# Help building a homemade controller.



## piotrsko (Dec 9, 2007)

quick and dirty but not exhaustive: get a scrap electric forklift controller that works. do some more research for which one and see how cheap you can go. I've heard of free forklift controllers.

good luck


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## TigerNut (Dec 18, 2009)

rickyd123 said:


> Hi. I've been kicking around this site for about two weeks now. I've been kicking around the idea of building an electric car for a couple of years. I never realized so many people had already done it till I found this site. That said here's what I want to ask.
> My situation is basically financial. There appear to be four main components to building an EV. The motor. The batteries. The donor car. The motor controller. All of those I can get fairly inexpensively except the motor controller. Now many will say the batteries are expensive. True, but I can buy one deep cell battery from the auto store and know my vehicle runs properly and save up for a bigger pack. The motor controller appears to be the only piece that is very expensive and is a must have for a good EV.
> I've looked at the ones that are made by electronics know how. ie. printed circuit boards, capacitors, mossfits ect... That's way is over my head. I would have to go to the community college and take electronic courses before I could grasp it, but I've seen another way.
> IGBT I've seen controllers designed using "igbt". I don't know what they are or where they come from. They look like a way that I might be able to understand, but I haven't found any direction on how to build them. If anyone knows about building instructions please direct me to them.
> I would also like to know what other products use these igbt. Do tv, microwaves, ect... I'm really good at getting parts from one thing to use for another. Thanks for any help


Based on where you appear to be at in your overall electrical system knowledge, taking a basic (highschool or introductory college level) electronics course is probably the cheapest and safest thing you can do at this point. High voltage, high power electric systems can kill you in the blink of an eye, and unlike internal combustion engines, they don't announce the peril with loud noises or heat radiating off of the lethal parts.

Second, IGBTs are not magic... their use in a motor controller doesn't make the controller any less complex and they don't save you from having to know any of the basic theory of electric power systems. Go take the courses, or spend some time on the web reading about electrical theory until you at least understand the basic functions of the various electronics components, and you have a grasp of Ohm's law so that discussions about power, voltage, and current have some meaning.


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## MPaulHolmes (Feb 23, 2008)

An IGBT has the same purpose as a mosfet. You turn it on and off really fast so that it can act sort of like a light dimmer. One advantage of dual igbt modules in motor controller design is you can use 1 or 2 of them, and a big capacitor, then all you really need is a little driver board and control board. To get a control board and driver board to work, all you have to know how to do is solder. Designing your own boards can be complicated, but people have already done that, so you would only have to play where's waldo, and stick the resistor labeled "R1" in the little spot on the board that's labeled R1. It's not too bad.

http://ecomodder.com/wiki/index.php/Open_ReVolt/Control_board

As for the driver board, powerex did a board so you would use their drivers.

Now, having no idea what's going on can be a problem for debugging.


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## Ziggythewiz (May 16, 2010)

While we've got you here Paul, how does the IGBT controller compare to the mosfet version pricewise? I've been planning to do a build for some time, but the IGBT version on the revolt wiki seems to still be in the works. Am also still saving up my pennies.


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## ga2500ev (Apr 20, 2008)

rickyd123 said:


> Hi. I've been kicking around this site for about two weeks now. I've been kicking around the idea of building an electric car for a couple of years. I never realized so many people had already done it till I found this site. That said here's what I want to ask.
> My situation is basically financial. There appear to be four main components to building an EV. The motor. The batteries. The donor car. The motor controller. All of those I can get fairly inexpensively except the motor controller. Now many will say the batteries are expensive. True, but I can buy one deep cell battery from the auto store and know my vehicle runs properly and save up for a bigger pack. The motor controller appears to be the only piece that is very expensive and is a must have for a good EV.
> I've looked at the ones that are made by electronics know how. ie. printed circuit boards, capacitors, mossfits ect... That's way is over my head. I would have to go to the community college and take electronic courses before I could grasp it, but I've seen another way.
> IGBT I've seen controllers designed using "igbt". I don't know what they are or where they come from. They look like a way that I might be able to understand, but I haven't found any direction on how to build them. If anyone knows about building instructions please direct me to them.
> I would also like to know what other products use these igbt. Do tv, microwaves, ect... I'm really good at getting parts from one thing to use for another. Thanks for any help


Ricky,

I've been here for 4 years and I'm just getting to the point where I've learned enough to build a motor controller from scratch.

