DIY soft start with toggle switches?

Phoenix PAL · 09-19-2021, 05:58 PM

I've been reading about the $300 Easy Starts and Softstarts. As I understand, they stagger power to the fan, then the blower, and lastly the compressor. Thus eliminating the surge.

What I don't know is if they also ramp up the voltage on the compressor.

But if all they do is stagger the power, why couldn't I do that manually with individual switches?

Also, I've been looking, but if anyone has a schematic they'd like to share, I'd love to see it.

Thanks

JimD · 09-19-2021, 07:46 PM

I would think they would want the compressor to start first which would eliminate the current draws from the fans. If the fans started first they would be drawing their current when the compressor fired up. If they do start up the fans first you could simply set the thermostat to fan ON rather than auto. It would stay on regardless of the compressor.

There has to be more going on besides staggering the startup sequence. I think I read somewhere where these soft starts have to "learn" your AC. It may chop the AC waveform going in to bring things up slower rather than at full power. Sort of like a dimmer switch chopping the wave to lights. Just thinking out loud.

Now I want to search the net for how these things work. Groan.

**JFlightRisk** · 09-19-2021, 08:01 PM

Our A/C unit shuts completely down when the set temp is reached, and restarts up again as the thermostat calls for cooling. Would you have to stay inside and manipulate the switches off and on constantly as it wants to cycle? Just a weird thought...

Jay2504 · 09-20-2021, 03:32 PM

From what I have read Soft Starts do much more than just stagger the start up of each motor. They have a capacitor to boost current and a way to make the AC compressor motor start up over a longer period of time (like a couple of seconds) to flatten the current spike on motor start up. One guy over at Forrest River Forums actually made one from scratch, but he is an EE, I am not. Jay

Phoenix PAL · 09-20-2021, 04:06 PM

Thanks guys for the feedback.

To answer a couple of your remarks: If you check out this Micro-air EasyStart promo , at about the 2:30 mark the guy explains that it turns on the fans first (4.5 amps) and then turns on the compressor for a total 14.5 amps (versus 50 amp spike w/out the unit). But to me, all he is explaining is a sequential power up.

As for the cycling on and off when temp is reached, yeah I thought about that too. But mine only shuts completely off if it's in Auto mode. If the fan is set to low or high, the fans stay on, and only the compressor cycles off and on when the temp is reached.

All that tells me so far is that yes, switches would seem to do the same thing.

My background is in electronics too, which is why I'm curious to see a schematic for an RV ac softsart.

Paul

Phoenix PAL · 09-20-2021, 04:11 PM

Actually, you'd only need one switch: on the compressor. Keep it switched off while you turn on the ac as normal (fan in low or high mode), then after fans power up, flip the compressor switch on.
Could save this cheapo $300 ;-)

I think I'll try it next time I'm out there tinkering.

Jay2504 · 09-20-2021, 05:54 PM

Our AC unit is 13.5K Dometic Brisk Air II. (2020 24RBS). When we run the AC, we always set the fan on LOW then turn on the AC to the desired temperature setting. I don’t like to try and sleep with the fan cycling off and on. On initial startup, the blower fan comes on first, then about 5 seconds later the compressor starts up. In effect, our unit already does what the OP is talking about. We just finished a weekend “on the generator” and believe me you can tell there is a current spike when the compressor kicks in, even when the fan is already running. Just switching on the fans first helps some, but it doesn’t stop the compressor start up current spike like a true soft start does. Jay

Route 66 Traveler · 09-20-2021, 06:05 PM

Quote:

Originally Posted by Phoenix PAL

My background is in electronics too, which is why I'm curious to see a schematic for an RV ac softsart.

Paul

I got this wiring diagram off the SoftStart RV website. I installed mine a year ago and it still works great..

https://www.softstartrv.com/coleman-diagrams/

https://www.youtube.com/watch?v=tzIes4KAODc

JimD · 09-20-2021, 06:59 PM

The soft start does indeed modify the voltage going to the compressor. Much more than staggering the turn on sequence. It appears they take the start capacitor out of the equation and then do their own thing. One article mentioned multiple triac control of the voltage going to the compressor.

Your idea of staggered start ups may help a bit but probably not anywhere near what the softstart does.

Since you are into electronics, rather than using manual toggle switches you may want to think about relays that you control with timer chips. You could electronically stagger the turn on to each by electronically inserting a delay to the controlling relay. Might be a fun hobby project but still wouldn't be as good as the real thing.

Rustic Eagle · 09-20-2021, 08:31 PM

Quote:

Originally Posted by JimD

snip......The soft start does indeed modify the voltage going to the compressor. Much more than staggering the turn on sequence. It appears they take the start capacitor out of the equation and then do their own thing.......snip......staggered start ups may help a bit but probably not anywhere near what the softstart does.....snip

I agree.......,

With the Micro-Air Easy Start, once it has been taken through the A/C system "learn process" then the real benefits are realized with a generator and shore power....., I've experienced:

* Quieter A/C compressor @ start-up and under normal operation.
* Reduced 'start-up' load on my 2400 watt generator.
* Reduced generator RPM during A/C operation.

As mentioned in an earlier post, before installing the Micro-Air my Dometic A/C start-cycle started the blower motor first, then 5-10 seconds later started the compressor.

