Thank you all for your reply and suggestions.
Question of safety: I am using a DC current supply to pass 50amp to a load of about 10mohms, so the voltage across the load is very low, and the power is very low, but the current is till high. Should there be any safety concerns for this setup?

 

Thank you all for your reply and suggestions.
Question of safety: I am using a DC current supply to pass 50amp to a load of about 10mohms, so the voltage across the load is very low, and the power is very low, but the current is till high. Should there be any safety concerns for this setup?

I doubt there would be any special safety concerns. If the load generates heat good work practices and anything OSHA (in the US) should be followed. Beyond that, based on what you have mentioned, I can't think of anything.

Ron

 

50amp to a load of about 10mohms

REALLY? To get 50 amps to flow through a 10 MEG Ω load you'd need 500 MEGA Volts.

I think you may be confusing with supply and demand. Your supply (whatever the voltage) may be capable of supplying 50 amps. But if your circuit is only using 5 amps then only 5 amps will flow through the circuit. Didn't we cover this already?

Voltage is equal to amperage times resistance. Hence, voltage divided by amperage equals resistance, and voltage divided by resistance equals amperage.

E (volts) = I (current) X R (resistance).

If you have a power supply that is capable of supplying only 1 amp and you had a 50 volt source and 10 ohms of load, you would have 5 amps of current being drawn - or trying to draw 5 amps. Being the supply is only capable of 1 amp then no more than that is going to flow because that's all that is available. And the voltage on the circuit will go way way down.

Before you go any further I think you need to get a solid grounding on what is going on when something says it's capable of 50 amps. That's all that means - it can give you 50 amps at its rated voltage. Draw any more than that and the voltage will begin to drop fast.

10 meg ohms is a LOT of resistance. It's like a freeway with 10,000,000 lanes of traffic being squeezed through one lane. It's going to take a long long time to get home tonight honey. Conversely, if you had a 10 ohm resistor, it's like a 10 lane freeway being squeezed down to only one lane. The analogy is flawed, I know. But it gives you a better idea of how resistors work. Electrons are just like cars. Resistors are just like lane closures. it's GOING to slow down traffic. (electrons) Slower traffic, less current. Higher voltage will force more traffic through, but will also generate more heat. Higher wattage.

And wattage is something you shouldn't neglect either. If your supply is 12 volts (just guessing) and it supplies 50 amps then 12 x 50 = 600 watts. Grab hold of a 100 watt light bulb. Too hot to handle. SIX OF THEM AT ONCE ? ? ? More worry about the insulation's ability to withstand the heat as opposed to keeping the current from going to something else.

 

REALLY? To get 50 amps to flow through a 10 MEG Ω load you'd need 500 MEGA Volts.

I think you may be confusing with supply and demand. Your supply (whatever the voltage) may be capable of supplying 50 amps. But if your circuit is only using 5 amps then only 5 amps will flow through the circuit. Didn't we cover this already?

Voltage is equal to amperage times resistance. Hence, voltage divided by amperage equals resistance, and voltage divided by resistance equals amperage.

E (volts) = I (current) X R (resistance).

If you have a power supply that is capable of supplying only 1 amp and you had a 50 volt source and 10 ohms of load, you would have 5 amps of current being drawn - or trying to draw 5 amps. Being the supply is only capable of 1 amp then no more than that is going to flow because that's all that is available. And the voltage on the circuit will go way way down.

Before you go any further I think you need to get a solid grounding on what is going on when something says it's capable of 50 amps. That's all that means - it can give you 50 amps at its rated voltage. Draw any more than that and the voltage will begin to drop fast.

10 meg ohms is a LOT of resistance. It's like a freeway with 10,000,000 lanes of traffic being squeezed through one lane. It's going to take a long long time to get home tonight honey. Conversely, if you had a 10 ohm resistor, it's like a 10 lane freeway being squeezed down to only one lane. The analogy is flawed, I know. But it gives you a better idea of how resistors work. Electrons are just like cars. Resistors are just like lane closures. it's GOING to slow down traffic. (electrons) Slower traffic, less current. Higher voltage will force more traffic through, but will also generate more heat. Higher wattage.

