Fridge Conversion 2way to 3way??

[keelz]

Is the protection offered on these inverters the same or equal to the standard RCD/ELCB?. I guess my question is will it trip in under 20 milli seconds as required for most RCD's in home and commercial applications?. If it can't trip in that time and cut the power you would still have a very lethal device potentially sitting in your van.

The importance of the MEN is critical when the van is used without the 15a power cord (i.e. when free camping or running on the road mobile).

Look at it from this perspective - when you're van is parked at home or parked in a van park, you're power cord earth's the van, the van chassis and any metal framed appliance plugged into your van powerpoints (eg the fridge) back to an earth stake which is located near or adjacent to your house switchboard or the switchboard in the van park. Even if (touch wood) the RCD failed or did not act in under 20mS, the van's chassis, power outlets and anything attached to the vans chassis/earth (eg aluminium frame, cladding,etc) all has the same ground potential as the chunk of dirt back at the main switchboard that the earth stake is hammered into. i.e. in a fault situation eg where say active bridged/shorted to earth (in a faulty appliance such as a fridge) then the most conductive route to earth for the fault will generally be back via the van's power cord, not via your body (although you may still get a good tingle or jolt ). This is the basic fundamental of having an earth wire, earthed appliances, etc which have been around for years before RCD/ELCB's were introduced.

Now consider this - you and the missus/kids pull up for a rest stop on the side of the highway, you leave the car running with inverter running away in the van. Your car is sitting on 4 well insulated rubber tyres. You're van is sitting on 2 or possibly 4 well insulated rubber tyres. There is no path for a fault to ground/earth potential. Assuming you didn't get zapped when stepping from the car, when you go to put the keys in the van door you become the best water filled conductor between the van and the ground (hope you're wearing those thongs!). If the inverter device hasn't detected the fault and your fridge 240v heater element became faulty (eg insulation breakdown shorting to earth - a common fault with heater elements) and made the frame of the fridge (and thus the van chassis live) you have a deadly situation.

I think the inverter option is feasible, but you'd really want some guarantees that the safety devices in the inverter equipment are up to scratch/standard required.

My other question is that when using inverters in a mobile situation as mentioned in these posts above, what replaces the earthing of the van usually provided via the 240v 15A power cord?

The 12 volt heater element option and decent 12 volt wiring from tug to van is so much less hassle in comparison for when you're driving.

cheers

Keelz

[Deleted]

Keelz,
My sentiments exactly, you cannot get zapped from a 12 volt system but 240 volt AC will kill you. That is why fridge manufacturers made 12 volt elements so their fridges could be run safely when on the road.

Frankidownunder.

[Deleted]

Ultimately I believe it's horses for courses.

1. The inverter is a neat easy way of providing FULL power to a 2 way/3 way fridge whilst mobile. The 150 - 200 watt absorption fridge will work at full capacity (on 240 volts) with 6mm cabling to the van.

2. It's much safer than gas.

3. All the literature advises that 'cheap inverters' MUST operate in a standalone configuration. ie battery to inverter to fridge (or wotever). The chances of any misdemeanour with all components safely secured, is extremely unlikely.

You have to somehow get your body across the inverters active and neutral feed. That is really very difficult unless you are quite creative.

Earth returns don't come into it, as the inverter is isolated.

[keelz]

hey guys I think we should note that the three ways are generally designed to run the same on all 3 heat sources - gas, 12v or 240v.

the 12v element is often a different wattage to the 240 element, not always the same wattage. The problem why the 12v element doesn't work well at times and people often whinge & moan about them is often due to voltage drop issues and poor wiring efforts from the car battery to the rear of the car, use of a poor choice towing connector, poor wiring from vans towing connectors back to the rear of the fridge. If they spent the time to fix this, they would have a better outcome.

The 12v element does not have a thermostat so it runs continuously, providing quite good heating in the cooling unit. The advantage of using 240v is that you get the ability to set the thermostat, however it should be noted that with the fridge sloshing around the cooling unit while driving it will inherently work and behave a little differently than when it is sitting perfectly still, idle and level.

