Question about using run/start capacitors

Start capacitors (and run capacitors) for single-phase induction motors all work by altering the phase angle for different motor windings; without that, the motor would not start at all. (There are some induction motor designs that use other means to generate the phase shift, but that's a different matter entirely. Probably the most common of them is the shaded-pole induction motor used in many relatively low-power, low-starting-torque settings.)

Micro-air sells and has pictures of their boards out of their enclosures on their web site. Theirs are clearly a lot more complex than the one you show above.

I would guess the gizmo you pictured probably just acts as an AC current limiter, based on an opamp/comparator that samples the current via one of the power resistors and switches whatever semiconductor switching device that is on the heatsink. If so, it seems like a good way to kill off a pesky air conditioner compressor you didn't really want to be carrying around on your roof. I can't make out the part numbers on the little IC, so I may be way off base in what it does or how it works.

FYI to all the nay sayers.... IT WORKED!!
I hooked up the 5k but ac to the 1000w generator that had just arrived.
Started the fan on low. after about 10 seconds kicked on the compressor....the generator "faulted" and quit.
Well today the supco "hard start" capacitor arrived and I immediately proceeded to try it out. Went through the same process and when the compressor kicked in the genny faltered for just a second then kicked up just fine. So now I have ac running on a 1000w inverter generator.

Anyone ever use one of these?..... I believe this is the same "soft starter" as the one made by microair that they sell for $300 online.....it just doesnt have the name or a fancy plastic housing. From what i gather......a "soft start" changes the phase in the windings rather than store electricity creating a lower surge requirement. I found this online from a company in china for $46. It's specifically designed for motor loads up to 25 amps, the voltage rage is 110-120v. I'd be willing to BET, that this is the same "guts" thats in the $300 unit sold by Microair

I designed and built analog synchronization stations for gensets up to 100 Kw. What I read above is IMHO absolutely right on the mark. With analog versus digital control it takes a trained operator and specially matched generators to have an -effectively- paired set. Constant monitoring is a must.

Just for chatter, improper monitoring provides the possibility of a leading/lagging pair in which the leader is dragging the lagger, which will overload and overheat the former.

The idea of large inverter gensets appeals to me. Tweaking waveform automatically (limiting THD is one benefit). The second is variable prime mover speed according to load. Of course with diesel and turbocharging the speed range is limited.

I did handstands finding a top quality 12 turn small head (generator), and invested a fortune into modifying a Kubota diesel to effectively have power at 12 turns (1,200 RPM). It agonizes me to see that generator loaf at perhaps 2Kw. Still rotating at 1,200 RPM

I'm envious :)

ktmrfs wrote:
So..... only do this with generators DESIGNED to be paralleled.

Yes, Drew already pointed this out.

2oldman wrote:

cajundood wrote:
those parallel devices.......do they work well? do they require same wattage generators on both sides?

It's just wires. I can't say for sure, but like paralleling batteries, it's probably a good idea.

well, yes it is "just wires" but the key to them being able to be paralleled is INSIDE the generator. your working with AC here. the generator outputs must be absolutely synced in frequency and phase. So.... they both have to have a means of syncing the phase and frequency, then regulating the voltage.

So..... only do this with generators DESIGNED to be paralleled.

MEXICOWANDERER wrote:
The problem with live digital to capture peak events is the sampling rate per second.

If it's "too slow" it'll never see the peak as it passes over its head.

If it's too fast, changing numbers for instant updates turn the numeric segments into a blur.

To rate high speed sampling it takes a processor and enough random access memory. It would be a real eyebrow raiser to see that in an inexpensive device.

My Columbia analog meter uses a (something like) 9 jewel D'Arsonval movement of extremely low mass to minimize inertial lag and over run. "Warning Hermetically Sealed" can still be made out of the case halves seal. This was a pricey instrument in the 1940's. Supposedly has its origin in Hanford, WA. The meter is now encased in 2" charcoal gray block foam. The pickup was a killer. Two hundred dollars from Meter Master. Back in the late 1980's. The 2" loop diameter allows for compound wire winding for 2x 4x 8x. One of my treasured no-touchee gizmos.

Even with all that the meter is not precise. It can only give a rough approximation of inrush current. I would love to find an instrument that is digital, has max min storage and re-call. That and a peak-to-peak meter.

Dream-On Mex

very good summary of measurements. And the Tek power analyzer is one nice piece of equipment.

many of the newer quality meters (e.g. not low cost by any means) have a "Peak Hold" function which will display the peak reading. Some even have min-max-avg functions.

When I measured by starting current with the micro air I used a Tektronix clamp on current probe, NIST traceable cal that had the peak hold function.

On the Mach III on my trailer locked rotor amps were near 60A, while peak current with the micro air was 20A or less. I measured with each "learn cycle" that micro air has you do, and the first cycle was near 60A, by the 4th it was down to 20A.

And the meter sample interval was 10ms, so at 60hz, it should have captured the true peak current.

Meanwhile again using a Tek true RMS DMM I measured the honda 2000 Voltage during startup with the microair looking for the min voltage. Don't have the exact data, but from what I recall, it didn't drop below 110V during startup then settled to only a few volts under 0 load voltage.

cajundood wrote:
those parallel devices.......do they work well? do they require same wattage generators on both sides?

It's just wires. I can't say for sure, but like paralleling batteries, it's probably a good idea.

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5 mW standby power measurements to IEC 62301
Color Graphics Display
Two Current Shunts
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I won't mention the price. It brings tears...

The problem with live digital to capture peak events is the sampling rate per second.

If it's "too slow" it'll never see the peak as it passes over its head.

If it's too fast, changing numbers for instant updates turn the numeric segments into a blur.

To rate high speed sampling it takes a processor and enough random access memory. It would be a real eyebrow raiser to see that in an inexpensive device.

My Columbia analog meter uses a (something like) 9 jewel D'Arsonval movement of extremely low mass to minimize inertial lag and over run. "Warning Hermetically Sealed" can still be made out of the case halves seal. This was a pricey instrument in the 1940's. Supposedly has its origin in Hanford, WA. The meter is now encased in 2" charcoal gray block foam. The pickup was a killer. Two hundred dollars from Meter Master. Back in the late 1980's. The 2" loop diameter allows for compound wire winding for 2x 4x 8x. One of my treasured no-touchee gizmos.

Even with all that the meter is not precise. It can only give a rough approximation of inrush current. I would love to find an instrument that is digital, has max min storage and re-call. That and a peak-to-peak meter.

Dream-On Mex