Power supply for small 12V air compressor - Page 1
Forum section: electronics / projects

author: soldar
author_rank: Super Contributor
timestamp: January 07, 2024, 11:15:44 pm
content: I have a small air compressor, of the type you plug into the 12V car connection but I use it at home and I use a lab power supply which is a pain to set it up etc.On the other hand, I have quite a few 12V transformers of the type used to supply halogen lamps at home. Remember those?Those transformers are quite inefficient and in normal continuous use heat up more than I would like.I think I found the perfect use for them.The compressor takes about 4 to 5.5 amps.I put two transformers, each one with its own rectifier bridge and then both connected to two 10000 uF capacitors in parallel. This means each transformer is supplying about 2.5 amps which is well within its specs and the same with the rectifier bridges.Testing shows1.5 A = 15 V3 A = 14 V4 A = 13.5 V5 A = 12.8 VRipple is below 2 V pp. which is good for this application.This type of application, a compressor motor, does not really need voltage regulation and I have tested it and it works very well and I am quite satisfied. I will probably mount the compressor on the same base as the PSU.As this is for very discontinuous use and the transformers are well below their limit heating should be an issue at all.I might still add a mains switch and fuse even though there is a fuse in the output.I would have used a metal enclosure but I didn't have one at hand and they are too expensive anyway. So I used a piece of scrap particle board.

author: Benta
author_rank: Super Contributor
timestamp: January 07, 2024, 11:29:50 pm
content: Why waste money on capacitors? The compressor doesn't care.

author: soldar
author_rank: Super Contributor
timestamp: January 07, 2024, 11:35:15 pm
content: Quote from: Benta on January 07, 2024, 11:29:50 pmYou are probably right but it can't hurt and that way I can use it for other uses where it might be relevant.I am thinking of maybe adding a switching buck regulator module (I have several unused) and that way I can have some regulated voltage for other things.BTW, they cost me $1.00 each, less than 1 euro, on eBay, so it's not like it really matters much cost-wise.

author: inse
author_rank: Super Contributor
timestamp: January 08, 2024, 12:47:16 am
content: Ah, one of those devices that convert electric power into noise with a little air movement as byproduct ;-) have one myself.Nice recycling project though, just take care of compliant wiring.

author: BrokenYugo
author_rank: Super Contributor
timestamp: January 08, 2024, 03:00:34 am
content: Quote from: inse on January 08, 2024, 12:47:16 amI have one out of a junkyard Kia tire repair kit that works at a reasonable speed for the size and noise, like you can see the needle on the decent quality gauge moving, nice brass screw on connector. I think it pulls around 10A to do it though, it burned out some thermal fuse in my car's lighter socket after a while.

author: IanB
author_rank: Super Contributor
timestamp: January 08, 2024, 03:12:35 am
content: I have used a PC power supply for this application, until I found thatthisis far more convenient.

author: soldar
author_rank: Super Contributor
timestamp: January 08, 2024, 07:32:23 am
content: Quote from: inse on January 08, 2024, 12:47:16 amI couldn't have put it better myself. It produces more noise than tire inflation.Yes, recycling is the main aim of this project. I have quite a few of these transformers and would like to recycle them. am asking my friends if they could use such a PSU and none have this type of compressor but one says he would be delighted to have one for a pump that he uses to extract motor oil through the dipstick hole. Unfortunately for he also has a pile of these transformers and says he will make the power supply himself with my plans. That is the kind of person I am and the kind of person he is, the kind that hang on to junk in the hope of recycling it.And yes, when the project is finished it will comply with all laws and regulations, national and international.

author: soldar
author_rank: Super Contributor
timestamp: January 08, 2024, 07:35:40 am
content: Quote from: BrokenYugo on January 08, 2024, 03:00:34 amMine pulls around 5 A when running but probably pulls a lot more on startup. Some years ago I asked a neighbor if I could plug it into his car and it blew the fuse instantly so I am not trying that again.

author: soldar
author_rank: Super Contributor
timestamp: January 08, 2024, 07:44:10 am
content: Quote from: IanB on January 08, 2024, 03:12:35 amMore convenient definitely but more expensive and defeats the purpose of recycling.If you use it a lot then it makes sense but I would not buy it for very occasional use as is my case.Also, a small compressor like that will pump bicycle tires in short time but I have used my compressor to pump a car tire and it took quite a long time. I would not want to do that with a battery operated compressor.

author: IanB
author_rank: Super Contributor
timestamp: January 08, 2024, 08:14:07 am
content: Quote from: soldar on January 08, 2024, 07:44:10 amI have used that Ryobi compressor to inflate a car tire from 15 psi (1 bar) to 35 psi (2.4 bar) and it was pretty quick. Also, it runs a long time on a single charge and does not overheat or anything bad like that. I have nothing but good things to say about it.On the other hand, I have one of those 12 V compressors like the one you pictured, and I had to fix it to a piece of wood and stand on it to prevent it vibrating all over the floor. By the time I have got it out, connected up the power supply, and then connected it to the tire valve, it is quite a fuss to use.

author: soldar
author_rank: Super Contributor
timestamp: January 08, 2024, 09:02:27 am
content: Quote from: IanB on January 08, 2024, 08:14:07 amI have no doubt the Ryobi compressor must be much better that my little piece of junk which, as you say, makes more noise and vibration than anything else. On the other hand I think I paid like $10 for mine and I would expect the Ryobi to cost quite a bit more.But this makes me think I could perhaps try to run my 12 V compressor from an 18 V Ryobi battery. I could try with a step-down converter or even a resistor or even ... nothing. The cable which comes with the compressor is so thin there must be a substantial voltage drop in it. It would be a good experiment. I have used my Ryobi batteries in the past to charge USB devices when power outages. I just rigged a step down module.

author: Zero999
author_rank: Super Contributor
timestamp: January 08, 2024, 06:42:04 pm
content: Quote from: soldar on January 07, 2024, 11:35:15 pmIt's not true that is can't hurt, maybe it's fine in this case, due to the high impedance of the transformer and you probably used far too smaller value to make a difference, but the capacitor increases the average output voltage. If you tried it with a larger transformer and larger capacitor, then it could cause the motor to overheat.