AERL "Maximizer" MPPT Charge Controller

AERL "Maximizer" Maximum Power Point Trackers
Specifications and Description

Note: This page is an exact (except for minor updates and typographical corrections) copy of the AERL Maximizer specification booklet. It is not quite complete, we have not scanned in the diagrams yet.

Due to slow shipments and variable product availability, we no longer stock all of the AERL specialty items. Currently we have the 600B, 800B and the 900B in stock. We stock several of the CP controls.

For the solar race car Maximizers, please contact AERL directly in Australia. (011) 61 741 689 308. Fax = 61 741 689 197. Email at aerl@hotkey.net.au

Australian Energy Research Laboratories (AERL)
Stuart Watkinson
M.S. 660
Proston, Queensland 4613, AUSTRALIA
011-6171-689308
011-6171-689197 (Fax)

Australian Energy Research Laboratories P/L

Incorporated in Queensland 1985

Higher battery charge currents when they are needed most

The MAXIMIZER boosts charging currents in wet and/or dull and/or winter conditions typically by 20% to 30% compared to direct-connected systems. Like no other charge regulator,the MAXIMIZER converts higher PV maximum power voltages whenever panel temperatures drop, directly into extra charging current. It does this automatically at the times when the charging current needs boosting the most. Using a 12 volt battery system in a simple example; on a bright but cloudy day the panel temperature may typically drop by 20 degrees Celsius, with a 7% rise in panel maximum power voltage, from say 14.5V to 15.5V for a 36 cell panel. If the battery goes into a net discharge state, as typically happens in cloudy or dull conditions, the battery voltage will also drop down to around 12.5V. The MAXIMIZER takes this 3V (15.5V - 12.5V) 24% difference and DC-DC converts it into a 24% increase in charging current, compared to direct-connected PV systems.

Operating Manual & Technical Specifications for the Battery Charging Maximizers

Removing and replacing the clip-on cover

The polycarbonate MAXIMIZER cover is held firmly in place by 8 plastic spring clips. Follow this simple procedure to remove the cover. Working on one of the four corners first, with both hands, one hand for each clip: With the unit mounted or sitting on a bench with the metal finned heat sink facing away from you, firmly pull each clip outwards with the forefingers, while firmly easing the cover upwards by pressing against the protruding shoulder of the metal base plate with one of your thumbs. Once the one pair of corner clips are sitting released, repeat for the 2 corners opposite until the lid pops off. If one corner seems to be sticking or difficult to release, move to another corner. If a corner clip slips back on, simply repeat the procedure. Follow this procedure exactly and the cover is simple to remove. DO NOT FORCE OR LEVER THE COVER WITH ANY SORT OF TOOL, THIS IS NOT NECESSARY!. To replace the cover, sit it symmetrically with all 8 clips above their respective guide slots on the plastic base plate and push firmly and evenly down to engage all clips. Ensure that all of the clips have latched by squeezing each one individually, ensuring a good waterproof seal. [NAWS note: this is not always as easy as it sounds if the unit is mounted in tight quarters. If a weatherproof seal is not required (i.e., inside another box), some of the non-corner tabs may have to be broken off, or the cover can be left off].

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Note: Special lightweight customized "Race-Trim" versions of the Battery Charging MAXIMIZERS for Solar Powered Racing Cars, weighing 1.1Kg and measuring 225mm x 110mm x 150mm are available directly from AERL. The LCD Digital Meter Module is optionally available on these units with a ribbon extension cable to permit dashboard mounting. These units are shipped without the polycarbonate enclosure. On these units, maximum available output current is 12 Amps and maximum throughput power is 1200 Watts.
[Note: These version MUST me ordered directly from the manufacturer in Australia].

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MAXIMIZER

Introducing the Battery Charging Maximizer

The MAXIMIZER is a revolutionary power electronic device that connects between any Solar Photovoltaic (PV) Power Source and the Battery Bank to automatically maximize the electrical power delivered from the PV panels to the Battery.

It combines innovative simplicity with space-age power and electronic technology to solve, once and for all, the problem of reliably extracting the maximum available power from all types of PV solar panels.

Why do PV Solar Systems Need a Maximizer?

The MAXIMIZER is to Solar Photovoltaic (PV) what a perfect gearbox is to the automobile. They both link the power source to the load and permit the most efficient operation of the power source by exactly matching it at all times to the ever changing requirements of the load. The gearbox performs this mechanically, while the MAXIMIZER uses high reliability solid state power electronics in a DC-DC step down converter.

