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Old 07-13-2021, 01:31 PM   #1
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I Built my own AC soft start here is how.

I did this and it works very well for me I am satisfied now with the results. You Are responsible for your own screw ups donít blame me if you get shocked, burn up something, or canít make it work! I am just laying it out there for those who can understand it.

I posted this following letter originally elsewhere, I just went back and edited it with the highlighted things and added stuff. No need to re-invent the wheel I had a lot of info in it. I had some mistakes that I point out.

MY Installation of Ametherm inrush current limiter project.

First this is what I am working with:

Coleman AC model 48204-669 = 15K BTU. Measured current with Fluke T5-1000 meter.

My Steady State Current=(SSC) after running for a few minutes fan on high = 13 Amps. The Fan alone on high=3 Amps and 2.6 Amps on low fan. A/C compressor 10 amps SSC.

My Generator is a Harbor Freight open frame Predator Inverter 3500/4400 that has a 29 Amps max output. If 29 amps is exceeded the safety trips and the Generator will not shut off but the electricity quits outputting. Then you would have to restart the generator to restart power output. I like safety, so I am ok with this save the generator function. Plus, I like it has a carbon monoxide sensor.

Watt/Volts=current 3,500/120=29.1amps MAX. It will handle this amount I have the picture to prove it.

https://www.harborfreight.com/4400-w...arb-58067.html

Problem: My inrush current kicking on the AC was so high it would go over 29 amps for to long tripping the generator.

Solutions available: Hard Starts and Soft Starts or bigger generator.

By putting a $13.00 (hard start) PTC relay capacitor on the unit it did allow for the A/C to start but after research. **** I find this solution boost the peak current possibly damaging the compressor coils. Should the PTC fail in the shorted state the capacitor would be throwing off the impedance damaging the circuit. It is a risk.

**** I was very wrong here above. I had read some B.S. All types of starting devices begin with adding a start capacitor in the circuit. All of them! It shifts the phase angle boost the current and shortens the RC time constant by getting the rotor turning quicker.

By putting a store bought $300.00 (soft start) BrandsMicro-Air, Hyper sure start, SoftstartRV and etc.) this will solve the problem. They will delay the compressor coming on to allow the fan starting first and limit the inrush current surge by putting a resister in series with the compressor to limit current then close a relay to bypass the resister for full current to flow after startup. I have not seen the schematics from the mentioned above but I found other schematic how to diagrams. Pretty simple stuff certainly overpriced at $300.00 IMHO. I could certainly build my own 4 way less. **** I was not entirely correct here but not entirely wrong either.

I searched Inrush current limiter and found a super simple solution that cost very little, and it worked very well to solve my problem initially. Ultimately it failed, upon further review and testing I will get to that why it fails in a minute. **** Problem solved now.

https://www.ametherm.com/blog/inrush...-motor-inrush/

It is an amazingly simple single device solution. No relays, capacitors, timer circuits, PCB boards, or complications. They made the math more complicated than need be on the Ametherm site. If you know your voltages and current (SSC) OHMS law is all you really need. **** not really but close.

https://www.ametherm.com/inrush-curr...ters-full-line = Product Chart.

R in the chart is your resistance value you choose. SSC is your Steady State Current. Round up when it comes to current. 15 amps running steady state is enough and 7 to 10 ohms for the resistance is fine. I am using 10ohms.

****TEST REUSULTS

**** ALL of the testing performed below had no extra start capacitor. It is a necessary item running with small generators.

My Compressor uses 10amps SSC with Fan at 3amps max.

My Fan uses 3amps on high, 2.6amps on low.

I was also running the frig, converter, A/C FAN and TV

I installed a couple variations, I Started with a MS32 7R015 = Rated for 7ohms initial @26C and for running steady state current up to 15 amps. It worked on the first initial startup no problem. However it struggled to start or it would fail tripping out the generator after cycling the Air conditioner. The 4 to 5 minutes being off was not long enough time to cool the inrush current limiter. Started out at 7ohm goes to 0.?? Ohmís as current flows heating up the device. I am in Florida it is hot here! So I tested the ohms with a good meter after 5 minutes and it read 2.5 ohms. So, this is a fail and the reason it does not allow for easy restart.

