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DC Motor surge voltage circuit

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windozeuser

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I am fixing a robot and we are using a 12 volt air compressor (off of one of those car tire inflator things that plug into the cigarette lighter).

The compressor runs fine to build up the tank pressure when first turned on, then when operating the pneumatics, if the pressure is > 30PSI the motor WILL NOT spin, it exhibs a current of 12 amps, and does not rotate. The normal current rating for the motor is around 9 amps operating.

Is there a circuit I can build like with a capacitor maybe to increase the voltage to the motor to get it spinning under the load?


Or does anybody have any suggestions?

I was thinking of actually oscillating the voltage like with PWM, or making a voltage doubler? But wouldn't that cut the current too much? It can't go below 9 amps


Thanks!
 
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The usual way is to put a check valve at the input of the tank, and then use a solenoid valve to release the pressure in the line between the compressor and the check valve. That is like starting against a zero tank pressure, every time.
 
It's no more complicated than valuing the power supply for an electronics device, the simple answer is you can't do what you want with what you have.

Those kinds of compressors weren't meant for continuous use, you're trying to operate the device way outside of it's design paramaters. The motors stops at that pressure because that's the ultimate limit of the mechanical system at the motors given voltage. Increase the voltage and the pressure will go a bit higher and the motor will heat up and destroy itself, even if you don't increase the voltage the motor is eventually going to fail from overheating because they weren't designed to be run for any length of time at their max pressure, it's only supposed to fill up a tire and then it's done, and then it's supposed to be let to cool to room temperature before it's used again.

30psi pneumatics are going to be really weak anyways, you should be using a small pancake compressor from a home improvement store or try to pick one up used locally, they're not expensive and will easily handle 60-120psi of pressure generation, but you have to worry about how much volume you're going to need as well, that's a completely separate issue.
 
It's no more complicated than valuing the power supply for an electronics device, the simple answer is you can't do what you want with what you have.

Those kinds of compressors weren't meant for continuous use, you're trying to operate the device way outside of it's design paramaters. The motors stops at that pressure because that's the ultimate limit of the mechanical system at the motors given voltage. Increase the voltage and the pressure will go a bit higher and the motor will heat up and destroy itself, even if you don't increase the voltage the motor is eventually going to fail from overheating because they weren't designed to be run for any length of time at their max pressure, it's only supposed to fill up a tire and then it's done, and then it's supposed to be let to cool to room temperature before it's used again.

30psi pneumatics are going to be really weak anyways, you should be using a small pancake compressor from a home improvement store or try to pick one up used locally, they're not expensive and will easily handle 60-120psi of pressure generation, but you have to worry about how much volume you're going to need as well, that's a completely separate issue.


Yeah we're running the pneumatics at around 100 PSI but this compressor is not meant to go much over 30PSI for any substantial period. The robot is fairly small and the compressor you are talking about will be too big for the design. Would the solenoid idea as described by MikeMl be a good solution?

The compressor keeps the tank at 100PSI and just turns on and off keeping it at least above 85PSI at all times
 
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windozeuser did not specify what psi he was running his system at. He only said that he could not start the compressor when it was above 30 psi.

MikeMl's advice was right on the money. The setup he describes is called a bleed or bleeder valve. They are a good idea on any compressor system.

The little 12V does not deliver a lot of air and it may not last long. But it may work for you if you are not using too much air.


Have fun.

EDIT/PS:
Maybe fill the air tank from an external compressor prior to starting and just use the little guy to top off. It will prolong the life of the compressor and get you going faster. If you can forget the compressor and just run off the tank.
 
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Windowze, you're contradiction yourself.
The compressor keeps the tank at 100PSI and just turns on and off keeping it at least above 85PSI at all times

You said the compressor you're using will stall at 30PSI. This means that what you're doing is physically impossible. From what you've described so far the only way to achieve what you want is to run a hose from a 100PSI system to the robot, or you''d have to use C02 (900psi) through a regulator. There is absolutely no way you can do this electrically unless you want to completely gut the pneumatics.
 
What Mike is suggesting will not prevent the actual stall from occurring and will not increase the possible air pressure over your current setup over any usable value. To even use his suggestion your compressor needs to operate on a cycle, the type of compressor you described in your initial post will run until the motor burns out, and you won't get anything more practically out of it.
 
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What Mike is suggesting will not prevent the actual stall from occurring and will not increase the possible air pressure over your current setup over any usable value. To even use his suggestion your compressor needs to operate on a cycle, the type of compressor you described in your initial post will run until the motor burns out, and you won't get anything more practically out of it.
That's not necessarily correct. The op stated that once the compressor is running it will build up the pressure (I would assume to 100psi or so which is what those small compressors will do). The problem is that it will not start under a pressure load. That's a problem with all air compressors and why they use a relief valve as Mike stated, so the compressor starts with no load. The same scheme should also work with this small compressor.
 
The system will need to build a pressure up to at least 95 PSI, there is a pressure switch that will turn the compressor off. However, the relief valve idea sounds promising, how would this work though

The tank will be empty at startup, and the compressor runs fine and builds the tank pressure up. I use the pneumatics, and the tank pressure drops, if the tank pressure is still over 30PSI the motor will not turn on.

It doesn't make sense to dump the entire tank's pressure to reuse the tank pressure, the pneumatics aren't used all the time, it's a Low-rider robot, and the pneumatics are used to raise or lower the suspension.
 
Ahh, I see now, you said that it would work fine when it first started by wouldn't spin above 30 psi, I thought that you meant that it was stalling above 30psi, it going up to 100PSI for a single cycle wasn't mentioned and I wasn't aware that compressors typically did that, does make sense though, explains the slight hiss I've always noticed on industrial compressors I've worked around when they turn off, it's the feed line being bled off.

You could try using a large capacitor to buffer the incoming power, but a practical capacitor for that application might be too large physically, try a few of the largest electrolytics you have floating around and see where that gets you.

It's not being suggested that you dump the whole tank, only a feedline going to the tank that has a check valve on it so that the pressure vessle doesn't discharge. Basically when the compressor turns off a valve would open on the feedline somewhere to dump the air in that first portion of the line going to the actual tank, the checkvalve would keep the tank for emptying as well. Then when the compressor starts back up again that feedline is at 0psi and the motor has some time to gain some momentum before the pressure builds to overcome the check valve and fill the tank again.
 
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