Agree that lpg/gas is not a safe option for travelling, unless you like tearing down the freeway looking like a drag racer with flames behind you.

Even if you are going to go down the inverter route, you still have to install a 12v relay & resettable circuit breaker adjacent to the car/tug battery, then run heavy heavy duty cable to the rear of the car, terminate into an Anderson or 12pin plug. You still have to run heavy cable from the vans plugs back inside the van and terminate at in inverter.

So regardless of whether you use the inverter option or 12v heater element option we need to remind readers of this thread that they would still be up for the same comparable scope of works and cost. The 12v heater element will cost around $70-$100. A decent inverter is going to cost the same (eg entry level from Jaycar, etc) or probably a bit more for a more sophisticated safer and reliable model.

If you have to unplug your fridge 240v plug and plug it into an inverter 240v socket before every trip and then unplug it and plug it back into a powerpoint every trip you will eventually go nuts and will drive off on a trip one day and forget to change it over to the inverter outlet.

The 12v heater element can be left hardwired in to the 12v hot wire and every time you hitch up your van it will start working, without having to muck around with your fridge power plug. It's set and forget and doesn't take up room in your cupboards.

oh forgot to mention a lot of fridges are bolted in or screwed in some way shape or fashion most times.... ok if they are bolted into a plywood floor, it won't conduct. But what if like mine they have a metal bolted bracket connecting the metal chassis of the 3 way fridge back to the van wall and that bolt is threaded into the aluminium wall frame of the van which is consequently bolted/rivetted to the whole earth/steel chassis of the entire van, effectively linking anything on the van's existing earth circuit straight back to that stand alone inverter operation mentioned above?

Just my thoughts.

cheers

Keelz

[mike]

Hey hey, ;D

The many twists and turns... It is now becoming much clearer.
Thanks Keelz and wahroonga for all this.

Both of you have been very clear in these explanations... really clear.

What I see now is that I can have the benefit of the thermostat controlled 240v fridge with my inverter, as installed, because my fridge is only bolted to the timber floor (and not to any metal part of the van, producing a stand-alone system. OR

... from the same 12v wire that brings the current from the car battery to that inverter, hook it up to a 12v heater element in the fridge........................

..................without the benefit of the thermostat control BUT ALSO eliminating the danger of electrocution that exists in using the inverter for the same job, as a result of a road accident.

That's it!!! ;D ;D ;D


All the other points that have been made are relevant and need consideration BUT can divert attention from the real issues.

Things like
1. Unreliability of 12v elements??
2. Ease of installation
3. More chance of being wiped out by a 'B-Double' truck than being electrocuted by an inverter...
4. Earth wire connections
5. Using multiple devices at one time on an inverter (definitely not relevant because this thread
is only concerned with inverter use while travelling: other inverter use while stationary can be
dealt with elsewhere).
6. Alternative uses for inverters when camped.
7. Flat batteries due to 12v current being left on while stationary.
8. Connection to caravan batteries.
9. Types of batteries.
10. Isolation of solar panel battery charging
11. etc

This is great stuff!!! ;D ;D ;D

I'm now considering installing a 12v element AS WELL, (and possibly a relay switch to the ignition switch??). This will be an ALTERNATIVE 12v method of cooling for the fridge.
(At the time I installed the inverter 2003, I did not realise you could retro-fit 12v elements.)

Huge!!! ;D ;D ;D ;D ;D ;D ;D

Cheers
Mike ;D ;D ;D

[keelz]

hey Mike

yes you can DIY retrofit a 12v heater element - but only to some fridges - you need to open up the inspection hatch on the metal shrouding where the heater elements are......have a peek before committing to buy additional element.

If your fridge was built with the option for 12v provision, it will probably have a spare tube/slot which is attached to the main boiler tube of the cooling unit adjacent to the 240v element. Some of the old dometics have the provision.

If you don't.....well........ it would be a job for professionals or put in the too hard basket. However.....