Trying to supply any battery bank directly from the PV panels is like attempting to drive a car one only one gear. Efficiency and performance are reduced and valuable power is wasted.

Why Hasn't a Maximizer been Developed Sooner?

Although the electronic gear-box function of the MAXIMIZER is a simple enough concept, the long sought after solution to technically achieve this automatically, efficiently, reliably, and cost effectively has had to wait. Only now, with the very latest advances in electronic technology has the problem finally met it's solution in the MAXIMIZER.

Your Solar Battery Charging System Needs a Maximizer

For Battery Charging, the MAXIMIZER will increase the overall yearly PV output power by up to 10%. In situations where the average panel temperatures fall below 25 degrees Celsius, on cloudy or windy days or in winter, the MAXIMIZER can easily produce 25% higher battery charging rates than would result without the MAXIMIZER on the same day. This is achieved by a combination of;

1. Always operating the individual PV panels at their maximum power voltage regardless of panel temperatures or battery bank voltages; converting all extra panel output voltage into extra charging current. (Note: PV panel output rises by approximately 4% for every 10 degree C drop in panel temperature. See STEP1 on Page 6. The MAXIMIZER turns this directly into a percent increase in charging current).

2. Eliminating reverse blocking diode losses.

3. Slashing input cabling losses by permitting the configuration of the PV array at a higher voltage and lower current - utilizing the DC-DC step down conversion capabilities of the MAXIMIZER.

Battery Charge Regulator and Control Center

All battery charging MAXIMIZERS can be used to charge a wide selection of battery bank voltages and feature smooth, user adjustable, float-charge regulation. A built in LCD meter module permits all input and output voltages and currents to be monitored with the flick of a switch. Battery levels can thus be set accurately and the charging current monitored continuously.

All MAXIMIZERS have an automatic 108% of float voltage equalization anti-sulfation charging profile. Automatic ambient temperature float level voltage level compensation of -2.5 mV/C/2V Cell is optionally available).

All units have a low battery detect function that lights a red LED and changes the state of a small relay when the battery voltage falls below 1.83V/cell The LED and relay remain in this Low Battery state until a complete 108% equalization re-charge has been achieved.

This Low Battery Alarm function is suitable for automatic generator control in generator backed up systems. The relay contacts are rated at 1 Amp or 30 Watts and they have 1000 volts of isolation from the PV system. A second red LED lights to signal that the MAXIMIZER has entered the fully charged Float Charge mode.

The MAXIMIZER provides a smooth continuous regulation characteristic - continuously trickle charging the battery at a level just sufficient to sustain the pre-set float voltage level.

Using a MAXIMIZER adds design versatility and cuts overall system costs, while providing all the automatic house keeping functions essential for maximum battery life in all PV battery charging systems.

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A Versatile DC-DC Step-Down Voltage Transformer

The MAXIMIZER uses a DC-DC voltage step-down conversion to ensure that the PV array input voltage is always maintained at the optimal maximum power point voltage. This inherent characteristic leads to many of the desirable features that make the MAXIMIZER such a powerful PV system designers tool.

With the MAXIMIZER, any PV array input voltage, up to the rated maximum open-circuit voltage of the particular MAXIMIZER being used,can be selected. (This voltage limit is marked within the unit). Maximum PV power can then be supplied automatically at any voltage below the corresponding PV array maximum power point voltage.

The actual MAXIMIZER output voltage is determined by the battery bank requirements. As long as the PV array and the battery load are configured to achieve some level of DC-DC step-down between the Maximizer input and output, maximum power will always flow from the PV source to the battery bank via the MAXIMIZER.

As variations occur in the PV array and battery voltages, the MAXIMIZER instantaneously adjusts the DC-DC step-down ratio between it's input and output to maintain it's input voltage at the critical maximum power point of the PV array. This ensures that the maximum possible charging current is always delivered to the battery.

Useful Design Consequences of the Unique "Maximizer Action":

The PV array or battery bank can now be expanded, modified, or reconfigured with little effort and without creating energy wasting voltage mismatch problems between the array and the battery bank.

Cable and wiring loses are minimized because of the efficient higher voltage/lower currents that can now be used. Longer wire lengths of smaller size can be used from the PV array to the MAXIMIZER with minimal losses. The MAXIMIZER, located near the battery, automatically steps down the voltage and increases the current to exactly match what is needed.

