Places to Stay, Things to do.

I spent most of last weekend crawling around in and under my Pajero and my Jayco reorganising the lighting wiring and the electric brakes wiring. I also added in the signal and earth cables for the yet to be installed caravan rear vision camera.

I have purchased a wireless reversing camera for my rig but when I was testing it I discovered that the wireless signal was not strong enough to get through the caravan to the display. That makes it less than useful so I had to do some re-thinking. There are a couple of options available. I could run an extension cable to link the wireless transmitter module from the camera to the front of the caravan. Or I could get a different type of wireless camera and test to see if that one can get from the back of the caravan to the display.

Just so happens that I got a quadcopter for Christmas from the kids and my wife. It has a wireless camera on it and a FPV screen. With this I was able to get a strong picture on the display through the caravan and the car. This proved it was possible now to choose a camera. Much searching online resulted in the purchase of a small waterproof wifi camera. Only needs 12V DC to run and nothing else attached to it. Let you know how it works in a couple of weeks when it arrives.

Back to the wiring.

The 4 sq mm cable I bought from the electrical warehouse only just squeezes into the back of the flat plug but it does fit. I couldn't parallel it with the original cable so I'll find out if the brakes work OK. It is very interesting that in my last post about choosing the right cable size I talked about installing the correct size but at the first hurdle I fell. The calculated correct size doesn't fit.

Fortunately the rule of thumb for copper conductor of 6 x sq mm in this instance says that the amperage can be 24A continuous. The cable I ran in for the camera is rated at 17A according to the nice young man I bought it from but he was unable to tell me what the cross-sectional area of the copper was. I suspect 3 sq mm which will be perfectly fine.

I have tidied up the connections under the caravan, they were all hanging loose and the earth (white) and auxiliary (black) were in in blue point style blocks. The remainder were in a multi-terminal strip block but not attached to the caravan. I have added two more multi-terminal blocks and screwed them to the underside of the caravan. Much cleaner and less chance of a wire breaking due to vibration and stress.

In my crawling around the back of the Pajero I discovered that the black wire is actually supposed to be the reversing light signal not the auxiliary 12V. Since it has been hijacked for other nefarious purposes I have spliced into that one for the link to the camera. It should only turn on when reverse is selected. I have added a run for a switch on the dashboard so I can turn on the camera manually to check what vehicles may be behind me while travelling. It's not compulsory but I think it could be useful.

I attempted to fit a replacement 240V outlet on the van but found that the item supplied was in fact an inlet not an outlet so there is a delay until the correct unit can be sourced, picking it up tomorrow.

Next weekend, clean out the wheel bearings, check them for wear and check the electric brake units. Might take some photographs for you.

There is discussion all over the Internet about cable rating for trailer / caravan lights brakes etc. Unfortunately most of it is confused, misleading or just plain wrong.

I will attempt to shed some light and clarity to this as I have just been through this exercise, for about two weeks.

Just a quick aside to put my credentials.
I have an Advanced Diploma in Electronic Engineering (Analogue) and an Advanced Diploma in Electronic Engineering (Digital). I work, for the last 10 years, in the Electrical Industry as a line designer for both overhead and underground.

OK, let's just totally ignore the automotive industry cable sizes, they are just plain deceptive. I will come back to this with a couple of tips which will help identify the real ratings.

The correct way to describe cable is through the conductor size in square millimetre. This is the International standard and all conductor of the same size and type will have the exact same rating.

I have used two terms here which are often used interchangeably but should not be mixed up.

Conductor describes the material which conducts the electricity, cable is covered conductor. The covering used for a cable determines it's voltage rating nothing else.

Conductor can be made up of wire, tubing, flat bars, solid billets etc. Conductor doesn't care about the voltage, just the current. Too much current will melt it. A very large voltage with no current has no impact at all.

For the purposes of this post I'll just talk about the makeup of the cable we will use for our wiring harness. The conductor will be made up of multiple strands of wire but I don't care about how many strands or what size they are because the all important current rating is the same for all square millimetre of conductor of the same type regardless of the number of wires.

