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Electric Motors

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cmrusso87

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Err...I'm planing on building an electric gocart sometime in the near future, but I honestly don't know what I'm doing when it comes to electronics, so I hope I came to the right place.

I found this while looking for supplies on the internet and I have an important question:

What would be the most efficient set up for a battery-motor system:

12VDC batt - 12VDC to 120VAC inverter (800W) - 120VAC 800W motor

-or-

12VDC batt - 12VDC 800W motor

Or should I use more than 12V? What would be the best way to get the most out of a battery? The way I see it, the AC motor is only pulling 6.7 amps while the DC one is pulling 66.7 amps. Am I correct in saying this?

Anothing question, how do I know how much weight my gocart motor can handle? Is it the current, voltage, or power?

Please don't hassle me if I don't know what I'm talking about. I just need some good advice. Thx
 
They are basically drawing the same power and for a Lead-Acid batter the current source is abt 60-100A max.

Either scheme the battery will draw 60 odd amps (full load), you need to check the Amp-hours of the lead-acid battery to see how long it will last at that load.

Also at that load the battery will get hot.

what you have to weigh up here (no pun intended) is the overall weight. The inverter will add extra weight to your go-cart

Also in using the inverter you might (if you get a goodun) be able to vary the output voltage thus be able to vary the speed

probably not answered your question but a start

as to your second question what governs wieght will be power. If you weigh down your cart it will take more torque to make it move. Torque ~ current and also power = Torque x ang velocity
 
We use electric golf carts at work ..They are 36vdc, six 6volt batteries in series...You might want to take a look at the controls of one for some ideas 8)
 
Hi,

or You can use a 12V DC-motor adjusting speed via PWM. At this high current levels Your wires should be as short and as thick as possible.

btw: Does anyone know if there are inverters 12VDC->120 (230)V 3phase 0-120Hz? This would be ideal for Your project: Higher voltage means thinner wires, use of a cheap asynchronous motor, adjust speed by adjusting frequency.

hth
regards
joachim
 
http://www.dcacpowerinverters.com/ has some good inverters, not sure if it has the one you need...

As for my cart, I was thinking of using a simple rheostat to manage the voltage. Question: at lower voltages, there will be a higher current, and at max voltage, there will be a lower current. How do I cope with this fluctuating current?

You said that the battery could get hot if it is no heavy. What exactly makes the battery heat up? Would a higher voltage reduce this heat?

This battery here claims it can generate 400 amps, max 1000. Would this be decent to use with an 800W motor?
 
oh, btw...I'm building this cart for speed, not torque...if I ever do get around to building it, I might even fit a little transmission on it, if possible.
 
cmrusso87 said:
12VDC batt - 12VDC to 120VAC inverter (800W) - 120VAC 800W motor

-or-

12VDC batt - 12VDC 800W motor

Or should I use more than 12V? What would be the best way to get the most out of a battery? The way I see it, the AC motor is only pulling 6.7 amps while the DC one is pulling 66.7 amps. Am I correct in saying this?

the inverter wud be pullin bout 80 amps from the batt for a 800 watt load. also if u use an 800watt motor u shud use a 1kw inverter (prevent as much overheating)
 
Hi,
maybe You can 'borrow' some ideas here:
**broken link removed**
regards
joachim
 
cmrusso87 said:
oh, btw...I'm building this cart for speed, not torque...if I ever do get around to building it, I might even fit a little transmission on it, if possible.

you might want speed but you will reqire torque. If your cart is heavy the drive will draw more current to establish the required torque to move.

The battery heats up when it is drawing high current (it ESR and all). Think of it in power sense. Higher voltage would require less current to be drawn. Higher voltage is always preferable.

REmember

VOLTS = speed
AMPS = torque

if it is light then not alot of torque will be required and you will go at full speed. As you start to load the cart the machine wll draw more current to keep the machine going at constant speed
 
Cmrusso87,

I think the best way is 12V battery to 12VDC motor. You should consider a deep cycle type battery. There are some drawbacks going the 120V way, 120V is dangerous, the conversion is losing energy (efficiency is 80% at best), the possibilities to control the power (rpm) is limited (expensive with AC) and it will carry more weight to your vehicle (and more space). A assume you want a speed control?

Ante :roll:
 
I was thinking that the DC would be the best way to go...everyone has seemed to help quite a bit. I have joined my schools "science team" for next year, so I will see how things go. Perhaps i will build the cart somehow involving the science team...I'm not sure...if I ever get around to building the cart, this forum will be the first to know.

Thx for everyone's help!
 
Don't touch the 120VAC motor. It likely has only one speed, and doesn't have much starting torque to get you up to speed. Neither the motor nor the inverter tolerate voltage variations well either. Plus the inverter will drop 10% or more of the efficiency.

DC is fairly straightforward as long as the motor voltage is equal to, or lower than, the battery voltage.

It is true that you 24V, 36V, or 48V will generally get better results than 12V, the current levels will be more manageable. Moving a person around requires more current than most 12V batteries handle.
 
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