100watt- 400 watt transistor to drive dc motor

[Mechatrommer]

assuming your current knowledge, i will do this (attached) when i was a kid, this is my "invention" called "dpdt bridge" no bodged power resistors mess, no transistor and math headache, and the cheapest and most efficient possible solution.

[krayvonk]

Thats excellent thanks.  I bet that operates at the full power of the battery!

When does what we do get into the stage of "impressing others" instead of making you look like a lunatic on the internet?

[ratatax]

i think what you are searching for is:

[Mechatrommer]

Thats excellent thanks.  I bet that operates at the full power of the battery!

yes thats the idea when driving a motor, power needed is what power given (to the motor, not to the power resistors). want slower motor? use smaller voltage battery like 1.5V AA. another solution is $1 buck converter from china. but if you insist well, i've given you the other solutions much earlier.

[krayvonk]

NEEDZ MOR RESISTAHZ!

[gcewing]

So is the difference between 400 watts and 100 watts significant?

The difference is 300 watts -- that's a serious amount of power!

You don't seem to have much of a feel for what these numbers mean, so to put it in perspective, here's something that dissipates 500 watts:

http://www.goldair.co.nz/product-catalogue/heating/panel-heaters/gph150-500w-mechanical-panel-heater

And you're thinking of wasting this kind of power for each axis of your robot. If your robot has 3 axes, that's getting on for 1000W -- enough to heat your living room in winter!

Do you see how impractical the idea is now?

As you've found, transistors are cheap. 300W power resistors, by comparison, are not cheap -- Mouser is listing them for around $30 each, and that doesn't include all the heatsinks, fans etc. you would need to get rid of the waste heat.

Just use a 4-transistor H-bridge, or a chip made for the purpose. It's the only sane thing to do.

[HackedFridgeMagnet]

Here I found a 400W transistor for you.

Guys just answer his question, no need to overthink this.

[krayvonk]

Thanks gcewing for the info.  (Yes I am way out of whack still,  I need to take in more information.)

$30?  Thats more like it,  all the transistors I was looking at were cheaper than the photo resistors! It was a little illogical seeming.

Base in the middle is the only way to do it.

[Mechatrommer]

haha thats a nice trick! TO-18 can for 400W, you'll need to buy 10 of them until you figure out the truth. but then (if it is), you are going to need 500W PSU, my earlier link will cost you $1000 china brand. here's better deal i just remember i built (invent?) a "h-bridge esc" a while a go for my rc project, made the pcb but have not assemble and program it since i put rc project on hold. its designed to accept PPM or PWM signal and also from potentiometer, to control both directions and speed. in the rc market this kind of board only can control bldc 3 wire motor, and only PPM signal from radio receiver, where my board can use normal 2 wired brushed motor controlled from either 3 types of signal. for your project i guess potentiometer will be a convenient one. if you want i can assemble, program and sell to you at $60, no need upgrade psu, no need to buy even 2pcs 2N2906 to find out that you will be left with nothing. your 30V 3A PSU can make your 100W motor jump across room if you want or if not careful, and can be as slow as snail controlled with potentiometer, 80% efficiency guaranteed. with 2 pairs of IRF3205 and IRF4905 combo in the bridge, it can drive up to 1000W motor theoritically. just upgrade to 1KW PSU and start killing living things if you want to, cheers

[krayvonk]

I dont need a 500 watt psu if i can just put a couple of wires in the wall socket. (+ and -) and I dont even need to wire up an oscillator either!

Wow man, you know alot.   Did you draw that whole schemmy up for me?  Very nice.  (I actually like it alot, I wish ppl would show work here more often, is it uncool?)
The $60 offer is nice,  for my project ill at least be spending about $100 on my components, But it just doesnt seem honest if I dont do the hard work myself.

And... Whats everyone got against potentiometres!  arent they as good as a relay if u glue them to a dc motor?

[TheHolyHorse]

I dont need a 500 watt psu if i can just put a couple of wires in the wall socket. (+ and -) and I dont even need to wire up an oscillator either.

If you're actually considering putting some wires in the mains outlet, please don't for your own and everyone else's safety.

I'd suggest you start over from the beginning, forget everything you know about electronics and get someone to teach you and actually listen.

[atmfjstc]

There is NO WAY this guy isn't trolling. The only other possible explanation for his style is if he were a 13 year old kid - but his Youtube channel disproves that.

[TheHolyHorse]

There is NO WAY this guy isn't trolling. The only other possible explanation for his style is if he were a 13 year old kid - but his Youtube channel disproves that.

I wouldn't be so sure, he seems dead serious. Not everyone is meant for electronics and some should outride stay away from it. That's just how it is.

[krayvonk]

I agree with you.   Maybe I should just stick to raytracing, newton physics engines and artificial intelligence on the gpu...  and never bother making a computer, cause its just too hard...  assembler is just gobblegook better stick with high level its much easier, and get back into the kitchen where i belong.

[Zero999]

half goes in the motor,  half is wasted.  its only half.   

A linear power supply controlling a load will dissipate half the power, but that's only when half the voltage is being dropped across the load.

Consider a 1 Ohm resistor connected to a 10V power supply. The maximum power dissipation will be P = 10²/R = 100/1 = 100W.  If a resistor is connected in series with the load to control the power level. Say we select a resistor value to sweep the voltage across the load between near 0V and 10V. We can't go all the way to zero or 10V, because it would involve a resistor value with zero or infinite resistance, which is impossible and will give a division by zero error. The plot shows the maximum power dissipation in the series resistor is only 25W.

Note how the power in the load shows a square relationship with the voltage. The maximum power dissipated in Rs is a quarter of the maximum power dissipated in the load.

 linear PSU power dissipation.asc (0.74 kB - downloaded 33 times.)

[Mechatrommer]

There is NO WAY this guy isn't trolling. The only other possible explanation for his style is if he were a 13 year old kid - but his Youtube channel disproves that.

NO. this guy reminds me of my younger brother. this type of guys is for real... if you have family of this type, you'll understand when they stated...

I never went to uni,  and in electronics class I was only a teenager so I thought it was more cool to not listen to the teacher.

i guess they got sucked by a mentality/propaganda/idea that skills is more important than knowledge/academic. the good thing is he got some balls in trying electronics, better than be on the street.

[Ice-Tea]

I dont need a 500 watt psu if i can just put a couple of wires in the wall socket. (+ and -) and I dont even need to wire up an oscillator either!

Feel free to ignore everything everyone is saying *except* for this: don't jam wires into the wall socket. Just... don't.