The only real difference between single strand cable and multi-strand cable of the same rating is how flexible it is. Lots of thin wires are way more flexible than one single thick wire. When you have to pull it through a frame or wall cavity you'll appreciate the multi-stranded cable. The sheath doesn't just protect the conductor from it's surrounds electrically but also physically which is why we use cable, no bare conductor for this type of wiring.

If you want to charge the battery in your caravan or camper while travelling then you will need a specialised circuit and you should be using heavy duty cable via an Anderson plug/socket set. A solar panel on the roof of your caravan or camper will also do this job while travelling. This is not part of this post.

This is just about the lights and electric brakes.

For the lights you really only need 3 sq mm copper conductor. This is good for a continuous current of 18A. Your tail and stop lights are probably rated at about 21W. 21 watts at 12 volts is 21 / 12 = 1.75 amps.

The other thing you need to take into account is voltage drop. The formula for voltage drop is length in metres x current in amps x 0.017/conductor size in sq mm = voltage drop. Juggling this around to get the minimum conductor size and assuming that your total length of cable is 10 metres (from the source in the tow vehicle to the lights on your caravan / camper) we get 10 x 2 x 0.017 / 0.36 = 0.944 square mm. 0.36 is the largest acceptable voltage drop on a 12V line, is used 2 amps so we had a buffer in case your lamps are 24W.

Anyway, at just under 1 square mm that's a pretty easy conductor size to buy. This means that the cheap 7 core trailer cable sold almost anywhere is good enough for these lights as that is usually at leas 3 sq mm copper core..

It isn't any where near good enough for the electric brakes though. The electric brakes typically draw 4 amps per wheel at full braking load. You'll almost never need this amount of current but you should make sure that it is available. Running the calculation again we get 10 x 4 x 0.017/0.36 = 1.88 square mm. This looks easy but you have to remember that this is for one wheel, for a single axle this is 3.76 sq mm and for a tandem axle this is 7.52 sq mm at the connector.

You can't buy these fractional sizes so you need to buy the rounded up size so that's 4 sq mm for a single axle and 8 sq mm for a tandem. You will also need to have the equivalent size for the earth wire in the connector so all that current has some way of returning to the battery. Most professional tow bar installers will use 5 sq mm for the electric brake installation for two main reasons. That's the size which easily fits the flat plug they use and it is good for about 80% of the maximum load that could be required. Mostly you won't use 80% load, you will usually be around 20% load so 5 sq mm is fine. It will also carry the 100% load for a few seconds which is probably all it will ever need in an emergency stop situation.

I'm a bit more of a belt and braces type so my rewire will be using 4 sq mm in parallel with the existing 3 sq mm from the Jaycar trailer cable. The Jaycar cable may be bigger than 3 sq mm but I cannot find out what it is so it's safer to assume a smaller size. By running these cables in parallel it's the same as having a 7 sq mm cable installed. I'll do the same for the earth return cable.

I trust that makes a bit of sense to you. Ask questions if you need more clarification.

Here are a couple of links to help out.
The first is here on this site but reproduced from another site.
http://thetravellersportal.com/index.php/2016/02/26/auto_cable_by_collyn_rivers.

The second is here http://electrical-engineering-portal.com/electrical-thumb-rules-you-must-follow-part-1#thumb-rules the only bit relevant to you is the first section.

There are some things you need to take into consideration when playing with these and other calculations. All results have some caveat or other placed on them. The ability of a cable to carry current is determined not just by conductor size but also the length of circuit, the type of cover, is the cable exposed to the air, is the current momentary (pulse), steady or variable, what voltage is the circuit and many other things.

For a 2.5 sq mm copper cable, the current-carrying capacity can vary from around 15A to around 36A, depending on the factors described above. I would not use 2.5 sq mm for anything bigger than the tail lights on my caravan and nor should you.

In the rules of thumb from the second link using 4 x sq mm of cable is relatively safe as long as you also check for voltage drop. The 6 x sq mm is for copper conductor for a sustainable current in your circuits. It is assumed that the cable is electrical cable not automotive cable.

