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Patrick

Tue Aug 31 2010, 04:45PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Klugesmith wrote ...

If one breaker trips (or has tripped) while you have a load or arc between the
two HV secondary terminals, all outlets on the tripped circuit
will be back-fed with voltage from a MOT running in reverse.

I woke up I the middle of the night! I tried to post but my internet connection wouldnt work. Im glad Klugesmith pointed this out. I meant to warn Grenedier of this very point.

Adam Munich

Tue Aug 31 2010, 10:00PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Never thought about that. That's not good at all... I wonder if this guy thought about that.

Kristian wrote ...

OK I had a go at this. Posted a video. Here it is

These are not current limited. Each mot is on its own 20A circuit. I put the caps in a bucket just in case of a catastrophic failure.

I will be trying 4 mots and 4 strings of 4 caps this weekend. I'll post a vid next week.

My goal was to try the resonant MOT thing when I got a few more caps, but the biggest I have is a 20A circuit...

ScotchTapeLord

Tue Aug 31 2010, 10:48PM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635

What if you paralleled the circuits and then hooked the resulting wire containing the current from both breakers up to both MOT primaries? Just make sure phasing is correct or you'll short out your mains. That way if one fails, the other one will take over and fail cascade style.

klugesmith

Tue Aug 31 2010, 11:49PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

ScotchTapeLord wrote ...

What if you paralleled the circuits and then hooked the resulting wire containing the current from both breakers up to both MOT primaries? Just make sure phasing is correct or you'll short out your mains. That way if one fails, the other one will take over and fail cascade style.

1. The current will split between the two "hot" wires in the same ratio as the wire resistances (including extension cords). Same for the two neutral wires. If the neutral ratio is different from the hot ratio, you could have a sustained overcurrent in a neutral that is not protected by a circuit breaker. If you -must- do such a foolish thing, at least have a clip-on ammeter and verify the balance of both the hot and neutral currents.

2. If one circuit breaker opens, its circuit will be back-fed. If load stays on and the second breaker suddenly takes the full current, it could stay closed for 10s of seconds, depending on what fraction of the full current it started with, and the mfg. differences between the two breakers. How will you know when one breaker has tripped?

Patrick

Wed Sept 01 2010, 12:45AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

yeah im beginning to think this may not be such a good way to proceed. But its up to Grenadier.

ScotchTapeLord

Wed Sept 01 2010, 12:48AM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635

If you do this, I recommend plenty of external fuses, especially on the neutrals, because of what Klugesmith said. Perhaps for better balancing, you could use some inductive ballasts before paralleling the lines? Even if it's just an extension cord coiled up for both of them to even out the resistive and reactive impedance. You'll have to adjust your resonant capacitor to account for the added inductance, but it should help.

Although if the one circuit breaker backfeeds through the ballasts that could get interesting. Though I don't see a huge issue as long as you have breakers that are completely dedicated to this project, as in nothing else plugged into them.

"Foolish" is in the eye of the beholder...

Though it would probably be a better idea to do this with a car/marine/lawn mower battery and inverter instead. Or a generator!

Adam Munich

Wed Sept 01 2010, 01:18AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I don't know of any inverter that can swing that many watts. At least none I can afford. Plus inverters are typically non-sinusoidal, and that could cause a problem.

Also, assuming 100% efficiency of the inverter, it'll be drawing 150A per MOT on the batteries. I have 2 100Ah 12V gel cells, but I doubt they could supply that kind of current.

Patrick

Wed Sept 01 2010, 01:27AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

for best safety i think you would need isolation transformers, that would solve at least your holding tripped circuits high. but for your wattage they would be big.

how high is your output voltage unloaded?

radiotech

Wed Sept 01 2010, 01:27AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

Grenadier wrote "I don't have a 240VAC line installed"

Many homes dont. Two 120 volt plug circuits add up to 208 volts. Reversing the polarities of loads of series transformers connected to different circuits give interesting voltages.

This can happen when the power company replaces pole pigs and mixes up the connections.

Believe it of not, today with UPS backed systems you may run into areas that have 50 Hz on some recepticals and 60 Hz on others.
Mix those circuits for neat efects on lighting.

Adam Munich

Wed Sept 01 2010, 01:28AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

120 + 120 = 240.

208V is the voltage across two lines of a 3 phase. I don't have a three phase!

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