Fuse ratings
- Thread starter Ilanortho
- Start date
Thank you; interesting site. Will keep me busy for a while.When faced with discussing what feels like a simple subject, yet the discussion sounds confused, I resort to identifying the data. Stated in post 7 @Ilanortho says the books are not identifying the issue.
Perhaps this link will help.
Fuse and Types of Fuses - Construction, Operation & Applications
What is a Fuse? Construction & Working of a Fuse How to Select Proper Rating Size of Fuse? Characteristics of a Fuse Classification of Fuses Types of Fuses DC Fuses AC Fuses Cartridge Fuses D - Type Cartridge Fuse HRC (High Rupturing Capacity) Fuse or Link Type Cartridge Fuse High Voltage Fuses...www.electricaltechnology.org
In review some of what has been stated by all is valid.
That's incorrect.
Yes, you are wrong!
No, Don, that's incorrect
Incorrect.
More precisely, withstand. But the details are more complicated.
Correct! We have a winner!
I don't like to appeal to authority, but I'm an electrical engineer. I am appalled at the incorrect information that people supply here as answers to this question. They demonstrate a lack of understanding of fundamentals of circuits and devices.
Agree with all of the above rectifications. Thanks because I had the same concerns.
Don't be appalled; My diesel guy feels the same way about the engine I tinker with. Read a whole bunch of books carefully - enough to be dangerous. But smart enough to know the danger present and that I needed to get this cleared up.
Feels really good to get these answers to something that was bothering me for a long time and just couldn't seem to figure out - wrong basic assumptions were incorrect (as usual) creating a roadblock to the correct answer.
Way, way back in a former life, I asked this question of my Navy instructor. I knew his answer was BS but nodded as if I understood. I kept searching until the truth came through. The problem at the time was that reference books didn't have a search engine.
While we are on this topic, I will share some info. Someone mentioned batteries. If you want to see a good fire, short the battery through a length of wire. First the insulation burns and if the wire is small enough it will burn. The resulting fire can be spectacular. Always keep a fuse in-line as close the the battery as possible.
I have a battery at home for emergency lighting and backup power for my ham radio. You can bet that it is fused.
I have a battery at home for emergency lighting and backup power for my ham radio. You can bet that it is fused.
I was being pretty quick before and didn't add the link to the page about battery fusing:Battery Bank Fusing by Compass Marine How To
That kind of reminded me of what Dylan said:
Half the people can be part right all of the time, an'
Some of the people can be all right part of the time,
But all the people can't be all right all of the time.
My batteries all have fuses right on the terminal: MRBF's on thermal blocks from Blue Sea Systems.
MRBF == Marine Rated Battery Fuse
I think mine are 100A. You can do a lot of damage with 100A, but at least you won't blow up the battery or melt the (properly sized) wires.
MRBF Terminal Fuse Block - 30 to 300A 5191
MRBF == Marine Rated Battery Fuse
I think mine are 100A. You can do a lot of damage with 100A, but at least you won't blow up the battery or melt the (properly sized) wires.
MRBF Terminal Fuse Block - 30 to 300A 5191
That battery mentioned above is what powers my Minn Kota. I have wanted to fuse it when on the boat. The MRBF will do it.
Since we've gotten off track here, anyway, here's an explanation of how a fuse might behave in a circuit.
On the left we have the circuit during normal operation. Let's say the battery is 12VDC, R1 is 1Ω and R2 is 1Ω. The fuse is a 10A fuse. In normal operation I1 and I2 are equal, I3 is zero. The current is 6A: 12V/2Ω. V1 = V2 = 1/2 the battery voltage = 6V, assuming the resistance of the fuse is zero. When the fault occurs - represented by the switch, "S," closing - for a moment the currents I1 and I3 become 12A, I2 goes to zero, V2 goes to zero volts, and the fuse, "F," blows. When it blows it opens, and all currents go to zero, and V1 goes to 12V.
Note that in normal operation V1 and V2 are (virtually) equal, and after the fuse blows the voltage across the fuse, V1 - V2, is the battery voltage, 12V.
On the left we have the circuit during normal operation. Let's say the battery is 12VDC, R1 is 1Ω and R2 is 1Ω. The fuse is a 10A fuse. In normal operation I1 and I2 are equal, I3 is zero. The current is 6A: 12V/2Ω. V1 = V2 = 1/2 the battery voltage = 6V, assuming the resistance of the fuse is zero. When the fault occurs - represented by the switch, "S," closing - for a moment the currents I1 and I3 become 12A, I2 goes to zero, V2 goes to zero volts, and the fuse, "F," blows. When it blows it opens, and all currents go to zero, and V1 goes to 12V.
Note that in normal operation V1 and V2 are (virtually) equal, and after the fuse blows the voltage across the fuse, V1 - V2, is the battery voltage, 12V.
Attachments
If you want to see what will happen placing a fuse wrong place watch this, its almost at the end of the video.
Seminar: Marine Electrical Basics - Part 3 of 6 | Pacific Yacht Systems (pysystems.ca)
Seminar: Marine Electrical Basics - Part 3 of 6 | Pacific Yacht Systems (pysystems.ca)
Can you please net it out for me so I don't have to watch a 58 minute video to get your point?
Thanks. That's actually pretty good!
There's a way to share a youtube video starting at a particular point. Here's this one starting at about 44 minutes:
No lesson is complete without a test. Is the lamp on or off? Sorry for my crappy artwork. You can only do so much with
Paint!
Paint!
It would appear that it's on, since the circuit is complete. But, you don't say what the battery voltage is, or what the rating of the lamp might be.
You are thinking too hard. The lamp is OFF because that is a BLEW fuse.
Sorry, all this brought back memories.
A 10A fuse can handle 10A. Period. Aside from the interesting AC/DC arcing discussions, voltage difference provided to the circuit is irrelevant, since it's NOT what the fuse will see under normal operating circumstances.
In the case of "oops"--a short circuit or other abnormal situation--the fuse might see the total voltage difference provided to the circuit. If this occurs, then the fuse will do its job and melt in a hurry.
There really is no need to bring up the math for Ohm's law and power, especially if you want to use 12V, 24V etc. for voltage in these equations. Keep in mind the fuse will generally only see a very very very (did I say very) small chunk of the total voltage being provided to the circuit.
Peace,
Josh (a calculus based electricity & magnetism instructor)
In the case of "oops"--a short circuit or other abnormal situation--the fuse might see the total voltage difference provided to the circuit. If this occurs, then the fuse will do its job and melt in a hurry.
There really is no need to bring up the math for Ohm's law and power, especially if you want to use 12V, 24V etc. for voltage in these equations. Keep in mind the fuse will generally only see a very very very (did I say very) small chunk of the total voltage being provided to the circuit.
Peace,
Josh (a calculus based electricity & magnetism instructor)