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Old 06-09-2018, 11:35 PM   #1
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Question Running A/C on Generator?

I always thought it couldn't be done, but a boating friend of ours told us about the Dometic Smart Start. He is able to run his 16,000btu unit on his Honda eu2000 but the only problem is that it needs more gas every 4-5 hours.

Our I.T. guy just came into work and overheard us discussing things, and he mentioned the $20 Supco SPP6E. He states that it's a capacitor that has to be installed on the actual A/C unit, but makes it easier to run while on the generator.

(He also mentioned that the Yamaha 2400 has a 30 second surge when it needs it, whereas the Honda does not, but thats another discussion.)

Since my unit is already modified and out of warranty, I see no reason not to install the Supco SPP6E before completing the full install and save a little money in the long run.

Has anyone heard of these? Used these? Have any input on them?
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Old 06-10-2018, 06:59 AM   #2
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The Supco unit is a simple capacitor that parallels the existing start capacitor. If your genset will almost but not quite start your A/C then it might work. And it is cheap.

The Dometic Smart Start has a microprocessor controlled capacitor that reportedly helps even more than the Supco.

Neither will do anything for fuel consumption.

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Old 06-10-2018, 07:15 AM   #3
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Good luck trying that.
A VFD for up to 1HP can be bought here for $150
And what can the EU2000 handle for continuous amperage?

About soft starters and VFD
https://www.element14.com/community/...requency-drive

https://www.wolfautomation.com/produ...v-single-phase
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Old 06-10-2018, 09:14 AM   #4
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Quote:
Originally Posted by toocoys View Post
Our I.T. guy just came into work and overheard us discussing things, and he mentioned the $20 Supco SPP6E. He states that it's a capacitor that has to be installed on the actual A/C unit, but makes it easier to run while on the generator.
Hard-start kits, or Start Assist kits as some prefer, do nothing to reduce the load on the power source. They exist to increase the starting torque within the compressor, usually for old/worn compressors and/or due to excessive voltage sag during starting. Starting current would normally be something like 4-8 times the FLA of the motor, some of which is due to poor power factor, but mostly due to the motor starting off in a stalled condition as all induction motors do (it was off and therefore not turning, after all) with the current draw being very high for most of the ramp-up time, tapering off quickly as it approaches loaded speed.

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(He also mentioned that the Yamaha 2400 has a 30 second surge when it needs it, whereas the Honda does not, but thats another discussion.)

Since my unit is already modified and out of warranty, I see no reason not to install the Supco SPP6E before completing the full install and save a little money in the long run.
It's just a capacitor with a potential relay to cut it out of the circuit once the rotor is up to speed. It will do nothing to cut energy consumption rate while running at speed. Nor will it do anything if the compressor starts normally, with no low-voltage problems other than potentially reduce current draw and time to speed a bit while starting. Which can help when running on a small generator.

Compressors use two-phase motors*, meaning there are two windings inside, one connected directly to the incoming power, the other connected with a capacitor in series with it. The capacitor 'delays' the current through the second winding, causing a time shift in the magnetic peaks. The higher the capacitance, the more the angular shift, and the greater the starting torque. Once it's up to speed, the start capacitor is cut out, and only the run capacitor remains on that second winding. Since it's spinning fast, only a small angular shift in magnetic peaks is required.

Hard-starting due to low voltage can be mitigated by increasing the angular shift in that second winding even further, which is what the start assist capacitors do. And that's all that they do.

So a start assist kit may be helpful when trying to start a compressor with a small generator that's limited in its ability to provide the high starting current needed, usually resulting in severe voltage sag during a start. An electronic generator may simply refuse to provide enough current, though, even with a start assist kit. But the kits are cheap enough, and there's no harm in adding one AFAIK.

*Two-phase meaning there are two windings that see current through each that is time-shifted slightly through combinations of resistance and capacitance and inductance - not to be confused with the two phase conductors of 240V which is still single-phase power at the source.
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Old 06-10-2018, 09:16 AM   #5
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Quote:
Originally Posted by djmarchand View Post
The Supco unit is a simple capacitor that parallels the existing start capacitor. If your genset will almost but not quite start your A/C then it might work. And it is cheap.

The Dometic Smart Start has a microprocessor controlled capacitor that reportedly helps even more than the Supco.

Neither will do anything for fuel consumption.

David
Several years ago we installed westinghouse programables on 3 of the 4 units but it was not because of the generator it was because with all units running we would blow shore breakers when 2 units started abut the same time
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Old 06-10-2018, 05:24 PM   #6
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So what I’ve gathered is that the capacitor will help with the extra juice to start the compressor, but after that it’s useless in the configuration? Which means that the generator may or may not continue to run depending on the needed running voltage? And with a 12,000btu unit it’s a little of a gray area as to whether that can happen. Most people who don’t know the exact numbers resort to an experiment and just have to try it out.
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Old 06-10-2018, 06:42 PM   #7
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I am assuming that a"generator" does not refer to a properly sized "GenSet" but to a portable generator from Harbor Freight??


I have a Westerbeke 8kwGenSet and have no problems.
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Old 06-10-2018, 07:05 PM   #8
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I am assuming that a"generator" does not refer to a properly sized "GenSet" but to a portable generator from Harbor Freight??


I have a Westerbeke 8kwGenSet and have no problems.

