micro-air easy start

[rockwind1]

all i can say is wow! best money ever spent on this total piece of **** 2007 fsakg33 Attitude toyhauler trailer. almost insulting to the micro-airs to be on the trailer. i had looked at micro-airs a couple years ago and for some reason didn't get them, probably price. i bought a supco for my front 13,500 ac. that thing is useless. so i bought 2 honda eu2000i's, one a companion and my plan was to run them together to start and run my 13,500 unit only cuase i don't think it would start my 15,000 unit. anyway, recently had the start capacitor go out on my big unit and was messing around on the forums and found the micro-air mentioned again. i was highly skeptical. but i called their tech line, talked to some guy who sounded pretty smart. then i emailed the sales dept and bought 2 of them. put them in both my units. simply unbelievable, i can use only a single honda to start either one of them and run them,,,,probablky won't do both though, i didn't even try. i didn't use eco mode though, but i suspect it will work.

when i get to finally upgrade to a real trailer that wasn't built by mentally handicapped people (or simply built by idiots who don't care about quality), i will remove them and put them on the new one.

if you are on the fence, they get my seal of total approval, i mounted mine from underneath, just inside the grill of the cold air side of the big unit, and just inside the grill of the return air on the dometic 13,500. had to route the wires differently but it worked out slick and i think they will stay a lot cooler there since i live in las vegas

[TurnThePage]

MEXICOWANDERER wrote:
The eleven thousand horsepower 3800 volt three phase motor at the refinery was a real trip when starting...

General notification went out hours in advance to all refinery process units to minimize usage. PG&E Pacific Gas and Electric boosted nominal distribution voltages to achieve 260 volts phase to phase, a few minutes before startup.

Then right out of a movie scene in a prison when "The Chair" dimmed the lights in prisoner cells, voltage slumped by 10-15 volts phase to phase.

I forgot the motor-start time limit. It was something like 15 seconds. The stator resonance shook a three foot thick unit concrete pad. About a third of the time the isobutane compressor failed to cycle. The motor was shut down and had to cool for seven hours before a re-start was attempted.

The start switch used a pump. A U-Handle with a foot long grip prong. About a dozen pumps in all. The contact lever had to be pushed up and with a BANG the contactor closed. The smell of ozone permeated the air.

Shell ended up purchasing the PG&E brick generating plant located on Shell Avenue. 28 Megawatts.

After seeing this, regular motor starting shrank in perspective 🙂

Not tryin' to change the subject, but that describes pretty closely my vasectomy experience. :B One moment laying there with florescent lights shining down, a Jackson Brown cassette playing over the doctor provided head phones, then the lights dim, the music sloooowwws, there is an arc of light, a puff of smoke, the smell of burning flesh, then everything returns to normal, except of course the Valium's effect wore off instantly. And I still had one more to go.... :E

[time2roll]

That is a lot of power although I always understood 3-phase motors were far easier to start as the natural rotating vector forces are the same as the power generated.

[Travelin2]

MEXICOWANDERER wrote:
The eleven thousand horsepower 3800 volt three phase motor at the refinery was a real trip when starting...

General notification went out hours in advance to all refinery process units to minimize usage. PG&E Pacific Gas and Electric boosted nominal distribution voltages to achieve 260 volts phase to phase, a few minutes before startup.

Then right out of a movie scene in a prison when "The Chair" dimmed the lights in prisoner cells, voltage slumped by 10-15 volts phase to phase.

I forgot the motor-start time limit. It was something like 15 seconds. The stator resonance shook a three foot thick unit concrete pad. About a third of the time the isobutane compressor failed to cycle. The motor was shut down and had to cool for seven hours before a re-start was attempted.

The start switch used a pump. A U-Handle with a foot long grip prong. About a dozen pumps in all. The contact lever had to be pushed up and with a BANG the contactor closed. The smell of ozone permeated the air.

Shell ended up purchasing the PG&E brick generating plant located on Shell Avenue. 28 Megawatts.

After seeing this, regular motor starting shrank in perspective 🙂

Wow, that must have been a scary thing to be around when trying to crank it up.

[MEXICOWANDERER]

The eleven thousand horsepower 3800 volt three phase motor at the refinery was a real trip when starting...

General notification went out hours in advance to all refinery process units to minimize usage. PG&E Pacific Gas and Electric boosted nominal distribution voltages to achieve 260 volts phase to phase, a few minutes before startup.

Then right out of a movie scene in a prison when "The Chair" dimmed the lights in prisoner cells, voltage slumped by 10-15 volts phase to phase.

I forgot the motor-start time limit. It was something like 15 seconds. The stator resonance shook a three foot thick unit concrete pad. About a third of the time the isobutane compressor failed to cycle. The motor was shut down and had to cool for seven hours before a re-start was attempted.

The start switch used a pump. A U-Handle with a foot long grip prong. About a dozen pumps in all. The contact lever had to be pushed up and with a BANG the contactor closed. The smell of ozone permeated the air.

