Hella fan conversion

It’s a rare boat indeed that doesn’t have at least one Hella fan aboard. We have eight on our boat. The popular but expensive Hella 12-VDC fans use motors with sleeve bearings and brushes. After a while, the brushes wear out and the sleeve bearings run dry. Hella now advertises that their motors have a 5,000-hour life, but they sold many thousands of the older models with the original 2,000-hour motors. These older models are just begging for this modification to update them to long-lived brushless ball-bearing motors. Don’t discard your noisy or inoperative old Hella fan. Spend a couple hours of your time and less than U.S. $15.00 to upgrade your worn-out Hella fan with this easy project. (A bit of dumpster-diving or a call on the morning VHF net will probably yield a few discarded Hella fans! Both activities worked for me.) 

Assemble the following tools and supplies: 

• Table knife

• Dremel tool or other rotary tool with cutoff disc

• Tube of RTV silicone sealant (white or black to match your fan)

• Soldering iron and rosin core electronic solder

• Wire cutting pliers

• Coarse (80 to 100 grit) sandpaper and sanding block

• Two 1-inch (25mm) lengths of 1/16-inch (1.5mm) heat shrink insulation

• Roll of masking tape

• 5/16 inch (8mm) nut driver or socket wrench

• 12-VDC muffin fan with brushless ball bearing motor 4.68 inch (119 mm) size, www.jameco.com part number 163619 or equivalent.

First, disconnect the power wires from the Hella fan. Carefully remove the Hella fan blades by prying out the center cap on the fan blades with a table knife to gain access to the collet chuck within. Loosen it with the nut driver or socket wrench and pull the fan blade assembly off of the shaft. Discard the fan and center cap, as they will not be reused.

Turn the frame over and place a strip of masking tape over the switch hub and the side of the frame. This will serve as a reference marker to allow you to correctly position the switch hub during reassembly. The switch hub will fit in any position, but only one position will work! There is a very small index arrow on the housing, but it is very hard to see. Now slip the table knife in between the fan frame and the switch hub, cutting the strip of masking tape. Continue with the table knife, twisting the knife carefully to dislodge the three fingers that hold the switch hub to the frame. Set the switch hub aside for later use.

Now remove the circuit board and the fan motor, and set them aside. Using the rotary tool with cutoff disc, carefully cut the motor mount cone along the ridge. The end result will be a flat surface in the fan frame against which the muffin fan will be mounted. 

Using the coarse sand paper, remove all four of the corners of the muffin fan evenly until the muffin fan will fit easily into the Hella frame. You can shorten this chore by first trimming the corners with a hacksaw, but take care to not remove too much material. Take your time: work slowly and make a neat job of it. 

When you are satisfied with the fit of the modified muffin fan, apply some RTV silicone to each corner and insert it into the Hella frame with the fan blade side of the muffin fan out (otherwise, it won’t turn!). Route the fan wires to the center. A few pieces of masking tape at each corner will help make a neater job with the RTV silicone. 

While the RTV is curing, unsolder the two original motor wires from the circuit board after making careful notes on which wire goes where. Red is positive and black is negative. Discard the motor. (It has some powerful magnets in it, and you surely don’t want it around your compass.) If the original two-speed switch on the Hella fan still works, by all means reuse it. Cut off all but about 3 inches (76mm) of the muffin fan wires and solder them to the circuit board, making sure that you connect red to positive and black to negative. If your muffin fan arrives with a small plug on the end of the wires, just cut it off. If there is a ferrite on the wires, just leave it be. It won’t hurt anything. Its function is to suppress any electrical noise from the motor.

Carefully route the wires into the center of the Hella housing, and guide the circuit board into position. With the circuit board in place, line up the tape marks on the switch hub and frame, and push the switch hub down until the three fingers snap into place. This completes the modification. When reinstalling the newly modified Hella fan, be absolutely certain to connect positive to positive and negative to negative. A polarity error will destroy your new fan motor instantly. Use your volt meter to determine polarity.

Here’s a handy tip to prevent a polarity error from destroying your newly modified fan:

Crimp a female socket connector on the positive supply lead from the boat, and a male spade connector on the positive lead of the fan. Also crimp a male spade connector on the negative supply lead from the boat, and a female socket connector on the negative lead of the fan. Now, it is impossible to incorrectly connect the wires. 

If the original two-speed switch is worn out, replace it with a single pole (or double pole) three throw (On-Off-On) subminiature toggle switch. Remove and discard the copper switch bar from the inside of the switch hub. Drill a hole in the Hella switch hub for the new toggle switch. Clip the power leads from the circuit board, and scavenge the 22-ohm 1-watt resistor (red, red, black) from the circuit board, discarding the rest. Solder as indicated in the following diagram and insulate the joins with heat-shrink insulation. Install the new toggle switch in the switch hub and carefully route the wires in the center. Line up the tape marks on the switch hub and frame, and push the switch hub down until the three fingers snap into place. 

Following good electrical practice, make sure that there is an in-line fuse in the positive lead of each fan. A 2-amp fuse will provide good protection for this small motor. Just an afterthought: many 12-VDC refrigeration units use this same muffin fan, so keep an extra one aboard. Better yet, team up with a friend and order at least 10 fans, as the price drops significantly.

Enjoy thousands of hours of trouble-free cool breezes.

Harry Hungate and his wife, Jane, live aboard their Corbin 39 cutter Cormorant, and enjoyed their cool Hella breezes while cruising up the Red Sea in 2009.
By Ocean Navigator