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Author Topic: One for the HVACR experts...  (Read 2881 times)
Sean
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« Reply #15 on: July 30, 2014, 09:09:33 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.

Thanks for the advice.  Just to be clear, though, the "start" winding is always energized -- its a PSC model, with one coil energized full-time direct from line voltage, and the other energized full-time but with a run cap in series.  The PTC only shorts the run cap; once the PTC stops conducting, that coil remains energized but with the run cap in series.  (I will try to attach a photo of the circuit diagram.)  Does that change your recommendation?

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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.

So, again to clarify -- you are suggesting replacing the PTC with a two-wire Hard Start based on a potential relay.  So rather than the PTC shorting the run cap, the run cap and the start cap will essentially be in parallel until the potential relay cuts out.  Is that correct?

-Sean
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« Reply #16 on: July 30, 2014, 10:49:47 PM »

Sean, it's nice to see your new thread..   Like many I frequent your blog.    I do have a question.

Awhile back you mentioned that you were going post your new boat rewire..   The Magnum and dual alternator 24 volt upgrade?   I missed the link..   Can you post some details on your rewire/upgrades..
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« Reply #17 on: July 30, 2014, 11:14:14 PM »

***** 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 *****

Personally I've never had a problem with Hard start run parallel UNLESS it was underrated, never thought about one being overrated - FWIW
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Sean
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« Reply #18 on: July 31, 2014, 05:25:16 AM »

Awhile back you mentioned that you were going post your new boat rewire..   The Magnum and dual alternator 24 volt upgrade?   I missed the link..   Can you post some details on your rewire/upgrades..
.

You didn't miss anything -- I haven't gotten it done yet.  It's on my (long) list of things to do.  The issue here is the diagrams; a text write-up won't make a lot of sense without wiring diagrams, and I have to start from scratch now and climb the learning curve on a new drawing program.  A year or so ago I moved off Windows entirely, and, honestly, even when I got a new Windows machine a few years back, I did not bother installing the ancient drawing software I used to do the bus.

I've dabbled with a few of the programs available for Linux, but so far none has proven easy to use for circuit diagrams.  I hope to have something in the next couple of months and then I can make the drawings and write the article.  I think it will be useful for bus nuts, too, so I might even send it to the magazine.

-Sean
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« Reply #19 on: July 31, 2014, 09:42:15 AM »

Yes, the start winding on a PSC motor is always in the circuit but puting a start cap in parelel with the run cap and having only the PTC to get it out of the circuit after the motor comes up to speed could be risky. Originaly with only the PTC the start winding current draw would be high and heat up the PTC, with a start cap in the circuit the current will be lower due to the phase shift provided by the start cap so it may not heat the PTC and the cap may stay in the circuit.

I am not recomending a 2 wire hard start. I would go with a potental relay, that would require 3 wires, 2 are avaiable at the run cap Start and Run, the common will neet to be picked up at the compressor.

It's more old school but the potental relay has been used for years,I am kind of suprised that a refrigerator would have a PSC motor. No chance of it starting till the pressures equalise.

Thanks for the advice.  Just to be clear, though, the "start" winding is always energized -- its a PSC model, with one coil energized full-time direct from line voltage, and the other energized full-time but with a run cap in series.  The PTC only shorts the run cap; once the PTC stops conducting, that coil remains energized but with the run cap in series.  (I will try to attach a photo of the circuit diagram.)  Does that change your recommendation?

So, again to clarify -- you are suggesting replacing the PTC with a two-wire Hard Start based on a potential relay.  So rather than the PTC shorting the run cap, the run cap and the start cap will essentially be in parallel until the potential relay cuts out.  Is that correct?

-Sean



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Sean
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« Reply #20 on: August 01, 2014, 06:45:39 AM »

.... Originaly with only the PTC the start winding current draw would be high and heat up the PTC, with a start cap in the circuit the current will be lower due to the phase shift provided by the start cap so it may not heat the PTC and the cap may stay in the circuit.

OK, that makes sense.

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I would go with a potental relay, that would require 3 wires, 2 are avaiable at the run cap Start and Run, the common will neet to be picked up at the compressor.

Great, that's what I will do.  Just to confirm, the PTC would then have to be removed from the circuit (because otherwise it will just short not only the run cap, but also the start kit), correct?  Also, the big question:  These kits seem to be commonly sized at either 1/12-1/5 HP, or the next size up at 1/4-1/3 HP.  Want to take a guess at which one I need?

