PDA

View Full Version : PWM help



jriggs_18
09-03-2008, 06:59 AM
Now that Ive built my first cell/unit, im getting ready to make it road ready but Im a PWM dummy. The cell is 2 sequential "smack" cellls, they are a little different than the smack but similar. For this unit I am equipping it with 2 simple 30a Pwms ordered off fleabay. But for my other unit I am working on I want to use a high accuracy PWM with precise frequency tuning, the problem with building one is i am a dummy, I am a freshmen in the electrical engineering program:o Is there anyone out there that would be willing to talk to me about what I have to do, or would anyone be willing to help assemble my board if i buy the parts? I have big ideas in mind for my unit, but I need some help and dont really have time to take to learn all the PWM / Microelectronics. Honestly, If someone could explain to me in simple english i could probably do all the assembly

Now I know the first thing is choosing my circuit, and to answer that question I have to know what features I want. I want all the frequency and waveform controls I can have, also want current limiting and so on...
This cell is capable of carrying well over 200A constant by using the .5A per sq in of + surface area. And I intend to use as much current as I can. The cell is constructed of a SS Tank and SS cell, however im sure 200a constant would overheat it

I also am going to build a dry graphite cell and will want the same deal with that at less Amps, maybe 50 or 60 amp pulsed
My intentions are to achieve resonance, I have read a fair deal on it and believe it is going to be difficult put possible

Can anybody help?

Dewayne
09-03-2008, 09:27 AM
Most PWM's are two NE555 timers wired front to back. The first timer controls the on/off time of the second one. The second one is set to the frequency that produces the most gas.

There is no real current limiting in most PWM's. With the 1st stage controlling the on/off time it is more of a heat limiter.

I have found a PWM circuit that has a current limiter in it, but there is no text with it.
with no text it's hard to guess it's design capabilities.

http://www.uoguelph.ca/~antoon/circ/pwm324.html

I'm guessing that R10 in the lower right corner is a rather high wattage resistor.

I suggest a PWM that will go up to 30khz.

bdannels
09-03-2008, 06:36 PM
Hello:

Go to http://www.youtube.com/watch?v=bjxKsCdpr0Y&feature=user

5 Videos will walk you through everything! :)

Later
Bill

jriggs_18
09-08-2008, 09:44 AM
Could anyone tell me what components will need to be used to handle high current like 100-150A pulsed at 50-75% Duty? Any webpages I can get a parts list from? I think If I have a schematic & parts list/source I can assemble the board?

How do you setup the 555's to handle the high current? What device sets the frequency? What is the purpose of the MOFSET? Any thing else important to know? (besides everything)

jriggs_18
09-14-2008, 04:39 PM
Well I decided to go with Zero Fossil Fuels design, I built it and now the problem I am having is that I cant adjust the current limting, when I give the PWM 12V it allows my cell to draw it max current. The pots dont work right, I double checked the pot wiring its all correct. The 4700uf cap is wired from 12V to GND, is it supposed to be to the Cell (-)? Also I am confused now about the transient diode, I have it wired Cathode @ Source of Mosfet and Anode @ Drain? is that right? What could be going on with it?

Is anybody familar with or even replicated it, can you help me out??? Ill try and get pics up of what I got today.

jriggs_18
09-14-2008, 05:08 PM
Here are the pics, sorry they are so crappy Ill try to get better ones up soon

H2OPWR
09-19-2008, 04:43 PM
The 555 chips do not handle high current. They will only handle milliamps. The Mosfets handle the current. The 555's are only timers that turn on the Mosfet with a low current pulse. A mosfet is just a solid state relay. A PWM is just a dc motor speed control that produces square wave pulses of whatever voltage you are working with. They are simple but tedious to make. Unless your time is worth less than .50 cents an hour I suggest buying one. A 30 amp PWM can be found for around $25.00 part #MX066. Just google it and you will find the same things the screwers on you-tube and e-bay are charging sometimes 100 to 200 dollars for. There is a frequency adjust kit for it that is easily added on for around $11.00. As for a 100 to 150 amp cell good lock. It better be huge or all you will make is steam after an hour or so of operation.

jriggs_18
09-22-2008, 06:12 AM
Well I ended up just buying a premade Zero PWM, works well, and I am now done with the PWM, next time I need one I will just buy it, and not try to build it, no Thanks:eek:

RICHARDDOBYNS@HOTMAIL.COM
02-20-2009, 11:15 AM
can you tell me where s+ and s- go? this printed board thanks

RICHARDDOBYNS@HOTMAIL.COM
02-20-2009, 11:20 AM
no c7 from + to _ not cell