# Generator/Hookup Changeover Relay?



## 96509 (Oct 12, 2005)

Can anyone suggest a method/source for switching (automatically) between generator and site hookup so that the mains distribution system in the motorhome can be used for either/or?

I have an underfloor mounted Onan 2kva LPG generator which I hope to resurect out of storage and fit to the new Hymer I have on order. When last installed (on a Hymer) I used a small relay which I came across at a MH show. This relay ensured that if a hookup was attcahed the generator output connections were automatically taken off line and the hookup power would not be connected until this had happened - the idea being to avoid connecting the generator to the national grid.

I may still have this relay stored somewhere but it was a flimsy-looking thing with exposed terminals and I would like to do better. It worked and was safe enough when installed within a suitable enclosure but I am hopeful that there is a more modern and robust switching option available these days.

Stuart Ormerod


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## Snelly (Aug 20, 2005)

I havent used an automatic relay on my mh, but instead a switch to manually change between hookup and invertor (or generator in your case). Apologies for the drawing quality... I really must work on a better one! If your interested, get in touch and i'll get you a price from my local supplier. They also do cheap beige uk sockets!

BTW, the switch comes in a professional enclosure, my drawing shows the naked version for wiring purposes.


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## olley (May 1, 2005)

Hi sormerod I don't know if anybody makes a dedicated unit just for that, I intend to do a simular set up, but its too disconnect the invertor when on shore or genny power.

I wouldn't use a relay as they tend to be harder to get in the high power ranges, much better to use a 20amp contactor and put it in a suitable enclosure, you can get these from any electrical trade outlet. 

Olley


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## DABurleigh (May 9, 2005)

Stuart,

I do something analogous in my MH, but it is inverter instead of your generator, and frankly is easy as the switching is part of a Victron integrated inverter/charger.

However, more specifically to answer your question, I have the following tucked away on my hard disc; it may enlighten, or it may not. Again, it is for inverter rather than generator, but other than the issues in the first para that you needn't bother about, as genny would be OK with these but inverter not, the issues are the same.

Dave

"You need to isolate the mains sides of the electric water heater, mains electric fridge. mains battery charger / PSU (and any other consumer of significant mains power or those items that would be better run from 12 volt directly or gas/oil ) from the rest of the van mains wiring. The reason is that you don't want an inverter to try and power any of this gear. Its pointless using the battery power to run an inverter to provide the mains to run the charger to charge the batteries!!

Having got this aspect covered then connect this "real mains only" gear via suitable fuses to the output of the incoming mains circuit breaker. Also connect the output of this circuit breaker to the coil and the normally open contacts of a chunky 16 amp or 30 amp AC rated mains two pole relay. Connect the normally closed contacts to the output of your inverter. Connect the common contacts to the fuse box that feeds the rest of the vans mains system. This relay will then default to INVERTER unless the real mains is present.

On the 12V DC side control the inverter from a chunky DC relay, like a 50 or 150 amp contactor from Albright Engineers in Sunbury. Get a contactor with an auxiliary switch contact. They make them.

On the inverter control panel in the van you would benefit from a couple of pilot lamps, one for MAINS on and one for INVERTER running.

Connect the coil of the DC contactor to the battery supply via its own normally open auxiliary contacts and also via the normally closed contacts of a second small AC relay powered from the incoming real mains. Fit a normally open START push button in the control panel to short out the auxiliary contacts to initially energise the DC contactor which will then remain held in via its auxiliary contacts - now closed. Fit a second normally closed push button in series with the DC contactor coil to drop out the contactor manually if you wish. Fit suitable small fuses into this control circuit.

This system will never switch on the inverter automatically (not a good idea as you may not even need it if you are not there) but will always switch OFF the inverter when the real mains re-appears. The only manual intervention is to press the START button."


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## 88934 (May 10, 2005)

I have an auto relay fitted, which switches between my invertor and hookup.

The hookup gets priority, but if the hookup/mains fails, then the relay throws over to the invertor.

The relay/kit came from A B Butts at Leicester. Butts attend most of the MH shows, so you may have seen them.

Alternatively.. look here >>A B Butts<< for contact details.


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## haylingchrist (May 15, 2005)

I used a 20a changeover, twin-pole mains relay to do a similar job with my inverter. Got it from farnell electric for about a tenner, plus another couple of quid for a DIN socket to suit.

Had a problem ordering through their web site or I could quote part numbers.

If you're really stuck I have a spare somewhere and could get the numbers off that, but we're going full-time in 6 days and the chaos can't be imagined 

Chris


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## BERTHA (May 21, 2005)

Stuart,

Not wanting to change the subject but under a diffrent post would it be possiable to explain how you installed the gennie to your MH.

I am interested on installing a generator to our Alko chassis?

Regards
Hugh


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## 96509 (Oct 12, 2005)

*Inverter/generator Changeover Switching/Relays*

Thank you everyone for some fascinating replies. IT looks like I could connect both a generator and an inverter safely using these methods. I use a company called CPC (part of the Farnell Group) so I should be able to find something in their catalogue. I still have over three months to wait before the motorhome arrives so no hurry.

Installing the underfloor Onan generator was not that difficult on the old Hymer (a 1991 B694) because there was plenty of vacant underfloor space. Floor comprised two plywood layers with insulation in between. I just found a suitable space where there would be access above (under a settee) drilled holes which match both the genny frame and a steel spreader plate which I had made, then used coach bolts from above. Spreader plate was probably over-engineering, bolts and penny washers would have been OK. This meant there was a bit of low profile clutter on the floor inside the settee locker, but insignificant really. Gas supply and electrical connections were routed under the floor to where they needed to come up inside the van. It always seemed to take three or four goes to start, probably because I ignored the instructions to provide 3/8" id gas piping. Once running it was lovely and quiet. I wouldn't bother buying this type again, the wide choice of quiet portable generators makes it unnecessary to go to those lengths.

Stuart


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## 98383 (Mar 28, 2006)

sormerod said:


> Can anyone suggest a method/source for switching (automatically) between generator and site hookup so that the mains distribution system in the motorhome can be used for either/or?
> 
> I have an underfloor mounted Onan 2kva LPG generator which I hope to resurect out of storage and fit to the new Hymer I have on order. When last installed (on a Hymer) I used a small relay which I came across at a MH show. This relay ensured that if a hookup was attcahed the generator output connections were automatically taken off line and the hookup power would not be connected until this had happened - the idea being to avoid connecting the generator to the national grid.
> 
> ...


 Hi Stuart you have a pm.

Jenks


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