However I want to scale it up to the 50A. I know I can use a bunch of IRF7832s in parallel to support the 50A current however this can only be DC (from what I understand anyway). I wanted to know if there is another way which would allow true AC. An Op Amp does exactly what I am after, however the max amps is about 1A. Which means I would need a lot of them in parallel, which is not practical. Hence why I am asking this question.
what you mean by true AC and how does an op-amp fit the picture ? what you need is a 3 phase bridge and feed it with 3 phase signal (you can PWM the 3 phases to simulate "true" AC) generated by a micro-controller or FPGA or a dedicated BLDC controller chip.
By true AC, I mean both positive and negative voltages. I have now been successful in creating a 3 phase inverter circuit and I can used IRF7832s in parallel to handle the 50 amps. However I would like to experiment with a circuit I created using op amps (it works in a simulator), which gives me perfect sine waves phase shifted 120 deg apart, but because op amps can't handle more than 1 A, it won't work without additional components (which BTW is what I am asking for).
how does op amps fit the picture? Because no current flows in or out of its inputs, there is a separation between the low current part of the circuit (powered by the A20) and the high (powered by the battery). Not only that op amps can also handle true AC which transistors can't.
But anyway, it looks like I need to ask on a different forum, because there seems to be a bad culture on this forum. A culture where you only get a responses like "actually it's nearly impossible for a newbie" and no actual answers which I can research further on to find the right solution. In programmers land, most forums never give you "your not good enough" answers (I actually don't know any that do).
don't expect different answers on a different forum why ? you will realize it later on when you'll read your post few years later
if i understand you correctly.... then you wish to create some kind of 3 phase sinewave VCO out of opamps and drive the BLDC with that signal ? that won't work - you have to drive the BLDC according to the position of the rotor's magnetic field (therefore the hall sensors required or the other method - measuring the induced voltage on the wire which is not driven in that very moment).
another point is the current bigger than 1A - have you ever heard about amplifiers ? op-amp + external output stage stage will do the trick (like many of the audio amplifiers with op-amp input stage). but anyways ... driving any kind of motor drawing 50A in peaks with a sine-wave coming out of a B class amplifier.... good luck with that
probably you're confusing the BLDC with a 3-phase asynchronous motor (the squirrel cage one) - the variable frequency 3 phase sine-wave would be able to drive that squirell-cage motor but not a BLDC.
Those were the words I was looking for. Now I can do some research on the different classes of amplifiers and find the best way to handle the 50A draw.
Linear drive is certainly feasible but you will end up with something rack sized and heavy that will heat your whole room.
I'm working on sam me thing now, and I actually got spinning rc motor so far. I used 3x 4606 MOSFETs, and simple MCU to drive them. Just square waves. Check YouTube about how bldc motors works, that helped me a lot. Along with reverse engineering chinese ESC from ali. Next step for me is implementing induction feedback.
What I am now researching on, is what transistor to use. What I am confused about is the Power Dissipation figure they give you. Like for example the 4606 has a Power Dissipation of 2W. Does that mean that if Vds is 30 and Id is 6, that the heat generated by it will only be 2W?
What I am now researching on, is what transistor to use. What I am confused about is the Power Dissipation figure they give you. Like for example the 4606 has a Power Dissipation of 2W. Does that mean that if Vds is 30 and Id is 6, that the heat generated by it will only be 2W?
Absolutely not. The rated power dissipation of 2 watts means it can sustain 2 watts of continuous loss with some recommended printed circuit board pattern at 25C without melting. That could be 2 volts Vds at 1 amp or 4 Vds at 0.5 amps or 4 Vds at 4 amps with a 12.5% duty cycle or something else.
At maximum continuous rated Ids with full enhancement, power dissipation will be something like 1 watt = 6^2 A * 0.030 Ohms but the rated pulsed drain current is 5 times higher.
What I am now researching on, is what transistor to use. What I am confused about is the Power Dissipation figure they give you. Like for example the 4606 has a Power Dissipation of 2W. Does that mean that if Vds is 30 and Id is 6, that the heat generated by it will only be 2W?
