Hi all,

I have a small air compressor with the following electrical specs:

* Voltage: 12V DC
* Max. Amperage: 16A

This compressor was powered from a bench power supply at 12V 5.5A. At this current setting, the compressor is consuming 5.4A (which I an assuming is the max it can provide) and the voltage is dropping to 10V.
Although the maximum amperage is stated to be 16A, I am finding it strange that it is consuming all this current without any load (just the mechanism of the compressor). Is this normal? If not, what can be causing this high current consumption?
What i did notice is that the brushes may be a bit worn out. If this is the case, could this cause the current consumption to increase?

 

Those 12V DC compressors are not known for efficient operation, sounds normal to me.

 

As noted they aren't very efficient to start. You are still moving an unlubricated piston without a load. It might have some sort of coating to help, but it's just going to be enough to keep it from burning up after a few uses. The air coming out of the hose is somewhat pressurised also due to the size of the cylinder in relation to the hose diameter.

 

Consider that the 5.5 amps is only a third of the full load current, that value is probably reasonable. If the brushes are a bit worn, it already has had a fair amount of use, and so it might even benefit from a bit of lubrication. Is this one of the portable devices with a plastic case surrounding it? Have you opened the case and checked to see how freely the motor turns? A drop or 2 of oil on the bearings may help a bit. Likewise, the compressor may be in need of lubrication. If a hug it has been out of use for a while the cylinder lubrication may have deteriorated. And in some instances the polarity of the supply matters.
The realm of "small 12 volt compressors" covers a huge spread of quality levels, from those with ball bearings and teflon coated pistons at the top end to those with poor sleeve bearings and a wobble-plate for a piston at the bottom end. Those are seldom worth much effort.
In addition, if the 12 volt supply is dropping to ten volts then it is already overloaded, probably not doing the supply any good at all.
So the first advice is to see if some lubrication may improve the operation a bit.

 

Hi all,

Thank you for your replies. I dismentled the compressor, cleaned and lubricated. The current consumption went down to around 5.3A, but at least I am not seeing any voltage drop.

 

Now it will be an education to try using the compressor for something like inflating a tire. Or did you have some other application in mind? The small 12 volt compressors that I have seen are not intended for constant running applications.

 

Not surprising, the better ones I have seen consume 10 ~ 15 amps. Just don't use one in an accessory socket rated for 10 Amps max unless you want to replace automotive fuses. Most do have a fuse in their plug rated for their max current plus overhead.

Ron

 

I don't recall the specs off the top of my head (can't look it up right now), but fuses can hold more than their rated current for a time before blowing. The magic number is 1.6 times the rated current has to trip within a certain amount of time {one second I think). The wiring may or may not hold up depending on what is used. Obviously manufacturers aren't going to build the circuit to constantly push the limits, but a few minutes running a compressor probably won't hurt most of the time

Considering most automotive tires are around 30 : 40 psi and the compressors are usually good to 100 psi or more the chances of hitting the max current is relatively low.

 

Found an old one out in the garage. It's fused for 10 amps.

Ron

 

If you have an underrated power supply, such as one like yours, capable of 5.5A @ 12V, when you try to draw more current than the 5.5A the voltage WILL drop. If you're reading 10V then that and the 5.5A, you're running just about 15.5 amps rating, which should be expected.

Rather than testing a 16 amp DC motor on a 5.5 amp supply, try running it from a car battery. You'll see the voltage remain stable and the compressor will run at full power. Off hand I don't know how many amps those 12V compressors typically draw, so just going off your 16 amp comment, I'd say the 10V is expected.

 

OOPS! Moved to the jokes thread.
Thanks @MaxHeadRoom

 

Someone moved the jokes thread?

 

Hi all,

Thank you for your replies. I dismentled the compressor, cleaned and lubricated. The current consumption went down to around 5.3A, but at least I am not seeing any voltage drop.

What is the nature of the compressor? Often a simple piston type, small DC motor with a reduction GB.
At least that is what my el-cheapo I keep in the trunk is.

 

Once again, what is the intended use? If it is to pump up car tires then the very safe way is to use battery clips and connect it directly to the battery.
BUT the TS may have a different plan to use it for some other purpose, we have no clue.
AND this is certainly not the venue for poor jokes, as in post #11. Very much off topic, as well.

 

Oops. Don't know how I managed that.

One day a boy asks his dad - - - yada yada yada.
Edited out of this thread and moved to the jokes thread.

 

AND this is certainly not the venue for poor jokes, as in post #11. Very much off topic, as well.

Yes, I know. It's being moved to the jokes thread. You can make further commentary on it there. And yes, it certainly was "Off Topic" for this particular thread. It was an unintended mistake.

 

this is • • • not the venue for poor jokes

Sorry - didn't mean to offend the "Taste" police. You don't have to like everything but you also don't need to be critical of everything you disagree with.

And yes, this IS "Off Topic".

If we're talking about those little air compressors that run on 12 volts then it is quite likely being used to either inflate a flat tire or perhaps inflate pool toys. It's EXTREMELY unlikely anyone would ever think to use it for "Professional" work. Since it can take 30 minutes to inflate a small tire from flat to 32 PSI, in theory it would take four hours to pump up a small tank to 125 PSI. And that is IF it could manage to reach that much pressure. Ever. So I don't think we're talking about an industrial use for a pocket compressor.

 

* Voltage: 12V DC
* Max. Amperage: 16A
This compressor was powered from a bench power supply at 12V 5.5A. At this current setting, the compressor is consuming 5.4A (which I an assuming is the max it can provide) and the voltage is dropping to 10V.

I assume it is a small 12v automotive type you plug into the cigar lighter socket?
If so the current will gradually increase as the tire pressure increases, so with nothing connected, it will be a lot lower than max current.
Using the car battery you will not see any voltage drop.

This is mine.

 

Last year used my 12V tire inflator in winter with the engine not running. Then the engine did not start with the almost dead 6 years old battery. I used the power supply from a printer to charge the battery overnight and the battery has been fine ever since.
I never thought that a tire inflator uses so much current. Of course, I will turn on the engine next time.

 

Must have been a very poor battery condition for one of the ones illustrated to flatten it !?