PWM or not

[midnight1957]

Do you really need a PWM in a dry cell, I thought that you could control the temp with the amount of potasium hydroxide that you used?

Is a 1 liter resivoir/bubbler large enough if you cell produces 1 to 2 liters per minute?

Thanks and have a Blessed day,
Wade

[Painless]

In my experience, you need a PWM if any of the following are true:

1) Your cell does not produce enough LPM cold, but only achieves desired levels after an unacceptably long warm up period.

2) Your cell is overheating and drawing too many amps.

The ideal way to implement a PWM is to set your electrolyte to maximum strength and dial the PWM in to achieve the LPM you want (cold) at an acceptable amp drain. The PWM will then adjust duty cycle to maintain that amp drain and hence output / heat control.

If your only concern with a dry cell is overheating, then the addition of a pump (if you don't already use one) can go a long way to controlling heat. A bigger reservoir can also help, but would be a bigger help in conjunction with a pump.

[midnight1957]

Painless, thanks for the info.
I have looked at several PWM s and it seems that the most popular (popular doesn't always mean the best) one is the Extreme hho, is this the one you would recommend (its a little high) or is there another one you like better? Also I have heard about reasonce (sp) to help shake the bubbles off, does this one have that or do you have to buy something else?

Thanks and have a Blessed day,
Wade

[Painless]

I don't personally use a PWM, so wouldn't want to make any recommendations. I do know that one of the forums electrical guru's, ridelong?, has made his own PWM and can probably advise.

ZeroFossilFuel (www.alt-nrg.org) has also designed his own current sensing PWM, the plans for which are available on his website.

I don't think that a PWM is going to provide any resonance benefits, someone else please correct me if I'm wrong here, keep in mind that a PWM does not directly increase efficiency, it just allows you to stay within tolerable current, heat and output parameters.

[Jaxom]

Zero's PWM does have adjustable frequency for the output signal, but trying to tune it to resonance is a long shot at best. Ridelong's design is much more simple and straightforward, just an electronic current limiter. His schematic can be found here. (http://www.hhoforums.com/showthread.php?t=917)