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Old 17-06-2016, 06:09   #31
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Re: 5 amp fuse keeps blowing?

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Originally Posted by TurninTurtle View Post
Works for a resistance based incandescent light bulb... not for most electronics.

Generally its a bad idea to feed electronics the wrong voltage. While most "12 v" devices can tolerate 10.5 to 14.0 v (some a little wider range) due to expected output range of automotive alternators and batteries, some can't tolerate being outside 11.0 to 13.0 v.

Electric motors will attempt to deliver the power demanded by the load. Reduced voltage applied invariably results in increased current demand. Reduced voltage results in lower operating RPM which means lower "counter-electromotive force" which is the main "resistance" to current flow while a motor is spinning.

Actually the "fixed impedance" is mainly seen in lights (and not LED or fluorescent lights...)
OP is referring to 12Vdc marine instruments.

Most represent a fixed impedance to the supply, and hence, current drawn does not increase with reduced applied voltage.
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Old 17-06-2016, 14:56   #32
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Re: 5 amp fuse keeps blowing?

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Originally Posted by ramblinrod View Post
Refer to ABYC E11 - AC and DC electrical systems on vessels.

The panel current limiting device should be sized to protect the wire, not the devices connected to it...
Whoever wrote that (if indeed they did) is an idiot. The wire should be sized to provide the maximum device current at an acceptable voltage loss. The fuse or breaker should be sized so as to pass this current continously, this will protect both the wire and the device.
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Old 17-06-2016, 15:38   #33
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Re: 5 amp fuse keeps blowing?

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Originally Posted by nigelmercier View Post
Whoever wrote that (if indeed they did) is an idiot. The wire should be sized to provide the maximum device current at an acceptable voltage loss. The fuse or breaker should be sized so as to pass this current continously, this will protect both the wire and the device.
The panel breaker or fuse is sized to protect the branch circuit wire.

A 15 A panel breaker may be connected to 5 devices, each requiring current limiting of 3 A. (That the appropriate sized wire has to be run is a separate issue.)

In this case, the panel breaker does not protect any device in the circuit. It only protects the wire should for some reason, the sum of the device current or wiring short circuit attempt to draw more than 15A.

It's sole purpose is to prevent the branch circuit wire from passing more current than it can safely carry without burning.

Wire size selection is a separate issue and varies with max current carrying capacity, max voltage drop, bundling, and ambient temp.

Some devices may require current limiting.

For example, the panel may have a 15 A breaker marked "Instruments". This breaker may feed a fuse block to which a VHF, chartplotter, and a depthsounder (each with there own off switch) are connected.

If the required current limiting device for each of these 3 devices is 5A, the 15A breaker is fine (assuming the wire is correctly sized). However, each instrument requires its own 5A fuse, so if one fails due to a wiring short circuit, the others remain operational.

Sorry, no idiot here.
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Old 17-06-2016, 15:39   #34
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Re: 5 amp fuse keeps blowing?

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Originally Posted by nigelmercier View Post
Whoever wrote that (if indeed they did) is an idiot. The wire should be sized to provide the maximum device current at an acceptable voltage loss. The fuse or breaker should be sized so as to pass this current continously, this will protect both the wire and the device.
For your idea to work I would need to separately run my wind instruments, knotmeter, gps, ais, etc, back to the panel and find sub 1 amp circuit breakers for each.
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Old 18-06-2016, 10:29   #35
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Re: 5 amp fuse keeps blowing?

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Originally Posted by ramblinrod View Post
If the required current limiting device for each of these 3 devices is 5A, the 15A breaker is fine (assuming the wire is correctly sized). However, each instrument requires its own 5A fuse...
Agreed. Obviously an error in translation
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Old 11-09-2016, 03:47   #36
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Re: 5 amp fuse keeps blowing?

Here's an update.
I have installed my Antenna, Splitter and AIS. I have also placed the required fuses, in line to protect the devices.
I left the AIS and splitter running today and it blew A 15 amp fuse in about half an hour.
Below is what I need to run, can you let me know if you think a 15 amp fuse should have been sufficient? I cant tell you what the wire gouge is but it is very heavy for the purpose. So I think we can rule that out.
If a 15 amp fuse should be adequate. Then that leaves a short somewhere?
Click image for larger version

Name:	<a title=ICOM MA-TR.jpg Views: 41 Size: 31.9 KB ID: 130949" style="margin: 2px" />


Name:   AIS SPLITTER.jpg
Views: 79
Size:  11.8 KB

Click image for larger version

Name:	Chart Plotter.JPG
Views:	38
Size:	57.9 KB
ID:	130951
The Garmin is also running a transducer.

Regards Jeff
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Old 11-09-2016, 05:15   #37
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Re: 5 amp fuse keeps blowing?