I ordered more parts to continue my test.

Next I installed a MS32 10015 = 10 ohm and 15amps SSC. This time I also installed a SL22 30005= 30ohm and 5amps SSC current limiter in the Fans common side white wire to limit itís inrush current thinking lets kick them both on same time. I got the same result, it worked initially but did not cool fast enough when cycled. As a Matter of Fact it blew the inrush current limiter apart causing open circuit. The SSC rating is 15 amps max if the part has only cool down to 2 or 3 ohms it quickly goes to 0 ohms. The generator is then struggling putting out 29 plus amps and apparently the part cannot handle it steady state 29amps for very long, so it blows like a fuse.

**** Final Results, it failed. Reason: Cool time not enough between cycles.
**** I was Wrong It did not fail. It Failed mostly because I had tested with no start Cap in the circuit to help the startup phase shift angle. Every start help device I could find begins with a Capacitor in the circuit. Although this Inrush current limiter did work with no cap if it was cool room temp.
I hoped for better the data sheets showed faster cool time 240ish seconds but it did not say at what temp certainly not (90F).

My current configuration for now is I still have the inrush limiters installed. AS32 10015 and Fan SL22 30005 along with the SPP6 across the Cap. I can be running everything with the generator in eco mode and cycle the A/C.

**** Adding the Capacitor with the Inrush current limiter is key to success here. One step further I moved the Inrush current limiters to the return Air inside. With the air flow fan on low it cools all the way down in 4 minutes. I deal for a very small generator to operate.

****Solved the following see drawing. I suggest everyone check theirs.

**** Lesson learned: Crazy thing if you disconnect the power from 120V house plug for a few seconds then plug it right back in the compressor delay is gone on my Coleman. So it will power on with a charged head pressure. Be aware and careful of this. I would say if you lost power at the parks immediately turn off your AC until at least 5 minutes time has passed. If the (Micro-Air, Hyper sure start, SoftstartRV and etc.) have a delay built in after a power outage then they are worth the money. IDK. I donít like that in a brown out you could lose a compressor starting up with head pressure.

Note: If I were to buy a store-bought soft start it would be the SoftStartRV brand. They use 5 wire connections allowing for more in the way of controls. Micro-Air has only 4 connection points. I donít fully get what they are doing the claims are a little out there IMHO. Now that being said I would put what I have done up against any of them in performance and compressor saving technology. I cannot upload a .MP4 file here to show you the ramp up of current but it starts at 8 amps range and within 3 seconds Full 10.6 amps to compressor. No Jolt at the compressor or the generator. Eco mode to running is incredibly soft ramp up. The potential 60amp inrush is fully eliminated. True soft start.
__________________________________________________ ___________

OK time to continue new stuff with following information.

The Drawing is the key. Pretty much all the info is there, as it pertains to my Coleman AC. If you do not understand the drawing, I cannot help you. I do not know about other brand ACís, but the science is solid. If you are a tech U get it and can run with it.

The inrush NTCís work good especially for use with a small generator if the NTC is cool. To solve this issue, I moved the NTCís to the inside intake area of the AC and leave the fan on low. You do not have to run the fan on Shore power in the park or if your generator is 3500 Watt the PTCR Capacitor can handle that. In 4 minutes cycle time the NTCís cool enough to be of some benefit with out running the fan. However, fan running on low 4 minutes of air flow completely cools the NTCís to give full benefit for tiny generators. I am using 4 minutes because that is my thermoset timer if you off on it in my situation.

