Paul & Sabrina's cheap DIY 144v motor controller

[MPaulHolmes]

I was sort of half-thinking of something like that, but I didn't know what I was thinking until you just mentioned it! We could find top speed for a given voltage, torque (my loose impression of it), and other stuff if there is anything else you could think of. This is a really good idea!


Let's do it!

[Intrigued]

Originally Posted by MPaulHolmes

I was sort of half-thinking of something like that, but I didn't know what I was thinking until you just mentioned it!

LOL!!!

<<This is your sub-conscience speaking, Paul. You will never stick a fork in your eye. It is too important for completing this mission. You will then make lots of people happy by selling them controller kits...>>

< happy people...

[MPaulHolmes]

Here are the results of what I tried:

max rpm was completely unrelated to current limit. 24v max rpm was twice as fast as 12v. 36v was too fast to count, so I'm guessing that 36v max rpm was 3 times as fast as 12v.

Torque (I used a spring!) was completely unrelated to voltage.


5 amp current limit stretched the spring about 1 inch for 12v test, 24v test, ... , and 60v test. I thought that more volts would have given more torque. Oh well. hehe.

10amp current limit stretched the spring about 2 inches for each of the 12v, 24v, ..., 60v tests.

So, I remember someone telling me this, but I never really was sure I believed it. Current <==> Torque. Voltage <==> MAX RPM!

So, for a given power, you can have higher top speed but lower torque, or lower top speed and higher torque.

[Intrigued]

Originally Posted by MPaulHolmes

So, I remember someone telling me this, but I never really was sure I believed it. Current <==> Torque. Voltage <==> MAX RPM!

Way Cool!!!

I remember now of reading something like that, but I think it kinda bounced off of the "no way" cells in my brain, kinda like it did yours. It's really hard to absorb that current and voltage are so completely independent for performance.

I realize this may be a poor comparison, but it's kinda like current gives you the low-end power like a diesel (torque), and voltage gives you the high-end horsepower (RPMs) like an ICE.

You The Man, MPaul!!!

[Intrigued]

"We are learning all sort of neat things on the Mosfet Show tonight!"

[MPaulHolmes]

Originally Posted by Intrigued

I realize this may be a poor comparison, but it's kinda like current gives you the low-end power like a diesel (torque), and voltage gives you the high-end horsepower (RPMs) like an ICE.

I think you're exactly right! Isn't that weird?

[MPaulHolmes]

I did a video of the max speed and torque tests for 5 and 10 amp current limits, and various voltages.

The video!

[bennelson]

Originally Posted by MPaulHolmes

Current <==> Torque. Voltage <==> MAX RPM!

So, for a given power, you can have higher top speed but lower torque, or lower top speed and higher torque.

You got it Paul.

Also, keep in mind that batteries, especially lead-acid, care a lot about how many AMPS are being pulled out of them. If you are pulling twice as many amps from a battery, you will get less than half the total energy out of it.

So, lets compare a 72V battery pack to a 144V battery pack.
If it takes about 10 horsepower to push your car down the road, that comes to 100 amps at 72 volts. But in a 144 volt pack, it's only 50 amps.

Since the only thing the batteries car about is amperage, line up lots of batteries in a row (series) to get the high voltage.
In fact, using twice as many batteries, which are each physically half as big, will get you more range without changing the weight of the car at all!

You can also use thinner cabling and lower power connections as well. Look at the 4 power cables going into the motor on this AC Neon Conversion



The cables are about the thickness of a pencil, but the car will run at around 300 volts. At that voltage, the cables only need to carry 24 amps for the same 10 horsepower as the 72V car using 100 amps!

[MPaulHolmes]

That's amazing! Those look like regular anderson connectors that I have on my bike! Also, I've been thinking still, and I should have said higher torque at 0 rpm and slower top rpm, or lower torque at 0 rpm and higher top rpm.

And higher rpm can be cut in half with gears, doubling the torque so there is really no drawback to higher voltage! Finally the Peukert value works in our favor! Maybe if we do some sort of IGBT based 1200v controller, we can power it with calculator batteries. 1200 in series, drawing 8 amps or so. hehe. Well, maybe NiMH D batteries.

[bennelson]

Originally Posted by MPaulHolmes

there is really no drawback to higher voltage!

EXACTLY!

(Except that it costs more, you will need more chargers, or a single high-voltage charger...)

In the photo of the Neon, those are modular Anderson connectors. They can be put together in different ways. Handy to build a connection that you can't plug in backwards!

Another advantage of higher voltage is that the smaller (lower amperage) Anderson connectors are much cheaper than the big (high amperage) ones! Lugs and cables, etc, is similar that way too.