Look at Rds(on) - this will give you the Static Drain-Source on resistance, Typically 25milliohm. If we look at the maximums - If we push 6A through a 25millohm resistor ohms law give us a dissipation of 150mW, well within the 2W maximum.
Look at Rds(on) - this will give you the Static Drain-Source on resistance, Typically 25milliohm. If we look at the maximums - If we push 6A through a 25millohm resistor ohms law give us a dissipation of 150mW, well within the 2W maximum.
P=I^2R
6 amps through 0.025 ohms is 0.15 volts. 0.15 volts times 6 amps is 0.9 watts.
It is still comfortably within the maximum power ratings.
Look at Rds(on) - this will give you the Static Drain-Source on resistance, Typically 25milliohm. If we look at the maximums - If we push 6A through a 25millohm resistor ohms law give us a dissipation of 150mW, well within the 2W maximum.
P=I^2R
6 amps through 0.025 ohms is 0.15 volts. 0.15 volts times 6 amps is 0.9 watts.
It is still comfortably within the maximum power ratings.
Look at Rds(on) - this will give you the Static Drain-Source on resistance, Typically 25milliohm. If we look at the maximums - If we push 6A through a 25millohm resistor ohms law give us a dissipation of 150mW, well within the 2W maximum.
P=I^2R
6 amps through 0.025 ohms is 0.15 volts. 0.15 volts times 6 amps is 0.9 watts.
It is still comfortably within the maximum power ratings.Sorry, you confused the hell out of me, until I Googled the actual formula:
V = I * R
P = I * V
Therefore P = I * I * R = I^2 * R
So to confirm my understanding of it. If I pick a transistor that has 0.0021ohm Rds(on) and I have a 50A load. The power loss would be:
V = 50A * 0.0021ohm = 0.105V
Because there is a diode in a transistor, I have to add 0.7V which gives me a total of 0.805V. So:
P = 50A * 0.805V = 40.25W of power
Using a RthJC of 2.0 C/W. The heat generated by the transistor is Max 2 C/W * 40.25 W = 80.5C (or Typical 1.4 C/W *40.25W = 56.35) above Ambient. Given that the current temp in Brisbane is 29C, the actual temp will be 80.5 + 29 = 109.5C Max (85.35 Typical). And if the Max temp for the MOSFET is 150C, I am well within the specification.
And to get the thing to turn on (Vgs = 1.2V), I need a min D and S of 0.805V, and 1.2V on G.
Have I understood all of this correctly?
Look at Rds(on) - this will give you the Static Drain-Source on resistance, Typically 25milliohm. If we look at the maximums - If we push 6A through a 25millohm resistor ohms law give us a dissipation of 150mW, well within the 2W maximum.
P=I^2R
6 amps through 0.025 ohms is 0.15 volts. 0.15 volts times 6 amps is 0.9 watts.
It is still comfortably within the maximum power ratings.Sorry, you confused the hell out of me, until I Googled the actual formula:
V = I * R
P = I * V
Therefore P = I * I * R = I^2 * R
So to confirm my understanding of it. If I pick a transistor that has 0.0021ohm Rds(on) and I have a 50A load. The power loss would be:
V = 50A * 0.0021ohm = 0.105V
Because there is a diode in a transistor, I have to add 0.7V which gives me a total of 0.805V. So:
P = 50A * 0.805V = 40.25W of power
Using a RthJC of 2.0 C/W. The heat generated by the transistor is Max 2 C/W * 40.25 W = 80.5C (or Typical 1.4 C/W *40.25W = 56.35) above Ambient. Given that the current temp in Brisbane is 29C, the actual temp will be 80.5 + 29 = 109.5C Max (85.35 Typical). And if the Max temp for the MOSFET is 150C, I am well within the specification.
And to get the thing to turn on (Vgs = 1.2V), I need a min D and S of 0.805V, and 1.2V on G.
Have I understood all of this correctly?
