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Please, how do I limit a peak DC voltage to 2.45 volts in a car MAP circuit?

Thread starter #41
The expensive part of the puzzle is not the electronics, the expensive part is the labor removing the supercharger from the engine to get to the map sensor.

This is not something I want to "experiment" with via trial and error, if it can be solved properly in these initial stages.

However, if your BZX55B2V4 idea is a viable solution, I hope others can chime in that it will likely work... or it won't work.

That will help me better understand the odds of it working, and perhaps i roll the dice with the BZX55B2V4.

With my limited knowledge on this topic, it seems the only downside to the BZX55B2V4 would be how it affects the signals at idle, when the manifold is in vacuum, and voltage signals from the MAP are very low. If it disturbs those signals, then it is not a viable solution.

Im in east coast USA
 
#42
Yes, entirely understood !

With my limited knowledge on this topic, it seems the only downside to the BZX55B2V4 would be how it affects the signals at idle, when the manifold is in vacuum, and voltage signals from the MAP are very low. If it disturbs those signals, then it is not a viable solution.
I don't know the answer to that, never tried it. But it does concern me that the only invalidating comment we've had about the Zener was based on a 2V5 not a 2V4. The effects of dynamic resistance and temperature coefficients are unknown, although from your previous posts I don't think low temperatures will be an issue.

Is there a way to set up a bench top prototype to test the idea ?

Edit: There is some useful information in the graphed data on the datasheet ..

S
 
Thread starter #43
This is good info you provided. I'm a logical person but ignorant on the topic. So the more you can teach me, the more I can understand and thus roll the dice with your BZX55B2V4 idea.
 
#44
So the more you can teach me, the more I can understand
LOL .. .. I'm amazed that comment has been visible on ETO for 2.1/2 hours and the queue of folk talking about ' .. .. .. the blind leading the uninitiated . .. ' has not yet formed in orderly fashion ! :D

I can't see anything detailed in the graphed info that suggests a problem .. .. … that may be because I can't see .. or maybe because there is so much info about the behaviour of the signal voltage that is not available.

As I understand it .. the Zener will have little or no influence on the signal line until 2.4v(Nom) is present ( possibly 2.45v at Max ) You stated that the critical voltage is between 0.2v & 2v; anything above that is inconsequential .. .. .. that being the case, it should do the job nicely.

I do think that adding an additional 12v supply, which may be very noisy, into the equation may cause other problems.

S
 
Thread starter #45
So, I am looking into the zener idea further, i found a video that explains the setup for the circuit, and it, like other videos, explains that I need to add a resistor to the circuit.

I am worried that this resistor will drop voltage even when the current is not going through the zener diode, and thus I am worried the resistor will interfere with idle signals of the MAP in vacuum at low voltages.

It seems I need an exactly calibrated resistor for the job. I guess that is the next puzzle I will need help with.

This video uses 2volts as the zener limit, and it is linked below, as well as a screen shot picture supplied as well.

https://www.khanacademy.org/science...regulator-class-12-india-physics-khan-academy

Screen Shot 2018-10-07 at 9.03.42 AM.png
 

crutschow

Well-Known Member
Most Helpful Member
#46
I am worried that this resistor will drop voltage even when the current is not going through the zener diode, and thus I am worried the resistor will interfere with idle signals of the MAP in vacuum at low voltages.
As the green trace in my post #27 simulation shows, the zener circuit will likely affect voltages below 2v, since the zener still conducts a small current at that voltage.

The circuit with the TLV431 should not significantly affect voltages below 2V, since the series resistor is only 250 ohms.
But you'd need to measure the input resistance of the MAP computer to know for sure.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
#47
This http://www.eltekgroup.it/p/pressure-sensor-27 is an AUTOMOTIVE sensor boasts a power supply of:

Operating Voltage (nominal)5.0 ± 0,25 V, so on the surface it looks like a 0-5V output sensor. The notes say The sensor output is ratiometric with the power supply, so it clearly isn't.

It does say:

Output Voltage (Vout)0,5V....4,5 V ratiometric
Digital Standard I2C
Digital Custom OWI

It's also typical to use the rails for diagnostic output:

Diagnostic Functions output goes above 4,75V and/or below 0,3V in case of failure

You could take a MAP sensor on the bench and vary the power input (Nominally 5V) and watch the output. It will be a voltage that is a % of the power supply voltage.
 
Thread starter #48
Again, i agree that is how the map operates... but i do not believe that is how the computer reads. I believe the computer looks for a certain voltage, and once it is met, game over. Error is thrown.
 
Thread starter #49
what is a good website or vendor to purchase a hallow plastic enclosures to store a circuit in, and fill it with epoxy to insulate and solidify the circuit?
 
Thread starter #51
The circuit with the TLV431 should not significantly affect voltages below 2V, since the series resistor is only 250 ohms.
But you'd need to measure the input resistance of the MAP computer to know for sure.
I have been informed by a creditable source that the MAP sensor is 4.4K ohms, and is supplied exactly 5.01 volts, regulated by the stock ecu. Does this sound accurate/logical?

Does this affect the circuit diagram you provided above in post 27?... or would it need updated resistor values again to be viable for this exact application?
 
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KeepItSimpleStupid

Well-Known Member
Most Helpful Member
#52
Here http://www.robietherobot.com/storm/mapsensor.htm (Datasheet too) is a 3-bar GM sensor, possibly similar to or identical to yours.

Note, it is tested at 5.1 V and 25 deg C and Vs is part of the output equation. It also must have a 51k load.

Limits for Vs is 5.1+-0.36V; Vs needs to be isolated an filtered with less than 10 mV of ripple.

This
Delphi / GM 3 Bar Style Map Sensor - 12223861 - 16040749 (US Made)

Due to a decrease in quality of the "Genuine" Delphi 3 bar MAP sensors due to moving production to China and cutting corners in their budget, we are now stocking a USA made GM Style 3 bar MAP sensor. This sensor meets the same calibration data and meets or exceeds all Delphi specifications. In the future, we will continue to stock the Genuine Delphi part (SNSR-03075) as a case quantity only purchase and will be stocking this sensor (SNSR-03074 in our standard price breaks).

from: https://www.bmotorsports.com/shop/product_info.php/products_id/1584
 
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Thread starter #53
See post 11. Not the same sensor at all. It may coincidentally have same identical characteristics as the one I am working with, but I doubt it.
 
Thread starter #55
yes and no... it won't go below 2.5 volts, so it won't limit to 2.3 or 2.4 where i need the limit to exist.

there is also no guarantee that it is exactly calibrated as he shows, it could be that there is a voltage drop through the unit, and he zero'd out the second volt meter to not show this voltage drop. Either way, i will give them a call tomorrow and pick his brain. Thank you for the post
 
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gophert

Active Member
#56
I do not want to scale the voltage signal, i want to trim or clip it... only eliminate anything above 2.45 volts and leave everything below 2.45 volts unchanged and not scaled in any way. I believe the original supply voltage is 5 volts, if that matters.
crutschow But the lower end is also clipped in your circuit (min output at 1.7v).
Is that a glitch in the simulation or did I miss something 8n the explanation in another post?

1BFFF344-8FE2-4E5B-96B9-3BE15376797F.jpeg
 
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crutschow

Well-Known Member
Most Helpful Member
#58
@crutschow But the lower end is also clipped in your circuit (min output at 1.7v).
Is that a glitch in the simulation or did I miss something 8n the explanation in another post?
Nope. Good catch.
I missed that when looking at the simulation. :arghh:
So the right-hand circuit in post # 27 would be better (and simpler).
 

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