Nuevo 30 amp fuse melting

Hi  

BobK wrote:I've carefully read through these posts and I'm with "jimthefish"  - changeover relay is at fault.

Well I’m sitting firmly on the proverbial fence at the moment.  

jimthefish wrote:  This relay is also shows an earth so this changeover relay might be at fault going to earth hence blowing or heating the 30a fuse.

Presumably it’s the coil earth. A short from the main contacts to the coil earth can and does happen. I saw it on a Peugeot 406 a few years ago. With drastic results, part of the wiring loom burnt out and filled the inside of the car with acrid black smoke.

It’s certainly a theory worth investigating but there are still things that don’t seem to make sense. Why is the fuse on the leisure battery side getting hot. The fault(short) is only present when the relay is closed so it’s on the alternator side  (otherwise it would be present when engine was not running).

I’d expect the alternator to be providing the bulk of the current. If the short was low enough resistance to draw current from the alternator AND the leisure battery the problem would be self limiting (at least as far as the fuse heating was concerned) because once the leisure battery was flat it would never recharge.

Unless -- it’s been on EHU in between runs! I wonder  

Also If there is a short on the alternator side why isn’t it draining the starter battery?

I’ll certainly be interested in what it turns out to be.

Brod

I'm sat on a very misty site in St Malo and have (for the first time ever) found a FON wifi site I can use for free.

I've had a good read and can follow everyone's logic but without hands on the van its very difficult.

One thing however is a fact, the fuse is getting hot. That must be because there is resistance to the current, whatever it is and wherever it goes. The fuse design would not allow it to get that hot when passing current at its rated value therefore the resistance causing the heat must be at one (or both) of the physical connections to the fuse.

PS a way to establish roughly the current is to gradually reduce fuse sizes till one blows eg 25A, 20A, etc.

Peter

Ok hope this is how to let members see the wiring diagram and I haven't put my life in pictures on the site.
=136355993&filters[recent]=1&sort=1&o=0]https://s1276.photobucket.com/user/jimthefish55/media/Nuevocircuit_zps415098f8.jpg.html?filters[user]=136355993&filters[recent]=1&sort=1&o=0

OK looks as if I have also put my cab collapsible table pictures on. Used to think I was good with computer for my age as I'm on several CNC and technical web sites and run a stained glass website but this takes the biscuit for uploading stuff.

I'm guessing that this diagram was drawn for Ford conversions as the split charge relay that connects the vehicle and leisure batteries together when the alternator is running is missing. Ford supplied that (and the leisure battery) as part of their installation.

The relay shown disconnects the leisure battery from the habitation circuitry and connects it to the fridge when the alternator activates the relay.

On a Peugeot conversion - Nuevo - there will be an additional split charge relay and wiring on early models. Newer vans have it in the PSU.

Further to my last post, I assume it is only the fuse itself that is getting hot as that's all that's mentioned. If the wiring is not rated for 30A and there is a fault current near that, then the heat could be generated in the wiring and conducted, as heat, to the fuse.

Peter

Ok Peter, the drawing I put on the forum is the schematic drawing that was supplied with the Peugeot Nuevo ES I purchase in 2005 from new. Are you telling me they have supplied the wrong electrical plans for my van. If yes can you tell me as to the position of the additional split charger relay as I have traced all of the wiring when I had my blown fuse problem in 2009 but could not find any additional relays. According to my manual the switching of battery charging is done with a switch on the internal control panel manually when plugged into 240 supply. Again it look like another Autosleeper not paying attention to detail problem when supplying the paperwork with the van, I will contact them and ask for a correct drawing as in the write up it does talk about a second relay?

IF you have a Sargent PSU then the relay is in there. If an MES unit I'm not sure. Am moving on today and using Aires for the rest of the week so may not be online for a few days.

Peter

Hi  

Peter Brown wrote: The fuse design would not allow it to get that hot when passing current at its rated value therefore the resistance causing the heat must be at one (or both) of the physical connections to the fuse.

Careful, fuses can (depending on type) and do get hot close to rated value. The power dissipation can be calculated from the manufacturers data but it is up to the designer to take account of it in his / her application.

In this case the fuse and holder are new so connection resistance is unlikely to be the  problem unless the holder is of poor design or underrated (admittedly this may be the case).

Time to plug in some numbers in.  Here is a link to the spec sheet for the “Littlefuse” range.

http://www.littelfuse.com/~/media/Automotive/Datasheets/Fuses/Passenger-Car-and-Commercial-Vehicle/Blade-Fuses/Littelfuse_ATOF_Blade_Fuses.pdf

The cold resistances run 1.44 to 123 milliohms depending on value.  Taking the 40A fuse as an example the cold resistance is 1.44milliohms. At 40 amps this means the fuse is dissipating about 2.24 watts actually more because the resistance will have gone up with temperature). OK it may not seem a lot but in the small space of the fuse element it means a noticeable temperature rise.  

