Soft start capacitors

[MNRon]

Should every ac have a soft star cap installed? If so, why don’t they come that way? Is there any downside?
Thanks

[mntnflyr4fun]

I recently installed a "hard start" capacitor and an AC fan delay circuit to my Coleman Mach III 13,500 AC unit.

As I was investigating the AC starting load requirements, I realized that to get the most performance (ie: max reduction in load to my generator) I needed to not only have more power available, but I could also reduce the total load at startup by delaying the fan for a couple seconds which is another motor being started at the same time as the compressor motor.

Amazing difference in performance. Prior to the install (which took about 20 min.) my Honda EU2000i would choke out trying to start the AC unit due to the very high load required at startup. In fact last summer on a trip to Louisiana, I tried to start the AC with my gen. and blew both Capacitors in the AC due to low current during startup.

Not only is the generator trying to start the AC motor, it is also trying to start the fan at the same time along with any added loads like maybe your converter trying to charge a battery etc. and 2000 watts was nowhere close to enough.

By installing the hard start capacitor to increase the available starting current AND by delaying the start up of the fan by a couple seconds, as if by magic the AC starts and runs with no trouble and my EU2000i doesn't seem to be struggling to run it after it has started. I am sure I don't have alot of extra power to do much else with from my 2000watts, but on a hot day, a little AC can be just what the Dr. ordered.

Amazing what a little booster and a smart delay circuit can do for about $100 bucks and 20 min. on top of the RV with a couple hand tools. Both parts installed in the AC unit on top of the RV with minimal effort or technical proficiency needed.

I bought the RV Coleman Dometic Duo-Therm A/C Compressor Hard Start Kit + tips +instructions and the RV-AC Starter prevents Generator Stalls, Overload trips at Air Conditioner Start on Ebay.

Cheap upgrade, simple to install and I immediately called my brother and told him he should purchase as well. Living in Oregon, we don't get much call for the AC when dry camping so we both run undersized suitcase generators and this little mod. was a game changer.

Now I can sell one of my EU2000i generators and use the money for a solar kit....seems like a great value to me.

[ktmrfs]

AC motors come in several varieties. two common ones are

split phase. No starting capacitor, very low starting torque. Usually in small motors with low starting torque needs.

Capacitor start, what the "soft" start kits like supco supliment. changing the standard capacitor for one that lowers starting current but still a capacitor start motor. Cap start motors have much higher starting torque. Once the motor comes up to speed the starting capacitor is taken out of the circuit.

Capacitor start, capacitor run. they have capacitors in the starting and runing circuit. Many Air conditions have this. IIRC my coleman is cap start cap run.

AC motors have very high current inrush until the rotor starts to turn and develop a "back emf" as it comes up to speed current demands decrease. And if the motor is turning a load during startup this starting current can be quite high. RV AC motors can draw 50-70 AMPS during initial startup even with some form of capacitor, factory installed or supco.

Now to dramatically reduce the starting current there are devices such as the micro air easy start (which I do have) that keeps the starting current in the 20A or so range. Still takes the same energy to get the motor running, but spreads it over a longer period of time with lower current.

Kits like the supco are really just a different value starting capacitor. they will help reduce the starting current, but not by much in a unit that already has a start cap, which is the majority of RV AC units. It will get you from almost adequate to barely adequate. If your not in the almost adequate to start with it won't solve your problem.

I tried the supco kit. it did slightly reduce starting current and load but not enough to start the AC at other than sea level with my honda 2000. My coleman already had a factory "soft start cap" or whatever you want to call it installed since it was a cap start motor.

Kits like the micro air go much further. My honda 2000 in eco mode will easily start my coleman MachIII at 4500ft. no surge, just a smooth rpm ramp up.

What's the downside? doesn't change running current. At high altitude around 4000Ft the honda 2000 goes into overload after 15 minutes or so.

[laknox]

MNRon wrote:
Should every ac have a soft star cap installed? If so, why don’t they come that way? Is there any downside?
Thanks

From my reading, a lot of these are simply a capacitor that stores a charge to help kick the compressor on so you don't have the huge draw spike you normally do. Helps reduce the impact on both a pedestal that might have a marginal breaker as well as on generators/inverters, so the breaker on =them= won't trip.

Lyle

[GordonThree]

MNRon wrote:
Should every ac have a soft star cap installed? If so, why don’t they come that way? Is there any downside?
Thanks

by my understanding...

soft start means some form of software is controlling the current limiting. microair for example, is a soft start controller

hard start means plain old physics is controlling the current limiting. SUPCO spp6 for example

why don't all ac units have one installed? cost and need. Most RVs that spend their entire life sitting at a seasonal or full time site, wired into the grid, don't need any help starting and restarting the motor. so the hard start cap would be one more thing that can wear out and need service, and it's not providing much benefit.

for soft starters, they're very expensive and again, mostly redundant.

why trailer manuf haven't switched over to inverter type split unit AC, with a digital compressor motor and separate fan motors, who knows ... these mini split roll off assembly lines by the millions and have decades of industry experience behind them now.

the old fashioned Coleman (assorted brands) rooftop units really seem dated, but maybe Elkhart has an enormous warehouse full of the Coleman, so they keep using them and keep building more?

[Lwiddis]

Unnecessary for those that plugin on every campout and there lots that favor horizontal apartment RV parks.