DC Fuse

[Oxia]

I am working on a small project and need to fuse two outputs at 24v DC (2A) and 12v DC (2A). A panel building friend of mine has told me to use MCBs at 2A each but in my tests the breakers had no tripped at 2.9-3.1A and they were getting quite warm.

I would like your input on the best fuse for the job and why he thinks MCBs are OK to use?

 

[RF Lighting]

http://uk.rs-online.com/web/p/produ...-3633baf8113b&istItemId=xwipwpxpl&istBid=tzit

 

[PrenticeBoyofDerry]

What type of breaker were they?
Did you use DC breakers?

 

[Oxia]

I was told to use normal type B

 

[PrenticeBoyofDerry]

I was told to use normal type B

They react differently on DC, will take higher amperage to trip them, likely to be somewhere near double. If I recall, DC does also reduce the life of an AC breaker.

 

[SimonH2]

Some manufacturers quote DC specs for their breakers - I recall reading about this on Merlin Gerin's site some time ago as I had an idea for a project (that didn't happen).

The thermal element should trip the same for DC as AC since AC currents are quoted as RMS. The magnetic trip may operate differently, but that possibly depends on the time constant of the magnetic circuit.

The breaking capacity is likely to be significantly lower on DC than on AC, and the voltage rating might be lower.

 

[JohnW2]

I am working on a small project and need to fuse two outputs at 24v DC (2A) and 12v DC (2A). A panel building friend of mine has told me to use MCBs at 2A each but in my tests the breakers had no tripped at 2.9-3.1A and they were getting quite warm.

As SimonH2 has said, when using a standard AC MCB on DC, the magnetic trip behaviour will probably be different from that with AC, but the thermal trip should be essentially the same ...

However, I wonder how long you waited. A B2 MCB will take about 1 hour to trip (thermally) at 2.9A (I2 = 1.45*In) and, I imagine, not much less than an hour to trip at 3.1A.

Kind Regards, John

 

[Oxia]

would a quick blow glass fuse be better?

 

[ricicle]

would a quick blow glass fuse be better?

It depends on what the fuse is protecting.

 

[Oxia]

would a quick blow glass fuse be better?

It depends on what the fuse is protecting.

Its for a 24v control circuit that will power panel lights, timers and contactors etc

 

[JohnW2]

Its for a 24v control circuit that will power panel lights, timers and contactors etc

Where are you wanting to put these fuses/MCBs - between the power source and the 'panel'? If so, what sort of power source is it? If it's an 'electronic' mains-powered power supply, there could well already be adequate current limiting built into it (unless you're wanting 'belt and braces'). If it's 'car batteries', then you certainly would need a fuse!

Kind Regards, John

 

[ban-all-sheds]

Look for automotive/marine/aviation breakers, made for 24V DC applications.