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Author Topic: Portable Power  (Read 4152 times)
AA9ZY
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Posts: 9




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« on: September 27, 2011, 06:54:54 AM »

I have an FT817ND and have been wanting to try portable qrp. Recently I was in our local hobby shop (I'm also an O-gauger) and I noticed 12v 7Ah gel-cell batteries and charger for the r-c folks.

Would that be enough battery for a day of operating, or should I buy 2 and wire them in parallel?
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W8JX
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« Reply #1 on: September 27, 2011, 07:18:51 AM »

I have an FT817ND and have been wanting to try portable qrp. Recently I was in our local hobby shop (I'm also an O-gauger) and I noticed 12v 7Ah gel-cell batteries and charger for the r-c folks.

Would that be enough battery for a day of operating, or should I buy 2 and wire them in parallel?

I would get two and parallel them as you will get more than 2x run time that way. Unlike a glass of water that yields same volume of output regardless of flow rate a battery recovers more energy if you discharge it slower. (optimum discharge rate for recovering a full 7amp capacity from a gel cell is about 350ma/hr) Also battery will last longer if not pulled low with usage. BTW 8ah version can be found on Ebay cheap and even 9ah versions on same battery as well.
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WB6BYU
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« Reply #2 on: September 27, 2011, 07:25:12 AM »

7Ah is a very common size - they are often available as pulls from emergency standby equipment,
as well as from many other sources.  I'd look around and compare prices - don't forget shipping costs
from the mail order houses, since they are heavy.

How long will it run the radio?  I carried a 4.5Ah gel cell around with my HW-8 and Argonaut and
figured on a week of casual operating in the evenings, or 24 hours of fairly steady operation
(such as Field Day, though I doubt I operated more than 8 to 12 hours.)  Your FT-817 draws
a lot more current, especially on receive, but you still should get a few hours of operation out
of one cell.  It depends on the mode you use, power level, and the ratio between talking and
listening, so it is difficult to give an exact number.  (Also, I generally don't plan to pull more than
half the rated battery capacity when calculating my operating time.)  I'm sure there are other
FT-817 owners on here who will chime in with their experiences.

I'd suggest getting one battery and trying it out.  Rather than connecting two in series, I'd use
them individually.  A good investment is one of the multi-state chargers with mating plugs so
you can use one while the other is charging.  That gives you more flexibility to take one or two
(or more) batteries along each time you go, based on your operating plans.
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W8JX
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« Reply #3 on: September 27, 2011, 08:01:12 AM »

7Ah is a very common size - they are often available as pulls from emergency standby equipment, as well as from many other sources.  I'd look around and compare prices - don't forget shipping costs from the mail order houses, since they are heavy.

Kinda silly to by used 7ah pulls when you can get new 8ah ones for under 25 bucks shipped on Ebay. I have bought several over year to replace batteries in several UPS i have that use two of them.

Rather than connecting two in series, I'd use them individually.  A good investment is one of the multi-state chargers with mating plugs so you can use one while the other is charging.  That gives you more flexibility to take one or two (or more) batteries along each time you go, based on your operating plans.

I would stick with 2 in parallel if you plan to work a lot. You will get more run time than using one battery at a time. It will also fade much slower as end comes never too.
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WB6BYU
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« Reply #4 on: September 27, 2011, 09:38:06 AM »

Quote from: W8JX

Kinda silly to by used 7ah pulls when you can get new 8ah ones for under 25 bucks shipped on Ebay...

Depends on your personal preferences.  I've got 8 to 12 of them, sometimes free, sometimes a couple bucks
each at a hamfest.  I don't think I've paid $25 for all of them combined.  If you want to experiment with them,
that's a good way to get started with a minimum investment, rather than putting out a chunk of money for
new ones and discovering that they really don't suite your operating style.


Quote
I would stick with 2 in parallel if you plan to work a lot. You will get more run time than using one battery at a time. It will also fade much slower as end comes never too.

Again, that depends on your personal operating preferences, rig, etc.  If you're using a real current hog of a
radio, you might need two batteries, depending on how long you plan to operate.  (In that case I'd use one
of my larger 33Ah batteries.)  For a one-day outing, one of the 7Ah batteries is far more capacity than
I need, so I see no reason to carry two of them, especially for backpacking or other applications where
weight is important.

