240V circuit

[Steve928]

So you're sitting in an aire or on site with a hook-up happily watching the TV, it's 2 laps to go in the MotoGP and Rossi is challenging for the lead..

Then - click - the electricity engineer up the pole in the nearby road, or perhaps the site owner needing to do a bit of re-wiring in his connection box (the one standing in the wet grass), switches off the supply!

In your haste, not wanting to miss the exciting race climax, you don't think about the manual steps involved, such as pulling out your EHU lead, and fire up your inverter.

Whayhay!!! on comes your TV.

Now what's that commotion outside? Turns out that someone has been electrocuted - by your inverter back-feeding power into the mains circuit.

 

I don't know whether or not this is a possibilty with your plan but is a real danger when people using generators during power cuts don't isolate their house using a failsafe double-pole switch.

Please do check that this scenario could in no way arise before you go ahead.

[bolero boy]

a low wattage (700w) kettle is all we use when on ehu (3kw arghhhhhhhhh) and a small gas kettle when we are not.

 

no need for inverters to have a cuppa.....bonkers, if you ask me.

 

we have an inverter which powers our (mains only) sky HD box when away from ehu, no hair dryers, drills, blow torches etc...

 

all we need, runs on gas (cooking, heating) or 12v (chargers, LED lights, tv etc)

[Brian Kirby]

aka4ajax - 2015-09-16 11:28 AM

 

Thanks for the advice on the Kettle, maybe i need to rethink the use and get a 12v travel one, keeping the inverter for the TV as you mentioned.

 

Neil

Don't bother, just get one that works on the hob. Far simpler, quite cheap, and a lot more efficient!

[aka4ajax]

Three way pole switch, eliminates this risk.

 

The feed from the Inverter can only be connected to the plugs and not the consumer panel.

 

Position one - normal operation inverter to ring main (no connection to consumer panel or Hook up to campsite as completely isolated)

Position two- Plug ring main completely isolated from both Inverter and Hook up

Position three- plug ring main connected to consumer panel hence hook up (inverter not connected to anything)

 

It is now designed to be manual pole switch rather than the auto sensing i requested, as i was advised too complicated with relays and stuff to go wrong, so "keep it simple stupid".

 

[aka4ajax]

All good advice chaps and keep it coming.

 

I am learning from your experience rather than the hard way. :)

 

[Charles]

SPTT Switch required then (Single Pole Tripple Throw)... But what if the site has reversed polarity? It wouldn't be a problem in reality but your inverter 'neutral' would have the sites live on it, which is sensetive to earth... Which is still connected..

So to be ultra safe DPTT switch required (Double Pole Tripple throw). That's if you can actually get one.

[Charles]

Actually thinking more on the subject, you could use a DPDT switch which would be much easier to get. you'd have 6 pairs of switch poles, Wire the caravan L+N to the centre ones, then say the top ones to the inverter and bottom pair to EHU. You would need a rating of 20amp to be safe, the bigger the better really.

I still wouldn't bother faffing about with it though :-D

[aka4ajax]

Many thanks to all for the input on this topic.

 

I have taken it all onboard and now have a clear understanding of the best practise way forward.

 

The main lessons learnt are;

 

Gas Kettle

Forget the Toaster or again use gas grill

12v TV and satellite box

3-way pole switch and isolation circuits, currently being made for me then fitted in a couple of weeks, but only into the 240v plug ring main.

 

Thanks again and onto next project.

 

[Brabander]

A bit belatedly.

I have read this discussion with great interest!

The dangers of connecting a 230V output from an inverter directly to the mains circuit in a motorhome are very considerable if no adequate protection is taken to ensure that:

1. The motorhome is not connected to the site power supply

2. The inverter is not overloaded

The solution is obviously a TWO POLE (both neutral and live must be switched) transfer switch.

Such switches are readily available from suppliers of small standby generators.

Make sure the switch can carry the maximum site supply current (up to 16 Amp)

 

Alternatively you can cobble one together from two 2 pole contactors mounted on a common plate with auxiliary contacts wired in such a way so that if the first contactor is closed the solenoid coil of the second contactor second is disconnected so that it can never be closed. This is a safe and automatic system as the contactors are HELD in the closed position by the solenoid coil.

 

This system requires no manual switching ie it is automatic.

16 Amp contactors are reasonably easy to get but ensure that each contactor has an auxiliary switch.

 

Good luck

[aandncaravan]

Keithl is right, any Invertor of 1000w can draw over 100 amps (they are not 100% efficient and conversion losses can be as high as 20% as they get hot) that is battery destruction time. Just running a 1000w Inverter for 10 minutes can seriously shorten the life of your batteries. Especially if they are not a wet acid battery where the acid circulates by convection to help keep the Plate surface cool.