The PV array can now be optimally be placed away from trees and other shading without having to run expensive cabling to the battery bank. Wiring resistance losses are minimized because of the high voltage/low current between the array and the MAXIMIZER. Battery charging systems, when configured with sufficient step-down, no longer need power wasting blocking diodes to prevent night time battery discharge back into the PV array.

Good News for the PV System Designer:

The frustration over complex design and component matching is finally over. With the MAXIMIZER, the PV array's electrical operating point voltage is no longer dictated by the battery bank voltage. This allows the PV array to always operate at it's maximum power point, ensuring delivery of the maximum possible PV power into the battery bank.

The higher array voltage configuration permissible with the MAXIMIZER overcomes the problem of early self-regulation, as can happen when the PV cells are operated in high ambient temperature environments. Because of the high ratio of PV voltage to battery voltage, the PV cells will always be providing the maximum possible current to the battery.

Features of the Maximizer:

1. The Maximizer is a universal maximum power point tracker, suitable for use with all types of PV modules, without any pre-adjustment or tuning to setup the input PV array operating voltage point. The Maximizer will operate automatically at any point within the specified range.

2. All Maximizer have a built in LCD digital Amp/Volt meter that permits all input and output voltages and currents to be monitored in one compact package.

3. Fully self contained - 2 wires in, and 2 wires out, with large terminal blocks to accept up to 25mm cable.

4. Ultra high power transfer efficiency, ranging typically from 96% to 98.5% (depending on power and output current).

5. Maximum power point extraction accuracy is better than 98% over complete power range on all models.

6. Compact and rugged all weather, water-proof aluminum and polycarbonate packaging measuring 9" x 7" x 7", and weighing only 5.3 pounds.

7. Electronic current limiting, providing a high degree of overload and short circuit protection.

8. 400 Amp "crowbar" diode, input and output reverse polarity protected. The crowbar diodes will force the 40 Amp output fuse to blow in the event of a reverse battery bank connection. Spare fuse is provided.

9. Isolated Low Battery Alarm relay contacts (NC and NO) for automatic control of an auxiliary generator or alarm signals.

10. Two wire remote On/Off facility (NO and NC).

11. The outputs of any number of Maximizers can be paralleled to feed a larger common load. (Note - arrays should be wired separately so that the loss of one array does not shut the system down).

12. Battery charging units have a wide range of continuously adjustable battery float levels, with an automatic 108% of float voltage auto-equalizing, anti-sulfation charging characteristic.

13. Automatic battery float voltage ambient temperature compensation is optionally available.

14. No blocking diodes needed due to the DC-DC step down operation

15. All battery charging units can be used for water pumping if required (although we recommend using the pumping versions for most applications).

16. Night time current drawn by internal circuits from battery bank is approximately 25 ma.

17. Visual LED indication of "Input Alive", "Output Alive", "Low Battery", and "Battery Charged" conditions.

18. All control electronics are contained in a sealed plug-in hybrid module. This, together with conformal coating and gold plated switch contacts ensures long term reliability in harsh tropical and marine environments.

19. Complete input and output electrical RFI filtering and RF noise suppression to meet all FCC requirements.

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Page 4

Maximizer Specifications

Note: all input and output voltage and current ratings and operating limits are clearly marked on the aluminum extrusion within each Maximizer. In particular, the OPEN CIRCUIT voltage limits should be strictly observed when designing the PV system.

Range of Battery Charging Maximizer Models

Note: PV panels referred to in the table below are the standard 36 cell type having an open circuit voltage of 18 to 21 volts at normal cell operating temperatures in the range 40-60 degrees C.

Page 5

Operating Guidelines

1. Warning: the DC voltage levels at which the Maximizer operates can be potentially lethal if handled without adequate caution. Installation must therefore only be carried out only by suitably qualified personnel and all electrical safety codes must be followed. For Maximum safety, the aluminum heatsink is not electrically connected to any inputs or outputs - it is electrically floating. It has an insulating anodized coating for safety, but care should be taken when making all connections.

2. All input and output voltage and current ratings and operating limits are clearly marked on the aluminum heat extrusion within each Maximizer. In particular, the open circuit voltage limits must be strictly observed.
   Always check the PV array open-circuit voltage level and polarity with a meter before connecting to the Maximizer inputs. The Maximum number of panels in series for each Maximizer model is listed in the table on page 4, and must never be exceeded.
   Incorrect array polarity will not damage the Maximizer in any way, but may be accompanied by a dangerous hot arcing if the panels are in sunlight while attempting to make the input connection.

