Hello, I am a relative newbie and wanted to as for help with a circuit design.
I have a fridge/freezer with a dead inverter controlled compressor. I was thinking of using an Ssr connected to the ac voltage going to my condenser fan to trigger a regular compressor. (The type that has its own relay and overload device).
The compressor normally runs on just 2 to 5 amps. However it is rated for 15 LRA. I have been reading and am a little confused. Something I read indicated this would be considered an inductive load and the Ssr should be rated at 6-7 times the load. Does that mean I need a 90 amp Ssr?
One concern I have is the main board is what sends 120 v to the condenser fan. Would the Ssr cause excessive resistance or voltage that would damage the main board?
Another thing I read is inductive loads should use a random turn on Ssr. I have found it extremely difficult finding an ac to ac Ssr that is random turn on. Where would you go to find one if that is what I need?
Lastly, also reading about circuit and Ssr protection. Read about putting a mov across the terminals of the Ssr but having a little trouble understand the selection of the right one that won’t fail closed. Also for protection, would you use any resettable circuit breaks in line with the compressor or thermal cut out?
I apologize for the questions. Any help is appreciated!

 

Very simple to make your own SSR using a triac, see Fairchild APP notes AN-3005 & AN-3003
Random phase opto couplers are the Fairchild MOC301x to MOC305x.
Protection is also covered.

 

Very simple to make your own SSR using a triac, see Fairchild APP notes AN-3005 & AN-3003
Random phase opto couplers are the Fairchild MOC301x to MOC305x.
Protection is also covered.

Can you refer me to something explaining how to do this for a semi newbie?
Is it possible to make one with ac to ac 40 amp or higher that would be designed for inductive loads?

 

Normally a fridge compressor would not be triac controlled, unless it is the zero switch type , i.e. not random phase turn on.

 

Hello, I am a relative newbie and wanted to as for help with a circuit design.
I have a fridge/freezer with a dead inverter controlled compressor. I was thinking of using an Ssr connected to the ac voltage going to my condenser fan to trigger a regular compressor

I must be missing something here. Why use a SSR to turn on the new( I'm assuming your replacing the dead compressor) instead of a standard electromagnetic relay? Do you have the required vacuum pump, gauge set and refrigerant to recharge the new set up when you replace the compressor?

 

I must be missing something here. Why use a SSR to turn on the new( I'm assuming your replacing the dead compressor) instead of a standard electromagnetic relay? Do you have the required vacuum pump, gauge set and refrigerant to recharge the new set up when you replace the compressor?

The Ssr would be used to turn on the relay on the compressor. It would be triggered by the condenser fan. The dead compressor is an expensive inverter type. I would be replacing it with a regular compressor.
Yes I have the equipment to recharge and vacuum.

 

Normally a fridge compressor would not be triac controlled, unless it is the zero switch type , i.e. not random phase turn on.

This is a regular compressor with a regular relay.
Any ideas on where I could find an ac to ac random turn on 20 amp or higher Ssr? Been having difficulty

 

If this is a regular AC induction compressor motor, you should not be using phase angle control in order to control it, IMO.
It should be either on or off , which would require zero-cross switching Triac.
As to the different types, I already posted the AN-3006 by Fairchild, Digikey or Mouser should have them,

 

If this is a regular AC induction compressor motor, you should not be using phase angle control in order to control it, IMO.
It should be either on or off , which would require zero-cross switching Triac.
As to the different types, I already posted the AN-3006 by Fairchild, Digikey or Mouser should have them,

I am sorry. I am a newbie when it comes to circuits. I believe the an-3006 is not an Ssr, but something that can be used to build an Ssr?
Not sure what you mean by phase angle control….

 

https://oztekcorp.com/controlling-power-with-scr-phase-angle-vs-zero-crossing-mode/

 

The Ssr would be used to turn on the relay on the compressor. It would be triggered by the condenser fan. The dead compressor is an expensive inverter type. I would be replacing it with a regular compressor.
Yes I have the equipment to recharge and vacuum.

