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Old 10-07-2012, 09:53 PM   #1
mjohnson
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Default Using a 10A controller with older frost free freezer - safe or no?

I have a older frost free upright GE freezer that I'd like to turn into a kegarator. I have an STC-1000 wired up on a small fridge that I use for fermenting. I thought I'd do the same for the freezer.

The freezer's operating current draw is 5 amps. I got to thinking that it probably draws more than 10 amps (the STC-1000 ratings) on startup.

1. If I went ahead and just used the STC-1000, what would the failure mode be? Would it fry the controller? Start a fire? Kill the freezer?

2. If I wanted to use it "safely," I think I'd need to have an AC to AC relay that can handle it - does such a thing exist? Where do folks get these?

3. Should I just sell this one and get a 16 amp Love controller.

Thanks for the help.

mj

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Old 10-08-2012, 03:18 AM   #2
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Some of the STC1000 controllers actually have 15 Amp relays in them. Open it up and take a look.

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Old 10-08-2012, 12:03 PM   #3
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Oh really? Is there a trick to opening it up without destroying it? And once its open, is it fairly easy to tell the amp rating of the relays (I assume its stamped on them)?

Thanks for the reply!

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Old 10-08-2012, 03:10 PM   #4
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Ok, its easy to take apart. The relay's say this:
12VDC-1HS(551)
12A 125VAC
15A 125VAC

Part # looks to be JQC-3FF.

Anyone understand why there are 2 different ratings there? Which one matters?

I think its this one:
http://www.hongfa.com/pro/pdf/HF3FF_en.pdf

Looks like it supports 15A. So using a rule of thumb of supporting 3X running amps, I should be fine with a 5A freezer, Correct?

Thanks.

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Old 10-08-2012, 06:06 PM   #5
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I did a bit more reading over lunch. In case someone else comes by this post, maybe it will help them. I'm not 100% sure of any of this - use at your own risk. Please let me know if I'm way off base.

I think this is the spec sheet (please let me know if you disagree): http://www.hongfa.com/pro/pdf/HF3FF_en.pdf

There are 2 ways this relay can be wired up. Form A and form C.

Form A is like a light switch. Power comes to the switch, if it is thrown to the on position, it completes the circuit. It is also called SPST (Single Pole, Single Throw).

Form C is more like a light switch that toggles between 2 lights. One light is always on, the switch picks the light. These are also called SPDT (Single Pole, Double Throw).

I'm guessing here, but I'm guessing that this relay is using SPST, or Form A. Heating and cooling each have a relay that is normally off. They each get activated independently. So, if my spec sheet is correct, the max current is 15A in this mode.

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Old 10-12-2012, 07:02 PM   #6
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Right, it has two separate relays, one for heat and one for cool. Those relays are SPST, or at least only the NO contact is run to the terminals if it is SPDT. The relay may be rated to 15A but looking at the solder traces in there makes me wonder if those solder traces can take that much current. Or what the current rating of the screw terminal connectors is.

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Old 10-13-2012, 02:21 AM   #7
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There's some discussion of this on another STC1000 thread. Probably if we're just talking about startup spike, you'll be nowhere near 15 amps, even with the old compressor. I think you'll be fine, but if you fry your STC1000, your fault!

BTW - found this bit of info on the interwebs. Can you find the "maximum wattage" rating for your compressor? The article states it should be on the compressor, but who knows.

Quote:
Substitute the maximum wattage and the appliance voltage into Ohm's Law to determine the starting current. Ohm's Law, often expressed as I = P/V, where I is the current, P is the power in watts and V is the voltage, states that the current equals the wattage divided by the voltage. For example, a 720-watt compressor running on 120 volts draws a starting current of 6 amps: 720/120 = 6.
http://www.ehow.com/how_12083846_calculate-starting-amps-compressor-freezer.html
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