can i draw 10 amps

[annoyin_kid]

aye wassup guys hope u guys had an awesome new year

i was wonderin if u guys knew if i can draw 10 amps from an 08m if i put 10A into it so i can power a high speed motor.

can i also take this circuit:
http://i14.tinypic.com/29mljqb.jpg
(the grounds are ment to be joined)

and instead of the 9v battrey for the uln2003 can i add a series of 10,000mAh battries for a total voltage of 7.2V and still be able to draw 10A from the uln2003 to run the motor.

the motor is a mabuchi 540 which uses 7.2V and a maximum of 10A. it is a high torque motor and comes with built in capacitors.
(the motor is the kind used in power drills)

ak

 

[BeanieBots]

Asolutely no chance whatsoever. You are WAY off mark.
The PICAXE can supply about 20mA.
The ULN2003 can supply about 500mA per output.

You can double up outputs to increase current but the chip total must not be exceeded. I can't remember what it is.

The 540 motor which you want to drive is a "standard" in the electric car racing circuits and can be driven at several hundred watts for short bursts. To do this, racers use banks of FET transistors. This is not so much because one FET cannot handle the current but to reduce the on resistance to an absolute minimum to get the most out of the battery pack.

Consider getting yourself an RC car speed controller and using the PICAXE servo command to control the motor speed.
If you only want on/off, then your simplest solution would be to use a hefty relay. (don't forget to use a transistor to switch the relay on and off).

 

[Marcwolf]

Or read up on Power MOSFETS

They are semiconducting switches that can handle a lot of power.

This link has soem basic information
http://www.dse.com.au/cgi-bin/dse.filereader?459b686d050d9722273fc0a87f9c0716+EN/catalogs/SUP1000100

as for power this one

http://www.dse.com.au/cgi-bin/dse.storefront/459b686d050d9722273fc0a87f9c0716/Product/View/Z1853

can handle 600v at 60A

Have a look on google and see what you can find.

Take Care

Dave

 

[annoyin_kid]

are u sure that an esc is completly compatable with picaxe beaniebots? is there any way i can construct my own simple esc with forward and reverse capabilities?

also what does a mosfet do in simple terms? i saw the link with "basic information" and totally blanked out.

ak

 

[Jeremy Leach]

Wikipedia is a great resource for all sorts..
<A href='http://en.wikipedia.org/wiki/Field_effect_transistor' Target=_Blank>External Web Link</a>

And the electronics club is excellent too, although it only seems to cover junction transistors.
<A href='http://www.kpsec.freeuk.com/components/tran.htm' Target=_Blank>External Web Link</a>

 

[BeanieBots]

Yep, used RC speed controllers with PICAXE frequently. The newer ones tend to have auto 'stick' calibration which means you need to write a little routine to do whatever the documentation that comes with it says you need to do.
I even use the cheap &quot;do it yourself&quot; kit from Maplin with larger transistors for higher currents.
Many of my robots can be either PICAXE or RC controlled so it makes life much easier for me to use ready made speed controllers that can accept a standard servo signal. Also, you can get 150A capable ones that fit in a matchbox for around &#163;30 if you shop around.

I just did a quick search to see if could find you some cheap ones. There's loads out there but have a look at the tech notes for some of the higher specs ones at the site.

http://www.towerhobbies.com/products/duratrax/dtxm1055_n.html

1200A continuous, 4700A peak and little extras such as traction control for around $80. OK, overkill for a 540 motor but you'd be hard pushed to make your own to that spec for less money.


Edited by - beaniebots on 03/01/2007 21:10:58

 

[annoyin_kid]

would the motor burn out if i got it to turn forward and then suddenly got it to turn back? its the tyres that get affected right?

if it doesnt then i dont really need a esc with abs, traction control or brakes even cuz i want the tyres to skid so i can get the car to go into a drift and cuz i love the noise of tyres ripping up on concrete

 

[BeanieBots]

The motor will only burn out if you over rate it. Are you doing that by reversing it?

There are a million and one variants of the 540 motor ranging from about 50W to 400W. You've not said which one you have or what voltage you will drive it at. Unlike many other members of this forum, I'm sorry to say that I am not clarevoyant.

Your original design was uni-directional so I assumed you were building a plane.

As I said, there are hundreds of speed controllers available to cater for however simple or complex you want. The link I gave was only a single example of what is available and to show just how cheap they are and what other features they come with. The top of the range one shown can handle enough power to drive a full size car!

Edited by - beaniebots on 03/01/2007 22:39:27

 

[andrewpro]

I'd be careful about that beaniebots! I have a really big feeling they're full of...well...they're not telling the whole truth.

