I’m working on a project, where I want to go from 5 Lithium-ion cells in series, to 5 Lithium-ion cells in parallel, for versatility purposes i.e. in time, I want to be able to change the output voltage from 5-60V, hence the step-up voltage regulator approach.
What I want to achieve is:
To connect a 3.7V Lithium-Ion powersource, to a DC motor (from a powertool) rated at 18V.
Later I would like to repeat this for other voltage motors as well.
Is it realistic to build this on a print at the size of circa 10x10x1 cm or 4x4x0.4 inches
For now, I have tried to use an off the shelf Pololu U3V70X Step up voltage regulator with some success. I can get the correct output (18V), however at a very small Amperage, not enough to run the motor.
I have also tried to put 3 regulators in parallel, to get higher Amps with some success, but this is not optimal as the Voltages need to be perfectly adjusted.
I have tried to put 3 regulators in series with individual cells as a source, this is needed as the voltage regulators share a common GND (GNDin = GNDout), with an output of 6V each = 18V. This works, however, I still find the Amp output to the low side as I would like to reach 20A max discharge, as this is needed when i start this specific motor.
I can se from the answers, that one of the main concerns are the stall currents of 130A.
A few specs for my setup:
Current working setup from the battery manufacturer:
5x LGDBHE21865 2.5Ah in series = 20V (5x4V) * 2.5Ah = 50Wh
Std. discharge 500mA
Maximum discharge 20A
Link to cell specs: https://secondlifestorage.com/showthread.php?tid=1938
Wanted setup:
5x LGDBHE21865 2.5Ah in parallel = 4V * 12.5Ah (5×2.5Ah) = 50Wh
With a step-up boost controller taking 4V->18V with approx. 2.5Ah and stil a max discharge of 20A
Motor specs:
Mabuchi RS-775WC-8514 Vin = 6-20V Imax 18.7A
Link: https://product.mabuchi-motor.com/detail.html?id=129
Voltage regulator specs:
3x Pololu U3V70X Adjustable Step up voltage regulators
Link to Voltage regulator: https://www.pololu.com/category/243/u3v70x-step-up-voltage-regulators
Best Answer
Ouch.
If the stall current is 130A, the converter now needs to handle over 600A at the input, not merely 100A.
It is time to stop and reflect why you are abandoning a simple solution which works, for a difficult and expensive one which probably won't.
If you want adjustable 5-60V (exceeding 18V only once the motor is running and lightly loaded, otherwise you are only making the stall current problem worse), then start with 60V (15 cells in series) and use a buck converter to reduce voltage (increasing current) instead.