# Electronics 2000 Forum

## Topic: ohms law

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### ohms law

im only just starting to learn electronics and im trying to work out how many amps my load is trying to draw im using 240volts ac and i used my mulimeter to check resitance through my load i switched it to 20k and it read 1.94 does any body know how to calculate pls

thanks david
hydro

Posts: 6
Joined: Sun Sep 21, 2008 2:59 pm

### Re: ohms law

Hi

Firstly what is the load - this may make a difference as in some cases the resistance of the load won't equate to the power drawn.

If the load is purely resistive (e.g. a fillament lamp or heater) you can work out the current drawn using ohms law as you suggest:

V = I * R re-arranges to I = V / R
V = 240V
R = 1.94 k ohms = 1940 ohms
I = 240 / 1940 = 0.12 amps.

To work out the wattage of the load from this you can use:

P = V * I = 240 * 0.12 = 28.8 Watts.

As mentioned before this only holds true for a purely resistive load. See the calculators section of the website for an easy way of working these out, and to check my calculations!
Simon Carter
Electronics 2000
http://www.electronics2000.co.uk
Simon (Webmaster)

Posts: 159
Joined: Tue Jan 29, 2008 7:05 pm
Location: Nottingham, UK

### Re: ohms law

Thanks simon
thats what i thought but when i test it, the fuse went (13 AMP)
The load is two stainless steel plates submerged in salt water im trying to build a hho cell and need to lower the amps allowed to flow to my load to 8 amps and was trying to find out what i need to step the volts down to any ideas are greatly welcomed
cheers david
hydro

Posts: 6
Joined: Sun Sep 21, 2008 2:59 pm

### Re: ohms law

David,
You're not having us on are you?
What you're doing sounds lethally dangerous. It appears as if you putting mains power through a virtual short circuit. In wet conditions!
If you are still alive please send a description or better, a photo of your setup before switching it on again?
Anyway AC does not work if you're trying to electrolyse water. All you get is an explosive mixture of hydrogen and oxygen.
Martin.
Martingrove

Posts: 15
Joined: Tue Aug 26, 2008 1:13 am

### Re: ohms law

No response.
Oh, dear.
Martingrove

Posts: 15
Joined: Tue Aug 26, 2008 1:13 am

### Re: ohms law

lol hi martin
sorry for not responding had computer problems and i am trying to produce hydrogen and oxygen check this as an example

any help would be great

thanks david
hydro

Posts: 6
Joined: Sun Sep 21, 2008 2:59 pm

### Re: ohms law

Hi, David
First of all, I'm not the expert. Like you I'm a newby around here, but I have been an electronics enthusiast for yonks. The old hands here probably think I'm too forward! I have a medical background so my first concern on reading your post was for your safety. Raw mains is lethal to play around with if you're not well versed with what you're doing. The guy on Youtube used 12v!
Sorry for the lecture. You score full marks for enthusiasm though!
My first advice would be for you to join a forum dedicated to HHO cells. I know squat about it, indeed I don't quite understand the rationale behind it, since the energy expended to produce it seems more than the usable energy you get out of it. Please correct me if I'm wrong!
But more in line with what you're interested in I would suspect that you would need to find out what the ideal DC voltage is to electrolyse water. After generating the power you will need to control the current. Using a dropper resistor would defeat the object of energy effiency (if that's your goal) because part of the energy is dissipated in the resistor as heat. The more current, the more heat.
So I guess your best way forward would be a pulse width modulator which switches the power to the cell on and off rapidly, with a variable ratio between the time spent in the "on" state and the "off" state. The average "on" time determines the average amperage delivered to the cell. By varying the ratio you can control the current. Since little heat is spent by the switching transistor (usually a FET) while it's on or off it is far more efficient than the aforementioned resistor. The net abounds with circuits that do this. Perhaps one of the more experienced members here could point out something more specific.
Good luck, David.
Martin
Martingrove

Posts: 15
Joined: Tue Aug 26, 2008 1:13 am

### Re: ohms law

hi martin
i do undestand the extrem danger of watts and water, i also think your probably correct that it would use more power to
create the hho than you could get out but i wish to use it as a gas cutter and produce my own supply on demand from my
van instead of carrying heavy gas bottles from job to job and not worry about traveling to refil or running out.
I read about the use of a PWM in creating hho before but did'nt understand what it was but after researching a pulse
width modulator i have a little bit of an understanding and you have pointed me in the right direction now all i have to
do is to find or bulid a pwm cuircit to test it.
thanks martin you have been a great help

p.s. if i do make a mistake and give my self a jolt i know who to contact
hydro

Posts: 6
Joined: Sun Sep 21, 2008 2:59 pm

### Re: ohms law

Thanks for the kind words.
Another thought came up since my last reply:
If you are electrolysing water you'll need electrodes suspended in water salted with some electrolyte to enhance conduction. If this concentration is held constant and the power supply is well regulated, the current should be determined by the surface area of the electrodes. Temperature may also need factoring in. You can experiment with a car battery and some copper clad PCB, monitoring the current with an ammeter. I think you will find that the relationship is linear, so you'll be able to extrapolate what area of electrode would support the current desired at the given voltage. I may be wrong, but if it works you won't need PWM.
This is becoming interesting!
BTW, with a bit of surgery redundant computer power supplies make excellent low voltage regulated sources (around 20A @ 5V). If you're interested I'll send you a link.
How will you dry and compress hydrogen? It's tricky stuff.
Martin
Martingrove

Posts: 15
Joined: Tue Aug 26, 2008 1:13 am

### Re: ohms law

been off the net for a while computer trouble maybe i will use the power supply off this computer lol , somebody else pointed me in that direction before but it burnt out (maybe the e-mail directions were incorect) but if you could show me the plans you have maybe they differ from the ones i had
cheers martin
hydro

Posts: 6
Joined: Sun Sep 21, 2008 2:59 pm

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