Stupid Electrical Question

[buffo]

i know you can do it with 2 Honda generators/inverter and the cross over cable they sell

See that box on the front of the second unit (the one on the left)? That's not found on a standard unit. It's what handles the synchronization. Also note that it only works with certain generator models, and they're usually the smaller ones (because they're easier to synch up - you can be +/- 30 degrees off when you parallel and the lightweight rotors will jerk themselves into alignment).

Bottom line: if you don't have a generator that specifically states it can be paralleled with another A/C source, that cable won't work.

Adam

[dnar]

lightweight rotors will jerk themselves into alignment

I know some people like this!

FYI, I designed and manufactured the synchronization and load-shedding equipment for the Ord River Hydro-electric plant back in the mid 90's.

[buffo]

HAHA! Love it!

True story follows...

I actually watched an electrician parallel two running A/C generators (big machines - 300KW each) without a synchroscope. Unintentionally, of course.

It was when I was in Nuc prototype training in the Navy. I got assigned to the S1C site (the Tullabee prototype) in Connecticut, and at that facilty all the major breakers for the electrical plant were operated locally. (The electrical operator actually stood watch out in the spaces, right next to the switchgear, rather than in the maneuvering room like on other boats.)

Anyway, we were in the middle of a scram drill. Unlike real boats, at a prototype facility, when the reactor scrams, the steam stops shut automatically, so you lose all steam. So naturally the tubine generators (TG's) go off-line as well. Remember that the electrical plant is split in half (port and starboard) with a large TG feeding each side. When you lose steam, the output breakers on the TG's open automatically, and the breakers that connect the TG bus (or non-vital bus) to the rest of the plant also open on interlock.

Part of the recovery was to re-energize the non-vital A/C buses by closing a pair of tie breakers between the vital buses (powered by AC/DC motor-generator units that are fed from the main battery) and the non-vital buses which had just gone dead when the TG's shut down. This is a fairly simple affair; the electrical operator simply closes the breakers by hand right at the switchgear. The non-vital bus is completely dead, so there's no need to wory about paralleling anything.

OK - no problem so far. But this particular plant also had a tie-bus that connected the two non-vital buses. We had a few loads that came off this tie bus, so it had to be powered up as well. (The tie breakers also opened on interlock when the TG's went off-line.) But you only needed to close one breaker from one of the non-vital buses to power up the tie bus. If you closed the other side as well, you'd be paralleling the motor generator units. (Essentially turning the split electrical plant into a big ring.)

This is exactly what I saw a staff electrical operator do! He recognized the scram, motorized the motor-generator units to keep A/C power up on the non-vital buses, and then began closing the breakers to re-engergize the non-vital and tie buses. He only had 3 breakers to close, and they were all right in front of him. Except in his haste, he closed all 4 breakers! Yep - he closed *BOTH* of the tie breakers, and amazingly he got lucky and nothing blew up.

Obviously the two motor-generators were close enough in voltage and phase that the breaker held. However, he immediately recognized his mistake, and with a horrified look on his face, he reached down and re-opened the starboard tie breaker. Moments later, we heard an announcement over the 2MC: "Electrical Operator, report the position of the starboard Tie breaker!"

The Engineering Officer of the Watch in Maneuvering had noticed the breaker indicator turn green, signifying a closed breaker, and then it switched back to red, meaning it was open. From his perspective, it looked like it had closed and then immediately blown open (which it would have usually done if someone tried to parallel out of phase). They were concerned that damage to the motor generators might have resulted. (Remember, these are 300KW machines with a honkin' big DC motor on one end. Unlike a small portable generator, they don't take well to being "jerked" into phase...)

It took a lot of talking to calm everyone down about it, and in the end I think the poor guy got a letter of reprimand out of it. But in fact he just got lucky and everything was fine. Still, it's not something I'd ever want to try! Like playing russian roulette...

Adam

[heroic]

The Honda EU-series inverter generators don't need any additional hardware in order to parallel- the extra box is just a safety interlock to stop anyone going to meet Jesus (which you have a strong chance of doing, using a Jesus cord with two plugs on it...) Their output is synthesized by electronics anyway.

As for running stuff off inverters- I can't say this often enough, buy a true sine wave one. I have a bunch (a big 3 kW Xantrex ProSine 3.0, and a couple little GoPower ones.) The big Xantrex is none too portable, so I have a little 600 watt GoPower one with a PowerPole tail on it, for those times when I need power somewhere there isn't an outlet. Being a pure sine wave output, everything works with it, without exception. No funny noises, no problems with audio stuff.

For your purposes I'd recommend this: http://www.gpelectric.com/content/pr...t/?i=GP-SW3000 which you should be able to pick up at a pretty decent price.