Plasmatronics Regulators

Following my electrics workshop at Barcaldine, about twenty attendees sought advice about their Plasmatronics solar regulators. Most were finding that whilst the inbuilt monitors showed 'energy in' far exceeding 'energy out', batteries seemed to be less charged than the regulators' amp/hour readings (and percentage charge) readings indicated. Further queries related to batteries not being adequately charged from solar panels that were clearly adequate for the task.

A quick check showed these claims to be valid. One regulator was even showing over 50 amp/hours/day coming in, and a mere 2 to 3 amp/hours going out (rather than my estimated 45 amp/hours/day minimum!).

The problem in all cases seeming to have only two main causes, I checked several other vehicles with Plasmatronics PL 20 and PL 40 regulators and found a generally similar situation. A couple of members subsequently reported this happening with another brand of solar regulator.

I should stress that the Plasmatronics is an excellent regulator. And that there is nothing wrong with these regulators. They have simply been installed incorrectly!

There is a clearly widespread misunderstanding of the function of their 'Load -' terminal. The result is that only part of the load current (or even no load current at all) is being recorded. The problem relates primarily to vehicles with a chassis earth return (i.e. nearly all motorhomes and most caravans). It rarely affects domestic and other solar systems.

A further and related problem is that, unless a 'current shunt' and Plasmatronics PLS2 adapter (the PLS2 has replaced the earlier PLS) has been fitted, loads supplied by all but the smallest inverters are not registered at all. This applies also to all other loads that have their negative connected to earth or the battery directly. Whilst most vehicles that I checked had inverters, only one had the necessary shunt and adapter.

Why This is Happening

For sound technical reasons to do with efficiency, many solar regulators, and all Plasmatronics regulators made so far, have a common positive, i.e. solar module/s positive, solar regulator positive, and battery positive are all directly linked together.

Because of this, load current can only be by monitoring the negative (-ve) lead, and/or via the current shunt and adapter mentioned above.

As may be seen in Plasmatronics' very clear installation instructions, the negative of each load is taken to Load- on the regulator. What seems less apparent (to many installers at least) is that, for load current to be registered, this must be the only negative path.

If an appliance is also connected to vehicle earth (and many are because the internal negative lead and enclosure are in electrical contact with vehicle metalwork) that will form the main negative return path. Then, little if any load current will be registered by the Plasmatronics regulator.

Compounding this, the Load- terminal can handle only limited current. For the PL 20 it is twenty amps; for the PL 40 only five amps (or seven amps for PL 40s made since the beginning on 2002).

Inverters may draw 100-200 amps so installers invariably (and here correctly) connect the negative lead directly to the chassis earth (or via a heavy cable direct to the battery negative).

By so doing, the load current totally bypasses the regulator, but installers are overlooking, are unaware of, or are failing to advise owners, that, unless a current shunt and adapter is installed such heavy energy draws are not recorded at all. As an inverter may draw 50% or more of the total daily energy consumed, non-inclusion of that draw results in hugely incorrect readings and assumptions about battery charge. The associated batteries are not simply dying - they are being massacred because of incorrect information.

A few vehicles have the regulator installed such that all appliances are connected directly to chassis negative earth (i.e. the LOAD- terminal is not used at all), but without a current shunt and adapter. Nor the unfortunate owners being made aware of their need. Such installations are easy to identify: input current is shown correctly, LOAD current is shown as '0' and the battery's Percentage of Charge shows a totally meaningless '127%'.

Solving the Problems

There are two approaches with existing systems.

1. For systems that do not include inverters (or have inverters of less than 100 watts or so). Isolate all appliances electrically from chassis earth (but difficult and often impossible with car radios) and then run the negative lead from each appliance to the Plasmatronics Load- terminal, or via common non-earthed points or cables, to the Load- terminal. This is a difficult and tedious job that should have been done by the installer if the Load- terminal was used.

2. For systems that include an inverter. It is also a simpler alternative to '1' above but costs more unless you do the former work yourself.

Disconnect all leads from Load-. Wire the negative leads from all appliances to chassis earth, or directly to the negative battery terminal (i.e. Load- is no longer used). Then install a 'current shunt' in the positive main battery lead. The current shunt is connected to a close-by Plasmatronics PLS2 Shunt Adapter. This, in turn, is connected by a lightweight cable to a socket behind the pull-off plastic cover of the Plasmatronics regulator. You can tell if a shunt if fitted by the presence or absence of this cable.

