RV AC 521 compressor saver

[high5]

Has anyone installed a 521 compressor saver on an AC unit? I know hard start 'boosters' are popular but, I haven't seen anything about the 5-2-1 compressor saver. They are usually installed on residential units but they do make a kit for 1 to 3 tons (12,000 - 36,000 btu). It looks like a good low cost alternative to the $300 Micro-air EasyStart unit. They both substantially reduce compressor start current. Thanks for viewing.

[SoundGuy]

high5 wrote:
The EasyStart 'smart' unit is looking more attractive the deeper I get into this.

Another software driven soft starter you might want to look into are those by Hyper Engineering. 🙂

[high5]

Chris Bryant wrote:
Here's the Dometic kit that uses the potential relay for a decent price. This kit should act identically to the 5-2-1 device.

That does look like a 521 kit. I downloaded the installation manuals for Dometic and all wiring diagrams show PTC kits as installed or optional. The 'RV Parts' part number listed is a PTC type with an optional relay. The installation docs say that this circuit may not work in high ambient temperatures. That's what I expected from a PTC circuit and means a small inv-gen will not be able to start the AC when it's hot outside. So, I don't think it's a true 521 circuit. Supco makes an adjustable potential relay that works with all single phase AC's. They also make one that adjusts automatically for 120 or 240 vac operation. Amamzon has this same kit for $107 so, $48.20 is a very good price if it will work. The EasyStart 'smart' unit is looking more attractive the deeper I get into this.

[Chris_Bryant]

Here's the Dometic kit that uses the potential relay for a decent price. This kit should act identically to the 5-2-1 device.

[SoundGuy]

Link 1

Link 2

[high5]

This first video demonstrates the reduction of inrush current on a large residential AC. The Fluke 334 is specifically designed to capture inrush current. (I hope the links work)

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

This next video is less precise but still valid tests of the PTC and 521 circuits.

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

[high5]

Thanks SoundGuy. Here's the wiring diagram. It shows both the PTC and 521 options. I left the image a little large for detail. (The preview option was not available.)

[SoundGuy]

high5 wrote:
If someone can tell me how to post an image from my computer ...

Upload your pic here, copy the url, and paste it into your post. It would be helpful though if you limited the size of your pic so it's not so large as to force many of us to scroll in order to see it. You can do this by inserting "width=450" just before (/IMG) (or some similar number) ... preview before you post and you'll see what you have.

[high5]

Chris Bryant wrote:
I hav emailed the 521 folks and they do not have a model for 120 volt operation- I haven't measured the back emf voltage on a running unit though. The Supco SPP6E is a relay based unit, and while Supco used to spec it for 90-270 vac, now they spec it at higher- and don't recommend it for 120 volt units. I'm not sure what changed.
Dometic does make a potential relay based start kit- I'll look up the number. It is specifically meant to run a Penguin low profile unit on an Onan 2800 microlight.

Here's the Dometic instruction sheet for the relay based kit-
http://bryantrv.com/docs2/docs/quickstart.pdf

The 120 VAC problem may be why I haven't seen a 521 on an RV AC. And, I did not see at what voltage the 521 1 - 3 ton kit was rated. I'm interested in seeing what Dometic has to offer. If someone can tell me how to post an image from my computer, I'll attach a photo of a 13,500 btu(1.125 ton) Airxcel (Coleman Mach?) wiring diagram showing the 521. The Dometic wiring looks somewhat unconventional to me.

[SoundGuy]

high5 wrote:
Has anyone installed a 521 compressor saver on an AC unit?

It looks like a good low cost alternative to the $300 Micro-air EasyStart unit.

SoundGuy wrote:
Testimonials from those here on rv.net who have installed the Easy Start on their roof top A/C unit indicate this does solve the problem of successfully and repeatedly being able to start & run a 13,500 BTU A/C using a 2K genset such as the Honda EU2000i. If that's your intention the Easy Start is the solution I'd be looking at.

high5 wrote:
That is my intention and I've seen the EasyStart testing. It clearly is the superior unit but with a cost/benefit issue.

The EasyStart reduced inrush by 70%+ but the $320+ cost may not be required to achieve the desired result. If the EasyStart was more affordable, I'd buy it in a heart beat - it's a remarkable piece of engineering.

