Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Ben Nelson's Electro-Metro Build thread

bennelson · 04-03-2008, 11:38 AM

Hey Metro,

A while back, you mentioned the idea of using a 36/72V parallel/series setup in my Metro.

If I understand correctly, a Citicar uses several contactors to connect and disconnect the various batteries so that all are used at the same time, but sends differing amounts of voltage (12/24/48) to the motor, thus different speeds.

What if I used a 36 volt pwm controller (Cheap! as there are a zillion of them for golf carts) and then had a contactor set to disconnect the controller and instead connect all the batteries in series. A reversing contactor might be able to do both at the same time, right? A reversing contactor disconnects one set of power, then connects a different set of power cables (break before make) Do I have that right?

The controller would be used for smooth and easy speed control and accelleration. Then for top speed (72V) the contactor would flip. There would no longer be any speed control, but this would be used for cruising only. That contactor could be set with a momentary-on switch so that as soon as you want to stop "cruise mode" you just release it. It could be some sort of hand switch or lever, or a button under the gas pedal that is only closed when you have the "pedal to the metal". I guess it might be best to have a manual control, so that power could be let off thru the controller before kicking over to 72V. Having full voltage running through the controller, then doing a hard disconnect from it, doesn't sound healthy for the controller.

Does this seem like a reasonable idea for a cheap experimenters way of not having to buy a 72 Volt or more controller? It would also allow max amps at 72 volts, would that help with hill climbing?

This setup would also mean my battery pack could be charged by a 36V charger (which I already have). One monsterous forklift charger (which I would have to see about lowering the output on!) and one little tiny 36V smart charger. I could always get a nicer 36V charger later, and it would still be fairly inexpensive.

Would I be getting into arcing issues with the contactor? Is there some other way anyone can think of to help keep my budget down / have fun / DIYerself mentality while still making this a very safe and drivable car?

04-03-2008, 11:38 AM	#256 (permalink)
bennelson EV test pilot Join Date: Jan 2008 Location: Oconomowoc, WI, USA Posts: 4,435 Electric Cycle - '81 Kawasaki KZ440 90 day: 334.6 mpg (US) S10 - '95 Chevy S10 90 day: 30.48 mpg (US) Electro-Metro - '96 Ben Nelson's "Electro-Metro" 90 day: 129.81 mpg (US) The Wife's Car - Plug-in Prius - '04 Toyota Prius 90 day: 78.16 mpg (US) Thanks: 17 Thanked 663 Times in 388 Posts	Hey Metro, A while back, you mentioned the idea of using a 36/72V parallel/series setup in my Metro. If I understand correctly, a Citicar uses several contactors to connect and disconnect the various batteries so that all are used at the same time, but sends differing amounts of voltage (12/24/48) to the motor, thus different speeds. What if I used a 36 volt pwm controller (Cheap! as there are a zillion of them for golf carts) and then had a contactor set to disconnect the controller and instead connect all the batteries in series. A reversing contactor might be able to do both at the same time, right? A reversing contactor disconnects one set of power, then connects a different set of power cables (break before make) Do I have that right? The controller would be used for smooth and easy speed control and accelleration. Then for top speed (72V) the contactor would flip. There would no longer be any speed control, but this would be used for cruising only. That contactor could be set with a momentary-on switch so that as soon as you want to stop "cruise mode" you just release it. It could be some sort of hand switch or lever, or a button under the gas pedal that is only closed when you have the "pedal to the metal". I guess it might be best to have a manual control, so that power could be let off thru the controller before kicking over to 72V. Having full voltage running through the controller, then doing a hard disconnect from it, doesn't sound healthy for the controller. Does this seem like a reasonable idea for a cheap experimenters way of not having to buy a 72 Volt or more controller? It would also allow max amps at 72 volts, would that help with hill climbing? This setup would also mean my battery pack could be charged by a 36V charger (which I already have). One monsterous forklift charger (which I would have to see about lowering the output on!) and one little tiny 36V smart charger. I could always get a nicer 36V charger later, and it would still be fairly inexpensive. Would I be getting into arcing issues with the contactor? Is there some other way anyone can think of to help keep my budget down / have fun / DIYerself mentality while still making this a very safe and drivable car? __________________ 300mpg.org Learn how to BUILD YOUR OWN ELECTRIC CAR CHEAP My YouTube Videos Last edited by bennelson; 04-03-2008 at 11:55 AM..