View Full Version : Hard start, Soft Start, Inverter???

25-07-2007, 05:45 AM
I have been researching a solution to a problem I have. I am trying to run a small window air conditioner (8.2 amps running) on a generator (rated output 13.8amps). The generator is more than capable of running the unit except for the momentary current surge when it starts. I keep reading about air conditioners designed with a soft start. So far they seem to be only in Australia. If someone would please take a moment and educate me I would be very appreciative. What is a soft start? Would it be a possible solution to my problem? Are there any other possibilities?

25-07-2007, 07:54 AM
The usual soft start is when the unit monitors the current being consumed by the motor as it runs up to speed and keeps the current below a certain value, usually the FLC. The soft start unit itself will ramp up the frequency to the motor in order to increase the motor speed to full speed at, 50 or 60Hz. Sometimes the soft start units are used the other way round and the time taken to start is the chosen parameter rather than the current. The small ones are very easy to set up. I use a clamp-on ammeter and set the ramp time to a fairly long setting and monitor the current being consumed and adjust the ramp up time until the shortest ramp up time for an acceptable starting current is achieved. These small soft start units are very cheap now and easy to use. They are available in self-contained screw-on-the wall boxes and I feel that you could buy one of these for your A/C unit and wire the soft start between your generator and the incoming terminals of your A/C unit.

25-07-2007, 11:15 AM
They're just a current sensing relay that runs an extra capacitor on start up. They're an add on part mostly, but we fit them only on single phase 6kw+ units. (edit: 6kw cooling capacity that is)
Most manufacturers selling units in australia make their own just for our market. However here is an australian manufacturer that supplies them to panasonics sold here.
www.hypereng.com (http://www.hypereng.com)

25-07-2007, 02:02 PM
Walden, Paul thanks for the response.
The information you both supplied is good news as the alternative of supplementing the current supplied is cost prohibitive.
Walden I am particularly interested in the unit you referred to that seems to be adjustable. Can you give me any leads as to who makes these units?
Paul I will be following up on the lead you gave me. I checked out the site and I will be contacting that company requesting further information.

25-07-2007, 02:23 PM
:eek:Oh! one other note.
Over on this side of the pond small air conditioning unit such as this are powered by 110 to 120 volts 60 cycle AC.

25-07-2007, 03:04 PM
I think the ones walden is referring to are the fully programmables ones that we use on large three phase equipment, and they go for $1k+ each. Not really the thing you are looking for when considering an 8A window air con.
As far as whether the ones we use here work on 110V/60hz, I don't know, as they are only used here. You best bet is to contact hyper engineering.
I heard a guy say that france uses them too, so your best bet for domestic soft starters is the AU or french market.
I would say contact your manufacturer, as if they market their a/cs in those countries they may have developed their own, but then again, I've never seen a soft starter in a window mount a/c.

25-07-2007, 04:03 PM
Telemecanique make a little single phase soft start unit with a couple of control dials on the front and you would get a little change out of £110.You would have to fit it in a small plastic box - I donít think Telemec make an enclosure for it. Iíve used these and they work OK.

Telemecanique Ref: Altistart 01N112FT

25-07-2007, 04:18 PM
I'm surpised you've had no problems with them. Half the stuffed up contacters I've replaced are tele's, while other brands like s+s goes for 10 years. Most of the three phase gear we replace with the $1k+ stuff are tele's. Reason being is that the three phase tele's do stuff all, they only limit two of the three phases, meaning burnt out compressors to boot when they invariably fail.
If there's a single phase soft starter they're probably no worse than any other, but from what I've seen they're not that great. I wouldn't mention 'recommended' and 'telemecanique' in the same sentence, but for an 8A RAC they're probably adequate.

The MG Pony
25-07-2007, 05:48 PM
Well I'd solve it by ditching the 120 Gen and make my self a 200/300 Amp DC gen and a battery bank with an inverter system to run the place, get a 3Kw inverter.

Or get an Automotive A/C compressor and make a direct gas driven A/C that can be run from an electric motor as well! Few options there :)

28-07-2007, 09:47 PM
How about buying some cheap inverter on Ebay?