An Experiment:
Here’s a mock up I made using a 40A fuse (I didn’t have an inline fuse holder to hand but the characteristics should be similar). In fact the connections using spade connectors are tighter than a normal fuse holder.



The graph below shows the temperature rise on the plastic body of the fuse over two minutes with a constant current of 30A. I couldn’t leave it any longer because the 30A power supply was not continuously rated.
The temperature got up to about 73 degrees C . It would have gone (a little) higher if I could have run the test for longer,  probably between 75 and 80 degrees, looking at the shape of the curve.  The fuse is at only three quarters of rated current and already decidedly hot to the touch.



That's with the fuse in free air so some level of cooling is possible.If the fuse is in a closed holder the temperature rise is likely to be higher.

Brod.

That is a very helpful test and very illuminating. I was amazed that a typical voltage drop across a 40A fuse should be as much as 0.1V. And with those levels of temperature rise I am amazed that car fuses are almost always enclosed in boxes.

I had same problem 04 Nuevo advised to fit 30 amp maxi fuse and maxi fuse holder from halfords this worked for me 
                     Ww inkyWw inky

It's my Nuevo that Peter Brown helped repair in France. The fuse box melted a couple of years ago with a horrible smell of burning. Attempts to wedge another fuse in failed miserably. Anyway, Phil West gave me two spade connectors and we cut the wires to the super melty super naff fuse block, crimped on the spades, addes lots of insulation tape, replaced the fuse and low and behold, 300 miles of successful driving with the fridge on engine feed.

The two wires from the back of the fuse - One goes to the fridge, one loops around to the relay. There was plenty of slack on both.

Conclussion. High resistance fuse mounting due to the inferior plastic being unable to hold the fuse contacts tightly causing arcing which melts the fuse.

Thanks to Phil, Peter and Baz for advice and help.

brains wrote:As someone with a degree in electronics I ought to be able to suss this, but in vain. My AS manual has a circuit diagram that does not represent what is in the van, and nobody at AS seems able to provide an accurate description.

To the fault: Green 30A fuse under the drivers seat has melted. AS advised replace with an inline fuse which I have done. I was aware of no problems with the 12V systems until the smell of burning plastic.  But after fuse replacement I have these symptoms:
1. with engine off, the 12V LED does not light on the fridge, but all other 12V systems seem to be functioning ok. control panel shows yellow on both batteries.
2. with the engine running, the fridge LED comes on, but no lights, pump etc. work, and control panel voltmeter does not register at all
3. with master switch and fridge off, from cold, driving the van a quarter of a mile up the road, the replacement fuse is now red host, and will presumably burn out again.

A few hours prior to the initial burnout I had gently nudged a tree while reversing into a parking space, which broke the top offside rear lamp casing. No other damage apparent, bulb intact, and lamp still works. Could this have somehow(!!) precipitated the fault? Trapped wiring is my only guess.

Can anyone explain this and suggest where the fault might lie?


(mod request:  could you do an intro please as we request when you join the forum - thanks roli)

If you are really melting a 30 amp fuse you have a potentially dangerous problem. Something is drawing way to much current. A 30 amp fuse is fitted to allow for peaks in consumption but there is nothing fitted in your van that would draw 30 amps plus off one circuit so you have a problem. I agree that you should start at the battery, however if it was a bad as some suggest it will be giving off a very fishy smell and even be hot to touch. All wiring should be checked for chaffing or pinching and look for wiring going darker in colour in places, suggesting it is cooking. All things considered you should not be attempting to run your MH until this is checked out by a profesional for your safetys sake. I would immediatley remove your leisure battery, remove the offending fuse and have a fire extinguisher handy!!! This is not a joke !!

Have at last got round to testing the battery, and its clearly duff. After a few idle weeks voltage was 5.6V. Put it on mains charge for a couple of hours and it got to 12.5, but had self-discharged to 11.5 within an hour.

Looking to replace it I can't get the bloody thing out. The driver's seat is fixed with 2 13mm bolts at front - no problem, but at the back there are two allen key bolts with (I think) a 16mm nut underneath. Not enough room to get a socket onto the nut, or even a ring spanner, Tried a long allen key and it will obviously break if I push any harder - it seems AS just don't want you to remove the seat - why didn't they just use 4x13mm bolts?  Anyone got a tip? The battery is just too large to tip over and slide out - its got to be through the seat.