1400w Transformer at 1/2 voltage?

[gary350]

I am curious, what exactly are you doing in t

Now there is a new problem. My 2.2 Kw variac is rated 10a it over heats on 9 amp.

Without buying a 5kw variac for $400 what can I do?

 

[Les Jones]

From the way you show the variac in post #21 you do not understand how a variac works. IT DOES not work like a variable resistance. It is variable auto transformer where the tap is moved up or down the winding to change the ratio of the auto transformer. The rating will refer to the output current. If the output voltage is set to a low value the input current will be lower than the output current.

Les.

 

[gary350]

From the way you show the variac in post #21 you do not understand how a variac works. IT DOES not work like a variable resistance. It is variable auto transformer where the tap is moved up or down the winding to change the ratio of the auto transformer. The rating will refer to the output current. If the output voltage is set to a low value the input current will be lower than the output current.

Les.

YouTube video shows to wire a variac like this.

 

[gary350]

The circuit has been running for about 3 hours on 9 amps variac is very warm but not over heating. Variac contacts need to be cleaned 9a keeps dropping to 2a wiggle knob it goes back to 9 then 30 minutes later its on 1a or 4a. I put a fan of the variac it is 97° here today.

 

[Nigel Goodwin]

YouTube video shows to wire a variac like this.View attachment 146303

So why didn't you wire it like that? - your previous diagrams don't show that, and only two wires are visible on the pictures.

 

[gary350]

So why didn't you wire it like that? - your previous diagrams don't show that, and only two wires are visible on the pictures.

I changed the circuit to this.

 

[MrAl]

I changed the circuit to this.View attachment 146305

Hi,

Well to start, transformers used with rectifier circuits have to be derated. Using a 10 amp transformer with a 9 amp load is probably too close.

One way to look at this is because of the harmonics, but the simpler way is to realize that the current waveshape of a capacitor filtered full wave rectifier circuit is very different from a pure sine wave. The capacitor charges for a much shorter time than would be present if there was a sinusoidal current waveshape.
For example, if the capacitor voltage was 100v then the diodes would not conduct again until the input voltage got up to 100v. That results in a current waveshape that is very narrow with a high peak. You can easily see this if you do a simulation which I highly recommend, or someone else does it and shows the results here.
The transformer heating would be different for this kind of waveshape than for a sine wave, and transformers are usually rated in terms of waveshape.

This was known a very very long time ago, and that is why inductor input filters became in vogue. The inductor causes the diodes to conduct over a larger span of the input wave and so the waveshape of the transformer current is more sinusoidal again. One solution then is to add an inductor in series with the secondary. This is not that simple either though because the inductor might have to be rather large, but you can look into this.
You can instead add an inductor at the output of the rectifier, but then it has to be able to handle the full DC current.

Another solution may be to see if you can just reduce the capacitance. Of course that means less filtering, while the inductor addition actually means better filtering.

Another possibility is to add a high velocity fan to cool the variac. Maybe a regular computer fan would do, but you may need a better fan than that. Look at the power use of the fan it may have to be as high as 20 watts or so. These are more expensive and make more noise, but they blow a lot of air.

 

[ZipZapOuch]

To reduce current, use sodium carbonate instead of sodium chloride and reduce concentration to control current flow. Over voltage when using sodium chloride can generate chlorine gas (poisonous at high concentrations).

 

[ZipZapOuch]

Are you electroplating or are electropolishing or doing some other electrochemistry?

 

[gary350]

Are you electroplating or are electropolishing or doing some other electrochemistry?

Electrolysis of saturated salt water.

 

[ZipZapOuch]

Electrolysis of saturated salt water.

Why? For the chlorine or the hydrogen?

 

[Les Jones]

How are you planning to separate the chlorine and hydrogen ? I am guessing that you want the chlorine for a swimming pool.

Les.

 

[MrAl]

Hello again,

I used to use a small amount of salt dissolved in water for etching metal. Works pretty fast too.

 

[gary350]

Hello again,

I used to use a small amount of salt dissolved in water for etching metal. Works pretty fast too.

I did etching to make PC boards once. I don't remember the mixture is was something like 4 table spoons of salt per gallon of water.

I am trying to make sodium chlorate weed killer. It is a none selective weed killer it kills everything even the roots. Fence around the yard is 8 ft tall brush neighbors won't cut there side of the fence so brush spreads to my side. Some of the sticker vines with big thorns are illegal to allow them to grow. Poison ivy grows in the shade among the brush and illegal to allow it to grow in town. Round Up has lots of warnings and law suits because it causes cancer. 10 years ago you could still buy Sodium Chlorate 50 cents per lb., Round Up was $9.99 then now Round Up is $30. I have been buying 50 lb. bags of salt $6 per bag, salt water kills many things but not all the roots die then plants grow back. I don't think making my own sodium chlorate is going to work the 22 gauge wires attached to carbon rods keep burning off. I need to find another way to connect carbon rods to to the circuit.?

