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Air Conditioner Soft Start Upgrade
- Thread starter Ulma Doctor
- Start date
My understanding of a demand charge is "demand charge is based upon the maximum amount of power required over a single hour (or fifteen-minute period) in a given month" so the startup current of a 3-phase motor that is most likely over seconds would not be significant if the assessment of peak consumption window is calculated over 15 minutes, but would be impactful if it was just the peak at any time. That being the case, a small reduction or tuning of the motor RPM could result in significant reduction in power consumption, which is the bases for most variable speed pool pumps. Since fluid pumps are variable torque, a small reduction in speed say 10% decrease in flow could result in a 30% decrease in power consumption (there are calculators for this). Fuji VFDs are often used in this application as being quite cost effective in particular if you are using them with single phase input in a derated mode. The other factor is that with variable speed you could optimize flow over time and reduce power significantly, same idea with variable speed pumps in various applciations.
Another factor is how the demand charged is applied, if it is variable based on the peak demand, or just fixed if you pass a ceiling amount for peak demand or more of a steeped teir rate.
I have some reservations about continuing the upgrade.
I opened the control enclosure and found a possible fly in the ointment.
Up in the right corner there is a small control board.
I’m not sure if adding the soft starter would create havoc with the boards function or blow da sumbeyotch up.
So i decided to pause and gather more information before proceeding.
I don’t want to fix a problem that I just caused on something that wasn’t broken already.
(Yes it was dirty and full of cobwebs, but I cleaned it out and feel better about it!)
I opened the control enclosure and found a possible fly in the ointment.
Up in the right corner there is a small control board.
I’m not sure if adding the soft starter would create havoc with the boards function or blow da sumbeyotch up.
So i decided to pause and gather more information before proceeding.
I don’t want to fix a problem that I just caused on something that wasn’t broken already.
(Yes it was dirty and full of cobwebs, but I cleaned it out and feel better about it!)
Mike I do not know about California but here the rates go up and down depending on the time of the day. During the heat of the day the Power company charges more because they can, and there is more demand when everyone is at work in the factories and offices. Then it goes down during the off hours of the daily cycle. I do not care what it cost when it is hot outside I want to be cool inside so during the summer season my monthly bill is usually tripple. How ever if your house is empty during the day meaning kids at school wife at work and you at work it might be worth looking into setting a range of temperatures in the thermostat during the work day. Weekends can also be set differently. I have a programable thermostat but I just leave it on 76 degrees F in the summer and usually around 74 in the winter. I look at it like this I can save money on my utility bill by being hot and the kids can spend the money when I am gone or I can stay cool. Sorry Kids LOL
Quick question on the control board, is it for diagnostic purposes, are they LEDs that light up when operating. Looking at the wiring, at least what I can see it appears that the board connections are in parallel, but the wire from the capacitor seem to be directly connected to the compressor (brown wire) and fan (blue wire), but there seems to be some other additional wires. I would also check the oil capacitor uF, in hotter climates they can lose capacitance over time.
When I installed my soft starters, I replaced the contactor and oil capacitor, the Micro-Air puts a delay in the starting of the compressor, so the contactor closes and the fan starts, after about 5 seconds the compressor starts so I assume they must be using some form of SS switch and the start capacitor is also electronically switched out after a short delay.
When I installed my soft starters, I replaced the contactor and oil capacitor, the Micro-Air puts a delay in the starting of the compressor, so the contactor closes and the fan starts, after about 5 seconds the compressor starts so I assume they must be using some form of SS switch and the start capacitor is also electronically switched out after a short delay.
They are in areas where they are billed for max current draw. So yeah it makes a difference.Soft starters won't lower your bills, but they can make a generator much happier!
Btw, the optimal point for fancy A/C systems is two speed. That is done with dumb relaysproprietary vfds suck, are expensive, and go out of production fast.
Two speed is a pretty significant efficiency boost, and can improve humidity control quite a bit.
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proprietary vfds suck, are expensive, and go out of production fast.
I agree Woody there is a reason they spent all the money up front to install all the smart meters other than the labor to read the meters once a month. We are living in a world that is now just a huge microwave oven. My water meter is even a smart meter . Not to mention the hundreds of cell towers in the county. And when it comes to the issue of AI data centrs I have the Right to Remain Silent.
Nutfarmer, your demand charge isn't likely for instantaneous max current. I thought it was Max used over something like a 15 minute period, but I could be wrong.
If that's the case, running a smaller pump for longer or this pump at a lower speed, would be a solution that would lower the demand charge.
If that's the case, running a smaller pump for longer or this pump at a lower speed, would be a solution that would lower the demand charge.
Your 30 hp motor could easily be drawing 150 to 180 amps during startup. Thats going you be a pretty impressive hit on your peak power! 180 Amps at 460 is 140 kW or 190 hp for a couple of seconds!
A simple soft starter will set you back $1k or so new. It can pull the 5-10x full load starting surge down a LOT. How much depends on the application. Its adjustable! The starting surge depends on the motor design and what its connected to. The soft starter wants a bypass contactor to close after the startup; that may not be built in. It takes the soft starter out of the load path.
The modern simple ones use a semiconductor switch on one leg or multiple legs to lower the voltage applied to the motor. Think of it as a half-assed VFD. Noisy, not suitable for continous operation, but reasonably priced. There are also old-school autotransformer based soft starters built many years ago out there. These are pure sine wave devices, but they can have moisture issues with the transformer, as its not normally in use/hot.
A VFD costs a lot more but gives you total control of the startup process. It can hold your startup peak to full load current if you want! The ability to control motor speed and thus pump flow/pressure may be valuable, especially if you were throttling with a valve before.
If you have a picture of your motor's nameplate we can be more helpful!
Sent from my SM-S911U using Tapatalk
A simple soft starter will set you back $1k or so new. It can pull the 5-10x full load starting surge down a LOT. How much depends on the application. Its adjustable! The starting surge depends on the motor design and what its connected to. The soft starter wants a bypass contactor to close after the startup; that may not be built in. It takes the soft starter out of the load path.
The modern simple ones use a semiconductor switch on one leg or multiple legs to lower the voltage applied to the motor. Think of it as a half-assed VFD. Noisy, not suitable for continous operation, but reasonably priced. There are also old-school autotransformer based soft starters built many years ago out there. These are pure sine wave devices, but they can have moisture issues with the transformer, as its not normally in use/hot.
A VFD costs a lot more but gives you total control of the startup process. It can hold your startup peak to full load current if you want! The ability to control motor speed and thus pump flow/pressure may be valuable, especially if you were throttling with a valve before.
If you have a picture of your motor's nameplate we can be more helpful!
Sent from my SM-S911U using Tapatalk
@Ulma Doctor that board is likely either an anti-short cycle control, a control so the fan and compressor dont start at the same millisecond, a two-speed control, or an interface to the thermostat.
There should be a schematic in an envelope inside the control area. Maybe a quick scan?
Sent from my SM-S911U using Tapatalk
There should be a schematic in an envelope inside the control area. Maybe a quick scan?
Sent from my SM-S911U using Tapatalk