Community Forums

Superbee Jim · 03-14-2017, 01:46 PM

I have a 09 Entegra Aspire and I see that there is no battery protection on the start and house batterys. I was going to put an inline fuse at the battery for both banks and would use a slow blow fuse? Is the amp rating ok to use on the start battery to start the diesel motor or would the starter take a lot more amps and blow the fuse? What amp ratings should I use for house and start batterys? thanks, Jim https://www.amazon.com/Go-Power-F-40.../dp/B0015357RW

Old Car Nut · 03-14-2017, 10:22 PM

Something with that high of an amperage would normally be done with a breaker as opposed to a fuse. Also better if you are in the middle of nowhere and it trips.

What sizes would be required would have to be determined by the max load + surge. You may be able to get that info from the manufacturer but if not you will have to do or have done a load test to determine the most effective sizes.

Hope that helps.

Sweetbriar · 03-15-2017, 04:48 AM

It's not uncommon to not have fuses (is a triple negative still a negative) at the batteries considering each circuit or device downstream will be fused. Slow blow the chassis to allow for the initial surge of the starter motor. House side you can use either. Just always have spares. DC power is the lifeblood of a coach. I would stick with fuses rather than a circuit breaker. Nothing mechanical to fail even though the failure rate is very low.

400 amps in a 12 VDC circuit is 4800 watts of work which further converts to 6.43 mechanical horsepower not accounting for line loss and other inefficiencies.

l1v3fr33ord1 · 03-15-2017, 05:10 AM

Superbee Jim-

What problem are you trying to protect against? Where would these protection devices be installed? Would they come standard on a modern Class A? Were they supposed to be on your Entegra, but aren't?

Just curious because my coach doesn't have such fuses, as far as I've found, on either battery set. I don't have an inverter or solar, which I understand can have fuses like that.

twinboat · 03-15-2017, 08:14 AM

It is an industry wide standard, not to fuse starter cables.

It has to do with fuses blowing in cold start, hot start and weak battery situations. Adding a fuse to your starter motor is like kinking a water hose to a faucet. Just more resistance.

As far as house feeds, the industry requires each cable leaving the battery area to be fused, to protect that particular gauge wire. You need to follow the positive cables and find them.

You shouldn't have a 250 amp inverter fuse protecting a 8 gauge house feed wire.

Superbee Jim · 03-15-2017, 11:56 AM

What got me to thinking about all this is that I had a problem with my inverter and when I called Magnum energy for tech help he said to check my fuse going to the inverter and I said there isn't any and he said " THERE BETTER BE ONE!!! " so I thought it would be a good idea to put one in. I looked and there isn't one for the inverter and the diesel generator. With all the shaking and vibrating that goes on when I am driving a 41ft box of wires, it would seem wise to fuse it. I can see that the start battery may not have a fuse, but with a 4/0 battery cable feeding all the accessories from the house battery bank, it would seem prudent to have some sort of protection? I was thinking an inline fuse would bolt to the top of the battery post and then hook the 4/0 cable to that and if the fuse ever blew, I could remove the fuse and hook the cable back to the battery post to get home. Also, if something catastrophic happened like dropping a wrench on the batterys when servicing them, it could save the day! I may be overthinking all of this, but that is why I am asking for others opinions. Thanks, Jim

twinboat · 03-15-2017, 12:24 PM

If your going to use a fuse like this, make sure it's in a holder designed for it.

I've seen where they are simply used as a link between the battery terminal and the cable end.

When they blow, the halfs can seperate, and the loose cable end could land on the same or another positive battery terminal. Now you have no protection from whatever made it blow in the first place.

Superbee Jim · 03-15-2017, 12:25 PM

Well, forget everything I just posted!! The factory is a lot smarter than I thought. After removing a bunch of panels in the engine compartment, I found a large class t fuse for the Magnum inverter and 4 other 120 amp circuit breakers for the other accessories! That problem is solved. Now I can overthink something else!

Thanks for the help, Jim

Old Car Nut · 03-15-2017, 12:41 PM

Look in any motor vehicle and you will find some type of fusing or breaker within 2-3 ft of the battery connection. In a car or truck the wires are pretty safe in the engine compartment for that distance. The are up high. Newer cars there is a fuse panel with a main fuse, commonly 150-200 amp. From there it distributes to smaller circuits 60 amp and below. Clean solid connections offer little resistance. Just don't make several of them along the way as they do add up.

In a home the power comes from the pole (or underground but overall still the same) which has its own overload protections into the service panel right into a main breaker into buss bars and out to smaller circuits.

It is NEVER a good idea, factory or otherwise to run a circuit capable of 200+ amps in distance without some sort of protection withing 3 feet of the source. That cable gets shorted due to worn insulation, road hazards or accidents and it will set anything it touches on fire. I have seen this far too many times when some putz runs a wire through the firewall into the car and under his carpet to an amplifier in the trunk. I worked in or owned mobile electronics stores from 1989-2001 as a tech. Have done plenty in high end DP's and Yachts and have fixed a lot of bad work in my day. Seen a lot of damage. Any electrician will tell you I'm right on this.

Fuse vs breaker. I'm no fan of auto reset breakers. Manual breakers for vehicle use are sealed, waterproof, designed for vehicle loads and are extremely effective. Connections to these should be COPPER and both swedged and soldiered then insulated with waterproof heat shrink (it has hot glue in it). A breaker will have a total of three connections, 2 terminals and the breaker contacts. A fuse will have 4, 2 terminals and 2 on the fuse. The ones on the fuse are subject to corrosion over time. Every connection is resistance and in this case serial which means they add up. Corrosion adds even more. Resistance makes HEAT and degrades amperage.

If you are having electrical issues, trying to repair, think you have it and then install your spare only to discover something else is still shorted...... your stuck. Manual breaker can be reset again and again. Only catastrophic failure will damage them, like trying to force them not to trip, or hundreds of cycles. Manual shut off of the circuit does not have the same effect as tripping on the life of the breaker. Finally large capacity fuses can be difficult to find outside of a large city. Goobers gas station won't be able to help you if you need one.