If the Inverter is 3000w, a draw of up to 300amps will take a single 100Ah battery down to 50% DOD in 10 minutes.

 

It is not just the Batteries that will be hammered, some poor device will be given the job of throwing all that energy back into the tortured Battery.

Each use of a big Inverter will place an increasing load on the charging system (usual the Alternator for most Wildcampers). The charger will have to work just a little harder each time as it not only has to put back the power drawn, but overcome each little bit of degradation in the batteries. Eventually, as the batteries get past middle age, the load on the Alternator reaches critical.

Ask yourself why Alternators rarely fail on a Car, I don't know anyone who has suffered such a failure in 40 years of driving (or on a van or Lorry) yet regularly fail on Motorhomes at low mileages? This Forum has had 3 threads mentioning Alternator failure just this week.

 

We repair Alternators as well as other charging systems and the failure trend is rising, when Alternators have never been better made or more powerful. They should be getting more reliable, and they are on Cars. Even on Lorries and Vans that cover hundreds of thousands of miles, Alternator failure isn't common.

 

The charging systems, Alternator/Mains charger, get handed a really hard time by an Invertor equipped Motorhome. A load they were never designed to handle.

 

I know that the Inverter publicity says they can be used in a Motorhome, but can any one show me where it says in any Battery manufacturers blurb that taking 150amps out of a battery solidly for 10 minutes to Microwave that frozen Curry is a good idea?

 

A was once unfortunate enough to own a Ford Cortina 1300 MkII that was a pig to Start. The Hand Book said that if the engine didn't start in 10 seconds to stop trying and let the battery rest or the battery would suffer damage. That little starter motor probably drew no more than 70amps, yet running it for more than 10 seconds risked battery damage. I know Battery capability is massively improved, but 300amps for 600 seconds?

 

 

[Brabander]

I agree with your comments.

I once had a boat with stern and bow thrusters which were basically driven by large starter motors.

However when mooring in strong currents and/or on a windy day they might run solidly for up to several minutes.

The thruster motors never gave up but my batteries never lasted more than a season!

Expensive to replace.

Motorhoming is a less expensive hobby!

[aka4ajax]

Hi Aandncaravan,

 

I have read your stuff with great interest on your webpage, actually I have bookmarked it i like it so much.

Reading all on the batteries and why alternators fail and eboxs ect.

I read it so much as soon as i seen your post and without reading the username at the bottom i knew it was from you.

 

I have just bought the MH and had to renew the alternator, last month as it had failed as i picked it up. Plus the old owner had the ebox repaired by yourselves and bought a new one too off you, so i have 2 of them in the MH one hooked up and the other next to it as a spare for emergencies.

 

The batteries are new now too just changed in August, all your information has sunk in and were prepared.

 

The inverter will be on a 6 pole 3-way switch with complete isolation to ensure it can not energise the consumer panel, ebox or 240v external feed.

 

I am still going to install it for using the inverter when not hooked up to mains for things i don't even have an idea yet to be fair. As the kettle are now gas and the TV will soon be 12v also.

 

But since i employed an electrical engineer to design and install the switch, i am going ahead with the design. I am sure one day it will come in handy.

 

But above all else I 100% agree with the battery drain and degradation on the charging systems. Because of your website and sound advice I have also replaced the batteries to ensure I can look after these and know there history.

 

I also have read with great interest the solar section and generator points, all which I will soon be employing too.

 

Thanks for a great website and you truly are an electrical expert.

[aka4ajax]

Initially the electrical engineer had designed an automatic system requiring solenoids as you mentioned, but it started to over complicate a simple 6 pole 3-way switch that it is impossible to have feed going to the 240v inlet from the inverter.

 

This is because the ring main is connected to the output, the selection to it can only be one or the other for instance:

 

Position 1 - feed from consumer panel to plug ring main / inverter isolated

Position 2 - No feed

Position 3 - feed from inverter to plug ring main / consumer panel isolated from inverter

 

I do not now have any planned use for the switch, as its initial requirement has been advised to use a gas kettle, so that done now.

But since the engineer has been commissioned and paid for i might as well have it installed and keep it for future use, with consideration to the amp draw on the batteries the inverter can request.

 

I can see it being used for iphone/ipad chargers and stuff like that if ever....

 

Any how, thanks for all the advice from everyone its all been appreciated and well received.

 

Neil

[aka4ajax]

Hi All,

 

Well i got the unit fitted it worked perfectly bit........

 

The relays were humming away and as it was mounted to the wooden frame of the wardrobe the noise was unbearable, i could not live with it. So out it comes and a simple socket replaced it.

 

So now the inverter is available but just to a double socket, simple.

 

All this has been a great learning curve though . :-S