# How can I use an air compressor (12V DC, car plug 180W) in a 120-240V AC wall outlet?

#### rambomhtri

Joined Nov 9, 2015
501
So, I have this typical portable tire inflator (air compressor) for cars, which has a car plug, and that's 12V DC. I want to be able to use it at home, so I need to convert those 120-240V AC of a wall outlet to 12V DC.

First I thought about these "small" transformers were you can select the output of 5V, 9V or 12V, but they are only rated for 40W maximum.

My first question is, how in heavens a car plug can provide 180W but a house generic mini transformer can only deliver 40W. Where do you need more power/flexibility, in the plug of a car or in a house? It really shocked me that I can't use any of my spare mini transformers for a car device.

My second question is, what to do?

#### paulktreg

Joined Jun 2, 2008
820
Car 12V outlet sockets are typically fused at 15A which is 180W.

You need a 12V DC power supply that can output 15A.

A cheap computer ATX power supply capable of >15A on the 12V rail will do the job.

#### jpanhalt

Joined Jan 18, 2008
11,088
Why in the world would you want to do that?

#### rambomhtri

Joined Nov 9, 2015
501
No way, the compressor was about $20, I can't buy a$40 thing to make it work.

Car 12V outlet sockets are typically fused at 15A which is 180W.

You need a 12V DC power supply that can output 15A.

A cheap computer ATX power supply capable of >15A on the 12V rail will do the job.
Oh, that's a great idea, thank you. I might have one of those. Anything more portable? Like a laptop charger size or something?

Do you know why on earth a car outlet lets you supply 180W of power?
A car outlet is for lightning cigarettes, or charging phones, small devices or things, it's really weird you can get so much power out of it. I have to admit a few months ago I thought the car socket was exactly like a USB on a PC, a 5V with max 3A or so, like 20W of power maximum.

Why in the world would you want to do that?
Because I have never needed to inflate my tires nor use my car outlet but I find it very useful if I could use it in my house to inflate my bike tires, soccer balls, etc... I can say I have never ever used a car outlet, not even to charge a phone, because I use like 20Ah external batteries.

#### narkeleptk

Joined Mar 11, 2019
548
return the pump, buy the jump pack+pump much more useful.
If you have available to you, just use a old car battery or mower battery with the clamps it has.

most all power outlets in cars actually use 20A or 25A fuses. I know this because the OBD2 works on the same fuse and I need to replace them quite often for diagnostics and flashing.

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#### kjohnson1

Joined Jul 24, 2019
3
look around you house. Somewhere you have a wall wart that converts 120vac to 12vdc. Lord knows i have a pile of them. You may need to cut and solder a connector to make it work with that Chinese compressor...but that's not a big deal. If you don't have a wall wart that meets your specification, let me know. I'll sell you one for almost nothing and ship it to you.

#### narkeleptk

Joined Mar 11, 2019
548
@kjohnson1
I'm not sure how much current those compressors will pull but I don't have many 12V wall warts that go past 3a and most are 1-2a
Don't think that would be enough.

I removed a motor from one awhile back from a jump pack gone bad. Then hooked it to my dc power supply and it was pulling at least 5a If my memory is working. .

EDIT:
Memory did not work, as usual.... Just found It, and it was at about 3.3 on the bench. I would imagine under the load of pumping the tires it would go up more.

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#### rambomhtri

Joined Nov 9, 2015
501
It supposedly draws 180W of power. That means the air compressor must get close to that consumption under the worse circumstances, which I guess it's when it's almost full of air and it is reaching its nominal maximum pressure, right?

Yes, Narkelept, I've found plenty of mini wall transformers, but they are all rated for 40W maximum or so. I guess if I use one of those, the compressor will work for a few seconds, but when the pressure inside the deposit starts to build up and it's harder and harder to push air in, it will stop because 40W wouldn't be enough. Am I right?

#### narkeleptk

Joined Mar 11, 2019
548
Yes if current is to low it will start to stall out as the psi of tire gets higher.

#### shortbus

Joined Sep 30, 2009
9,650
Because I have never needed to inflate my tires nor use my car outlet but I find it very useful if I could use it in my house to inflate my bike tires, soccer balls, etc... I can say I have never ever used a car outlet, not even to charge a phone, because I use like 20Ah external batteries.
Just use it powered by the car when you need to do those things. You don't take your bike in the house to inflate the tires do you?

