Refrigeration compressor circuit, help trying to reverse engineer it

Question

I have disassembled the motor controlling circuit for my refrigerator. I am trying to understand how it works, so I hopefully reduce the start surge-current and make it work with my 1000w inverter. Currently the fridge sometimes draws 1100w on start, othertimes only 600w.

The fridge is brand new, high-efficiency, "BEKO" with a Donper AG100CY1 compressor.

I've checked the circuit a hundred times, and it really is like this:

^{simulate this circuit – Schematic created using CircuitLab}

But it seems to go contrary to what I've read about refrigerator controller circuits.

• The start winding is permanently connected (normally it would be disconnected after start, e.g. by a PTC)
• The run winding is current runs via PTC at start, then via capacitor once hot

My main surprise is that the surprise winding is permanently connected.

(And additionally, I am hoping to add a start capacitor...)

Why isn't the start-winding disconnected? Does this make any sense?

Answer 1

That is a permanent split capacitor (PSC) motor.

Answer 2

Why did you check the circuit "a hundred times"? This is a technical site and "a hundred" means 100. ;^)

The 43 Ω winding is the primary one as it is directly across the mains.

The 26 Ω winding is the start winding as it has the series capacitor. I can't guess at the inductance but we could do some guesses about the currents.

The impedance of the capacitor is given by \$ Z = \frac {1}{2 \pi f C} \$. At 50 Hz this will be 1061 Ω and at 60 Hz 884 Ω. Worst case on 230 V 50 Hz is 230 mA and on 120 V is 135 mA. These seem a little low to me but maybe they're enough to give rotational torque to the motor to get it started but low enough not to waste significant power. The start winding does, after all, do some useful work even when up to speed.

Answer 3

Something that is being overlooked is the freon side of the circuit. Most likely the freon system has a cap tube as the metering device. When it is running there is at least 100 PSIG difference between the input and output of the compressor depending on the refrigerant. The system when shut down needs to sit for five to ten minutes, depending on the system to allow both sides (High side & Low side) to equalize. If you do not allow for this your start load will be extremely high and it may not start at all. Most systems have some type of protection to protect for this, one of the most common is a thermal disk usually mounted on the compressor. I expect the compressor is cooled by the return saturated gas from the evaporator so changing compressor speeds other then momentary can be a very bad thing. The compressor needs a given amount of energy to start under all normal conditions. Trying to circumvent that can cause compressor burnout or spoiled contents in the refrigerator as it will not maintain temperature. My suggestion is to simply get a bigger inverter, it will be the most cost effective in the long run.

Answer 4

Motors in consumer products are typically carefully designed to do exactly what they need to do at the minimum manufacturing cost with no safety margins. Any alteration of the circuit is likely to result in the motor not starting reliably.

I believe that refrigerator compressor motors often require less starting current when they are started after not running for some period of time. I have seen a refrigerator with a "minimum off time" circuit. If this refrigerator does not have such a circuit, consider adding that. That might result in the motor requiring only 600 watts every time rather than 600 some times and 1100 other times.

Answer 5

That is a permanent split capacitor (PSC) motor. The starter wire in the case of an electromagnetic or electronic relay, which disconnects it after starting the engine, always has a greater resistance because it is built with a very thin wire, so as not to take up space, so that the aggregate comes out with the smallest possible dimensions . When the starting coil remains connected through the capacitor, a balance is found between the cross-section of the wire and the size of the capacitor, so that the current that will pass through it does not burn it. The currents at the beginning of the pump are the largest, not only from the moment of the start, but during the entire time that the refrigerator has a large evaporation of gas, which returns to the suction pipe of the compressor. when it reaches low temperatures, the compressor works more easily, because the amount of gas in suction is much lower. The refrigerators are built by groups of engineers and scientists in this field and they have found the balance of minimal electricity consumption. Your inventions will cost you enough to buy two new refrigerators and again you will achieve nothing.

Answer 6

use a $20 SSR to start your fridge or AC it switches only ON when the AC sinus wave is at the 0 crossing point, explained in the youtube channel from GreatScott! titled how to make an AC softstarter ...