effect of incorrect fuses?

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Pat

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I was checking the purpose of a couple fuses attached to the 12v batteries this week.  One fuse holder says "not to exceeed 7.5 amps."  The other holder says "not to exceed 25 amps."  The fuses removed were 25 amps and 30 amps.  The person who removed them didn't notice which was in which fuse holder.  Assuming the 25 was in the 25, and the 30 was in the 7 1/2, what are the possible repercussions of having such a disparity in rating?  The 25amp goes to the sofabed, and the 7.5amp goes to the solar panel. 



--pat
 

Carl L

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The effect of a 25 amp fuse in a 25 amp rated circuit is that it will work.

The effect of a 30 amp fuse in a 7-1/2 amp rated circuit is exposure to damage to the protected device and even a possibilty of fire. 
 

Gary RV_Wizard

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A fuse protects the circuit from literally burning up if something goes wrong and the power (electrical current) goes too high, e.g. a short circuit.  In the case of the solar panel, where power is being generated rather than consumed, the fuse is essentially protecting the batteries from overcharging in case the panel goes berserk and begins generating excessive current.  That's probably very unlikely, since it would require intense sunlight (or equivalent) to do so. I suspect the solar panel was blowing fuses when in bright sunlight and somebody "fixed" it by inserting a much larger fuse. Maybe the 7.5 amp rating is too conservative, but I wouldn't go over 10 amps. If the solar panel output exceeds that, you need to add a regulator (or replace the one that's there, if there already is one).

It just occurred to me that perhaps the solar panel was upgraded in size (more output amps) and somebody just put in a larger fuse to accommodate it? That's risky, since the wiring may be too small to handle the output current. In that case, running a new and larger wire is the proper solution. The new wires can safely be fused for a larger current (amps).
 

John From Detroit

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And depending on the size of the solar panel... I woudl not be so sure of the 7.5 amp going to the panel.

However there is an easy way to find out... You said you thought the 25 amp went to the sofa bed.. Put a fuse in just that holder and try to operate it.  If it works... You can label it "Sofa Bed"  If not it's the 7.5 amp fuse
 

Gottasmilealot

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A given sized wire can only carry so much current before heat develops.  The purpose of the fuse is to be the weakest link, so if too much current is drawn through the circuit, the fuse will fail first, thus protecting the circuit from overheating.  A light bulb is basically a very thin conductor carrying a lot of voltage such that it is caused to glow, producing light, getting hot as a result.

Having a 30 amp in a 7.5 holder will keep the circuit from blowing, but allow 4 times as much current to go through the circuit, allowing overheating.  That's not safe. That's why different sized cartridge fuses are now made different lengths so one size won't work in another sized holder.

Having a 7.5 amp fuse in a 30 amp holder will be safe, but inconvenient, because it will probably keep blowing because it will only allow 1/4th the current that the circuit was designed for, so devices stop working because the fuse keeps blowing.

Some day put all the right sized fuses in all locations.  If a fuse keeps blowing, correct the problem rather than increasing the fuse size.

Be safe!
 

Pat

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No fuses blew.  An RV repair person and I were talking about disabling the solar panel, and he found and removed the two fuses by the batteries.  The solar panel display inside visibly stopped working.  The fact that we also disabled the sofabed wasn't discovered till later, and I didn't make the connection to those fuses out by the batteries.  All the other appliances in here are in the fuse box in the kitchen.  Once I replaced the 25amp fuse in the correct cap and attached it to one of the bases, the couch mechanism worked fine.

I left out the 7 1/2 amp fuse, because I wanted the solar panel not to charge the batteries.  I was told this is OK. I'm hooked up to shore power about 363 days a year.

These fuses have never been replaced, so they are original equipment.  Therefore, the manufacturer used the wrong fuse(s).  I don't know if both were in wrong cases, or just the solar panel 71/2 amp one. 

Only the caps of the fuse holders were labeled, and I was told that both bases go to the battery, so either base works with either cap. 

My maintenance and repair list is now empty.  Life is good.

--pat

 

John From Detroit

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It is possible that rather than use the wrong fuse, the solar installer may have used the wrong fuse holder

To be sure I'd have to see the wires, most all of them on that circuit.  Or have someone who knows wires look at them.

However if you never plan on using the solar panels

1: Why bother and
2: Can I have them?
 

Pat

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JID:  I spoke with the Chinook tech who said that the solar panel fuse was the 7 1/2, so the fuse holder seems correct.  Interesting thought, though.

I'd be thrilled to get rid of the solar panel, but it would involve patching fiberglass holes in the roof where the panel is now.  I'd love to recover that part of the roof.  The panel was in a different spot and was moved when they installed the satellite dish, which I also don't use.

--pat
 

John From Detroit

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Well, patching fiberglass holes which are 1: round and 2: 1/2 inch in diamater or less, is fairly easy,  Patching EDPM rubber is a bit harder but with a roll of Eternabond.. Still easy.  (Match the roll color to your roof color, this stuff sticks to EDPM rubber rather well and stays stuck,, Like forever, hence the name,, See other thread on it currently active here in the forum)

7 1/2 amp sounds like it's a sixty watt panel or there abouts (7 1/2 amps could be as much as 90 watts)
 

Pat

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JID:  Chinooks are one big fiberglass mold.  No idea how big the holes are.  Sure would love to free up that real estate on the roof and simplify things.  When I realized what a waste this satellite dish is, I offered to give it back to Chinook, if they'd remove it and patch the roof.  The tech said that would cause more problems than just leaving it. 

I need to read up on fiberglass patching.  I was told it's permanent and solid.

--pat
 

Pat

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JID:  The power went out in the park here a week or so ago.  I discovered the solar panel does have its uses keeping the batteries fully charged, at least in sunlight, during such outages, as long as I don't run battery-intensive appliances.  So I put the fuse back in the solar panel.

The fuse holders are on too-short wires way to the back of the battery drawer.  They are almost inaccessible. 

1.  Does it make sense to splice longer wires on the fuse wires to bring them forward in the drawer?

2.  Does it make sense to attach some kind off on-off switch to the solar panel to activate it only when used?

In addition to the fuse outside going into the batteries, there are two fuses on the Mark 15 solar controller/monitor inside the RV on a wall.  One fuse is labeled "array fuse" and the other is labeled "battery fuse." 

3.  How do these differ from the fuse outside that goes between the solar panel and the batteries?

4.  Would removing one or both of them create the same turn-off effect as removing the fuse outside?  Would removing them do any harm?  Any good?  They are very accessible.

--pat
 

John From Detroit

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As for the switch: Depends on your solar charge controller,  If it's a good one I would not waste the money

As for the extension,  Yes, simple method,  Get an "In-line" fuse holder  and put male "Flag" connectors on the free ends of it's leads, plug the flags into the existing fuse holder (a bit of epoxy putty and be used around the wires and connection point to form them into a proper "Plug" no cutting of wires (other than the loop on the new holder) needed and it can be removed if you need to.

 

Karl

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Pat,
Cut the wire on each end of the fuse holder, splice in additional wire of whatever length you need with straight-through or butt connectors with a crimping tool (all available at Radio Shack), and be done with it. No Mickey-Mouseing around with epoxy. BTW, they're called 'spade' connectors; not 'flag' connectors.
 

Pat

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Will do the extensions and skip the switch.  Once I can reach the fuses, the switch is unnecessary.

Thanks.

-pat
 
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