Computer Fan For The Volvo Topic is solved

Oka · Post by **Oka** » 06 Apr 2022, 18:23

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Hello folks, I have an electrical question.

I need to use this fan from my old computer, in the Volvo, over the CEM module. All the fans I removed from the old PCs says 12VDC or DC 12V.

1. If the fan is ran by AC in the PC, why does it have a "12VDC" on the label?
2. Almost all the fans I have, has three wires (Red, Black and Yellow). For the car, I need to run one wire to the ground and the other to a fuse (Accessory/Ignition controlled). With the three wires, what should I do?

Thanks

Oka · Post by **Oka** » 06 Apr 2022, 21:54

https://www.swedespeed.com/threads/comp ... st-7931410

Post by **matthew1** » 06 Apr 2022, 21:56

The third wire is probably certainly a variable speed input.

Post by **abscate** » 07 Apr 2022, 09:11

Because the first thing the AC hits in a PC is a power module making regulated 5 and 12 V DC

EngineeringBloke · Post by **EngineeringBloke** » 12 Apr 2022, 12:54

As reported in a comment in the link to the other forum, the third wire is used to report RPM fan speed.

A PC power supply provides multiple different DC voltages. Case and other fans run on 12 volts DC. Modern PCs will reduce the supply voltage to allow the fans to run at lower speeds when reduced cooling is needed. Ends up being quieter and more energy efficient.

Just connect the red wire on your fan to 12 volts and the black to ground. Use a 12 volts connection that is switched off when the car is turned off, or you will drain the battery.

Some fans are 4 wire and these add a pulse width modulation input to the fan to directly control the speed.

02V70 · Post by **02V70** » 15 Apr 2022, 13:05

Cant, you just do Pulse Width modulation with the red/power wire?

Post by **BlackBart** » 15 Apr 2022, 13:59

Fan...?

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Post by **gnalan** » 15 Apr 2022, 21:24

Why do you need to add a fan to your CEM?

Post by **volvolugnut** » 16 Apr 2022, 08:31

There are a few reports of Volvos (early P2?) with over heating main computers under the dash. A solution is to add a fan or direct A/C flow at the CEM computer.
Search for more info.
volvolugnut

Post by **matthew1** » 16 Apr 2022, 17:44

https://www.matthewsvolvosite.com/decre ... ilure-fan/

That points to discussion in the forum.