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Author Topic: One for the HVACR experts...  (Read 2893 times)
Sean
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« on: July 30, 2014, 08:20:09 AM »

Greetings folks.  Yes, I am alive and well and I check in here from time to time, though I have not had much time to post.

I've come to the end of my technical expertise with a refrigerator issue, and I am hoping some of you refrigeration experts here can help me out.  If refrigeration compressors are not your thing, the rest of this post will probably make little sense, and you might as well skip it...

The short version is that I bought a brand new, household, 10.3 cubic foot fridge from Lowes (Haier HA10TG30S), and it drags the output of my Magnum MS4024 down from 120vac to ~85vac briefly when the compressor starts.  The Magnum is handling everything just fine, but there are a few other things around the house that don't like the momentary drop-out.

I've looked at the circuit diagram on the back of the fridge.  It's a pretty standard PSC design, two windings with a run capacitor in series with one of them.  What they are doing to start the compressor is simply shorting the run cap with a PTCR, which basically just drops the start winding right onto line voltage until the PTCR heats up.  It makes for a cheap design (hey, the whole fridge cost less than $400), but it depends on a basically unlimited power grid behind it to supply the inrush.  The output of a 4kW inverter is definitely not unlimited.

Haier won't tell me the value of the run cap, the temperature of the PTCR, or even the HP of the compressor.  I think what I need here is to simply add a start cap in series with the PTCR, but I don't know how to figure the proper size and rating of the cap.  If I use the existing PTCR, at least I can be reasonably sure that the cap will be out of the circuit in the proper amount of time.

The nameplate wattage of the compressor is 300w, which I would guess to be about a 1/4-horse model.

So my questions are:
1. Can anyone tell me what cap I should use in series with the PTCR (thus parallel with the run cap)?
2. If not, what's the risk in starting out with, say, 70mfd to see if it helps (in series with the existing PTC, which should take it out in plenty of time)?
3. Is there a better way, such as replacing the PTCR with a potential-relay hard start kit?
4. If so, what size kit?

Thanks in advance...

-Sean
who moved from a bus to a boat
(but still has the bus)
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« Reply #1 on: July 30, 2014, 09:23:49 AM »

Sean-How're Doin? Enjoying your blog about your boating adventures. I realize that you got that refer at a great price. I have changed my refer in the bus to a NovaKool 9000 and really like it. It pulls barely 5amps at 12vdc, uses the Danfoss compressor, and has a separate evaporator for the refer and freezer. Granted they're about 4 times what you payed. Plus they have front air discharge.

My first thought is either a larger capacitor or a separate start capacitor. A/C's have hard start kits-could you use that? I'm sure Nick Badame could answer these questions more intelligently. Good luck, TomC
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« Reply #2 on: July 30, 2014, 09:39:51 AM »

Tom
I had the same question.  Sean for years sang the praise of his 24 volt marine refer and freezer.  Seems the best set-up when you have a house batteries already; don't have the power losses through the inverter and you just use the inverter for loads that must be supported on AC.  I'm sure Sean had good reasons for going that direction.  Sorry I can't help on cap sizing.
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« Reply #3 on: July 30, 2014, 10:21:09 AM »

  Sean-How're Doin? Enjoying your blog about your boating adventures. I  have a NovaKool 9000 and really like it. It pulls barely 5amps at 12vdc, uses the Danfoss compressor, and has a separate evaporator for the refer and freezer. Granted they're about 4 times what you payed. Plus they have front air discharge.   

    Yeah, nothing to add regarding any knowledge but it is always good to hear from you, Sean.  Aside from the fridge issues, I hope that all is going well.

    I have a similar Nova-Kool to Tom's - mine is an 8700 (or something like that) so it's slightly smaller but it works like a champ.  It seems a little weak in 98º and 98% humidity in North Carolina (I have extra insulation behind the specified air space against the outside wall and it works OK, just seems a little weak) but on most counts I like it.  Oh, yeah, the other count I don't like is the $$$$ (ouch!!!).  And of course your 10.3 fridge is WAY bigger than the Nova-Kool.  Good luck on what it takes to make it work right.  Too bad that Haier's customer service (?) is as bad as we can expect from many companies these days.
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« Reply #4 on: July 30, 2014, 10:39:10 AM »

Thanks, guys.

To answer the question, as you know I have a Novakool in the bus, and for that application we absolutely loved it.  The boat also had a Novakool when we bought it, an RF8000 (now discontinued).

We had two problems with the Novakool on the boat.  First and foremost, it was simply too small.  The 7.5 cubic foot model in the bus was great -- it had the right mix of fridge/freezer, and it could hold about two weeks worth of provisions, which was really the limit of our remote boondocking capability anyway based on water and waste tank sizes.  So we could always count on being someplace where we could get some fresh groceries every two weeks.

The RF8000 on the boat, however, was only a 6.5 cubic foot model, and, worse, that one foot difference all came out of the fridge (the freezer portion was almost big enough).  On the boat, we are often unable to reprovision fresh food for a month or longer, and we expect that problem to just get worse when we start going further offshore.  With less than five cubic feet of refrigerator capacity, we were having trouble fitting all our food in the fridge.

The previous owner had worked around this problem by putting a marine-rated chest refrigerator on the aft deck (and if you thought Novakools are pricey, you'll plotz if you price Frigibar marine chest units -- this one retailed for over $4,000).  We wanted that space back for a table and chairs so we could eat and socialize on deck, and we ripped out the chest unit and sold it (for a paltry couple hundred on eBay).  Besides that, it was 120-volt, too, and had a heated lip seal that ran 24/7, so not exactly efficient.