See Drawing:

1. Installed a Start Capacitor PTCR in the circuit. = SPP6
2. Installed a NTC in the Fan circuit. It makes it much quieter kicking on. Cheap part and can only help.
3. Installed a NTC in the compressor line after a N.O. double pole double throw contactor.
4. Installed a safety circuit: Timer and a Contactor 120V coil.
5. 5 items total installed I had all the tools, wire, connectors and heat shrink etc.

Parts list links:
($12.82) Supco SPP6 Hard Start Kit. https://www.amazon.com/Supco-SPP6-Ha...0&s=hi&sr=1-12

($9.45) Supco Delay on Timer. https://www.amazon.com/dp/B01GS6L4OU...roduct_details

($11.66) N.O. DPDT contactor 120 volt coil. https://www.amazon.com/dp/B004Z0RLL2...roduct_details

Ametherm NTCís at https://www.digikey.com or https://www.mouser.com

($6.52) AS32 10015 or ($4.67) MS32 10015 or ($5.41) MS32 7R015

($1.64) SL22 30005 for fan circuit.
__________________________________________________ _____

$42.00 total, plus shipping from Mouser. I had all the other stuff needed.

I solved the electrical brown out issue with only 2 components and use the control contactor as place to put the NTC. Also acts as a bit of a heat sink.

Proís

By removing the high inrush current everything will have less stress i.e., the windings, capacitors, relay contacts, PC module board, Thermostat, and spikes to other things like TVís etc.

Can run AC off a tiny generator 2000 watt.

No potential 60-amp inrush current equals less potential to Arch anywhere. You will however be pulling full amps once running steady state.

Conís

Works best when starting with cool NTC thermistor. So, resolution with a tiny generator leave on the fan I sleep better with fan on anyway. It will fully cool in 4 minutes with air flow. With my 3500W Harbor freight I can do fan off or on does not matter now. Most AC will cycle off for way more than 4 min once cabin is cool so if no short cycle no problem.

I only have the one minor.


AS32 10015 NTC inrush current limiter start out at room temp 10ohms and goes to 0.0? ohms in the circuit. Current flow heats the device 200 +C deg. Internal. Happens fast. The last 2 digits in the part number is the steady state current rating while running. PTCís are the opposite they are shorts then open when heated via current flow. Often referred to as relays. P.T.C.R = SPP6.

I took this following from Supco Manual verbatim not my words

The start relay has normally closed contacts, so when the compressor starts, both the run and start capacitors are connected to the start terminal. This causes a very high current to go through the start winding when power is first applied. This high start current increases the starting torque of the compressor motor enough that the motor will start even though the refrigerant pressures havenít equalized, or in an ďunder-voltageĒ condition. Once the compressor begins running, the voltage across the start winding increases. This occurs because the motor acts partly like a generator and partly like a transformer. The start relay coil is connected in parallel with the start winding. When the voltage across the start winding increases above the pick-up rating on the start relay coil, the start relay contacts open. The start capacitor is then out of the circuit. Systems with capillary tubes or fixed restrictors usually donít need a full hard start kit, unless the compressor bearings are tight. In such cases, the compressor is probably near the end of its useful life anyway. These types of systems usually need only a start assist device that includes a PTC (positive temperature coefficient) relay wired in series with a start capacitor. These start assist devices are wired in parallel with the run capacitor and use only two wires. The PTC adds current to the start winding. When current passes through the PTC, it gets hot. The resistance of the PTC goes up as it gets hotter. This increases the heat output so the resistance goes up even more. The effect is that the PTC is super boosted and taken out of the circuit in a fraction of a second. The PTC needs to cool down before the start assist device can be engaged again. There are two reasons the start capacitor canít stay in the circuit full time. 1. The start winding of the compressor canít carry such a heavy current continuously without overheating and burning out. 2. The start capacitors are made very compact and would overheat in a short while because they arenít big enough to dissipate heat as rapidly as itís generated. The plastic casing on the start capacitor also plays a role in its tendency to overheat. When a start capacitor does overheat, the little putty filled hole in the top of the capacitor blows and all the fluid inside runs out, causing the capacitor to fail.