The other option if you don't have a spare tube slot/space could be - have a look at the wattage of the existing 240 element and it's size. There are now commercially available spare elements made for the newer fridges some of which have a combined 240v and 12v heating element inside the same element/fitting. You might be lucky enough to find something in the write size and wattage categories, however would suggest anyone considering this route get advice from an absorption fridge repairer before putting in something with an incorrect wattage which could cook the cooling unit.

Now - flat tug/vehicle batteries. This shouldn't happen if you install a heavy duty relay to switch on/off the hot wire from the tow vehicle battery once your cars ignition is turned on/off. If your not sure how to wire this, take to your local auto-electrician . This will automatically prevent flat batteries when you stop for a rest break or camp overnight. In situations where you stop for long periods away from 240v power you should switch to lpg! A simple feed from the ignition or accessories circuit in car will operate the relay. The relay and resettable circuit breaker should be located somewhere near your tugs battery or main fuse box in a well protected position, ensure you insulate with rubber booties the threaded lug terminals of the resettable circuit breaker and use insulated spade lug connectors to the relay to allow you to quickly replace the relay if it ever becomes faulty.

Whether you use inverter setup or run a 12v element, self-resetting circuit breaker and relay are essential to
a) prevent fire;
b) prevent flat battery in your tug.

Keelz

[Deleted]

A 'fridge switch' may be worth considering as a fully automatic solution. I think it's been mentioned earlier?



I've not used one, but it looks like a simple but excellent solution to the problem of 'protecting' the tug battery.

How Fridgeswitch works:

Fridgeswitch has an inbuilt electronic movement and vibration sensor which switches the 12 volt circuit of the caravan’s 3 way fridge ‘on’ when the vehicle is moving and turns the fridge ‘off’ when the vehicle stops.

Fridgeswitch has a varying timing circuit which may keep the fridge turned on for up to 3 minutes after the vehicle has stopped. This is to keep the fridge turned on while you are stopped at traffic lights.

I'd locate it in the van adjacent to the fridge. You could add a 'bypass switch' to have power permanently on.

PS A B-double incident is a trillion times more likely

[keelz]

Yup, Fridgeswitch yes also another option, but if you intend to have an inverter setup in the van the fridgeswitch wouldn't turn off the 12v to your inverter. So if you pull up and turn the car off, the inverter would still be draining your car battery unless you have a heavy duty 25A or so rated switch on your dashboard to turn the hot wire off.. So the relay comes into it's own i guess.

The fridgeswitch costs approx $62. I've sat in heavy traffic on the pacific (that darn cattle track highway) in holiday times sitting idle in bumper to bumper for longer than 3 minutes during roadworks with zip zero zilch movement of car and van......this means my fridge would get turned off by Fridgeswitch?

A Hella 12v 40A relay would cost apprx $5 to $8 - it keeps my fridge running as long as the car is running and the ignition key is at On or ACC.

The cost alone made the decision for me.

You still need to fit a resettable circuit breaker adjacent to the tow vehicle battery as mentioned in previous posts. This costs between $8 to $15 for a 25 to 30a unit.

cheers

Keelz

[mike]

Hey,hey,hey!!!! ;D ;D ;D

Even more good stuff!!

Thanks Keelz for the info on 12v alone and 12v-240v element retro-fit problems: that alone could have tripped me up nicely, if I'd just blundered into trying to 'invent another wheel'!!

Your info on wahroonga's suggestion of the fridge switch and how it can be a problem in use when caught in traffic jams, relative costs etc ... all good stuff.
I like this fridge switch's function of "cutting off the current" after say 3minutes: That would virtually eliminate the danger of electrocution from the inverter in that catastrophic road accident that's heading my way at sometime in the future! ;D ;D ;D

I'll probably end up with my current inverter system, but add
1. a relay switch to the 12v line ;
2. a 'push-button' circuit breaker $7.95 from whitworths.com.au , instead of from the re-setting fuse (as revealed on page 1). I now think that I don't want the 12v line being turned back on automatically if it has blown for some reason. I think it would be more prudent to check what caused the circuit break to occur, first, before turning the current back on manually.