3. Always ensure that the Maximizer is switched off before making any connections.

4. Exercise extreme caution to ensure correct battery polarity. The wrong polarity will blow the 40 amp printed circuit output fuse, which would then have to be replaced with the spare fuse. (the spare 40 amp fuse is located on the back of the circuit board, below the meter module board). If you need to replace a blown fuse, always.always bolt it on with the metal side down and with the nuts firmly tightened in place to ensure a good low resistance connection. Fit the spring lock washer only on the non-metal side of the fuse.

5. Caution! Once the battery is connected to the output terminals, both the OUTPUT ALIVE and the INPUT ALIVE LED's will be glowing. The input is also now "alive" at battery potential, due to back energization from the battery. Again extreme caution must be exercised NEVER to apply an accidental short circuit to the input terminals once the battery bank is connected. To do so will blow the output fuse, via a specially fitted 400 Amp "crowbar" diode included to protect the internal circuitry under such circumstances. Never apply a short circuit to the Maximizer inputs or outputs!

6. For maximum safety, don't switch the Maximizer on without the battery connected to the outputs.

7. Never mount the Maximizer where it will exposed to direct sun, rain, or rain run off.

8. Always loop the input and output cables downwards to below the level of the unit from where they exit. This form a "drip loop", and prevents water from flowing down the cables or conduit into the cable entry points. Always tighten the cable glands onto the cables. The rubber gland seals have tear-out centers to permit large cables up to 25mm to be passed through the glands.

9. Always mount the Maximizer in the coolest possible location and positioned so that natural convection airflow over the finned aluminum baseplate/heatsink is not restricted in any way. Mount with at least 6" above and below the nearest horizontal surfaces. Mount with the circuit board horizontal and nearest the ground, or on two brackets with the finned heatsink facing upwards and the circuit board vertical. Do not mount the unit with the baseplate/heatsink facing downwards, as this may lead to poor cooling. If the Maximizer is to be mounted in a cabinet, this cabinet should be ventilated. The cabinet must never be exposed to direct sunlight.
   Do not mount the Maximizer directly under the back of the PV panels; although shaded, this is an extremely hot and unsuitable location.

10. The use if input and output circuit breakers is highly recommended. On battery systems of 36 volts and above, it is essential. Suitably rated circuit breakers will provide a means to protect and isolate the sections of the system when making connections. Always ensure that the Maximizer is switched off when opening or closing these switches or breakers, as this will prevent unnecessary arcing of the contacts. High quality miniature circuit breakers such as those manufactured by Siemens or Weber are recommended. For battery voltage up to 48 volts, single pole breakers can be used, but for higher voltages (over 60 volts), double-pole breakers should be used, breaking both the positive and negative lines.

Installation

Please do not proceed beyond this point unless you have read the previous 3 pages.

As described on pages 2 and 3, the Maximizer relies on a DC-DC voltage step down conversion from input to output to ensure that it can always hold it's input voltage at the critical array maximum power point voltage. This is essential for maximum PV power flow to the battery bank.

The PV panels must be configured such that the battery voltage (Maximizer output voltage) is always less than the PV array maximum power point voltage (Maximizer input voltage).

So, as long as the battery voltage, at peak PV power output, is less than the input voltage, then the PV array is held at the maximum power point voltage by the Maximizer, and maximum PV power is delivered to to the battery bank. Design guidelines to help in achieving the highest system performance, by minimizing system component losses are presented below.

PV System Design Guidelines

The previous table provides information on all of the input and output voltages that apply to the complete range of battery charging Maximizers. When designing a particular Maximizer into a system, the PV systems must be configured so that none of the current and voltage ratings for the particular model are exceeded. It is therefore necessary to first work out realistic noon-day peak power, voltage, and current figures for the particular PV panels to be used in your system.

Step 1

[NAWS note - what follows in the original is a long elaborate method of figuring out max current, voltage and power and power requirements. We have found that it can be much simplified by using the method below]

1. For maximum current, use the panel specifications and add 10% for rating the Maximizer.
2. For maximum voltage, use the OPEN CIRCUIT panel specification and add 12% for rating the Maximizer.
3. In some cases, the voltage x current may be higher than the nominal power (in watts) rating of the Maximizer. This is OK as long as NEITHER of the voltage or current ratings are exceeded.