Linear Current Boosters for Pumps
How They Work & What They Do

Linear current boosters can be used to eliminate solar batteries and oversized solar arrays for operating direct current motors for a number of applications including pumping water and operating ventilation fans or ceiling fans when the sun is shining.  Here are some terms you need to know.  If you need more background read my solar calculations math tutorial.

Current = Amps
Power = Watts
Force = Volts
Volts x Amps = Watts

Solar panels are a relatively constant source of force. Force is measured in volts.  A solar panel exposed to sunlight early in the morning or late in the afternoon will
produce volts, but the amps produced may be close to zero. Volts times amps equals watts.  Without enough current to get the power moving, the motor will not run.

So, even though the panel may be producing volts, if the amps are near zero the watts will be very low to zero. With no amps, there is no current and a DC motor will not run.

A small pump motor that requires about 14 amps at 12 volts (like the Simple Pump solar water well pump motor) that requires about 170 watts of solar panel to run panel direct during full sun exposure may need as much as 320 watts of panel to run earlier in the morning and later in the afternoon, or to run at all on a cloudy day.  A linear current booster increases amps by sacrificing volts to create enough watts to allow the motor to run.

How A Linear Current Booster Works

Linear current boosters do two things: provide panel feedback and convert volts to amps.

When a solar panel is connected directly to a DC motor, if the motor does not receive
enough power (watts) to run, this creates what the panel perceives as a short circuit which limits the panel voltage and panel current, a self defeating situation. The linear current booster provides feedback to the panel that the load of the motor is really less than it is. This allows the current (amps) and volts from the panel to remain at maximum, thus delivering full available power to the booster.

The second thing a linear current booster does is convert available volts to amps. For example, most 12 volt panels will actually produce 18 to 20 volts. Using high speed switching power supply technology, an input of 11 amps at 18 volts may be output by the linear current booster as 15 amps at 12 volts. Power out equals power in minus a small conversion loss but at lower volts and higher amps. 11 amps at 18 volts = 198 watts. 15 amps at 12 volts = 180 watts. The efficiency loss equals about 10 percent in this example.  Most linear current boosters have an efficiency loss of about 8 percent.

This current boost creates the additional amps needed to start the motor. The trade off is  lower motor RPMs.  Lower voltage means lower RPMs. But, the motor is running!  Without the linear current booster the motor will not run until the solar panel delivers watts at near full capacity.  When the current exceeds the resting torque of the motor the motor starts turning.

Another Linear Current Booster Advantage

Another advantage a linear current booster provides for running a DC motor is that while
the motor may be running at lower RPMs, the additional amps provide an increase in motor
torque, which allows the motor to better power a fluctuating load, or keep a pump operating when a cloud passes over the solar panel. The RPMs may decrease but the motor will be more likely to keep running.  The increase in motor run time can be as much as an additional 30 to 100 percent compared to running solar panel direct without the booster.

We normally stock these linear current boosters:

  • LCB 12/24-7, array volts 12 or 24, current maximum 7 amps

  • LCB 12/24-15, array volts 12 or 24, current maximum 15 amps

  • LCB 12/24-30, array volts 12 or 24, current maximum 30 amps

Other models are available on special order.  Please contact us for assistance with selecting the right linear current booster for your application.

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