Thanks

Cheers
Mike ;D ;D ;D

[Deleted]

all good stuff.

The Whitworths cheapies really need panel mounting.



ABR Sidewinder have some nice breakers. They supply some good 12 volt stuff, with sound advice on tap.

What the heck, nothing's too good for the 70's. Let's spend our kids inheritance.

[keelz]

yeah either fuse or breaker is fine. Although one word of caution, don't go too high on the rating/amperage. Review your cable sizes and max capacities. Review what juice your inverter and/or fridge will pull. If you use too higher rated breaker or fuse your wires in tug or van will melt or fail first at weak points/connections. Melted cables running under some annoying plastic cover plate under your door arches or in some osbsure location in the boot can be a pain to fix, particularly when on the road. (Says he who use to fix his mates cars after they had installed their doof doof amplifiers in the boot pulling too much current through cables ;D)

If you have a say 120 watt heater element at 12.0v, it will pull approx 10 Amps current through that cable (Divide wattage by Volts to obtain Amps). A 20A fuse would be ample in this situation.

For inverters, a rough guide - use 100W at 240v your inverter will draw approx 10A at 12v.

A blade fuse in a rubber booty or plastic mount box (sometimes you can even better still use a spare slot inside your car's existing blade fuse box near the battery, nice and tidy).



or other option say a 20a resettable breaker - $7.04 from Caravansplus, similar to what you use when wiring in a brake controller......



Keelz

[Deleted]

Good advice Keelz.

And whattever you do .... don't buy cheap ones from ....



I had 15A one that simply melted in the fuse holder. It didn't blow!

I stopped an almost certain fire by reefing it out with a pair of Leatherman pliers. I know I wear them for some reason.

It took out the wiring loom to the lighter socket. The engine management system was shorted in the process, so no vehicle! Major problem!

It was caused by a cheap GPS 5v lighter socket supply which shorted internally due to heat deformation.

The fuse was a stamped piece of Aluminium!

So at the end of any installation it's always a good idea to actually short out the cable, to test that all is working as it should.

So.... cheap when it comes to DC cabling .... is bad!

[mike]

Hey, hey ;D

More good stuff!!! Unbelievable! ;D

wahroonga: Thanks for the info on the "In-line" circuit breakers: didn't know they existed!!!

Keelz: yes I wouldn't put in anything higher than 20amp; but are you suggesting a 10amp blade fuse would be better? I can see how it might be better, but my thinking is often wrong. I can see how 10amp would be very close to the current draw of the fridge, and would blow given any slight excess in current draw. This would be a safety factor, yes?

wahroonga: I take your point that I should use quality parts, even if more expensive, based on your experience. (Up to now, "expensive" didn't always mean 'good quality'; and I have had experience in some marketing where prices were set based on what the 'market would bear', not on the quality of the product: a bit like the price increases for van sites we see at Easter etc.)
ALSO, you appear to prefer blade fuses in your last post. Trouble with fuses is that when they blow, I never seem to have a replacement handy. I should get organised.

Cheers
Mike ;D ;D ;D

[keelz]

Hi Mike - 10A yep too low. It would probably blow. 20A would be fine. If you have an ammeter or suitable meter you can actually test how many amps are being drawn through your system when operating....

blade fuses yes i have seem them melt into all types of wonderful molten shapes also . If concerned suggest you consider to the old school glass type quick acting style fuse in a suitable holder. That said, i've also seen glass type fuses crack, etc and melt themselves into plastic holders This could perhaps be a good reason for the use of a breaker (either manual or auto-resetting)

Keelz

[mike]

Hey Keelz,


Got it!!

Circuit breaker 20amp plus
Relay 20amp

Done!

Thanks heaps.

Cheers
Mike ;D ;D ;D

[Deleted]

Yup the old tried and tested thermal auto reset breakers that you started out with are pretty reliable.

Haven't seen one of those melt ... yet.

Although that leads to another yarn.

