250w led psu supply 18A car air compressor - Page 1
Forum section: electronics / projects

author: sdancer75
author_rank: Frequent Contributor
timestamp: April 06, 2019, 09:29:48 pm
content: I tried to use my car 18A air compressor to my home using a 250W led PSU (20A - 12V). Unfortunately the compressor start for a half of a second, and then it stops. The start up current surge obviously is not enough for this psu. The prime circuit of the psu have a 100uF/400V capacitor. Should it help to raise this capacitor value ? Alternativaly what are my options to make it work ?

author: james_s
author_rank: Super Contributor
timestamp: April 06, 2019, 09:33:28 pm
content: Motors can draw quite enormous startup surges, any reasonably sized capacitor is likely to not be enough. What you could try is adding a RC filter in the current sense feedback loop to slow down the response slightly, however there is some risk that the power supply will be damaged by the momentary surge. You could also try a NTC inrush limiter in series with the compressor.

author: soldar
author_rank: Super Contributor
timestamp: April 06, 2019, 11:46:28 pm
content: You can try starting the compressor with no load and connect the valve once it is running. My guess is there is a good chance it will stall as the PSU cannot keep up.

author: james_s
author_rank: Super Contributor
timestamp: April 07, 2019, 02:16:06 am
content: Even with no load, the motors used in this sort of thing tend to draw a big enough surge that the fast short circuit protection in many SMPSs will be triggered. It may be possible to slow down the protection just enough to prevent false trips without compromising its ability to protect the PSU.

author: soldar
author_rank: Super Contributor
timestamp: April 07, 2019, 07:29:38 am
content: Yes, I have a little tire compressor that often will blow the fuse of the lighter/connector in the car so I have learned to connect it directly to the battery terminals.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: April 07, 2019, 08:00:26 am
content: A compressor that needs 18A is quite a lot for a 20A SMPS.DC motors without electronics need at least 5x the rated current at startup, and surges of 10x or even 20x the rated current are no exception.The simplest solution is to put a Power resistor with a small value in series with the compressor.If you put a resistor with a value of 12V / 20A = 0.6 Ohm in series with the compressor, then it can never draw more than 20A.Once the compressor starts running you can short the resistor.Because the compressor itself also has a bit of resistance you will need to add less.It might even work if you simply use quite long cables between the power supply and the compressor.

author: sdancer75
author_rank: Frequent Contributor
timestamp: April 15, 2019, 04:55:56 pm
content: Quote from: soldar on April 06, 2019, 11:46:28 pmThe air compressor does not have any load in my tests anyway !

author: sdancer75
author_rank: Frequent Contributor
timestamp: April 15, 2019, 05:06:58 pm
content: Quote from: Doctorandus_P on April 07, 2019, 08:00:26 amYou mean to add a resistor just across between the PSU output and the compressor connector?Anyway, an Acid 12V/7.2Ah battery did the job, but it would be nice to have my PSU connected to the main power.