How to use LM556 PWM for Freq & Duty cycle?

Discussion in 'Off-Topic' started by Elad, Jul 1, 2008.

  1. Elad

    Thread Starter Member

    Jul 1, 2008
    11
    0
    Am trying to make a simple PWM that has a wide range of frequencies and wide duty cycle of the frequency.
    So, to the experts out here am asking :p

    This is for HHO generations so do not know at this time where I have to be with frequency (from Hz's to MHz's).
    Will be driving 4, 2N3055 Transistors for high-current loads (not shown)
    Also, what is the max freq's of the LM556 & 2N3055's that I can expect?

    Came up combining from other 555 circuits into making this for the LM556.
    Before I assemble (need to order parts), will this work?

    [​IMG]
    I used the output (5) from left side (freq side) to the Control V (11) on Right side (duty cycle) [pin 5 out to pin 11].
    Is this proper way to do it?
    Values of components ok?

    Or, will this circuit be ok to do the same thing I want (Freq & Duty)?
    [​IMG]
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Try using the search function with the terms "PWM" or "pulse width modulator."

    You won't find any HHO "true believers" here. Use the search function with the term "HHO" to find why not. Optionally, you could search on "hype" or "urban myth."
     
  3. Elad

    Thread Starter Member

    Jul 1, 2008
    11
    0
    Requardless what my purpose is, I still have these questions.
    After many sites, I came up with this diagram of 556 (I made)...
    The 555 circuit came off the web somewhere....
     
  4. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Generally you won't get both in a single 555 (that's why the dual is shown), although I have seen some decent methods. Just for PWM on a 555 I like this circuit...

    [​IMG]

    The freq doesn't change (though you could change C).

    Another scheme for PWM is a Class D Amp...

    [​IMG]

    So how technical are you? I've never built either one of these circuits, but I'll get around to it eventually.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Most 555/556 timers "run out of steam" at around 500kHz.

    555/556 timers' output frequency will vary somewhat when the supply voltage fluctuates. If you manage to find the "sweet spot", you'll be quickly thrown off with a minor change in supply voltage. For example, your engine is idling, you find the "sweet spot" and step on the gas. Your alternator starts putting out a higher voltage, and your timer changes frequencies. To avoid this, you could use a low-dropout 10V regulator to ensure a somewhat more stable frequency output. Being an RC based timer, it will never REALLY be stable, but it will be better with "real" voltage regulation.

    You need caps across the 556's supply and ground pins. 0.1uF, 10uF, and perhaps 47uF to smooth things out. There are large supply surges when it changes states.

    The "rumor mill" has it that the target frequency range is somewhere between 19kHz and 45kHz, and that you won't get far with less than around 500v on your plates/wires/whatever you're using in your HHO generator.

    That's all hearsay right now; I have yet to try any such experiments myself, nor have actually seen something operate that I could lay my hands on, or have actually seen data published by a reputable source.

    But keeping the above particular range of frequencies in mind, I suggest that attempting to build your circuit with such an extreme range of frequencies will ultimately prove frustrating; as the frequency adjustment will be so coarse (even with a 21-turn pot) that you have a near-zero chance of finding that holy grail you seek.

    There are plenty of wild claims circulating around, and plenty of snake-oil salesmen are preying on the hopes and wallets of plenty of people who are desperately trying to find a way out of the high prices at the petrol pumps nowadays.

    This forum is rather conservative, and members generally try to keep replies consistent with published materials from credible sources.

    Generally accepted grid electrolysis methods of generating HHO from room-temperature water is about 27% efficient. High-temperature electrolysis of water is about 48% efficient.
    Source: http://www.fsec.ucf.edu/en/consumer/hydrogen/basics/production.htm

    Internal combustion engines are perhaps 25%-40% efficient; much of the energy from the fuel burned is dissipated as wasted heat via the radiator, exhaust, and IR. Now if you use some of that waste heat to heat your water up, you may very well be able to make your HHO generation more efficient. But don't try that with ordinary PVC or Plexiglas; it will melt (trust me on this.)

