Soft / Start for AC compressors ?

[Davebones]

( BriskHeat Compressor soft starters ) Are these soft /starts good to use for ac compressors ? One of the AC tech's that comes here says he recommends these for people to lower their starting current so they can run their AC's on their portable generator's .

 

[Besoeker3]

( BriskHeat Compressor soft starters ) Are these soft /starts good to use for ac compressors ? One of the AC tech's that comes here says he recommends these for people to lower their starting current so they can run their AC's on their portable generator's .

What size the motor and what size is the portable generator?

 

[gadfly56]

What size the motor and what size is the portable generator?

Two pieces of information that are exactly on point. Grainger has the single-phase soft starters for $389, but you can go to BriskHeat and get them for $316. Would that money get you enough peak watts from the generator to justify a larger generator?

 

[Davebones]

What size the motor and what size is the portable generator?

I would assume around a 5500w generator as most of the people I know backfeed with 30 amp plug into their panels . Even if not using to try to start a AC on a portable generator are these worth the price to have to lower the wear and tear on a compressor motor from the start-up ?

 

[jaggedben]

Following this thread. People need these even more for battery backup applications. One HVAC guy I talked to recently had never heard of a soft start.

 

[Davebones]

What size the motor and what size is the portable generator?

I understand the AC compressor was 4 ton .

 

[Jraef]

As an old Soft Start guy, I have a few concerns;

1. Not NRTL listed. That’s not only problematic for installing in North America, but is often indicative of poor design and/or quality, i.e. they know it will not pass so they pretend to not think it’s important.

2. Misleading advertising, another red flag. In one part they say “Reduces inrush start-current by 70%”, but in the specs it says “Start current reduction - 60%…70% of LRA”, then next says “Startup torque reduction - 30-40%”. If the inrush current were reduced BY 70%, the startup torque reduction would be to about 9% of normal, meaning it would most likely stall. With the startup torque reduction being 30-40%, that means the start current reduction is TO 60-70%. It seems on the surface to be maybe just a simple semantics mistake, but I have found over the years that people often make these sort if “errors” on purpose in order to further their efforts to push an agenda that has more to do with increasing their sales than helping their customers.

3. Any time I see a soft start device with zero heat sink, I am concerned that this is not what it appears to be. Electronic power devices are not 100% efficient, they give off a minimum of 1.5W/A/phase. That doesn’t seem like much, but with NO heat sink, it cannot get away from the components and they overheat and fail in short order. If it has bypass contacts that would be better, but they do not show an internal diagram of it nor do they say that is necessary.

Combine these last two technical issues with the lack of a listing and to me it starts to smell a little scammish.

PS: Also worth noting, the SCCR is only 5kA, making it further difficult to find places it can legally be installed.

 

[Davebones]

Googled AC soft starts and was surprised there seems to be a lot of soft/starts for RV's

 

[drcampbell]

I'm also a little concerned that it says "For ... scroll compressor applications". That's an odd thing to specify. Does that mean it's unusable with piston compressors? Doesn't really say.

It says to expect a minimum life expectancy of 100,000 operations, and that it will tolerate (enforce?) 15 starts per hour.
If it were short-cycled like that, (but within its spec) that would be about 7k hours ... about 7 years in the midwest. Not very confidence-inspiring.

I'm not as concerned as Jraef about the lack of [extended] heat sink. Their mounting bracket seems to provide an air gap, the entire case will serve as a heat sink, (if it's potted) and the inside of a condensing unit is not a severe environment -- there's a lot of airflow and the temperature's likely to be considerably below letgo temperature.

 

[synchro]

Some perhaps relevant info from Emerson/Copeland:

https://emersonclimate.custhelp.com/app/answers/detail/a_id/4151
https://emersonclimate.custhelp.com/app/answers/detail/a_id/5034
https://emersonclimate.custhelp.com...-compressors-with-permanent-split-type-motors

At the last link it says: "Single phase scrolls are designed with PSC type motors and therefore will start without the need of start assist devices in most applications. However, if low voltage conditions exist at start-up, protector trips can result. Therefore start assist devices (start capacitors & relays) are available to maximize starting characteristics under abnormal conditions.

