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The Dakota Digital PAC-2800BT

Dakota Digital PAC-2800BT Cooling Fan Controller

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This blog post is going to show you how to use the Dakota Digital PAC-2800BT to control your cooling fan with the Infinitybox system.  The PAC-2800BT is a powerful controller that lets you program the temperatures that turn on and turn off your cooling fans.  You have the flexibility to use any temperature sender, take in OBDII data from a modern ECU, even interface with the VHX & RTX gauges.  We’ve blogged before about wiring the VHX and RTX gauges with the Infinitybox system.  Click on the links to learn more.

There are multiple advantages to using the Infinitybox system with the Dakota Digital PAC-2800BT controller.  First, you can eliminate the external relay and the fuse.  These are built into the POWERCELL.  Next, you can streamline your wiring.  The PAC-2800BT would be located behind your dash, near the MASTERCELL.  The power for the fans comes from the front POWERCELL, which is located strategically where you need it in the car.  Lastly, the POWERCELL has the ability to soft-start the cooling fan.  This decreases the in-rush current to the fan and lets you drive a larger fan with a smaller gauge of wire.  You can read more about this at this link.

As always, we strongly encourage you to read and understand the manuals for anything that you are installing in your car.  Dakota Digital has a very detailed manual for the PAC-2800BT.  You can access it by clicking this link.  Also, this blog post is going to cover the wiring between the Infinitybox system and the PAC-2800BT.  This includes ignition power, the cooling fan triggers to the MASTERCELL and the cooling fan output from the POWERCELL.  Follow the Dakota Digital instructions for wiring battery power, ground, the temperature sender and the other optional features of the PAC-2800BT.

The following picture shows the connections between the Infinitybox MASTERCELL and the POWERCELL for the PAC-2800BT.

Picture of a wiring diagram showing how to wire the Dakota Digital PAC-2800 BT with the Infinitybox 20-Circuit Kit

Picture of a wiring diagram showing how to wire the Dakota Digital PAC-2800 BT with the Infinitybox 20-Circuit Kit

First, you need to get ignition or key-on  power to the PAC-2800BT.  This is going to come from the POWERCELL output for the ignition.  This is output 3, the light-green wire on the front POWERCELL in most systems, .  Please check your specific configuration sheet to confirm.  You can going to bring this ignition power to the IGNITION terminal on the PAC-2800BT module.  You are going to tap off your POWERCELL ignition output to get this power.  You can splice into this wire or you can use our Splice Saver kit to create an ignition junction point.

Next, you are going to connect your MASTERCELL cooling fan inputs to the triggers on the PAC-2800BT.  In most systems, your cooling fan is input 10, which is the blue wire with the green tracer.  Check your configuration sheet to confirm.  If you are using only one cooling fan, Dakota Digital tells you to use the FAN LOW terminal on the PAC-2800BT.  We strongly recommend that you install a diode in-line between the MASTERCELL and the PAC-2800BT.  This should be a 1N4001 diode that can be purchased easily from Amazon.  The orientation of this diode is critical and the system will not work correctly if it is wired backwards.  The diode lead on the side with the stripe should be connected to the PAC-2800BT.

Lastly, you are going to connect your POWERCELL output for the cooling fan to the wires on the fan motor.  The other wire on the fan motor should be connected to a good chassis ground.   This link will get you more details on wiring the cooling fan with the POWERCELL output.

The PAC-2800BT gives you the option to control two separate cooling fans.  If you want to use a second cooling fan, you would simply repeat wiring an unused MASTERCELL input to the PAC-2800BT and an OPEN POWERCELL output to your second cooling fan.  In most of our kits, output 8 on the front POWERCELL can be used as an auxiliary output.  You can use this one to power your second cooling fan.  See your specific configuration sheet for more details.

Here is how all of this works.  The PAC-2800BT takes in the temperature data from the temperature sender, the Dakota Digital gauge controller or the ECU via OBDII.  If the temperature it reads goes higher than the value that you programmed in it, it grounds the MASTERCELL input for the cooling fan.  This turns on the cooling fan input.  The MASTERCELL sends a command to the POWERCELL in the front of the car to turn on the output for the cooling fan.  When the temperature drops below the set point that you programmed in the PAC-2800BT, it turns off the MASTERCELL input for the cooling fan.  The MASTERCELL sends a command to the front POWERCELL to turn off the fan.  It is that easy.

If you choose the option to use two cooling fans, the PAC-2800BT will manage both fans together to control the engine temperature.

There is a PDF copy of this wiring diagram available on our website.  Click this link to download it.

Give our team a call at (847) 232-1991 if you have any questions about wiring the Dakota Digital PAC-2800BT with our Infinitybox system.  You can also contact our team directly by clicking this link.

