Solar Converters Inc. Model: EQ 12/2420
Constant Voltage Down Converter DC Autotransformer
These products take a variable higher voltage, typically a battery or solar panel and decrease the voltage to a fixed lower voltage.
Our Power Tracker(TM) Charge Controllers with MPPT, Linear Current Boosters and DC Autotransformers all perform down voltage conversions. The Charge Controllers and Linear Current Boosters may operate from solar panel, battery. wind, or alternator input and maintain a constant voltage (if enough power available), and/or charge a battery. DC Autotransformers operate from battery input only and provide a fixed output voltage.
Application
This rugged and versatile unit is used to power a small load at 12 V from a 24 V battery, or to power a small 24 V load from a 12 V battery.
It functions both ways, producing 12 V @ 20 Amps from a 24 V input or can be connected backwards to produce 24 V @ 10 Amps from a 12 V input.
When connected as a battery equalizer, it allows large transient 12 V loads to be taken off the centre tap of a 24 V battery (made of 2 X 12 V batteries) without fear of upsetting the voltage balance of the battery and destroying the 24 V battery system that would otherwise occur.
Features
· >95% efficiency, typically 96% over 20% load
· Simple to use
· Bidirectional power flow * Weatherproof
· NEMA 4 enclosure
Voltage Regulation Mode
Proportional:
This standard unit regulates the output voltage proportional to 1/2 the input when connected 24 V input and regulates the output to 2 X input when connected 12 V input. This characteristic, when connected across 2 X 12 V batteries in a 24 V configuration, will keep the batteries at equal voltages.
Fixed:
Special units are available for example EQ 12/2420 RXX where XX is the voltage on the 12 V side that the voltage is to be regulated to. For example, EQ 12/2420 R5 will output 5 V @ 20 amps.
Mechanical Specifications
· Enclosure: Weatherproof, NEMA 4 enclosure
· Dimensions: 4.5" X 2.5" X 2" nominal, resembling a junction box with feet
· Temperature Range: 40 deg C to 60 deg C
· It is recommended, as with all electronics, that the unit not be placed in direct sunshine.
· Terminations: 6" flying leads
o Red: High Input +
o Black common
o Neg  for input and output voltage
o White: Low Input +
· Wire size: red, black, white: Power leads #12 AWG
· Humidity: N/A weatherproof
Electrical Specifications

Input low side

Input high side

Input Voltage (nominal battery)

12V

24V

Output Voltage

24V

12V

Output Current

10A
Current Limited

20.0
Current limited

Ripple at load

30mV rms

30 mv rms

Efficiency

>96%

>96%

Why have a solar converter?
Introduction:
Solar power is proving itself to be a viable means of generating power for the people. Y2K may or may not be the problem many people predict, but it has energized many people to seriously rethink and educate themselves about the alternative energy option.
A common problem with renewable energy systems is the cost effectiveness of the wiring relative to the nonrenewable options. Solar power systems tend to have many components as well as energy storage at low voltages. To avoid voltage drops in the wire, and keep the system efficiency high, the system designer ends up wiring with much larger heavier (and more expensive) wire than would normally be associated with the power the appropriate Electrical codes would dictate if it was a typical AC powered circuit. At all times the local Electrical codes must be adhered to.
This effect is greatly magnified if there is a great distance between the panels and the battery. This article is aimed at identifying and suggesting a possible solution to this problem.
Why is this interesting:
The effect of cable drop in a low voltage system can be devastating. A 30 amp system which could typically be wired with #10 AWG wire if small distances are involved needs to be greatly upsized in copper and expense in a typical renewable energy system.. A typical electrical code wire size for 30 amps is # 10 AWG, such as you would find wired for a 120/208 V AC 30 amp service.  typically your clothes dryer at home.
This is best illustrated by example.
Let us look at a 360 Watt  12 V at 30 amp system with the panels 200 Feet away ( not uncommon) wired with # 10 AWG.
# 10 AWG cable is 1 milliohm resistance per foot (Wire Tables) 400 Feet (there and back ) of it is 0.4 ohm , The voltage drop in this cable is Voltage drop = CurrentI * Resistance = 30 * 0.4 = 12 V.  this would be 12 V in 12 V or 100 % power lost to the wire loss.
Clearly not a very viable system.
In reality the system would balance itself around the losses. At best the most you would get is 12 amps. i.e.: you paid all the cost of a 30 amp system and at best it will put out 12 A or only 40 % of what you paid for. This is a horrendous loss.
In order to get more reasonable power output, the only alternative is to increase the wire size, but this costs more money  the question is how much?
Let us assume we can tolerate a .5 V drop in the cable 4 % power loss to the wire.
The cable resistance must be .5 V loss / 30 amps = .016666 Ohms of resistance in the wire. There is 400 ft of this wire so the ohm per foot = .01666 Ohms / 400 Feet = .0000416 Ohms per foot
When we look this up in the wire tables, we find the nearest size available is 4/0 wire at .045 mohms per foot. This wire is approx. 1 � in diameter compared to 0.1 � in diameter for # 10 AWG.
After checking with the local electrical supply house , they quote 1,117.06 US for the 400 Ft of number 4/0 in suitable PVC Conduit vrs the originally thought of 214.91 US for # 10 AWG. in its suitable PVC conduit  AND you still need to buy the controller anyway. This is 902 US more expensive just for the wire. I think anyone would rather spend the money on more power.
There is another way
For long distance runs, why not transfer the power at a higher voltage and then convert to 12 V at the battery with a voltage converting Maximum Power Point Tracking controller (MPPT)? We can wire the same panels for 48 V producing the same power but now at 48 V. The same power (360 W) carried at 48 V nominal (actually 65V @ maximum power point) is 5.5 A amps in the same # 10 AWG wire.
The voltage drop in the cable if now wired with # 10 AWG is V = Current * Resistance = 5.5 X .4 = 2.2V.
Thus panels operating at their maximum power point (65 V) will �look� like 65  2.2 = 62.8 V at the receiving end. This would be a viable system as it has the same lower power loss to the wire, actually 3.3 % instead of 4 %. Same power, but lower cost and higher efficiency of power transfer.
As power is Voltage * Current , and if the efficiency is very high, say 95 % typical of Solar Converters Inc. Controllers, what will be the current at 12V ? After some quick math (I will be happy to supply the details if anyone is interested)
There is 328.2 watts delivered to the 12 V battery or 27.4 A @ 12 V
In this case, your 30 amp investment results in 27.4 amps of current, better than the at best 12.5 amps if wired with # 10 AWG or the 1,117.06 US tag if wired with 4/0 AWGand still get at best the same current (Actually 15 % less if not MPPT or its equivalent in upsizing the panels) , not to mention the cost of junction boxes, conduit etc. as well as just plain hassle in dealing with 4/0 AWG  and you still need to buy a controller anyway.
EVEN BETTER
There are a large number of panel manufacturers who already make �odd voltage� panels that already produce high voltages. For example the excellent CdTe panels, Amorphous Silicon, and many notable other technologies made by several different manufacturers. These panels are extremely cost effective,
with s sometimes 50% lower than normal silicon panels. If you use the high voltage anyway, why not from one of these inexpensive panels? Who would not want to save substantial costs in both the wiring and the raw panel and get more power to boot? Note these cost savings are available even if you have a short distance to wire.
