[Shop-talk] Fuses

[eric at megageek.com]

Thanks so much for this information.

I can't believe that I might actually be looking forward to my next short 
circuit!  8>)

Everyone, have a great day and thanks for all the help!

Moose



From:   JohnT Blair <jblair1948 at cox.net>
To:     Shop-talk at autox.team.net
Date:   01/12/2024 10:59 AM
Subject:        Re: [Shop-talk] Fuses
Sent by:        "Shop-talk" <shop-talk-bounces at autox.team.net>



 On 01/12/2024 6:21 AM EST Moose wrote: 
 
>This is brilliant (figuratively AND literally) 8>)   But is this safe? 
Couldn't it melt wires if there 
>is a short? 
 
 
Moose, 
 
Yes it's safe if you do it correctly.  You want to use a good socket, if 
it's not plastic wrap it with electrical tape.  We use this for finding a 
short in a piece of electronic equipment.  Put a 60W light bulb in a box 
in series with the outlet that you plug the equipment into.  This will 
limit the current to 1/2 amp. 
 
I also suggest (someone else mentioned this) that you make some sort of 
adapter to plug into the fuse socket.  For the old 
glass cylindrical fuses, solder a piece of insulated wire on each end so 
you can connect clip leads to the wire to connect to the light bulb or to 
the circuit breaker.  For the spade type, take a couple of spades and 
solder insulated wire to the spades. 
 
The secret is to use something to use limit the current to less that the 
original fuse, ie. if the circuit that has the problem has a 10A fuse, 
limit the current to 5A.  How?  Use ohms and Watts law, 
 
Ohms law:  E = I * R     E - Voltage,  I - Current,  R - Resistance. 
 
Watts law:  P = I * E      P - power (watts) 
 
So for a 10 A circuit in a 12 V system, R = E / I, you'll need 
R = 12V / 10A = about 1 ohm of resistance. 
 
You also need to account for the power:  P = I * E or 
P = 10A * 12V or 120 W. 
 
This is why you use light bulbs.  But they should be closely matched to 
the power used by the circuit being worked on. 
 
If you go too low of wattage, the light bulb will burn out,  If you go to 
high, then the light bulb won't limit the current enough to protect the 
circuit. 
 
>This is a really great idea I never hear of, so thanks for sharing! 
 

Yes, I use it for electronics.  But you need incandescent bulbs. 
 
https://www.instructables.com/Light-Bulb-Current-Limiter/ 
 
For automotive I prefer to have different size circuit breakers, 1, 5, 10, 
20, 30A breakers and clip leads. 
 
JohnT,

John T. Blair  WA4OHZ     email:  jblair1948 at cox.net
Va. Beach, Va                    Phone:  (757) 495-8229 
 
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