    I have not built nor simulated your circuit design. Right now, I think it would be best if you started off with a simple 50% duty cycle VFO that had a frequency range of what I'd previously mentioned.

    Take it slow. Be methodical. Document what you're doing.
     
    Last edited: Jul 2, 2008
  6. pntrbl

    Active Member

    Apr 21, 2008
    123
    0
    I've got a buddy with a homemade HHO device on his Toyota pickup. It's only a 4 cyl. with a 4 speed but he did get a 31.5 mpg run out of it. No baseline to compare to tho so the juries still out .....

    I don't think he wants to know.:)

    What's fun is when he takes the output tube and sticks it in a bottle of soapy water.The resulting bubbles blow up like a firecracker! The strange thing is you don't see or feel anything like an explosion. No heat and with a cigarette lighter for ignition you're thumb's right in the bubble. No light to speak of altho it was daytime. A big bubble will snap so hard it'll make your ears ring.

    Fun stuff.

    SP
     
  7. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    I suspect there are more than one person who would like to hear before and after results. The ones that drive us crazy are the folks who try to power the circuit off their alternator, which uses the fuel being burned to generate the electricity. Perpetual motion machines aren't real popular around here. Personally I don't see anything wrong with using batteries charged from house current to supliment the milage, but I would like to see some numbers.
     
  8. Elad

    Thread Starter Member

    Jul 1, 2008
    11
    0
    Thank You SgtWookie :)

    Yes, I do plan on using a voltage reg and filtering. Just not in here as want to get this part worked out to start with.
    500Khz :( rats... Thought it was 1mhz. Was afraid of that...
    Heard 45-185khz freq tests, but plate designs all different.
    Where is the 2N3055 frequency topping out at?

    I really wanted to know though if I am on track with pins 5 to 11 on the 556 if this is proper way to use frequency then duty cycle it.

    25 turn pots - humm, scratch the 15turn pots then I was considering... :cool:
    Was hoping the "holy grail" area would be a bit wider in range and not so narrow.
    I do figure that as the water heats up, will need to change freq on the go anyway, if this pwm idea even works.
    May be no different that brute force current, but worth a try for a few $ :rolleyes:
    At minimium. I can control the current on the fly as it will rise with water temp...

    Also, the plates will be drawing in the 15-20amp (@13.8v) area so water will be heating a lot :/ But melting? Not going to get over the boiling point of water. I selected a gallon plastic thermocooler for container.
    Am not running 100% HHO - just a supplement to make gasoline more efficent. Does not take a lot of HHO to do this. This is were others get this idea wrong.

    I don't think I can go the hi-voltage way do to freezing temps in winter (Northern Minn. USA) so will have to use windshieldwasher fluid and use of lye (electrolyte) to keep water from freezing.

    Am documenting as I go along... Here is my site with pics/progress...
    http://o-c-s.us/index.php/topic,340.msg3025.html#msg3025

    Me, I was top in my class in electronics course (Votech Insitute Mpls, Mn 1972 - Electricity)... However I went the mechanical ways since then and sorta missed the digital electronic revolution...
    At any rate - I will let all know the results. Good :D or bad idea :mad:
    And costs for parts is low ($100 area time done).
    Too many already have reported positive results to ignor this idea...
     
  9. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Perhaps, but how many have actually documented their results? Real numbers are important, they quantify results. Without them it is just hearsay.

    Like I said, I and others have a real problem using gasoline to generate electricity, then using the electricity to generate HHO, which in turn generates electricity, which generates more HHO... There is nothing wrong with electric cars, but the former can't work, and smells strongly of scam, perpetual machines are against the law, and these laws weren't made by man.
     
  10. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    No. To use pin 11 to control pulse width, voltage on pin 11 should be varied between 45% and 90% of Vcc. You can learn more here: http://www.uoguelph.ca/~antoon/gadgets/555/555.html

    Try using one of the timers as a variable astable and the other as a variable width monostable. This will allow you to experiment and find the combinations of frequency and pulse width at your given peak current to get your gases as quickly as possible. Note well: your "magic numbers" will not give you more HHO - they will simply give it to you in a shorter period of time.
     
