Using circuit breakers instead of fuses.

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bpratt

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Here's an interesting topic/question.

Why don't we use self resetting automotive circuit breakers instead of fuses in our lighting displays ?

I'm guessing it is because they are a lot more expensive than a ATO fuse.

Also one would assume that if you had an issue to blow a fuse/trip a circuit breaker, you probably wouldn't want power to be constantly reapplied to it.

Of course most boards are already fitted with a ATO fuse holder, but power to the boards can be fitted with either.


I didn't see a topic on this, but thought having a topic discussing automotive circuit breakers replacing fuses might be a useful thread for those who might consider using circuit breaker instead of fuses. :)
 
bpratt said:
Here's an interesting topic/question.

Why don't we use self resetting automotive circuit breakers instead of fuses in our lighting displays ?

I'm guessing it is because they are a lot more expensive than a ATO fuse.

Also one would assume that if you had an issue to blow a fuse/trip a circuit breaker, you probably wouldn't want power to be constantly reapplied to it.

Of course most boards are already fitted with a ATO fuse holder, but power to the boards can be fitted with either.


I didn't see a topic on this, but thought having a topic discussing automotive circuit breakers replacing fuses might be a useful thread for those who might consider using circuit breaker instead of fuses. :)
Click to expand...
You read my mind ? Looking forward to seeing the replys
 
You really don't want the power being restored to the circuit if there is a fault. The the self resetting breakers the power will keep getting restored which will increase the risk of damage if it's an intermittent fault.
The reason in particular that I wouldn't recommend them is that they are slow acting. If there is a fault condition you really would like the power removed as soon as possible. Fuses have a response curve that means that are semi slow at blowing in the case of a minor overload but self resetting breakers have a very long response time when it comes to overloads. The excess current needs to heat the bi-metallic element within the breaker enough for it to change shape. Theoretically the fuses should be sized to suit the full load of what they are connected to and they will only blow if there is a fault. If there is a fault you want the fuse to blow as soon as possible.
 
AAH said:
You really don't want the power being restored to the circuit if there is a fault. The the self resetting breakers the power will keep getting restored which will increase the risk of damage if it's an intermittent fault.
Click to expand...
Really? I thought circuit breakers like house circuit breakers don't keep switching the power back on? They would trip and stay off until a button or lever is flicked by someone.

This video shows the internals of both. I think @BradsXmasLights also did a video about house resettable fuses being used for DC.

View: https://www.youtube.com/watch?v=S0diAeysxVo


The main reason I see for not using resettable ones is that DC tends to arc.
 
I think its more about the cost as DIY is all about doing it as cheap as possible. CBs cost more than fuses but fuses generally have a slower trip curve than class B and Class C CBs
The response curve of a CB is determined by the class of CB being used, most commonly used is Class C but there are other classes of CBs with different trip curves. as listed below. Fuses tend to have a slower response time than a correctly rated class B and Class C CB

TRIP CURVE CLASS B
The MCB with class B trip characteristics trips instantaneously when the current flowing through it reaches between 3 to 5 times rated current. These MCBs are suitable for cable protection.

TRIP CURVE CLASS C
MCB with class C trip characteristics trips instantaneously when the current flowing through it reaches between 5 to 10 times the rated current. Suitable Domestic and residential applications and electromagnetic starting loads with medium starting currents.

TRIP CURVE CLASS D
MCB with class D trip characteristics trips instantaneously when the current flowing through it reaches between Above 10(excluding 10) to 20 times the rated current. Suitable for inductive and motor loads with high starting currents.

TRIP CURVE CLASS K
MCB with class K trip characteristics trips instantaneously when the current flowing through it reaches between 8 to 12 times the rated current. Suitable for inductive and motor loads with high inrush currents.

TRIP CURVE CLASS Z
MCB with class Z trip characteristics trips instantaneously when the current flowing through it reaches between 2 to 3 times the rated current. These type of MCBs are highly sensitive to short circuit and are used for the protection of highly sensitive devices such as semiconductor devices.

Another thing to take note is when using CBs with a DC voltage circuit is that you need to multiply the trip curve by 1.5 times because the trip curves are based on AC voltage, so this means a Class B trip curve is better to use with DC circuits rather than a C curve

Its important that CBs or fuses are rated correctly for the wiring that it is protecting as the main reason we use CBs and fuses is so the cables or device connected to it doesnt overheat if there is a short and cause a fire. on many occassions with a dead short the power supply should cut out on its own internal overload protection, but with higher wattage power supplies then this may not happen.
Note that an auto resetting CB is not commonly used and normal CBs do the same job as a fuse meaning that it protects the circuit from over current and wont reset. but a blown fuse needs to be replaced where a CB can just be reset
 
Mark_M said:
Really? I thought circuit breakers like house circuit breakers don't keep switching the power back on? They would trip and stay off until a button or lever is flicked by someone.
Click to expand...


The main reason I see for not using resettable ones is that DC tends to arc.
Click to expand...

Automotive circuit breaker reset automatically..... often used for car headlight circuits.

Yes, DC tends to arc, but that's why there are DC circuit breakers, design to quickly extinguish that arc.

Don't know why my text is so small in this reply though.
 
bpratt said:
Automotive circuit breaker reset automatically..... often used for car headlight circuits.

Yes, DC tends to arc, but that's why there are DC circuit breakers, design to quickly extinguish that arc.

Don't know why my text is so small in this reply though.
Click to expand...
If you have a problem with really small text there's a thingy to the top right that looks a bit like an eraser. It's a tool to remove formatting. Beside it is an icon that looks like a folded page which is for the BB Code editor.

The original question was about the self resetting ones which get used a lot in 4WD and trucks. These are designed for up to 24V and can withstand a fair number of overload cycles before the contacts get burned out from arcing. Arcing is another great reason not to use circuit breakers. Arcing produces nasty voltage spikes and this may damage electronics that is attached and pixels in particular are potentially susceptible.
 

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AAH said:
You really don't want the power being restored to the circuit if there is a fault. The the self resetting breakers the power will keep getting restored which will increase the risk of damage if it's an intermittent fault.
The reason in particular that I wouldn't recommend them is that they are slow acting. If there is a fault condition you really would like the power removed as soon as possible. Fuses have a response curve that means that are semi slow at blowing in the case of a minor overload but self resetting breakers have a very long response time when it comes to overloads. The excess current needs to heat the bi-metallic element within the breaker enough for it to change shape. Theoretically the fuses should be sized to suit the full load of what they are connected to and they will only blow if there is a fault. If there is a fault you want the fuse to blow as soon as possible.
Click to expand...

Ah, that makes sense, long response time because of how they are designed to react and recover.

I see in your later reply, there are some issues of voltage spikes that can damage the pixels.

Glad I made this post, it should help others coming in to this, and think car circuit breakers are a 'good idea'. :)
 
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