Joined Jan 15, 2015
6,991
If you look at the plug as pictured above, designed to plug into an automotive accessory socket they normally actually have a fuse inside them. The few I have say the same thing yours does as to 12 VDC 180 watts but mine have a 10 Amp fuse. Anyway if you use the 180 watt number you would need a 12 VDC 15 Amp source for your supply.

The end result when all is said and done is that it simply is not practical or economical to try and power these small compressors off of 120 VAC. Easy enough to do but just not cost practical.

For intermittent home use I can buy an inexpensive light duty 120 VAC compressor for under $60 USD which will do much more than the ones in my wife's truck. A six gallon capacity 150 psi unit for general light use can be had relatively inexpensive, I use mine with a few nail guns and a pneumatic stapler. Anyway trying to do what you are looking to do is very possible but just not very practical, all of the ways of doing it aren't worth the cost of effort in the long run. Ron #### crutschow Joined Mar 14, 2008 30,840 Do you know why on earth a car outlet lets you supply 180W of power? A car outlet is for lightning cigarettes, That's why. A cigarette lighter requires that amount of power for the resistance coil to get red hot in a few seconds (have you ever used one?). You can't do that with a few watts of power. Thread Starter #### rambomhtri Joined Nov 9, 2015 501 OK, so far, the PC power supply unit looks like the best idea. I know it's not that practical, but it's the only one I see efficient. I didn't buy it, they gave it to me, so I wanted to make it useful. A laptop charger would be perfect, but sadly they normally operate at 20V or so. Uh... I thought it would be easy as pie to use it in a wall outlet. Thread Starter #### rambomhtri Joined Nov 9, 2015 501 That's why. A cigarette lighter requires that amount of power for the resistance coil to get red hot in a few seconds (have you ever used one?). You can't do that with a few watts of power. Oh, that makes, sense, THANKS! No, I don't smoke, neither I let anyone near me, my house or car smoke neither, hahahaha. I though that you could light a cigarette with 20W via a spark or something, or a very small hot area. Can't you, with 20W, heat up a tiny resistance? I believe it's all you need... #### crutschow Joined Mar 14, 2008 30,840 Can't you, with 20W, heat up a tiny resistance? I believe it's all you need... Yes, for a small physical sized resistance. But the standard lighter has a thick spiral-wound nichrome coil about a half-inch in diameter which requires a lot of power to reach red heat. Thread Starter #### rambomhtri Joined Nov 9, 2015 501 Yes, for a small physical sized resistance. But the standard lighter has a thick spiral-wound nichrome coil about a half-inch in diameter which requires a lot of power to reach red heat. Then it looks to me like a very inefficient way to light a cigarette, isn't it? News: I just found a small bare transformer from 240 AC to 12 AC of course. All I need now is a rectifier, right? Any ideas? Do they sell 12V rectifiers that can stand 180W? #### Reloadron Joined Jan 15, 2015 6,991 Then it looks to me like a very inefficient way to light a cigarette, isn't it? News: I just found a small bare transformer from 240 AC to 12 AC of course. All I need now is a rectifier, right? Any ideas? Do they sell 12V rectifiers that can stand 180W? 12 volt be they 240 or 120 to 12 VAC are plentiful. Your problem with this is how much current the transformer can supply. You want 12 VDC (give or take a littel as automotive systems are not a steady 12 VDC). However, 180 watts at 12 volts = 180 / 12 = 15 Amps which is a very large and very heavy transformer. If you find one with a 12 volt 15 amp secondary it will be real costly. The 15 Amp full wave bridge rectifier is the least of the problem. On average a power supply with a 12 VDC 15 Amp output runs about$20 on Amazon and these are not transformer (in the sense we are thinking) power supplies, they are what is called a SMPS (Switch Mode Power Supply). So anyway it's not just about 12 volts but also about the power the transformer can supply. If your compressor does in fact use 180 watts and you leave a margin you are looking for maybe about 12 VDC out @18 amps.

Yes, the old automotive cigarette lighters were very inefficient but for short duration use they got the job done.

Ron

#### narkeleptk

Joined Mar 11, 2019
548
Then it looks to me like a very inefficient way to light a cigarette, isn't it?
I believe it's original design and Intent is for cigars,which need a lot more effort to lite.

#### crutschow

Joined Mar 14, 2008
30,840
Then it looks to me like a very inefficient way to light a cigarette, isn't it?
I suppose.
But we are not really concerned about the efficiency of that in an automobile (so how much added gasoline will lighting a cigarette require?)