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Author Topic: Field Day Power Suggestions  (Read 13119 times)
N7VEA
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Posts: 48




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« on: April 20, 2011, 06:04:31 AM »

Watching the earthquake and tsunami news a few weeks ago, and now all the tornado news this week has got me thinking about how to run my station in the event of that kind of destruction.  That, plus Field Day is not too far away... I've never participated in a Field Day but would like to give it a try this year.  Except for putting the rig in the car on a few occassions I've also never worked with battery power.  I have the Field Day book and an emergency power book on order, but I would also love to hear from you folks about what has and hasn't worked for you for Field Day/emergency power in a simple HF station (think 450D, tuner, laptop, a 33' vertical on HF and a 2-el yagi on 6M). 

The goal would be to work all weekend, not just a few hours.  Is one deep cycle battery enough?  If one or two batteries is not sufficient, how elaborate would a solar charger setup need to be that would keep this station on the air?  Generators are pretty low on my list, and a windmill is a non-starter in my HOA neighborhood... although perhaps I could get permission for a windmill tower easier than an antenna tower, hi hi.  Anyone want to share what's worked for them? 

Thanks.  Bill N7VEA
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K7RBW
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« Reply #1 on: April 20, 2011, 07:40:54 AM »

what are some of your limitations? e.g. budget? weight? ease/speed of set-up? size of load (for transport)?
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N7VEA
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« Reply #2 on: April 20, 2011, 08:54:23 AM »

I'm not interested in spending a four digit figure on panels, converters, and a bank of 200lb batteries.  Somewhere between that and hooking the rig up to the truck battery is where I want to be.  I would like to stay with reasonable sized batteries, no more than 60-70 lbs each (preferrably less).  And I don't need it to be "portable" in the sense of backpackable but something that could be set up as needed and stored in the garage when not would be ideal.  I expect it would be possible to run a Field Day with a couple of decent 12v batts, but if I can I'd like to do just a bit better than that, since the object is not simply to run the event but to build a home sized  emergency power source for the station.  Is it possible to find some sort of small solar set up that would run a battery powered HF station indefinitely for a couple hundred bucks? 
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K1CJS
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« Reply #3 on: April 20, 2011, 01:26:10 PM »

Deep cycle trolling motor battery.  Available at some retailers at around $100.  A little bigger than a standard car battery, and can be set up to be recharged with a $20 to $30 three stage charger--or by a set of light jumper cables off your car battery.
« Last Edit: April 20, 2011, 01:28:16 PM by K1CJS » Logged
WB6BYU
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Posts: 13488




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« Reply #4 on: April 20, 2011, 02:07:02 PM »

The first step is to look at the power needs of your station.  Things to consider include:

1) How much time do you expect to spend transmitting during a day?  How much receiving?
(You don't have to have the rig on full time - you could, for example, check into a net once
an hour in an emergency and leave it off otherwise to save power.)

2) How much current does your rig draw on receive?  On transmit?  How much output power
do you need to accomplish the required communications?  What is the transmitter current
draw at low power compared to high power?

3) How low of a battery voltage will your transmitter tolerate and still generate the desired
output power?  This is a major factor in the calculation - a lamp, or even a receiver, may
operate at a battery voltage of 10V, but many transmitters will drop out in the 11V to 12V
range.

4) What other equipment do you plan to operate from the battery?  Lights?  Antenna rotator?
Autotuner?  Computer?


Because one generally operates in receive mode more than transmitting, the receive current
draw is also a major factor.  Rigs designed for battery operation may draw less than 50mA on
receive.  (I have one 80m handheld receiver that draws less than 10mA.)  Those designed
for base or mobile use may draw as much as 2 amps.  One technique to extend battery life
is to monitor on a low-current receiver, then switch on the big rig only when you need to
make a call.  

Similarly, the lower the power level, the longer the battery will last.  Not only is the total
power drawn used from the battery less, but the peak current is lower, so the voltage under
load doesn't drop to the transmitter limit as soon.  Running the rig at 25 watts or 10 or even
5 watts can give you a lot more operating time - as long as the current drawn drops as one
might expect.  (It doesn't always - you may find that the radio draws 3 to 5 amps in transmit
even at minimum output power.)  How much power you need depends on what sort of
communications you plan to accomplish, and how good your antenna is.

Once you have these numbers you can calculate the total power requirement.  For example,
assume your rig draws 200mA on receive and 10A on transmit (which might be a typical average
for a 100W rig on SSB.)  For Field Day you plan to operate 24 hours full time, at 60% RX and
40% TX.  Then you can calculate the total power for each hour this way:

TX = 10A * 1 hour * 40% = 4Ah
RX = 200mA * 1 hour * 60% = 0.12Ah

total = 4.12Ah of battery capacity for each hour of operation

24 * 4.12 = 98.88, or say 100Ah of battery capacity.

Now you really can't do this with a 100Ah battery,  because the voltage would drop too low to
run the transmitter.  I normally assume a 50% factor, but it depends heavily on the drop out
voltage of your rig.  That would mean I'd plan on a couple of 100Ah batteries to last me though
field day at that rate.

In practice I typically operate about 8 hours at 5 watts, and a single 33Ah battery is more than
adequate to get me through Field Day - in fact, I've managed a couple times on a 4.5Ah battery.
It doesn't require a very big solar cell array to keep my HW-8 or 40-40 rigs running, but it may
take an impractically large one to maintain a 100W rig.

