One of the great things about CMCA Rallies is that they provide epidemiological information which, vaguely translated means that if a fair number of people are experiencing something (usually bad), there may well something out there causing it.

As with the rally at Barcaldine, I came across a surprising number of people who were not getting as much out of their solar modules as they should. This is usually due to inadequately sized cable, incorrect regulator connection, and (less commonly), incorrect regulator settings.

Depending on make and type, there are a few different ways of connecting solar regulators, but whichever it may be, it's essential to follow installation instructions to the letter. Problems are often caused by the installer attempting to 'second guess' the regulator maker, by taking a short cut with the wiring.

The most common example is this:

Many regulators (including the PL 20, 40 and 60) are intended to have a heavy cable from the positive terminal of the solar array direct to the positive terminal of the battery. A second and lighter cable then runs back up to the solar regulator - usually to a terminal marked 'Bat +ve', (Figure 1a).

But because the solar regulator is usually located much closer to the solar modules than to the battery, people wrongly assume that it would make more sense to eliminate one cable. So they wire the system as in Figure 1b. This inevitably reduces the charging rate and depth of charge. Here's why:

To optimise charging voltage, and to know when to reduce charging, the solar regulator must know the exact battery voltage.

If that separate voltage sensing wire is omitted (Fig 1b), the solar regulator 'sees' a voltage that is inevitably higher than the battery voltage (because the battery is at a lower voltage than the regulator because of voltage drop along that cable). Seeing this higher voltage, the solar regulator assumes the battery is more charged than it really is, and acts accordingly.

Even professional installers have been known to wire regulators this way. They do this because, unless the purpose of the separate sensing cable is fully understood, it makes sense to an electrician to eliminate what seems to be an unnecessary cable.

If there are two cables connected to the solar regulator 'Bat +ve' terminal it's probable that you have this condition, but you do need to check the installation details as a few solar regulators are intended to be wired this way.

Other types of regulator may be connected in other ways. The vital thing is to use adequate-sized cable connected exactly as shown in the installation instructions - even if it does not appear to make sense! (The people most likely to make this error are those with some electrical knowledge.)

Having the solar regulator wired correctly makes a huge difference to charging - in some cases it may double the charging rate.

Fig 1. Many solar regulators require interconnection as shown above. Only a light cable (1.00 sq mm is fine) is needed for the voltage sensing line.

Fig 2. If connected as above, many regulators (including the PL 20/40/60)

will read battery voltage incorrectly - resulting in lower charge rate and reduced depth of charge.

Fridges and 12 Volts

Also at Casino, was the usual crop of fridges performing badly on 12 volts. Again, without exception, every single one was due to inadequate wiring. I cannot stress too strongly the need for really heavy cable between batteries and fridge. This cable needs to be at least 6.00 sq mm for a maximum cable distance of two metres, and ten sq mm for three metres. If the cable needs to be longer than that you are up for either light starter cable, or redesigning the rig.

Climate Class

As long-term readers of The Wanderer (and of my books) will be aware I strongly advocate using tropical-rated three-way fridges. These are a total revelation to those used to the hot weather limitations of earlier models. I spoke to a number of owners of 'T'-rated fridges, at Casino, and every single owner was delighted by their fridges's performance.

Three-way fridges are rated in terms of Climate Class. The rating is indicated on the bottom line of a compliance plate that is usually readily visible inside the fridge. Next to the term 'Climate Class' is a box that will contain the letters 'N', 'SN' or 'T'. See pix in this article.

The designations 'N' or 'SN' (or nothing at all) indicate that the fridge is designed to operate in ambient temperatures up to 32 degrees C. The 'T' designation, and only the 'T' designation, indicates that the fridge is designed to operate at up to 43 degrees C ambient.

This rating classification applies regardless of the fridge's type number. In other words the same catalogue number fridge is liable to be available in any of the Climate Class categories.

You need to be persistent when ordering a three-way fridge as not every salesperson is aware of this classification system. When ordering specify clearly that the fridge must be 'Climate Class T'. Be aware though that some three-way fridges are not available in the 'T' rating.

Do note though that, even with the 'T'-rated model, installation must be as per the maker's instructions, with particular care taken to ensure adequate ventilation.

This shows the bottom line of the Approval Plate usually found inside most three-way fridges. The notation to the immediate right of 'CLIMATE CLASS'

indicates the ambient temperature range for which the fridge is designed. The letter 'T' shows the fridge is intended to run at ambient temperatures up to 43 degrees C. Other indications are SN, N, and ST. Only 'T' is the Tropical Rating.

