Question about using run/start capacitors

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Question about using run/start capacitors

Postby cajundood » Mon Oct 30, 2017 12:53 pm

This is for any electricians versed in the use of load and run capacitors to help with ac surges on the genny or the inverter.

I am in the middle of a teardrop build http://www.tnttt.com/viewtopic.php?f=2&t=69081 and I am
trying to get away with as small/light of a generator as possible. I ordered a 1000w sportsman inverter generator and I also have a 1000w inverter unit which will run off of 2 car batteries.
I will be running a small dorm refrigerator as well as a 5k btu ac unit.
Now....I havent tested it yet but i'm sure the surge when starting the ac unit will likely cause the inverter or the generator to fault out.
I noticed some videos that suggest adding a hard start capacitor that will help out with the surge.
I ordered one made by supco but am unsure on how it is wired into the system. I've also seen where some folks add a delay box on the fan so that
the compressor starts first then the lower draw fan starts after about 15 seconds. :roll:

If any of you electricians out there can enlighten me on this, it'd be most appreciated.

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Re: Question about using run/start capacitors

Postby daveesl77 » Tue Oct 31, 2017 8:15 am

I had the old HF 800 watt, 2-cycle generator (we now have the 2,000 watt Predator inverter generator from HF). I have a 1,200 watt Centech MSW inverter (also HF). We use a Rural King (Exide) farm duty, deep cycle battery (I think it is 80ah). We also have 150 watts of solar panels.

We have a 3.2 ft3 Haier dorm fridge in the camper and had a really old Haier 5k BTU AC. For years now the inverter/battery system has run the fridge with few problems. When traveling, we charge the battery with the minivan, when stopped solar. The old 800 watt gennie ran the fridge just fine. The inverter would not start the old AC without a capacitor.

I bought the exact same hard-start capacitor you have on the left side of your picture and put it in the old AC, gennie ran it up just fine. Once I started the ac the first time on shore power/generator, then the inverter/battery system could run it, but it used a lot of power. During hurricane Irma, that little generator actually ran the Haier fridge, an Igloo icemaker, a 19" lcd tv and a floor fan. It was loud as hell, but it worked. No go on using it for both the fridge and ac.

I have since bought the 2k Predator generator ($399) and a new 5k window unit from Rural King ($99). Sold the little gennie to my neighbor ($50). The Predator can run everything I have, at once. This includes a small 400 watt crock pot. The inverter/battery setup can run the fridge and icemaker, as well as some 12v fans, but not the AC with the fridge. It can run the AC by itself. That Predator 2k generator is fantastic. It is very, very quiet in Eco Mode. Sips gas, as I used a total of 2.5 gallons with over 25 hours of use in our last camping trip.

With the 150 watts of solar and the new MPPT controller, as long as I get about 5 hours of sunlight, I can keep the fridge running indefinitely at about 30 degrees F. with outside temps in the 80s-90s.

Now, as to whether or not a 1,000 watt gennie or 1,000 watt inverter system can run both the fridge and AC, that will be a really close call. Use a Kill-a-Watt meter to see what each individual appliance uses over the course of say 2 hours, then test both at the same time over say 4 hours. This gives you an average hourly use.

Under normal conditions, you will find that an initial, first time, start up may fully bog down the system, so don't try to initially run both at the same time. Start one, let it run for say 20 minutes the turn it off. Start up the other, let it run for 20 minutes. Then you can either keep the 2nd appliance running and restart the first, or shut down the second. This frees up the compressors and puts less start load on the system. Once you run up a compressor, then it can usually sit for anywhere from 24 hours to a week. Try to keep the time between starts low or do the sequence start.

