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Old 09-05-2014, 21:36   #1
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Home made power supply.

I have a Norcold 621 refrigerator. The power supply is shot and I would like to make my own 20 VAC power supply for the thing. Internet searching has failed. Just the term 20 VAC returns every listing for 20V AC power supply for laptops.

The original power supply is fascinating. It takes 110 VAC turns it into 50 VDC and then into 20 VAC. This has to do with 110/12 volt capability of the device. I don't care about that. I just need 20 VAC.

I priced out replacement power boards for some 700 USD. I don't know if that includes both boards or just one. Since I have a nice, modern thousand dollar inverter, it see,s pointless to mess with the 30 year old Norcold power supply.
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Old 09-05-2014, 22:42   #2
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Re: Home made power supply.

How many amps do you need at 20V?
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Old 09-05-2014, 23:20   #3
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Re: Home made power supply.

Forgive me if I'm missing something, but would a simple 6:1 transformer not do the job of converting 120VAC to 20VAC?
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Old 09-05-2014, 23:43   #4
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Re: Home made power supply.

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Originally Posted by Andrew Troup View Post
Forgive me if I'm missing something, but would a simple 6:1 transformer not do the job of converting 120VAC to 20VAC?
You are missing the other $649 dollars...but there might be more to it than just having 20vac?
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Old 10-05-2014, 00:18   #5
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Re: Home made power supply.

Have you looked at this one?

---------------
Norcold Board Kit (633280) 3-way board kit replaced 621270001

This board kit replaces the old 3-way board part number 621270001. This kit includes the new style power board and new style optical board along with instructions and the adapters necessary to connect each board to the refrigerator.
This board kit works with all Norcold 3-way model refrigerators that have a board that is no longer being manufactured.
If you have a 3-way style Norcold N6XX.3, N8XX.3, N1095.3 or 3-way 1200/ 1210 model refrigerator, this is the kit you need!
----------------

Price is 289.00 FOB US east coast, still pricey to me but not 700.00 anyway.
From norcoldparts.com.

Just in case...

Regards
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Old 10-05-2014, 15:50   #6
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Re: Home made power supply.

A transformer would work IF it was rated to carry the amps that the refrigerator needs, and IF you could find such a transformer. But how sensitive is the refrigerator to variations in voltage? if you have 120v input and a 6:1 transformer great, but what is the marina power is only 109v? or 130v? You could just try it, the worst that can happen is an electrical fire, you sink your boat and ruin the refrigerator.
Or you could find a schematic for a 20V voltage regulator circuit, build your own printed circuit board
or you could buy a programmable voltage regulator
any one of these options except the first is going to cost more than a brand new refrigerator.. unless you already know how to design and make the board and have parts laying around.
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Old 10-05-2014, 16:42   #7
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Re: Home made power supply.

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Originally Posted by dohenyboy View Post
A transformer would work IF it was rated to carry the amps that the refrigerator needs, and IF you could find such a transformer. But how sensitive is the refrigerator to variations in voltage? if you have 120v input and a 6:1 transformer great, but what is the marina power is only 109v? or 130v? You could just try it, the worst that can happen is an electrical fire, you sink your boat and ruin the refrigerator.
.....
Two thoughts:

If the OP was running off shorepower, any mains equipment on the boat would be subject to the voltage fluctuations of which you warn.

That has to be more of a fire risk than the 20V rising to the corresponding 21.6V, or dropping to 18.2V, surely? I submit that's not about to ruin the fridge, let alone burn the boat down.

I realise it's not directly comparable, but the DC voltage on a boat varies between under 11V and around 15V, a significantly higher range:
that would be like seeing 110-150V on the AC house wiring.


Second thought: The OP seems to be getting his 120VAC from an inverter, if I understand correctly. There should be minimal fluctuation in that case.


Third thought: (OK I lied about two thoughts)

eBay lists a number of 120V>20V transformers

(ON EDIT: It looks from a quick scan through the Service manual, available online from bryantrv.com as though you would want a 5A capacity on the 120V side - so some of the listed units will be too small)


At times, the advice on this forum seems designed to keep cruisers in poverty.
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Old 10-05-2014, 17:53   #8
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Re: Home made power supply.