This is what you can do to get something sensible from the automotive industry cable ratings.
They will often tell you that the cable is rated at, lets say 10A. This is obviously for 12 volt circuits and usually is the maximum rating of the core, just below melting. They are also usually assuming approximately 2 metres of cable being used. Start by halving the current rating, then divide it by 4. That should give you an approximation of the sq mm area of the copper which you can then work with.

However, if the insulation around the copper core seems excessively thick just walk away. Excessively thick is thicker than the diameter of the copper core.

As a preface to this article I should tell you that I attempted to find the original article on Collyn's site but was not able to do so. I found this here http://www.fridge-and-solar.net/wire.html. I duplicated it here because this should not be lost.

Auto Cable by Collyn Rivers
Auto Cable

There is increasing evidence that some RVs may have part or all 12/24 volt wiring that is substantially lighter than that intended by appliance makers. This will introduce a voltage drop up to 55% greater than intended - but in some circumstances it may be up to 70%. Where the original cable was over-specified this may not matter, but will cause a considerable loss of performance if that cable was originally specified to run close to its intended load.

The problem is caused by confusion between two cable rating systems that, in the smaller sizes, have apparently identical 'numbers', but are in fact specified in different ways. I earlier believed this to be a mainly (and recent) Australian phenomenon, but it increasingly appears to be a far wider problem than I suspected - and one that may have existed for many years. It does not appear to affect USA-built RVs as that country uses a different cable rating system (AWG).

It is caused as follows.

Manufacturers of 12/24 volt appliances specify the cable that must be used to connect an appliance, or supply that cable (where the cable is supplied and used there is no problem: unless it is lengthened).

This cable is almost always specified using the internationally recognised ISO (International Standards Organisation) rating system. The ISO system rates cables in terms of the cross-sectional area of the copper conductor - using the following increments. 1.0, 1.5, 2.5, 4.0, 6.0, 10, 16, 25, 35, 50, 70, 100 sq mm etc. Thus an ISO 4.0 sq mm cable is a cable that has a cross-sectional area of 4.00 sq mm. This is the cable used for mains wiring in Australia and is also fine for 12/24 volt RV use.

The auto-electrical industry however uses what is known as auto cable, and this is the cable that you will be sold if you buy it from almost anywhere except a general electric wholesaler. It is that sold by auto parts suppliers.

Unlike ISO-rated cable, auto cable is rated in terms of its overall diameter (ie. insulation and all). This insulation is typically 0.5-1.0 mm thick (but varies not only from maker to maker, but varies from one type of auto cable to another from the same maker). Thus the nominal auto cable size gives little indication of the amount of copper it contains (and hence current carrying capacity). The most commonly used auto cable sizes (in RVs) are 2-3 mm, 4 mm, and 6 mm.

The following Table shows the actual sizes (in the all-important square mm) of '4 mm auto cable' sold by various makers in March 2003.

Maker Marketed Size Cross-sectional Area

A 4 mm 1.25 sq mm

B 4 mm 1.80 sq mm

C 4 mm 1.85 sq mm

D 4 mm 2.00 sq mm

E 4 mm 4.00 sq mm

Cables C and D are made in Australia. Cable E is made in Italy.

Specified correctly, auto cable is a perfectly good product. The problem, from an RV point of view, is that auto cable, sold in some numerically identical sizes as ISO-rated cable, is being widely mistaken for the ISO rated cable usually intended.

In many instances auto cable's size in square mm is also marked on the drum (but in small print). But as very few people are aware of the situation, this marking generally has little relevance to them - and may only be noticed if one buys the whole drum.

There is also confusion about the current ratings usually attributed to most makes of auto cable.

These 'current ratings' are fire safety ratings. They relate only to acceptable temperature rise: what the cable can carry before the insulation becomes unsafe. Further, these 'ratings' often assume that current flow is not continuous.

One (imported) 4 mm auto cable of 1.85 sq mm is rated by its maker at an extraordinary 60 amps. Another 4 mm, 1.85 sq mm (Australian-made) auto cable is rated at a far more realistic 10 amps. But in no case are these ratings directly related to acceptable voltage drop.

