Ideas to modify a 12v air pump to pump high pressures

[caphair]

I have a 12v car air pump that you plug into the “cigarette lighter” socket (12v socket)

It works fine for pressures up to 50 psi but anything over it starts pulling a lot of current and blows the fuse.

First thing I tried was powering it off an old pc power supply at the 12v supply. This works well for pressures up to 80-90psi then it trips the power supply and turns it off.

The pump says 250psi on it but clearly it's not able to output that much.

My question is, could I add a capacitor across the motor leads to give it a boost that will let it pump out more air under pressure?

I'm trying to use it to fill bicycle tires that require 115psi and was hoping to modify the pump to do that

[R_J]

Re: Ideas to modify a 12v air pump to pump high pressures

How much current does it draw? what was the rating on the fuse it blew? you could connect it straight to the car battery and see if it will pump up to higher preasures, but I suspect the motor itself is on its way out.
I checked on google for 12 volt 250 psi compressors and a lot of people say they are a pos and not getting anything close to that preasure.
I found a (FBA_Kensun-AirComp-D1002) brand and it requires 10 amps.

[eccerr0r]

Re: Ideas to modify a 12v air pump to pump high pressures

Also make sure the pump is mechanically in good shape, oiled, etc.

My small shop compressor can't even get to 250PSI, though it gets to 115 fine.

[stj]

Re: Ideas to modify a 12v air pump to pump high pressures

these things are a joke once you get the plastics off and actually see the tiny piston.

[eccerr0r]

Re: Ideas to modify a 12v air pump to pump high pressures

The tiny piston really doesn't mean much, actually it's easier to get up to higher pressures with a tiny piston due to the physics involved - except it takes much longer to compress. The motor needs to turn faster if you want it to compress faster. However this means loss from friction is higher and you need to make sure it's well lubricated.

[caphair]

Re: Ideas to modify a 12v air pump to pump high pressures

@R_J not sure how much current it uses. But the fuse that blew was a 10amp

I used it last summer hooked to a old pc power supply and it worked fine up to the pressure I needed but would slow down and struggle.

When I tried using it yesterday the max it would output was 80 psi

Would placing a magnet on the motor help at all? Capacitor idea no good?

[R_J]

Re: Ideas to modify a 12v air pump to pump high pressures

You could check the brushes and see if they are worn, a magnet won't help and neither will a cap. a cap across might help if it had a hard time starting, but if the source can't supply enough current to run the compressor motor it won't keep the cap charged either.
It could also have worn bearings (if even uses bearings and not just bushings).

[caphair]

Re: Ideas to modify a 12v air pump to pump high pressures

You could check the brushes and see if they are worn, a magnet won't help and neither will a cap. a cap across might help if it had a hard time starting, but if the source can't supply enough current to run the compressor motor it won't keep the cap charged either.
It could also have worn bearings (if even uses bearings and not just bushings).

I'll check. I was thinking using a cap since it seems to have a hard time starting at higher pressures. Once it has momentum it'll keep going then slowly slow down and stops

[R_J]

Re: Ideas to modify a 12v air pump to pump high pressures

Hook it direct to your car battery, if it won't run from there a cap wont help

[goontron]

Re: Ideas to modify a 12v air pump to pump high pressures

Hook it direct to your car battery, if it won't run from there a cap wont help

Yeah, when that motor burns up, that 600+ CA ought to make for a nice show. I'll bet it makes it to 115PSI... Once.

[caphair]

Re: Ideas to modify a 12v air pump to pump high pressures

What type of grease should I use on the gears? Will try that first

[R_J]

Re: Ideas to modify a 12v air pump to pump high pressures

Yeah, when that motor burns up, that 600+ CA ought to make for a nice show. I'll bet it makes it to 115PSI... Once.

and you think the motor is going to draw 600 amps just because the battery can supply it. I would think it would be obvious to not leave it conected if it is slowing down and going to stall.

