DIY Electric Car Forums banner
1 - 8 of 8 Posts

·
Registered
Joined
·
22 Posts
Discussion Starter · #1 ·
Hi All,

I need a bit of help with my electric car build. I have a Dc forklift motor and i have made one of Damián Mcquires controllers . It is connected to a BMW throttle pedal and i have an ammeter through a shunt to measure the current. The issue I have is that when I accelerate the current draw gets up to 500 amps which is too high. I though thet maybe i could change the throttle pedal resistance or pulse width to limit the current .

I'm open to suggestions

motor and controller.jpg







Cheers Barry
 

·
Administrator
Joined
·
6,294 Posts
First - why is 500 amps too high? - that is about the usual current

The controller will operate by changing the pulse width modulation until its internal current sensor matches the "demand" from the throttle pedal

It sounds as if you are using one of the usual zero to 5,000 Ohm throttle pots

You can get into the guts of the controller and change things or you can simply add a 5,000 ohm resister in parallel with your throttle - this will mean that the zero stays where it is but full throttle is now only 2,500 ohms
If 5,000 ohms demanded 500 amps - 2,500 ohms will demand 250 amps

I use something like that my car is a little too exciting on road tyres on the normal streets so I limit it to about 40% power - about 500 amps
Full power is good for the track or if I want to spin the rear tyres - 1200 amps

The resister I use is in parallel with the throttle pot with a switch to open the circuit - to be a hooligan I simply open the switch
 

·
Super Moderator
Joined
·
1,342 Posts
Depends which of Damien's controllers you're using, but if it uses Johannes' Open Inverter project, it's all easy to set by changing the parameters over wifi. I have a feeling this is a quite old design?
 

·
Registered
Joined
·
22 Posts
Discussion Starter · #5 ·
First - why is 500 amps too high? - that is about the usual current

The controller will operate by changing the pulse width modulation until its internal current sensor matches the "demand" from the throttle pedal

It sounds as if you are using one of the usual zero to 5,000 Ohm throttle pots

You can get into the guts of the controller and change things or you can simply add a 5,000 ohm resister in parallel with your throttle - this will mean that the zero stays where it is but full throttle is now only 2,500 ohms
If 5,000 ohms demanded 500 amps - 2,500 ohms will demand 250 amps

I use something like that my car is a little too exciting on road tyres on the normal streets so I limit it to about 40% power - about 500 amps
Full power is good for the track or if I want to spin the rear tyres - 1200 amps

The resister I use is in parallel with the throttle pot with a switch to open the circuit - to be a hooligan I simply open the switch
thanks very much for the info, i will try the resistor, at the moment i am using a prius battery to provide the power , wanted to limit the power si i dont fry the battery to quickly. Im building this as an experiment and a learning process.

cheers Barry
 

·
Registered
Joined
·
22 Posts
Discussion Starter · #6 ·
Depends which of Damien's controllers you're using, but if it uses Johannes' Open Inverter project, it's all easy to set by changing the parameters over wifi. I have a feeling this is a quite old design?
Thanks for the reply,

yes its a very old DC design that has no programming. I was amazed that when i built it it worked.

cheers

Barry
 

·
Administrator
Joined
·
6,294 Posts
thanks very much for the info, i will try the resistor, at the moment i am using a prius battery to provide the power , wanted to limit the power si i dont fry the battery to quickly. Im building this as an experiment and a learning process.

cheers Barry
There are two different currents involved - motor current and battery current
Then you start off it takes very little voltage to drive the current through the motor

(very) Rough example
Start - Motor 15 volts 500 amps ------------- Battery 150 volts 50 amps
1000 rpm Motor 50 volts 500 amps ------------- Battery 150 volts 166 amps
2000 rpm Motor 80 volts 500 amps ------------- Battery 150 volts 266 amps
4000 rpm Motor 150 volts 500 amps ------------- Battery 150 volts 500 amps
 

·
Registered
Joined
·
1 Posts
Hey Bimmerbaz,
If from this thread you you do decide that 500 motor amps is okay, be sure to check the amp/temperature rating of your controller-to-motor conductors! Perhaps also use orange wires or orange electrical tape rather than those plastic wire covers to help the conductors transfer out heat as best as they can?
I'm speaking up on this because i'm dealing with conductor sizing in my own build now! also using a damien controller
 
1 - 8 of 8 Posts
Top