Current ratings provided with 12/24 volt cable are always of this nature. To determine cable size you must know:

The total conductor length,
The current that the cable will carry,
The permissible voltage drop (0.36 volts is fine for most 12 volt purposes, 0.72 for 24 volts).
From that it is possible to work out conductor size in sq mm as follows.

Length in metres x current in amps x 0.017/conductor size in sq mm = voltage drop.

In other words there is really no such thing as '5 amp' or '10 amp' cable. There is only cable that can carry 5 or 10 amps over a certain distance without exceeding 'n' volts drop. If that distance is one metre, 1 sq mm cable is fine. But if that distance were to be 100 metres, even starter cable is too thin!

This matter came to light during 2002. During that year I became increasingly aware that complaints of (mainly) gas/electric fridges working fine on 240 volts, but not on 12 volts, needed closer investigation.

There were simply too many to be random faults: there had to be some common cause.

I looked into about 50 instances of this (often via email/telephone) and found that that all but two were due to 4 mm auto cable having been used in place of that specified. This typically introduced about 0.8 volt drop between battery and fridge (the odd two were caused by corroded connectors) and were fixed completely by installing adequate cable (6 mm auto cable is usually fine - it is typically 4.9 sq mm).

Here are the typical calculations involved with gas/electric fridge wiring.

Some early fridges had low wattage 12-volt elements that were not particularly effective, but more recent models have generally similar performance on 12 volts and 240 volts.

Most 12-volt fridges typically draw 12.5 amps (current models draw 15 amps or more). Fridge maker usually specify a maximum voltage drop of 3% (0.36 volts). For this example assume a fridge that is three metres cable run from the battery (i.e. six metres of conductor).

Voltage drop = Length of conductor in metres x Current in amps x 0.017 divided by conductor cross section is sq. mm. For early gas fridges this is thus: 6 x 12.5 x 0.017 = 1.275. Here 4.0 sq mm cable results in a voltage drop of 0.318 volts. With 15 amps draw, the drop with 4.0 sq mm cable is 0.382 volts. This is a bit high, but marginally acceptable.

Looking at the above but substituting 4 mm auto cable (of 1.85 sq mm) we have:

6 x 12.5 x 0.017 = 1.275 divided by 1.85. This is a voltage drop of 0.69 volts. Or, at 15 amps, of 0.83 volts.

The thing to bear in mind is that, voltage loss is also power loss. Thus if you lose (say) 0.8 volt along a cable carrying 15 amps - the loss is 15 x 0.8 watts = 12 watts. If the fridge cycles on 10 hours every 24 hours - that's 120 watt/hours/day lost in heating up the RV.

Circuits running a few globes at 12/24 volts are often specified to run over 1.5 sq mm cable. Most auto cable of the closest apparent size (2 mm) has 1 sq mm of conductor, but some has as little as 0.5 sq mm. The latter will typically introduce a drop of a volt or so (or about 8%). Globe brightness of incandescent and halogen globes is proportional to the fourth power of the voltage so the effect of voltage drop is profound: e.g. 5% voltage drop causes 20% loss of brilliance. (For people who care about this stuff, the relationship is defined by the Stefan-Boltzman equation).

The larger 6 mm auto cable is less of a worry. This cable is typically 4.9 sq mm - and is a good substitute for 4 mm cable where 4.00 sq mm was intended. But it still pays to read the small print on the drum: plastic is much cheaper than copper.

In most instances the incorrect use of auto cable will degrade performance but is unlikely to present as a general safety risk (fridge cables may run hot - but not to the extent of being a fire risk. There may however be a specific safety risk.

There have been various magazine and website articles (and website correspondence) actually recommending 4 mm auto cable for electric brake circuits. Anyone following this advice is likely to have brake wiring with totally unacceptable voltage loss. Electric brakes are conservatively rated, but not to that extent.

This is a field that's a long way from rocket science and I seek no credit for apparently uncovering it. Any electrical engineer would have done the same (and probably much quicker because I'm a research engineer). But there appear to be hardly any electrical engineers working in the practical side of the RV industry. It might also have been spotted years ago if users' complaints re fridge performance had been taken more seriously. Seemingly they were not.

