Master FUSE on Battery terminal for PROTECTION

[H. John Kohl]

Capn Chris had a major melt down on his positive battery lead to his cut off switch. I posted this there but am starting it here so it is seperate from his problem.

His problem is the main reason I have installed this fuse on my battery feeds for my RV. (note I have two six volt banks in series so each cable off the positive 12 volt bank has this fuse on it.) I am using a 300 AMP fuse at each fuse location. Some other members have had the positive wire rub against the frame and short out causing a fire.

edit 3/23/14 A smaller fuse can be used depending on your demand. I have a high demand for my 2500 watt inverter

BLUE SEA 5191 MRBF FUSE BLOCK 30-300AMP



This should prevent a fire, melted wires or melted hydraulic lines that run parallel with the wires.

For safety reasons, I do not understand why all RV manufactures don't already install them. Oh yes it does cost more.

Good luck with a speedy repair. Sorry it had delayed your trip to Florida.

[Phil P]

Hi

How many batteries and how many fuses?

Phil P

[K0LCB]

Looks like a good idea. Auto manufacturers used to put a fuse link in the battery line. Did you fuse positive, negative or both

[Captain Joe]

Answers are in John's original post. Two batteries, two fuses, on positive side only. Just purchased mine on Amazon.

[H. John Kohl]

quote:Originally posted by K0LCB

Looks like a good idea. Auto manufacturers used to put a fuse link in the battery line. Did you fuse positive, negative or both

I fused only the Positive side. That is better than nothing.

[K0LCB]

Thanks! I guess the only way negative side would cause trouble is if it shorted to positive lead

[H. John Kohl]

These questions were asked on Capn Chris post of NO POWER. I answered them here to prevent hijacking his post.

quote:Originally posted by Irlpguy

I must be missing something here but if the 12V wiring in my unit was protected by a 300 amp fuse link on my battery terminal and "any" of the 12V wiring routed throughout the RV shorts out to ground on the frame, how is that going to protect the wiring from burning or causing a fire.

Edward, I believe you are thinking of the wiring coming from the circuit/fuse panel and if so you are correct. That is why all those line are fused at the panel. I am talking about the HUGH nr 4 wire from the battery to the converter/fuse panel. That system has fuses on the converter but there is no fuse on some of the feeds. My original installation has the feed from my battery to the cut off switch running through a resettable breaker. However Chris' problem obviously did not based on the photos I saw.

A 12 gauge wire shorted to the frame would not even tickle the 300 amp breaker and would destroy the wire or cause a fire or cook anything near it before it shorted out that 300 amp breaker.
It takes 4/0 wire to handle that kind of current, I have never seen any inverters wired with 4/0 wire, many use 2/0 which is not even close to being rated to carry 300 amps.

All the 12V circuits are protected by a 15 amp blade fuse in the panel, if any of those wires shorts out it should blow the fuse before causing too much trouble, we would not want to be replacing those with 30 amp fuses would we.

What am I missing and how does this possibly give anyone a sense of safety from shorting wires.

I feel the fuse on the battery (positive post) is a SHORT PROTECTION fuse so I would put one that is twice your expected maximum current usage.

The best answer is to buy a $200 Trimetric metering system and 500 amp shunt and actually measure you usage and go from there. For anyone really wanting to know the status of their battery it is worth the investment. Especially if you plan to add more batteries in the future and more so if you want to add solar and or an inverter.


Since that is expensive I would say the hydraulic motors for the slides runs about 30 to 40 amps max and the Level up about 80 amps so I would say 100 to 200 amps. Worse case if you blow one of these and there is no short then just increase its size.

My recommendation is a SWAG "Sweet Wild $$$ Guess". However I feel the intention is to prevent a fire from a dead short not protecting electrical equipment from too much current draw.

Protecting electrical equipment from too much current draw is the requirement of the individual fuse on each power drawing line.

quote:Originally posted by Irlpguy

John you further confused my with your last post. If the slides draw 30 - 40 amps maximum how is it possible that the same hydraulic motor draws in the neighborhood of 80 amps when operating the level up. It is the same motor doing a similar job albeit the pressure on the system when leveling might be higher. That is not noticeable by listening to the motor on my RV performing those two tasks.

Edward, I wrote this for multi systems. The older units that do not have the level up (mine) has just the slide motor. Those that have the slides and added levelup so two hydraulic sysem (like mine now) fit what I described. The new ones have the hydraulics all in one as you implied. Thanks for the question.

The hydraulic motor is protected by a 50 amp circuit breaker on my 3402RL no matter what job it is performing, on my RV it has never tripped that auto reset breaker although some have had problems with that actually happening, although I believe it is related to inadequate voltage and voltage drop with related rise in current because of the voltage drop.

What wires are intended to be protected by putting this 300 amp breaker at the battery.

Edward, the wire from the battery to any electrical connect before it goes to a protection fuse.
Many have added inverters and solar systems which are independent of the resettable breaker. The protection fuse comes into play more there. Again good questions.

