This describes how to construct an AuxPot 3-position switch to limit any of: Current, Power, Speed, or PAS Assist. The switch selects one of three percentages of the configured limiting parameter: (high, med, low) = (100%, Lmed, Llow) e.g. (100%, 66%, 33%). Although fixed resistors are used, a wide range of Lmed and Llow values can be configured using Setup.
Theory of Operation
The idea is to establish fixed switch-selectable voltages but shift the endpoints of the allowable AuxPot input voltage range to alter the way those voltages appear relative to one another and to the overall AuxPot range.
- In the illustration below, the red portion shows the maximum AuxPot voltage range and several voltages determined by fixed resistors.
- The green scales show three different possible working ranges of AuxPot input as determined by (AuxMinIn,AuxMaxIn). Although limits Llow and Lmed are bound to fixed voltages, the overall green scale can be shifted left or right or expanded or compressed by moving the endpoints - this changes the relative position of Llow and Lmed in that range and thus their effective values. So - it's all a matter of point of view....
- The relative values of the fixed voltages also impose certain limitions on the possible Limit Value configurations. The trick is to pick voltages that will allow a range of commonly useful limit settings.
The switch is wired as shown below. For accessory current inventory purposes, this circuit draws a maximum of 0.53ma. The switch can be any center-off SPDT toggle or rocker switch - or any of the commercially available ebike 3-position switches. Current is very low - resistor wattage can be anything available (1/8W, etc).
- Set appropriate Setup parameter (e.g. PLim->MaxCurrent, PLim->MaxPower, Pas->PasWatts) to desired maximum value.
- Determine LowLimit% = ( LowValue/MaximumValue)*100.
- Determine MediumLimit% = (MediumValue/MaximumValue)*100.
- Locate proper cell in table at (col,row) = (LowLimit%, MediumLimit%)
- Transfer cell values to Aux->AuxMinIn and Aux->AuxMaxIn.
- Go to Setup AuxPot Section Preview screen, verify switch settings (L,M,H) display limits of (LowLimit%, MediumLimit%, 99%).
- If limits are not exactly as desired, then locate the appropriate adjacent cell and modify both AuxMinIn and AuxMaxIn toward those new cell values.
This is a printable PDF of the settings table for shop use/road adjustments.
- Set PAS->PASWatts = 750W
- LowLimit% = 250W/750W x 100 = 33%
- MedLimit% = 450W/750W x 100 = 60%
- Look up row 60%, column 33% in table. Use nearest cell (60,32) and get (0.65, 3.57)
- Go to Setup PAS section
- Set AuxMinIn = 0.65, AuxMaxIn = 3.57
- Go to PAS section preview screen and operate switch - Asst% should show (99%,60%,32%)
There is a new Grin Tech 3-position switch that prompted this post - it uses the identical fixed resistance/adjustable min/max strategy, but with a slightly different four resistor circuit. The fixed voltages are: (L,M,H) = (1.66v,2.50v,3.33v). The 3-resistor circuit presented in this post appears to provide a bit wider adjustment range (I have an email out to Justin about this).
This ES switch can be used as a 3-position Preset Switch by setting (AuxMinIn, AuxMaxIn) to (2v, 3v).
The Grin Tech switch can be used as a 3-position Preset Switch by setting (AuxMinIn, AuxMaxIn) to (1v, 4v).
EDIT - This information is now part of the Guide.