breaker between house and starter batt help wanted

mexicowanderer, for some reason your image didnt show up for me??something to do with my preference setting, but cant seem to get into my settings..anyway Drewe I saw your pics on another computer I was on, I just dont have any room for that type of breaker and my fomoco battery cables dont have a spot for me to put a marine grade fuse on the post cable, I will have to make an adapter or something..thanks for the follow up guys.

If a battery cable is installed correctly, there is no need for a fuse or CB to protect it.
If you can't install it correctly, or if there is even a slight thought that it mite short circuit, then you need to have a more qualified person do your electrical work.

THIS



Is a battery combiner bi directional allows all batteries to charge automatically

THIS



Is a manual re-set high amp circuit breaker. This allows you to reset breaker in 10 seconds and eliminates fumbling with fuses

THIS



Is an 800 amp Ford starter solenoid which vastly prolongs the life of a battery combiner which is mounted next door. Battery combiners cannot pass high amperage without danger of frying the contact discs.

USE A FUSE when instantaneous reaction is demanded, not applicable when paralleling batteries. Burn 8 fuses trying to diagnose a fault is a loser.

Here are the pictures of what Coachmen did for my '98 class C (on an E-SuperDuty chassis, which is now called the E-450).

Here's a general view of that section of the hood.

Click For Full-Size Image.

A closer view of the fuse holder and protector to avoid shorting it out--a little bit redneck, perhaps, but straightforward and effective enough. The fuse proper is the wafer PCB thingy the tie straps go around. This is a limiter-style fuse, and Best Converter (presumably among other places) sells a holder with a neater looking cover arrangement.

Click For Full-Size Image.

As for the overall wiring, there are several variations that can be used. What I have is one of the simplest, where a continuous duty relay/contactor (pick your term of choice) is wired in the line between the two batteries and normally controlled by the run circuit for the chassis, so it connects when the engine is running. There is also a pushbutton on the dashboard arranged so that when pushed it disconnects this circuit (to avoid unwanted cross-connections) and connects power from the house battery to the relay control as an emergency start switch in case the chassis battery is discharged. This relay is not visible in these pictures; they located it at the other end of the wire, next to the house battery under the entrance steps.

Other arrangements commonly used include a solid-state isolator, basically a high current rectifier, which allows current to flow from the chassis to the house but not vice-versa (and introduces a voltage drop when charging), and some fancier bi-directional relay devices that automatically interconnect the batteries when either one is being charged.

Hope that helps.

thanks for the great responses folks....

I will explain a little better.
1: The cable goes from the starter battery directly back to the house battery through the charging relay, it DOES NOT CONNECT TO THE STARTER, now this may or may not make a difference in your responses and I am not knowledgeable enough to know.

2:The cable hooks up to a Blue Sea automatic charging relay, then connects to the house battery,I was told(thats why im checking here)that the auto relay could tell if there was a short and auto shut down power going from the house batt to the start batt?
A; anyone familiar with this?

3: the previous owner said he set it up this way in case I left the headlights on and drained the starter battery that the house battery, through the charging relay would start the vehicle?

B: it seems that if I put a breaker up at the starter battery I would negate this feature(even though I was told) that by manually turning the dial on the charging relay the house battery would send enough power to the starter battery, after 15minutes or so, then turn the relay off i would probably be able to start the vehicle?


thanks for your responses

NOT A GOOD IDEA AND HERE'S WHY...

Car and truck manufacturer's never fuse this wire. Between the battery and starter motor should be sacred -- no breakers no fuses. Too much danger of the protection device itself faulting unnecessarily and placing you in danger. Example is easy to come by...

YESTERDAY YESTERDAY YESTERDAY!! In traffic, my friend punched the throttle to clear incredibly dense traffic in the outboard lane only to have to jam on the brake as an idiot accelerated forward to try and cut him off. The engine quit, he restarted it pulled into the bank parking lot where I went to an ATM.

Try to leave there was nothing but a click. Both of us are/were professional mechanics.

Diagnostics lasting a full minute revealed the starter motor internals were absolutely shorted. "There is smoke coming from the starter motor and the cable is very hot".

I can guarantee no properly sized fuse would have restarted that car in traffic.

CAVEAT! Let's skip the "How, If, But, Where, Why, Arguments and go for the Jugular".

Have you ever measured extreme cold weather current to a starter motor?

A motor that consumes say 150 amps at 70F can easily demand 275 amps in cold weather. Due to engine oil viscosity resistance. Connect THREE batteries in parallel and the engine can still crank slowly demanding lots of additional amps. I used to use an eight plus a six volt battery to jump start in horridly cold weather. Amperage was insane but the car started.

How do you fuse for this? You don't.

Instead of wasting money adding an item that itself causes the odds to rise against you, protect that wire...

NYLON SPIRAL WRAP available online not only reduces but utterly stops the chances of a starter lead cable from shorting via abrasion or a cut.

This is the split convoluted split tubing (which is virtually worthless for abrasion resistance). Spiral wrap is just that. It has to be spiraled onto the cable. Measure the OD of your battery to starter cable. Choose one size smaller spiral wrap.

How tough is this stuff? Use a sample length of cable. Then wrap it with nylon spiral wrap.

Now take a sharp HATCHET. And whack the stuffing out of the protected cable. SURPRISE! Many whacks of a 10 lb wood splitting maul is needed to breach the nylon spiral wrap. The resilience of cable within the spiral wrap is incredible.

This is the system I used on commercial fishing trawlers to protect 24 and 32 volt starter cables that were 20' in length. And then proper size nylon spiral wrap went over the alternator power cable.

Do it once and do it right IMHO

I would use a fuse. Resettable circuit breakers are notorious for tripping for no reason. I had to take a 30A breaker out of my air pump circuit in my motorhome because it would trip at random and and the bags would leak down as a result. I replaced it with a fuse and it hasn't blown once.

Another anecdotal story: I added a 2nd battery in the trunk of my limo to power the A/V systems. I installed a solenoid to isolate the batteries which required running some fat cable from the trunk to the partition where the 2 battery systems came together. I, too, was afraid of a short given the long run. I installed a 200 amp fuse much like time2roll posted about a foot from the battery. It worked great.

Starting cables are usually not fused by OEMs. I would tend to add some wire loom, grommets or other protection and skip the fuse.

I would be close to 300 amp fuse.
300a Mega Fuse

300a terminal fuse

My chart says 280/330 ampacity with 105C insulation.
http://www.genuinedealz.com/voltage-drop-calculator

First of all, you need to put a fuse on BOTH ends of the hot wire. Both the engine and house batteries are voltage sources that can cause problems if the hot wire gets shorted to ground.

Second, why a circuit breaker instead of a fuse? If space is tight, you could use marine type fuses which mount directly to the battery.

https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A

2/0 wire has an ampacity of 190 amps. A 120 or 150 amp fuse will protect the wire from short circuits easily, and never blow under any normal load.

A fuse would be just as good as a breaker here, assuming you don't need to open it manually frequently. You should have one (fuse or breaker) on each end of the line, since either battery can supply lots of current. For 2/0 cable, something around 175A or 200A would be appropriate (or lower if desired).

On my E-series based class C, Coachmen mounted this fuse on the top of the front cross-rail above the grille and under the lip of the hood. There's a little plastic shield over the works to make sure it doesn't short out. That seems like as good a place as any to me. I can post a picture tomorrow if you want.