Introducing, LikeTheSandwich!

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Hey-o! I'm Reuben, as spelled like the Reuben sandwich (now you understand my forum username). I am almost 30 and have two little boys, 5-½ and almost 3. I live near Albany, Oregon. Since I was in middle school, I've wanted to own my own personal go kart track (on my own land, right next to my home). Still working on making that happen. Gotta save up, and buy a home with a bunch of land on which to do such a thing.

Right now, I want to obtain my own go kart. Definitely gonna go electric, because I love electronics (and I'm an electrician). I'm debating on building vs buying a frame, but I've already got most of the parts planned out, and I got a free old car alternator already configured to run as a DC motor. I'm actually almost ready to start work on my first go kart...just gotta convince my wife to let me...
 

landuse

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Welcome to the forum. It will be interesting to see if you can get the alternator going as a functioning and long lasting motor :thumbsup: Alternators generally don't like to be run for long periods.

Post some pics of the parts you have, as well as any specs you might have for the alternator.
 
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The only part I own right now is the alternator. Some websites say 12V 60A, others say 12V 78A. The latter would be just shy of 1kW. But I don't expect it to last long because I plan on running it at 48V. I know that's bad for it, but it's not worth the effort to me to run it at spec. So I'll run it until I feel like buying a new one, or it dies.
 

itsid

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So I'll run it until I feel like buying a new one, or it dies.
So for roughly 6 minutes then...
hmkay ;)

Oh and you're aware that you're NOT getting a 4kW motor then, right?
not in terms of mechanical power out that is.
You make a 2.5kW heater that tends to power a shaft with about 1.5kW at best.

'sid
 
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I'm aware of all this. I'm not an engineer, but I'm an electrician, so I have a fair bit of experience with motors. I have a 2kW 48V controller selected, max 45 amps. If I run it around 1~1.5kW at 48V, with low duty cycle, I'm hoping it'll last a little while at least.
 

landuse

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I'm aware of all this. I'm not an engineer, but I'm an electrician, so I have a fair bit of experience with motors. I have a 2kW 48V controller selected, max 45 amps. If I run it around 1~1.5kW at 48V, with low duty cycle, I'm hoping it'll last a little while at least.

Go for it. Lets see how it goes :thumbsup: :D

Even if it doesn't work, it will be an opportunity to learn
 

itsid

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I'm aware of all this. I'm not an engineer, but I'm an electrician, so I have a fair bit of experience with motors. I have a 2kW 48V controller selected, max 45 amps. If I run it around 1~1.5kW at 48V, with low duty cycle, I'm hoping it'll last a little while at least.

Sounds like a good idea,
but it's the motor that dictates the current not the controller.
I hope that controller has a current limiter inside for protection,
otherwise it'll just fry first.

I'd say your only chance would be to gear for a relatively low power request currently (excuse the pun ;)).

'sid
 
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Sounds like a good idea,
but it's the motor that dictates the current not the controller.
I hope that controller has a current limiter inside for protection,
otherwise it'll just fry first.

I'd say your only chance would be to gear for a relatively low power request currently (excuse the pun ;)).

'sid

What kind of controller won't have a current limiter?
 

itsid

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What kind of controller won't have a current limiter?

well most we see regularly don't!
like all the ones that come packed as a kit with the BLDC motors from china for example.
NONE actually is current limiting
Same goes for nearly every cheap brushed controller out there.

finding a current limiting controller for less than 150bucks is kind of
a challenge already..
programmable kellys are current limiting (well in fact power limiting..)
other than that I can only think of controllers for 300 or more.

there are some that are overcurrent protected;
but depending on the actual controller,
that can mean it just refuses to run a certain (higher power) motor
at all.

