Member Avatar for vett93

I just bought a new Dell Dimension E521 and want to replace its case fan with a quiet fan. It is a 120mm fan that blows from the front of the case, over the CPU heat sink, and ehausts to the rear.

The fan uses a 5-pin connector to plug in to the mother board. But it only has 4 wires to the fan. The new fan I have in mind only has 3 wires.

Can someone please answer my questions below:

1. What does the 4th wire do? Will I get an alarm if I only use 3 wires to the new fan?
2. Where can I find a 5-pin to 3/4-pin conversion kit?

Thanks.

David

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A short, practical summary and safe fixes that work years later.

Several members already spotted the root: Dell used a proprietary 5‑pin fan header on the Dimension/E521 and similar systems. The easiest, lowest‑risk route is to replace the fan with a direct Dell‑style 5‑pin unit (OEM/compatible 120mm Dell fans are sold by third‑party vendors). If you want a quieter aftermarket fan, there are off‑the‑shelf 5‑pin→4/3‑pin adapter cables that map the important signals so the BIOS still sees a fan. (cwc-group.com)

A reliable DIY method that keeps the motherboard happy (used by many builders) is to preserve the original connector as the RPM source while powering the new fan from the PSU: cut the stock fan cable close to the motor and leave the Dell plug intact; power the quiet 3‑wire fan from Molex/SATA; then connect or splice the original fan’s tach lead back to the Dell header so the board still reads RPM. Verify grounds are common and never drive the tach/PWM pins with 12V. If the replacement fan has a tach lead you can rehouse that wire into the Dell connector instead; if it does not, a salvaged donor tach or a simple pulse generator can be used. The fan tach is typically an open‑collector signal (usually two pulses per revolution), so feed the board pulses rather than full motor voltage. (pcbheaven.com)

Final notes: adapters and donor‑tach hacks avoid BIOS alarms but require care—don’t swap pins blindly, check continuity to the board silkscreen, and test RPM reporting in BIOS before closing the case. If unsure, buy the Dell‑style fan or a validated adapter; miswiring can short the board or damage the fan. (studylib.net)

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Member Avatar for dcc

The third wire on the fan you want to add is for sense, you don't need this for a case fan. Just connect the fan to a molex connector and let it run at speed.

Member Avatar for vett93

Thanks for the response. However, this case fan blows over the CPU heat sink and graphic card heat sink. The only other fan in the computer is the one in the PSU.

Additionally, if I don't plug the fan to the motherboard, there will be an alarm. The Dell BIOS does not allow you to disable it either.

Any other ideas? Thanks.

David

Member Avatar for dcc

This is another example of Dell being proprietorial. I'm sure that there is some way to shunt those pins on the motherboard, but I have no ideas how. The only thing that I can suggest is to google around to see if there is an adapter.

Member Avatar for waltereo

Hi

I have the same problem too. I want to replace the fan but the 5 pin connector is not common. I plan to install the Nexus 120mm fan (model D12SL-12).

Did you find a solution to your problem ?

Thanks for help !

I just bought a new Dell Dimension E521 and want to replace its case fan with a quiet fan. It is a 120mm fan that blows from the front of the case, over the CPU heat sink, and ehausts to the rear.

The fan uses a 5-pin connector to plug in to the mother board. But it only has 4 wires to the fan. The new fan I have in mind only has 3 wires.

Can someone please answer my questions below:

1. What does the 4th wire do? Will I get an alarm if I only use 3 wires to the new fan?
2. Where can I find a 5-pin to 3/4-pin conversion kit?

Thanks.

David

Member Avatar for vett93

No, I have not found a solution. I spent hours with Dell tech support and they said that they would get back to me. But I have not heard from them yet.

Member Avatar for Straconis

I'm faced with the same issue currently. The fan I bought has its own thermal sensor and only a 3 wire connector. currently I'm running it straight from the power supply and pressing F1 on boot up to ignore the fan error. Since I haven't been able to find a converter cable for this application I'm thinking about making one from the connector of the stock fan. If I make the custom connector I will post and let you know how well it works.

Member Avatar for jermaghs07

you could leave the original fan plugged in and just move it to a different location then just run a new fan directly from the PSU with the 4pin Molex.

Ideally you need 2 fans anyway. 1 pulling air in the front and one exhausting air out the back.

Member Avatar for jermaghs07

about the different pins.

1- the 3wire conector is just the standard one speed fan one hot wire one neutral and a ground

2- the 4wire connector can either be a multi-speed fan or it can have a thermometer on it.

3- The 5pin is juat another stupid way that dell can stop people from using non-Dell parts. therefore if a fan goes out you have to spend $20 to get a fan from dell instead of spending $4 to get a cheaper fan.

hope that helps

Member Avatar for 4th&3wood

about the different pins.

1- the 3wire conector is just the standard one speed fan one hot wire one neutral and a ground

2- the 4wire connector can either be a multi-speed fan or it can have a thermometer on it.

3- The 5pin is juat another stupid way that dell can stop people from using non-Dell parts. therefore if a fan goes out you have to spend $20 to get a fan from dell instead of spending $4 to get a cheaper fan.

hope that helps

The three wire fan has power, ground, and sense.

The four wire fan has power, ground, sense, and PWM control.
(The 4-wire fan has the addition of a Pulse Width Modulation (PWM) input signal for switching the power to the fan via an internal mosfet for controlling the speed of the fan.)

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