Author Topic: Now I know what you were talking about with DC  (Read 1811 times)

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george65

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Now I know what you were talking about with DC
« on: February 19, 2017, 06:02:32 AM »

Got some used solar panels and put them up today. I think that officially makes me a greenie dosen't it?

Hooked them all up and remembered I hadn't tested them.  Stuck a meter across them and got 225V which was right on the money.
Standing there with these 2 lethal wires in my hand and thought, as one does, I give them a flick to short them out and see what sort of a crack and a spark they can throw.

Mother of sweet baby Jesus!
No crack or spark but the arc went at least 4" and was like something from a Movie! I couldn't believe what I saw. Never seen anything like it.
So of course I did it again...Several times after putting on sunglasses wondering if it was the same as looking at a welding arc which I presumed it was only not as strong.
It was like Mad science! I touched them gently and then pulled an arc about 1" that lasted about 3-4 sec till the wire burned away.
Awesome!

Now I understand what I have read about DC arcing.  Never seen that before. I have those HV coils from fleabay that crack and make a racket with a thin little spindly arc and seen Jacobs ladders but this was fat and quiet and freaking amazing.  I had no idea only 200 Odd volts could do that.  Wait till I hook up my other 3 play panels and take it up to near 400V. I'll have to wire the leads to a couple of nails and just see how long I can get an arc to hold.

Might have been arsing around but geez I sure learned something about DC power today. Mucked around with it since a kid but obviously not at these voltages.
This stuff is FUN!

Ungrounded Lightning Rod

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Re: Now I know what you were talking about with DC
« Reply #1 on: February 19, 2017, 09:05:18 AM »
It isn't so much that DC is more prone to arcing as that AC is to some extent self-extinguishing.

AC keeps STOPPING.  If you don't have enough ions left to re-strike the arc by the time the voltage starts showing up the other way, it just quits.

It's easy to see why you need DC rated breakers and switches to handle DC circuits.  They don't get any help from the stop-and-restart of the current, and have to do the whole job themselves.

It gets even worse if there's some inductance in the circuit.  Start interrupting it, trying to slow the current, and the inductor will dump its stored magnetic energy into kicking up the voltage to try to keep the current flowing.  (That's what the capacitor in point-type ignition systems was about:  It gives the current somewhere to go until the points get opened enough to break the circuit.)
« Last Edit: February 19, 2017, 09:11:54 AM by Ungrounded Lightning Rod »

george65

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Re: Now I know what you were talking about with DC
« Reply #2 on: February 19, 2017, 05:35:15 PM »

I had a double Gang breaker lying round so I switched both the pos and the neg into the inverter.
last night I thought there is no break in the circuit itself If I want to change something. I thought I'd put another breaker in series between the panels so I could cut the power before the output leads.

Put one in last night and went out today and for no particular reason, thought I'd switch it off.
As soon as I flicked it, I could hear an internal arc for about 2 Sec. 
OOPS!  Don't want to do that unless I have to or no more switch!

joestue

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Re: Now I know what you were talking about with DC
« Reply #3 on: February 19, 2017, 06:32:21 PM »
you may be able to use a RCD snubber for your breaker.

a diode and capacitor across the breaker's contacts. a resistor across the diode.

the diode is needed so that when you close the breaker, the capacitor does not discharge through the circuit breaker contacts, which would kill them quickly, instead it discharges through the resistor.

the diode needs to be rated for the currrent flowing through the circuit at the time its opened, but you can get away with a much smaller diode. like 3 amps for a 15 amp circuit because the time is so short. but if you go with too small a diode, it just might explode.

the capacitor needs to be large enough to keep the volts across the breaker low enough, long enough, for the breaker to open.

so if you have 15 amps flowing, and you need to keep the volts below 50 for at least 1 millisecond, you need 15 amps times .001 second divided by 50 volts. so that's only .0003 farads, or 300uf. but it has to be rated for the open circuit voltage of your system. so 450 volts maybe. such a capacitor will be about an inch in diameter and 2 inches long.  you can probably find a few of them of similar ratings in a plasma tv.

Ungrounded Lightning Rod

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Re: Now I know what you were talking about with DC
« Reply #4 on: February 20, 2017, 02:28:34 PM »
Remember that if you put a snubber across your disconnect, and it fails shorted (or the voltage is high enough to push through it), you didn't disconnect.  This is a safety issue.

Snubers are for modulation switches, such as thermostats, not for disconnects.  Using them there means you just broke UL and code approval.  If your house burns down - even if the thing you did didn't cause it - you get no insurance payout.

george65

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Re: Now I know what you were talking about with DC
« Reply #5 on: February 20, 2017, 10:08:42 PM »

Codes and certifications are the last thing I need to worry about in this setup. It would not come near compliance and I couldn't care less frankly.  The way standards are here, even New installs  by qualified people are questionable due to conflicts in said code. It has been well pointed out that complying with one part would void another and there is a 3rd conflict as well so really depends on where you want to point the finger.

