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VHF blowing fues once mic is keyed

Old 08-15-2011, 07:58 AM
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Default VHF blowing fues once mic is keyed

I've got an in-line fuse wired in to my VHF radio along with the fused buss bar. My spade 3 amp fuse blows as soon as I key the mic to transmit. This is a new problem. The radio worked fine for the past couple of years transmitting- never blowing the 3 amp fuse. What is likely the cause of this new issue?

Last edited by Tundra Troller; 08-17-2011 at 07:41 AM.
Old 08-15-2011, 08:04 AM
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Are you sure that's the right fuse? Mine uses 6 (amps). These things need significantly less juice to receive than they use to transmit which would explain your problem.

If you don't have a manual to consult then post exactly what tadio you have so another user can tell you if it matches their set-up.

Good luck!
Old 08-15-2011, 08:22 AM
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Kamper,
Thanks for the quick reply. I bought the boat used 2 seasons ago. I have never needed to replace the fuses yet and the radio has worked fine up till this last trip. As a matter of safety, I always do a radio check w/ the Coast Guard every trip out and the 3 watt fuses had never blown until this most recent trip. (I know that VHFradios spikes a lot more power transmitting ( about 25 watts right?) than receiving.
I THINK the radio is a Standard. (I won't be getting back to the boat to check for sure until the weekend).
Old 08-15-2011, 09:08 AM
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Fuses are rated in amps, not watts. 3 amps is too small for VHF on high power but wouldn't blow on low power. Check radio manual for proper fuse size. Probably 6-10 amps.

Eric
Old 08-15-2011, 08:56 PM
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7A minimum...check the owners manual, it will tell what amp draw is on transmit...
Old 08-16-2011, 09:40 AM
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Standard Matrix series recommends 6 amp fuse. Icom usually recommends 10 amp. Anything between those should work but you should go by manual recommendation.

Eric
Old 08-16-2011, 06:49 PM
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sometimes low battery voltage will cause the condition you are seeing. could be corrosion on a power terminal causing voltage loss @ radio power cord.
Old 08-17-2011, 04:28 AM
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Low voltage doesn't cause the fuse to blow.

Eric
Old 08-17-2011, 04:37 AM
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Originally Posted by fairbank56 View Post
Low voltage doesn't cause the fuse to blow.

Eric
when voltage goes down, current draw goes up - its ohms law
Old 08-17-2011, 07:08 AM
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that was happening to me when i had too small of a fuse in there a while back as well.

replaced with a larger fuse, all is well.
Old 08-17-2011, 07:44 AM
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All valid points- thanks guys. I don't think it's low voltage since I never shut the IO engine off while trolling. Could it be a bad ground?
Old 08-17-2011, 09:07 AM
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Originally Posted by slayride View Post
when voltage goes down, current draw goes up - its ohms law
Doesn't work that way. Ohm's law doesn't say that. VHF radio's have voltage regulators in them. You can vary the supply voltage from around 10v up to 14v and the current remains essentially steady as does the RF power output. Keep going below 10v and the current will drop slightly before the radio just shuts off.

It really can be frustrating being an experienced service technician trying to help out in these forums dealing with folks with little or no formal electronic/electrical training. It sure is entertaining reading through the BS though

All valid points- thanks guys. I don't think it's low voltage since I never shut the IO engine off while trolling. Could it be a bad ground?
Is it still blowing the fuse when you changed to a proper size fuse?

Eric
Old 08-17-2011, 09:15 AM
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Eric,
Nope, I haven't been to the boat yet and won't get their until this weekend... I will call the marina today and ask them if they can take a look to let me know brand and model...
Old 08-17-2011, 09:31 AM
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I just called the marina. The confirmed the radio is a STANDARD HORIZON ECLIPSE. My anntenna is a Shakespeare Galaxy 8' if that makes a difference.
Old 08-17-2011, 10:32 AM
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That's an oldie. The manual calls for a 6 amp 250v fuse.

Eric
Old 08-17-2011, 11:12 AM
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Eric. Yep. It came with my boat (1998 Proline 241 WA). I'll go with a 6 amp fuse and see how it works.

Thanks.
Old 08-17-2011, 03:01 PM
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Originally Posted by fairbank56 View Post

It really can be frustrating being an experienced service technician trying to help out in these forums dealing with folks with little or no formal electronic/electrical training. It sure is entertaining reading through the BS though

Eric
dont let your ego get the best of you (a common problem with marine electronic techs) ............its possible your not the only tech on the message board.

check out the ohms law calculator at the link below, and you will see that as voltage drops, current consumption increases, thus a blown fuse.

http://www.the12volt.com/ohm/ohmslawcalculators.asp
Old 08-17-2011, 04:48 PM
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So, according to your theory, I better not let my batteries go low cause all my fuses will start blowing due to the increased current

Your obviously not one of the other tech's, I'm afraid you don't have a clue.

Eric
Old 08-17-2011, 05:01 PM
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Originally Posted by slayride View Post
dont let your ego get the best of you (a common problem with marine electronic techs) ............its possible your not the only tech on the message board.

check out the ohms law calculator at the link below, and you will see that as voltage drops, current consumption increases, thus a blown fuse.

http://www.the12volt.com/ohm/ohmslawcalculators.asp
I wouldn't be calling people names if I were you.

You are somehow misusing ohms law. According to your theory, once the voltage reaches zero, the current would be infinite. It just doesn't wotk that way.

With a 12 volt supply from the battery, any increase in resistance in the circuit results in a smaller current flow, not a larger current flow.
Old 08-17-2011, 06:28 PM
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Originally Posted by rwidman View Post
... According to your theory, once the voltage reaches zero, the current would be infinite. It just doesn't wotk that way.
...
Next, you're going to say you don't believe in perpetual motion!





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