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Harris Sh (Pyrohaz)
Intermediate Member

Post Number: 27
Registered: 8-2006
 Posted on Thursday, August 9, 2007 - 4:39 pm:

Hi! Im sorry but im just not sure where to put this! but i was wondering why in most electric cars that they use AC parts and motors, if you read up on the 'Howstuffworks' website, it shows the features of the car and it has 300v DC being put down to 240v ac, now wouldnt the excess energy be put off as heat? Also, why so they put it as such a high voltage iunstead of haveing say 36v but a very high ampage, is that a safety feature? Also, i finished off my electric scooter and its amazing! i got a 24v throttle controller of an electric scooter (£11.98) off ebay new, i also bought 4 20aH batteries for £30, your idea of the DPDT switch was great, just my 12v charger was taking AGES to charge (30+ hours) so i opted for a 24v 2amp charger which again was off ebay for £23.98, if you would like to have some pictures and know a bit about my scooter, just ask and i will explain ;) LOL

gosh that looks like an essay!

Simon Quellen Field (Sfield)
Senior Member

Post Number: 1761
Registered: 12-2004
 Posted on Thursday, August 9, 2007 - 4:55 pm:

Voltage is not energy.
When I convert 240 VAC to 120 VAC in a transformer, I don't lose half the energy.
If I then convert the 120 VAC to DC, I don't lose much either.

Resistance losses are a function of the current.
If you have less current, you have less loss.
So when we want to send electricity from one end of California to another,
we use transformers to step the voltage up to 110,000 volts (or more in some
cases), and keep the current down to about 600 amperes. That allows three wires
to carry 66 megawatts. If they need more, they add another three wires.
Sometimes you see a dozen wires going from tower to tower (264 megawatts).

My car uses 650 volts going to the three big electric motors for the same reason.
You can deliver a lot of energy with less loss when the voltage is high and
the current (relatively) low. My battery system operates at 288 volts, and is
boosted in the inverter to 650 volts. The air conditioner runs on 288 volts.
The power steering runs at 48 volts.

Harris Sh (Pyrohaz)
Intermediate Member

Post Number: 28
Registered: 8-2006
 Posted on Thursday, August 9, 2007 - 4:59 pm:

Ah! I sort of understand you now. So does your car run off DC or AC? Also, if they run off AC, how does this help because i may consider it on my next electric project (might do a gokart next :p)

Simon Quellen Field (Sfield)
Senior Member

Post Number: 1762
Registered: 12-2004
 Posted on Thursday, August 9, 2007 - 5:16 pm:

The big motors are AC.
The inverter converts DC to AC, and the AC can be converted to any voltage
you like with a transformer. For a scooter, you're better off with DC, so
you don't have to carry around an inverter and transformer. With short fat
wires, your losses will be low already, but you might want to use the highest
voltage motors you can find anyway, and configure your batteries to match.

Haz (Pyrohaz)
Intermediate Member

Post Number: 29
Registered: 8-2006
 Posted on Thursday, August 9, 2007 - 5:48 pm:

Nice! Big help, Thanks a lot for the help!

Haz (Pyrohaz)
Intermediate Member

Post Number: 30
Registered: 8-2006
 Posted on Thursday, August 9, 2007 - 6:03 pm:

Sorry to ask more! But how can i make my motor cooler without loosing any speed? I have added a sink from a PC PSU so what kind of controller or resistor would i need?

Michael (Michaelt)
Senior Member

Post Number: 168
Registered: 12-2005
 Posted on Thursday, August 9, 2007 - 6:46 pm:

"losing"
Making it cooler would probably help it gain some speed theoretically, as the cooler the windings are, the less electrical resistance there is. You need to find a way to get air to flow through the motor, helping further to keep it cool.

(Message edited by michaelt on August 9, 2007)

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