A phase-controlled SCR soft start intentionally reduces the RMS voltage during startup, and so perhaps that creates a risk of tripping low voltage protection as mentioned above (if it is present). By contrast, start assist devices having capacitors that are switched in would likely reduce the peak voltage drop from the power source during starting.

 

[garbo]

Side note: on a 7 year old building they had a soft start on the 250 HP fire pump. If a motor is not start & stopped more then a few times a hour doubt that heat rise due to lack of a heat sink would be a problem. While performing 4 times a year PM on this fire pump I always held my FLIR camera on the soft starter maybe 12 to 18 seconds that it was energized. Never observed any temperature increase. All of the compressors in that large building had VFD'S . Most amazing ones were two 1,750 HP 4,160 Volt refrigeration compressors. Each motor cabinet were at least 18' wide and feed from a 13,200 line.

 

[gadfly56]

Side note: on a 7 year old building they had a soft start on the 250 HP fire pump. If a motor is not start & stopped more then a few times a hour doubt that heat rise due to lack of a heat sink would be a problem. While performing 4 times a year PM on this fire pump I always held my FLIR camera on the soft starter maybe 12 to 18 seconds that it was energized. Never observed any temperature increase. All of the compressors in that large building had VFD'S . Most amazing ones were two 1,750 HP 4,160 Volt refrigeration compressors. Each motor cabinet were at least 18' wide and feed from a 13,200 line.

Yowzah!!

 

[Jraef]

Side note: on a 7 year old building they had a soft start on the 250 HP fire pump. If a motor is not start & stopped more then a few times a hour doubt that heat rise due to lack of a heat sink would be a problem. While performing 4 times a year PM on this fire pump I always held my FLIR camera on the soft starter maybe 12 to 18 seconds that it was energized. Never observed any temperature increase. All of the compressors in that large building had VFD'S . Most amazing ones were two 1,750 HP 4,160 Volt refrigeration compressors. Each motor cabinet were at least 18' wide and feed from a 13,200 line.

I guarantee that a 250HP soft starter had heat sinks on the SCRs. If you didn’t detect the temperature rise in the heat sinks after a startup, that is a testament to the heat sink design, meaning that the designer of that soft starter was not playing games with the temperature rise at and around the SCRs, which is the only place it counts. There are low-cost mfrs who do play a lot of games with that (I’m calling our Eaton on this for starting it, but others have now followed suit). The thing is though, you would NEVER see a Fire Pump Controller mfr. mess around with their reputation by playing the “cheap and dirty” game with soft starter designs. Heavy Duty all the way baby! So yeah, unless you were aiming the IR gun right directly ON the SCRs themselves, a good heat sink would have spread that heat out so far and fast that it would be barely noticeable.

 

[Jraef]

I'm also a little concerned that it says "For ... scroll compressor applications". That's an odd thing to specify. Does that mean it's unusable with piston compressors? Doesn't really say.

It says to expect a minimum life expectancy of 100,000 operations, and that it will tolerate (enforce?) 15 starts per hour.
If it were short-cycled like that, (but within its spec) that would be about 7k hours ... about 7 years in the midwest. Not very confidence-inspiring.

I'm not as concerned as Jraef about the lack of [extended] heat sink. Their mounting bracket seems to provide an air gap, the entire case will serve as a heat sink, (if it's potted) and the inside of a condensing unit is not a severe environment -- there's a lot of airflow and the temperature's likely to be considerably below letgo temperature.