History shows that air conditioning manufacturers agree that a start assist device is a necessary part of the equipment; all units included a starting device. They have been eliminated through the years as manufacturers reduce costs. In applications where starting every time is paramount, like refrigeration systems, start assist devices are included with each compressor.

So, what I get is manufactures save money not putting in the capacitor then make money selling you one as an option. Hmmmm. Sounds about corporate to me. They show them as option on the drawings they supply.
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Old 07-13-2021, 03:00 PM   #2
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Holy smokes I'm glad I paid the 300!
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Old 07-13-2021, 03:21 PM   #3
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Originally Posted by NJKris View Post
Holy smokes I'm glad I paid the 300!
my thoughts too
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Old 07-13-2021, 03:32 PM   #4
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Originally Posted by NJKris View Post
Holy smokes I'm glad I paid the 300!
LOL.... Where is the fun in that now. My wife just says "Engineers"
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Old 07-13-2021, 04:58 PM   #5
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Old 07-13-2021, 05:06 PM   #6
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There is SO MUCH AWESOME in OP!
Thanks mate, I am ordering stuff up!
Now, about the microwaveÖ..
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Old 07-13-2021, 05:26 PM   #7
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Yeah I'll spend the $300 and save a lot of headaches and fires and who knows what else
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Old 07-13-2021, 05:27 PM   #8
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To the OP: Thank you very much! I had wondered how ďsoft startsĒ like Micro air worked! Now I can build my own. You have also taught me something about generators. My SIL has a 2019 version of your AC unit. A 15K btu Coleman with no added components at all. (SPP6,soft start ect.) On my recommendation, he purchased a Champion Digital Inverter Hybrid generator with 4000 start watts and 3500 running watts. This generator has NEVER tripped the overload when running his AC. He always runs the generator in ďecoĒ mode unless they are also running a 1500 watt electric griddle at the same time as the AC, even then he sometimes forgets to flip the switch with no problem with the generator going into overload and needing reset. Jay
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Old 07-13-2021, 05:28 PM   #9
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Originally Posted by 22TBSFlagstaff View Post
I did this and it works very well for me I am satisfied now with the results. You Are responsible for your own screw ups donít blame me if you get shocked, burn up something, or canít make it work! I am just laying it out there for those who can understand it.

I posted this following letter originally elsewhere, I just went back and edited it with the highlighted things and added stuff. No need to re-invent the wheel I had a lot of info in it. I had some mistakes that I point out.

MY Installation of Ametherm inrush current limiter project.

First this is what I am working with:

Coleman AC model 48204-669 = 15K BTU. Measured current with Fluke T5-1000 meter.

My Steady State Current=(SSC) after running for a few minutes fan on high = 13 Amps. The Fan alone on high=3 Amps and 2.6 Amps on low fan. A/C compressor 10 amps SSC.

My Generator is a Harbor Freight open frame Predator Inverter 3500/4400 that has a 29 Amps max output. If 29 amps is exceeded the safety trips and the Generator will not shut off but the electricity quits outputting. Then you would have to restart the generator to restart power output. I like safety, so I am ok with this save the generator function. Plus, I like it has a carbon monoxide sensor.

Watt/Volts=current 3,500/120=29.1amps MAX. It will handle this amount I have the picture to prove it.

https://www.harborfreight.com/4400-w...arb-58067.html

Problem: My inrush current kicking on the AC was so high it would go over 29 amps for to long tripping the generator.

Solutions available: Hard Starts and Soft Starts or bigger generator.

By putting a $13.00 (hard start) PTC relay capacitor on the unit it did allow for the A/C to start but after research. **** I find this solution boost the peak current possibly damaging the compressor coils. Should the PTC fail in the shorted state the capacitor would be throwing off the impedance damaging the circuit. It is a risk.