At its heart, a motor controller isn't terribly complicated. The devil is in the details. There's a fine line between a working system and one that releases smoke.

Let's start with the basics. Motor RPM is directly related to the amount of voltage you put into it. Low voltage spins the motor slowly, high voltage spins it a lot faster. We need to be able to control this factor to control the speed of the vehicle.

Now there's two ways of doing this. One is to directly vary the input voltage to the motor. Frankly it's tough to do at the current levels required to drive a motor that large properly.

The second way is the standard for most motor controllers. It's called a buck regulator. The idea is to fix the input voltage at a single point, then instead of varying the voltage, vary the ratio of time that full voltage is applied to the motor. Buck regulators work because of a component called an inductor. At its simplest it's a coiled wire around a magnetic core (such as iron). The property of an inductor is that it can be "charged" with current from the input and "drained" of current from the load. It does its best to keep the current at its current value by only allowing it to rise and fall at a constant rate. Often the side effect of this property is the changing of the voltage to the load. This is a subject you will need to read up on. There are a ton of online references.

So there are 4 basic items such a regulator needs. The first two are

1) A switch to connect the input voltage to the inductor. Usually this function is served by one of two types of transistors: MOSFET and IGBT.

2) The inductor. It just so happens that in a motor controller, the motor itself serves this function.

Now the second two items are equally important, but not as obvious. The first are input capacitors. See the switch slams the voltage from input (which for an EV are batteries) on and off very quickly. The inductor requires quite a bit of power when the switch first turns on, and the batteries struggle to deliver this. So the input capacitors gives the system a quick burst of power when the switch first turns on, then recharges when the switch turns off. There are several important properties about this capacitors that needs to be researched. You will hear terms such as ESR, ripple current, and temperature. This is one of those details I referred to earlier. The controller will not work without the right types of capacitors.

The second item is a diode. A diode serves as an electronic check valve that permits energy to flow in one direction and blocks it from flowing in the other. It's important because of the behavior of the inductor. When the switch turns off, the inductor tries to keep the current steady. But with the switch off, that current has no specific path to deliver that energy. But the inductor will try anyway and will ramp up the voltage until a spark can jump from one random place to another. This is very very very very bad. Very bad. So the purpose of the diode, normally called the freewheeling diode, is to provide a path so that the energy can flow into the motor while the switch is off. Again there are some specific parameters about the diodes that are important to learn otherwise you'll release the "magic smoke".

These 4 components comprise the power system of a controller. Next up is the control and safety systems. Most controllers nowadays do this using a programmable microcontroller, such as an Arduino, and associated electronics. Again there are several levels of details of connection between the control system and the power system.

If you really want to learn how to do this, you should go and read at least the first 250 pages of Paul and Sabrina's motor controller thread. Paul started with just about the same amount of knowledge you have 4 years ago. He was able to deliver a cost effective and usable product. There are also several threads here by jackbauer and valerun (the latter is still active), on the implementation of IGBT based motor controllers.

What you will find is that the details really matter. There are several dozen pages of posts on subtle nuances about switching frequency and switching time, the Miller knee, and how much power is required to get the switch to work properly. Get the basics down first, then start looking at the details.

The final item is that you will always have casualties in construction. Each and every thread here has at least 1 post where the controller shorted out, blew up, or released smoke. One reason most don't do DIY for controllers is because of the large learning curve.

Hope this introduction helps.

ga2500ev


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## aeroscott (Jan 5, 2008)

ga2500ev said:


> Ricky,
> 
> I've been here for 4 years and I'm just getting to the point where I've learned enough to build a motor controller from scratch.
> 
> ...


nicely done


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## subcooledheatpump (Mar 5, 2012)

Yes, be prepared to blow up a few IGBTs.

They are sensitive to overvoltages and improper gate drive signals. 

Good luck


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