The second issue with the Novakool was the frosting problem.  Again, on the bus, this was not much of a problem.  We avoided hot, humid locations for the most part (except when we were chasing tropical storms with the Red Cross), and when we had to put up with them, we were generally able to run air conditioning -- finding power outlets was simpler on the bus, and we also had the ability to run some A/C off the batteries.  Here on the boat, however, we are almost always in more humid conditions, and we can seldom run air conditioning.  The Novakool needed to be defrosted at least monthly and sometimes more often (on the bus we did it maybe every half year), or its efficiency plummeted and it could not keep the food cold.

The largest Novakool that would fit in the space where the RF8000 lived is the newer RF8500 (IIRC, the 9000 like you have, Tom, was a hair too big in at least one dimension), and that would only have given us another one or two cubic feet of fridge.  Plus, we'd still have the frosting problem,  After fighting with too little space and losing too much food to spoilage from the frost problem, I finally decided I'd pay the energy penalty of a frost-free household model to solve both problems at once.

Honestly, I did not expect the MS4024 to have any trouble running a tiny 10cf household fridge.  I think Haier took a design shortcut here by omitting a start cap.  But it was pretty much the only model I found on the market that I could squeeze into the space I had available (barely -- I posted the installation on the blog http://ourodyssey.blogspot.com/2014/05/fridgeapalooza.html).  I'm sure something a bit higher end, even if it was a giant side-by-side, would work fine on the MS4024 with no issues.  As you know, I've run full-bore air conditioners from SW inverters before, and lots of expensive boats have big household refrigerators and Magnum inverters.

I'm very happy otherwise with my choice.  Having 10cf (vs only 8cf in the larger Novakool) is really helpful, and I am enjoying not having to empty and defrost the fridge on a regular basis.  So far, energy usage seems to be better than expected, with only perhaps a 5% premium over the much smaller Novakool we removed.  If I can just fix this one issue, it will be bliss.

-Sean
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« Reply #5 on: July 30, 2014, 12:24:18 PM »

Hello, Sean. Glad to see you back on the forums.

I do not have an answer for you. On your 300 watt compressor: 737 watts is one horsepower. Also Ohm´s law: volts times amps equals watts.

Perhaps you might do well to get a separate inverter just for the fridge.
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« Reply #6 on: July 30, 2014, 01:24:35 PM »

Hello, Sean. Glad to see you back on the forums...
Thanks.

Quote
.. On your 300 watt compressor: 737 watts is one horsepower. Also Ohm´s law: volts times amps equals watts.
...

It doesn't really work that way... yes, if you are talking about either input, or output.  But an electric motor that consumes 737 watts does not generate one horsepower of mechanical output.  300 watts is the electrical input, and I need to know how big that motor is in mechanical HP, not how many "electrical HP" it consumes (yes, you can measure electrical power in HP, but by convention, we don't).

-Sean
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« Reply #7 on: July 30, 2014, 02:22:50 PM »

    Thanks for the discussion, Sean.  Yeah the defrost thing is a pain at times.  But you're right, that's much easier taken care of in a bus.  I just wish the people at Haier were better informed.  I appreciate the info.
    I used to laugh at the "boat is a hole in the water that you throw money into ..." jokes -- then I bought a bus.  Shocked
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« Reply #8 on: July 30, 2014, 03:42:21 PM »

check the Hertz?....wire size too small?
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« Reply #9 on: July 30, 2014, 04:27:01 PM »

If you measured its Power Factor with a Kill A Watt meter, would that help you choose different start or run capacitors?   It seems to me that a lot of Chinese-made electrical items (such as Iota chargers) have lousy PFs on start-up, no big deal if on-grid but a major problem if drawing from a limited power source such as in boats and buses.

John
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Sean
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« Reply #10 on: July 30, 2014, 05:38:34 PM »

If you measured its Power Factor with a Kill A Watt meter, would that help you choose different start or run capacitors? ...

I don't think the Kill-a-Watt can give me the starting PF, John -- I'd need a scope (which I don't have).  It could capture the running PF, but the run cap adds a different lag than what's seen at start.

-Sean
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« Reply #11 on: July 30, 2014, 05:42:08 PM »

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« Reply #12 on: July 30, 2014, 05:56:17 PM »

We had a couple of those in the restaurant for short time ours had Bristol Compressor maybe they could help,I use one in the shop from the restaurant and it seems to struggle on start up on a 110 degree day
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« Reply #13 on: July 30, 2014, 05:58:58 PM »

We had a couple of those in the restaurant for short time ours had Bristol Compressor maybe they could help,I use one in the shop from the restaurant and it seems to struggle on start up on a 110 degree day

Thanks, Clifford, that's great information.

-Sean
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« Reply #14 on: July 30, 2014, 07:56:10 PM »

I do not think I would put a start cap in series with the ptc. You are looking to reduce the starting current and the cap will do that but it will also reduce the current thru the ptc and that will cause it to keep the start winding energized longer while it heats up.

Go with a Potential relay and a cap around 110 MFD.  Even the 3 wire all in one Hard Starts are sometimes flakey. As far as picking a potental relay, thats a tough one as the compressor was never speced to use one. Mars (and others) do offer an adjustable relay so you can tweek your pick up and drop out voltages.

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