Quote:
Originally Posted by Andrew Troup View Post

At times, the advice on this forum seems designed to keep cruisers in poverty.
If you spend most of your adult life making enough money to go cruising, all you might know is spend more money to fix something. You can't expect an Oyster captain to have mucked about jury rigging little transformers.
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Old 10-05-2014, 18:27   #9
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Re: Home made power supply.

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If you spend most of your adult life making enough money to go cruising, all you might know is spend more money to fix something. You can't expect an Oyster captain to have mucked about jury rigging little transformers.
You paint a grim picture, Guy. Are you saying kids don't have toy trains anymore?

Regardless of that, I would have thought today's "Oyster captain" could well have grown up with a model railroad in his or her bedroom big enough to have its own toy trains inside the model houses...

PS: I was thinking the OP might have a Roberts, rather than an Oyster
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Old 11-05-2014, 04:36   #10
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Re: Home made power supply.

Which input voltage, 110VAC or 12VDC?
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Old 11-05-2014, 11:04   #11
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Re: Home made power supply.

So I want to run the compressor off 110v. Selecting the right Volt/ Amp combo isn't too much of a worry, however fitting the thermistors into the circuit is a problem. I don't know where or how those would go into a circuit.

New refrigerators seem to be very simple electrically. I think I need to dig into one of those when I get a minute and find out how they work.

It seems just last week there was a whole cluster of old fridges being thrown out. Now nothing.
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Old 11-05-2014, 12:48   #12
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Re: Home made power supply.

Quote:
Originally Posted by dohenyboy View Post
A transformer would work IF it was rated to carry the amps that the refrigerator needs, and IF you could find such a transformer. But how sensitive is the refrigerator to variations in voltage? if you have 120v input and a 6:1 transformer great, but what is the marina power is only 109v? or 130v? You could just try it, the worst that can happen is an electrical fire, you sink your boat and ruin the refrigerator.
Or you could find a schematic for a 20V voltage regulator circuit, build your own printed circuit board
or you could buy a programmable voltage regulator
any one of these options except the first is going to cost more than a brand new refrigerator.. unless you already know how to design and make the board and have parts laying around.
I think you might be referring to 20VDC regulators, 20 VAC is a little different

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Old 11-05-2014, 13:35   #13
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Re: Home made power supply.

Robert, I think you will find that the US does not actually use "110 VAC" mains power. The typical spec set by utility regulators and grids is 117 VAC plus or minus 10%, as I recall. So when you plug into a "perfect" socket it may give you 110, or 117, or 120, or even 106 volts on a hot summer day. If you just stick that into a transformer without regulating it on one side or the other, your fridge may be very upset at the variations in voltage.

It ain't rocket science but it ain't garden hoses either. You might reconsider buying a new power supply that has been engineered for the job, instead of trying to build one from scratch. And buying electronic components in "quantity one" tends to be damn expensive, too.
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Old 11-05-2014, 13:39   #14
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Re: Home made power supply.

I expect someone will soon suggest a variable transformer (Variac) but I'd recommend against it.

Mine's an old Claude Lyons and although it will provide 0 - 270V at 20A from a 240V UK mains supply autotransformers aren't safe to use unless you understand their characteristics.

Big heavy thing, open terminals, the opposite of plug'n'play/consumer friendly.

Somewhere there's probably a welding transformer or some such that would work - but losses would be considerable I think.
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Old 11-05-2014, 16:07   #15
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Re: Home made power supply.

jimbunyard,

I miss typed the model of refrigerator. It is a DE461 model and the power supply is $500.

I purchased a capacitor to replace the obviously blown one, but will have to wait until I find my gas powered soldering iron before proceeding. I just can't seem to make electric guns work. Lack of patience I suppose.

I don't feel making my own board is unreasonable either. I can't be that bad at soldering, although I may soon find out. I know I need relays to work with the thermistors, but I don't know anything about the compressor motor control. That is, if there is more to be regulated than voltage on / off. And for that I need a schematic, or at least another refrigerator to take apart.

All I really need is the supply with two thermistor inputs. Now that I realize this, I realize that I have two separate circuits of refrigerant, for fridge/freeze. I will have to think about this some more.

Sunday isn't turning into a good day for working on the boat. Too much alcohol the night before and the radio drama coupled with cold, dark skies just make the day a write-off.
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