The extent of the problem is beginning to be realised following my original writing about it in the CMCA's 'The Wanderer' magazine Tech News column. This column has been picked up by global Internet search engines and recently became 'number one on the Google hit parade' (search for 'auto cable' + 'sizes'). It is too early to comment but the issue is definitely not confined to Australia.

I alerted the Australian auto electrical industry about this problem (via an article in Automotive Electrical & Air Conditioning News in January 2003). Feedback from that initial article confirms that few auto-electricians are aware of ISO cable ratings - and several rightly point out appliance makers often specify 4 sq mm cable simply as 4 mm cable (i.e. the square millimetre bit is implied!).

When faced with the 12-volt fridge problem etc, auto electricians quickly pick the cause and fit heavier cable (usually 6 mm auto cable) but dealing as they are with isolated cases, were not aware that the problem may be so common.

Electricians (ie. other than auto electricians) seem well aware that with appliance cabling, cross-sectional area is implied (ISO is the Australian mains-wiring standard). Several I've discussed this with are well aware that auto cable is quite different - but all assumed that this was common knowledge.

Since the publication of my original articles on this matter I have been commissioned to write a complete series on electrical installation in RVs. This will be published in Automotive Electrical & Air Conditioning News, and may eventually be expanded and published as a specialist RV book for the auto electrical industry late this year or early 2004.

The generality of this Update Note will be incorporated into future editions of Motorhome Electrics but it may be a year or two before the full story is known.

There no easy fix for the fridge cable. It simply has to be replaced. For lighting circuits that use incandescent globes, a relatively simple fix is to replace the fittings or globes with halogen equivalents of half the wattage. These give the same light for half the current and thus half the voltage drop.

If you have the problem and are already using halogens you can either replace the cable - or wait for the shortly forthcoming LED (Light Emitting Diode) cluster globes, a few of which are already on the market (but costly). These will draw so little current that the original voltage drop will be no problem.

I should stress that I am attributing no blame whatever to RV manufacturers. It is an unfortunate but understandable problem that remained unsuspected for years. Some people are unlikely to thank me for uncovering it - but there's no reason to perpetuate it. If blame is to be attributed it should perhaps be directed at whoever thought up the auto cable method of rating without considering its possible repercussions.

Collyn Rivers (March 2003).

Do please note that the above column is copyright but may be reproduced subject to the following:

Copyright, 2003 - reproduced by permission of Collyn Rivers, www.caravanandmotorhomebooks.com</a>

I had a discussion recently with another caravan owner who tows with a Holden Commodore. He told me that you didn't need a 4 x 4 to tow a caravan and he is absolutely correct. What you do need is a good understanding of the safety and legal ramifications of towing a load in excess of the rated capacity of your tow vehicle.

I also read a report in the AC & RV magazine about the Subaru Forester towing a small camper van. The report said that the Forester handled the tow fine except under braking the the camper pushed it a bit. Total vehicle mass was only 2500kg. The Forester has a towing capacity of 1800kg and the Cub only weighs 710kg dry. Loaded up it may come in at 1000kg so the Forester should be able to handle it but the Subaru manual states that you should use electric brakes if you are towing over 750kg and this Cub would be over that limit.

However, you will also load up the Forester with perhaps another 500kg counting people, fuel etc. and you can see that there is little or no margin left. This is not a vehicle for towing this type of load. My apologies if I just burst your bubble.

To add to the problems I found that the Holden Commodore, most models, have up to 3 different towing ratings depending on gearbox and motor combination. The PT Cruiser is rated at 450kg un braked and 454kg braked. This equates to a small tinny or perhaps a two motor bike trailer.

This link is a downloadable pdf so you can check your own vehicle but the real information should be in your vehicle handbook.

The whole website at http://www.towingguide.com.au is worth a read.

Just remember that the GVM of your vehicle/trailer/caravan combination is a legal and safety limit. It is the total mass (weight) of both vehicles fully loaded. Full water tank, full fuel tank, all food, clothing, toys, spares etc. You can probably get weighed at a nearby weigh bridge, you may get charged for the privilege but you should also get a slip for documentary proof should you need it.