This nomenclature was originally a DIN standard - it is now a current CEN standard. Only some models of some fridges are 'T-rated'.

Generators and Battery Charging

People still continue to have problems running battery chargers from motor generators, particularly those fitted to large motorhomes. Assuming the generator is large enough for the charger, the problems are often fixed by having a 100 watt incandescent light globe switched on whilst charging.

(The techo explanation is that the genny's self-excitation circuitry is not responding to the charger's inductive load. Adding a resistive load kicks it into action). Someone pointed out, at Casino, that: 'this shouldn't be necessary'. I know, but I write books and stuff like this, I don't make the gen sets. One reason I switched from engineering to writing is that, to a writer; things that don't work are often an even better story than things that do!

Another cause of such problems is that basic battery chargers need a much bigger generator to drive them than many people suspect. As a rough guide, a 500-watt charger (about 40 amps at 12 volts, 20 amps at 24 volts) will need a generator about twice that size to run it. The reasons are that:

(a) These chargers are only about 70% efficient,

(b) They have what electricians call 'low power factor', and this requires the generator to produce 20%-25% more current than is actually used,

(c) Most generators cannot be run at their maximum output for more than a few minutes.

Improving Generator Charging Performance

Also uncovered at Casino was that the charging performance of those otherwise great little 50 cc Honda dc generators can be improved by replacing the existing battery leads by leads of at least twice the original size, or doubling up the existing cables, or shortening the existing leads by half. Tests showed this may increase the charge rate by as much as one third!

Millenium Modules

In recent articles and seminars I have mentioned BP's Millenium range of amorphous technology solar modules. For reasons that are currently unclear, BP has decided not to continue with this technology.

Isolating Solenoids

Ongoing postings to the CMCA website seek advice on paralleling batteries for charging whilst driving.

The simplest way is to use a large manually operated switch. This is fine if the need for charging this way is rare. But if used routinely you will sooner or later (probably sooner) forget to turn the switch - possibly leaving you with two flat batteries.

Next simplest is a simple isolating solenoid. But as interconnected batteries self-equalise the charged starter battery tends to discharge into the lesser charged house battery. This is rarely a problem in routine starting - but becomes one if you turn on the ignition (thus actuating the solenoid) but do not then start the engine - maybe because there's a king brown approaching - or you have an urgent need to…..…(Collyn - this is a family publication! - Maarit). Then it is quite likely that the starter battery has discharged into the generally much larger house battery, leaving neither (or both) able to start the engine.

It thus makes sense to have the solenoid to close only when the engine is running and preferably after the starter battery is topped up. The latter incidentally takes only a minute or two (starting an engine requires only the same energy as a car sidelight draws in about ten minutes - if you don't believe this, work it out).

The above can be done by taking a signal from the oil pressure gauge, but this can result in the solenoid being actuated as the engine is spun but not necessarily starting. It can also be done via a temperature switch, but a generally better way is to have a system (such as a Redac relay) that senses starter battery voltage and actuates the isolating solenoid at 13.2-13.6 volts. This has the additional advantage that a semi-crook starter battery will receive charging priority if at any time it drops more than a few per cent below the triggering level.

The previous and commonly used isolating diodes are simple and have no moving parts. Unfortunately, they automatically give priority to the least charged battery - which may not be the starter battery. Further, the diodes commonly used introduce an unwelcome 0.6 volt voltage drop. This seriously degrades charging performance (unless compensated for - which is rarely done, and not always do-able). Diodes with lower voltage drop (or similar devices that act like diodes) are available but cost an arm and a leg.

Diode isolation is a simple solution, but not one that I'd recommend except with gel cell batteries: these charge happily from a lower voltage. Or where a smart regulator is installed (these compensate for voltage drop by monitoring battery voltage directly at the battery).

One little known problem with isolating solenoids can occur where there's a combination of normal starting battery voltage, but low house battery voltage, combined with someone wishing to use the microwave oven (this happens a lot with hire vehicles). If the engine is started to boost the house battery, starter battery current plus most of the alternator current is drawn by the microwave (via the inverter) through the isolating solenoids contacts. Unless this solenoid is massively rated, the contacts are likely to burn out.

Future Tech Notes

In view of the extent of the problem with 12 volts fridges and wiring, plus installation generally, a near future column will be a simple guide to correct installation.

A far more complete guide to isolating solenoids etc, and this issue's content generally, is included in 'Motorhome Electrics'. This $42.50 book is obtainable from the CMCA (see advertisement in most issues of The Wanderer). Full details of this book, including sample chapters, are available on the website www.caravanandmotorhomebooks.com