[R_J]

Re: Ideas to modify a 12v air pump to pump high pressures

What type of grease should I use on the gears? Will try that first

I don't know, I'm sure whatever I suggest someone will come up with some reason its wrong

[eccerr0r]

Re: Ideas to modify a 12v air pump to pump high pressures

Probably doesn't matter way too much on gears, but if they're clean, probably don't worry about greasing them. Worry about the bearings and possibly the compression chamber. Compression chamber lubrication will depend on what the seal is made of...

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Speaking of compressors, I also have one of these mini compressors which work fine for car tires (though is extremely slow, hence I tend to use my shop compressor). Now how to test its upper end... I don't have a bike tire that I can pump to 115PSI, so I'll need a jig of some sort, perhaps if I can pump into my shop compressor's tank, which will take forever with the puny piston...

[goontron]

Re: Ideas to modify a 12v air pump to pump high pressures

and you think the motor is going to draw 600 amps just because the battery can supply it. I would think it would be obvious to not leave it conected if it is slowing down and going to stall.

Well, when you have seen the needle on a 1200 Amp meter on a bank of 3 batteries parallel get pegged, caused by a 12v bilge pump burning up, all in the mater of 3 seconds or so, you tend to see these things as "record it when you do it, because it's going to be a show"

[Sparkey55]

Re: Ideas to modify a 12v air pump to pump high pressures

Yeah, when that motor burns up, that 600+ CA ought to make for a nice show. I'll bet it makes it to 115PSI... Once.

I have to agree with goontron also. Bypassing the original 10 amp fuse is dangerous. If a short develops the smallest gauge wire (witch in this case is most likely to be the motor winding) would be the new fuse.

These types of pumps are rated for use with a duty cycle of about 10 minutes ON and 20 minutes OFF. anymore than that is risking it.

[redwire]

Re: Ideas to modify a 12v air pump to pump high pressures

It's chinese 250psi, so useable to much less.

I think the motor is simply too small. Once loaded heavy, the motor's efficiency drops off and if the magnets are not strong enough the motor just cooks.
You would need a slower motor (or smaller piston pump) to do the same amount of work (generate 115psi).

In the good old days, these 12V compressors "Grasshopper" used a 1960's Ford windshield wiper motor, and just chugged along at 115psi. But massive in size compared to these toy compressors.

[eccerr0r]

Re: Ideas to modify a 12v air pump to pump high pressures

Not sure if it also takes into account that older PM motors are likely using alnico or some other iron based magnets, and newer ones may be using neodymium magnets, which will reduce size. But yes if it's loaded down to stop, that compressor is done.

I don't know what the gearing is like on compressors too, to reduce costs, direct drive is preferred of course.

I tried playing with my Campbell Hausfeld mini compressor. It's so cheap it doesn't have a pressure gauge. I hooked it up to my "big" bench psu and measured it drawing 4A @ 13.8V (btw, increasing voltage may help it pump but at risk of quicker overheating of windings). I also seem to be able to block off the pressure with my thumb, and during which it draws 10A. If I'm pressing 5lbs (I'm not sure how much pressure I'm actually holding against that hole however), that's the equivalent of about 200PSI which means that this thing is under the spec of 250PSI or my finger is pushing more than 5lbs. However the compressor continues to spin, it doesn't stop...

Sorry I'm not converting pressure/weight to SI, I write the imperial units for you convert to SI you SI nuts

[R_J]

Re: Ideas to modify a 12v air pump to pump high pressures

Caphair: did it blow the fuse in the cigar plug attached to the pump or was it the fuse that protects the lighter plug?
I thought it blew the fuse in the ligter plug in the vehicle and NOT the fuse in the cigar plug, thats why I said to connect it direct. Also the wiring to the vehicle plug could be too light to run the pump, thats why it worked better connected to the power supply.

[caphair]

Re: Ideas to modify a 12v air pump to pump high pressures

Caphair: did it blow the fuse in the cigar plug attached to the pump or was it the fuse that protects the lighter plug?
I thought it blew the fuse in the ligter plug in the vehicle and NOT the fuse in the cigar plug, thats why I said to connect it direct. Also the wiring to the vehicle plug could be too light to run the pump, thats why it worked better connected to the power supply.

It blew the lighter plug fuse in the car