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... I am kind of suprised that a refrigerator would have a PSC motor. No chance of it starting till the pressures equalise.

Yes, me too.  As I wrote, I think I would not have this issue with a slightly higher-end fridge, because they'd have used the correct setup to begin with.  But this model is clearly aimed at a lower price-point at the expense of, for example, Energy Star certification, so I suppose it makes sense that they cut some corners here.  I'm happy to add the start cap to the setup, I'm just trying to avoid long-term motor damage from either too much or too little starting current.

Thanks so much for your help.

-Sean
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« Reply #21 on: August 01, 2014, 09:18:24 AM »

Yes, the PTC would be removed as it would defeat the start kit. If I had to guess the smaller hard start would work, I could not imagine that a box that size would be 1/4 or larger.

I have never used an all in one start kit, I always built them with a potential relay and cap but as long as it has some sort of relay built in it should work.

Do you have a Link to the one you are looking at?
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« Reply #22 on: August 01, 2014, 06:18:11 PM »

...
I have never used an all in one start kit, I always built them with a potential relay and cap but as long as it has some sort of relay built in it should work.


I would prefer to do that, and I know how to source the cap, but I've never selected a potential relay for an application like this before, and I'm not sure where to start.

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Do you have a Link to the one you are looking at?


I was thinking of maybe the Quality Engineering QSR-15, which seems to be widely available:
http://www.qequality.com/categories/85/HARD_START_KITS/products/179/HARD_START_KITS_FOR_REFRIGERATION.aspx

-Sean
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« Reply #23 on: August 01, 2014, 07:43:22 PM »

I have used the supco adjustable in applications that I was unsure of the voltage requirements

http://www.supco.com/images/pdfs/Manuals-Instructions/APR5%20man.pdf

The link you posted for the all in one also looks good as it contains a relay, cap and overload in 1 neat package.It looks to have 5 wires, I am assuming 2 are line 120v + and neutral and the other 3 are common, run and start.

You would need to keep your existing run cap in the circuit as the compressor was designed for it and it helps reduce current draw (that phase shift thing again). It would be wired to the run terminal and the 120v +
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« Reply #24 on: August 02, 2014, 05:45:17 AM »

I am so happy I followed this thread all the way through!
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« Reply #25 on: August 02, 2014, 08:23:42 PM »

Sean, I was looking to purchase a Hailer fridge a few years back. I could not get a clear answer on any of my rather simple questions! I wound up with a 3.8 CF model from Magic Chef. I was running a 1,500 watt inverter in the truck. I noted that on startup it would take about 800 watts for a fraction of a second, then run at 30 to 40 watts.
Hope y'all are well!
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« Reply #26 on: August 10, 2014, 03:52:39 PM »

Hello Sean,

Glad to see you posting again!

Hope boating is as fun as bussing!
 
Here is the Supco 3 in 1 hard start diagrams and sizing if you didn't have it.
http://www.supco.com/images/pdfs/AC%20Hardstarts%20Booklet.pdf
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« Reply #27 on: August 11, 2014, 01:31:57 PM »

Sean! So so great to see a thread started by you! I clicked on it the moment I saw it even though I no ZERO about refrigeration  Smiley  Your blog is so interesting. Really enjoying seeing the contrasts and commonalities of boat v.s. bus living. Cool stuff. Ok...back to your fridge issues.  Cool
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« Reply #28 on: August 21, 2014, 08:28:24 AM »

Sorry for the delay here... thanks, everyone, for the help.  I had to set this aside for a while as our schedule got a bit tight.

Sounds like I will be ordering a Supco kit and see if that takes care of the issue.  At the moment it is more of an annoyance than a major problem.  We are otherwise very happy with both the fridge and the inverter, so I'd rather not change either of those out.

Nick, we will be stopping in Cape May on our way south, maybe two weeks from now.  If you carry these I'd be happy to give you the business.

-Sean
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« Reply #29 on: August 21, 2014, 10:12:01 AM »

When you say it isn't an issue except for the devices that don't like the brown out, what devices are we talking about?  If they are computers or costly electronics and you are running them off of a generator or inverter, you might want to think about putting a UPS on them.  That would solve the brown out issue and add protection to those devices. 
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