Again I'm missing something in your thinking. Why would you need anything at all to run the compressor? The condenser fan and compressor should come on together, so just run a wire from the fan directly to the new compressor.

My worry would be how are you bypassing the controls of the original inverter compressor, since it may have something to do with the fan also.

 

The condenser fan is triggered by the main circuit board. The thought being an Ssr used as a control signal would be easier on the main board.
I did test and the fan does come on with the inverter disconnected.

 

The circuit drawing provided shows that the compressor is a brushless DC type driven by an inverter, controlled by the computer assembly.
What leads you to believe that the inverter has failed??? Are you able to replace the compressor assembly, as Short asked??
THAT is a very big deal, even for a pro with all the right tools.

Have you gone through the checking sequence described in that service information file?

 

The circuit drawing provided shows that the compressor is a brushless DC type driven by an inverter, controlled by the computer assembly.
What leads you to believe that the inverter has failed??? Are you able to replace the compressor assembly, as Short asked??
THAT is a very big deal, even for a pro with all the right tools.

Have you gone through the checking sequence described in that service information file?
Yes. The current compressor gets hot and hums. The correct poet is going to the inverter however the inverter changes power to 3 phase from 50 to 123 hz to the compressor. I have no way to check the out put of the converter.
Yes, I have gauges, vacuum pump, torch, scales, and refrigerant.

 

OK, then it makes sense.
It seems that the original compressor is a variable speed device, and that is probably more efficient. It is also my guess that the redand black wires from the computer to the inverter are a speed command and not an on/off signal, which is why you would use the condenser fan control to start the compressor. Now it is much clearer..
The most reliable scheme for controlling the replacement compressor would be to get a solid state relay that operates on the 120 volts feeding the condenser fan, and the use that relay to operate a relay rated for the compressor motor current. That relay will be available from where you buy the compressor. Probably it will be rated for ten amps. It is a bit strange to have one relay operate another, but because of not wanting to risk damaging the computer board from an overload it is the cheap insurance choice.
The condenser fan motor power claims to be 4.1 watts at 115 volts, which is about 36 milliamps and hard to believe. If the SSR draws 20 mA that would be a major increase. Hopefully there is an adequate safety factor in the driving circuit. But that is why I suggest an SSR as the intermediate stage. Most relays able to switch ten amps draw more power than that. One option for the SSR would be one that uses a neon bulb as the light source. The neon bulb draws much less current.

 

OK, then it makes sense.
It seems that the original compressor is a variable speed device, and that is probably more efficient. It is also my guess that the redand black wires from the computer to the inverter are a speed command and not an on/off signal, which is why you would use the condenser fan control to start the compressor. Now it is much clearer..
The most reliable scheme for controlling the replacement compressor would be to get a solid state relay that operates on the 120 volts feeding the condenser fan, and the use that relay to operate a relay rated for the compressor motor current. That relay will be available from where you buy the compressor. Probably it will be rated for ten amps. It is a bit strange to have one relay operate another, but because of not wanting to risk damaging the computer board from an overload it is the cheap insurance choice.
The condenser fan motor power claims to be 4.1 watts at 115 volts, which is about 36 milliamps and hard to believe. If the SSR draws 0 mA that would be a major increase. Hopefully there is an adequate safety factor in the driving circuit. But that is why I suggest an SSR as the intermediate stage. Most relays able to switch ten amps draw more power than that. One option for the SSR would be one that uses a neon bulb as the light source. The neon bulb draws much less current.

Not sure what you mean about the Ssr being a major increase or using it as an intermediate step??

 

OK, then it makes sense.
It seems that the original compressor is a variable speed device, and that is probably more efficient. It is also my guess that the redand black wires from the computer to the inverter are a speed command and not an on/off signal, which is why you would use the condenser fan control to start the compressor. Now it is much clearer..
The most reliable scheme for controlling the replacement compressor would be to get a solid state relay that operates on the 120 volts feeding the condenser fan, and the use that relay to operate a relay rated for the compressor motor current. That relay will be available from where you buy the compressor. Probably it will be rated for ten amps. It is a bit strange to have one relay operate another, but because of not wanting to risk damaging the computer board from an overload it is the cheap insurance choice.
The condenser fan motor power claims to be 4.1 watts at 115 volts, which is about 36 milliamps and hard to believe. If the SSR draws 0 mA that would be a major increase. Hopefully there is an adequate safety factor in the driving circuit. But that is why I suggest an SSR as the intermediate stage. Most relays able to switch ten amps draw more power than that. One option for the SSR would be one that uses a neon bulb as the light source. The neon bulb draws much less current.