**** I was very wrong here above. I had read some B.S. All types of starting devices begin with adding a start capacitor in the circuit. All of them! It shifts the phase angle boost the current and shortens the RC time constant by getting the rotor turning quicker.

By putting a store bought $300.00 (soft start) BrandsMicro-Air, Hyper sure start, SoftstartRV and etc.) this will solve the problem. They will delay the compressor coming on to allow the fan starting first and limit the inrush current surge by putting a resister in series with the compressor to limit current then close a relay to bypass the resister for full current to flow after startup. I have not seen the schematics from the mentioned above but I found other schematic how to diagrams. Pretty simple stuff certainly overpriced at $300.00 IMHO. I could certainly build my own 4 way less. **** I was not entirely correct here but not entirely wrong either.

I searched Inrush current limiter and found a super simple solution that cost very little, and it worked very well to solve my problem initially. Ultimately it failed, upon further review and testing I will get to that why it fails in a minute. **** Problem solved now.

https://www.ametherm.com/blog/inrush...-motor-inrush/

It is an amazingly simple single device solution. No relays, capacitors, timer circuits, PCB boards, or complications. They made the math more complicated than need be on the Ametherm site. If you know your voltages and current (SSC) OHMS law is all you really need. **** not really but close.

https://www.ametherm.com/inrush-curr...ters-full-line = Product Chart.

R in the chart is your resistance value you choose. SSC is your Steady State Current. Round up when it comes to current. 15 amps running steady state is enough and 7 to 10 ohms for the resistance is fine. I am using 10ohms.

****TEST REUSULTS

**** ALL of the testing performed below had no extra start capacitor. It is a necessary item running with small generators.

My Compressor uses 10amps SSC with Fan at 3amps max.

My Fan uses 3amps on high, 2.6amps on low.

I was also running the frig, converter, A/C FAN and TV

I installed a couple variations, I Started with a MS32 7R015 = Rated for 7ohms initial @26C and for running steady state current up to 15 amps. It worked on the first initial startup no problem. However it struggled to start or it would fail tripping out the generator after cycling the Air conditioner. The 4 to 5 minutes being off was not long enough time to cool the inrush current limiter. Started out at 7ohm goes to 0.?? Ohmís as current flows heating up the device. I am in Florida it is hot here! So I tested the ohms with a good meter after 5 minutes and it read 2.5 ohms. So, this is a fail and the reason it does not allow for easy restart.

I ordered more parts to continue my test.

Next I installed a MS32 10015 = 10 ohm and 15amps SSC. This time I also installed a SL22 30005= 30ohm and 5amps SSC current limiter in the Fans common side white wire to limit itís inrush current thinking lets kick them both on same time. I got the same result, it worked initially but did not cool fast enough when cycled. As a Matter of Fact it blew the inrush current limiter apart causing open circuit. The SSC rating is 15 amps max if the part has only cool down to 2 or 3 ohms it quickly goes to 0 ohms. The generator is then struggling putting out 29 plus amps and apparently the part cannot handle it steady state 29amps for very long, so it blows like a fuse.

**** Final Results, it failed. Reason: Cool time not enough between cycles.
**** I was Wrong It did not fail. It Failed mostly because I had tested with no start Cap in the circuit to help the startup phase shift angle. Every start help device I could find begins with a Capacitor in the circuit. Although this Inrush current limiter did work with no cap if it was cool room temp.
I hoped for better the data sheets showed faster cool time 240ish seconds but it did not say at what temp certainly not (90F).

My current configuration for now is I still have the inrush limiters installed. AS32 10015 and Fan SL22 30005 along with the SPP6 across the Cap. I can be running everything with the generator in eco mode and cycle the A/C.

**** Adding the Capacitor with the Inrush current limiter is key to success here. One step further I moved the Inrush current limiters to the return Air inside. With the air flow fan on low it cools all the way down in 4 minutes. I deal for a very small generator to operate.

