Adding a large capacitor to handle starting loads?? - Dutchmen Owners

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Old 01-06-2016, 03:38 PM   #1
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Adding a large capacitor to handle starting loads??

I added a KVAR capacitor system (650 micro farad/ 220V) to my house breaker box to " correct power factor" and "reduce energy consumption" some years ago.

I don't know if I ever realized any savings but I did discover that
after hurricane Sandy, my generator didn't struggle nearly as much when hit with the starting load of my well pump or microwave ..

My Aspen trail 1900RB has 30 Amp 110 V service and I was wondering if it would be a good idea to add a similar size capacitor to minimize the voltage drop during AC or Microwave starting.. I would plan to install it in parallel with the shoreline connection to my RV breaker box.. Are there any "sparkies" out there who would care to comment on whether this is a good idea and if so suggest what size capacitor I might use??
Its been over 45 years since I got my ME degree and just as long since I've done those calculations....

Pat
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Old 01-06-2016, 04:00 PM   #2
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I don't know anything about adding a cap in parallel with a shoreline connection. But adding/replacing/upgrading a hard start capacitor to an air conditioner is a common modification for the RV. I have done it for mine and while I do think it helps my Yamaha 2400 generator start the A/C compressor, it is still marginal.
RV Air Conditioner Hard Start Capacitor | ModMyRV
Amazon link to SPP6 cap
There is debate on whether SPP6E or SPP6 is the more appropriate capacitor for this, but Supco told me that the SPP6 was the more appropriate cap. While also telling me they do not recommend this modification as it does not make a marginal situation less marginal. This size generator is still inadequate, even under the right circumstances, to reliably run a 13.5 kBtu A/C.
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Old 01-06-2016, 04:42 PM   #3
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Thanks for the input.. Still a newbie here and doing my homework. I may be jumping the gun here a bit until we've had a chance for a shakedown trip. I read that the Dometic 13.5K BTU AC unit draws a lot of current on startup. Their manual recommends a minimum of a 3.5 KW Generator to handle the starting load, which translates to 29.16 amps. I was hoping to avoid turning everything off just to run the AC. It can get pretty hot and humid in our neck of the woods in July and August.


I just checked out your link and I'll definitely give the "hard start cap" a try. It would be the simplest solution.. Especially since you're able to start yours with a 2400 watt gen set.




I do plan on picking up a couple of Powerhorse inverter generators at Northern Tool for my no-hookup camping. Running them in parallel Delivers 3.6 K watts continuous and 4K surge watts. If the Capacitor doesn't work I would plan to run a separate line to the AC and install a switch to be able to run the ac from either the shoreline or Generator set.




It may be a while before my first shakedown trip but I will post my experiences when I do..
Thanks again
Pat
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Old 01-06-2016, 04:46 PM   #4
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A capacitor in the starting circuit of an AC motor only shifts the phase of the current on motor start up. The current inrush will lead the voltage developed by 90 degrees in a purely capacitive circuit causing the rotor to spin. It does nothing else after that. Power factor is only an issue in industrial applications where there is mostly inductive loads such as motors. Even then it isnít that big of a deal. At my employer before retirement, we had literally a thousand motors of all sizes from fractional to 1000 hp. Without power factor correction we were still near .94 power factor. My steel mill days we used power factor correction since we were pulling 60K amps per phase of pure inductive load on the furnaces. It was necessary then. Capacitors will store a DC charge, and will pass AC depending on frequency and capacitor rating. I canít see how it would be of any benefit. But hey, what do I know?
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Old 01-06-2016, 05:37 PM   #5
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I installed the SPP6 on my & my sons RV A/C units. We both noticed how much quicker the compressors kicked on. We both have large enough generators so that isn't a problem. we did connect our portable 3100 Watt Champion up to see how it reacted. We could tell by the the way the engine loaded that the capacitor made a difference. As cheap as they are they can't hurt.
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Old 01-06-2016, 06:20 PM   #6
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I can see getting some improvement in starting an individual motor if the original starting capacitor was not sufficient. I cannot see any value in putting one across your incoming line. Basic capacitor theory states that, in this case, it will block DC and pass AC. If anything, based on its Fared rating, it will do nothing, or increase energy usage by allowing current to flow from phase to neutral. Power factor correction is also much more involved than simply putting a capacitor across the line. Even then, if you knew the original power factor so you could install the correctly tuned static VAR device, benefits gained in a residential application would be negligible. I canít see it.
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Old 01-06-2016, 06:29 PM   #7
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Thanks for all your input..
Thompwil, I never expected power factor to be an issue in my home wiring and still have a hard time believing the KVAR unit represented any savings on my elec. bill. But I have to admit it really made a difference in how my generator accepted the inductive loads like my well pump when powering my home critical utilities after Sandy. I won't hesitate to admit that I just have a little knowledge which is a dangerous thing..


Think I'm going to see how things work and if necessary go with the starting capacitor first..


If it doesn't get me where I want to be, I found a neat transfer switch at the same site EWARNERUSA recommended Automatic Transfer Switch - PPL Motor Homes to automatically switch just the AC from shore power to my generator when power supplies are stretched to capacity..


I'll be posting the results most likely in the spring as I sort things out...


Thanks again and All the best.
Pat
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Old 01-06-2016, 08:35 PM   #8
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The power company has capacitors on their lines to maintain a power factor of 1. A power factor of one means the voltage and current are in phase and thus maximum efficiency is being achieved. If your incoming power is already corrected to 1 and you place a capacitor in the circuit, you are actually losing efficiency.

WHAT EVER YOU DO, DO NOT PLACE IT IN PARALLEL!!!! A 650 micro farad capacitor has about 0.25 ohms capacitive reactance to 60 hertz (Xc=2piFC). You will certainly pop a breaker and the capacitor may explode.

The bottom line is to leave things as they are.
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Old 01-06-2016, 08:59 PM   #9
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Quote:
Originally Posted by Handyman View Post

The bottom line is to leave things as they are.
Indeed !!
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Old 01-07-2016, 12:43 AM   #10
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Quote:
Originally Posted by Handyman View Post
The power company has capacitors on their lines to maintain a power factor of 1. A power factor of one means the voltage and current are in phase and thus maximum efficiency is being achieved. If your incoming power is already corrected to 1 and you place a capacitor in the circuit, you are actually losing efficiency.

WHAT EVER YOU DO, DO NOT PLACE IT IN PARALLEL!!!! A 650 micro farad capacitor has about 0.25 ohms capacitive reactance to 60 hertz (Xc=2piFC). You will certainly pop a breaker and the capacitor may explode.

The bottom line is to leave things as they are.
Wow, I'm glad I asked!!
Certainly not my forte..


Thanks
Pat
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