'sid
 

itsid

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Then how do the ones with multiple power settings control the power? And how do the throttles work? Limiting voltage?

limiting TIME!
pulse width modulation is what you're looking at
(in both cases)
the throttle signal is usually a simple HallEffect
reporting something between 0 and 5 volts (between 0.5 and 4.7 really)
the controller takes that and converts it with it's ADC
(usually compensated for specific throttles)
and in turn switches the mosfets very rapidly via a small gate transistor
(on or off.. no other limitations whatsoever)

for ease of math (and since it's not important for the explanation)
let's assume an 8bit PWM
means every powercycle is divided by 255
the "ontime" of that cycle therefor is between 0 and 255 (always off to always on)
a 2.5Volts throttle signal roughly converts to a 128 "ontime"
means the mosfet is switched on for half the cycletime. (128/255)
Now, in case a limiter is engaged,
the most common way of implementation is a simple bitshift divider
so that 128 gets divided by either 2 or 3 or 4
or whatever the manufacturer felt to be a reasonable amount of math for his limitation
(to get to 30%, 50%, 60%, 75% )
so in case of a 50% limit that 128 is just divided by two to get 64 ...
and the effective on time will be 64/255 of each cycle at the same throttle position.

.... because I love electronics (and I'm an electrician).
Sorry, but your love seems to be stricly platonic and from a far...

nothing wrong with that;
but I expected a bit more because of that statement ;)

'sid
 
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Well, I can love things I don't understand very well, like my wife.

I have very limited experience with electronics outside of lasers and home/portable computers. I'm familiar with the concept of PWM, but didn't know that was the primary method. Not being an engineer, it seems like just using a rheostat or something like that would be easier and cheaper. But that's a physical thing, so perhaps PWM it's more reliable than a physical rheostat. I've often thought I should've been an electrical engineer instead of an electrician. But I'm very happy with my work, and I don't regret it.

EDIT: knowing that most don't have any over current protection, perhaps I should get some automotive fuses/breakers to protect my electronics?
 

itsid

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Well, I can love things I don't understand very well, like my wife.
LOL.. well said !

Again, nothing wrong, I just preceived your statement differently ;)

A rheostat is essentially the WORST possible solution I'm afraid
while it's certainly feasible to use some kind of potentiometer on a low power signal input (like the throttle usually is)

it's a dumb idea to use such to 'control' any high power device..
and that you really should know as an electrician I'm afraid :(

A circuit breaker or single blow fuse will not help you much either..
the current WILL be drawn, and there is very little you can do about it.
yes the fuse can protect against high currents and a fast blowing fuse might even be able to fully protect all electronics.
BUT it will just trigger the instant you press on the pedal too hard,
or try to climb a slightly too steep incline...
in fact with a motor/controller combi like yours,
chances are it'll blow just before moving.

since in order to protect it needs to be less tolerant than the electronics it's meant to protect,
and quicker than the weakest internal to blow.
(and that means you need a max50A quick blow 60V fuse..
and that will very likely trigger on any unfiltered commutational spike
from a ~50V 60Amp device)

Using an alternator is doable, also all but trivial.

Usually I'd suggest people getting a controller that is rated for ~20% over the max rating of the motor it's meant to power,
simply because it's worth running a controller in it's comfort zone,
to be prepared for the slightly too aggressive throttle input (pedal to the metal and such)
without risking it boiling it's internals because of some impatient driver.

In your case that'd be the next bigger size (100A constant rating I think)
as a programmable unit in order to dial in the sweet spot for the motor seperately and safely.

You try the exact opposite, which not only isn't a good idea,
it'll eventually cost you MORE than picking the more expensive controller directly.
(since after blowing two or three of the cheap ones, you'll buy it anyways in order to make the kart move ;))

And just to have it said.. picking a truely current limiting controller in 50Amps is likely just as expensive as one that's meant to provide 100Amps.. so choose wisely ;)

So, get you meters out,
measure the motors induction and resistance,
calculate the respective current draw,
and then go hunting for a matching controller..
be sure to pick one that's suitable for your actual configuration.
(2 phase, or four.. three in star or delta config etc.etc.)

'sid
 
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I wouldn't blow more than one controller. If/when I now the first one, is straight to a motor and controller designed to work together.

