I have been attempting to figure out what to use as a sensor for my HHO cell control circuit. I recently thought about using a sensor from a car to act as my fluid level sensor. I have to be able to figure what is the upper output level for when the electrolyte is touching the sensor and the lower output level is when the electrolyte is not touching the sensor. I know there are a LOT of different sensors on a car, but which one do you guys think will fit the role as my fluid level sensor for my cell. right now i have only a simple switch setup in the program for the microcontroller, but I will change it to fit when I get some more info on the sensor i need to utilize. Thanks a lot.
A float switch with an IR infrared photoptical sensor is probably best for clear liquids.
There is also a possibility of an acoustic reasonant column sensor - but it is
a lot more work to do.
:S:MarkSCoffman
Regarding your inquiry.....
I have experience in both conductivity based liquid level sensors and also mechanical. I would strongly recommend a mechanical based float switch. Such unit should employ internal magnetic reed switch design. I would further recommend an overall switch that had 2 stages (2 individal magnetic reed floats at heights you determine). Here is the reasoning, a single switch will end up fluttering on and off in an attempt to retain a precise water level. I am presuming you are using a water solenoid in this system so this would also flutter on and off. Not good for life expectancy of the presumed water solenoid.
By using a 2 stage approach, solenoid opens when lower float switch activated , solenoid closes when upper float switch activated, thus reducing number of cycles on solenoid over time.
http://www.fluidswitch.com/pages/fh0708.htm
I have personal experience with this very switch and highly recommend it. They are reliable and inexpensive. More importantly I believe they will do what you want them to do.
Cheers!
, MW383
Quote from: MW383 on November 03, 2009, 12:51:25 PM
I have personal experience with this very switch and highly recommend it. They are reliable and inexpensive. More importantly I believe they will do what you want them to do.
Cheers!
, MW383
Agreed! The float portion can be inexpensively filled with unsinkable plastic foam rather
than leakable gas. You may need to consider fluid baffles if in a large free standing tank
subject to physical motion.
:S:MarkSCoffman
Float type switches probably wouldn't work as well in the tightly cramped space of a HHO cell. I should have made it clear when I first posted. I only want just a little section of the sensor to actually be within the cell. I know modifications will have to be made to the sensor for it to work like I want it.
Quote from: Draco Rylos on November 03, 2009, 01:23:24 PM
Float type switches probably wouldn't work as well in the tightly cramped space of a HHO cell. I should have made it clear when I first posted. I only want just a little section of the sensor to actually be within the cell. I know modifications will have to be made to the sensor for it to work like I want it.
OK, staying with float concept for now, only build your own.... Mount 2 magnetic reed switches on outer surface of your vessel at desired heights. In this case the vessel would have to be a non-magnetic material. Within the vessel itself have a small diameter vertical rod. Attached to the rod are small floats that have a very small and light weight permanent magnet mounted to them. Magnet size tuned to activate reed switch on outside of vessel. This could be made quite small in size. I still recommend trying to get this stye of switch to work. This home made one would also eliminate the need for sealed bulkhead fittings (like in purchased item I posted a picture of).
You can brave into contuinity based switching. In this case you literally have 2 automotive style spark plugs. They are mounted externally having the electrodes positioned to be in contact with your liquid. Thus only a very little bit of interior tank real estate is consumed. You get back into hacing the need for bulkhead sealing though. Word of warning on continuity based scheme, be prepared for erratic behavior and probably more so in your hydrogen generating environment. No-switching when it should be and Switching when it shouldn't be. I have used these before too and have totally abandoned them due to poor reliability. I really cannot reccommend doing this with a good conscience.
Best of luck,
MW383
That sounds pretty interesting. I was planning on using a Sched 40 PVC pipe for the cell, so that would be non-conductive. You would have to go through the body of the cell to mount the floats on small rods that would support the floats. I would need 2 because one would be the upper limit and the second would be my lower limit. Where is the best place to put the lower sensor that would not have the risk of a random spark which would cause ignition of the generated hydrogen in the cell?
I've posted my source code at pastebin here pastebin - HHO Control Circuit Control Prog - post number 1644595 (http://pastebin.ca/1644595)
Quote from: Draco Rylos on November 03, 2009, 02:35:23 PM
Where is the best place to put the lower sensor that would not have the risk of a random spark which would cause ignition of the generated hydrogen in the cell?
