Fuse ???

[IanCC]

So when the manual says:

"Connect a 12 V dc supply (9.6 - 15.6 V) capable of supplying 2 A peak to the dc power cable"

That means I use a 1 amp fuse that blows at 2 amps?

Thanks as always.

 

[peteK]

I would use a 3amp fuse,2amp plus 50%= 3amp.

 

[Whaup367]

Not necessarily; fuses protect cables, so the fuse rating is linked to the size of the DC power cable, rather than the rating of the PSU... The requirement above is for the PSU to be able to supply 2A, the fuse should just ensure the cable (which must be rated for more than 2A) doesn't melt and a 1A fuse could well blow unnecessarily in this case. Even a 1 sq mm cable is likely (depends a bit on environmental conditions) to be able to carry over 15A safely, so a 5A fuse would be more than adequate to protect it and would be very unlikely to blow in normal operation.

What size is the "dc power cable"?

 

[IanCC]

Not necessarily; fuses protect cables, so the fuse rating is linked to the size of the DC power cable, rather than the rating of the PSU... The requirement above is for the PSU to be able to supply 2A, the fuse should just ensure the cable (which must be rated for more than 2A) doesn't melt and a 1A fuse could well blow unnecessarily in this case. Even a 1 sq mm cable is likely (depends a bit on environmental conditions) to be able to carry over 15A safely, so a 5A fuse would be more than adequate to protect it and would be very unlikely to blow in normal operation.

What size is the "dc power cable"?

I can choose my cable. The cable will be protected. I just assumed the instructions were talking about the protection required for the device. Your saying the device does not require protection?

 

[IanCC]

I would use a 3amp fuse,2amp plus 50%= 3amp.

Thanks for input, but surely a 3 amp blows at 6 amp. Which is 3 times peak power of the manual.

 

[Whaup367]

Sorry, no: when you wrote "connect to the DC power cable, I foolishly assumed the power cable was supplied with the device...

The device will need protection & the manufacturer ought to specify the appropriate fusing requirements in the installation instructions- might be for a "slow-blow" fuse, if surge currents are likely. Is there a plate on it? Technical specifications in the manual? A website?

Go on, give us a clue: what's the device?

 

[IanCC]

Sorry, no: when you wrote "connect to the DC power cable, I foolishly assumed the power cable was supplied with the device...

The device will need protection & the manufacturer ought to specify the appropriate fusing requirements in the installation instructions- might be for a "slow-blow" fuse, if surge currents are likely. Is there a plate on it? Technical specifications in the manual? A website?

Go on, give us a clue: what's the device?

The instructions, in their entirety for power connection, are as quoted in my OP. AIS transponder.

 

[Alex_Blackwood]

Not necessarily; fuses protect cables, so the fuse rating is linked to the size of the DC power cable, rather than the rating of the PSU... The requirement above is for the PSU to be able to supply 2A, the fuse should just ensure the cable (which must be rated for more than 2A) doesn't melt and a 1A fuse could well blow unnecessarily in this case. Even a 1 sq mm cable is likely (depends a bit on environmental conditions) to be able to carry over 15A safely, so a 5A fuse would be more than adequate to protect it and would be very unlikely to blow in normal operation.

What size is the "dc power cable"?

The fuse will protect against fault anywhere in the circuit. It cannot differentiate between the cable and the unit, whatever that is? However the cable must be rated at a higher current capacity than the fuse! depending on the unit and any starting or inrush current I would hazard a guess at 3 or 5 amp. Not enough information on the application. Again!

 

[PaulRainbow]

The instructions, in their entirety for power connection, are as quoted in my OP. AIS transponder.

3a blade fuse.

 

[IanCC]

3a blade fuse.

Cheers, thank you.

 

[Whaup367]

Yeah, not enough info for a definitive answer... 3A sounds like a good bet: uprate or try a slow-blow version if you get nuisance blows.

Here's the equivalent text from an AIT 1500 class-B transponder user manual:

5.10 Connecting to a power supply
The Class B Transponder should be connected to the ship’s 12V or 24V DC power supply typically provided by the vessel's battery.
It is recommended that crimped and soldered lugs are used to connect the AIS transponder to the power source. It is recommended that the power supply is connected via a suitable circuit breaker and/or 3A fuse
▪ Connect the red wire to a 12V or 24V power supply positive terminal.
▪ Connect the black wire to the supply negative terminal.
The Class B Transponder will only operate correctly as a Class B transponder when it is connected to an external supply that has a voltage greater than 9.6v. If the supply voltage is less than 9.6v or the Class B Transponder is only powered through the USB cable, then the Class B Transponder’s GPS circuitry will be powered down and the unit will only operate in AIS Receiver mode.
+-----

Good luck.