Shell ended up purchasing the PG&E brick generating plant located on Shell Avenue. 28 Megawatts.

After seeing this, regular motor starting shrank in perspective 🙂

[ktmrfs]

when you first apply a voltage source to a AC synchronous motor several things occur. First, when the rotor is stopped, the voltage source is looking into an very low impedance inductive load. that means the voltage source needs to supply a very large initial current. But, as the motor starts to rotate, the motor rotation creates a "back emf" that is the rotating motor acts like a voltage source as well, bucking the incoming voltage source. Once the motor is up to speed the current draw is determined by the inductance and the back emf of the rotating motor.

So, to start an AC synchronous motor you either (a) wack it with a very stiff voltage source, or (b) limit the starting current in some manner until the motor is synchronized and let it start rotating and keep increasing the current (and likely voltage) to get it up to full voltage to keep the current down.

I suspect micro air is using technique (b)

method (b) is a pretty common approach to starting large motors, and with modern electronics, lots of ways to accomplish it effectively, reliably, and at reasonable cost.

[road-runner]

I've several times criticized micro-air's claims but I'm going to back them up on the "slowly raising the voltage" statement. I'll place my bets that they're using a microprocessor controlled thyristor for the hardware. There's no need to keep that a secret as it's not rocket science and commonly used. For somebody who knows how AC speed controls work, it's obvious and there's no need to say it. For others, an explanation would just be a tutorial of something that's pretty common. The "magic" is the algorithm in the microcontroller that determines how to ramp the peak and RMS voltages. That's a trade secret that they will be tight-lipped about. What makes or breaks their product isn't so much in how it works, but in the time and effort of designing and perfecting the control algorithm. Here's an application note for hardware that could be used for what the micro-air does:
http://www.fecegypt.com/uploads/dataSheet/1480855364_triac.pdf

Sure I could be wrong. Based on the size, price, and description of the micro-air, it just looks like it's a thyristor device.

[suprheat]

That's why I said, "I don't think they're telling you the whole story on how it works..."

[road-runner]

suprheat wrote:
watts=volts x amps so if you lower the voltage, amps will go up. I read the FAQS at Easy-Air and it mentioned slowly raising the voltage. I don't think they're telling you the whole story on how it works, probably at the risk of someone making a home-made one and them losing out.

The micro-air mostly likely uses a thyristor to control the AC waveform, same thing that's used in light dimmers. It's not as simple as the basic power calculation. If they lowered the voltage via added resistance the heat dissipated by the micro air would be big, and if they did it with a transformer the size, weight, and price would increase a lot.

[time2roll]

Not quite that straight forward with inductive/reactive load on alternating power.
You need to get into how the phase angle is changed with the capacitor.

I don't completely understand it but I have read enough to know it is over my head and a bit more complex than W=V*A

[suprheat]

watts=volts x amps so if you lower the voltage, amps will go up. I read the FAQS at Easy-Air and it mentioned slowly raising the voltage. I don't think they're telling you the whole story on how it works, probably at the risk of someone making a home-made one and them losing out.

[Unyalli]

ktmrfs wrote:

Unyalli wrote:
So guys, this video details install and tests this unit real time with inrush peak current meter. He has links to the specific times for each test etc.
https://www.youtube.com/watch?v=soP0uZFd0nQ&t=1835s

- Jeff

similar results to what I obtained. see my post on micro air install results.

Yep saw your post, just offering supporting info.
I had a set of twins with parallel kit, upgraded to dual/fuel 3400 electric start. According to champion the propane device is auto altitude compensating. Additionally running off RV propane system I have extended run via propane auto switch over.

- Jeff

[ktmrfs]

Unyalli wrote:
So guys, this video details install and tests this unit real time with inrush peak current meter. He has links to the specific times for each test etc.
https://www.youtube.com/watch?v=soP0uZFd0nQ&t=1835s

- Jeff

similar results to what I obtained. see my post on micro air install results. I went from 60A inrush on the compressor alone down to about 25A inrush on 30A service line and when hooked to the honda 2000 on eco mode, had about a 10V peak voltage drop and 22A inrush current. ramped the honda up smoothly, even better than starting my low current draw, low inrush polar cub on another trailer I have.

before, the honda 2000 was iffy on the start even with eco off at sea level and 80F or less temp. hit and miss on overload trip or not. Not anymore. Still end up with about a 1300VA draw on the honda 2000 which is rated at only 1600VA continous, so it's not going to give much headroom, but good for many occasions.

Don't expect to run the AC and charge batteries, or run a fridge on AC, or turn on the microwave at the same time.

[Unyalli]

So guys, this video details install and tests this unit real time with inrush peak current meter. He has links to the specific times for each test etc.
https://www.youtube.com/watch?v=soP0uZFd0nQ&t=1835s

- Jeff

[Almot]

Good to know that there is something better on the market than previous capacitors circuits.

I think our RVs are not built by mentally handicapped people, but, rather, designed by them :). And built by low-paid workers who don't care about quality.