That would be a correct assumption, because if it were a true generator, we wouldn't be having this conversation.
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Old 06-10-2018, 07:13 PM   #9
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I have met many people who run 12k BTU ACs off a Honda 2000. I have met one person that runs a 16k BTU unit off the same generator. It is possible, but maybe not with every AC. You need to find one that runs at 1600 watts or less. A Dometic 16k BTU unit lists its max cooling amps as 10.4. That should easily run off a Honda 2000.
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Old 06-10-2018, 07:39 PM   #10
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I have met many people who run 12k BTU ACs off a Honda 2000. I have met one person that runs a 16k BTU unit off the same generator. It is possible, but maybe not with every AC. You need to find one that runs at 1600 watts or less. A Dometic 16k BTU unit lists its max cooling amps as 10.4. That should easily run off a Honda 2000.

Interesting. The compressor on my unit has been replaced and is not a Matsushita 2p17s3r126b. If I search that part, Grainger's website has it listed as a discontinued product, but the specs say the amps are 9.3.
https://www.grainger.com/product/PAN...mpressor-6D643

So maybe I dont need a capacitor at all then?
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Old 06-10-2018, 08:08 PM   #11
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Install it , wont hurt the unit, but might help in a low voltage situation.
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Old 06-10-2018, 08:53 PM   #12
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You said that you only get 4-5 hour run time from a tank of gas. Buy a six gallon outboard motor gas tank and replace your Honda generator cap with one of these. Now you have six gallons of gas. Click image for larger version

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Old 06-10-2018, 09:41 PM   #13
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One of these capacitor kits will also help when the shore power is poor.


Weak breaker on the pedestal, low voltage...


I've always wondered why the (profanity deleted) AC manufacturers didn't install them at the factory, both marine and RV, we all see "power issues" on generators and transient power poles?


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Old 06-10-2018, 09:47 PM   #14
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I don't know but we live rull time in our RV and have 50amp service with two Coleman Mach rooftop A/C's. I'm sure it would help with them as well. Especially if we got stuck with no power during a hurricane event.
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Old 06-10-2018, 11:39 PM   #15
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Interesting. The compressor on my unit has been replaced and is not a Matsushita 2p17s3r126b. If I search that part, Grainger's website has it listed as a discontinued product, but the specs say the amps are 9.3.
https://www.grainger.com/product/PAN...mpressor-6D643

So maybe I dont need a capacitor at all then?
The 9.3 is max amps once running. The startup will be much higher. I think you will need the capacitor, but no harm in trying without it. For example, the Dometic I mentioned above states is max running amperage is 10.4, but its max startup is 62 amps! The startup amps will only be for a fraction of a second, so the capacitor should be able to supply that no problem.

https://www.dometic.com/en-us/us/pro...specifications
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Old 06-11-2018, 01:37 AM   #16
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I only had a 5K btu air conditioner on Possum. It took about 600 watts to run it and the little March pump to supply the water to it.

I couldnít get it to run on a Honda 2000i generator until I installed a Supco. Then it started and ran fine. I even tried it on a little Honda 1000 and it started and ran fine.

A marine AC guy told me to look at the label on the compressor for LRA or Locked Rotor Amps and that will tell you how much power you need to get the compressor moving. You only need it for a fraction of a second and thatís where the Supco comes in. My old 5K btu unit needed over 3000 watts to start and the Honda just couldnít do it.
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Old 06-11-2018, 02:25 AM   #17
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I only had a 5K btu air conditioner on Possum. It took about 600 watts to run it and the little March pump to supply the water to it.

I couldnít get it to run on a Honda 2000i generator until I installed a Supco. Then it started and ran fine. I even tried it on a little Honda 1000 and it started and ran fine.

A marine AC guy told me to look at the label on the compressor for LRA or Locked Rotor Amps and that will tell you how much power you need to get the compressor moving. You only need it for a fraction of a second and thatís where the Supco comes in. My old 5K btu unit needed over 3000 watts to start and the Honda just couldnít do it.

Mine says LRA58.
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Old 06-11-2018, 06:35 AM   #18
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"You only need it for a fraction of a second and that’s where the Supco comes in. My old 5K btu unit needed over 3000 watts to start and the Honda just couldn’t do it

A unit to help start a big load is fine , but how does a claim to use less amperage once started work?
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Old 06-11-2018, 08:27 AM   #19
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Some things to consider. I read and wasn't sure what you already owned.

A split AC setup would be very efficient, Built in soft start, might last longer than a rooftop a/c and be much quieter(I have a rooftop 12k btu coleman) and it's crazy loud. the downside is you'd have to mount the compressor somewhere on deck. They are popular in the islands and i've seen many with brackets hanging off the back of the flybridge for space(doesn't look great).

My portable 8k BTU LG doesn't use much energy and puts out tons of cold air. Just as much as the 12k rooftop, less than half the price, and quieter. I suspect an honda 2000 would run it no problem.

Harbor freight sells inverter generators that get really good reviews.. Should cost half as much as a Honda(if you don't already own one).
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Old 06-11-2018, 09:04 AM   #20
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Good luck trying that.
A VFD for up to 1HP can be bought here for $150
And what can the EU2000 handle for continuous amperage?

About soft starters and VFD
https://www.element14.com/community/...requency-drive

https://www.wolfautomation.com/produ...v-single-phase

VFDs are really handy devices, but only work to power 3 phase motors. But our class of boats all run on single phase power, so all motors (and compressors) are single phase unless already powered by a VFD.
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