Beseler enlarger fan modification

Reducing potential fan vibration in my enlarger head. Replacing the old fan with a 12volt DC axial fan used in computers. This not only eliminated vibration but was also quieter.

Beseler enlarger modification installing an axial fan inside a Dichro 45s head.

Beseler enlarger modification replacing an old fan inside a Dichro 45s  enlarger head with an axial fan. Why? To reduce enlarger head vibration during print exposure and maximise print quality.

Disclaimer: Warning! modifying or making alterations to any electrical equipment can be dangerous and should only be carried out by a qualified electrician.

The following describes how I replaced the 115 volts AC internal cooling fan of a Beseler 45S Dichroic Colour Head with an axial Thermaltake Smart Case Fan II 12 volt DC.

In Australia, the AC power is 240 Volts. However, in my darkroom, I use a step-down transformer to convert to 115 Volts AC. My legacy darkroom equipment such as Zone VI cold light head and stabiliser as well as my RH Designs Analyser Pro are all set to use 115 Volt AC.

Replacing a Zone VI Cold Light Head with a Beseler Dichro 45s

As my stock of graded photographic papers ran out I recently replaced my Zone VI cold light head on my Beseler MX enlarger with a second hand Beseler Dichroic head. This would allow me to take advantage of the fibrebased multigrade papers.

However, I struck a problem. The internal cooling fan seemed to be creating a lot of vibration, noticeabledown to the lens turret. I decided to replace the old fan with a new 12volt DC axial fan used in computers. This not only eliminated the vibration but was also much quieter. Below is a description of what I did.

I use a Beseler MX 4×5 enlarger. When I swapped my Zone VI cold light head for a second hand Beseler 45S Dichroic Colour Head I immediately noticed the fan. My Zone VI cold light was silent. Turning on the Dichroic Head I had noise.

Enlarger Fan Vibration

Touching the lens barrel to adjust the aperture I could feel a significant amount of vibration. I have owned a Super Chromega 6×7 colour enlarger in the past. It too had an inbuilt fan. I never felt the vibrations to the extent that I was feeling with the Beseler.

With the Beseler Dichro Head I made an 11×14 inch print. I then compared to the same print made with ZoneVI cold light. This confirmed for me that vibration in the Beseler head was giving softer focus prints. Which kind of defeats the purpose of using 4×5 format in the first place. It was time to have a peek inside the big black box and find out what was going on.

Beseler enlarger modification dichro 45s head
Removing the back cover exposes the fan assembly

Looking inside the Beseler 45S Dichroic Colour Head

The Beseler Dichroic 45S head I own is not the computerised model. I am assuming it was made around 1997 from a label I found inside. The internal fan is located opposite the 250 watts 82 volt light source. Above is a close up picture of the head with its back removed, revealing the column style fan, mounted on a U shaped chassis. Beseler dampens the fan in at two points of contact with the head:

1) the blue coloured dampeners located left and right of the middle of the fan where it attaches to the U chassis and

2) the 4 rubber dampeners used to connect the U chassis feet to the floor of the head. Refer to the arrows in the pic above.

Whilst the blue dampeners looked OK, the 4 dampeners attaching the U chassis to the head were compressed and hard from age. This was not surprising given the age of the head. It was obvious that the fan mounting would have to be removed and the rubber dampeners replaced.

Take care! There are two power cables supplying the Beseler dichro 45s!

The head has two 115V power leads, one for the fan and one for the light source. There is also a switch located at the bottom left front of the head which turns on the fan. As a safety feature the lamp will not run unless the fan switch is on.

Beseler enlarger modification
External fan On/Off switch

However, the lamp will run even if the external power cord to the fan is unplugged, so long as the fan switch remains ON. This provided two options. Either install a new fan on a separate electrical circuit or install an external fan unit.

Removing the old fan unit

Removing the head from the enlarger and disconnecting both power cords I set about removing the fan. First by removing the units top cover and rear panel which are hinged as one piece. Second, I removed the fan blades by loosening the circlip, then the nuts around the two blue rubber dampeners. After this, I unplugged a black lead to a switch box and a white lead from a plug at the fan base. This now gave better access to remove the 4 nuts connecting the U chassis to the base of the head.