****Solved the following see drawing. I suggest everyone check theirs.

**** Lesson learned: Crazy thing if you disconnect the power from 120V house plug for a few seconds then plug it right back in the compressor delay is gone on my Coleman. So it will power on with a charged head pressure. Be aware and careful of this. I would say if you lost power at the parks immediately turn off your AC until at least 5 minutes time has passed. If the (Micro-Air, Hyper sure start, SoftstartRV and etc.) have a delay built in after a power outage then they are worth the money. IDK. I donít like that in a brown out you could lose a compressor starting up with head pressure.

Note: If I were to buy a store-bought soft start it would be the SoftStartRV brand. They use 5 wire connections allowing for more in the way of controls. Micro-Air has only 4 connection points. I donít fully get what they are doing the claims are a little out there IMHO. Now that being said I would put what I have done up against any of them in performance and compressor saving technology. I cannot upload a .MP4 file here to show you the ramp up of current but it starts at 8 amps range and within 3 seconds Full 10.6 amps to compressor. No Jolt at the compressor or the generator. Eco mode to running is incredibly soft ramp up. The potential 60amp inrush is fully eliminated. True soft start.
__________________________________________________ ___________

OK time to continue new stuff with following information.

The Drawing is the key. Pretty much all the info is there, as it pertains to my Coleman AC. If you do not understand the drawing, I cannot help you. I do not know about other brand ACís, but the science is solid. If you are a tech U get it and can run with it.

The inrush NTCís work good especially for use with a small generator if the NTC is cool. To solve this issue, I moved the NTCís to the inside intake area of the AC and leave the fan on low. You do not have to run the fan on Shore power in the park or if your generator is 3500 Watt the PTCR Capacitor can handle that. In 4 minutes cycle time the NTCís cool enough to be of some benefit with out running the fan. However, fan running on low 4 minutes of air flow completely cools the NTCís to give full benefit for tiny generators. I am using 4 minutes because that is my thermoset timer if you off on it in my situation.

See Drawing:

1. Installed a Start Capacitor PTCR in the circuit. = SPP6
2. Installed a NTC in the Fan circuit. It makes it much quieter kicking on. Cheap part and can only help.
3. Installed a NTC in the compressor line after a N.O. double pole double throw contactor.
4. Installed a safety circuit: Timer and a Contactor 120V coil.
5. 5 items total installed I had all the tools, wire, connectors and heat shrink etc.

Parts list links:
($12.82) Supco SPP6 Hard Start Kit. https://www.amazon.com/Supco-SPP6-Ha...0&s=hi&sr=1-12

($9.45) Supco Delay on Timer. https://www.amazon.com/dp/B01GS6L4OU...roduct_details

($11.66) N.O. DPDT contactor 120 volt coil. https://www.amazon.com/dp/B004Z0RLL2...roduct_details

Ametherm NTCís at https://www.digikey.com or https://www.mouser.com

($6.52) AS32 10015 or ($4.67) MS32 10015 or ($5.41) MS32 7R015

($1.64) SL22 30005 for fan circuit.
__________________________________________________ _____

$42.00 total, plus shipping from Mouser. I had all the other stuff needed.

I solved the electrical brown out issue with only 2 components and use the control contactor as place to put the NTC. Also acts as a bit of a heat sink.

Proís

By removing the high inrush current everything will have less stress i.e., the windings, capacitors, relay contacts, PC module board, Thermostat, and spikes to other things like TVís etc.

Can run AC off a tiny generator 2000 watt.

No potential 60-amp inrush current equals less potential to Arch anywhere. You will however be pulling full amps once running steady state.

Conís

Works best when starting with cool NTC thermistor. So, resolution with a tiny generator leave on the fan I sleep better with fan on anyway. It will fully cool in 4 minutes with air flow. With my 3500W Harbor freight I can do fan off or on does not matter now. Most AC will cycle off for way more than 4 min once cabin is cool so if no short cycle no problem.

