Wire resistance/voltage drop

[macona]

I had thought of DC/DC converters but that just adds more wasted heat in the system. Plus, finding a 30 amp model in 12v in 12v out is kind of difficult.

I have been looking for power supplies with sense but they dont seem to exist at reasonable prices. And I would have to run another set of wires for sense.

[Evan]

And I would have to run another set of wires for sense.

If the load is fixed all you need to do is up the voltage enough to compensate for the drop.

As for sensing, you don't need remote sensing. You can sense across a micro-ohm resistor at the source. The current is the same at all points in the circuit.

[macona]

Ideally I would like to chance cable lengths for the situation. And if I am running multiple lamps off a single power supply all radiating from the central supply it would cause issues for one on a short line.

I just ordered some real copper. Ill post my results when I get it.

-Jerry

[J Tiers]

Come on, low voltage will heat the connection just as well as high. It's the power available that matters. If it were otherwise welding wouldn't work and car wiring harnesses would never burn up.

The low voltage MAY not be sufficient to force enough current through to produce teh power you refer to.

or it may be......

Welding is generally at more than 12V. Double that is common..... the arc does not strike well at low voltages... although MIG may be low voltage, particularly the short-circuiting type as opposed to spray transfer.

And harness fires are as often shorts heating the wire and burning off insulation as they are loose connections at legitimate connectors..... probably more so. A short is a good connection in the wrong place...... not a bad connection in the right place.

[Black_Moons]

The low voltage MAY not be sufficient to force enough current through to produce teh power you refer to.

or it may be......

Welding is generally at more than 12V. Double that is common..... the arc does not strike well at low voltages... although MIG may be low voltage, particularly the short-circuiting type as opposed to spray transfer.

And harness fires are as often shorts heating the wire and burning off insulation as they are loose connections at legitimate connectors..... probably more so. A short is a good connection in the wrong place...... not a bad connection in the right place.

*Sigh* Ok, You go find any 20' wire thats not made outta nichrome that won't burn off its insulation when shorted across a 12V car battery, And you might have a point.

Otherwise, Don't say stupid stuff like low voltage won't cause a fire because it can't 'force enough' current through a wire.

On a *VERY* long run, or *VERY* low voltage, That *MIGHT* be true. But in most cases, it is not, and low voltage is just as likey to cause a fire when improperly rated for the current (or improperly connected)

[J Tiers]

*Sigh* Ok, You go find any 20' wire thats not made outta nichrome that won't burn off its insulation when shorted across a 12V car battery, And you might have a point.

Otherwise, Don't say stupid stuff like low voltage won't cause a fire because it can't 'force enough' current through a wire.

On a *VERY* long run, or *VERY* low voltage, That *MIGHT* be true. But in most cases, it is not, and low voltage is just as likey to cause a fire when improperly rated for the current (or improperly connected)

IF YOU WOULD READ THE FREAKING POST INSTEAD OF CALLING ME AN IDIOT BEFORE COMPREHENDING THE POINT.....

I SPECIFICALLY SAID that the battery could burn up a shorted wire...... I blamed most harness fires on that, in fact.....

My point was that a BAD CONNECTION *may* be bad enough (or get that way rapidly), that it limits current in a lower voltage system, and doesn't heat up as much.

In a higher voltage system, the current limiting is not so effective, since so much more voltage is available to force current through the higher resistance of the bad connection, so the risk of a fire from a BAD CONNECTION is quite a bit more.

It is also a lot easier to start and sustain arcing in a high voltage system than a low voltage system. That is one reason why the current rating of a relay or switch may be 10 or more times higher at 12V than at 125 or 250V.

SHEESH........... SOME PEOPLE.........................

[Forrest Addy]

I love the way a simple little Volt Amp Ohms problem can degenerate into a food fight AND a geek-speek war.

[darryl]

There is nothing to be arguing about here. The point we should be taking from this is that more and more you can expect to be 'faked out' when buying a product. Wire in particular is supposed to be copper- we've all known that for a long time, and used miles of it successfully. Suddenly you get what seems like the same stuff you've used before, and it doesn't work the same. When the application is to be able to pass lots of amps with acceptable and expected losses, and the product is not capable of it, now there's a danger. Wire should not get hot in use, and to say that it has high temperature insulation so don't worry about it- or feed it more voltage so you still have enough at the end- sorry but this is bs. It violates the principles of the safe use of electricity, regardless of low voltage, high voltage, whatever.

