ElectroClassic EV
Classic Cars Reborn into the Electric Future

Throttle Back

curtis_pb6_bad_potboxRecently, I began experiencing hiccups in the main drive power stream. My console display indicated the motor current was randomly spiking up and down, even when I tried to hold a steady cruising speed. The motor also started fluttering during slow acceleration in low gear. After perusing the EV forums, I decided my throttle had gone bad. Shown above is the original Curtis PB6 potbox throttle, mounted in the motor bay and controlled by an accelerator cable. The name  “potbox” comes from an internal potentiometer that creates a variable resistance depending on the position of the throttle lever, which is used to control the speed of the motor. Unfortunately, a potentiometer is a mechanical device, with a contact brush that slides along the windings of a coil, eventually causing wear and/or dirt to introduce dropouts and noise into the line.

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hall_effect_throttle_newpartI originally planned to purchase a Hall effect throttle, which has no contacts and uses magnetic fields to create a variable voltage, somewhat like a transistor. So I browsed the usual online EV parts stores, and landed on the above Evnetics unit sold by EV West as a Hall effect throttle, made from milled aluminum and looking fairly bulletproof. So I bought it. It runs about double the cost of the original PB6, but it’s well worth it to me. To be fair, Curtis offers their own Hall Effect throttle, but you tell me which one looks cooler.

** NOTE – A later reply to this blog post alerted me that the product description on the Evnetics website describes this unit as a TPS (throttle position sensor), and never mentions Hall effect. Also, a post on DIY Electric Car Forums by Evnetic’s Chief Electron Herder clearly states this TPS unit is a potentiometer. However, the output is the same as an Hall effect throttle, so it should be connected the same as one.

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hall_effect_throttle_to_bracketI removed the throttle bracket from the motor bay and unmounted the PB6 potbox, seen at lower left of the frame. The new holes I drilled to mount the Evnetics throttle to the bracket allowed the accelerator cable to line up perfectly.

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firewall_upshotBecause the Evnetics TPS throttle produces a variable voltage of 0-5 volts (same as an Hall effect device, rather than the potbox’s variable resistance of 0-5K ohms), the connections to the controller needed to be reworked to match the HPEVS schematic. Since I had neatly bundled and dressed out all of the controller wiring during the original install, there was no way to work on it except from underneath the car. The above shot is my view looking up at the controller harness, which occupied my full attention for the next few hours.

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hall_effect_throttle_installHere is the blingy new throttle installed in its permanent home. After tinkering with the cable attachment, I confirmed that clamping closer to the pivot gave the throttle arm greater travel and offered a bit more tension. The pedal action was immediately firmer, quieter and cleaner than the potbox.

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spyglass_throttle_cuThe finishing touch was calibrating the new throttle to the controller. The car could actually drive without calibration, but wouldn’t rest or accelerate properly without knowing the new throttle min and max values. One cool feature of the software update performed at HPEVS (see Brain Boot), allows the end user to program the Curtis controller using the Spyglass display and menu button (the little red dot at the top of frame). I nixed my Spyglass from the center console when I installed the Orion BMS and Galaxy II tablet, but the connector pigtail still dangles under the dash for such occasions. Holding the menu button during ignition toggles the controller into program mode, and then allows stepping through various parameters, including Throttle, Brake, Fine Tune, Idle Control, Display, and Orion BMS implementation. For now, the Throttle menu seen above provides a way to assign throttle type, min/max pedal positions, acceleration rate, and proportional throttle mapping. Once the parameters were dialed-in, the flutter and spastic throttle disappeared, and driving became super fun again!

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2 Responses to “Throttle Back”

  1. The EVNetics throttle is actually a pot. Third post in this thread is from the EE at EVNetics explaining why they used a pot insteasd of a hall sensor. http://www.diyelectriccar.com/forums/showthread.php/tps-vs-hall-effect-throttle-61543.html

    It seems a lot of retailers hear hall effect when they see the product described as a throttle body sensor. At any rate, the part is of much higher quality than the PB-6 and there are no reports of problems as far as I can tell.

    • Thanks Joey. Here’s the link to the throttle on the Evnetics website, implying that it is a sealed potentiometer, although the retailer is selling it as a Hall Effect throttle, and they haven’t been able to explain how the TPS (throttle position sensor) potentiometer is outputting a variable voltage. Only non-contact type TPS should be able to do that – inductive or magnetoresistive sensors, according to this Wiki entry. Mine is connected to the controller per the Hall Effect (0-5 volts) configuration, and is working just fine.


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