YMMV

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Re: Question about using run/start capacitors

Postby cajundood » Tue Oct 31, 2017 11:38 am

i connected my kill a watt meter to the little ac on shore power to measure the surge and run wattages. it showed a 640watt surge on startup.....but i had a few tell me that a kill a watt meter isnt fast enough to give an accurate surge reading and that a clamp-on meter will give a better result. They said the surge on the 5k btu unit is higher than what the killawatt recorded and will likely fault out my 1000w generator. :x
Rather than the supco hard-start capacitor that i already have ordered, they suggested a soft start unit made by microaire. Heh.......$300??? :shock: "I don't think so Bill"
It's not that i don't have enough genny. I also own a 5500 continous honda generator. but its too heavy, too loud, too gas hungry, and i'm trying to scale down because my lower back isnt too forgiving these days. Upon ordering the 1000w gen. I had to cut down power usage items to the bare minimum. All of the kitchen electrical devices were eliminated(even the coffee maker is gone)
I want to dry-camp in places without hookups and keep things down to a bare minimum. but in summer months, a 5k btu ac unit is absolutely essential. :x
my back certainly dowsnt appreciate the handling of the 5500w honda & this little 1000w is only 20lbs......so I just gotta keep trying to go bare essentials to make this work somehow :thinking:

A sequence start is what will certainly have to be implemented. Reminds me of the Apollo 13 movie where they had to start up devices and not to over 15 amps..... :applause:
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Re: Question about using run/start capacitors

Postby daveesl77 » Wed Nov 01, 2017 6:52 am

On the surge thing. As I said, I originally had this really, really old 5k window unit. I bought it at an RV salvage yard for $10. It had been out in the elements for years. It was ugly as hell, but it ran. After adding in the hard-start capacitor, I could easily start and run the thing from either my little 800 watt HF generator or from my 1,200 watt inverter. The AC was a long ways from being efficient, but that little 2 cycle gennie ran it fine.

As to using an 800 watt+ generator for multiple things, as I said, we used it to simultaneously run the dorm fridge, my igloo icemaker, a floor fan and a tv set - for 2+ days. After the storm we got the Predator 2,000 watt inverter and went on a 2 week boondock camping trip to West Virginia. That generator is fantastic. Weighs 50#, ran every single 120 volt item we had (no AC as it was cool outside) and it seldom ran above a fast idle. It is super quiet.

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Re: Question about using run/start capacitors

Postby Padilen » Wed Nov 01, 2017 7:22 am

FLboy and I, each tried the hard start. Found that some AC's have a "brown out" feature. The sensitivity of that feature still causes unit(compressor) to shut off. Hope I described that correctly. Flboy found an AC not as sensitive. I have put mine off to next year.

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Re: Question about using run/start capacitors

Postby Heavy_Fuel » Wed Nov 01, 2017 3:46 pm

Is there a downside to using a hard start capacitor? It reduces the start up current, but does it raise the running current as a trade off?
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Re: Question about using run/start capacitors

Postby GPW » Wed Nov 01, 2017 5:26 pm

A Capacitor is basically like a Bucket for electricity , you can fill it up or empty it quickly , and it doesn’t “use” electricity, only stores it … For starting assist , when the voltage drops during the start, the ”bucket” empties out quickly to help … just like a booster battery , sorta’ ...
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Re: Question about using run/start capacitors

Postby Heavy_Fuel » Thu Nov 02, 2017 10:46 am

GPW wrote:A Capacitor is basically like a Bucket for electricity , you can fill it up or empty it quickly , and it doesn’t “use” electricity, only stores it … For starting assist , when the voltage drops during the start, the ”bucket” empties out quickly to help … just like a booster battery , sorta’ ...


I thought the capacitor had something to do with power factors, phase angles, motor winding inductance, and all that magical AC stuff, which I never fully understood?
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Re: Question about using run/start capacitors

Postby Socal Tom » Thu Nov 02, 2017 12:12 pm

I've got the fridgidaire cheap 5K BTU unit. The killawatt shows that it hits about 700 watts on the initial startup surge, and then sits at about 450 ( with compressor on) after that ( at least when I tested it last weekend in a cool garage). I was running it on a Honda EU 1000i when I tested it. It carries it just fine, the only time I managed to stall it was when the compressor was running, I switched to fan only, then switched back quickly and the load went over 1K and the generator overload tripped.
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Re: Question about using run/start capacitors