Picture of a Spal Cooling used in our 1967 Mustang wired with Infinitybox

Cooling Fan

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We’re getting towards the end of the outputs that we need to wire on this 1967 Mustang project.  The cooling fan is next.  We’ll talk in later posts about how to wire the cooling fan triggers to the MASTERCELL input.  This post is going to talk about connecting the POWERCELL output to the fan motor.

In most cars, the cooling fan is connected to the radiator in the front of the car.  When the engine coolant temperature exceeds a set point, the cooling fan turns on to blow outside air through the radiator.  The fan will continue to run until the coolant temperature drops below a set level.

There is a dedicated output on the front POWERCELL in the 20-Circuit Kit that our customer is installing in this 1967 Mustang.  It is output 10, which is the tan wire on the A connector.  Check your specific configuration sheet to confirm the wire color.

Our POWERCELL acts as both the fuse and relay box, except we don’t use relays.  We use what is called a MOSFET.  Think of this as a solid state relay.  Each of the outputs on a POWERCELL can carry 25-amps continuously.  These outputs can also tolerate in-rush currents up to 100-amps.  Like our previous post about headlights and high-beams, you need to consider the in-rush on a motor when you are planning on wiring your car.

When an electric motor is started, the rotor appears to be stalled at the instant the current is applied.  This stalled current will flow through the motor windings.  As the motor starts to turn, the amount of current flowing to the motor will drop.  When the motor reaches its steady-state speed, the current will level off.  This initial in-rush current can be 4 to 5 times the steady-state current depending on the size of the motor.  The graph below shows an example of this in-rush current.

Graph showing the start-up current of a cooling fan

Graph showing the start-up current of a cooling fan

In the case of this fan motor, the initial in-rush is approximately 100-amps.  Within 2 seconds of starting, the current levels off at about 25-amps.

In most cooling fans, the manufacturer will tell you that you need to use a 70-amp relay to turn the fan on and off.  This is because of the starting current or in-rush current going to the motor.  With your Infinitybox system, you can drive most cooling fans directly without adding an external relay.  The outputs used in the POWERCELL outputs are designed to handle this in-rush current.

In addition to just handling the in-rush current, we use an extra trick to help manage this in-rush current.  As mentioned above, we don’t use relays on our outputs.  We use MOSFETs.  MOSFETs can be turned on and off thousands of times per second.  You can’t do that with a relay.  This on and off lets us do something called Pulse-Width Modulation or PWM.  There are two important parts of PWM.  The first is the frequency.  This is how many times you turn the MOSFET on and off each second.  Our PWM frequency is 20,000 Hertz.  The second part is duty cycle.  This is the ratio of the on time over the off time.  A 50% duty cycle would have the output on for the same period of time as it is off.  A 100% duty cycle means that the output is on all the time.  A 0% duty cycle means that the output is off.  This picture shows the PWM pulses and different duty cycles.

Examples of three different PWM duty cycles

Examples of three different PWM duty cycles

By changing the duty cycle, we can control the amount of power going to the fan.  The higher the duty cycle, the more power is coming out of the POWERCELL output.  When we turn on a fan, we soft-start it.  This means that we gradually start the fan over about one second.  This minimizes the in-rush current.

We get lots of questions about cooling fans and whether or not they can be driven directly from the POWERCELL.  Most can.  A good rule of thumb is to look at the gauge of wire on the cooling fan.  If it is 14-AWG or less, you can certainly use our POWERCELL directly.  In most cases, the manufacturer of the fan will publish the running current or steady-state current for the fan.  Most commonly used fans in aftermarket applications draw between 8 and 20-amperes.

In some cases, our customers want to use two large fans to cool their engines.  The two fans together would draw more than the 25-amps maximum of a single output.  In this case,  you can use any of the OPEN outputs on your configuration sheet.  OPEN means that there is no specific function assigned to them.  You can use them as auxiliary outputs.  We’ll talk about wiring the cooling fan triggers to the MASTERCELL in a few more posts.

DC fan motors have a direction to them.  One of the fan wires will connect to the POWERCELL output and provide battery power to the motor.  The second wire must be connected to ground.  You must check the manual that came with your fan to determine which wire is power and which is ground.  You can also watch the rotation of the motor.  Most fan manufacturers put an arrow that indicates the correct direction that it should spin.  If the fan spins in the wrong direction, reverse the wires.

You can splice the POWERCELL output wire to the wires on the fan in the same way that we described in our headlight post.  You can get to that post by clicking this link.

Keep watching for updates on this 1967 Mustang wiring job with our 20-Circuit Kit.  If you have questions or comments, you can click on this link to get in touch with our team.