In my youth I had an XA panel van. Great bus, but it scared the shitter out of me one very dark night on a twisty road crossing the Great Divide, up Casino way.

Seems that after about 10minutes on high beam, deep into the ranges, the thermal relay decided to kick in and ... instant blackness.

Amazing how you can replay the road from the on board 'camcorder'.

[mike]

Hey wahroonga, ;D ;D ;D

Good to see you survived to tell the tale.

On the topic of relays,
I was hoping that installing the relay would operate to cut-off the inverter line whenever we stopped to camp ... not while on the road!!!!

Also

I was going to replace the resetting breaker with a manual reset circuit breaker of the type shown in your post earlier,
.....BECAUSE I reckoned that if the circuit was broken at that point,
...........I wouldn't want the resetting breaker doing its job of turning the circuit back on..... IF

....... there was a short circuit of the 240v line!!

I would want to check out the reason for the break in the circuit before turning it back on manually.

Is this thinking right?? or Not???

Cheers
Mike ;D ;D ;D

[Deleted]

Yup, I do really like the manual reset DC breakers.

Like all these things there's a million ways to skin a cat.

[Deleted]

Hi Guys,

Just a thought.

If there is a question on the inherent safety of an inverter you are using, then surely that question would arise whenever the inverter is used whether on the move or free camping?

It is still producing 240V from its outlet socket.

Would one of these Ring Grip 'in line' RCD units plugged into the outlet socket of the inverter provide a bit more protection or does it only work when connected into a MEN system. I bought mine about 3 or 5 years ago for about $30.

I use mine, just to be safe, whenever I have to plug a drill or something into 240 V power away from home and I am uncertain as to whether there is an RCD built in to the switchboard.

I have not used it in conjunction with an inverter. I tested it with the Jaycar tester that wahroona mentioned and it trips the circuit at 30mA. PS I am not a Sparky hence the query?

Cheers, techron

[Deleted]

Hi Techron,

To be sure that it's actually working on site, always test it with the Jaycar unit first. It will only protect you if the supply is MEN compliant.

More importantly test the inverter -> rcd -> Jaycar tester and see what happens. 95% of cheap inverters are not be MEN compliant. Or in other words .... I haven't found one that is!

So, I think the short answer for most cheap inverters, is that an RCD will do nothing to protect you.

In many the earth pin is not even connected.

Your best precaution is to:

• Be careful
  
• Use good extension leads.
  
• Use it to power double insulated devices in good order
  
• Never use the inverter to 'power' your van/house etc ie fixed points.
  

I've probably said all this here

ditzygypsy.proboards107.com/index.cgi?board=techno&action=display&thread=316

[Deleted]

Thanks Wahroonga,
Great advise as usual. I had read your inverter post but apparently not as well as I should have. The answer was already there.
Thanks, techron

[mike]

Thanks wahroonga for the final notes on the circuit breaker for the 12v line.
Another great series of posts with great advice.
Thanks also to Keelz and to all other contributors...
Cheers
Mike ;D ;D ;D

[viscount78]

Thank you a great idea. I will run the inverter from the Anderson plug and install an RCD to protect all the 240v

[mike]

Postscript: ;D ;D ;D

On p1 I mentioned that the wiring had been working satisfactorily using 4mm wire.

Well, it was, ... but ...

I later found the fridge didn't work any more! While on 12v.
What later began to happen was that the car battery began to age and while perfectly capable of starting the car, its capacity to store energy slowly dropped.
Then, at traffic lights or similar, the voltage at the invertor dropped below the critical cut-off point, and the invertor would shut down... and was not capable of re-setting itself .
Result, no cooling.
The CAUSE OF THIS PROBLEM was the 4mm wire that suffers voltage drop.
This WOULD NOT HAPPEN if I had USED 6mm WIRE to do the hook-up. ;D ;D ;D
See wahroonga's excellent info on this in earlier pages.

Cheers ;D ;D ;D
mike

[atouchofglass]

Thanks for the heads up Mike

We all make some mistakes in our rebuilds but knowing how to avoid others is always a good thing

Cheers
Atog