car starter moter mod

[dstich]

i am lookin at using a carstarter moter for my bot because i have a low budgit and can get one at a scrap yard for a couple of bucks i was wondering if they can go in reverse if the curent is reversed i know that i have to cut the field winding coil wires and conect them directly to a battery and take out the selanoid but if i reverse the curent after that will the motor reverse or is there some kind of mecanical catch to stop it from reversing

 

[falleafd]

I don't understand you muchie, but did you mean you need something as a H bridge to run, stop and reverse the motors? With a H bridge, you don't have to cut your motors from power supplies but you just switch the H bridge to make it turn clockwise or ccw.

There are many ways to stop a free running motor, you may use a resistor to receive the inversed voltage made by the motor, or you may use a zener diode as a recharged battery to do so. As this inversed voltage be received by zener or resistor, the total energy of the motor will be decreased, that is the kinetic energy of it is decreased and the motor should be stopped faster than you leave it free.

 

[goodpickles]

Yes the moter will reverse. Anyway that was my expirance.

 

[falleafd]

You should try with H bridges such as L298, TA7288P or some similar driver chips. And use a zener in your application.

 

[ante]

Falleafd, have you tried to parallel 100 L298? This is if you want to handle the current to a car starter. It will be an interesting PCB layout. Good Luck.

Ante :roll:

 

[falleafd]

Truthfully, I'm in Vietnam, and I don't have enough money to buy even 10 L298, I cannot imagine to use upto 100 chips. And of course, I've never try to use 2 L298 in parallel, because with one L298, I got 4A driver, and it's enough for my stuffs.

But if you had built your board, would you pls send meeh it? I will a worth pcb in my future applications. Perhaps, I will build 8A or 20A motor driver with it??? I don't know, but if I will build a board for a real manipulator, perhaps it's needed.

For starter, I think I got another one. I can buy old industrial mosfets upto 100A and it's no problem.

 

[nettron1000]

Dstich, if you have access to an auto scrap yard go for the wiper motors and some vehicles have power window motors, obviousely both can go forward or reverse (cw,ccw).

 

[falleafd]

Sorry, I didn't understand the question clearly, because my english is not good enough. Then as dstich say many thing around going forward and inverse, I didn't read the first line clearly. He need to driver a carstarter, but I think he is a starter on robot . so sorry.

I don't know muchie bout car, but the honda motorbike starter. I can buy starter with ease and of course, it work with 12VDC batteries. In my country, motorbike is the main means of transportation.

However, starter creat a great tours upto dozen thousands rpm. And I don't think it's good for a robot.

Besides, the max current on the starter can get is about 4A only, because I used the small 4A - 12VDC batteries to drive it. The normal motor is only about 180mA, 250mA or higher such as 500mA.

I don't know what ante means as telling meeh to use 100 L298, were you teasing meeh? Well, sorry because my English is not good, and I didn't understand ur joke.

As I know about motorbike starter, it creat a great rpm and via the gear, it generate a strong torque to start the motorbike.

You can imagine that, a normal fan is only 40W which use 220VAC, that is the current is only about 260mA.

And I think it's the same to car starter in principals. And for sure, you can build 7A motor driver with D718.

 

[Nigel Goodwin]

Besides, the max current on the starter can get is about 4A only, because I used the small 4A - 12VDC batteries to drive it. The normal motor is only about 180mA, 250mA or higher such as 500mA.

Hi falleafd,

Your motor bike starter motor will take a great deal more than 4A, the 4A isn't the maximum current your battery can provide - it's the batteries capacity, it should be able to provide 4A for 1 hour, so it's rated at 4AH.

I would imagine the starter probably takes upwards of 30 amps?.

I don't know what ante means as telling meeh to use 100 L298, were you teasing meeh? Well, sorry because my English is not good, and I didn't understand ur joke.

No joke (except that you wouldn't use L298's for a starter motor), a car starter motor takes in the 100's of amps - just look at the thickness of the cable they require! - bearing in mind that both the cable and the motor are only rated for short term use.

 

[falleafd]

Yeah, thanks Nigel, car starter generate much stronger current than motor bike starter.

I'll measure again the motor bike starter for sure, but I did drive it with D718 of which max current is only 7A.

And I have a 12DC motor which has the thickness of wires similar to my starter, but as I measure the current, it's only 1A. The thickness is about 1.5 mm.

Well, may we compute like this?

We can use the hand to push the lever to start the motor. And our hand can generate about 70 W for normal, and about 200W in a short time. (as I remember) Then the starter use 12VDC, the current can reach 200/12 = about 15 A. Yes, now I can imagine if the starter can get 30A at beginning.

But I still don't think my starter get that current. Because my board wasn't burnt. Thanks muchie nigel for this info.

What happen if we do this? I accelerated my robot with a spring and after that apply the voltage to it. Then we can pass the start current through the motor? But the normal current, if i get 30A Well, I dont know.

Yup, but if you need 100s of amps, we can use the industrial mosfet here. I got one at 100A, and I think we can find 200A ones or higher. How bout this nigel?

 

[goodpickles]

on the robot the starter motor doesn't have to work as hard. So it only takes 1/3 to 1/6 as much current as it was intended to.

 

[falleafd]

No, as nigel say, I have to test again with the motor, because if the motor is at 30A, you cannot run it with 4-7A driver. But these days I'm so busy, but as I test it, I will tell people here.

As a motor start even a starter or a normal motor, it will reach peak current at the first moment, and it will damage the unsuitable drivers. 2 years ago, I burned one of my driver for this reason, because I didn't take the first moment current into account.

With some special control algorithm and some protection, you can reduce this damage, but normally, we should drive the motor lower than the usual current of course, we never drive a motor at peak current.

Well, anyway, thanks nigel and goodpickels, I'll test and tell you later.

 

[Nigel Goodwin]

With some special control algorithm and some protection, you can reduce this damage, but normally, we should drive the motor lower than the usual current of course, we never drive a motor at peak current.

Aso be aware of the stall current - although you would probably struggle stalling a car starter motor - but it's going to be a huge current.

Your motorbike starter may work quite happily under low loads, but under high loads (or stall conditions) the current will increase by a massive amount.

I tested a small DC motor in a robot a couple of years ago, under normal running it took only a couple of 100mA or so - but when stalled it took over 6A, and I suspect that was limited by the battery I was using.

 

[falleafd]

I tested a small DC motor in a robot a couple of years ago, under normal running it took only a couple of 100mA or so - but when stalled it took over 6A, and I suspect that was limited by the battery I was using.

No, we never drive a motor at that current. We usually drive it at normal current. And that why I used the spring to accelerate the starter before running it.

For high current, that is the motor seems to stop, and the robot seems to not move, we should stop the motors and move the robot back.

The real problem is coming as we first accelerate it. Because at that moment the motor is stopping, and as you want you accelerate it, you need strong current.

And to solve this problem, I use a spring to let the motor turn first, after that, everything is oki.

 

[ante]

Please explain the “spring start” of your motor.

Ante :roll:

 

[falleafd]

The fact that, I use a mechanical spring to acelerate the robot before it start. I used it on a competition, and I wanted it to go fast to a target. Only in this case, I use motorbike starter. I've never used starter for the robot in normal applications.