And wattage is something you shouldn't neglect either. If your supply is 12 volts (just guessing) and it supplies 50 amps then 12 x 50 = 600 watts. Grab hold of a 100 watt light bulb. Too hot to handle. SIX OF THEM AT ONCE ? ? ? More worry about the insulation's ability to withstand the heat as opposed to keeping the current from going to something else.

I am using a DC current supply to pass 50amp to a load of about 10milli-ohms, not megaohms.

 

I am running the device from a 50amp DC current source, not a voltage source.

How do you get 50A to flow without any voltage to shift it along?

 

How do you get 50A to flow without any voltage to shift it along?

It's a current supply like this one:
http://www.mastechpowersupply.com/v...ltage-over-current-protection-220v-input.html

 

I don't believe that I have ever personally insulated a wire. They used to have what we called an electrical varnish. You could dip, brush or spay it. I think it was good for 600 volts or such. That was long ago. Sometimes we would apply it to metal chassis to prevent arcing.

I'm sure they have better stuff now.

Search on google.

From various posts; I deduce that the voltage is very low, from that point of view; insulation won't be very demanding.

The issues I see are mainly the 50A current that may demand a high tolerance to temperature. The solid wire gauge mentioned will be rigid, in certain situations that can be arranged to eliminate touching anything else - perhaps there are other things in its environment that could touch it. That probably rules out any spray on insulating coating that could be easily abraded. I'd go for some kind of push on sleeving, there are many choices. PVC is probably cheapest if temperature isn't an issue. There's various kinds of silicone rubber sleeving for moderate to high temperatures - or the polymer coated woven glass fibre sleeve like they use in electric heaters.

Heat shrink sleeve gives a nice neat tight fit, but it isn't so cheap, and carries on shrinking till it splits if it gets too hot.

 

We can only ponder. 50 amps sounds like a coil to me. At what rate is the 50 amps applied?
Any circuit reactance?
Are you using the 25 watts of heat or flux? If it's flux.......one can get a high voltage reaction.

I would use regular insulated wire just for the oxidation protection of a 50 amp surface.

 

REALLY? To get 50 amps to flow through a 10 MEG Ω load you'd need 500 MEGA Volts.

Tony, he used a lower case m which I think would imply milli Ohm rather than Meg Ohm.

Ron

 

10milli-ohms, not megaohms.

Oh. 0.01Ω. Well, 0.01Ω x 50A = 0.05 v ? A wire all by itself dead shorted - depending on length - can be more resistance than that.

How about you tell us about your supply and your load. We'll tell you how many amps it's going to draw.

 

Oh. 0.01Ω. Well, 0.01Ω x 50A = 0.05 v ? A wire all by itself dead shorted - depending on length - can be more resistance than that.

How about you tell us about your supply and your load. We'll tell you how many amps it's going to draw.

My power supply is this DC current source:
http://www.mastechpowersupply.com/v...ltage-over-current-protection-220v-input.html
The load has about 10milliohm resistance

 

Oh. 0.01Ω. Well, 0.01Ω x 50A = 0.05 v ? A wire all by itself dead shorted - depending on length - can be more resistance than that.

That's what is being done. He is either "vacuum metalizing" of some other type of vacuum coating of a material. They do it also when coating high end lenses . It's how they make the film for making film capacitors and many other things in industry. Not every thing electric is/does apply to electronics. Somethings are done out there that is done purposefully to defy normal electronics , to get a job done. See Gopher's post earlier in the thread.

One place I worked did vacuum metalizing on car interior parts, like dash boards and other trim. Metalized ~100 dashboards at a time in a big chamber similar to an autoclave, just vacuum instead of steam. The chrome on plastic car trim is not chrome but aluminum.
https://www.muellercorp.com/vacuum-metalizing-process/

 

You are wired up to the through the bulkhead connectors correct? All you want to do is insulate a short run of wire on the other side of the through the bulkhead connectors correct? To avoid I*R loss in your feed lines they should be AWG 6 or AWG 4. Unless heat is an issue all you need is some insulation sleeving. Did you look at the links I gave you earlier? Since your load is very low resistance you want your feed lines to be a low AWG to avoid line loss with the 50 amp load. Use decent quality copper terminal lugs.

