Nuevo 30 amp fuse melting

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)

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

Think you'll find that 1 & 2 are correct.
Fridge doesn't work on 12v
When engine is running, fridge will work but all other 12v system will shut down.

Can't help with the fuse problem though.

PB

I had a period of 30amp fuse failure on my 2005 Nuevo. For year I charge up the battery with an external charger before we went away for the weekend. I didn't find the fuses till 2008. I solve the problem by replacing the leisure battery under the seat, the garage man said it was shot and would not hold a charge the plates were buckled and he though that's why the fuse blew. Never did find any other thing wrong but since a new a new battery in 2009 no problems, mind you changing it over was a problem the drivers seat weighs a ton, getting it out was easy getting it back in is a 2 man job. Hope this helps. Jim

jimthefish wrote:................. the plates were buckled and he though that's why the fuse blew. ...................

Hi there,

I think Jim may have hit on the solution as to why the fuse is blowing!

If the battery is indeed knick-knacked and the plates are buckled enough to touch the charger will effectively be shorting out and therefore the fuse will blow!

Sounds reasonable to me! 

Best regards,

One other possibility comes to my mind. 

If the wiring to the fridge has a short or near short somewhere then that would also cause the fuse to get red hot.  Try disconnecting the leisure battery negative lead from the battery , wrap the disconnected lead end carefully so that it does not short anywhere (strictly not necessary but just in case of something really weird in the electrics) and do your half mile from cold.  If the fuse still gets hot then the fault is in the fridge wiring, if not then the battery is likely to be dead or dying.  If it is the fridge then you may be able to get at the wires by removing the bottom outside vent.
Let us know how you get on.

Hi  

To prove if the fault is in the battery or due to a short circuit why not simply measure the current to determine if it’s flowing in or out of the battery.  Even if a meter with a suitable current range is not available it should be possible to measure the direction of the voltage drop across the fuse.

Brod.

brodco wrote:Hi  

To prove if the fault is in the battery or due to a short circuit why not simply measure the current to determine if it’s flowing in or out of the battery.  Even if a meter with a suitable current range is not available it should be possible to measure the direction of the voltage drop across the fuse.

Brod.

To measure 30A needs a professional meter, preferably one that works by induction. It would seem that the current flow through the fuse is from alternator towards battery or fridge (as it only happens when engine is running) so the direction won't tell you which of those two is taking that current. Or is the fuse under the driver's seat right next to the battery and merely protecting the battery from taking/providing excess current?  Even if it is the voltage drop across it is likely to be very small because fuses are very low resistance and may not register on a domestic multimeter.

Hi  

Ah, I sense a good old disagreement looming  

inspiredron wrote:.To measure 30A needs a professional meter, preferably one that works by induction

Not true I'm afraid. Any meter that works using induction would be useless. Such meters can only measure changing currents. Although they could in theory measure any constantly changing DC current waveform, in practice they are only normally used for AC.
The problem being addressed here is a steady current of close to 30A so induction is not a viable method for measurement.

i.e.
V=L(dI/dt)

If dI/dt = 0 then no matter how large I is, V will be zero.

Non contact (clamp) meters that measure DC need to be able to detect a steady magnetic field and so cannot use induction. Most non contact meters typically use a Hall Effect device to achieve this.

inspiredron wrote:. Even if it is the voltage drop across it is likely to be very small because fuses are very low resistance and may not register on a domestic multimeter

In practice fuses coming close to their rated value drop a measureable voltage. A 30A fuse with a resistance value of 5 milliohms (not an unreasonable assumption for such a fuse) will drop some 150 millivolts (0.15 V) at rated value. Even the cheapest meters usually have a 200 mV range.

inspiredron wrote:. Or is the fuse under the driver's seat right next to the battery and merely protecting the battery from taking/providing excess current

Admittedly that’s not 100% clear from the original post but I assume that that is exactly what it’s for. Most of the split charge circuits I’ve seen have a fuse in that position and even if a modern system with a separate charger is fitted I’d still expect a fuse as close to the battery terminal as possible.

That said my van has no fuses in the spit charge system. Just a 70A relay connecting both batteries in parallel when the engine is running so I’ll only know if there is a fault by the smoke!

Brod

NO - I am not going to argue!   

Sorry, induction was the wrong word to use - I meant a clamp meter. I did realise that it needed one to measure a weak static magnetic field and not a changing field.
And I badly underestimated the resistance of a HOT 30A fuse. Cheap meters will register 10mA quite happily on their 200mA range.
My van has the Sevel fuse/relay unit behind the driver seat and another fuse (I think) close to the battery (in a bed locker several feet away). I had not picked up from the OP his battery location relative to the fuse.
And Peter's diagnosis of a poor connection to the fuse holder or between fuse and holder fits the symptoms very well. That might show up as slight sparking which might be visible in the dark with the engine running.

