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Author Topic: Power Problem  (Read 8616 times)
SM5MDN
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« on: October 24, 2013, 09:25:55 AM »

Kenwood ts 480sat wired direct to battery only showing 70/80 watts transmit with engine off,, start engine 100 watts transmit now showing, also have a ft 7900 wired direct to battery, engine off display shows 12.6 volts, engine running 14.6 shows, no probs with the 7900, but cant work out why the power drop with the 480 and engine off, its getting the volts it need according to the manual and if the battery cant supply the 20 amps it needs then I,m pretty sure my jeep wouldn't start, voltage drop in the cable run maybe, but as said the ft 7900 display show 12.6 v, both radios are using 12AWG wire runs and length from radios to battery are approx. 8 ft. anyone got an idea.
thanks
« Last Edit: October 24, 2013, 10:09:40 AM by SM5MDN » Logged
W8JX
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« Reply #1 on: October 24, 2013, 11:39:26 AM »

It is nothing to get in a twist about as it will never be seen down range. Some rigs like 13.8v for full output. You are loosing 1 volt in feed with 20 amp load. If you up-size to two 12ga wire in parallel for each leg (which is equal to a single 8 ga) the loss will only be .4 volts.  
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N6AJR
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« Reply #2 on: October 24, 2013, 11:50:25 AM »

find a set of auto jumper cables, and use that for your radio. fat cables, well insulated, and cheap. cut the ends off and add yours
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K5LXP
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« Reply #3 on: October 24, 2013, 12:50:35 PM »

Most rigs are spec'd to 13.8V +/- 15%.  On the low end that would be 11.73V

Your 7900 is reporting 12.6V at "no load" (not transmitting).

16ft of 12ga has .559V of drop at 22A.   12.6-.559=12.041V.

That should still be enough voltage for full output, so something else might be dropping voltage like a connection or a fuseholder.  Check the voltage at the back of the radio during transmit to see what you're actually getting.

Mark K5LXP
Albuquerque, NM
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SM5MDN
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« Reply #4 on: October 24, 2013, 01:03:26 PM »

ok thanks for the reply's, will have a tinker a bit more over the weekend if the rain and winds hold off.
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M6GOM
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« Reply #5 on: October 24, 2013, 02:49:27 PM »

Nothing you can do will address it unless you buy a voltage booster.

Don't worry about it, nothing is wrong. If you tried it in the house on a variable PSU you would see the output power drop as you lowered the voltage. My TS480 does the same and my Icom 7000 dropped down to 50W. The difference between 100W and 80W is maybe 1dB, 1/6th of a S point at the other end.
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K1CJS
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« Reply #6 on: October 25, 2013, 06:09:19 AM »

Many times the battery can and does supply sufficient amperage to start the vehicle--even if the battery voltage falls below 12 volts when the car is being started.   Chances are that the battery is nearing the end of its useful life.  Could be that is why the rig is showing lower transmitter power when the vehicle is off.  Check and clean the battery terminals first--that may be all that is needed.  But...  

I just had that happen to one of my vehicles--sitting the voltage was just above 12 volts, but when I tried starting the car it dropped drastically and the car wouldn't start.  Battery terminals were OK.  (I disassemble and clean them every three to six months.)  I turned on the headlights with the car off and the voltage supplied dropped down to below 11 volts, and continued to drop.  Alternator was and is OK, and with a new battery, everything was back to normal.

Are you in an area where it's starting to get colder now?  If you are, I would seriously consider replacing that battery because it may give out on you one morning.  Good luck and 73!
« Last Edit: October 25, 2013, 06:17:29 AM by K1CJS » Logged
WX7G
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« Reply #7 on: October 25, 2013, 07:10:16 AM »

What you experience is normal for the TS-480 (I have one in the car). You have three choices:

1. Run reduced RF power when the automobile engine is OFF
2. Run full RF power when the automobile engine is ON
3. Run full RF power when the automobile engine is OFF by using an MJF-4416B Battery Voltage Booster
« Last Edit: October 25, 2013, 07:18:57 AM by WX7G » Logged
SM5MDN
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« Reply #8 on: October 25, 2013, 07:21:16 AM »

ok thanks guys, I'll leave it as is and stay in the warm this weekend and not play around with it anymore, good to know its a ts 480 thing Smiley and not my install.
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SM5MDN
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« Reply #9 on: October 26, 2013, 05:57:48 AM »

just ordered me a MFJ-4416B so all well and good I'll pop that in in a few weeks when Walters and Stanton get there shipment in from mfj and post it off to me in Sweden.
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N4ATS
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« Reply #10 on: November 05, 2013, 12:19:25 PM »

All you need to do is put the radio on FM , use two needles, one poked into the RED wire and one poked into the BLACK wire right smack where they enter the radio. Take a reading with a DVM BEFORE and AFTER keydown on FM FULL power and tell me what the voltage drop is with out the engine running. 12 gauge is not enough , more like 10 or 8. You want less than 2/10ths of a volt drop between loaded and non loaded conditions.
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KE4DRN
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« Reply #11 on: November 07, 2013, 05:41:32 PM »

hi, agree that #8 wire will do the job with no voltage loss problems.

please check the connections at the factory fuses on the kenwood cables,
sometimes they need a good cleaning to get the radio to put out full power.

Are you using direct to battery for the negative or the car chassis?

73 james
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KJ4RQX
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« Reply #12 on: November 08, 2013, 03:25:26 PM »

K5LXP, Did you use a table to compute that voltage drop or did you use a formula.  Thats good information to have for a new install I'm doing.
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K5LXP
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« Reply #13 on: November 08, 2013, 07:13:39 PM »

Did you use a table to compute that voltage drop or did you use a formula. 

I used a wire table for the resistance per foot for standard AWG wire, then ohms law to figure the drop.

Mark K5LXP
Albuquerque, NM
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K0BG
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« Reply #14 on: November 09, 2013, 03:30:50 AM »

The vast majority of solid state transceivers will have reduced power out sat voltages. This is true of the 7900 as well.

A good example of this is the Icom V8000. It is factory rated at 13.8 vdc, and an output of 75 watts. The ARRL lab couldn't get more than 73 watts out at 13.8, but could at 14.0. At 12.2, the resting voltage of most lead acid batteries, the output was a scant 47 watts.
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