I only have the one minor.


AS32 10015 NTC inrush current limiter start out at room temp 10ohms and goes to 0.0? ohms in the circuit. Current flow heats the device 200 +C deg. Internal. Happens fast. The last 2 digits in the part number is the steady state current rating while running. PTCís are the opposite they are shorts then open when heated via current flow. Often referred to as relays. P.T.C.R = SPP6.

I took this following from Supco Manual verbatim not my words

The start relay has normally closed contacts, so when the compressor starts, both the run and start capacitors are connected to the start terminal. This causes a very high current to go through the start winding when power is first applied. This high start current increases the starting torque of the compressor motor enough that the motor will start even though the refrigerant pressures havenít equalized, or in an ďunder-voltageĒ condition. Once the compressor begins running, the voltage across the start winding increases. This occurs because the motor acts partly like a generator and partly like a transformer. The start relay coil is connected in parallel with the start winding. When the voltage across the start winding increases above the pick-up rating on the start relay coil, the start relay contacts open. The start capacitor is then out of the circuit. Systems with capillary tubes or fixed restrictors usually donít need a full hard start kit, unless the compressor bearings are tight. In such cases, the compressor is probably near the end of its useful life anyway. These types of systems usually need only a start assist device that includes a PTC (positive temperature coefficient) relay wired in series with a start capacitor. These start assist devices are wired in parallel with the run capacitor and use only two wires. The PTC adds current to the start winding. When current passes through the PTC, it gets hot. The resistance of the PTC goes up as it gets hotter. This increases the heat output so the resistance goes up even more. The effect is that the PTC is super boosted and taken out of the circuit in a fraction of a second. The PTC needs to cool down before the start assist device can be engaged again. There are two reasons the start capacitor canít stay in the circuit full time. 1. The start winding of the compressor canít carry such a heavy current continuously without overheating and burning out. 2. The start capacitors are made very compact and would overheat in a short while because they arenít big enough to dissipate heat as rapidly as itís generated. The plastic casing on the start capacitor also plays a role in its tendency to overheat. When a start capacitor does overheat, the little putty filled hole in the top of the capacitor blows and all the fluid inside runs out, causing the capacitor to fail.

History shows that air conditioning manufacturers agree that a start assist device is a necessary part of the equipment; all units included a starting device. They have been eliminated through the years as manufacturers reduce costs. In applications where starting every time is paramount, like refrigeration systems, start assist devices are included with each compressor.

So, what I get is manufactures save money not putting in the capacitor then make money selling you one as an option. Hmmmm. Sounds about corporate to me. They show them as option on the drawings they supply.
Im wondering how long it took to write out this post?
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Old 07-13-2021, 05:33 PM   #10
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Maybe Jim Moore wrote it for him.
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Old 07-13-2021, 05:43 PM   #11
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I just want to give major kudos to the OP for the design and process undertaken. I do not understand a dang thing you wrote after Ametherm inrush current limiter project.

I applaud you for the great write up and solution....:

I will still spend the $300 on a system but....

Other engineers who understand this will totally geek out.
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Old 07-13-2021, 05:52 PM   #12
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Yeah I'll spend the $300 and save a lot of headaches and fires and who knows what else
The difference betwern DIY and purchased unit is usually extensive reliability testing and "fireproofing".

Took me about as much time to instal my Micro Air as it did to read the post.