Postby Socal Tom » Thu Nov 02, 2017 12:39 pm

Personally, I recommend at least a 2K generator, they aren't a lot bigger than the 1K units, but they can do much more. A coffee pot uses 1500 watts, and they can easily carry a fridge and a small ac unit.
However, if you want to run a fridge and an AC unit on a 1K unit it can be done if you also have a 12V invertor setup. Plug the AC unit directly into the generator power, plug the fridge into your inverter. Assuming the inverter is sized to carry the load of the fridge compressor, the generator will charge the battery while the fridge compressor is not running. The info I can find says that a fridge needs something like 700 to 1000 watts per day, that's about 30 to 40 watts per hour. My convertor can supply up to 45 watts per hour so as long as the generator runs 24 hours I can power the fridge and not lose battery power
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Re: Question about using run/start capacitors

Postby cajundood » Fri Nov 03, 2017 11:45 am

Anyone ever use one of these?......It is called a soft starter. I believe this is the same thing as the microair soft start that they sell for $300 online.....just doesnt have the name or a fancy plastic housing. :thinking: 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 from china for $46. It's designed for motor loads up to 25 amps, designed for 110-120v. I'd be willing to BET, that this is the same "guts" thats in the $300 unit sold by Microair
https://www.microair.net/products/easystart-364-3-ton-single-phase-soft-starter-for-air-conditioners?variant=30176048267:roll:

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Re: Question about using run/start capacitors

Postby GuitarPhotog » Fri Nov 03, 2017 11:54 am

Heavy_Fuel wrote:
GPW wrote:A Capacitor is basically like a Bucket for electricity , you can fill it up or empty it quickly , and it doesn’t “use” electricity, only stores it … For starting assist , when the voltage drops during the start, the ”bucket” empties out quickly to help … just like a booster battery , sorta’ ...


I thought the capacitor had something to do with power factors, phase angles, motor winding inductance, and all that magical AC stuff, which I never fully understood?


The bucket analogy is true only for DC. In an AC circuit, the starting capacitor does indeed change the phase angle across the windings (i.e., the magical AC stuff). That change of phase angle causes the motor to act like the rotor is already turning, reducing the startup current.

Surge currents can be WAY bigger than running current. The split-phase AC motor on my dust collector draws about 11A when running. It draws a whopping 63A at startup. But only for a few milliseconds.

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Re: Question about using run/start capacitors

Postby GPW » Sat Nov 04, 2017 5:15 am

Thanks GP … Good to know about the AC … :thumbsup:
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Re: Question about using run/start capacitors

Postby John61CT » Sat Nov 04, 2017 10:11 am

Socal Tom wrote: The info I can find says that a fridge needs something like 700 to 1000 watts per day, that's about 30 to 40 watts per hour. My convertor can supply up to 45 watts per hour so as long as the generator runs 24 hours I can power the fridge and not lose battery power


Watts per day, watts per hour is not meaningful.

Maybe you mean watt-hours?

For people more oriented around running loads from batteries rather than long genny runs, amp-hour at 12V are commonly used.

As an example for illustration

An efficient 12V fridge can use as little as 20AH per 24 hours. On freezer settings in hot weather, can get over 40AH per day.

That converts to 200-500 wH per day.
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Re: Question about using run/start capacitors

Postby Socal Tom » Sat Nov 04, 2017 4:28 pm

John61CT wrote:
Socal Tom wrote: The info I can find says that a fridge needs something like 700 to 1000 watts per day, that's about 30 to 40 watts per hour. My convertor can supply up to 45 watts per hour so as long as the generator runs 24 hours I can power the fridge and not lose battery power


Watts per day, watts per hour is not meaningful.

Maybe you mean watt-hours?

For people more oriented around running loads from batteries rather than long genny runs, amp-hour at 12V are commonly used.

As an example for illustration

An efficient 12V fridge can use as little as 20AH per 24 hours. On freezer settings in hot weather, can get over 40AH per day.

That converts to 200-500 wH per day.
whatever



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