can i llimit the current of a circuit ? - Page 1
Forum section: electronics / beginners

author: raff96
author_rank: Newbie
timestamp: December 24, 2015, 08:39:49 pm
content: Hi everyone , i want to make a hydrogen generator by electrolysis , i already have the prototype tank set up , but when i tried using a 230v > 24v 4A transformer (something like thisthis) after some time the insulation on the transformer coils melted because of the continuous current draw.I only have some bases in electronics ( mostly learned through youtube since at school we are still doing diodes and resistance) so i tried ohm's law and it should absorb 1.3mA ( the tank is 18k resistance with tap water ) but why the transfomer failed ? And can i limit the current ?I wanted to buy another transformer with more ampeage (the reaction was slow) , isthisa good one ? and if so , how can i use the full capability ?Thanks for the help and sorry for the grammar errors

author: Seekonk
author_rank: Super Contributor
timestamp: December 24, 2015, 08:47:24 pm
content: What were your electrodes? Clean water is a poor conductor of electricity but once you add some ions it will conduct. I would not add an elaborate supply. Adding a light bulb in series with the transformer primary would limit the current.

author: raff96
author_rank: Newbie
timestamp: December 24, 2015, 08:54:01 pm
content: I'm still building the tank so right now i just have 2hexagonal screws, but i'm making some metal sheets to increase the surface .

author: IanB
author_rank: Super Contributor
timestamp: December 24, 2015, 08:55:52 pm
content: Have you rectified the current? You need DC to make hydrogen or with AC you will get HHO gas.As noted, pure water has high resistance. It won't burn out the transformer. I think something else went wrong.For electrolysis it is traditional to help the conductivity by adding a little acid (hydrochloric) or alkali (sodium hydroxide). For less current, add less of it.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: December 24, 2015, 08:57:28 pm
content: A more appropriate device would be a variable output power supply with a current limiting setpoint. Then you can set the voltage you want while trusting the power supply to limit the current. It will do that be reducing the voltage down to your limiting point.

author: raff96
author_rank: Newbie
timestamp: December 24, 2015, 09:02:40 pm
content: Quote from: IanB on December 24, 2015, 08:55:52 pmYes , the transformer has its own rectifier, and i'm aware of the bad conducivity but i don't have any chemical shop near my city and this project is for my last year thesis , so i will only use it once in front of the professors to let them see that it works.Quote from: Tomorokoshi on December 24, 2015, 08:57:28 pmI don't want to spend a lot of money on this project and variable power supplies are too expensive for this.

author: daqq
author_rank: Super Contributor
timestamp: December 24, 2015, 09:10:42 pm
content: QuoteYou can get one for as little as 50 EUR. Also, assuming you are in a school, you should have access to some kind of lab-ish power supply in your physics lab?What kind of current would you like? Milliamps? Tens of milliamps? Single amps?

author: raff96
author_rank: Newbie
timestamp: December 24, 2015, 09:15:23 pm
content: Quote from: daqq on December 24, 2015, 09:10:42 pmI would like enough current to see the reaction , and the variable power supply that i have at school only reach 800mA and i can't take them home or take my project to school since it's still a prototype.

author: Seekonk
author_rank: Super Contributor
timestamp: December 24, 2015, 11:41:41 pm
content: Obviously the water became very conductive as the screws went into solution. Lamps are cheap and pretty good regulators as more current is drawn their resistance will increase seven times. Increase current by adding more lamps till the desired current is increased. It is likely that the diodes failed first. That may have been your only problem.

author: Vgkid
author_rank: Super Contributor
timestamp: December 24, 2015, 11:49:55 pm
content: Hes baaaack!!!