With the above arrangement (2) the regulator monitors all loads (including the inverter). It still seems like a lot of work - but it can all be done in two or three hours.

The current shunt and PLS2 adapter are obtainable from Plasmatronics dealers. Clear instructions are provided and both units are simple to install. The work can be done by any electrician, or anyone accustomed to working with heavy current 12/24 volts systems.

Plasmatronics current shunts handle 100 amps and 200 amps and must be matched to the maximum current drawn from the batteries with everything likely to be used simultaneously. Larger shunts can be used (providing their electrical characteristics are suitable) but the 100 or 200 amp shunt will be adequate for caravan and motorhome use. If you have a microwave you'll need the 200 amp shunt. If not the 100 amp shunt is likely to suffice. It matters not if you use a 200 amp shunt where a 100 amp shunt would have been fine. So if in any doubt, choose the 200 amp shunt (they just cost a bit more).

The manufacturer is actively working on a new regulator that has common negative connections. This unit, probably available next year, eliminates the problem that current drawn by appliances that are earthed via the vehicle earth return is not registered. But heavy current devices such as inverters are still likely to need a current shunt.

Adjusting the Regulator

A further cause of Barcaldine woes were traced to regulators that were incorrectly programmed. Two regulators,(one non-Plasmatronics) were set by the installer to a lower charging voltage program intended only for gel cell batteries - and thus grossly undercharging the conventional lead-acid batteries used. According to one owner, the installer did this deliberately to 'stop the batteries being overcharged'. As a result his $1000 or so of deep-cycle batteries were virtually wrecked by the installer, and inside a few months.

Plasmatronics regulators have five manually selectable programs. Of these, '0' and '1' are the only settings likely to be of interest to the great majority of users. Program '4' enables the system to be tailored for individual needs. It can be useful in a few applications (particularly for domestic systems), but is best avoided unless you are experienced in programming.

As supplied, the regulators are set to Program '0' - that required for conventional lead-acid batteries. Here, if the Load- terminal is utilised and correctly wired, loads are automatically disconnected when the battery voltage falls below a safe level. However loads that bypass the regulator will continue to drain the all-but exhausted battery.

Program '1' does the same as above, but for gel cell batteries. This program will also suit AGM batteries.

Settings and functions are monitored by 'long' and 'short' pushes on the button on the front of the regulator. A long push requires the button to be held depressed for about two seconds. A short push is a momentary push and release.

To check which program is in use: Long push on 'SET' (which then changes to 'TIME'), then a short push to 'VOLT', and another short push to PROG - which then shows which program is in use.

Changing the Program

To make changes: once whatever is to be changed is selected (e.g. 'PROG') give a long push until the readout starts flashing, successive short pushes then cause the change required. Once the desired setting is obtained, make a long push until the readout stops flashing. Further short pushes take you back to 'DATA'.

It's worth checking the setting for 'BCAP'. This setting is the total capacity of your 'house' battery bank in amp/hours and must be set correctly for the percentage charge indication to be meaningful. Set as described above.

With the current shunt and adapter installed, the automatic 'low voltage shut off' no longer automatically operates. This is not necessarily a loss as if batteries are discharged this low, they are already being damaged (and most fridges have inbuilt low voltage cut-outs anyway). Better to use the monitoring facility and ensure the batteries do not go much below 50% charge. If you really do need low-voltage cut-out, it can still be done via a big contactor driven by the Load- terminal - but this necessitates reprogramming the regulator using program '4. Not recommended unless you know what you are doing.

All of the above is explained in the booklet supplied with the regulator. The information may also be found on the company's website (address below).

If Programming Appears Locked

Try this first. Long push on 'DATA', then short pushes until you see 'TEMP'. Whatever the reading, that reading should be followed by an 'A' (e.g. '0A'). If there is no 'A' then the regulator has been locked to prevent adjustment. Disable the lock by a long push (the 'A' will then appear). Then short push back to 'DATA'.

Early units had a physical link under the cover which, when removed, achieved the same purpose. If this has been done, contact a Plasmatronics dealer (and/or look at www.plasmatronics.com.au)

My thanks to Plasmatronics' Brendan English and Virginia Graham for their invaluable assistance in checking and correcting this article.