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View Full Version : What all do PWMs do?



Tremorfalcon
09-14-2008, 06:54 PM
I know they adjust the frequency of the power being sent to the cell.
I know they can limit the amount of power going to the cell.
I know they help reduce heat because of the above two items.

However, I've seen things such as "a PWM with voltage stepping from 1kdc up to 20kvdc pulsed anywhere from 10khz to 45khz. "

Do PWMs also act like an ignition coil does and increase the voltage from a low 12volts to as high as 20kilovolts?

I'd like to know because the cell I am an designing is currently planned to use only 6 plates, due to having 12volts powering it. If a PWM could even up the voltage to 50Volts DC I'd be happy becuase then I could run as high as 20 plates instead of the lowly six. I am looking at an amp draw of 30 amps. So, would a PWM make it possible to up the voltage to at least 50 volts and still run as high as 30 amps?

mytoyotasucks
09-15-2008, 12:31 AM
that would be a good idea, i was wondering that myself, cause my 2nd cell puts out .5 LPM at 12V and 18 Amps, but at 24V and 15 amps it puts out .65 LPM.

So i am looking at different V's to see what is better and make a PWM with a voltage jump, still testing more V's though.

ridelong
09-15-2008, 06:49 PM
A pwm does not boost voltage in any way.

The pwm can only turn on and off like a switch. The more on time, the more average current. The more off time, the less average current.

The pwm can never draw more current than applying straight battery voltage, only less.

They are great for preventing overheating.

Tremorfalcon
09-16-2008, 10:13 AM
When building a PWM you use a MOSFET transistor. You want it to be able to hold at least 30amps for hydrogen generator experimentation.

However I was wondering. Does the voltage rating of the transistor matter? A cars alternator puts out aroudn 14.5volts, so anything at least 15volts should be fine right? I dont need to get one of those crazy 400V rated ones?

Tremorfalcon
09-16-2008, 10:48 AM
I plan on building this PWM
http://www.rmcybernetics.com/projects/DIY_Devices/homemade_pulse_controller.htm

PWMs can adjust the frequency and can adjust the pulse width and they are also used for limiting the amount of amps to the device.

What part of this PWM actually limits the amps? The schematic uses a 10Amp transistor, however I want the PWM to limit the current to 30amps. How would I go about limiting the current to 30amps? Would I have to get a 30amp transistor? Or could I get a 50amp transistor and somehow adjust it to limit the amps to 30?

Q-Hack!
09-16-2008, 12:52 PM
I plan on building this PWM
http://www.rmcybernetics.com/projects/DIY_Devices/homemade_pulse_controller.htm

PWMs can adjust the frequency and can adjust the pulse width and they are also used for limiting the amount of amps to the device.

What part of this PWM actually limits the amps? The schematic uses a 10Amp transistor, however I want the PWM to limit the current to 30amps. How would I go about limiting the current to 30amps? Would I have to get a 30amp transistor? Or could I get a 50amp transistor and somehow adjust it to limit the amps to 30?

These are the most common type you see on the web. The LM555 timing chip sets up a frequency that is adjustable by VR1. This frequency is fed into the LM393 comparator chip which is used to turn on and off the IRF740 MOSFET. The MOSFET is what pulses the current fed to the generator. The more the MOSFET is turned on, the more current applied to the generator.

Tremorfalcon
09-16-2008, 09:40 PM
Thanks for the replies, I think I'm starting to understand them fairly well. I have one more question. If I am running 30amps, I should probably use at least 10AWG wire. However, if I am using a PWM could I use 12AWG safely? I have 12AWG around the house, but I do not have 10AWG on hand. I'd like to be able to possibly run the positive wire down into the electrolyte solution and around the cells once or twice. That way it would create a nice pulsing magnetic field as well. I figure 30amps would create a fairly decent size magnetic field too.

So, would 12AWG be ok?

mytoyotasucks
09-16-2008, 10:08 PM
here is a table for ya

http://www-personal.umich.edu/~olmsnj/images/truck/12VDC_wire_gauge_chart.jpg

H2OPWR
09-19-2008, 04:29 PM
A pwm is necessary to prevent any cell from run away voltage. It will not increase voltage just limit current. The hotter your cell runs the more voltage it will draw. Also the more water is used as hho the stronger your electrolite will become. In the end you will either run your battery dead or melt down your cell without a way to control current. Google MX066. That will take you to the manufacturer of the most common PWM on e-bay. It is only about $20.00. They are selling them on e-bay for much more. I know I bought my first one there. Thankfully it had the part number stamped on it.

resago
09-20-2008, 11:50 AM
could one of these be modified to use the temp feedback thing?

HHO King
10-06-2008, 08:36 PM
I have complete units with gauges and cooling fans and built in gauges.

I also have adjustable frequency models.

http://www.extremehho.com