author: aaronwiz
author_rank: Contributor
timestamp: December 25, 2015, 03:11:41 am
content: Current limiting through a fixed voltage source will almost involve burning off the excess voltage as heat. So instead of your transformer heating up, the current limiter would.A better approach that limits wattage (not current) is to use PWM (pulse width modulation). Basically, instead of having your electrolysis device constantly on you can rapidly switch it on and off hundreds or thousands of times per second. You can vary the wattage by adjusting what percent of the time the device is on and what percent it is off, this is known as the duty cycle.You can either buy a dedicated chip that incorporates all the electronics into one. Or, it is almost as easy to use a 555 astable timer circuit to generate a square wave, then feed that into a mosfet that is in series with your load.

author: raff96
author_rank: Newbie
timestamp: December 25, 2015, 11:10:08 am
content: Quote from: aaronwiz on December 25, 2015, 03:11:41 amCan you give me an scheme so i can build it ? I don't have the expertise to build it without scheme.

author: Seekonk
author_rank: Super Contributor
timestamp: December 25, 2015, 11:39:46 am
content: Yup, a 90 euro solution to a 1 euro problem.

author: IanB
author_rank: Super Contributor
timestamp: December 25, 2015, 11:43:54 am
content: Quote from: raff96 on December 25, 2015, 11:10:08 amYou don't want to use PWM for electrolysis, that's bad advice. You need the lowest voltage possible to make the current flow. Use the advice of light bulbs in series. You can build that. Also, try to use a 12 V supply rather than a 24 V supply.You should use carbon electrodes (get them out of an old 1.5 volt zinc chloride battery, the super heavy duty kind, not the alkaline kind). Metal electrodes will corrode.You must add something to the water to make it conduct electricity. If you have nothing else a little table salt will do, although sodium carbonate (washing soda) is better, and sodium hydroxide (crystal drain cleaner) is better still (but read the safety instructions and only use a few crystals).

author: meeder
author_rank: Regular Contributor
timestamp: December 25, 2015, 12:11:06 pm
content: A little table salt sill do the trick to increase the conductivity. You don't need much, a little goes a long way to increase the conductivity.How high should it be? Normal tap water is around 300 to 600 uS/cm here in the Netherlands. A very small amount of salt is enough to increase it into the mS/cm range.

author: raff96
author_rank: Newbie
timestamp: December 25, 2015, 03:24:39 pm
content: Quote from: IanB on December 25, 2015, 11:43:54 amRight now i don't have any power supply , What do you recommend to buy?

author: Seekonk
author_rank: Super Contributor
timestamp: December 25, 2015, 04:55:06 pm
content: But, it is more than that. You may be accepting big ideas from people that may not have a lot of life experience. I'm thinking something in Denmark or Milan doesn't smell right. I restore vintage wooden boats. I made a steamer to bend wood out of some PVC pipe. Electrodes are just stuck in a tub of water and salt. That is 120VAC and I have never popped a 15A breaker with it. I am obligated for the children here to say this is dangerous. Don't try this at home. If your 4A transformer has insulation melting the current has to more than double that. With tap water that doesn't seem likely. You made no mention of water boiling away or the collection tubes launching off to the moon. This may only be an electrical problem with the wiring. Define the problem before making a solution.What did you use for diodes? They are likely shorted out. Transformer may look bad but it still may be good. Replace the diodes and try it again with an incandescent lamp in series with the primary.

author: raff96
author_rank: Newbie
timestamp: December 25, 2015, 05:54:23 pm
content: Quote from: Seekonk on December 25, 2015, 04:55:06 pmi don't know what diodes the transformer used (it's a transformer with a built in rectifier), but the insulation on the secondary coil is literally melted, i didn't checked if anything else was broken because i can't repair the coil.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 25, 2015, 06:10:09 pm
content: The voltage should be low - so even 12 V are rather high. Even 5 V should be OK. A lamp for current limiting and indication is a really good idea.It would help if the supply is adjustable in the 5 - 12 V range. It should also be short circuit proof - just in case.The higher the condictivity the less voltage you need. In principle something like 2 V are needed to split the water, the rest is just to overcome the resistance and increase the current.