Recommendations for use of power tool batteries

Submitted by furusato on Sat, 11/23/2019 - 19:17

Forums:

I'm planning to use either a Makita 18V 3Ah power tool battery or the smaller Makita 12V 1.5/2/4 Ah battery. Since I have a bunch of these batteries and chargers for them (as I have the power tools) they seem like a reasonable choice, especially since I can be reasonably assured they can handle the load of several small motors -- something that might not be the case with a regular cell phone style LiPo battery (such as the 5000 mAh or 12000 mAh PiJiuce batteries).

Two questions related to my project:

1. for the 12V and 18V Lithium Ion batteries, what should the minimum and maximum settings be when setting the battery limits using tbSetBatteryLimits.py?
2. I'm using four 9V motors (two pairs) and I can't seem to find where the setting is to drop the working motor voltage down to 9V.

Thank you.

piborg's picture

piborg

Wed, 11/27/2019 - 00:14

The cells they are using have a voltage range from 3.0 - 4.2 V. Usually battery voltage ratings are based around the nominal voltage of 3.6V, which is half-charged. I think the 12V is 3 cells, and the 18V is 5 cells.

If correct this would make the actual voltages:

  • 12V
    Minimum: 9.0V
    Nominal: 10.8V
    Maximum: 12.6V
  • 18V
    Minimum: 15.0V
    Nominal: 18.0V
    Maximum: 21.0V

You can check this by measuring the battery voltage when fully charged.

For setting the motor voltages, most of our examples have a power settings section:

# Power settings
voltageIn = 12.0                        # Total battery voltage to the ThunderBorg
voltageOut = 12.0                       # Maximum motor voltage

Set the voltageIn value to the nominal voltage, and voltageOut to the motor voltage. For example:

# Power settings
voltageIn = 10.8                        # Total battery voltage to the ThunderBorg
voltageOut = 9.0                        # Maximum motor voltage
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