50 amp dc output problems

jr2233

Hi, I need to connect a fuel injector harness (5 volt pulses) to the input of a basic stamp directly or thru a motormindB chip.· The stamp would read the injector pulses, devide these pulses by 0-100 (adjustable) and then turn on or off a 50 amp 12 volt DC device (at idle the output would be off, any speed over idle the output would be on).· I am just giving you the overal picture.· Is there anyone here who can help me or guide me thru this?· I have been receiving Nots&Volts from 1990 until I moved in 2001.·thanks ...jr··

jr2233

I should mention that there will be 2 additional inputs and one additional output) into the basic stamp 1) the oxygen sensor data will go into the stamp, the data gets modified by a multiplication factor then that new data is outputted to the engine. 2) a basic temperature sensor shuts down the system if temp reaches above 200 degrees. thanks again everyone.

stamptrol

In terms of inputs and outputs, the stamp has lots of capabilty to do what you want. BUT, without knowing how fast all of these things have to interact, we're going to need a bit more information about the overall project.

If you're expecting real time control of some engine functions, the stamp may not be fast enough.

If its just being used to see some setpoint and turn on a relay for the 50A device, you'll probably be OK.

Cheers,

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Tom Sisk

http://www.siskconsult.com
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jr2233

Thanks for the quick reply Tom. I need a simple "OFF" state at the output when the engine is running at idle and an "ON" state once the engine starts to speed up (about 1,000 rpm's) an adjustable on board threshold would be nice with an led showing the onn/off state .The output must be able to handle 50 amps at 12 volts max (the load will be more like 30 amps, we wish a bit more headroom here). I don't know what kind of data is coming from the oxygen sensor, I will try and find this out. I don't think processor speed should be a problem. thanks again for your response...jr

Beau Schwabe

jr2233,

The 30Amps wouldn't be to turn On/Off an electric cooling fan by chance would it?· If so, you could go with a mechanical relay but watch out for contact arching especially if you are driving an inductive load·... or you could use a Solid State relay.· Our Jeep uses a PWM relay, that allows the BCM (Body Control Module) to adjust the fan speed based on various inputs as you mentioned.· You can buy a PWM relay from a dealer for about $60 ... or do a little shopping and find one for around $10.· Because of the nature of this application I would probably not want to roll my own.... just bite the bullet·and purchase something with a bit of a track record to control your 50 Amp load.· Reading your sensors and providing a signal to your relay with a BS2 would be fine.

·

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 6/5/2008 8:51:03 PM GMT

jr2233

Thanks Beau, I am driving a water cell not a fan. This water cell requires around 30 amps but sometimes raises to 35 amps when the water gets to around 180 degrees. That is why a nice feature would be to turn the output off whenever the water in the cell reaches around 190 degrees. A PWM circuit would be nice for the output side this way I could adjust and provide the cell with whatever maximum output I wanted. Frequency is also on my wish list. A perfect frequency of around 10K hz is ideal for the cell. Do you know of someone not so expensive who could draw us up such a circuit as a starting point? A back yard type guru who knows the BS2. Someone recommended I use a smart FET, I don't know how to draw up the circuit, but once drawn, I could place it on a breadboard and fine tune it. thanks....jr

Beau Schwabe

jr2233,

Not familiar with a water cell, unless your generating Hydrogen and Oxygen via electrolysis.... In that case I would use a mosfet from International Rectifier that has the right characteristics. You can still PWM the transistor to vary the effective output. An out-of-control water cell seems a little less threatening than a cooling fan.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 6/6/2008 12:55:22 AM GMT

Bobb Fwed

Question: is that 10kHz AC or DC? And I don't see why a MOSFET wouldn't work for your application.

jr2233

Thanks bob
10Khz DC ir correct.· As for the mosfet, you mean placing it at the output of the stamp?· could you draw up the output part of the circuit so I can try it out on the breadboard.· There are some inputs needed as well.· As I understand it, there are 3 types of oxcygen sensors out there. Type A produces a 100-200mV for a lean mixture, a 650-900 mV for a rich mixture with 450 being the norm.
Type B produces a linear output from 0-5 V.· Type 3 uses a resistance, with rich fuel indicated by a low resistance and a lean mix showing up as a high resistance.· Resistance change is 1000 times between rich and lean.· Since I want to build this circuit for anyone of the sensors, I must have 3 imputs on the stamp for all three even though I will only use one of them.· I would like to be able to lower or raise the data perhaps by an adjustable percentage factor. If the data for a type 1 sensor is indicating 450 mV (normal) then I would like to adjust that to a·higher number perhaps 650 mV so the Vehicles cpu would then reduce the amount of pulses of fuel to the injectors.· Is this something the BS2 can do? thanks again.

DJSandberg

JR,

Trying to make this a universal fit for many cars will be difficult because they all use different types of sensors. Even making a product for one manufacturer would be difficult. You might have to make several different base electronic units.

The throttle positioner sensor will tell you if the vehicle is idling or if the throttle is depressed and by how much. Some are digital and some are analog, depending on year or model. Injector pulse will tell you how much fuel is being used but it's relative to vehicle type, load, fuel pressure and probably a few more variables. A crankshaft sensor will tell you the engine RPMs. The vehicle already has a temp sensor, and it will usually be analog ~0-5Volts.

Daryl

jr2233

Thanks Daryl,

I thought of taping into the injector only because most cars now have them. But as long as the BS2 knows when the engine is off, when it is at idle and when it is above idle, that is what I need. Only above idle would I want the PCM to turn on the mosfet. Now for the injectors, there are others that offer some type of an electronic device that connects to the engine (a universal device for all cars) that tricks the vehycle's cpu into lowering the amount of fuel. I am not sure how that circuit works nor where it connects. I wanted to incorporate everything into one board to simplify the install. I will try and get hold of one of them to study. As for temperature monitoring, I need to monitore the water cell temp so that if it reaches a too high temp, the PWM would either lower the current or turn the cell off. Once temp went back to normal, the system would go back to an on state. I would like to add here that the cell runs much better at higher voltages with less amps. I have tested 12, and 24 to 36 volts DC at 10K Hz and got best results at the higher numbers. Water temp also stayed cooler with higher volts and less amps. Thanks for helping...jr