If I wanted to use a dc to ac Ssr, could I use this to convert the 120v from condenser fan to dc? Acxico 5Pcs 5V 700mA Board Module Mini AC-DC 110V 120V 220V 230V to 5V 12V Converter Board Module Power Supply https://a.co/d/gIOrUSc
How hard would it be on the condenser fan circuit I am worried about?

Thanks for your help!

 

If I wanted to use a dc to ac Ssr, could I use this to convert the 120v from condenser fan to dc? Acxico 5Pcs 5V 700mA Board Module Mini AC-DC 110V 120V 220V 230V to 5V 12V Converter Board Module Power Supply https://a.co/d/gIOrUSc
How hard would it be on the condenser fan circuit I am worried about?

Thanks for your help!

The AC to DC modules mentioned would be easy, BUT WARNING!!! We have no data on how much current they draw. The advertising stated 3.5 watts input, which is almost what the condenser fan motor draws. So that is a bad choice.
But now I have another idea: Use a 5 volt SSR, which is a very common rating, and put a diode and a 5 volt zener diode across the SSR 5 volt input. The zener connected so that the 5 volts can operate the SSR, and the other diode to avoid reverse polarity at the SSR input. This will add NO ADDITIONAL LOAD to the fan drive circuit, and only drop the fan motor voltage from 10 volts to 115 volts, That should not make any detectable difference. So cheaper and safer and an easier to find part. AND, as the fan motor is claimed to draw 35 milliamps, you can use a ten amp, or 5 amp rated SSR and avoid adding a second relay. Othersmight have a better scheme for clamping the voltage to 5 volts, but probably not a simpler one.

 

The AC to DC modules mentioned would be easy, BUT WARNING!!! We have no data on how much current they draw. The advertising stated 3.5 watts input, which is almost what the condenser fan motor draws. So that is a bad choice.
But now I have another idea: Use a 5 volt SSR, which is a very common rating, and put a diode and a 5 volt zener diode across the SSR 5 volt input. The zener connected so that the 5 volts can operate the SSR, and the other diode to avoid reverse polarity at the SSR input. This will add NO ADDITIONAL LOAD to the fan drive circuit, and only drop the fan motor voltage from 10 volts to 115 volts, That should not make any detectable difference. So cheaper and safer and an easier to find part. AND, as the fan motor is claimed to draw 35 milliamps, you can use a ten amp, or 5 amp rated SSR and avoid adding a second relay. Othersmight have a better scheme for clamping the voltage to 5 volts, but probably not a simpler one.

So, are you saying instead of using an ac to ac Ssr to control the compressor relay, using a 10 amp dc to ac Ssr with a zener diode and a regular diode to control the compressor relay? What value diodes and where would I place them? Sorry for the newbie questions but this is interesting!

 

So, are you saying instead of using an ac to ac Ssr to control the compressor relay, using a 10 amp dc to ac Ssr with a zener diode and a regular diode to control the compressor relay? What value diodes and where would I place them? Sorry for the newbie questions but this is interesting!

The diodes will be in parallel, shunting the 5 volt DC input connection of the SSR. Use diodes rated for at least one amp steady current. The zener diode needs to point to the positive terminal of the SSR 5 volt control input, the other diode points in the opposite direction. thus there will be a positive 5 volts across the input to the SSR when the condenser fan is powered. You can use a resistor instead of the motor, and a direct mains connection instead of the controller module, for experimenting. That will assure that any mistakes will be far less costly.
The SSR will be one rated for controlling a 10 amp load, using a 5 volt DC control signal.