110v Transformer Problem

nedrawnep

Guest
I am in need of help. I have a 73 American Motorhome, it has a large 240 to 110 transformer. When we initially connect to campsites outlets it sometimes trips the campsite box. It is a noisy transformer and has to be switched off at night. If we switch on in the morning 95% of the time it trips. If I disconnect the lead at the box and get my wife to switch on inside and then reconnect it trips 50% of the time. I am contemplating buying a yellow site transformer and using that if it's possible. The transformer is probably a 4 or 5kva as it used to run 2 air cons.

Is there a device to stop the tripping?
Can I use a site transformer, I am probably ditching 1 of the 110v air cons, so a 3 kva would do I think?

Any help would be appreciated.

Peter
 
5kVA is more than 20 amps which is way over what is normally available in the UK and double or triple what is offered in most parts of the continent. In some Moroccan campgrounds, you would be lucky to be allowed 4 amps.

Fix depends whether it is tripping out from overcurrent or earth leakage. Large transformers often have large inrush currents which although of very short duration, can be big enough to trip overcurrent breakers.

Another problem could be caused by having an extra Neutral to Earth link somewhere inside your motorhome. It depends on how they have connected the transformer into the rest of the MH electrics but it is common practice to provide a NE connection inside things like inverters and generators - so the earth leakage breakers on each power outlet works correctly. Unfortunately this connection will cause earth leakage tripping so to get around it, they have a relay to break the connection between N and E when the MH is plugged into shore power.

Bit hard to diagnose sight unseen, but I would question why you have such a large transformer when most campgrounds cant supply the current required.
 
Many sites have very limited current draw allowances. Some are at 12-16 amps.

I'm presuming your air con and other devices are not switched on at hook up up time. If they are, switch them all off as many devices have a much higher current draw on start up. Then start them one by one

If nothing is connected it's the transformer that is tripping the box on it's own. Seems strange, but you could go for a lower rated transformer or maybe fit an inductor in the circuit. Inductors are used in some industrial applications to limit switching currents. The initial surge in a coil builds up a magnetic field which opposes the current like a brake or at least I think that's how it works :D
 
You don't say if it is tripping the RCD or the MCB on the site outlet, Also you don't if it has been OK in the past, this info would help to diagnose the problem.

If it is the MCB that trips what Peter & Tony say is correct.

If it is the RCD it could be a faulty transformer or any unit connected to it.
Disconnect the transformer from the 110v circuit make sure you disconnect both live & neutral then try it, if it's a faulty transformer the RCD will trip, if it is due to current surge either RCD of MCB or both could trip.

Might be worth borrowing or hiring a PAT tester & checking transformer & all the appliances out.

Lenny

Must stop replying to these posts & do some work I need the dosh so I can afford to use the van.
 
If it is an American system, they are rated at 60 cycles per second as opposed to 50 in the UK system. I suppose this will have some impact but I think it is just drawing too much power.

Another problem could be with a voltage drop at the hook up point. If the length of cable to the power point is too long, there will be a voltage drop which will increase the amps.
 
We had the same problem with the conversion on our Winnebago. I found the problem was the change over relay, when pluging in the hook-up the relay for half a second appeard as a dead short to the hook-up supply RCD. I never had a problem with my set up at home (old style fuse box) and on quite a few sites until I encountered an RCD supply!

I can't remember exactly now but all it required was a minor re-wire of the 240v/110v change over relay so there was no dead short when the relay energised.
 
We have done many mains conversions on imported RV's and have always fitted "Soft Start" relays. Pending on size of transformer, these devices bring in the AC slowly, rather than the traditional Thump, which typically causes the UK trip to throw.

Normally we then link to a 5KVA transformer pending on the specification of the RV we are converting.

Hope this is useful.
 
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