Beseler enlarger modification dichro 45s Top view: the pic above shows the head with the top and rear removed. The central light diffuser is also removed. On the left hand side, rear, is the fan. On the right is the dichroic globe, CMY filters and adjustment controls.
View from front: Dichroic head with the top and rear removed. Two power supply cords visable.
Beseler dichro 45s Top view: the pic above shows the head with the top and rear removed. The central light diffuser is also removed. On the left hand side, rear, is the fan. On the right is the dichroic globe, CMY filters and adjustment controls.
View from the top: Dichro head with the top and rear panel removed. The central light diffuser is also removed. On the left-hand side, at the rear, is the fan. On the right is the dichroic globe, CMY filters and adjustment controls.
Beseler enlarger modification Beseler dichro 45s
Rear view with panels removed.

I initially tried dampening the fan by using 5mm wet suit material as an additional gasket between the U shaped chassis and the head. With the fan blades cleaned up and the new gasket in place, I reassembled the head. Placing the head onto the enlarger, I turned it on. Everything worked, the vibration felt at the lens had much improved, but there was still some which I felt was still likely to affect print quality.

Beseler dichro 45s Before and after photos, top image with fan, second image with fan unit removed. Note white wire which should be capped
Fan unit removed. Note white wire which should be capped.

Replacement Axial Fan – 12 volt DC

In talking to a colleague about the fan vibration, he suggested I use an axial fan to replace the column fan. Initially, I first started looking for 115 Volt AC axial fans. Whilst they are available mainly in the US, freight charges made them uneconomical. I then decided to look at computer fans as they came in a range of sizes with variable speed controls.

Beseler dichro 45s Axial 90mm 12v DC 3 in 1 fan with 5mm wetsuit foam dampener gasket.
Axial 90mm 12v DC 3 in 1 fan with 5mm wetsuit foam dampener gasket.

I settled on purchasing a 90mm Thermaltake Smart case Fan II which runs on 12 Volt DC. It had two bearings which I hoped would give smoother operation. In addition to this, it came with options for full speed, variable speed or temperature control.

Rather than physically modify the walls of the head I wanted to attach the fan case to the rear panel of the head using the existing airflow grate holes to pass the securing bolts through.

Beseler dichro 45s fan motor
Original Beseler dichro 45s fan motor

After removing the original fan, I taped up and placed an insulating cap around the exposed white lead as a safety precaution. I also taped up the external power cord to the fan so it could not be accidentally plugged in.

Mounting the new fan to the Dichro Head

I cut a 5mm wet suit foam gasket for the fan case to sit flat against the inside of the head’s rear panel. The fan direction was orientated to expel air from the unit. The fan case area was smaller than the airflow grill in the rear panel. Air had to be prevented from being sucked around the fan exterior.

To close this gap a rectangle of firm black plastic sheet was cut to cover the grill. A hole the size of the fan was cut into the centre. Four bolts provided with the fan kit secured everything into position. They passed from the fan case through the gasket, the black plastic, and the airflow grill. The fan is secured externally with washers and nuts.

A 12 Volt DC power cable was also passed through the airflow grate to which I attached a common 240 Volt AC to 12 Volt DC converter to power the fan.

The fan unit was wired so that as soon as I turned on the power to the enlarger motor the fan automatically turned on and stayed on.

AC to 12 volt DC transformer in external motor plug powers fan
Beseler dichro 45s showing the axial fan fixing to the rear panel using existing air grill holes.
The axial fan fixes to the rear panel using bolts and existing air grill holes.
Beseler dichro 45s Showing black plastic fitted over the grill to block excess air pathway (fan is sucking air from unit)
Showing black plastic fitted over the grill to block excess air pathway
Beseler dichro 45s Top view from front, fan fitted
Top view from front, fan fitted

After reassembling the head, it was placed onto the enlarger and turned on. The fan performed beautifully and I couldn’t detect any vibration when I touched the lens. The axial fan design had made a big improvement.

Beseler enlarger modification dichro 45s
Rear view showing 12V DC wire exiting from rear grill.
Beseler dichro 45s Top view from front, fan fitted, diffuser in place.
Top view from front, fan fitted, diffuser in place.
Variable-speed fan control.

If you are having vibration problems with your old Beseler 45S then you may want to consider this as a possible solution.

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alexbond

Since 1989, Alex Bond has published cards, calendars, books, and posters under his imprint Stormlight Publishing. His images showcase the West Australian environment. Bond's handcrafted, silver-gelatin, fibre-based prints are personally made by the author in his darkroom.

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