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SmartGauge fuse.


fudd
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Good isolation everyone.

my SmartGauge has a 20amp fuse with a 3 amp fuse in the positive cable. The 20 amp blew but the 3 amp didn’t. Has anyone got any ideas as to why it blew in the first place and why the 3 amp didn’t. Thanks. 

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Can you explain exactly what you have?

It can't just be a standard SmartGauge, surely, as these just connect directly to the battery bank with a quite thin gauge 2 core cable, and would normally have just a single low value fuse in line.

Where (exactly!) is the 20A fuse connected to in this set up.

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Because the access to my batteries isn’t very good I disconnected my old broken monitor out and just connected the SmartGauge to the old cable and put a 3 amp inline fuse in the positive cable. It worked for about a year and then stopped.

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10 minutes ago, fudd said:

Because the access to my batteries isn’t very good I disconnected my old broken monitor out and just connected the SmartGauge to the old cable and put a 3 amp inline fuse in the positive cable. It worked for about a year and then stopped.

I’m not sure it would have worked correctly, as the instructions for smartguage are quite explicit. The wires need to be connected directly from the unit to the battery terminals.

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1 minute ago, Tony Brooks said:

I would suggest either age fatigue or a short to negative between the fuse and the 3 amp one.

Do you mean fuse age or the actual unit itself?

Just now, Phil. said:

I’m not sure it would have worked correctly, as the instructions for smartguage are quite explicit. The wires need to be connected directly from the unit to the battery terminals.

They are. The 20amp is about three inches from the + terminal and the 3amp is 2” after that. 

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8 minutes ago, fudd said:

Do you mean fuse age or the actual unit itself?

 

The fuse itself - or the holder if its a torpedo continental style fuse. I can't see a Smartguage heating a 20 amp fuse enough to cause thermal stress but whatever you ha don it before might have done.

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6 minutes ago, Tony Brooks said:

 

The fuse itself - or the holder if its a torpedo continental style fuse. I can't see a Smartguage heating a 20 amp fuse enough to cause thermal stress but whatever you ha don it before might have done.

It’s a modern blade fuse. The 3amp is a glass type. I’ll try and connect it up without the blade fuse in it. I still can’t understand why the 3amp hasn’t blown. 

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My only thought is that the 20 amp fuse had almost blown on a previous occasion (maybe because the the previous system had failed) and was hanging on by a thread (almost literally), and now has finally worn out.  Its a bit unlikely but all I can think of. Fuses do fail from old age.

 

................Dave 

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3 minutes ago, dmr said:

My only thought is that the 20 amp fuse had almost blown on a previous occasion (maybe because the the previous system had failed) and was hanging on by a thread (almost literally), and now has finally worn out.  Its a bit unlikely but all I can think of. Fuses do fail from old age.

 

................Dave 

I’ve tried 3 new fuses. Blows straight away. 

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28 minutes ago, fudd said:

It’s a modern blade fuse. The 3amp is a glass type. I’ll try and connect it up without the blade fuse in it. I still can’t understand why the 3amp hasn’t blown. 

I assume there is some distance between the 20 amp fuse and 3 amp fuse and from what you say about how you connected it and best practice I assume the 20 amp fuse is closest to the batteries. If so DO NOT just take the 20 amp fuse and holder out and connect the wires. There is every possibility a positive cable has chaffed through between the 20 and 3 amp fuses and if so just joining the wires may well result in burned fingers and possibly a fire.

21 minutes ago, fudd said:

I’ve tried 3 new fuses. Blows straight away. 

OK so that makes a short circuit in the wiring even more likely.

 

Please clarify the run from battery to gauge. I assume its battery > 20 amp fuse >>>>>>>>>>>> 3 amp fuse > gauge

Edited by Tony Brooks
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11 minutes ago, Tony Brooks said:

I assume there is some distance between the 20 amp fuse and 3 amp fuse and from what you say about how you connected it and best practice I assume the 20 amp fuse is closest to the batteries. If so DO NOT just take the 20 amp fuse and holder out and connect the wires. There is every possibility a positive cable has chaffed through between the 20 and 3 amp fuses and if so just joining the wires may well result in burned fingers and possibly a fire.

OK so that makes a short circuit in the wiring even more likely.

 

Please clarify the run from battery to gauge. I assume its battery > 20 amp fuse >>>>>>>>>>>> 3 amp fuse > gauge

That’s exactly how I’ve done it. I’ve checked the flex and it’s all ok. It could, I suppose have been an old fuse. 

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3 minutes ago, fudd said:

That’s exactly how I’ve done it. I’ve checked the flex and it’s all ok. It could, I suppose have been an old fuse. 

 

37 minutes ago, fudd said:

I’ve tried 3 new fuses. Blows straight away. 

 

4 old fuses ? Not likely.

 

You have a problem, which as Tony says is almost certainly a short.

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Have you checked the 3amp fuse? its not been replaced by a nail has it?    Are you sure about your 20 amp fuses? they are not 20milliAmp or something daft like that?

 

Are you really sure the cable between the fuses has not shorted to ground?   Can we have some photos?

 

................Dave

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48 minutes ago, fudd said:

That’s exactly how I’ve done it. I’ve checked the flex and it’s all ok. It could, I suppose have been an old fuse. 

Flex? Not cotton covered rubber insulated by any chance like very old lamp drops?

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1 hour ago, Loddon said:

What happens if you take out the 3 amp 0ne and replace the 20?

I’ll look tomorrow. Thanks

Just now, Tony Brooks said:

Flex? Not cotton covered rubber insulated by any chance like very old lamp drops?

No. Twin red-black multi strand 

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Take the 3 amp fuse out and the 20 amp fuse. connect a multimeter set to the lowest Ohms rage (probably 200) between the BATTERY side of the 3 amp fuse holder and any 12V negative or even bare hull/engine metal. The meter should read infinity - that is an I that looks like a 1 on the right of the dial. If the meter reads zero or a very few Ohms you have a short along the cable somewhere

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8 hours ago, fudd said:

Because the access to my batteries isn’t very good I disconnected my old broken monitor out and just connected the SmartGauge to the old cable and put a 3 amp inline fuse in the positive cable. It worked for about a year and then stopped.

Not sure how that works, as the old unit was wired to a shunt.

  • Greenie 1
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Good morning. I got a couple of new fuses from a friend and put one in and it’s all fine now. Still not sure why the 3 amp fuse didn’t blow. Thanks all. 

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On the basis of what you say and without any images or direct inspection the symptoms all point to a short circuit between the two fuses. The 3 amp fuse would never "see" the short circuit current so won't blow.  It could be something to do with vibration moving the conductor away from  metal at times or you may have moved something while trying to fix it but the only thing that fits several 20 amp fuses blowing is a short circuit between the two fuses.

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19 minutes ago, Tony Brooks said:

On the basis of what you say and without any images or direct inspection the symptoms all point to a short circuit between the two fuses. The 3 amp fuse would never "see" the short circuit current so won't blow.  It could be something to do with vibration moving the conductor away from  metal at times or you may have moved something while trying to fix it but the only thing that fits several 20 amp fuses blowing is a short circuit between the two fuses.

I’ll remove the 20 amp fuse and connect directly to the terminal. It’ll be a bugger of a job but for peace of mind........

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1 hour ago, fudd said:

I’ll remove the 20 amp fuse and connect directly to the terminal. It’ll be a bugger of a job but for peace of mind........

If you do that and you have an intermittent short somewhere before the 3A fuse as seems likely then you’ll soon find where it is as the wire glows red hot and melts. 

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