Circuit Breakers

[loganlane68]

I'm moving my battery to the trunk and want to get a circuit breaker to protect the + cable.
My question is Ive seen people using 150 amp breakers and that sound low to me,is it?

Is 200 amps to much?

Thanks

 

[black64]

The breaker is there to protect the wiring so sizing should be gauge wire you are running and total load carried by the cable. There are breakers used in marine application that have different size ratings. And they are switchable so you can shut battery off for any thing on that circuit.

 

[loganlane68]

The breaker is there to protect the wiring so sizing should be gauge wire you are running and total load carried by the cable. There are breakers used in marine application that have different size ratings.

View attachment 507925

Thanks
I have welding cable running from the trunk to the front inner fender. I was planning on putting a breaker on the inner fender and then cable to the starter and everything else.
I have a 383 with a mini starter. I haven't had this running yet,any idea what the starter draws ballpark? 150 amps maybe.

Would I be better off getting a 200 amp for the starter and a 150 amp for the rest.

I just hate to let the smoke out of all my electrical stuff.

Thanks again

 

[black64]

Thanks
I have welding cable running from the trunk to the front inner fender. I was planning on putting a breaker on the inner fender and then cable to the starter and everything else.
I have a 383 with a mini starter. I haven't had this running yet,any idea what the starter draws ballpark? 150 amps maybe.

Would I be better off getting a 200 amp for the starter and a 150 amp for the rest.

I just hate to let the smoke out of all my electrical stuff.

Thanks again

The battery cable to the starter should not go to the breaker since cranking amps can hit 400 amps. You are better off running the batt cable to the starter then run another cable to the breaker to power your other electrical loads it would also be a good tie point for the alt output.

 

[loganlane68]

The battery cable to the starter should not go to the breaker since cranking amps can hit 400 amps. You are better off running the batt cable to the starter then run another cable to the breaker to power your other electrical loads it would also be a good tie point for the alt output.

Well rats, I was wanting something to protect the cable from the trunk to the engine.
Any suggestions?

 

[black64]

Well rats, I was wanting something to protect the cable from the trunk to the engine.
Any suggestions?

Use grommets to route cable through sheet metal. I used convoluted tubing over my cable under the car all the way to the front.

 

[Glenwood]

It really depends on what starter you're using since that's mainly what the battery and cable is for. Breakers and fuses are rated for the load not the wiring, the wiring is rated for the load as well.
A mini starter might be rated at about 1.5kw for example, which at 12v means it could draw about 125 amps, but the rule of thumb is to fuse them at about 175% or 218 amps in this case to account for inrush and locked rotor current. The cable then needs to be rated about 125% of the motor or about 156 amps in this example.
A 1/0 awg cable for example can handle current up to about 200 amps if not bound tight to other cables. So a 150A breaker may be too small for this motor depending on its rating. This needs to be known before sizing the breaker properly. More also needs to be known about the breaker your looking at to understand how much it can handle above its current rating.
For a starter that is used periodically, a breaker seems overkill to me. Any short circuits to grounds along the cable's length probably wont be caught in time with a large breaker anyway. You need some sort of ground fault protection for that.
I'd want to disconnect that cable if the car sits for extended periods though.

 

[loganlane68]

I was looking at either a 150a breaker or a 200a from Summit. I wasn't going to use it so much for the starter but more as protection for the 0 cable from the battery in the trunk to a (sorry) Ford type solenoid on the inner fender of the engine compartment. From the solenoid I would run a cable to the starter and the rest of the electrical system.

Maybe I should look a fuses instead?

Thanks so much for any suggestions.

 

[Glenwood]

I was looking at either a 150a breaker or a 200a from Summit. I wasn't going to use it so much for the starter but more as protection for the 0 cable from the battery in the trunk to a (sorry) Ford type solenoid on the inner fender of the engine compartment. From the solenoid I would run a cable to the starter and the rest of the electrical system.

Maybe I should look a fuses instead?

Thanks so much for any suggestions.

