Fuse Rating for Automotive Application

[alpha_uma]

I have a regulated DC Adapter with the following specs:

input: 12V DC (from cigarette lighter socket)
output select: (3, 4.5, 6, 7.5, 9, 12)V DC, 0-300mA

Is a "1A, 125V" fuse safe enough to use (for the sake of protecting the car
battery and the electronics connected to the adapter)? What is a "typical"
fuse in such an environment for use with portable electronic gadgets? Any
hard data for typical ranges for current and voltage spikes during car
ignition?

Thanks
Al-U

 

[Landon]

I have a regulated DC Adapter with the following specs:

input: 12V DC (from cigarette lighter socket)
output select: (3, 4.5, 6, 7.5, 9, 12)V DC, 0-300mA

Is a "1A, 125V" fuse safe enough to use (for the sake of protecting the car
battery and the electronics connected to the adapter)? What is a "typical"
fuse in such an environment for use with portable electronic gadgets? Any
hard data for typical ranges for current and voltage spikes during car
ignition?

Thanks
Al-U

Hi,

A 1 amp fuse is probably the smallest you are going to be able to find
for automotive usage.

As far as protecting the battery etc. remember that the cigarette
lighter circuit already has a fuse in case something goes horribly wrong.

I wouldn't think that there is a "typical" fuse for anything, it depends
on what your load is going to be, that is where the "typical" comes
in. Your total load for the adapter is never going to be above 300mA
which is less than one amp, your adapter probably has some kind of
thermal overload built into it that will shut it down if the load goes
over 300mA.

Check under the dash for your cigarette lighter's circuit's fuse, it is
probably 15 amps, as long as you do not plug anything into the cigarette
lighter socket that exceeds your fuse rating you should be fine.


-Landon

 

[alpha_uma]

Hi,

A 1 amp fuse is probably the smallest you are going to be able to find
for automotive usage.

As far as protecting the battery etc. remember that the cigarette
lighter circuit already has a fuse in case something goes horribly wrong.

I wouldn't think that there is a "typical" fuse for anything, it depends
on what your load is going to be, that is where the "typical" comes
in. Your total load for the adapter is never going to be above 300mA
which is less than one amp, your adapter probably has some kind of
thermal overload built into it that will shut it down if the load goes
over 300mA.

Check under the dash for your cigarette lighter's circuit's fuse, it is
probably 15 amps, as long as you do not plug anything into the cigarette
lighter socket that exceeds your fuse rating you should be fine.


-Landon

Thanks for replying.

Yes, the car's cigarette lighter circuit already has a 15A fuse under the
dash. The "1A" fuse (specified by the DC adapter's manufacturer caution
against fire hazard) is actually inside the DC adapter. It has burnt out.

... your adapter probably has some kind of
thermal overload built into it that will shut it down if the load goes
over 300mA.

I hope so. Is there any relationship--direct or indirect--between the 1A
rating of the fuse and the 300mA output rating of the adapter? Or is that
something only the manufacturer's engineers would know? Would a max rating
of 300mA be enough to power a laptop computer?

Al-U

 

[Landon]

Thanks for replying.

Yes, the car's cigarette lighter circuit already has a 15A fuse under the
dash. The "1A" fuse (specified by the DC adapter's manufacturer caution
against fire hazard) is actually inside the DC adapter. It has burnt out.




I hope so. Is there any relationship--direct or indirect--between the 1A
rating of the fuse and the 300mA output rating of the adapter? Or is that
something only the manufacturer's engineers would know? Would a max rating
of 300mA be enough to power a laptop computer?

Al-U

Your adapter has a 1 amp fuse because that is the smallest that you can
find for automotive uses, there are probably some that are smaller but
they are hard to find.

1 amp also equals 1000mA.

I seriously doubt that 300mA is going to power your laptop, my little
portable CD player runs on something near 400mA and all it is is a
little motor, a laser, and a small audio amplifer to power the headphones.

Check the sticker on the laptop for its power requirements, it probably
says 120 volts; 50/60 Hz.; and then the amperage is probably something
between 3 and 6 amps (3000mA and 6000mA), or it may not have the
amperage and just list the wattage.

Your best bets for running it from the cigarette lighter jack are
getting an adpater that was specifically made for your laptop to run
from the cigarette lighter jack, or getting a power inverter that
converts the 12 volts DC to 120 volts AC then just plugging the laptop
into that.

Good luck.


-Landon