They're running 1200 amps continuous through 14 gauge wires? The whole thing is only a few cubic inches? The heat sink for this 1200 amp continuous current is less than 1.4 ounces, and has to dissipate at least 720 watts? And all of this is at 100% efficiency, which isn't possible.

It doesn't add up, especially for only 80 bucks, for a lot more reasons than that as well.

Just an observation

--Andy P

 

[moxhamj]

That power mosfet marcwolf suggests looks good to me. You don't need to understand much mosfet theory. Can it turn on and off with 5V (yes), can it handle 10A (yes) and what is the on resistance (0.028 ohms - probably lower than the wires connected to it). All for $5. One picaxe and one mosfet and you can have the motor going on and off. Then add pwm. Then add a reversing relay. Do it in stages and keep it cheap!
Re skidding tyres - failure modes could be an overheated stalled motor, stripped gears, cooked mosfet or overheated batteries. If none of those things happen, you can have the skidding tyres.

 

[BeanieBots]

andypro, I agree. 1200A, 14 gauge?
However, I have seen and used similar units at 250A with very little heating of the unit itself so although it sounds a little far fetched, I would not regard it as impossible.

 

[annoyin_kid]

so wait a mosfet is kinda like a relay -
to turn it on i have to put voltage through the gate. i then add a higher voltage/current into the source and i get the same higher voltage/current from the drain.
if i stop power going into the gate then the source and drain stop conducting.
is this description of the mosfet kinda right?

about the 540, i thought it was kinda obvious that i was making a car but i see why u got confused beaniebots because i didnt really say i was making a car.
the motor didnt really say how much watts it uses but its max specs are 7.2V and 10A so that means it should use 72W.

Dr_acula:
what does a pwm do? i looked it up on wikipedia and it said it controls the pulse width to send information. but in my circuit what would i be sending informaion to? is it to the reversing relay?

ak

 

[Dippy]

Yup, its kinda like a relay. But not so simple...

But, (to pre-empt a 500 line post describing FETs with no breaks or paragraphs) I would seriously suggest you find a page/book with good picture-based descriptions and examples. It sounds like you are awesomely new to electronics.

To use them without the demon smoke it is essential you grasp the basics. Maybe you could forget undestanding them and just find some example circuits somewhere. But, unless you want to copy all your project circuits, it is important to get the basics and learn to understand Data Sheets - especially if you are doing something novel.

And yes dude, I had an awesome New Year, along with an awesome headache.

 

[annoyin_kid]

yea im tryin to look for some kinda electronics for dummies

 

[Dippy]

How about &quot;Electronics for Dummies&quot;. There are loads of books around.
2 disdavantages:
1. You'll have to buy it - unless you local lending library stocks it.
2. You'll have to read it ...

The basics are really necessary. After all, if you ask a question but can't get your head round the answer then that's going to set you back - and produce a 10 page thread.

 

[moxhamj]

New project I started last night and almost finished - a proportional RC car controller using picaxes and 433Mhz modules. Annoyinkid, I'll keep you posted as I am solving most of the problems you are up against. PWM is pulse width modulation, and is used to control the speed of motors. Eg if you turn a mosfet on half the time and off half the time, and do it 100 times a second, it behaves as if you are putting half power in. Very useful for controlling speed.
Mosfets are more like on/off switches. It is possible to run them like transistors where the output current is proportional to inputs, but it is much simpler to turn them on and off very quickly and change the ratio of on and off. The picaxe has a single command - pwmout, that does this. Pulsout also works.
An RC car is a great place to learn about all this as the mechanicals are already done. You can then scale up to bigger things.

 

[Marcwolf]

One of the advantages of MOSFETS over transistors is that when a MOSFET is turned on fully (as in a switch situation) it does not dissipate much heat.

I have driven from a 30ma LED to a 120W headlight without any issues with MOSFETS.

Hope this helps.

Dave

 

[premelec]

I'd like to try clarify this a little... A transistor when driven ON has a small voltage from collector to emitter with current - a FET when turned on looks roughly like a small resistance = Rdson so the voltage is amps times Rdson - depending on application one or the other may be best and there is a hybrid IGBT Insulated Gate Bipolar Transistor which combines the best of both for some applications. Rdson is low for low voltage MOSFETs but gets higher as their voltage rating goes up. In general at low voltages the MOSFET is easiest to get low V drop - note that MOSFETs need more careful handling as static can injure their gates - and you need to use 'logic level' units to drive the MOSFET with a PICAXE.