1 - 5 of 5 Posts

Functional Artist

·
Registered
Joined
·
519 Posts
Discussion Starter · ·
I set up a go kart with a 24V 450 watt motor & speed controller

I then added a "Turbo" button where I could jump up from 24V to 36V at the flip of a switch

The motor is a
...24V 450W DC brushed motor
...rated current of 25A
...rated speed 2.500 rpm

So, if we divide 2,500 rpm by 24V = 104.17 rpm's per volt

Seems a bit high
...that's probably max motor speed, not average

So, for simpler math & maybe a bit more realistic numbers,
...lets try our calculations @ 2,000 rpm

So, if were getting an average of 2,000 rpm's & we divide that by 24V = 83.33 rpm's per volt

When we kick in turbo,
...the motor rpm should increase to ~3,000 rpm's (84 rpm's per volt x 36 volts = 3,024)

That would be a instant 33% increase in rpm's coming out of the motor

So, if the kart did on average 15 mph during the speed tests
...it should do ~20 mph (15 mph x .33 = 4.95)

Nothin' to write home about speed wise but, a 33% rpm increase @ the push of a button is substantial

So, to go by that:

If a bigger faster kart, did lets say 40 mph

a 33% boost would provide a 13.20 mph increase

40 mph to over 50 mph instantly

electro wrks

·
Registered
Joined
·
947 Posts
So, to go by that:

If a bigger faster kart, did lets say 40 mph

a 33% boost would provide a 13.20 mph increase

40 mph to over 50 mph instantly

Almost, if you were in a vacuum. Not counting the small increase in rolling resistance, the power needed to push a vehicle through the air increases as the cube of the velocity. So, the increase in velocity would be much less. The power (and RPM) output from the motor increases as a linear function of the voltage (within limits) and the power required to go faster increases exponentially. So, to take full advantage of the increase in motor power (RPM) at a higher voltage, your drive needs to be geared lower(higher numerical ratio). This effectively limits the increase in velocity.

BTY, As an illustration of this, Tesla partially overcomes this drag by running their Hyperloop vehicles in a partial vacuum. This is partly how they're able to achieve such high velocities at relatively low power inputs.

Functional Artist

·
Registered
Joined
·
519 Posts
Discussion Starter · ·
Almost, if you were in a vacuum. Not counting the small increase in rolling resistance, the power needed to push a vehicle through the air increases as the cube of the velocity. So, the increase in velocity would be much less. The power (and RPM) output from the motor increases as a linear function of the voltage (within limits) and the power required to go faster increases exponentially. So, to take full advantage of the increase in motor power (RPM) at a higher voltage, your drive needs to be geared lower(higher numerical ratio). This effectively limits the increase in velocity.

BTY, As an illustration of this, Tesla partially overcomes this drag by running their Hyperloop vehicles in a partial vacuum. This is partly how they're able to achieve such high velocities at relatively low power inputs.
Ok, so like "passing gear" in a car?

When you "punch it" the transmission drops down a gear as the motor accelerates to speed up & pass another car.

Functional Artist

·
Registered
Joined
·
519 Posts
Discussion Starter · ·
...but, will increase speed/power output

I was interested in
..."how" much speed/power increase (the theoretical 30%?)
...would intermittent use be OK?
...could it be done without back feeding the overvoltage to the controller?

Yes, it can be done

No, it's not a good idea (even intermittently)

* Conclusions

...this motor/controller/kart would do 15 mph consistently before these tests

First test run:
...top speed w/controller 15 mph, then jumped to 20 mph with Turbo engaged

After the second or third Turbo burst
...the kart's speed topped out at ~13 mph & with Turbo burst it only jumped up to ~17 mph

So, this motor seemed to draw 30-32 amps normally to propel this kart to 15 mph
...then when Turbo was engaged, this motor would draw 50-100 amps to ONLY go 5 mph faster
...that's a 30% increase in speed
...but, a 200-300% increase in power draw
...& it's a complicated set up
...plus I think it damaged the motor internally

Not only is this concept BAD on the motor
...but, it's probably even worse on the batteries

Because
...there is NO under voltage cutoff to protect the batteries

They could be easily & permanently damaged by draining too much power out of them
...& they are being drained unevenly
(by pulling 12V for solenoids, 24V for motor/controller & then 36V for Turbo boost)
...the third battery is being drained hard (by powering Turbo)
...the second battery even more (by powering normal mode & Turbo)
...& the first one is being sucked dry (by everything, the solenoids, normal mode & Turbo)

So, I don't think overvolting (even if/when possible) is a good idea.

Really smart engineers design electric motors to "function within specified parameters" as Data would say

To increase the success rate I (now) try to only operate motors within their specified voltage range & to use the proper matching speed controller.