I doubt very much the overheating was due to fatigue in the fuse, since the new fuse is also getting very hot, but presumably not carrying more than 30 amps (where to is the question, when nothing is on except the feed to the battery - to which it is directly wired about 8 inches away). For a fuse to get hot but not blow suggest poor design anyway - something the AS technician was effectively recognizing.

Hi  

brains wrote:I doubt very much the overheating was due to fatigue in the fuse, since the new fuse is also getting very hot, but presumably not carrying more than 30 amps (where to is the question, when nothing is on except the feed to the battery - to which it is directly wired about 8 inches away).

I think that’s why people are suggesting that the battery is at fault. There is certainly something taking excess current. It’s unlikely to be a direct short circuit or the current would be well in excess of 30A.

Another thought is that something may be flattening the battery when the engine is off and the 30A is coming from the alternator charging a very flat leisure battery. With that in mind it would be useful to measure the terminal voltage on the battery before you start the engine. You say the fuse is hot after a quarter of a mile but what happens if you drive for longer, does the fuse start to cool down?

brains wrote: For a fuse to get hot but not blow suggest poor design anyway - something the AS technician was effectively recognizing.

I don’t think it necessarily means poor design. Fuses are just not ideal protection devices. When they get close to their rated value they do get surprisingly hot (and not blow)!
It’s quite normal, after all the wire inside is operating very close to its melting temperature. It can be improved to some extent by the design of the fuse holder but where the fault current just happens to be the same as the fuse rating, overheating is always going to be a problem.

Brod

thanks brod - I'm pretty sure the battery voltage is OK - certainly shows OK on the control panel when the engine is off. Unfortunately the van is in storage at present as we're about to go away for a week sans van, so I can't do any more tests until we're back.. I'm certainly thinking the battery needs checking/testing - how? I guess just turning on the interior lights for an hour should show if the voltage drops quickly.

Hi  

brains wrote: how? I guess just turning on the interior lights for an hour should show if the voltage drops quickly.

I’d suggest removing it from the van(since you are not sure exactly what’s going on in the van), charging it up with a mains charger and then connecting a known load (e.g.a headlamp bulb). You can then see how long it takes to get down to 10.5 /11V (ish) and if it’s giving anything like the AH rating you would expect. Bearing in mind that if the AH rating is at the 20A rate as many are you should get a bit more, discharging at less than 20A

If you have something that will take 20A or so all the better. The test won’t take so long. Keep an eye on it and make sure you don’t take the battery below 10V though. If it really is continuously taking 30A from the alternator it probably won't fully charge. Ether way you'll have proved something.

Brod.

Hi  
Another thought (ouch). 
What control system is fitted in your van?  In my last post I was assuming that the alternator charges the leisure battery directly. It may not do.

Brod.

I've given up trying to put pictures on the site so I will try and describe the area by the drivers seat. I have a wiring diagram for vans from 2003-on and the 30a fuse is for the protection of leisure battery charging so if its not a duff battery can I suggest that its the Changeover relay. According to the drawings it is linked to the 2 fuses by the drivers seat. This Changeover relay switches the charge from the alternator or the internal motorhome charger to the leisure battery whilst driving or stationary. According to the drawing I have, the fridge system protected with the 15a in the same block after it comes out of this relay The vehicle battery protected by a 35a fuse on the same block is not active whilst the vehicle is stationery and goes direct to the control panel in the van. The feed from the alternator come in at Changeover relay connection 86 and　connection 87A for the 240v charger in the motorhome, it then switches into the circuit protected by the 15a fuse when driving so if you had a fridge fault this fuse would be the first to blow,　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. Looked on my van and its a bit of a Heath Robinson　contraption and hard to find.

PS if you want a copy of my drawing I will send it to your personal email. Guess what I'm saying is that if it was a motorhome conversion fault in the living area the 15a fuse would blow first. If the 30a fuse overheats it could be a faulty relay going to earth so continually calling for maximum current. Jim

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

Bob

thanks jim - useful extra info, and yes please, I'd love a copy of your diagram.

As to the changeover relay, that was my first thought. I have 2 identical relays on the panel (fridge changeover?) but no clear idea on how they relate. In any case I swapped them round to see if anything changed and it didn't appear so, so I'm doubtful the relay is faulty, but I need to do some more testing, especially on the battery which is still prime suspect here. It'll have to wait a week or so though - too busy this week.

I must add that having only just joined this forum I'm really very impressed - lots of good ideas from lots of people willing to give my problem some thought. Many many thanks to all, and hopefully I'll see a resolution in a couple of weeks time - I'll keep you posted.

brian

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

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.

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?

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.