  11. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The lousy old 2N3055 transistor has a max saturation voltage loss of 3V when its collector current is only 10A and its base current is a whopping 3.3A.
    So your driver transistor will burn up because it cannot supply 13.2A to your four 2N3055 transistors.
    The driver transistor will need a huge base current that far exceeds the 200mA available from the 555.

    The halogen bulbs are almost a dead short when cold and the 2N3055 transistors will instantly burn out if the current is too high for a moment. It takes time for a light bulb to light which increases its resistance to what you think it should be.
     
  12. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Ah, I see. I suggest using poly caps for the timer portion, they have much better characteristics than alum electrolytic.

    OK, that's "in general" for your typical NE/LM/whatever 555/556 timer. There supposedly ARE some 555/556 compatibles out there that have a much higher limit (perhaps 2MHz) but I don't know who makes them offhand.
    Yes, there are myriad configurations out there.
    ON Semiconductor's datasheet for the 2N3055/MJ2955 claims a 2.5MHz current gain bandwidth product.

    I really don't have time to model your circuit at the moment. However, on a 555 timer, pin 3 is normally the output, and in bjt versions is capable of sourcing/sinking 200mA. If you take your signal from other pins, your mileage will vary considerably.

    Something you must consider is the hFE of the 2N3055. With Vce=4, Ic=4A, hFE=20. With Vce=4, Ic=10A, hFE=5. With the 555 putting out a maximum of 200mA, you'll be lucky to get Ic=3A.

    I threw out 25 turns as an arbitrary number. I have some 21-turn mil-spec trimmer pots, various 10-turn 2W pots and some really nice 10-turn Bourns KnobPOTs, but I haven't seen pots with more than 21 turns from min to max. I got the KnobPOTs for $3/ea from salvage. They are very linear, very repeatable, and very pricey if you buy them new.
    Something more significant is the change of dielectric between the immersed conductors. Distilled water has a dielectric constant of around 77 when close to room temperature, and drops to the mid-50's near boiling. However, air has a dielectric constant that's a small fraction over 1.

    The formula for capacitance is:
    C= K*Eo*A/d, where:
    Eo= 8.854x10-12 for metric dimensions in mm2 and mm
    Eo=0.2248 for dimensions in square inches and inches
    K = Dielectric constant of material between plates
    A = Overlapping surface area of plates
    d = distance between the plates
    C = Capacitance

    So, guess what happens to the capacitance of the load when you start generating gas?

    Oh, distilled water has an insulation strength of about 80v/mil; air somewhere between 30 and 70v/mil. I don't know what HHO's insulation strength is, but it could be hazardous to find out! :eek:

    Well, you're not going to get "brute force current" using just a 555/556 timer as a driver for the 2N3055's; you'd need to supply the base with around 3A to get some serious current through the collector.

    Consider using power MOSFETs like IRFZ34's instead of the 2N3055's.

    OK, so preheat your oven to 210 degrees for a half-hour. Then put your 1 gallon plastic thermocooler in the oven for 4 hours. If it survives that test, you should be good to go. If it doesn't, you saved yourself some headaches later.

    Well, you certainly won't be running on more than a smidgen of HHO unless that magic frequency is found, or you're dumping tons of current through the plates.

    I don't know how WW fluid will react under electrolysis. You should ascertain the ingredients. I believe it's alcohol, but I don't know what KIND of alcohol.

    Cool. Yeah, it's easy to get rusty. You blink, and suddenly there are thousands of new devices and myriad technologies kicking around.

    Now, if you REALLY want to have some more precise control over your generated frequencies, look at using a uC (microcontroller) like a PIC (a Microchip Technology Inc. trademark), for more precise than a standard uC, use an external crystal oscillator in a temperature controlled oven. That way you can divide down the clock frequency in a very precise manner, and the uC has the capability of monitoring numerous inputs and controlling numerous outputs. Your frequency accuracy will increase by several orders of magnitude.
     