Micro-Air 'learn process', page #27 here: http://www.micro-air.com/support-doc...stallation.pdf

Bob

Phoenix PAL · 09-21-2021, 02:10 PM

You guys are right. Now that I think about it, I think my fans start up first as well, and then the compressor kicks in, and then the 2000w geni breaker trips...

Thanks Bob for the manual. Too bad they don't talk in general terms about how the SoftAir is working its magic. The whole "learning" process sounds like vodoo to me. But then, I didn't expect this thing would be processor controlled.

So nix the toggle switch, as well as a simple relay delay circuit. (they actually sell them on ebay with a 2 second delay for $14. They're meant for audio power amps, but the relays are rated at 30amps)

But... now I'm wondering if I could use a rheostat on the compressor to slowly dial up the current over say 5 seconds. Would that hurt the compressor? It sounds just like what softstart is doing anyway but with a much fancier circuit.

Phoenix PAL · 09-21-2021, 02:16 PM

But then, I'd be back in the situation that JFlightRisk was getting at: I'd have to be there every time the compressor cycled as the thermostat reached set temperature.

Thanks everyone for helping me think this through. I wonder if the price will come down on Black Friday/Cyber Monday ;-)

JimD · 09-21-2021, 02:25 PM

Quote:

Originally Posted by Phoenix PAL

So nix the toggle switch, as well as a simple relay delay circuit. (they actually sell them on ebay with a 2 second delay for $14. They're meant for audio power amps, but the relays are rated at 30amps)

But... now I'm wondering if I could use a rheostat on the compressor to slowly dial up the current over say 5 seconds. Would that hurt the compressor? It sounds just like what softstart is doing anyway but with a much fancier circuit.

A rheostat to deal with that amount of current would be the size of a car tire and put out a lot of heat. An electronic version of a rheostat may do it by altering the sine waveform being fed to the motor. There is always a way to do something with electronics. Probably not worth the aggravation though. There are motor speed controllers out there which is the concept you are working with.

If you are a tinkerer and have time and think this project would be "fun", go for it. I love these kind of things but in this instance I would just bow to the professional controller that is specifically made for the RV air conditioner.

poohbear · 09-21-2021, 08:06 PM

You could put a " delay on make " timer on compressor 12v relay control & a start relay/capacitor ( hard start kit ) on the compressor. A lot less $. You could go all out & add another relay to bring on condenser fan during the compressor delay to lower headpressure for a few less starting amps required.
This is a proven method of lowering starting amps in the residential/commercial AC trade. Carrier used this method on its high end equipment in the 60's & 70's

JebTN · 09-25-2021, 12:42 PM

Besides the ramping up of power and delay start one nice feature is it locks out starting the compressor for about 5 minutes after it shuts off so it doesn't try restarting under pressure and causing a big current draw and a bang that use to raise me about a foot off the bed in the middle of the night.

RichCarter · 09-25-2021, 01:25 PM

Quote:

Originally Posted by Phoenix PAL

I've been reading about the $300 Easy Starts and Softstarts. As I understand, they stagger power to the fan, then the blower, and lastly the compressor. Thus eliminating the surge.

What I don't know is if they also ramp up the voltage on the compressor.

But if all they do is stagger the power, why couldn't I do that manually with individual switches?

Also, I've been looking, but if anyone has a schematic they'd like to share, I'd love to see it.

Thanks

The fan and blower use very little power when running, a bit when first starting, but very little thereafter. Turning the them off is a drop in the bucket. IMHO, a kit that includes a timed sequence to these low load devices is using a marketing ploy to get your cash.

The soft-start kit switches in a larger starting capacitor for a few fractions of a second when the motor starts, this changes the phase between the voltage and current to provide a ramped startup sequence to the compressor. There are inexpensive soft-start kits available. They have a large capacitor and a relay on the top of the can. They switch in the larger cap on startup and after a short delay, switch it out. I've never used one but they should work. I've heard some say that they can run their rooftop AC with a 2KW inverter generator. Before you go running out to buy one for your AC, borrow one first and try it. At high loads these inverter generators are about as noisy as the regular ones.

Route 66 Traveler · 09-25-2021, 01:54 PM

Quote:

Originally Posted by RichCarter

At high loads these inverter generators are about as noisy as the regular ones.

That is simply not true. If you are using an inverter generator and it's that loud somebody stole your muffler!!

PaulB12 · 09-25-2021, 02:22 PM

X2 ^^^^^^^^^

PaulB12

videoarizona · 09-25-2021, 04:12 PM

The Easy Start does use microprocessors to ramp up your AC. It does so easily!
I agree with a previous post from Rustic! The learning process is not voodoo. If you have any electrical experience, you can see the actual amp draw change as the Easy Start goes through its " learning curve". My 13.5 AC now starts easily regardless of where the power is coming from. I can actually run it from a house 15 amp circuit.

It's not rocket science, but it's good science for RV'rs....

RichCarter · 09-25-2021, 05:24 PM

Quote:

Originally Posted by Route 66 Traveler

That is simply not true. If you are using an inverter generator and it's that loud somebody stole your muffler!!

I own a Honda EU2000. It makes about as much noise as any regular 2KW generator when under load. Now if you're comparing it with a 8700W generator like the one I power my house with, that's a different story. At light loads, the inverter generator hums along very quietly. You hardly hear it. Run it at load and you can't hear yourself think. As I said, borrow one and try it on your AC out before you buy one.

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