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Registered Member #4077
Joined: Tue Aug 30 2011, 11:40AM
Location:
Posts: 5
Hello,
Have been out of the HV hobby for a looong time.
Got a pretty big HV transformer that i need to ballast to around 3KVA. Input is 240v, output is 12Kv.
I know resistive ballast is not the best option but will this do the job for starters ? The output of the transfomer will only be used for 5-10sec at the time so 500W should suffice ?
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
those resistors need a LARGE heatsink to achieve their rated power dissipation. if not, the ends can blow off ... violently.
It is early morning so check my maths....
maximum power output with a resistive load on the 12 kV side and a resistive ballast is when half the input voltage is dropped across the balast resistor, 240 V / 2 = 120 V, 120 V / 20 R = 6A 6 A x 120 V = 720 W output = 720 W in ballast
if the transformer output is shorted then input current = 240 / 20 = 12A, input VA = 12.5 x 240 = 3 kW so the primary aim of limiting power drawn from the mains to 3 kW is achieved but at the cost of 720 W maximum useable power output (6 kV @ 120 mA)
A more economical and re-usable option would be 3 kW of resistive domestic appliances, electric (not electronic) hotplate, kettle, iron, heater, toaster (inbuilt timer !) etc. A new electric kettle would be much cheaper than that resistor, for more power put some bread in the toaster and you can have lots of tea and toast while you work :) For maximum effect do some extreme ironing whilst the tea and toast are preparing. (if you buy the new appliance for your mother or partner to replace the ugly old one, you will be a temporary mini-hero), (not a guy who buys stuff for his hobby but not for his loved ones) (or you can just 'borrow' an appliance if you are lazy like me)
Registered Member #4077
Joined: Tue Aug 30 2011, 11:40AM
Location:
Posts: 5
Ahh thanks, so that wont work. Did not take account for voltagedrop over resistor. I need 12Kv out and as high current as possible without tripping my 16A braker. Guess i need to go the induuctive or capactive route ? Any helpt would be much appreciated, pointing me in the right direction. Links, websites, products that could be used. Need to read up on this stuff, so long ago i forgot so much.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
1) Protect the incomming supply from your 'appliance' ... fuses, circuit breakers, RCD/ELCB, filter etc. 2) Protect yourself from the appliance ... some kind of Emergency Stop / Physically Disconnect facility 3) Protect your appliance from the incomming supply ... Metal Oxide Varistor, Transient Voltage Suppresor etc. 4) Protect your appliance from you ... understanding the load allows a better design. e.g. a3 kVA transformer, fixed or variable, with or without load, can randomly 'pop' domestic over-current circuit breakers, at switch-on a voltage-multiplier load is very different to an arc load etc.
Registered Member #4077
Joined: Tue Aug 30 2011, 11:40AM
Location:
Posts: 5
Its not going to power anything, only use the arc for different "experiments" I now use a 1kVA NST but i would like more power and to use the 12Kv transformer i got ballasted. From what i have gathered it seems an arc welder is the way to go. Feels a bit overkill for my purposes but i guess if its the best solution i will have to try that.
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Can i use this for ballast
