Tutorial Request : Fuses

Can we split the LiPo rant into a separate thread? I'd like to talk about fuses.

If LiPo's give you such heart palpitations then please, consider the lead acid battery. Why do they put all those fuses in my car if they serve no purpose?

I don't want to make LiPos absolutely safe. I just want to know how to stop the damned current when they get shorted.

Is this really beyond you guys?

They protect the wire between the fuse and whatever is being powered. If the wire shorts to frame it will blow the fuse rather than melt the wire and possibly catch on fire. The fuse amp value is selected in consideration of the wire current carrying capability.

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@2112
In the car, we still see the use of conventional fuses; why not using miniature fast-acting circuit breakers?

@GolamMostafa
I can only guess because of size and cost. Primarily cost.

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There is a 500 mA polyfuse on the Arduino UNO Borad. It protects both the breadboard and the Power Supply/USB connector of the PC. Does it get opened at over current or its resistance increases to limit the current?

  • IMHO, at its simplest, a fast acting fuse rated at 3/4 the amp rating of your maximum discharge rate of the battery might be a place to start.

  • Let’s assume your battery is rated at 30,000 mAh.
    Let’s assume the maximum discharge current for your application is 10A.
    It might suggest a fast acting fuse of no larger than 15A should be considered.

  • Are the batteries used in an environment where temperatures, ventilation and humidity might be a problem ?

Is it 3/4 (0.75 times) or 4/3 (~1.5 times)?

I don't have an adjustable bench top power supply so I use THESE and repurposed 19V laptop chargers
image

They have an adjustable current limit 5V USB output. You can current limit it down to the mA if needed. I find them very versatile with many uses.

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75% of 30,000mAh = 22 Amp (maximum) will give some headroom.

However, if the current taken was 10A there would be no need to use a 22A fuse when a smaller fuse would work i.e. 15A


Yes, an electronic current source set to some maximum, or even foldback current limiting.

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I don't know for sure but I imagine cost and reliability. Fuses are cheap and reliable, circuit breakers are expensive and, perhaps, not so reliable. Car fuses rarely blow, and if they do something probably needs fixing.

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I think this has been answered, if not then it would help to ask another related question to clarify whatever it is you still need explaining.

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These are set to a constant voltage (CV) until the set current limit is reached. Then they go into constant current (CC). At that point the voltage folds back while the current stays at its setpoint. The voltage doesn't cut out like a crowbar or LDO regulator. This can cause problems with certain circuits.

Even with that in mind, they are useable over-current protection devices. I won't say it can replace a properly sized fuse in any application but probably could have saved Delta_G's board.

I felt like I did. I was asking what sort of fusing would be appropriate for some various situation. Where are they needed and not needed. Instead I get information on how dangerous a LiPo can be.

This one I don't actually believe. I think there is some purpose there. That's the bit I'm wanting to learn about, not all the ways that they can fail.

It's really a general question not specific to any problem I am having at the moment. Just something I'd never thought of and didn't know anything about. Apparently I'm not alone. I though it'd be nice to have something here to share. I'll just go study it on my own.

I'll stick to coding tutorials and leave the grumpy old electricians to their hole.

I think I answered the second one and possibly the 1st and 3rd of those, if my answer didn't help then please clarify what you don't understand about my reply.

You mean this?

I think I've been misunderstood here. I figured if I didn't know then probably others as well and I was asking if someone could write a little. Like this fine example from @Grumpy_Mike about decoupling.

If "use fuses" is all it boils down to then that's cool. I figured there was more to consider.

They do serve a purpose, they stop the wires from going up in smoke and possibly setting the car on fire in the event of a short circuit.

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My reply #16 was in response to your #14 where you mentioned car batteries and lipo batteries, both of which can generate enough current to quickly make wires hot enough to start a fire. In the case of lipo batteries there's the added risk of the battery itself catching fire. So in either case I'm saying always use fuses for these types of battery.

Why are they all different sizes? Some are 5A and some are 30A. The wires coming out of the back of the fuse block are mostly the same size.

See, someone out there had to know how to choose the size. Someone had to know to put it on the hot side or the ground side. Someone made some decisions on that fuse in my car. What types of things did they have to consider?

It really doesn't matter. I think the tutorial request has been roundly rejected. I don't really wish to go any further here. That's all I really wanted to do and I think I've got my answer there.

If I have any further issues with a fuse I'll post a specific question about a specific circuit.

Fuses are primarily there to protect the wiring and the power source. In many cases there are components in the circuit that will overheat and catch fire at currents lower than the supply wire is rated for. In that case, a fuse is selected that will tolerate the amount of current needed by the circuit and still provide some protection against overheating in case of a fault.

Nothing would have prevented the vaporization of that laughably thin trace joining those two ground pours. When you replace it with a piece of wire you will probably find the next weakest link although nothing will save the circuitry from a short in the headset.

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I answered this in reply #10, others have also covered it.

You can't expect a tutorial to just appear as a response to a request like yours. This topic was never going to be a tutorial, but it might, hopefully contain enough relevant answers to give you the information you wanted, and it might prompt someone to write a tutorial. Good tutorials take weeks to write.

If you really want to learn about fuses challenge yourself to write the tutorial you are asking for.

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