The breaker or fuse protects the cable but has to be sized for the load connected to it, the starter in this case. What are the specs for the starter? The calculations I noted are how we size components for electrical industrial motors in general, but the principals can be applied to automotive electric motors. I think you'll be fine with a 200A breaker for the 0awg cable depending on the starter motor you are using.
However, excessive starting duration or a locked rotor condition may trip the breaker as inrush currents on starter motors can spike up over 350 amps. As mentioned, the breaker will not do much to protect the cable against short circuits to the sheet metal. Use insulated clips and grommets as vibration can make the metal cut into the cable's insulation.

 

[Badvert65]

I am in agreement with Glenwood. Breaker is overkill and would not protect you from what you are fearing. It would protect from a direct short yes, but what happens if the insulation is just chaffed a little and you get a partial, say 50 amp sized short? That is enough to do some pretty serious damage and is seriously under the limit of the breaker.
The other thing is that the breaker would need to be at the source, the battery, to offer any protection at all. If your cable shorts between the fender mounted breaker and the trunk mounted battery, you have a serious problem.
If you route your main cable carefully using good quality grommets and insulated wire clamps, you will be fine. I put the battery in the trunk of my 65 Plymouth in 1985-ish and I have not had any trouble at all in many, many miles of street driving, racing. My 2007 Dodge Magnum has the battery in the rear from the factory and doesn't have a breaker on it. Just use good quality parts and careful, sensible cable routing and it is unlikely you will have problems. (FYI, I have had 5 other cars with trunk mounted batteries over the years and never had issues other than explaining why I am opening my trunk to jump start someone). Don't over think things.

 

[black64]

I was looking at either a 150a breaker or a 200a from Summit. I wasn't going to use it so much for the starter but more as protection for the 0 cable from the battery in the trunk to a (sorry) Ford type solenoid on the inner fender of the engine compartment. From the solenoid I would run a cable to the starter and the rest of the electrical system.

Maybe I should look a fuses instead?

Thanks so much for any suggestions.

If you are set on protecting your battery cable there are fuses to handle starter current but they are for trolley buses and are not cheap. Just designing one into your car would be a chore but if that's what you want look into those. I'm sure the supplier could help in your selection of the proper fuse and gage wire to use. You would have to know max current flow to properly size the wire and fuse. I have two cars with battery in the trunk and I made sure that any pass through were grommeted and used convoluted tubing over the cable and rubber coated clips attaching to the body also avoiding sharp edges in the metal.

 

[451Mopar]

I'm moving my battery to the trunk and want to get a circuit breaker to protect the + cable.
My question is Ive seen people using 150 amp breakers and that sound low to me,is it?

Is 200 amps to much?

Thanks

Usually circuit breakers are quick acting. You may want to use a slo-blow type fuse like a Mega-Fuse, ANL fuse, or fuseible link. These will handle very high currents for a short time before blowing. Here is a link to the time curve for the Mega-Fuse:
http://www.littelfuse.com/~/media/e...urve/fuses/littelfuse_fuse_298_time_curve.pdf

 

[loganlane68]

Well guess I'm going without protection so to speak.
Its nice to hear from guys that have done this and lived to tell the story.

 

[Mike67]

The main breaker can be sized to protect the main battery feed. You rely on the individual fuses to protect the loads from the fuse block.
Wire is ( should be ), sized to the load and the circuit breaker in essence protect both. If load is larger than the rating of the wire and the breaker is sized to the load- wire burns up. If load is small and the main breaker is sized to protect the wire, you rely on the fuses as stated earlier.
There should be a fusable link, main fuse or CB on the feed to your fuse panel running from the hot side of the starter.
The CB on the main line I think is unnecessary though unless you are off roading that would result in damage...I think it's more important to protect the feed to the panel...

 

[HT413]

I dunno, circuit breakers and fuses that big are pricey. Why not just wire in a Ford solenoid near the battery? This way the starter cable is live only while ignition is in start position - dead all other times.