Since all electrical switching done on exterior of your vessel, random sparking not an issue. All you are doing inside the vessel is floating a couple of magnets so this in itself will not do anything.
Magnetic reed switches I am familiar with are small in nature (if bare switches). They remind me of the small style lights one would put on a Christmas tree. Basically it is just two contacts inside a small glass bulb, with small wire leads coming out the end. One contact does not move, other does. One that does, moves via magnetic field being applied to its vicinity which is your case the magnet on the other side of the PVC container.
Note, magnetic reed switches typically not rated for high currents. So you may have to use the reed switch to fire coil on a relay, and have the relay switching contacts do actual switching of heavier loads. (I'm not sure of your full setup yet)
Hope this helps,
MW383
What I meant when I said random spark is, that occasionally something may occur within the cell which could cause a small arc between the plates of the cell. Something like a piece of metallic debris that may enter the cell at any time but remain suspended until something happens like the fluid level going down to a level where the debris may cause a reduced gap between the plates causing an arc to occur. With the various voltages and amperages that are utilized in a HHO cell, a spark may occur if that does happen causing possible failure of the cell body and damage to the vehicle if the explosion is large enough.
I'm no hydrogen fuel cell expert but do know their principals. Regarding floating debris, could this scenerio be prevented by using a battery grade polypropylene seperator paper wrapped around your metallic plates? (assuming you are using 304 or 316L stainless) Such paper should not interfere with anything nor prevent H gas from exiting as it is a pourous material. The theory here is to prevent possible floating debris scenerio.
As far as arcing, I am in the dark. I am assuming plate to plate distances are being minimized in order to get more plates into the system, thus more H gas generated. I would also venture to guess that smaller distance between plates increases chances of arcing if said plates were not submerged in water. Again all guesses on my part as I have no practical experience with these devices.
As MW383 says, continuity based sensors can be a bit temperamental. But as you are reading the sensor with a microcontroller I would advise going with continuity sensor just because its solid state and reliable and the micro can filter out glitches using the scheme below:
I havent built HHO system with micro but I´ve done various other work in industrial systems.
You can use small stainless fasteners through the side wall of your tank with synthetic washers. Place fasteners quite a few cm apart at fluid full level through the tank side. In sticky fluids you have to go on opposite sides of the tank.
I always read the voltage using an ADC pin if I have one available because you can tweak the HI and LO thresholds in software.
In the micro read the sensor pin once a second. If you see the pin change state HI to LO and then it holds the new state for 20 more seconds without interruption then treat it as a drop in fluid level and run the 12V pump.
Some systems use two level sensors, lower one to trigger pump start and higher one to stop the pump, but I always use one sensor and when I see a 20 sec state change I just power the pump for a preset number of seconds and then stop it.
My HHO cell idea didn't start off using a uC, but it evolved into using a PIC. I'm using a PIC16F690 as the heart and brains of my switching system. I've got the logic down pretty simple
(Operation)
Upper (RA1) + Lower Sensor (RA2) = 1 Then Operation (RB6) = 1; Warn (RB5) = 0; Refill (RB3, RB4) = 0
Upper Sensor = 0 + Lower Sensor = 1 Then Operation = 1; Warn = 1; Refill = 0
(Refilling)
Upper + Lower Sensor = 0 Then Operation = 0; Warn = Flashing; Refill = 1
If Lower Sensor = 1 + Upper Sensor = 0 Then Operation = 0, Warn = Flashing, Refill = 1
If Upper + Lower Sensor = 1 Then Operation = 1; Warn = 0; Refill = 0
(End Refilling)
But I've changed how the system is set up, by swapping out the LEDs that were represented in this logic diagram with a 2x20 LCD. Port C is my LCD output, Port B is my General Outputs, and Port A are my inputs, with RA0 being my ADC port with the preset, and RA1 is the upper sensor and RA2 is my lower sensor. I have the rest of my pins pulled to ground with 10K resistors, except for my clock inputs.
cool, are you going to do PWM with the PIC too?
No, I'm going to use ZeroFossilFuel's current limiting Pulse Width Modulator. The Power on/off will be controlled by my control circuit along with the refill valve and the pump on/off switching.
That´ll work well. Have fun and good luck with it.
here's my circuit as it stands
http://yfrog.com/0hcontrolp