Electric Compressor

Joined: 28 Feb 2004 Location: DUBAI

A question for the electrical geniuses among you.

If you have a 3/4 hp motor. 230v what size converter would you need ie 12 to 230v to power it on full load.

This is for an OBA setup

Joined: 30 Dec 2002 Location: Adelaide

1hp = ~746w

But the surge current on start up of the motor would be most likely a lot more.

Joined: 31 Mar 2003 Location: Brisbane or 169.254.243.241

so are you going to OBA with a 240V bunnings air compressor ?

Joined: 30 Dec 2002 Location: Adelaide

RaginRover wrote:

so are you going to OBA with a 240V bunnings air compressor ?

Have Bunnings expanded to Dubai?! #Rofl

Joined: 31 Mar 2003 Location: Brisbane or 169.254.243.241

Lol I saw that after I posted but I am sure bunnings or home depot won;t be far away from dubai !!

Joined: 28 Feb 2004 Location: DUBAI

I found this

The only problem I have is wheather this thing will suck the life out of my battery or not? and if I can have it put in somewhere permenant

Joined: 19 Dec 2003 Location: Brisbane

Phill wrote:

I found this

The only problem I have is wheather this thing will suck the life out of my battery or not? and if I can have it put in somewhere permenant

The start up surge on a motor can be up to 10x its normal, rated current. You will find a lot of inverters will not start big motors - for one the current is too high, and secondly they often don't like highly inductive loads (like motors) - to either start them or run them.

May I ask what it is to be used for?

To figure out the amperage, your ~500W motor (3/4 hp) will draw (500/12) 42A *continuously*. That's assuming a 100% efficient inverter - more likely at 80% efficiency it will mean a current draw of about 53A.

I don't know what kind of Ah rating your battery has, but that is a LOT of juice. The average vehicle alternator is approx 80A, and this load alone is 2/3 of that.

Joined: 15 Feb 2003 Location: Shed.

it's far more efficient to get a 12v compressor - start here:

http://www.airbagit-store.com/product_list.asp?id=1999

other brands like clisby and oasis (http://www.windrockoffroad.com/part_finder.asp?Vendor=36&DeptID=1&Category=42&SubCategory=169&OnSale=on)

might be more like what you want.

alternatively have you considered an engine driven compressor? ie using a air conditioner type compressor for air?

the inverter/high voltage compressor setup will be very expensive to get set up, to make it run nicely you will need very high curge current capability and probably true sine wave inversion for it to run smoothly and without damaging the motor.

cheers

Brian

Joined: 24 Dec 2003 Location: Brisbane, Australia

I have an air brushing compressor running off my 1700w Inverter, no problems, though because it was tight and new, I blew a 1000w inverter the first time I tried it, despite running and a mates compressor with a few more hours on it off the 1000w before hand. Did a deal with the guy and upgraded instead of repaired.

You need to have an unloading valve setup, and even with this mine used to stall and just hum sometimes when restarting, it's loosened up a bit now after 2 years, but in hindsight, I'd go 12v next time, as you always have that worry of the purchase price of the inverter when it starts and could be left without air if the inverter failed. Runs fine though, great during blackouts, run the house fridge, TV, video, computer, fan etc without listening to a generator.