I added a couple of extra panels to the setup yesterday and flicked the double breaker off. I didn't detect any arcing. I was wondering if that was because I killed both poles at once?
If so, that will be OK because I can switch off there then on the mid circuit breaker just for good measure without having to worry about frying the switches.   Probably not going to need to do that much now anyway. I'm happy with the way it is set up and the safety of it. May not meet any theoretical far fetched code but it meets mine which is a lot more stringent in real world matters.

I think these rules and regulations have well gone past looking after the safety of people and far more into looking after the financial interests of the industry.

I'll wait for a sunny Day and do a YT vid of the arcing. I think it will be enlightening to a lot of people. It certainly was to me and I play with this stuff ( AC electricity) a lot more than most people not in the trade. 

littleharbor2

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Re: Now I know what you were talking about with DC
« Reply #6 on: March 15, 2017, 06:41:24 AM »
 1, High voltage DC can be lethal. Why are you playing with it?
 2, Disconnecting  a live high voltage array and creating an arc is going to ruin the contacts in the connectors.
2100 watt Suntech array, Midnight classic200, NEW (commissioned 2015) Trace SW 4024, 700 Ah @ 24 volt AGM bank, Bogart Trimetric and tons of Baja Sea of Cortez sunshine.

george65

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Re: Now I know what you were talking about with DC
« Reply #7 on: March 15, 2017, 08:35:52 AM »
1, High voltage DC can be lethal. Why are you playing with it?

Because I enjoy it. I'm learning a lot and find it relaxing.

Driving my car to the shops can be lethal.  Not one single Friend, relative or person known to me has died from being electrocuted.
Both my mother and brother were killed in car accidents and they are not the only people I have personally known to be taken away by that cause. While electrocution can happen no question, the thing most people wouldn't give a second thought to as against playing with high voltage has caused me significantly more grief.

And then there is my own position. I really don't care if I live or die.  I don't want to be sick but I'm not worried If I do inadvertently off myself.  If you think this is dangerous, you would not have wanted to be around about 18 months ago when I was really depressed and playing with my 3 phase induction motors.  I had death mm away from me day after day and I figured what ever happened was meant to be.  Still here so I figure I will be a while longer.

If there is one thing I absoloutley abhor it's over the top whining safety Sissy's.  They can wrap themselves in cotton wool to their hearts content and I won't say a thing If they leave me to look after my own personal responsibility without their constant whining.

Funny really. Everyone worrys about people killing themselves but never take into account some people may not actually care.

Quote
2, Disconnecting  a live high voltage array and creating an arc is going to ruin the contacts in the connectors.

Yes, I am aware of that and mentioned it here. Thanks for the heads up no matter how belated.

Soon as we get some sunshine again, I'm going to hook in my other 3 panels which should give me about Mid 300V. I want to shoot some vids of the arcing for my YT channel.  I find it quite fascinating and I know my viewers will too.  Normally it's just huge fires and molten metal I play around with but I think this will be something people will get a kick out of.... If I don't get a bigger kick first and never get to put it up!  :0)

Mary B

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Re: Now I know what you were talking about with DC
« Reply #8 on: March 15, 2017, 03:51:30 PM »
I used to play with ham radio amplifiers that ran at 4,000 volts and 1 amp... long as you are careful it is safe. But that big iron in the transformers got to be to hard on my back so now I run amplifiers at 50 volts and 40 amps...

1, High voltage DC can be lethal. Why are you playing with it?
 2, Disconnecting  a live high voltage array and creating an arc is going to ruin the contacts in the connectors.

george65

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Re: Now I know what you were talking about with DC
« Reply #9 on: March 16, 2017, 04:14:00 AM »
Quote
I used to play with ham radio amplifiers that ran at 4,000 volts and 1 amp... long as you are careful it is safe.

I agree.  I'm pretty pedantic despite my devil may care attitude. Well usually anyway. I think for a while there I was tempting fate but it didn't happen so all good.
You can always have an accident but repeatedly, the things in life that have caused me the most grief were not when I was doing something that was dangerous, it was when I was doing some everyday innocent thing that no one would warn you about or think twice over.

Just like car accidents. I have done my share of stupid things like thrashing cars round corners of wet roads in the small hours of the morning and never put a scratch on a vehicle or myself. Every single prang I have had was when I had been stationary for a time and some git ran into me.
Twice the car was parked properly and legally. Last time a few months ago I had been puttering along in traffic and not hit more than 30 km/h in over a Km and had been stopped over 20 sec and some bimbo watching her phone rather than where she was going cleaned me.
Good job it wasn't a guy because I would have belted the hell out of them because I was so livid at the stupidity of it and then I would have ended up in the pokey.

There is a whole world of difference between what most people whom sit on their butts and drone on about "safety" on YT all day and really putting yourself at risk doing something hands on you understand the risks and dangers of..... which are never what the safety Sissys drone on about.