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Author Topic: Operating Portable HF  (Read 1244 times)
N1IRF
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Posts: 37




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« on: April 11, 2014, 01:30:29 PM »

I was interested in operating HF using a FT-897D and I had a few questions.  I have been told that I can operate HF portable (not mobile) using my car battery.  I would like to try this but I am concerned about damaging the car, damaging the radio, and damaging the car battery.  I am aware that I would need to have a direct connection to the car battery and I would also need to operate while the car is running (so I don't drain the car battery).  What else do I need to consider to operate safely?  Does anyone have any advice and experience that they could offer?

Also, I was considering using a sealed lead acid (SLA) battery for HF portable.  I was going to use either a (12v 7ah) sla battery or a (12v 12ah) sla battery.  I would like to recharge and/or maintain the charge of the sla battery using my car; but, I don't want to damage the car or the battery.  Can this be done safely; and if it can, what is the best way to do it?  Thanks.       
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W8JX
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Posts: 5604




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« Reply #1 on: April 11, 2014, 01:46:54 PM »

Never heard of car radio being damaged in a HF mobile operation. Biggest problem is mobile noise and RF feed back into HF rig in some installations. You not damage battery but if you use rig transmitting several hours with car off you could run it down. As far as using a 7 amp gell cell for rig I think it is a waste of time because while it will run receiver only for several hours, transmitting even on low power will kill it in short order. A 7 amp battery is rated 7 amp on a 20 hour discharge, it delivers far less and a quick discharge. I would suggest at least two 7 amp batteries in parallel if you feel compelled to use them. Myself I use a second car battery under hood that I an isolate when car is off and not worry about killing main battery and not being able to start car.
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WB6BYU
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Posts: 13126




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« Reply #2 on: April 11, 2014, 04:30:31 PM »

Quote from: N1IRF

...I would like to try this but I am concerned about damaging the car, damaging the radio, and damaging the car battery...



You aren't going to damage anything, unless you run the battery down too far.

The connection to the battery can be the same thing as you would use in a mobile installation, or
you can just open the hood and run a pair of FAT clip leads to the terminals.  But you probably want
something bolted on to avoid voltage drop at 20A on transmit.

You don't have to leave the car running, but you might want to start it every couple of hours and
recharge the battery to make sure it isn't dead when you're ready to leave.

Some rigs don't do well when the voltage drops.  Turning the power down to 50 or 25 watts will
greatly extend the operating time because the voltage won't drop as much on transmit with the
rig drawing less current.  (Of course, many of use run 5 to 10 watts and get a lot more operating
time.)



Quote

Also, I was considering using a sealed lead acid (SLA) battery for HF portable.  I was going to use either a (12v 7ah) sla battery or a (12v 12ah) sla battery. 



How much power do you plan to run?  For how long?

Generally I don't like to draw more current than 1/4 the rated Ah capacity, though I may stretch
that sometimes.  While I have a number of 7Ah batteries that I use for temporary testing and
QRP operation, I wouldn't use anything smaller than a 33Ah unit at 100W, and even that is typically
at a low duty cycle on SSB.  Trying to draw 20+ amps from a 7Ah battery is NOT a good idea, and
it certainly won't maintain the output voltage for very long.  (The internal connections have too
much resistance.)  The 7Ah batteries are great for low power rigs that draw a couple amps at
most.

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KF7VXA
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Posts: 458




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« Reply #3 on: April 12, 2014, 02:46:42 PM »

The Car battery will be fine. Use a short run of 6 or 8 guage wire and put a 30 amp fuse one both positive and negative wire just a short way from the car battery. I'd leave it run if you want max power, if not, cut back some and I'd start the car every 1/2 hour as to not hurt the battery any. A cheap voltage meter bought from E Bay for less than $4.oo to let you know when the battery gets just below 11 volts is a good idea. Don't go under 11 volts with a car battery, start the car and re charge the battery.

The best idea is to get a RV type battery from Wall Mart or Sam's Club for about $80.00. These are deep cycle batteries with thicker plates that will not be hurt by high amperage draw. You can hook jumper cables to it from your car and start the car to charge it every hour or so and you will not take the chance of hurting the car battery. They are made with thin plates, not made for long use at higher amperage, just for short bursts.
This way you'll have an emergency back up battery also.

73's John KF7VXA
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W8JX
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Posts: 5604




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« Reply #4 on: April 12, 2014, 03:04:21 PM »

The Car battery will be fine. Use a short run of 6 or 8 guage wire and put a 30 amp fuse one both positive and negative wire just a short way from the car battery. I'd leave it run if you want max power, if not, cut back some and I'd start the car every 1/2 hour as to not hurt the battery any. A cheap voltage meter bought from E Bay for less than $4.oo to let you know when the battery gets just below 11 volts is a good idea. Don't go under 11 volts with a car battery, start the car and re charge the battery.

The best idea is to get a RV type battery from Wall Mart or Sam's Club for about $80.00. These are deep cycle batteries with thicker plates that will not be hurt by high amperage draw. You can hook jumper cables to it from your car and start the car to charge it every hour or so and you will not take the chance of hurting the car battery. They are made with thin plates, not made for long use at higher amperage, just for short bursts.
This way you'll have an emergency back up battery also.

73's John KF7VXA

Actually a RV or deep cycle battery produces far less peak current.  It has fewer but thicker plates which last longer structurally under deep discharge but few plates means lower peak current too.
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K5LXP
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« Reply #5 on: April 13, 2014, 08:48:09 AM »

few plates means lower peak current too.

Right.  But at the comparatively tepid currents drawn in ham radio applications battery Z isn't critical, and the deep cycle feature and $/Ah can be an advantage.

A "better" portable battery is an AGM, like the Optima yellow top.  Non spillable and low impedance but more $/Ah and requires an AGM charger.

Operating car portable I always use the car battery though, less stuff to schelp around and mess with.  Plug in and go.


Mark K5LXP
Albuquerque, NM
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