  13. Elad

    Thread Starter Member

    Jul 1, 2008
    11
    0
    Great link for info on the 555 thingmaker3 :)
    Will do your suggestion instead :)
    ---------------------------------
    Bill, there have been lots of documents, gov. funding, university research, and many who reported gains that already converted.
    A simple search yeilds lots of testimonies. Remember, this is only a supplement to aid in gas being used in the engine and not so much in the the exhaust.
    CoasttoCoastAM.com with George Norry did a show on this that got me started.
    Lex (his production assistant of the show) had one installed and is in testing now.
    George will air the results 2nd week of July.

    But this is an electronics forum and don't want to get off track. I am only here to get aid in this area as been out of touch with electronics for a few decades now :rolleyes:
    --------------------
    Wow, page 2 - I missed....
    Lots of great info/tips guys. I see I am using old & slow stuff (sorta like me :( )
    I only drive 1hr to work (52 miles 1way) so I should be ok before any major bucket meltdown using 3/4 of a gallon... Will take time for that to heat up.

    Yes, was going to use another transistor to drive the others. Looks like I will need to use the 4th 2n3055 to drive 3 instead @ 8amps ea max.

    H3 100w cold bulb ohms - humm. Point taken I didn't think of. Why I am glad I came here :)
    I just wanted a way to limit max current to prevent a burnout and a easy way to visually adjust each one. Am not after 15a/2n3055.
    Was looking to only drive around 5-6amps each on the 4 tranys (less than 1/2 the rating) and spread the load around.
    But thanks for your info, I will now have to use 3 and 1 for the driver. Remember, am looking keeping the cost down. These are only 90cents ea.
    Next one I build (if) I will use newer stuff!
     
    Last edited: Jul 2, 2008
  14. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The resistance of a cold light bulb is 1/10th or less than its hot resistance. So its cold current surge is 10 times or more. Have you noticed that they burn out only when they are turned on? (and when they are kicked)
     
  15. Elad

    Thread Starter Member

    Jul 1, 2008
    11
    0
    Well, I really do not even need them. I was just using them to quickly aid in balancing the base bias in case one is working harder, or less than the other ones.
    Would tell me if one is fried too
     
  16. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    I'm not sure if I'm using the FET correctly, and there is absolutely no short circuit protections, but I believe this will do variable frequency and variable duty cycle independent of each other nicely....

    [​IMG]

    It will have a wide range of freqs and the PWM will be independent, as well as being able to do 0 - 100%. Use something like a LM353 for the op amp, which is a drop in replacement for 1458's, but faster.
     
    Last edited: Jul 3, 2008
  17. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Add a driver between Bill's comparator and his MOSFET and it should work.
     
  18. Elad

    Thread Starter Member

    Jul 1, 2008
    11
    0
    Awesome :)
    I never looked into mosfets before. Been away from electronics too long. Nice little critters they are :)
    I live deep in the woods of Northern Mn so only source of electronic parts are from Radio Shack.
    I was going to be getting my parts from Electronix Express online: http://www.elexp.com/index.htm
    But I see they are limited on parts. Only 3 lower power mosfets there.
    Where you guys get your parts from?

    BTW, I found at a surplus store a bucket of these "
    SJ4842 T-3 package transistor, or something. Only 30cents ea but searching online, this part does not come up. Only reference is from http://www.netcomponents.com/results.htm?r=1&t=f&src=&so=&lgc=begins&d=1&pn1=SJ4842&slgc1=begins but you have to subscribe ($) to them. Am curious as to what these are.
     
  19. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Try:
    Mousers.com (they have a nice parametric search feature, and no minimum order req't)
    Newark.com
    Jameco.com - a discounter with no minimum order
    Electronics Goldmine is popular, they ship pretty quickly.

    For your requirements, like I mentioned before, have a look at IRFZ34's or IRFZ44's by International Rectifier. You can get those pretty cheaply online as well - they have a very low ON resistance, and can handle lots of current.
     
  20. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    What kind of driver do you suggest, BJT, CMOS, 555? I'll add it to the schematic if you have one. I'm still not clear on MOSFets (and the AAC book is unfinished in that area). I probably should have stuck a BJT there instead. :)
     
Loading...