If the wire is getting hot because heat from the powered device is conducting back along the wire, that's one thing, and the insulation needs to be spec'd to take it- but if it's getting hot simply by passing current, then this issue needs to be addressed and rectified. When Jerry get his 'real' copper wire, his problem will be solved. He's already done the math and selected the proper gauge of wire for the job. I'm sure I'm not the only one who's checked the math on that.

The writing on the wall is- you can't trust product anymore, and you should take care to test what product you buy and use to make sure it is what it should be and does what it's supposed to. Sometimes something less than this is just an inconvenience or a piss-off, but sometimes it's dangerous. Beware and take care.

[J Tiers]

There is nothing to be arguing about here. .

Nobody called you an idiot............ its cheap for you..... I don't particularly like being called an idiot, maybe you do. Although one must consider the source, who in this case shot off "mouth" without reading......

Oh, well, the perp may re-invigorate my ignore list. Most everyone else who was on it got banned eventually.

I love the way a simple little Volt Amp Ohms problem can degenerate into a food fight AND a geek-speek war.

Truthfully, that comment is beneath you, Forrest.

[Evan]

The writing on the wall is- you can't trust product anymore,

The problem is one of product labeling. Wire can be made from nearly anything and copper clad aluminum is very common in heavy gauges. With wire meant as a conductor it is especially important that it be properly identified. In this case it really is a case of Caveat Emptor.

A maxim of Roman law now part of British-tradition common law, that a buyer's omission to make fundamental inquiries and inspection(s) of property leaves the purchase of deficient property at the buyer's peril if he does not.

[macona]

There is no real way under a normal load that this aluminum wire will cause a fire. Even at my 1.5v voltage drop thats a whopping 18 watts dissipated in 20 feet of wire. It does not even get noticeably warm, at least not for the period I ran the light.

For it's intended purpose, car amps, it really does not matter. They dont have the continuous load that I am putting on plus they normally use stiffening caps at the amp end to supply the high peak current.

Though they do list the wire for use with other things like winches, many of those things will not notice much of the voltage drop. With these lights I am running there is a significant light falloff when I get below about 11.5v.

[Black_Moons]

IF YOU WOULD READ THE FREAKING POST INSTEAD OF CALLING ME AN IDIOT BEFORE COMPREHENDING THE POINT.....
It is also a lot easier to start and sustain arcing in a high voltage system than a low voltage system. That is one reason why the current rating of a relay or switch may be 10 or more times higher at 12V than at 125 or 250V.

I did'nt call you an idiot, I said you said something stupid. We have all said something stupid from time to time, And I considered the whole 'Low voltage might be safer' idea to be similar to 'No need to turn that small torch off before putting it on the ground, After all, Its smaller, it might run outta gas before setting the house on fire!"

Btw: Did you know that *DC* 12v current ratings can be lower then 120v/240v AC current ratings, Depending on load? Apparently not.

http://components.omron.com/components/web/pdflib.nsf/0/0EBF7B9FF347100085257201007DD582/$file/LY_0609.pdf

Note this lists 15A at 110v AC and 24v DC... resistive load.

10A at 110AC inductive load, and only 7A at 24V DC. (For SPDT, Contact data page 3)

DC is much easyer to sustain arcs then AC due to lack of zero crossing.
At higher currents, DC relays start to offer 'magnetic arc blowout' features.

http://pewa.panasonic.com/assets/pcs...js-catalog.pdf
Another good one: Page 3, Max switching capacity (resistive load, Long endurance type, The other type has a lesser current rated Normaly open contact)
Resistive load: 10A 250V AC, 10A 125v AC, 10A 227V AC, 5A 30V DC.
Also, it has a chart stating that current rating does not incress below 30v DC, but does rapidly drop off above 30v DC, while AC loads do not suffer such a dropoff untill over 250v

Never trust an AC current rating to hold true under low voltage DC. Even if its speced for 250v+ at 10A, It might only be speced for half that at 12v!
And for extra fun, Not all relays are rated the same current on all contacts!

Now, You go find me two 12v DC 100A relays that spec 10A at 120v AC.

[J Tiers]

I did'nt call you an idiot, I said you said something stupid.

Which I did not...............

[macona]

Got my real copper wire yesterday. What a difference. On a 15' length I am getting a .3v drop. That's better.

Ill post later this week or next on these lights. They are pretty incredible.