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Originally Posted by Hoohaa View Post
Here's an update.
I have installed my Antenna, Splitter and AIS. I have also placed the required fuses, in line to protect the devices.
I left the AIS and splitter running today and it blew A 15 amp fuse in about half an hour.
Below is what I need to run, can you let me know if you think a 15 amp fuse should have been sufficient? I cant tell you what the wire gouge is but it is very heavy for the purpose. So I think we can rule that out.
If a 15 amp fuse should be adequate. Then that leaves a short somewhere?
Attachment 130949

Attachment 130950

Attachment 130951
The Garmin is also running a transducer.

Regards Jeff
Search the Internet for the specs of each of the devices. They will list the power draw in Amps. Add all the Amps from the spec sheets, if they are over 15, then you need a bigger fuse (the fuse should be about %20 over the required draw).

Based on the items you have listed, I'm guessing a 15A is to small. The VHF will draw 8-10A when transmitting. This would explain why the fuse didn't blow right away and took some time! I would probably try a 25A for that circuit (if the wire is sufficient).
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Old 11-09-2016, 05:18   #38
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Re: 5 amp fuse keeps blowing?

Thanks T . I will do some homework.

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Old 11-09-2016, 06:00   #39
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Re: 5 amp fuse keeps blowing?

What do the inline fuses add up to? If they all add up to significantly less than 15 amps then current to blow the 15 has to be coming from somewhere else.
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Old 11-09-2016, 07:24   #40
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Re: 5 amp fuse keeps blowing?

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Originally Posted by Hoohaa View Post
I have recently installed a new AIS and splitter. We wired in a bus, which takes its power from the instrument switch on the pannel. If everything is running, the fuse will blow after a minute or so. I suspect we are overloading the 5 amp fuse but would like some input on what size I should be running. Note that the fuse does not blow if the AIS is switched off.
Here is a list of the equipment currently using that fuse and the manufacturers power consumption specs.

Class B Icom AIS MA-500TR, with its own gps antenna - Uses TX 1.5 amps & RX 0.7 amps (could someone explain what TX & RX mean?).

GME AIS Splitter (AISS120) - uses 1.15 amps.

Garmin GPS map 550S plotter with a Transducer - uses 1.25 amps.

If this data is correct then its a total of 4.6 amps..

Thanks for your help.
Jeff
TX transmit
RX receive.
as your addition makes 4.6 amps, and you blow a 5 amp fuse, why not wire the fuse to be 10 amp. perhaps then you might find comfort and function as opposed to dysfunction and aggravation.
and check to ensure your wires are not providing too much resistance which also causes breaker fail. (too skinny)
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Old 11-09-2016, 14:08   #41
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Re: 5 amp fuse keeps blowing?

Thanks Zee. I should have read my own posts.
The last fuse i blew was 15 amps.
I will have closer look at the wire I am using. I am almost certain its significant Guage.
If there was a short. Wouldn't that blow the fuse straight away?
Can I rule out a short?

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Old 11-09-2016, 14:24   #42
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Re: 5 amp fuse keeps blowing?

The VHF should be wired directly to the battery with its own inline fuses. Wire size as recommended by the manufacturer for the length of the wire run; which should be as short as possible.

Remember the fuse is there to protect the wire not the instrument on the end. Find out what your wire size is and fuse accordingly. The instruments can be fused individually if they don't have built in fuses.

5 Amp should be fine for the rest of what you show there. If they are blowing a 15A without Tx on VHF you have a problem.
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Old 11-09-2016, 14:47   #43
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Re: 5 amp fuse keeps blowing?

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The VHF should be wired directly to the battery with its own inline fuses. Wire size as recommended by the manufacturer for the length of the wire run; which should be as short as possible.

Remember the fuse is there to protect the wire not the instrument on the end. Find out what your wire size is and fuse accordingly. The instruments can be fused individually if they don't have built in fuses.

5 Amp should be fine for the rest of what you show there. If they are blowing a 15A without Tx on VHF you have a problem.
Where did a VHF come into this?

If there was a dead short the 15 amp would blow right away.

If your 3 inline fuses add up to less than 15 amps then the total current has to be less than 15 amps, or one of the other fuses would be blowing. So there has to be something else connected to this circuit than these 3 items.

For completeness - if the inline fuses are slow blow and add up to nearly 15 amps and the 15 amp fuse is a fast blow, then you could blow the 15 amp fuse. Typically though you put fast blow fuses on electronics.
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Old 11-09-2016, 15:36   #44
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Re: 5 amp fuse keeps blowing?

If I get this correctly you have devices that draw less than 5 amps but they are blowing a 15 amp fuse. I would stop messing with this immediately and find someone that knows how to troubleshoot electrical problems. We don't even have a wiring diagram to help us help you.
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Old 11-09-2016, 15:39   #45
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Re: 5 amp fuse keeps blowing?

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Where did a VHF come into this?

.
I don't see one in the pics but almost everybody else in the thread is wittering on about one, perhaps there is one associated with the AIS or something.

Unlikely the the three items pictured would be anywhere near blowing any type of 15A fuse.
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