In this configuration, there is a constant hot wire (much smaller than 1/0) that while running is used to charge the battery and while off can power accessories like the stereo. Then just fuse the constant hot wire.

 

[451Mopar]

I dunno, circuit breakers and fuses that big are pricey. Why not just wire in a Ford solenoid near the battery? This way the starter cable is live only while ignition is in start position - dead all other times.

In this configuration, there is a constant hot wire (much smaller than 1/0) that while running is used to charge the battery and while off can power accessories like the stereo. Then just fuse the constant hot wire.

One reason a large gauge wire and no fuse or fusible link is used is to keep the resistance and voltage drop down.
10 Awg wire is about 1 ohm per 1,000 ft, so if you had an internally regulated alternator putting out 14 volts at 100 amps through 20 feet of 10 awg wire battery or load at the end of the wire would only see.... 1ohm / 1000 is 0.001 ohms per foot. Times 20 feet is a total resistance of 0.020 ohms which does not seem like much, but at 100 amps (100 * 0.020) = 2 volt drop in the wire. The load or battery at the end would be 14 volts - 2 volts = 12 volts.
A 1/0 gauge wire has about 0.1 Ohm resistance per thousand feet. If you had 15 feet of the 0/1 awg wire to the engine compartment / starter, and only 5' of 10 awg from the alternator to the 1/0 wire, there would be much less voltage drop. The 5' of 10 awg would now drop 0.5 volts and the 15' of 1/0 would drop 0.15 volts, or 0.65 volts total, so 14.0 - 0.65 = 13.35 volts.
This is hypothetical. normally you would not have constant 100 amp loads, so the voltage drop would be much less, but it makes the math easier.
With a remote sense external voltage regulator, you could "sense" the voltage at the battery to have the alternator output more voltage.

 

[HT413]

One reason a large gauge wire and no fuse or fusible link is used is to keep the resistance and voltage drop down.
10 Awg wire is about 1 ohm per 1,000 ft, so if you had an internally regulated alternator putting out 14 volts at 100 amps through 20 feet of 10 awg wire battery or load at the end of the wire would only see.... 1ohm / 1000 is 0.001 ohms per foot. Times 20 feet is a total resistance of 0.020 ohms which does not seem like much, but at 100 amps (100 * 0.020) = 2 volt drop in the wire. The load or battery at the end would be 14 volts - 2 volts = 12 volts.
A 1/0 gauge wire has about 0.1 Ohm resistance per thousand feet. If you had 15 feet of the 0/1 awg wire to the engine compartment / starter, and only 5' of 10 awg from the alternator to the 1/0 wire, there would be much less voltage drop. The 5' of 10 awg would now drop 0.5 volts and the 15' of 1/0 would drop 0.15 volts, or 0.65 volts total, so 14.0 - 0.65 = 13.35 volts.
This is hypothetical. normally you would not have constant 100 amp loads, so the voltage drop would be much less, but it makes the math easier.
With a remote sense external voltage regulator, you could "sense" the voltage at the battery to have the alternator output more voltage.

What's the drop across 20' of #6 wire? That's what I used for my alt wire back to the battery.

 

[451Mopar]

6AWG copper wire is about 0.4 ohms per 1,000 feet at 25 degrees C (77 degrees F). 0.48 ohms at 75C (167 degrees F).
(0.4/1000)x20 = 0.008 Ohms (for the wire, there may be some resistance in the terminals?)
The Voltage drop depends on the current. At 20 Amps, voltage drop is only 0.16 Volt, at 100 Amps the voltage drop is 0.8 volts.
Again that is at 25 degrees C. If you de-rate for under hood temps or thermal increase due to current, the wire resistance increases.
The wattage (I^2*R) for the 100 amps would be 80 Watts, but the unknown is how much cooling is going to take place depending on ambient air temp, insulation, bundling and such. What this amounts to, is as current raises above the point where the wire can be cooled, the resistance rises, and if the current does not go down with the increase in resistance, that the wire will continue to heat until either the resistance reduces the current , or the wire melts and breaks the circuit.