Maker Pro
Maker Pro

Opening Curcuit via MicroController

Hu_Chai

Nov 16, 2023
3
Joined
Nov 16, 2023
Messages
3
Hey everyone!

I am getting into electronics just now. i think i have a basic understanding of how things work and coding is also not a problem for me.

My plan is, to open the curcuit of the fuel injectors for a given interval (pulses)

I have looked around a bit and also asked ChatGPT and generally speaking, the common answer was a Relay.
What i couldnt find tho, is how fast are Relays? Since its a Vehicle, it runs on 11-14.4 V (DC), there is an Injector Relay already in the Vehicle, which is Fused with 30A.

If a Relay is the way to go, i would use a normally closed Relay and only open it whenever the MicroController tells it to. The Curcuit should be opened as fast as possible and the pulse duration should be between 10 and 200ms (stays open for this long) and pulse interval somewhere between 50-200ms (stays closed for this long).

Is this possible with a Relay?
Could you maybe suggest a Relay for this application? I have found this https://www.12voltplanet.co.uk/mini-break-make-relay-normally-closed-nc-contacts-12v-20a.html
Is there a better alternative?

I appriciate any help :)
 

Bluejets

Oct 5, 2014
6,852
Joined
Oct 5, 2014
Messages
6,852
No, relay is not a good idea.
Use a mosfet of suitable current rating plus some for leeway.

When used with uC , you cannot get a much simpler interface between the uC voltages (usually 3.3 or 5v depending on which you use) and the vehicle voltage normally of anywhere between 11.5 and 14.5v.

All it needs (on an N-channel......switching from positive rail, through the load, through the mosfet to ground) is say a 100R resistor series on the Gate, and say a 10k from Gate to Source (ground) to make sure the mosfet doesn't go firing when it isn't supposed to due to any stray voltages or noise.

Must use a logic level mosfet though, others will not work.
Plenty of details on the web on how to use and if you go for some of the Arduino or other elaborate supported uC, guys at Arduino forum are really knowledgable and helpful.

Just double check your English and punctuation though as it will catch you out in the coding.
Why..??? because "circuit" is wrong above.
 

Harald Kapp

Moderator
Moderator
Nov 17, 2011
13,632
Joined
Nov 17, 2011
Messages
13,632
pulse duration should be between 10 and 200ms (stays open for this long) and pulse interval somewhere between 50-200ms
Possible with a relay: Yes.
Meaningful: No (as stated by @Bluejets).

Why?
  1. Operating time of a relay is on the order of milliseconds, e.g. 10 ms. This is your stated minimum pulse time, therefore the delay of the relay would be very noticeable and would heavily influence the performance of your circuit.
  2. A relay can handle only a limited number of switching operations. Endurance is typically on the order of 106 switching actions (some relays last longer, some perform even worse). 106 switching actions at an interval of 200 ms result in 200 000 seconds of lifetime, i.e. 3333 minutes or 55 hours or 2 1/2 days only.

This is the reason @Bluejets recommends using a MOSFET.
 

Hu_Chai

Nov 16, 2023
3
Joined
Nov 16, 2023
Messages
3
No, relay is not a good idea.
Use a mosfet of suitable current rating plus some for leeway.

Just double check your English and punctuation though as it will catch you out in the coding.
Why..??? because "circuit" is wrong above.

I am sorry for my English, i am not a native English speaker.
Coding isnt a problem for me, i do it as a fulltime job :p

Possible with a relay: Yes.
Meaningful: No (as stated by @Bluejets).

Why?
  1. Operating time of a relay is on the order of milliseconds, e.g. 10 ms. This is your stated minimum pulse time, therefore the delay of the relay would be very noticeable and would heavily influence the performance of your circuit.
  2. A relay can handle only a limited number of switching operations. Endurance is typically on the order of 106 switching actions (some relays last longer, some perform even worse). 106 switching actions at an interval of 200 ms result in 200 000 seconds of lifetime, i.e. 3333 minutes or 55 hours or 2 1/2 days only.

This is the reason @Bluejets recommends using a MOSFET.


Could you please provide me with an example for a MOSFET that would be somewhat applicable for this Project? I am seeing alot of different Versions online and i am not entirely sure which one does what. Just to point me in the right direction
 

Harald Kapp

Moderator
Moderator
Nov 17, 2011
13,632
Joined
Nov 17, 2011
Messages
13,632
Could you please provide me with an example for a MOSFET that would be somewhat applicable for this Project?
Select e.g. from this page.
The main filter criteria were:
Vds >= 20 V
Vgsth <= 3 V (so it can be driven by a logic level e.g. from a microcontroller)
Ids >= 30 A
 

AnalogKid

Jun 10, 2015
2,860
Joined
Jun 10, 2015
Messages
2,860
Please be more clear with your use of the terms "open" and "closed". In electronics, an open circuit is when a switch is in the OFF position, and a closed circuit or switch is when the switch is in the ON position. This probably is different from the way automotive people describe fuel injectors, and makes post #1 confusing.

I'm not a car guy, but I think when the electrical circuit is closed (ON), the fuel injector port is open (spraying). yes / no - ?

ak
 

Bluejets

Oct 5, 2014
6,852
Joined
Oct 5, 2014
Messages
6,852
Coding isnt a problem for me, i do it as a fulltime job :p
Maybe, but the statement remains.
Make spelling or punctuation errors and you'll be chasing your tail.
Not difficult to do a spell check these days .....you might just learn something new.
 
Top