Ron

 

You are wired up to the through the bulkhead connectors correct? All you want to do is insulate a short run of wire on the other side of the through the bulkhead connectors correct? To avoid I*R loss in your feed lines they should be AWG 6 or AWG 4. Unless heat is an issue all you need is some insulation sleeving. Did you look at the links I gave you earlier? Since your load is very low resistance you want your feed lines to be a low AWG to avoid line loss with the 50 amp load. Use decent quality copper terminal lugs.

Ron

Thanks. What's your recommendation on how tho connect the feed line to the lesker feed through? soldering? wirenuts? barrel connector? crimp connectors?

 

I like Solid Copper Lugs from McMaster Carr Supply or just about any industrial supply store. Get the lug best suited for your wire gauge and make sure the screw hole is adequate. When absolutely necessary I have used aluminum but copper is always my first choice.

Ron

 

Oh. 0.01Ω. Well, 0.01Ω x 50A = 0.05 v ? A wire all by itself dead shorted - depending on length - can be more resistance than that.

How about you tell us about your supply and your load. We'll tell you how many amps it's going to draw.

So what? The SAME current flows through the wire as it does the load. BIG Whoop!

Actually, your big issue will be how to support the wire upon exiting the feedthrough, so it may not be the best solution. Other solutions use large posts and allows the use of welding cable and terminals would actually be more robust.

It's more of something that has to be thought out from start to finish and it may even require a bit of machine shop work. Something like this http://www.mdcvacuum.com/DisplayProductContent.aspx?d=MDC&wr=US&p=i.4.5.4.3&g=m61035 may have been better in the long run.

These https://www.grainger.com/product/3LR08?gclid=CP3jmcmPudICFUVWDQodeSsNCQ&cm_mmc=PPC:GOOGLEPLAA-_-Electrical-_-Wire Connectors-_-3LR08&AL!2966!3!166588026391!!!g!81032123037!&s_kwcid=AL!2966!3!166588026391!!!g!81032123037!&ef_id=WLQwxAAAAN9aMvy0:20170303005326:s sorts of things would help in attaching.

You specifically asked about insulating BARE wire. Here http://www.newark.com/webapp/wcs/st...tegoryId=800000004054&langId=-1&storeId=10194 are some options.

The real point here seems to be inexperienced and not knowing what's available AND you need to take care of the electrical aspects as well. All of the parts have to work together and survive a certain amount of abuse.

Most of the stuff I did was in the 30-40 A range and < 40 V. In the end we needed about 14 of these into the chamber. The outside connector was a real connector and I used #8 wire. I also had available "resistance soldering" (search for American Beauty) which made pin soldering easy. I stocked #8 stranded in 4 colors.

Externally on one system, I took a different approach and created a DIN terminal strip. so, you had chamber to Terminal and Terminals to power supply. This helped in a a number of ways.
1) Easy to disconnect and troubleshoot; 2) You can move stuff around easily; 3) little disturbance on the vacuum side of things.

I THINK in the latest iteration, we had custom solid soft copper wire feedtroughs made similar to the TC feedthroughs of 4 wires each. We needed 3-4 sets and one thermocouple feedthrough. That company was basically able to take a threaded tube with a vacuum o-ring flange and pot/seal bare wires through the feedthrough,
A DIN terminal strip was used to connect to the #8 wires on the exterior of the chamber and you had bare on the inside. You could buy bare screw couplers from a vaccum company.

We also needed the same number of thermocouples in various types. That was a "custom part" . Leads in leads out with TC connectors on both sides.

On one system, the design was really difficult for three 240 VAC heaters. Again, a real connector was used on the outside for each heater with a shielded power cord. Stainless rods on the chamber side with slip fittings on the rods. It was quite unique.

It was engineered to work. any breach in vaccum would have let very deadly hydride gases into the outer ventilated enclosure. This was a UHV system.