# EV conversion wont go forward if rolling backward



## jmann22 (Dec 5, 2009)

So we built a EV, using a Curtis 1238-6501 72v system. Its installed in an older VW bug, We were able to drive it donw the street the other day, and we loved it!! But, Im having a problem moving forward if the car is rolling backwards in gear. Its setup for direct drive(using 3rd gear) 45mph at 4000 motor rpm. 

For example im in gear pointing UP a hill. remove foot from brake pedal to accel pedal, car starts rolling back, causing the AC induction motor to spin in reverse direction. Give it throttle and nothing happens, the ac motor doesnt start up. I beleive the controller is detecting the motor is spinning the incorrect way, and belays the signal from the pot box. So in order for me to accelerate i have to pull the ebrake, torque the motor up then release the Ebrake. then it goes. Is there a parameter that can be set to allow the motor to spin forward under these conditions. 

Thank You,
Jmann22


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## cruisin (Jun 3, 2009)

First of all, you need to drive this car in 2nd gear, not in 3rd up to about 60mph. Too many amps are being used at lower motor RPM. Also, drive it like a automatic, left foot on the brake and right foot on the pot box. This is a no brainer. I have a converted 70 VW and have put a lot of miles on it using this method. I removed the clutch pedal altogether and put in a auto pedal assembly.
Thank You,
Jmann22[/quote]


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## jmann22 (Dec 5, 2009)

"left foot on the brake and right foot on the pot box". Is not a viable option, people that are custom to driving a stick generally dont drive an automatic in this fashion. There must me another work around, possibly with the interlock and EM brake. 
Anyother ideas?

How many rpms is your motor turning in 2nd gear @ 60 mph? 

Thanks again


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## cruisin (Jun 3, 2009)

If you use the speed indicator on the VW speedometer, about 40mph is the minumum you should be in 3rd. Check your amp meter and look at how many amps you are using at say 40mph in 2nd and then shift to 3rd and compare. Big differance. If you dont have a tachometer, get one. If you want to get the most our of a EV, you need to monitor the volts, amps and RPM of your ride. All these devices are cheap and necessary. If you take your clutch pedal out, you will be more inclined to drive it as a automatic, which is really what is is since shifting is not necessary. Also, Dont provide power to the motor to go forward when you are going backward. BAD BAD thing to do.


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## Voltswagen (Nov 13, 2008)

JMann -
I drive my 120v, DC motor, '77 Beetle almost like an ICE powered vehicle.
It is clutchless and I also cut the clutch pedal off.

I start in first....15-20mph....lift foot off accelerator...slowly shift.....2nd......30mph.....lift foot....slowly shift.......3rd......40mph .....lift foot......slowly shift into 4th.
I allow about 1 second between gears to let the motor spin down a little with no grinding whatsoever.
The trans is not new and has 124k on it.
I've never tried to start out on a hill by rolling backwards. I'm usually on level ground.
If you need to park that Bug on an incline, until you can get a workaround on that controller, I would park it facing downhill.

Roy Mann


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## piotrsko (Dec 9, 2007)

how about setting the parking/hand brake at the top and releasing it when you start to go?

adding a resistance or resetting the pot box such that there is small residual current at the stop?


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## major (Apr 4, 2008)

jmann22 said:


> Anyother ideas?


Hi jmann,

Induction motor drive vehicles I've driven had no problem doing this. They did not use the Curtis. Are you using torque control? Have you talked with Curtis about it? To my knowledge, it is not detrimental to the induction motor or inverter to apply torque opposite to rotation (that's just regeneration, right?) or at standstill. Now granted, extended duration of high current at low or zero speed on the motor may be thermal trouble depending on the type of motor cooling employed.

Regards,

major


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## Forklift Guy (Apr 20, 2009)

If you have axcess to a Curtis programer, you will have to increase the plugging current. As you roll back, while in Forward, you are now in "plugging". If you increase the plugging current, it will hold the load and stop the roll back, and the allow forward direction. 

Brad
Forklift Guy.


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## etischer (Jun 16, 2008)

If the motor is being controlled in sensorless vector mode (no encoder), the motor controller does not know how fast the motor is spinning when you first start it up because the field is not established. Without knowing the actual motor speed, the contoller cannot control torque. If you are not using an encoder, adding an encoder will probably help. To catch a spinning motor there is a technique called fly catching, this is typically used on large fans or windmills being controlled in sensorless vector. 


You may also check the regen torque limit. If the motor is spinning backwards and you are trying to move it forwards you are actually trying to regen stop the motor first. If regen torque limit is set to zero you will not produce any braking torque and you will roll backwards. 

Does the motor jerk and buck around when you try to accel forwards while rolling backwards, or does it just not produce any torque?


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