What amp fuses to use

B

breakdown

Junior Member
I am running a flathead with a 6V system. I built a little fuse panel for the car that has fuses for the brake lights, headlights, ignition, and battery. What amp fuses would one use for each of these? Thanks
 
Fuse size is related to wire size. The fuses are to protect the wiring. Does your car have original wiring? Need to build a table/chart that list the wire size that will be connected to each fuse and go from there.
 
JSeery is absolutely correct......can't be emphasized enough! Fuses are always sized to protect WIRING in a circuit, rather than any device powered by that wiring. DD
 
breakdown said:
I am running a flathead with a 6V system. I built a little fuse panel for the car that has fuses for the brake lights, headlights, ignition, and battery. What amp fuses would one use for each of these? Thanks
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Only one fuse is normally used for all the lights, interior and exterior. All power for these lights go through the single 20 amp fuse located on the firewall for prewar cars, while from 1940 to, I believe, early 1947, Fords have what is called a circuit breaker in the same location. This device will rapidly open and close the circuit if overloaded, in order to provide at least some lights in a kind of a strobe effect while driving home after dark. For circuit protection after 1947, I haven't a clue what was provided.

Ignition is not fused, and from battery to solenoid would never be fused either.


(Remarkable! Is anyone keeping track of how many fuse questions there have been in this week alone? :D)
 
Here a table for a guide.
 

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To determine amperage capacity of a circuit, in addition to the circuit's wire gauge one needs to also consider the length of the wire running to the item served. Doing this accounts for amperage consumed by the inherent resistance of the wire itself.

Here are three (*.pdf) attachments which have tables to assist in identifying the maximum amperage capacity of a circuit. Apparently you will need to download them to open them for reading.
 

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What Drbrown posted is good information for establishing wire size requirements. Then the fuse size is based on than wire size.
 
The charts are a good guideline, but also take into consideration where the wire goes----a wire running along frame rail with nothing but metal near it can be fused to the max of the wire ---but a wire running through the headliner---or near stuff that easily ignites should have a fuse just large enough to not have nuisance failures
 
Hi breakdown, To directly answer your question on fuse values without getting into a heap of technical calculations you can use the following fuses with safety in a 6 volt system. Headlights 20 amp fuse providing bulbs are not exceeding 50 watts. Tail and park and dash lights 10 amp fuse. Stop lights 10 amp fuse for 2 x 21watt bulbs. Indicator lights 10 amp fuse. You say battery fuse so I guess you want this fuse in the main power supply for all items in the car including generator which is what capacity ? I think you might require a 30 or 35 amp fuse here. If you have a good test ammeter you could test the individual current draw on all these circuits to give you an accurate idea of the current used. The fuse needs to have some leeway higher rated than the current draw of the circuit by at least 30%. Regards, Kevin.
 
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