Running dorm fridge with inverter - Page 2 - Fiberglass RV


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Old 01-11-2013, 12:22 PM   #15
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It's been about a week since I last tried the fridge on the inverter. I just tried it again and what do you know it beeped but started!

Inverter plus running fridge takes 9.2 amps at nominal 12v.

I guess my inverter is just on the ragged edge.
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Old 01-11-2013, 12:35 PM   #16
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Norm, I have propane. My combination of AC compressor fridge and Coleman upright ice chest is working fine for my needs. For me a 3-way is a no-way. I suspect there are more owners of older 3-ways who carry an "auxilliary" ice chest than will admit it. There are some that will. I would love to have a 6-900$ trailer refrigerator but don't choose to spend the money. I'm sure you understand.

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Old 01-11-2013, 12:54 PM   #17
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The reason I bought the dorm style was cost of the 3 way, afterall we were only keeping our little trailer for the 2 month across Labrador trip.

Oops, that trip has turned into 3 trailers and 5 years.

We stll have the fridge and generator

As to coolers we've learned to live within the confines of our small Scamp fridge. We don't like to carry coolers, pets and the like though many RVers do
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Old 01-11-2013, 01:19 PM   #18
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I may be beating a dead horse, but older working 3-way fridges are available. I would not pay more then $100 for one, but I have got them for free as well. At one point I had three spare RM211's. I sold one, one is a hot swap-able spare, and the other is now a bone yard. I also have a Spare RM36E I got for $25 at the wreckers. I found, but did not purchase an older Norcold 12 VDC compressor fridge at the wreckers as well.
We do have a portable 12 VDC solid state cooler in the van. It keeps the snacks and drinks cool while we drive.
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Old 01-11-2013, 04:57 PM   #19
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A fridge compressor needs a lot of extra power to get it going. Would the addition of a capacitor give the inverter a little extra boost it needs to get the fridge running? Perhaps this is a way to get the existing fridge and inverter to work more reliably together. A capacitor can react much faster than a battery. It will provide that sudden extra kick needed to the compressor going. Usually these capacitors are sold for car audio, but there is no reason they can't be used in other applications. Thoughts?

Car Audio Capacitors | Stereo Capacitors
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Old 01-12-2013, 09:05 AM   #20
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The capacitor noted above is for a 12v dc load. My problem is the fridge motor drawing too much 110Vac from the inverter. I have plenty of 12v capacity and short fat cables connecting the battery to the inverter.

Anybody know if the theory would work for AC?

The hard start kits, I think, are just caps somehow wired to the motor windings.
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Old 01-12-2013, 09:32 AM   #21
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Capacitors are commonly used for air conditioners run by generators in RVs. Perhaps one of the EE's here can comment on the practicality of usign a capacitor with an inverter.

RV Air Conditioner Hard Start Capacitor | ModMyRV
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Old 01-13-2013, 07:26 AM   #22
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Thanks Thomas, that was exactly the link I was looking for but could not find. My fridge compressor is about 1/10 the power of the AC units mentioned in the write-up so I'm going to contact Supco and see what they recommend. Fixing my problem for $6 is the kind of solution I was looking for!
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Old 01-13-2013, 09:59 AM   #23
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Quote:
Originally Posted by MCDenny View Post
Thanks Thomas, that was exactly the link I was looking for but could not find. My fridge compressor is about 1/10 the power of the AC units mentioned in the write-up so I'm going to contact Supco and see what they recommend. Fixing my problem for $6 is the kind of solution I was looking for!
I'm not an electrical engineer, so I don't know if it will work. I'd encourage you to research it first as there may be some interaction between the inverter and capacitor that is different from similar usage with a generator. I'm sure someone else has explored it and posted, if you look long and hard enough.
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Old 01-13-2013, 12:23 PM   #24
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AC motors require a second winding producing a magnetic field out of phase with the first to start rotation. One way to achieve that phase shift is with a start capacitor.

Since the fridge is designed to work on household AC it should work just as well with a properly sized pure sine wave inverter/battery combination. Because the battery you described should be more than adequate, I would be inclined to agree that the inverter might be marginal for the surge required. Since the power rating on an inverter is a figure used to market, like horse power on lawn mowers, it's in the manufacturers best interest to inflate it's value. Perhaps 600 watts is wishful thinking??

Another possible issue could be the frequency of the AC output. Nominally it should be 60 Hz. I don't recall the tolerance but power companies stay very close to that. I don't know how tight the tolerances are on generators or inverters, especially under load, but a change in frequency would effect the phase angle of the start winding. It could be the additional capacitance (i.e. Hard Start Capacitor Kit) is intended to compensate for a decrease in frequency due to loading. Having never owned an inverter or a generator, I have never had the opportunity to take measurements. The best I can offer is an educated guess. Good luck, Raz
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Old 01-13-2013, 09:11 PM   #25
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As I understand them, the Honda EU2000i generators commonly used by dozens of posters on Thomas's modmyrv link are dc generators driving true sine wave inverters. Nearly everyone reported a marked improvement in starting. I suspect those who saw no improvement wired the cap in wrong.

How or why this works is well beyond my "electricity is like water flowing through a pipe" understanding.

I emailed Supco today and will share their response with you all.
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Old 01-14-2013, 02:28 PM   #26
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Supco said:

Dennis,

We do not have experience with this type of equipment. You might try using our SPP6 which is connected to the compressor run capacitor using 2 wires. Do not use a SSP6E style.


So I bought one and will see if I can wire it in in about 10 days when we are back at the kids house where I have good tools and an empty fridge.

I'll update you again then.
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Old 01-26-2013, 07:27 AM   #27
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The Supco cap had no effect. I don't know if the problem was my dorm fridge has the wrong kind of motor or what. It did have a tiny cap (about the size of a dime) across two wires that went into the motor. Connected the Supco cap in parallel with it as per the directions. No change, inverter still tries to start the compressor then gives up with an overload fault.

I did notice on the data plate of the fridge a LRA spec of 7.0 amps. That would 840 watts even though the unit is supposed to draw only 80 when running. My Samlex TSW inverter is capable of 600w continuous and 1000 for less than 2 sec.

I'd love to get a 12v unit like Norcold or NovaKool but really reluctant to spend $1000. A $100 MSW 1000w inverter might be my next move.
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Old 01-26-2013, 10:24 AM   #28
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I have a 69$ Black & Decker (rebadged Haier) from Walmart and 1500watt (2000 surge) pure sine wave inverter on a 6' 1/ought leash to a group 27 battery. The starting amperage of the compressor motor has NEVER been a problem for this inverter even starting with the fridge at ambient temp., but I must make clear that I do normally cool the fridge from a warm start on 120VAC shore power and plug into inverter on the road and off grid when conditions are good for solar recharging with an 80watt panel. Not a perfect system. Knowing how, knowing how much, and knowing when to switch to a cooler with ice is something you learn and learn to plan around in terms of days on the road, interval between on grid plug ins, and daily hrs. of sun. I suspect that your inverter's peak watt output is inadequate.

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