack Lau W1VT
Jul 13th 2013, 09:17


Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Hi Mark. A few things to consider. Max power drawn on TX for your radio is 11.5 amps. That would be on the high power setting. If you are trying to use high power, that could be what "kills the voltage" on transmit. Another thing that I have found is that the factory fuse holders sometimes add enough resistance to cause an unacceptable voltage drop across them during high power transmit. I have replaced the cylindrical fusees and holders on my radio that draw more than a few amps on transmit with spade type automotive inline fuse holders and appropriately rated fuses.

I would try using low power or mid2 power settings. As you seem to know, you should only charge deep cycle and gel cell batteries in a well ventelated area, and do not overcharge them or try to charge them too fast.

A solution might be to to get two 7-12 amp/hr 12V gel cells. Use one while slow charging the other. You could keep a charged battery in the suitcase (disconnected) and remove it a few feet away when in use.

Just my $20.00 worth ($0.02 adjusted for inflation!)

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