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N2EY
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« Reply #5 on: April 20, 2011, 02:12:02 PM »

http://www.eham.net/ehamforum/smf/index.php?topic=74567.0

73 de Jim, N2EY
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N7VEA
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« Reply #6 on: April 21, 2011, 05:30:37 AM »

Dale, thanks, that's helpful.  And Jim, I missed that thread, thanks for pointing it out.  Are you getting tired of answering the same question?

The emergency power book arrived yesterday so I'll dive in there and see what it has for maintaining power.  Ideally a couple of batts and a small solar charger is what I envision but I'm not as electricvally savy as most of you guys so it takes me a little longer to "get it".  Thanks for the help.

Bill N7VEA
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W3JKS
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Posts: 201


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« Reply #7 on: April 21, 2011, 05:31:51 AM »

Hey, no moving parts, quiet, what's not to like?   Cool

http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator

Got Plutonium?
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K5LXP
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« Reply #8 on: April 21, 2011, 09:03:48 AM »

What you do for Field Day is pretty different than a disaster like Katrina or Japan's tsunami.  It's one thing to run a station for a 24 hour period vs for weeks at a time but this 24 hour exercise will give you a taste of what it might take to be truly energy self sufficient.

My contribution to this thread would be to get some batteries now and play with this before Field Day.  A few trial runs of real world loads will reveal what the exact limits are for your equipment and operating requirements, and gives you time to tweak before you need it for the real thing.

You didn't mention if you were going for the A or B Battery class or if you'll be just running some rigs and other equipment off of batteries.  That would make a big difference on the scale of what you need.  If you ask me the Field Day Battery classes are pretty stupid but them's the rules.


Mark K5LXP
Albuquerque, NM


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N7VEA
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« Reply #9 on: April 22, 2011, 05:21:14 AM »

Thanks Mark.  Actually, I had thought that "Class E-Home Stations on Emergency Power" would be what I was aiming at.  I know that pulling a 12V batt into the shack would get me a few hours of airtime, but I'd like to use the experience to learn a little bit more about what it takes for real emergency power, like you said.  Otherwise it'd just be an exercise in trying to fit a different contest category.

Does anyone have any experience using the smaller solar panels available at some of the tool and hardware outlets?  Are they worth the effort, or should I save the coins until I can go with a more "robust" system?  Perhaps I'll visit the RV shops and see if they have anything... 
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WB6BYU
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« Reply #10 on: April 22, 2011, 07:06:28 AM »

They will keep your battery from self-discharging between uses, which isn't a bad thing.

A typical small solar panel for that purpose might have an output of 60mA (it should be marked on the package
somewhere.)  12 hours of sunshine in one day would add about (12 * 0.06) 0.7 Amp-hour to your stored charge
in the battery.  In the previous example ( average draw 4.12 A) that gives you about 10 minutes of operating.
A QRP station optimized for low current draw might get a few hours of operation.

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N4OGW
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Posts: 314




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« Reply #11 on: April 22, 2011, 08:44:19 AM »

I did field day as 1B single op a few years ago and it was a lot of fun. For power I used a trolling battery from Walmart which cost less than $100. I ran an Elecraft K2 and an old Gateway laptop for close to the full 24 hour period with 5W rf output.

You can get by on just a single cheap battery if you run qrp and pay attention to current drain: the K2 for example has very low power needs in receive mode. Many other rigs take >1 amp even on receive which would be a problem. The laptop I used was such that I could simply wire the battery directly into the laptop battery terminals- this saved the power loss in typical auto/laptop voltage converters. If you log on paper you could get by with a lot less power.

Tor
N4OGW
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N4OGW
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« Reply #12 on: April 22, 2011, 08:58:15 AM »

Just to expand on what I was saying: Yaesu 450D: current on RX=1.3 A; Elecraft K2: 0.150 A

Tor
N4OGW
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K5LXP
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« Reply #13 on: April 22, 2011, 10:32:17 AM »

Does anyone have any experience using the smaller solar panels available at some of the tool and hardware outlets? 

There's the "small" ones, basically battery maintainers like WB6BYU detailed and then there's the "small-ish" systems they sell which are big enough to actually power things.  I think the latest harbor freight flyer has one such system currently listed for around $150.  How effective they will be depends a lot on how you will use them.


Are they worth the effort, or should I save the coins until I can go with a more "robust" system? 

You need to define your goal first, then see if it's even feasible.

The issue with the Field Day battery class is the power needed is so mall (QRP) you likely don't even need a panel to run the whole contest.  Of course you want a panel to claim the AE bonus but that's about it.  At that point it wouldn't matter if it's a 1 watt panel as long as your battery is big enough.  At QRP, a big enough battery isn't hard to do.

If you intend on running a 100W class transceiver plus some other stuff for 24 hours, then sizing the components becomes a bit more critical.  If you want to run a home station entirely from AE sources, then you're into a full blown systems engineering exercise.

If you're just interested in tinkering, you can get a modest size panel, a marine battery and see what that will do for you.  You can always use the battery charged from AC mains or genset, and the solar panel will at least deliver a supplementary level of power.  Understand though that solar power and storage battery systems can be fairly accurately predicted, so if you wanted to design a system with specific capabilities you can do that before buying anything.


Mark K5LXP
Albuquerque, NM
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K1CJS
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« Reply #14 on: April 26, 2011, 10:38:08 AM »

Be careful with the solar power station that Harbor Freight offers.  It will not power too much.
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