Question regarding 5V vs. 12V sensors

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jars121
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Joined: Mon Mar 06, 2017 9:22 am

Question regarding 5V vs. 12V sensors

Postby jars121 » Thu Mar 08, 2018 7:51 am

Morning all,

More of a generic automotive sensor question than a Haltech-specific one. Are there any aftermarket sensors which are typically pulled up to 12V rather than 5V? Having spoken to Haltech engineers via email regarding a MAP sensor I installed, they mentioned that all the Haltech sensor specification sheets are based on a 1kOhm pullup to 5V. This has me wondering if there are any sensors which are designed for 0-12V output rather than 0-5V. Even 12V powered sensor units (like a wideband controller) output a 0-5V signal, so I can't think of a 0-12V example.

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HaltechMatthew
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Re: Question regarding 5V vs. 12V sensors

Postby HaltechMatthew » Tue Mar 13, 2018 1:30 pm

The pullup reference is for resistive sensors (temperature 2-pin) which are not powered. They need a 5V reference to generate a 0-5V signal that the ECU can use so they have the pullup. Powered sensors like a MAP sensor do not use a pullup because they are generating the 0-5V signal.

5V is used in automotive applications because it is regulated to that voltage and not influenced by external loading. If they used 12V for sensors the voltage reference would not be accurate when you cranked the engine and voltage is down around 8 to 9V, and also not accurate when the alternator is charging the system at 14V+. Some sensors like crank or cam Hall sensors take a 12V power in but only send out a 5V signal.

This also goes hand in hand with your ECU requiring around 6.0V or more system voltage. Much lower than this and it becomes difficult to regulate the 5V accurately and consistently.

jars121
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Joined: Mon Mar 06, 2017 9:22 am

Re: Question regarding 5V vs. 12V sensors

Postby jars121 » Thu Mar 15, 2018 6:20 am

That makes perfect sense, thanks Matthew :)


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