Your argument 'though certainly understandable is really no different than the argument as to whether a Honda or Yamaha genset is worth a premium price compared to the competition which in some cases cost considerably less. For some the answer is obvious - Honda or Yamaha without question - for others it's a real struggle justifying anything but the cheapest solution they can find. I've owned 2 EU2000i gensets and am convinced the cost / benefit ratio is easily justified ... I just wish I had known about the Easy Start at the time, otherwise I'd have not sold my last EU2000i. :R

[Chris_Bryant]

I hav emailed the 521 folks and they do not have a model for 120 volt operation- I haven't measured the back emf voltage on a running unit though. The Supco SPP6E is a relay based unit, and while Supco used to spec it for 90-270 vac, now they spec it at higher- and don't recommend it for 120 volt units. I'm not sure what changed.
Dometic does make a potential relay based start kit- I'll look up the number. It is specifically meant to run a Penguin low profile unit on an Onan 2800 microlight.

Here's the Dometic instruction sheet for the relay based kit-
http://bryantrv.com/docs2/docs/quickstart.pdf

[high5]

SoundGuy wrote:

high5 wrote:
Has anyone installed a 521 compressor saver on an AC unit? I know hard start 'boosters' are popular but, I haven't seen anything about the 5-2-1 compressor saver. They are usually installed on residential units but they do make a kit for 1 to 3 tons (12,000 - 36,000 btu). It looks like a good low cost alternative to the $300 Micro-air EasyStart unit. They both substantially reduce compressor start current.

The 5-2-1 Compressor Saver is clearly a hard start kit as is a Supco SPP6 but the Micro-Air Easy Start Soft Starter Kit is not. Testimonials from those here on rv.net who have installed the Easy Start on their roof top A/C unit indicate this does solve the problem of successfully and repeatedly being able to start & run a 13,500 BTU A/C using a 2K genset such as the Honda EU2000i. If that's your intention the Easy Start is the solution I'd be looking at.

That is my intention and I've seen the EasyStart testing. It clearly is the superior unit but with a cost/benefit issue. In the tests I saw, using equipment capable of capturing very quick peak inrush current measurements, the 521 3-wire reduced peak current by almost 50%. That reduction plus the addition of a delay relay for the fan, brings the starting current well within the capability of a 2000W inv-gen. The total for a 521 3-wire/fan delay mod is ~$50. The EasyStart reduced inrush by 70%+ but the $320+ cost may not be required to achieve the desired result. If the EasyStart was more affordable, I'd buy it in a heart beat - it's a remarkable piece of engineering.

[high5]

prichardson wrote:
5-2-1 and SUPCO are both hard start kits and consist of a potential relay and capacitor. Ideally the potential relay operating parameters should match the electrical properties of the compressor. Thus the best and safest hard start accessories to use are those available from the manufacturer of the A/C unit involved.

According to the tear-down/installation videos of the Supco, there was no relay - only PTC(s). So, it's operation is dependent upon how fast or slow they heat (and cool) with surge current. A 521 does use a potential relay which is directly dependent on motor back emf. I noticed on an installation video in a 13,500 RV ac, that both the PTC and 521 were shown on the units wiring diagram. So, if the manufacturers wiring diagram includes 521, then I think my question has been answered. That diagram also shows there is no relay in a PTC 2-wire circuit.

[SoundGuy]

high5 wrote:
Has anyone installed a 521 compressor saver on an AC unit? I know hard start 'boosters' are popular but, I haven't seen anything about the 5-2-1 compressor saver. They are usually installed on residential units but they do make a kit for 1 to 3 tons (12,000 - 36,000 btu). It looks like a good low cost alternative to the $300 Micro-air EasyStart unit. They both substantially reduce compressor start current.

The 5-2-1 Compressor Saver is clearly a hard start kit as is a Supco SPP6 but the Micro-Air Easy Start Soft Starter Kit is not. Testimonials from those here on rv.net who have installed the Easy Start on their roof top A/C unit indicate this does solve the problem of successfully and repeatedly being able to start & run a 13,500 BTU A/C using a 2K genset such as the Honda EU2000i. If that's your intention the Easy Start is the solution I'd be looking at.

[prichardson]

5-2-1 and SUPCO are both hard start kits and consist of a potential relay and capacitor. Ideally the potential relay operating parameters should match the electrical properties of the compressor. Thus the best and safest hard start accessories to use are those available from the manufacturer of the A/C unit involved.