Later today I will buy 150 lbs. of salt again its is very easy to mix up in 20 empty 5 gallon buckets then spray the fence row. As long as I keep spraying salt water plants stay dead and it cost much less than Round Up and is safer.

 

[MrAl]

I did etching to make PC boards once. I don't remember the mixture is was something like 4 table spoons of salt per gallon of water.

I am trying to make sodium chlorate weed killer. It is a none selective weed killer it kills everything even the roots. Fence around the yard is 8 ft tall brush neighbors won't cut there side of the fence so brush spreads to my side. Some of the sticker vines with big thorns are illegal to allow them to grow. Poison ivy grows in the shade among the brush and illegal to allow it to grow in town. Round Up has lots of warnings and law suits because it causes cancer. 10 years ago you could still buy Sodium Chlorate 50 cents per lb., Round Up was $9.99 then now Round Up is $30. I have been buying 50 lb. bags of salt $6 per bag, salt water kills many things but not all the roots die then plants grow back. I don't think making my own sodium chlorate is going to work the 22 gauge wires attached to carbon rods keep burning off. I need to find another way to connect carbon rods to to the circuit.?

Later today I will buy 150 lbs. of salt again its is very easy to mix up in 20 empty 5 gallon buckets then spray the fence row. As long as I keep spraying salt water plants stay dead and it cost much less than Round Up and is safer.

Hello,

Do the carbon rods have to be completely under water ? If not any attaching wire would not have to be under the water. Not sure if stainless steel wire would help or not here.

I think motor oil stops plants from growing, but it might take a lot of oil if it's a larger area.
Vegetable oil also helps I think and is more friendly to the general environment.

 

[gary350]

Hello,

Do the carbon rods have to be completely under water ? If not any attaching wire would not have to be under the water. Not sure if stainless steel wire would help or not here.

I think motor oil stops plants from growing, but it might take a lot of oil if it's a larger area.
Vegetable oil also helps I think and is more friendly to the general environment.

The industrial chemistry book I have uses carbon rods for the + anode and stainless steel for the - anode. Their chlorate tanks are 100' wide, 100' long, 6' deep, they produce 20 tons of sodium chlorate every day from rock salt. Book does not say how many tanks they have. + anode should be .3a per sq inch about 3v to 4v adjustable to get .3a. .3a is more important than 3v or 4v. Dial in what even voltage is needed to get .3a. Stainless steel cathode is .1a per square or less.

Motor oil does kill weeds & grass but it takes a lot of oil that I don't have.

50 lbs. bags of Salt is extremely low cost I can kill a lot of weeds & grass with several $6 bags of salt. The hard to kill weeds need something stronger Diesels fuel works great. It is easier to buy something that kills weeds than to make something that kills weeds and it all costs less than Round Up.

I'm not sure my chlorate tank will ever produce enough weed killer to do much but its a fun project. Certain brands of laundry bleach contains sodium chlorate a $3 gallon of bleach kills a lot of weeds.

Yellow powder Sulfur from farm supply store turns to sulfuric acid in the soil it kills weeds too.

None of these weed killers cause cancer like Round Up.

 

[For The Popcorn]

Sounds like you're creating a hazardous waste site.

 

[gary350]

Sounds like you're creating a hazardous waste site.

I'm not making anything yet just using salt water to kill plants. Google says, The USA puts 24 million tons of salt on highways every winter. Is table salt a hazardous waste?

 

[For The Popcorn]

Spreading diesel and motor oil on the ground pollutes ground water. I suspect it's illegal even in backwards square states.

 

[MrAl]

The industrial chemistry book I have uses carbon rods for the + anode and stainless steel for the - anode. Their chlorate tanks are 100' wide, 100' long, 6' deep, they produce 20 tons of sodium chlorate every day from rock salt. Book does not say how many tanks they have. + anode should be .3a per sq inch about 3v to 4v adjustable to get .3a. .3a is more important than 3v or 4v. Dial in what even voltage is needed to get .3a. Stainless steel cathode is .1a per square or less.

Motor oil does kill weeds & grass but it takes a lot of oil that I don't have.

50 lbs. bags of Salt is extremely low cost I can kill a lot of weeds & grass with several $6 bags of salt. The hard to kill weeds need something stronger Diesels fuel works great. It is easier to buy something that kills weeds than to make something that kills weeds and it all costs less than Round Up.

I'm not sure my chlorate tank will ever produce enough weed killer to do much but its a fun project. Certain brands of laundry bleach contains sodium chlorate a $3 gallon of bleach kills a lot of weeds.

Yellow powder Sulfur from farm supply store turns to sulfuric acid in the soil it kills weeds too.

None of these weed killers cause cancer like Round Up.

Hi,

Yes, I wasn't sure how much area you needed to kill weeds in so I mentioned motor oil.

Next up: Radioactive waste (ha ha).