Because there is a diode in a transistor, I have to add 0.7V which gives me a total of 0.805V. So:
P = 50A * 0.805V = 40.25W of power
And to get the thing to turn on (Vgs = 1.2V), I need a min D and S of 0.805V, and 1.2V on G.
Technically not power, but that's nitpicking I don't want to go in to.
The diode is probably reverse biased, so I don't see how adding 0.7V would help.
Moreover, getting a diode drop of 0.7V at 50A is a very good diode.
You need to multiply 50A x 0.105V = 5.25W loss.
RthJC = thermal resistance Junction-Case. That is not ambient.
You need the RthJA figure, which is the total "series" thermal resistance from junction to a typical use-case of free-standing TO-220 for example. That is usually in the order of 60 C/W.
As a general rule of thumb, assume you can dissipate 1-2W in side a single TO-220 with no heatsink, but at 2W it's really really hot.
The gate voltage is measured against the source voltage voltage.
For a low-side driver the gate is tied to ground. 1.2V (compared to the gate.. so compared to GND) the MOSFET will open very slightly (note: the Rds on is huge and you will blow the arse out of the MOSFET with any significant current).
For a high-side driver N-channel mosfets are usually a bit of a pain, because you need to drive a voltage above the supply voltage (e.g. VCC is 12V, you would need 13.2V for the threshold voltage). A P-channel MOSFET or MOSFET driver are quite useful for that, but you may need to take into consideration if there are any duty cycle limitations.
VDS is a maximum voltage the MOSFET can withstand when it's OFF. If you exceed it, you will kill the MOSFET. The diode that is drawn is more of an "artifact" during the production processes than actually desired, and you need to remember that it's there (i.e. it is not a bi-directional switch) but I personally would not intend on using it.
Now I know enough about transistors and power dissipation, I just need to pick one that meet my specs, then start building the thing and testing it. That's where the fun will hopefully start.
Now I know enough about transistors and power dissipation, I just need to pick one that meet my specs, then start building the thing and testing it. That's where the fun will hopefully start.
Based on drawer filled with blown transistors and pieces of transistors and my experience with learning how to design high power switching regulators, I recommend picking up a good face shield as well. A hockey mask might intimidate the design into working or at least not exploding. A catcher's mask has a certain amount of style but I would wear eye protection under it:
https://www.youtube.com/watch?feature=player_detailpage&v=0ds0wYpc1eM#t=132
Are you going to start a power transistor failure mode pool? My vote is disappearance.
[...]
It depends on what you call fun. Over the past 2 months I have had so much fun learning about how electronics work, and how sub-circuits work. I also have been successful in building a circuit that can read the 3rd wire and power a small BLDC motor (I am a fast learner).
However I want to scale it up to the 50A.
[...]
[...]
It depends on what you call fun. Over the past 2 months I have had so much fun learning about how electronics work, and how sub-circuits work. I also have been successful in building a circuit that can read the 3rd wire and power a small BLDC motor (I am a fast learner).
However I want to scale it up to the 50A.
[...]
Rolling the discussion back a bit. By your own words you are a raw rookie (see above & nothing wrong in that). As others have already pointed out, in your project this (50A) is the point where a) it gets tricky and b) far more than elementary knowledge is required. Fast learning is good, but it won't replace experience. You are trying to build a (relatively) high current PWM driven polyphase modulator - in the entire recorded history no rookie has ever accomplished this. You might be the first one but what are the chances of that...?
Please don't take offense because this is not meant as such. But frankly, you need to aim lower initially. You do have a steep and high learning curve ahead and need to recognize that your confidence springs from ignorance. You know - fools go gladly where angels fear to tread.
... Things that seemed to work nicely just failed spectacularly and unreasonably a moment later. ...
Have it hang, or miscalculate your dead time and youre blowing up fets. Too much gate resistance and youre overheating and blowing up fets.
Do you have a scope though? It would be rather difficult to diagnose and figure out exactly why youre blowing up FETs if you dont have one.
When you find a limitation to that board that you cant fiddle with or tweak, then you move onto making your own since you know why you need, and what makes up a better one.
I know how CPUs can stop working for no reason at all.