Parallel operation of batteries is not without problems:  when they aren't identical or both at the same level
of charge, one battery can discharge the other.  If you charge them that way, there is no guarantee that
the charge is equally distributed between them.  My solution is to use (and charge) them individually. I do
have an adaptor so I can connect two of them in parallel if needed for higher current draw (or to run two
loads off the same battery, thanks to genderless PowerPoles).  But if the battery is properly sized to the
application the difference in capacity is small, and the convenience of only using one battery at a time
and not worrying about whether they are in the same state of charge makes it worthwhile.
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W8JX
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Posts: 5785




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« Reply #5 on: September 27, 2011, 11:25:09 AM »

Quote from: W8JX

Kinda silly to by used 7ah pulls when you can get new 8ah ones for under 25 bucks shipped on Ebay...

Depends on your personal preferences.  I've got 8 to 12 of them, sometimes free, sometimes a couple bucks
each at a hamfest.  I don't think I've paid $25 for all of them combined.  If you want to experiment with them,
that's a good way to get started with a minimum investment, rather than putting out a chunk of money for
new ones and discovering that they really don't suite your operating style.

It is a crap shoot with a pull and many do not even have full capacity. Again given that new ones are so cheap online I do not go looking for someone throw outs here. And. you get more capacity too (because they are new and higher capacity.)  9 or 10   8ah  battery would replace 12 7 ah ones and 7 or 8  9ah would do same too. (unless you like have lots of dead weight around)

Quote from: W8JX
I would stick with 2 in parallel if you plan to work a lot. You will get more run time than using one battery at a time. It will also fade much slower as end comes never too.

Again, that depends on your personal operating preferences, rig, etc.  If you're using a real current hog of a
radio, you might need two batteries, depending on how long you plan to operate.  (In that case I'd use one
of my larger 33Ah batteries.)  For a one-day outing, one of the 7Ah batteries is far more capacity than
I need, so I see no reason to carry two of them, especially for backpacking or other applications where
weight is important.

Parallel operation of batteries is not without problems:  when they aren't identical or both at the same level
of charge, one battery can discharge the other.  If you charge them that way, there is no guarantee that
the charge is equally distributed between them.  My solution is to use (and charge) them individually. I do
have an adaptor so I can connect two of them in parallel if needed for higher current draw (or to run two
loads off the same battery, thanks to genderless PowerPoles).  But if the battery is properly sized to the
application the difference in capacity is small, and the convenience of only using one battery at a time
and not worrying about whether they are in the same state of charge makes it worthwhile.

At a serious outing, one 7ah will not make it with a 817 all day. A 9ah one might (about 30% more capacity than a new fresh 7ah one.)

As far as parallel problems, I have seen it one time in 40 years and that was in a dual battery SUV that does not see much use. Old aux battery developed a short in one cell and slowly pulled main battery down and it was dead (10.5 volts) when I went to start it. Never had a problem otherwise car or gel cells and currently have two vehicles with dual batteries too and have never bought matched sets for them either.   
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AA9ZY
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Posts: 9




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« Reply #6 on: September 27, 2011, 05:21:26 PM »

Thanks for all of the info. I figure if I buy two brand new 7Ah gel-cells and run them in parallel, that will be enough for a half a day of picnic table operating at the local state park. BTW, Palisades state park north of Savanna, IL is a great operating location in nw Illinois.
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W8JX
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Posts: 5785




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« Reply #7 on: September 27, 2011, 07:14:04 PM »

I figure if I buy two brand new 7Ah gel-cells and run them in parallel, that will be enough for a half a day of picnic table operating at the local state park.

Yes come prepared because there is nothing worse than being on 0 mhz because battery quits before you do.
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WX7G
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« Reply #8 on: October 04, 2011, 09:51:22 AM »

That should be enough battery for 12 hours on receive. As transmit is usually low duty cycle I'd expect nearly 12 hours of actual operating.
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AA9ZY
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Posts: 9




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« Reply #9 on: October 05, 2011, 03:49:20 PM »

More than enough for an afternoon of casual operating. And I am a casual qrp'er!

Thanks all Smiley
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AA4GA
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Posts: 118


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« Reply #10 on: October 11, 2011, 12:35:15 PM »

Would that be enough battery for a day of operating, or should I buy 2 and wire them in parallel?
I used two 7AH SLABs for Field Day this year for my FT817ND - I got 14 hours use out of the first one alone...read here for more details:  bottom line is you should be fine with one 7AH SLAB. 
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W1JKA
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Posts: 1667




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« Reply #11 on: October 16, 2011, 02:15:18 AM »

   Portable power for me is a cheap auto jump start no frills battery from the VIP auto store,frequently on sale for about $40.00.It is a handy size for patio,campground,boat and short mountain hikes for my SOTA activities.I get 2 days of casual use with my MFJ Cubs,MFJ 90s and SWL units.I have these in my autos for Maine winters anyway so I get double use of them.Next project,a cheap solar panel to keep them topped off.Have fun with QRP portable.

73, JIM
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