Electrics

[Richard J]

Hi All,

I have a 2004 Swift Lifestyle motorhome. I've had an issue with the Omnistep not retracting on start up, the fridge on 12v whilst travelling and also the mcb has been tripping for the fridge,water heater,battery charger mains circuit. There are three fuses under the bonnet with the relays controlling the 12 volt cut out when the engine is running and step retraction and 12 volt fridge operation. The (cheap) 15 Amp fuse had melted and on replacement everything was working fine. Could anybody tell me where I could find a wiring diagram or shed some light on how the 12 volt and 240 volt systems are connected. What Amperage should the 3 fuses be and which protects which circuit ?

Thank you all in anticipation of your replies.

Richard

[Robinhood]

This will give you a 2005 diagram (there is no 2004 version on the Sargent site for the Sundance - which is the closest to your 'van).

 

https://www.sargentltd.co.uk/tech-support/article/25/download/255

 

I doubt there will be much, if any difference.

 

There may be something in the Swift technical handbook archive for 2004 - I'll have a look.

 

There is, and it is somewhat different. Check the distribution panel model for the correct one between this and the above.

 

(You need to scroll through this)

 

https://tinyurl.com/swiftelecs

[Alanb]

Hi Richard,

 

I think that the links provided by Robin, will answer your queries regarding fuse duties etc. The step retraction failed because the retraction relay is controlled via the fridge supply, and not directly from the alternator field circuit (D+). (Ypu will probably have worked this out.) The indirect method of control is probably aimed at minimising the load on the alternator field circuit. If too many relays are connected at this point, there will be difficulty in getting the alternator to start generating.

 

You mention a 240V MCB tripping. This could be due to either a short circuit, or a faulty or incorrectly rated (replaced?) MCB. Hovever do check that it is the MCB, and not the RCCB that is tripping. (The RCCB is the one with the test button). If the RCCB is tripping, an earth fault is probably the cause. Try switching OFF, Fridge 240V, Water Heater, and Mains Charger, in turn to identify the faulty unit..

 

Sorry if I am preaching to the converted.

 

Alan

 

 

[Richard J]

Thanks Alan and Robin.

Richard

[Alanb]

Richard,

 

In my previous post I forgot to mention that aanother possible cause fo your your 240V MCB tripping could be a damaged 240V cable. However as this would require the cable rubbing against a sharp edge, I would rule out an appliance (fridge, water heater, charger) fault first.

 

You ststed that the fridge fuse had melted, but may not have noted whether the fuse element had just melted as you state, or had the element vapourised completely? If the latter it would indicate a large current surge. I do not know if it is possible for the 12V and 240V elements on the fridge to short together, but such a short circuit could conceiveably cause both of your problems with such a current surge.

 

Now may I digress with a short story. Many years ago I was called out by my employer to fault a piece of electronic equipment, that required both 50V DC and 240V AC supplies. The covered supply connections in the equipment were perhape one inch apart. I soon found that the 50V DC fuse had blown at the 50 DC distribution board. I could not find out why, and with some trepidation replaced the fuse. All OK, and subsequent examination of the 50V supply cable failed to reveal any damage.

Fast forward a few years, and I was by chance present when the equipment was being scrapped. Under cover and resting across the supply terminals was a mumified mouse. Original cause of fault located.

 

Alan

[aandncaravan]

It is quite common for the 20a Fridge supply fuse on Hymers to be melted into the Fuse Holder. Probably accounts for around 20 in every 100 of the 12v Fridge supply issues we see each year?

 

I don't know the reason, but we have measured the big Fridge Freezers running at 17amps, which is obviously too close to the 20a fuses 'running' limit.

 

I think a combination of corroding fuses/holders, poor connections and cheap fuses is a potential cause?

 

We now suggest that on the Fridge/Freezer equipped vehicles, that a 25a fuse is used instead of 20A.

 

Even the smaller Fridges tend to draw around 13amps, so a 15a fuse seems a bit undersized to me.

 

 

 

[Alanb]

My original 1990 Pilote was delivered with a 10A fuse to supply a RM4xxx? fridge. The fuse was patently inadequate, After a temporary fix with aluminium foil, the holder and fuse were replaced with a 13A BS1362 mains fuse. Perhaps not ideal, but no further problems with many years of use. On my current vehicle the original fuse was 30A, and I reduced the size to 15A many years ago and have not had any subsequent problems, but we have only averaged about 3000 miles annually.

 

One thing to consider is the size of the RM7xxx 12V tail lead, which may be too small to carry 20A for a long period.

 

Alan

[Brian Kirby]

When changing fuses for ones of a higher rating, don't forget that the fuse is there to protect the wiring, not the appliance. Before uprating a fuse one should first check the wiring between the fuse and the appliance, as this may be the limiting factor. If the wiring can't handle the load it will run hot, possibly hot enough to soften/melt the insulation, possibly hot enough to start a fire. If the fridge demands more amps than either fuse or wiring can safely accept, the place to start is with the wiring (by replacing it or duplicating it with the appropriate grade) and only then up-rate the fuse accordingly.

 

OTOH, there is nothing against down rating an "oversized" fuse - but equally no real gain either, since a low rated appliance will only draw the current for which it is designed, however large the fuse/wiring.

 

But, as above, - always first check that the wiring itself is adequate, especially if you are not the first owner of the van. It may be that a previous owner found the OE fuse inadequate and installed a higher rated one, without checking that the wiring was adequate, and the wiring may have been damaged in the meantime.

[Alanb]

I would have liked the converter of my PVC to have used similar wisdom to that given by Brian.

 

On delivery as new, the power supply for automatic retraction of the step was "plugged" into the +ve coil connection of an unused relay socket on the Fiat RHS fuseboard, This supply was originally protected by a 10A fuse on the Fiat LHS fuseboard. In order to cope with the demands of the step the fuse had been replaced with a 25A fuse. I considered that this seriously degraded the protection given to the vehicle wiring, the step supply retraction supply was taken from a different source and the fuse replaced with the correct value.

 

A regards Brian's second paragraph the as delivered fridge fuse was 30A , with 2.0mm cable rated at 25A used in the wiring, again I considered the fuse rating to be too high, and as I have already stated I have reservations about the size of the fridge tail cables, a decrease in fuse rating was indicated.

 

I was the original owner of the vehicle, so it is not just about what previous owners may have done.

 

Alan