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Old 07-23-2013, 10:16 AM
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Current Draw

Greetings from the sunny hills of Colroado,

Today's hot flash is to determine what ratings of fuses or circuit breakers I need to design my wiring system.

I'm planning a master disconnect as close to the battery as practical and to provide an inline fuse or breaker for the heavy cable that goes to the starter or master ground cable.

How much amperage does a starter draw? I know it varies with starter, number of cylinders, compression ratio and something about the acceleration of a rotating mass as in a blower drive, etc. I have a SBC with 9:1 and an under driven 4-71 blower.

Also, I've done a tad of snooping here on the forum bet didn't come across a listing or drawing of what fuse I will need for various circuits.


So, to (finally) get to the point....
What might I expect for starter amp draw?
What fuse ratings are typical for the most common circuit you have?

Thank you for your consideration.

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Old 07-23-2013, 05:09 PM
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Starter current draw could be around 250-275 on initialize and 175 -200 or a tad more for continuous .
Kinda hard to be too specific.
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Old 07-23-2013, 06:43 PM
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Unless you check the current draw of each component with an ammeter, you'll probably have to copy the fuse ratings used in a production car to get a ballpark figure. It's not a common practice to fuse the starter cable. None of the manufacturers do it.
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Old 07-24-2013, 04:36 AM
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The main battery cable is seldom fused in current vehicles. Its possible to put a fuse or breaker, but even very large maxi fuses won't handle the starter draw.

Unless you are trying to duplicate the accessories in a modern luxury car, use the fuse box from a mid-eighties vehicle to get an idea of what you need for each circuit. Just add your requirements for fuses for electric fuel pump, electric fan, electric water pump, high output sound systems, etc., since they are not included in the basic fuse box in an 80's car. Also remember that fuse size requirements are directly related to wire size. For example, putting a 40 amp fuse on an 18 gauge wire makes the fuse nearly useless because the wire will burn before the fuse blows.

Also remember that the main circuit in many GM cars uses fusible links instead of fuses. For a 10 gauge main power lead (common in 70's vehicles) they use a 14 gauge fusible link (two sizes smaller) so the link will burn before the vehicle wiring. A fusible link reacts slower than a fuse so it allows the amperage to spike for a short time without burning. This allows some flexibility for intermittent draws/spikes, but still provides protection against an actual short. Most folks seem to prefer maxi fuses now, but fusible links still work fine.

Bruce
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Old 07-24-2013, 07:51 AM
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A main battery disconnect in a street car is impractical IMO for the reasons already stated. If you intend on installing one look at disconnects for race cars. They are not a switch as much as they are physical disonnect.

Vince
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Old 07-24-2013, 08:56 AM
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Check out Tony Candela's site. And pick up his books.
Automotive Wiring and Electrical Systems
If you are going to do ANY rewiring or even a full car I highly recommend going through both of his books.
You would also do well to check out Mad Electrics site. TONS of knowledge and info there also...
MadElectrical.com - Mad Enterprises
Fusing the stater circuit is not recommended. Tony's books outline how all of this should be done.
I am rewiring my Astro van at this time so I am doing the same things you will need to do. Any questions just ask.
Mark
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Old 07-24-2013, 01:56 PM
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Thank you all Gentlemen.... lots of great advice.

On my drag bike a few years back I burned up my electrical system when the one wire from the battery to the fuse panel didn't have protection. The fire melted through my air shifter plastic line and the CO2 released put out the fire.

Doug
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Old 07-24-2013, 08:36 PM
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from the folks at AC Delco: ACDelco TechConnect - Alternators/Generators - Typical Loads
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Old 07-25-2013, 10:26 AM
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Ween, Thanks - just what I needed
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