Question about using run/start capacitors

Relative Humidity

WET BULB / DRY BULB

https://www.youtube.com/watch?v=2265UNflXT4

cajundood wrote:
Hmmmm very true..... My test conditions were 80 degrees or so and my area is perhaps 15ft. above sea level. (very low around here)

the true test will be how it functions when your camping at your typical temperatures and altitude.

actually it is density altitude that is key. takes into account actual barometric pressure, humidity and temperature in comparison to the defined conditions for sea level. and sea level conditions are for 15C, roughly 60F.

this summer when I was at 4500ft and 95F, and low humidity, as I mentioned in a previous post, I was overloading the generator. A quick calculation showed my density altitude was 6200ft!!

No wonder I was running out of power

here is a link to a site that will give you density altitude if you know pressure, temperature and dew point

density altitude calculator

here is another one if you know temperature, pressure and relative humidity.

density altitude calculations with RH

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Are hard on the digestive system. Involved is a liberal shovel full of aged crow.

Without hard numbers to work with - this is true "Shake The Jar Dewey And See If They Fight"

If that generator is running at 98% theoretical load capacity then you aren't going to like the outcome.

Hmmmm very true..... My test conditions were 80 degrees or so and my area is perhaps 15ft. above sea level. (very low around here)

SoundGuy wrote:

cajundood wrote:
FYI to all the nay sayers.... IT WORKED!!

For now. Unfortunately there's a lot more to it than this simple test you've done ... not only will higher ambient temps and increased elevation make this much more difficult but so too will repeated attempts by the compressor to restart repeatedly. Lotsa luck if you actually believe the "naysayers" don't know what they're talking about. :R

yup. been there done that. thought I solved the problem with a better start cap. went from instant overload to start with a obvious grunt. This was near sea level and temps in the 80's. Went camping, sea level temps in the mid 90's and after about 3 tries I got it to start. inland at even 2500 ft and the mid 80's. nope. no luck

even the microair is not a complete solution. temps in the upper 90's at 4500 ft easy start on our coleman MachIII with the honda 2000 in eco mode, but the little honda is rated for 13.3A continous at sea level. that's close to the Mach III draw. after about 10 minutes the micro air would detect source overload and cut the compressor for 5 minutes, then restart. i suspect the generator inverter was either showing a voltage droop or varying current. The EMS didn't indicate low voltage, but close to it, around 110V afer 10 minutes. Initally the honda was around 115 and that's what it would stay at near sea level.

above about 4000 ft depending on temperature I need to parallel generators even with the micro air.

So..... before you claim success, test it in YOUR real world conditions.

cajundood wrote:
FYI to all the nay sayers.... IT WORKED!!

For now. Unfortunately there's a lot more to it than this simple test you've done ... not only will higher ambient temps and increased elevation make this much more difficult but so too will repeated attempts by the compressor to restart repeatedly. Lotsa luck if you actually believe the "naysayers" don't know what they're talking about. :R

ScottG wrote:
The start up current is much higher than that but your KAW can't catch it.

X2
And, the LRA of a 120V frig and a 5K BTU AC can't be handled by a 1000W inverter, either in sequence or simultaneously. A 1000W inverter will handle a small compressor fridge (I do it). If you can split the loads, you may be able to run the fridge and start the A/C. It will depend on the LRA of the A/C compressor.

The naysayers are going on numbers, experience and physics. You are going on plug it in and see what happens. Keep in touch with how it works out for you, it could be valuable for those who want to do the same. It's not one size fits all (altitude, temperature etc) so it may work in your situation.

DrewE wrote:
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.

I agree, it is nowhere near a clone of the micro air. I have the micro air. it has way more circuitry, a learn circuit with reset mode, AND guess what, it's own starting cap to replace the start cap in the factory AC unit. And it's wiring is more complex. It also has a delay circuit to let the fan start and get the generator rpm up a bit before it kicks in to start the AC compressor.

And the micro air has an overload detector that kicks in if it sees the compressor power source appearing to overload and will kick off the compressor before it is damaged.

cajundood wrote:
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.

given the results, be careful before you claim success. Wait till it is near 100F outside and try to start it. If that succeeds, see what happens when you get to 3,000 or 4000 ft in altitude.

you may find yourself back in a no start situation.