Plastic is a thermal INSULATOR more than it is a thermal conductor, so even if this thing is potted in epoxy, that is a poor way to deal with heat rejection in a thyristor (SCR or diode). They MAY be getting away with it KNOWING that this is to “only” be used on scroll compressors. Scroll compressors are for the most part a centrifugal load, like a fan or pump, so full design load is not expressed on the motor until after the speed gets to about 80% or more. So with that taking probably under 2 seconds, plus the fact that it appears to control the duty cycle by not allowing successive starts, they are playing a numbers game here, dancing on the edges of failure.

If someone were to not know what that note meant about scroll compressors and applied this to a recip, it would likely fail in short order. When they go to get their money back, the mfr will probably point to their “CYA” statement about it only being used on scroll compressors and refuse to refund on it.

 

[jaggedben]

SCR means what?

 

[Jraef]

Silicon Controlled Rectifier. It is the electronic “switch” used to facilitate things like “soft starts”. A small electronic pulse is used to turn the SCR from an insulator to a conductor for a brief moment and allow a larger amount of power to flow through to the load.

 

[synchro]

Just to add some more info, an SCR is a 4-layer PNPN device that can be equivalently thought of as a PNP and an NPN transistor connected to provide positive feedback. This positive feedback allows them to "latch" and turn on with a low voltage drop once they are triggered with a short pulse, as Jraef has mentioned. For AC applications, two SCRs are connected back-to-back in an anti-parallel configuration so that they can conduct on both positive and negative half cycles. Such anti-parallel connected SCRs are sometimes called a Triac.

https://www.electronics-tutorials.ws/power/thyristor.html

For those that might be curious:
To help protect integrated circuits from a static discharge, they'll often use SCRs near the bond pads of a semiconductor die that will latch up and conduct a static discharge to other pins (thus preventing it from entering internal circuitry). Typically such SCRs are made using semiconductor layers that are already being used to make the active devices (MOSFETs, bipolars, etc.)

 

[mtnelect]

They are also used in "Switch Packs" to control traffic signals which are designed to switch at the "0" point.

 

[Besoeker3]

Just to add some more info, an SCR is a 4-layer PNPN device that can be equivalently thought of as a PNP and an NPN transistor connected to provide positive feedback.

Yes, I have viewed that way when people have tried to explain it that way. But it really is what it is - the SCR or thyristor in UK. There are a few versions. including asymmetric. These days much if them have been replaced by IGBTs for variable frequency drives including slip recovery drives.

 

[Davebones]

As an old Soft Start guy, I have a few concerns;

1. Not NRTL listed. That’s not only problematic for installing in North America, but is often indicative of poor design and/or quality, i.e. they know it will not pass so they pretend to not think it’s important.

2. Misleading advertising, another red flag. In one part they say “Reduces inrush start-current by 70%”, but in the specs it says “Start current reduction - 60%…70% of LRA”, then next says “Startup torque reduction - 30-40%”. If the inrush current were reduced BY 70%, the startup torque reduction would be to about 9% of normal, meaning it would most likely stall. With the startup torque reduction being 30-40%, that means the start current reduction is TO 60-70%. It seems on the surface to be maybe just a simple semantics mistake, but I have found over the years that people often make these sort if “errors” on purpose in order to further their efforts to push an agenda that has more to do with increasing their sales than helping their customers.

3. Any time I see a soft start device with zero heat sink, I am concerned that this is not what it appears to be. Electronic power devices are not 100% efficient, they give off a minimum of 1.5W/A/phase. That doesn’t seem like much, but with NO heat sink, it cannot get away from the components and they overheat and fail in short order. If it has bypass contacts that would be better, but they do not show an internal diagram of it nor do they say that is necessary.

Combine these last two technical issues with the lack of a listing and to me it starts to smell a little scammish.

PS: Also worth noting, the SCCR is only 5kA, making it further difficult to find places it can legally be installed.

I see also there is a ( Easy start 368 soft starter by Micro-Air ) . Are these really worth the cost and will they save on the wear and tear of a ac compressor motor starting up ? Will they help extend the life of the compressor ?