As for knowing that a rheostat is bad, I don't see why I'd have any reason to know that as an electrician. I wouldn't ever build a DIY speed controller in an industrial or even commercial environment, I'd buy one made for the purpose, most likely a VFD, because I would want it to be reliable.
 

itsid

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As for knowing that a rheostat is bad, I don't see why I'd have any reason to know that as an electrician.
because a rheostat is a variable resistor
and what a resistance does in an circuit should be known to an electrician.

dissipating energy (joule heating)

as an electrician you should be able to troubleshoot electrical installation.
And know what to look out for (like hotspots.. resistance between phases to find creeping currents etc.. )

And that wasting a limited supply of energy (batteries) to produce unwanted heat
instead of keeping it stored to be used to power the motor a little later
is simply not exactly a smart move, you'll certainly agree to that ;)

I'd buy one made for the purpose, most likely a VFD, because I would want it to be reliable.

And again I get the feeling you have very little idea what a variable frequency drive is, or rather how it works...
else you'd know that it's essentially doing the exact same thing as I explained above:
switching transistors by means of pulse width modulation based on the given control signal ,
either MosFets or (now mostly) IGBTs or sometimes IBCTs
taylored for specific applications (constant loads and or constant speeds)
A VFD is meant to keep a constant speed under variable load
or (as VTD) a constant torque under variable (ramping) speeds
very few exceptions.
Usually all but a highly variable load and - speed application
(like say... uhm... go karting for example)

And while the main difference is in fact code and
a rectifier circuit (a dc motor controller does not need one of course)
there are a few other missing bits n bobs for electric vehicle control.

there is in fact a close relative to a VFD made specifically to power electric vehicles (other than trains or trams)
they too use quasi sinusoidial modulation to power the phases of a mostly BLDC. and as that are called sinusoidial controllers
in fact even closer related to a VTD I think... nevermind...

Anyhow,
this is an introduction thread and
I managed to fill it already with tons of technical babble, apologies.
So I'll step out of this thread to not spoil it any further ;)

I'd like to ask you to create a thread in the electric-projects section
with some pictures of what you got already;
so we can have something to look at while thinking about your project ;)
And in case you have a question there will be help.

And with that..
welcome aboard!

'sid
 
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because a rheostat is a variable resistor
and what a resistance does in an circuit should be known to an electrician.

Resistance reduces the flow of current, therefore limiting power. In my small DC motor projects, it's a great, cheap, easy way to control speed.

as an electrician you should be able to troubleshoot electrical installation.
And know what to look out for (like hotspots.. resistance between phases to find creeping currents etc.. )

Electrician, not electrical engineer. Experience with the internals is minimal. I can troubleshoot the installation, and some of the internal stuff, but not all. That's for a technician, often trained/hired by the motor manufacturer of it's a high power situation.

And that wasting a limited supply of energy (batteries) to produce unwanted heat
instead of keeping it stored to be used to power the motor a little later
is simply not exactly a smart move, you'll certainly agree to that ;)

Agreed. But sometimes, especially if one can't afford a controller or just enjoys living on the edge, the cost of wasted energy is worth it.

And again I get the feeling you have very little idea what a variable frequency drive is, or rather how it works...

Again, electrician, not engineer. I figured that a "variable frequency drive" would VARY the FREQUENCY to DRIVE the motor, allowing the motor to start up slow, essentially performing the same function but through a different method, since the RPM of AC motors is (normally) directly tied to the frequency of of the AC power.

Anyhow,
this is an introduction thread and
I managed to fill it already with tons of technical babble, apologies.
So I'll step out of this thread to not spoil it any further ;)

I'd like to ask you to create a thread in the electric-projects section
with some pictures of what you got already;
so we can have something to look at while thinking about your project ;)
And in case you have a question there will be help.

And with that..
welcome aboard!

'sid

I appreciated your information. I will start the thread later when I actually have something with posting. Right now all I have is a motor, so little reason to bother.
 

ShadowNightmares

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Hey, saw that you're wanting to use a converted alternator.
Unfortunately cheap BLDC controllers won't limit current, and VESCs (that can be found cheaper usually are kept on 36V)
But if you still want to follow this route, i recommend you to install hall sensors on your alternator and use a programmable controller
(from YT/Austiwawa, an example of hall sensor installation)
 
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