[Bigboomer]

Great post John. A lot of folks do not realize how powerful DC current is what it can do if not contained and protected. For example, it only takes 225 amps to start a 3/16" weld in 1/2" steel plate. If the average 2 -6V 225 amp battery set up is installed in an RV then if you were to touch the positive lead to the steel trailer frame you would be able to strike a good welding arch with a welding rod. If you were touching that steel frame you would be severely burned or DEAD!

The fuses are cheap, do not leave home without them!

[BB_TX]

I like that idea of adding the fuse on the battery terminal. However, the 300 amps bothers me. The wires on my battery are 4 AWG/75C which are rated for 85 amps. I only have one 12v battery. So I think a 100 amp fuse would be sufficient.

A wire rated to carry 300 amps would be huge, 300 kc/mil wire size over 1/2" diameter (4 AWG is less than 1/4" dia). I don't know that anyone has wires that large on their batteries. So I am not sure a 300 amp fuse would protect anything unless you had huge wires on the batteries since theoretically you could pull up to 300 amps without ever blowing the fuse, enough to melt insulation on a smaller wire.

[H. John Kohl]

Bill,
Your are correct. I forgot I have 2/OO wire to my inverter. My answer to Edward is a better answer. Thanks for the clarification.

[Irlpguy]

Thanks John for starting this new thread and for responding to my questions. I see what you are getting at now and must admit it does indeed make sense should any of the cabling to the converter or disconnect switch become shorted.
I think what I was having a difficult time with was the enormously high rating of the fuse. I will in the near future put such a fuse at my batteries but more in line with 100 amps maximum.

Sure like the battery monitoring system you referenced but a bit expensive to monitor batteries like mine which are not used much for dry camping and I have no inverter involved.

Thanks for posting.

[jfaberna]

So is the consensus use a 100A fuse at the battery for a non-modified Monty with one battery with Level UP and slide hydraulics?

I assume the Blue Sea 5191 block does NOT come with a fuse. Is that correct??

[Simpson9508]

The fuse block is available on Amazon. You do have to order the fuse separately. AMZN: Blue Sea Systems 5191 Fuse Block Terminal 30-300 AMP http://amzn.com/B0019ZBTV4

[H. John Kohl]

quote:Originally posted by jfaberna

So is the consensus use a 100A fuse at the battery for a non-modified Monty with one battery with Level UP and slide hydraulics?

I assume the Blue Sea 5191 block does NOT come with a fuse. Is that correct??

Jim I would say 100 to 125 ceramic fuse. If you have the level up then 80 amps is what my system is fused at. I would never expect you to run both hydraulic systems at the same time.
If you blow the ceramic fuse from use then upgrade it by 25 as long as a direct short did not cause it to blow.

As stated above you order the holder and then the size fuse you want. I don't have a spare and probably should get one also.

I hope this helps
Safe travels.

[davidaf]

Here's something I just thought of, I have 4 6v batteries in Series. What would happen if a single fuse were to pop in the bank, say the second or third battery in, would it be possible to leave me with a 6v system and if so what would that do to the Montana? What about just adding a fuse to the positive side of the bank that feeds the coach rather than all 4 batteries?

[BB_TX]

Since the 6 volt batteries are wired in series popping a fuse would isolate those two batteries. Popping a fuse on the second bank would cause a loss of all 12 volts. No danger of dropping to 6 volts.

[Bigboomer]

quote:Originally posted by davidaf

Here's something I just thought of, I have 4 6v batteries in Series. What would happen if a single fuse were to pop in the bank, say the second or third battery in, would it be possible to leave me with a 6v system and if so what would that do to the Montana? What about just adding a fuse to the positive side of the bank that feeds the coach rather than all 4 batteries?

David,

You do not need to put a fuse between each battery. You should have one on the positive side leading to the coach 12v system. If you have a monitor you can add a shunt on the negative side. In my system I have a 400 amp fuse on the positive side and a 500 amp shunt on the negative side where the monitor comes off.

[davidaf]

That makes sense, thanks. This is the first 6v system I've had.

quote:Originally posted by BB_TX

Since the 6 volt batteries are wired in series popping a fuse would isolate those two batteries. Popping a fuse on the second bank would cause a loss of all 12 volts. No danger of dropping to 6 volts.

[H. John Kohl]

quote:Originally posted by davidaf

Here's something I just thought of, I have 4 6v batteries in Series. What would happen if a single fuse were to pop in the bank, say the second or third battery in, would it be possible to leave me with a 6v system and if so what would that do to the Montana? What about just adding a fuse to the positive side of the bank that feeds the coach rather than all 4 batteries?

The Montana operates in a 12vdc mode as far as batteries go.
You say you have for six volt batteries in series. Actually you have two banks of a pair of six volts wired in series = 12 volts and then the second bank wired in parallel with the first keeping 12 volts feed to the trailer.
I post this just the prevent confusion to others.
Good luck and safe travels.

[Phil P]

quote:Originally posted by H. John Kohl



His problem is the main reason I have installed this fuse on my battery feeds for my RV. (note I have two six volt banks in series so each cable off the positive 12 volt bank has this fuse on it.) I am using a 300 AMP fuse at each fuse location. Some other members have had the positive wire rub against the frame and short out causing a fire.

Hi

The way I understand your post is you installed the fuses in the location where the two "X" are in this drawing?

Phil P