Out of Control Amperes

Are you sure you are authorised to play with 700V ? a quick background check (prompted by the question- the answer to which is too basic) shows no.

I have followed all the regulations required by my government, there for due to me being a freelance researcher that follows all the safty rules involved. And yes I am registered with my government. Yes to You which has a strong back groung in Electrical Engineering it is simple. But myself which knows buildings and mechanical, then no its not simple.

But may be there is some ohm value of load already that will come in series.

Whats the point passing 1ma in resistance otherwise?

No, there is nothing using enough before it reaches its destination, thus requiring the additional control. And for testing purposes I will play with the amount that is allowed through. Hopefully no more burnt wires!

thanks for your assistence!

Just a clarification:

700 x 0.001 = 0.7W

The voltage, generally (not exactly, but for most of practical purposes) is independant of normal currents. (Consider your normal 1.6V cell- is the voltage dependant upon the load? it give 1.6V on cellphones, torch,...)

So you have to put a resistor in series so as to get the required mA

I = V/R

R = R₁+ R_L , R1= the resistance you have to put in series with R_L : the load resistance.

R should be rated for the voltage.

Remember any voltage above 110V is possibly fatal and 110V also is not necessarily excluded from the list. 700V is necessarily fatal and should not be handled by one not certified to handle.

Hey, you are being hard on yourself.
I'm sure a Gremlin with your experience could kill someone with far less than 110v.
60V should be plenty
Del

Not Safe, but Safer. 220 hurts like a bitch, but 110 only tingles. Depends on how you get bitten and where. Deep puddles suck!

Quite honestly a taser gun runs on 10 kv, its the ampers you have to worry about.

The taser gun in fact provides a very high ampere too.

The thing to worry is not the amperse here

a) What is the duration

b) What is the zone through which the current is flowing.

Doe to the extremely small values of both these, the taser gun are likely non fatal.

However playing with 700V power supply is an entirely different ball game.

Your right 700V is minor whan compared to 10,000V and I have experienced a taser in my training. and taser guns usually run on 5 milliamps. I have 5oo Amps to worry about every time I change a car battery. I need to make sure I am only pulling milli amps out ov the 500 amps.

I'm not sure if you are kidding or not, but in the US 50 volts is considered lethal by OSHA, but people have been electrocuted by 24 volt sources. You are correct that it is the amperage that kills you, but that amperage value is very small: 3 milliamps or so through the chest is adequate. Because of ohms law, and the rather high resistance of skin, 50 volts is a reasonable figure for the dividing line, but if you have sweaty palms, less than that can be lethal.

My small welder goes to 100 amps, but has an open circuit voltage of just 35 volts. Its potential amperage output has nothing to due with its lethality: I could grab the table and the electrode and have only a very remote chance of being electrocuted. 35 volts is not enough to push .003 amps through the typical person, but plenty for pushing 100 amps through steel.

You question suggests that you are unacquainted with Ohm's law, so you may not be adequately evaluating the risk. I hope you realize, for example, that even with a resistor in the circuit that limits current to 10 milliamps, you are still risking death.

Be careful.

sb your words implies that poster is/may not be authorised or untrained for the work under consideration, and lets assume thats true.

Still remember- kids medicines are useless without sweeteners,

Rest assured that I have some experience in handling HV, Proper insulating gear is used and I don't handle live wires and make sure charge in capictors laod is released befor handling. OH! I still wear protective equiptment. I appreciat your concern and glad to see people still care!

I have full confidance on you arthur, I was just making point a point for sb.

While you might be able to cobble something together with dissipative components (Like Dell's resistor) there are two things that I would suggest.

Firstly, to get sweet and smooth control for 700V (Or any voltage source) you should be looking at solid state DC supplies with adjustable current limiting output. I know that I've seen 400V and 1000V around, so I'm sure that if you ask around the manufacturers there will be one suitable.

Secondly, protect the downsream circuit with a fuse or circuit breaker. These are much cheaper than trouble shooting "smoked" circuits and are designed for the task.

You haven't mentioned whether this is AC or DC, so please also remember that with DC the isolation distances for opening the circuit need to be a bit larger.

I am not a high voltage engineer, in fact I resist the thought of repairing TVs or anything with high voltage, did it once, got the burn, and the pain. Once was enough.

700volts DC is a very seriously dangerous voltage and makes an arc welder look like a playtoy for under 5 year old kids......

BE VERY VERY CAREFUL ARTHUR!!!!!

What you are trying to do sounds very dangerous and you give us the impression that you have little idea of what you are doing, as if you REALLY knew, you would be doing it and not asking us here on CR4 what to do!!!!!

You sound like a possible future candidate for Darwin Awards website......

Turn this circuit the the other way up (and add a low power rail) so that most of the stuff your looking at is close to ground.

Of course the PNP will need to change to an NPN.

The voltage drop across the zener is 5.6V

The base emitter diode removes 0.6V, so you've got 5V across 5KOhms.

Make sure all component are rated for the voltage.

You can add protection components between the collector and the "load".

You can "trim" the 5K if you need more accuracy.

Does this help/make sense?

Hi Randall,

No, don't turn it upside down. Once this is made and secure it is safe. the "bits" he is experimenting with will be more likely to be open and touchable.

On a rather simplistic tack, a trick used when testing power electronics (inverters) is to use a tungsten light bulb to act as a limiting resistor. This has the effect of being a low impedance source at low currents but if a short or overlload occurs then the lamp lights, the element resistance increases and an effective shutdown occurs.

Halogen bulbs are often have a ΔR of 10 so that a 10W bulb, nominally taking 40mA from a 240V source will appear to allow 0.4A when cold. This means that pulsing loads won't be distorted by the low (but still limiting) cold impedance of the source. It also helps with finding the problem should an unexpected short circuit occur.

Arthur's problem with using this method is the 700V. Not too many lamps at that voltage.

regards

Chas

arthur,

capblanc is right. Depending on whether your going to spend more time looking at the current control element of this project, or more time looking at the rest of it.

You can build and debug the above circuit just as it is using a 12 V battery or power supply then transfer it to the 700V rail, BUT, you will then need to create a new (700-12)V rail or simply change the value of R2 to say 5MOhms.

We're assuming that you're talking about 700V DC here.

Make sense?

The short answer is, you can't!

Once you start controlling the amps you are going to change the amount of voltage drop across the load. If the load is a fixed value and the amps are a fixed value then the voltage will depend on these two values. If you change either one of these two values you change the corresponding voltage. You can, however, control the amps if you are willing to control the resistance of the load to maintain 700 volts at a particular amperage. This new load may consist of a limiting resistor and the original load. However, you will find that you are no longer dropping 700 volts at the load. You are dividing the voltage between the two resistances.

E=IR <-- Ohms law

Your point is valid,but still in many cases this method can be applied very well.

High voltage/breakdown testers are good example where ratio of load resistance to limiting resistance is very high that allow max voltage drop across the load yet at a low current.

If the limiting resistor is 100 M Ohms and the load is 100 M Ohms the voltage drop across the load will be 350 volts.

Limit Resistor = LR = 100 M Ohms

Load = LO = 100 M Ohms

_______________________________

LR 100 M Ohms = 70 volts

LO 900 M Ohms = 630 volts

_______________________________

LR 99 M Ohms = 693 volts

LO 1 M Ohms = 7 volts

_______________________________

Get the picture?

(Pun intended)