Pwm question

[CJLOTTI]

i was wanting some feedback on this pwm from hydrogen garage.

http://stores.homestead.com/hydrogen...ith/Detail.bok

it is a soilder it up kit, cost 45 has the 2 adj potts and sounds pretty good.
the same unit already built is 145, so obviously 1 hundred more to put it together seems a bit steep.

has anyone purchased the u soilder unit, and how is it working??
thx

cj

[PeteVamped]

I have not personally tried that one yet I will try to put it on my to do list for up coming reviews of products for hydrogen fuel cells.

[marchlabs]

i wouldnt buy it... there is a new type of PWm out there called constant current with 3 adjustments .. duty cycle, frequency, and limit ... i cant remember who has the analog version but we have the digital version with computer control and LCD . if you can hold off for 2 weeks , ill make some analog boards and send you one for review..

jeremy
www.marchlabs.com
www.hybridconversions.com

[rcflyn]

2 weeks up yet???

i wouldnt buy it... there is a new type of PWm out there called constant current with 3 adjustments .. duty cycle, frequency, and limit ... i cant remember who has the analog version but we have the digital version with computer control and LCD . if you can hold off for 2 weeks , ill make some analog boards and send you one for review..

jeremy
www.marchlabs.com
www.hybridconversions.com

[Drafty-01]

Hi, I'm quite new to this whole HHO thing, but have read a lot about various successes & failures on these forums - Great education! I have a question;
I'm making a PWM unit, and it's mentioned here & there that a 20k ohm one is best (can't remember where I saw that though). this particular resistance is quite difficult to find though, and I was wondering if a different resistance one would do. I can get 1K, 5K, 10K, 50K, 100K, 500K, 1M & 2M pots, in 16 & 24mm sizes. Also some 3W wire wound ones. Which ones would be best, or would any of these actually be fine? or does it depend on the 555 chip it's connected to?

[Drafty-01]

Bring on the New PWM! Three adjustments sound pretty cool! Could be so useful. What frequency does it go down to. I have seen some large MOSFET relays, but they are pretty slow in response, so the frequency would need to be way slower.

[Philldpapill]

Drafty-01, you really should AT LEAST post a schematic. A PWM isn't a generic circuit that everyone knows by heart. Also, you should really make your own thread. Also, lose the avatar picture... A lot of smart guys on here, that would normally be willing to help you, might not be as friendly with an offensive avatar like that.

[Drafty-01]

Hi Philldpapill - My apologies. I think I may have read (or heard on Youtube) something about these (the 20K pots) being the best option - but just found one that uses a 250K pot. Must have read too much and gotten confused... as you probably guessed, i'm not an electronics whizz, but I have dabbled a little over the years.

There's a pretty clear diagram etc on this link; http://www3.telus.net/chemelec/Projects/PWM/PWM.htm

This is copyright to Chemelec 2003 2004.

[Philldpapill]

Ok, I THINK the potentiometer that you are refering to controls the duty cycle. The basic quad op-amp PWM design uses a potentiometer as a voltage divider in order to control duty cycle. If this is indeed the case, then the pot value isn't really that important. However, with the 555 type of circuit, then yes, it makes a tremendous difference.

After checking into the schematic more, yes, the potentiometer value matters...