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Author Topic: FT-8800 Battery Draw  (Read 3267 times)

Posts: 1

« on: February 20, 2008, 10:35:10 AM »

I purchased an FT-8800 as my first mobile. I hoping to really utilize the cross-band repeat function of the radio but am concerned about the possiblity of draining my batteries. The radio will be installed in a Hummer H1 which has two batteries already. Is it recommended to add a seperate batter for this application with a batter isolator? Will the draw me significant enough to worry about?
Thank you.

Posts: 1042

« Reply #1 on: February 20, 2008, 10:58:13 AM »

you will need to read the manual for the radio.  Current draws do not change when doing x-band repeat.

Total consumption depends on duty cycle plus you selected output power - if you are using maximum power both ways, then you will use much more power than if you are using 5-10 watts on each side.  Good Amateur practice dictates you use the minimum power that does the job.

Keep in mind that you need to operate within your licence and legal operating limits for repeaters.

and I always, always, always use Tone both ways on the link to avoid unauthorized use.

Posts: 10248


« Reply #2 on: February 20, 2008, 11:56:51 AM »

You have another consideration too. Make real sure you understand the rules governing crossband repeat before you set it up.

Alan, KØBG


Posts: 5446


« Reply #3 on: February 21, 2008, 11:54:00 AM »

"Draining batteries" needs to be quantified.  It can range from draining to the point the vehicle won't start, to draining to the point where service life is affected, and then to what degree.

If you envision operating it long enough to drain to the point the vehicle won't start you have more to consider than just using an auxilliary battery, since it too will be drained and deeply cycled, affecting it's life (though you won't have to worry about getting home).

If you're just worried about leaving the radio on accidently you can build or buy a timer that will shut the rig off after a predermined time, and save you the hassle and expense of dealing with an auxilliary setup (some rigs have built in shut off timers already).

If you only cross band semi-frequently there is a point where even if you drain the SLI battery to the level where it affects it's lifespan, it may not be enough to justify the expense of an auxilliary battery.  Just replace the SLI a little more frequently, or choose one rated with a higher reserve power.

So like any load you put on a rechargeable battery, it comes down to Ah, time and cycles.  Once you define how much, for how long and how often you need it, you can then intelligently configure a power source for it.

Mark K5LXP
Albuquerque, NM

Posts: 14455

« Reply #4 on: February 22, 2008, 04:25:14 PM »

The other thing to consider is that when a battery mfg specifies a capacity of x AH that is usually down to a voltage of around 10 volts. The problem is that most mobile radios won't function properly (if at all) below around 11.5 volts. The radio will quit before the specified battery capacity is fully utilized. You therefore need a larger battery than you calculated using its specified AH capacity.

Bob  AA4PB
Garrisonville, VA

Posts: 9930

« Reply #5 on: February 23, 2008, 01:48:48 PM »

look into something called a constant duty solinoid.  it is like a ford starter solonoid but made to be on for a long time   ( ford  solinoids melt after about 20 minutes. don't ask)  these are about 10 bucks at a autoparts store.  run the heavy positive cables to charge the battery on the solinoid and a small 12 v switch will make or break the 12 volt high current line.  if you put the switch on a "key on" line, it wioll disconnect automatically when you turn the car off.

Posts: 172

« Reply #6 on: February 25, 2008, 07:39:50 AM »

Assuming you can legally crossband...

You might want to check the FT-8800 specs for low power X-Band operations.  Anything higher will fry the radio over a short time due to heat build up.

Posts: 227

« Reply #7 on: February 27, 2008, 08:12:33 PM »

I have never needed to crossband at more than 10 Watts out. Usually 5 W. The trick is to use a good location for the vehicle and do an efficient antenna installation with a good ground plane. Window mount and mag mount antennas are mostly second rate. There are a few large mag mounts that are efficient, but all of them are a safety hazard. Yes I have used them for temporary situations like a public service event in a rental car.

I like to use a dual band HT into the vehicle radio which repeats into the repeater the HT will not bring up. Almost always I hear the repeater fine from the HT so I do locked-band repeat. I hear the repeater on the HT on one receiver, and transmit to the repeater on the other side. The mobile radio does not retransmit the repeaters output. This avoids the need for the mobile to identify. The D710A can automatically identify in crossband mode, but it does it every 10 minutes whether it is keyed up or not. I have not yet needed to use that feature. Use PL or DCS on your input freq to the mobile and if using a D710A you can earn to take the radio out of locked band repeat remotely from the HT using remote control DTMF codes for the radio commands.

The radio will not overheat as it has a fan cooling the heat sink and a time out timer, plus it will cut back the power if heat sink get too hot.

Have fun,

73 de Walt N2IK

73 de Walt N2IK
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