How to control a DC motor with pressure? 1

[AMouser]

Hi guys, Im new to the forum. The lay out of this board is new to me so I apologize in advance for not performing a search and introducing myself in the proper forum. I'm a Journeyman Electrician of 5 years and a sophomore in college majoring in Electrical Engineering. That about sums up me. On to my question.

I am currently working with local race shop to develop an independent oiling system, with a broad application, that is capable of maintaining a static 35-45 psi. This is the pump they have selected:

http://www.rbracing-rsr.com/partnumbers.htm#oilscavenge

it is located at the bottom of the page, the "standard" size. It is a 12v dc brush motor driving a gear pump. We did a test today and the pressure was way too high. With a 10w-30 oil at 75 degrees F, the pressure was roughly 95 psi. At 220 degrees, the pressure dropped to around 50 psi. We want to hold around 35-45 psi and planned on doing so using a user controlled pulse width modulator. Could we use some type of pressure to voltage transducer to control the pulse width modulator? Or is there a controller that could do all of this for us? Preferably this would all be analog and of course, the cheaper the better. Reliability is the important part though.

Thanks in advance for all of the help.

 

[OperaHouse]

A simple mechanical switch would be cheap set to the pressure. Actual pressure sensors can be expensive. Since this is a low voltage set up I would suggest something like an ARDUINO UNO board and a FET to control the motor. You can buy versions of this board for as little as $15. This board will do PWM. Use a program something like this.

Start notor at nominal speed
Slow motor to some minimal speed
Count time till pressure drops and switch opens
If over a certain time increase PWM / motor speed or drop if over

A fluid accumu;ator would help. There are tons of features you could add. The development system is free and you can get started for less than $20. Time to learn some software development before the world passes you by. Too bad an automotive oil switch is only about & psi. At some point you could move to your own board.

 

[waross]

Most factory engines use a relief valve to limit the variable oil pressure from the pump to a fairly constant value. If your engine has a relief valve, measure the pressure on the downstream side. This may be a non-issue.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[AMouser]

This system is an independent oiling system for a turbo charger. It is comprised of a tank that gravity feeds a pump, the oil is pumped through a filter and up to the turbo, then gravity drains the oil to the tank.

OperaHouse, thanks for the input, the Arduino is basically plc with pwn capabilities? The pressure switch you are referencing, are you suggesting that be the minimal pressure desired, 35psi? Are the channels on the board robust enough to handle the current this motor will draw? What is the FET used for? Sorry for the rookie questions, I really havent been exposed to this stuff in college yet. I'm only going off of the knowledge gained through the electronics and controls classes I had to take as an electrical apprentice. I have had a few quarters of c++ programming though at school. I appreciate the patience.

 

[waross]

It is hard to beat the robustness of a simple switch and a pressure relief valve. Every fancy augmentation adds possible failure modes.
If you want to impress your friends you may try calling the relief valve a "Hydraulic-mechanical proportional controller with an ultra narrow, tamper proof, proportional band".

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[OperaHouse]

The Arduino UNO has 12 digital in or outs. Three of them are capable of PWM. With this output one or two FET in parallel can give enough current. I think one of the PWM has a frwquency of 460hz which would be good for a motor. There are 6 analog inputs so you could have an adjustment pot and a real pressure transducer if you wanted. Programs with USB printer cable to your laptop so very portable. That cable can feed serial data out to a convenient data monitor screen in the dev system. High and low limits on the PWM could be programmed in to signal leaks or blockages, higher pressures on startup to make sure everything is lubed, temperature monitors on oil for warnings or to increase flow rate. Lots of possibilities. Think of this as a chance to increase features. Drive the market, don't be a follower. The 2011 version can be had on ebay for less than $20. It is a type of C. Most functions you would ar already there. Most programs actually end up under two dozen lines.

 

[AMouser]

Thanks for the help guys!The shop I'm working with is in favor of the valve, simply for reliability, this time around. However, I would like to build this controller for myself and possibly use it later.

OperaHouse, your saying that the FET's would be hooked up to the output of the Arduino, correct?

 

[OperaHouse]

The chip is 5V so you need a FET that will turn on hard with 5V. Many FET require double that. Search around for typical design configurations. You will need a gate drive resistor and high speed diode accross the motor.

If you don’t do this by yourself, you will never know if you are any good. And you will never be any good if you don’t know you are.

Bill Murray, Get Low

 

[AMouser]

waross, is there a specific valve I should search for?

 

[AMouser]

I looked for 3 hours tonight and I couldnt find anything that looked promising in the way of valves. The valves that meet the specs of the operating temp, dont meet the pressure specs. They seem to be way too high. I need a 3 port valve that operates up to 220F, maintains around 40psi, and has threaded connections.

 

[burnt2x]

Did you get yourself a sample valve (though higher relief pressure rating) and tinker with its spring? I did have a problem (opposite that of your problem; I needed a higher pressure relief setting and what i got was just low) and just did some shimming on the spring bore!
Sorry for the off-thread answer here!