FWIW, the Micro-Air unit has a nice large and prominent UL label on it. DIY "projects" don't so good luck if you need to explain to your insurance company at a future date.
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Old 07-13-2021, 05:57 PM   #13
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Nice job thanks for sharing!
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Old 07-13-2021, 06:03 PM   #14
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Interesting project and definitely a great deal of your time, thought and knowledge was put in for the build. Now, enjoy your hard work and cool off, you deserve it
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Old 07-13-2021, 07:10 PM   #15
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There is SO MUCH AWESOME in OP!
Thanks mate, I am ordering stuff up!
Now, about the microwaveÖ..
HA HA funny you should say that. I worked at a microwave shop way back when I was in school as a part time job. I can tell you from experience you must short the capacitor as soon as you take the cover off. It has potential pain stored.
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Old 07-13-2021, 09:24 PM   #16
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HA HA funny you should say that. I worked at a microwave shop way back when I was in school as a part time job. I can tell you from experience you must short the capacitor as soon as you take the cover off. It has potential pain stored.
It seems to have very close to the same inrush load. Sometimes my inverter can handle it, sometimes not. I have 1/0 wiring round trip length from lifepo4 280 ah battery, and it seems that is a tad too light. Should have ponied up for 4/0. I read a little about the inductive load on the microwave startup, and unlike the ac unit, there isn’t any thing that can really alter it. I considered a huge cap (like the audio bass heads use for huge thumping car stereos) at the input to the inverter, but the math says I need 50+ Farads to maybe make a difference. Big and pricey, and a stupid solution.
I would never run the ac off the inverter, but it might be fun to be able to start it to win a drink. It will be cool (!) to run it on the 3000 watt generator in eco mode though.
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Old 07-13-2021, 09:50 PM   #17
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I always say, ďIt only costs you a little bit more to do it yourself!Ē

Not to ask, what is your time worth?
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Old 07-14-2021, 07:20 AM   #18
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I always say, ďIt only costs you a little bit more to do it yourself!Ē

Not to ask, what is your time worth?
Sometimes the fun is had by beating the system and coming out ahead. It certainly is not for everyone. I DIYíd my own 289 ah lithium battery for 1/3rd the cost of battle born, my own digital transmitter for drones, flight control system for drones, speakers, equalizer for home theater, etc.

Not for everyone, but fun and interesting for those that indulge.
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Old 07-14-2021, 09:45 AM   #19
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It seems to have very close to the same inrush load. Sometimes my inverter can handle it, sometimes not. I have 1/0 wiring round trip length from lifepo4 280 ah battery, and it seems that is a tad too light. Should have ponied up for 4/0. I read a little about the inductive load on the microwave startup, and unlike the ac unit, there isnít any thing that can really alter it. I considered a huge cap (like the audio bass heads use for huge thumping car stereos) at the input to the inverter, but the math says I need 50+ Farads to maybe make a difference. Big and pricey, and a stupid solution.
I would never run the ac off the inverter, but it might be fun to be able to start it to win a drink. It will be cool (!) to run it on the 3000 watt generator in eco mode though.
As far as the Microwave goes yes you will have a huge inrush it has a big transformer inside with a large capacitor. Probably 1000 watt unit so it will pull about 8 to 9 amps. You can open up the unit and install a inrush NTC in series with transformer load. Unplug unit from wall and short that Cap or it will get you. Disconnect power wire that feeds Cap then put NTC in between that connection.

Go here

https://www.ametherm.com/inrush-curr...ters-full-line

Select under R column about 7 or 8 ohms and with SSI column at least 12 amps from the chart. It will work initially while the NTC is cool to get it going on a tiny generator. On shore power it wont matter you can keep restarting.

Now are you running your inverter off of 12 volt or 24 volt? Because 12 volt requires some pretty hearty wire. If you up the Voltage you down the current load on the wire. Is your inverter capable of 24V? I can draw you a diagram and show you what switch you need to quickly turn your 2 batteries back and forth. Between 12 and 24 while keeping your trailer still running off of 12 volts on one of the batteries. I have thought about how I am going to set mine up when I get that far. Pretty simple idea. You would need this off of Amazon YaeTek 100Amp 2 Pole Disconnect Knife Switch Dual power Copper Power Disconnector Switch Semicircular Breaker Backup Circuit Generator .
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Old 07-14-2021, 01:50 PM   #20
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Holy smokes I'm glad I paid the 300!
I’m glad I bought 2 !
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