fAs the title says, I wish to limit the starting current of a small aircon compressor, The running current is just under 4A @ 240v, but the starting current is 19A. I need to run this unit off a generator which is capable of delivering 10A for a couple of seconds and 8A continuously.
I have tried an NTC thermistor SL15 40004. That almost worked.... I then put a second one in series with it and the generator managed to start the aircon once. Second time the compressor kicked in again the generator faulted on overload. I tried again after the thermistor was completely coldagain, but the generator couldn't start the aircon again. It works fine off mains.
My next thought is to try 3 or even 4 NTC thermistors in series, and then use a timer an relay to short them all out after a set time and let them cool down quickly - and not have 3 or 4 devices making a lot of heat.
What other options are there and am I on the wrong track anyway?
Kind Regards,
Joe

 

fAs the title says, I wish to limit the starting current of a small aircon compressor, The running current is just under 4A @ 240v, but the starting current is 19A. I need to run this unit off a generator which is capable of delivering 10A for a couple of seconds and 8A continuously.
I have tried an NTC thermistor SL15 40004. That almost worked.... I then put a second one in series with it and the generator managed to start the aircon once. Second time the compressor kicked in again the generator faulted on overload. I tried again after the thermistor was completely coldagain, but the generator couldn't start the aircon again. It works fine off mains.
My next thought is to try 3 or even 4 NTC thermistors in series, and then use a timer an relay to short them all out after a set time and let them cool down quickly - and not have 3 or 4 devices making a lot of heat.
What other options are there and am I on the wrong track anyway?
Kind Regards,
Joe

The 2 most popular methods are; a NTC inrush limit thermistor, or an ordinary resistor bypassed by relay contacts after a delay.

Most motors will continue drawing stall current till the magic smoke comes out if they fail to spin up. Adding inrush suppression might cause that to happen.

 

I was sort of afraid of that....Are there ways to pulse the starting current runtil the motor turns over - so that the cuttent isn't at fully duty cycle - which makes the overload protection trip on the generator?
I know I'm grasping at straws....

 

There is an add-on capacitor kit that is available from AC supply stores. It reduces the in-rush start-up current, and is then disconnected from the motor. ... Used one on a residence for several years with no problems.
https://highperformancehvac.com/start-capacitors-hvac-compressors/

 

Are you sure that the compressor is completely unloaded for starting? Any load increases the starting current a whole lot. AND one other possible fix is a centrifugal clutch, which allows the motor to get up to perhaps 1500RPM before engaging the compressor.

 

Like most air conditioners, this is a sealed unit. So no centrifugal clutch or unloader is really possible.
However, I found that the compressor has no starter capacitor, only a run capacitor. I'm reading about adding a starting capacitor, which sounds promising.

 

OK, I had not understood the "aircon" word in the first posting. I was thinking about an air compressor as used by contractors to operate power tools. This puts the whole discussion in a different direction. There are variable speed drives and there are soft-start electronic packages.I have used the soft start devices to start some fairly large motors on circuits that would only just support their running current. the soft-start devices do not use resistors to limit the current, since that reduces the power to start the motor and makes the problem worse. probably such a soft start package would cost less than a larger generator, and it would reduce the strain on all parts of the system during starting. So that would be your best choice.

 

Are you sure that the compressor is completely unloaded for starting? Any load increases the starting current a whole lot. AND one other possible fix is a centrifugal clutch, which allows the motor to get up to perhaps 1500RPM before engaging the compressor.

That probably isn't all that likely in this type of appliance - a solenoid operated clutch would solve it, but pretty difficult engineering to rebuild one into original equipment.

 

Oh, thanks for the topic, you gave me an idea how you can solve my problem. Up topic, useful information.

 

Oh, thanks for the topic, you gave me an idea how you can solve my problem. Up topic, useful information.

Joe, if you have any problems with the installation of the air conditioner, then just try to find a specialist who will tell you. Or let him write you a detailed guide on installing everything because this way you can do anything indefinitely. You should see exactly how many amps it costs to use, and so on. There are many little things in this case, and you need to have a lot of knowledge to cope with it. I'm telling you this as an engineer. And yet, before installing, you need to check the quality of the materials you bought because sometimes the whole system suffers from quality. It's good that I have many friends who are engaged in the installation of air conditioners and will always tell me what materials to buy...

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Running an air conditioner on a generator sounds a lot like the A/C is in a camper. That would put a different slant on the whole thing. The compressor being a sealed unit device is not able to be modified. There are soft-start boxes made for smaller loads, the one that I used that worked so well was for 50 HP motors. A totally different realm.