My set up has been chosen to give me plenty of margin. The Pajero has a 3000kg towing rating, the Jayco will weigh in at around 1800kg fully laden so I have a buffer of 1200kg before I put anything into the Pajero. I expect that to get up to around 400kg of load. When I have it loaded I'll try to get a weigh bridge certificate.

Travel safe people, enjoy your holiday and get home again.

Yep, we went to Burra and picked up our new caravan in our new Pajero.

There were a few things we needed to change before we could tow the van home.

The torsion bar load levelling block didn't fit on the tow ball tongue so we had to turn it upside down which raised the front of the van a bit and meant we couldn't open the rear door of the Pajero.

The electrical link was too short to do left-hand turns so we removed the bracket and relocated the cable, with zip ties, so we did have sufficient length.

Other than that though everything went to plan. We stopped at the Gaslight Collectables and Old Books in Market street for a Cornish pastie, yum.

Having satisfied the inner beast we began the trip home. Since we went to Burra via Gawler, Roseworthy and the Barrier Highway we decided that we needed to go home a different way so we headed home via Clare. We paused in Balaclava to check tyre temperatures, a little unbalanced but within spec.

It's a pretty easy cruise from there back to Adelaide so on the way through the city I dropped my offsider off at his place and headed for home through the rush hour traffic. Being my first tow with this vehicle and caravan I took it pretty steady straight down Tapleys Hill Road, up Cement Hill and left to Main South Road. Very easy up the hill so pretty happy with the overall performance of the Pajero at this early stage.

Arriving home one of the neighbours had left his car in a difficult position for me so I had to put the van in by swinging it left rather than the preferred right. Even though we had the brick facade on the carport removed the day before it is still a difficult manoeuvre and a reasonably tight fit but it does fit.

No, I didn't have help to guide me in except for the last few metres so I didn't hit the back wall.

We have had excited now fellow caravaners calling around to check it out and ask when we are taking it out for it's first run.

That will be soon. I have ordered the reversing camera for the van as I had to take several goes at getting it into the carport and I think the camera will make a big difference. A guide would also make a big difference but there won't always be one around.

I'll let you know when we are off on the first trip and how the camera turns out.

I cannot believe that it has been 7 years since I last posted to this site.

Hello to all those who actually visit, I have decided to make a few adjustments to this site.
I hope you like it.

I have travelled since the last trip recorded here. We have been camping to may places within South Australia and have taken a Mediterranean cruise.

All of these things were excellent and we had a wonderful time but I failed to record any of it here, as I should have done.

As I said at the start, time doesn't stand still. We have bought a caravan and a tow vehicle in preparation of doing a lot more exploring of our wonderful country.

What I plan to do here is to document how we set up the caravan and the tow vehicle, what equipment we use, where we go, what happened and what it all costs.

This might end up as a "warts and all" exposé of everything I do wrong but if that helps you that will be fine.

One of my favourite quotes is "Smart people learn from their mistakes, really smart people learn from other people's mistakes. Get really smart, you don't have time to make all the mistakes yourself."

Let's start then by telling you what we have bought.

The caravan we picked up from a couple who have reached the stage of not being able to continue caravanning around Australia. We bought a 2001 Jayco Freedom, I'll post a photo when we pick it up. The couple we bought it from threw in all of their travelling goods and accessories as they no longer have any need of them.

The tow vehicle is a 2011 Mitsubishi Pajero with 94,082 km on the clock. I have added a heavy duty tow bar, electric brake controller and a reversing camera. Not fitted yet but ordered are a nudge bar and side steps. When it's all kitted out I'll post a photo of the vehicle as well.

We were hoping to get this all set up for around $50,000. We went about $3,000 over budget but my wife is very happy with the total package and we feel that we have actually got a package worth more than we have paid out.

I want to add a Tyre Pressure Monitoring System to the car and caravan and am doing some serious research into these at the moment. I have also been looking for a centralised inflate/deflate system for the vehicle tyres but think I may have to make one for myself.

More details tomorrow.