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SKMT · 01-07-2020, 13:48

I have 2 Hella fans in aft cabin.

The other day I noticed them randomly (and not in synchrony) bogging down for a split second to 2 seconds. And then rev back to normal speed. It's continued to happen for the last few days since.

Battery bank is well charged. And the fans aren't on the same branch wire (although I'm unsure if those two branches eventually merge).

Also, possibly related. Yesterday a resistor burned out in 1 of the fans. The other fan is still experiencing same symptoms.

What might be the cause of this?

wingless · 01-07-2020, 13:51

My speculation is that the DC feed providing power to these fans is also supplying other devices. If correct, and that different device is drawing a large amount of current, then that will droop the voltage feeding the fans, causing them to slow.

SKMT · 01-07-2020, 14:02

Yeah that's a natural thought. But I can't think of what it would be. There's nothing power hungry that would be on that line.

Could it be some sort of intermittent short?

ThereAndBack · 01-07-2020, 14:12

You sure you don't have a hatch open that allows some breeze in? When a wind hits my running fans they'll sometimes seem to bog as they fight the flow of air.

SKMT · 01-07-2020, 14:39

It can't be caused by breeze, this is a new issue.

guyrj33 · 02-07-2020, 09:34

how many hours on these fans?
Perhaps the bearings are wearing.

Bycrick · 02-07-2020, 10:05

I had a number of Hella fans, which over the years have been "refurbished" using 5” square computer fans. But, when I used the Hellas:
1. They work and they’re quiet for the amount of air moved.
2. They’re relatively expensive.
3. The bearings last a long time if you keep the fans clean and remove the blades and switch cover every couple of months to lubricate the bearings.
4. When the bearings get dirty/sticky, the load on the motor increases, the current increases, you’ll eventually burn out one of the resistors. They can be replaced, but if the bearings are dragging you’ll just end up doing it again.
5. Even if you keep the bearings clean and oiled, eventually you will wear out the motor brushes. Worn brushes will produce the symptoms that you described. There’s no reasonable way to open the motor to replace the brushes. IIRC, the original motors were rated for 2000 hours, which isn’t very long if you run them 8-10 hours/day. About 20 years ago, Hella changed to a motor which was "rated" at 5000 hours. At that point, they put a sticker on the box bragging about the increased life.
6. At least in theory, you could find a similar motor from one of the small motor manufacturers and replace the motor, but that will take a lot of research for a $5 motor. I found several that might almost fit from several of the electronics surplus houses. If you found an exact replacement motor, changing it is simply a matter of unsoldering the two motor connections from the PC board.

I finally got tired of caring for them. I discovered that a 120 mm computer fan can be fitted into the Hella frame with only a little bit of cutting of the frame. I use a small magnetic reed switch to turn it off/on. Total parts cost is under $10. Total conversion time is about an hour. The converted fans run at a single speed and are usually (depending on the specific surplus fan used) noisier than the Hella.

The box fans can be bought with ball bearings, not sleeve bearings, and with brushless motors for about $7 from the surplus houses. Some really good German ones are available from Digikey for about $30. These have a rated life of several tens-of-thousands of hours.

ABJ87 · 02-07-2020, 12:06

Are you hooked to shore power? Ours will change speed slightly as the battery charger changes from bulk, acceptance and float.

SKMT · 02-07-2020, 13:51

Quote:

Originally Posted by guyrj33

how many hours on these fans?
Perhaps the bearings are wearing.

It's way too sudden. It went from never happening to all of a sudden happening with both fans, starting on the same day.

CarinaPDX · 02-07-2020, 13:56

Bycrick is right - the Hella fans have a limited life. IIRC the Turbo model is rated at 2000 hours MTBF, and the Jet at 1500 hours. They use bushings rather than true bearings, and that is what you get - for a very high price. None of the fans I have looked at are any better, and I got tired of replacing them every couple of years. So I use 120mm 12VDC case fans as well, although I have not tried to fit them into the Hella fixtures. These case fans can be had with either bushings or bearings, and again the MTBF is much higher for fans with bearings - typically 30k-50k hours for bearings. Pay a bit more and be done with it. I used to buy my fans at computer stores, which used to offer them with manual fan speed control (an external pot) which is very convenient - for about $20.

Greg

Frankly · 02-07-2020, 15:00

I have 11 Hella turbos on Cbreeze, I am convinced the slight speed modulation is usually the bearings (battery voltage can also produce speed variations). When mine start to change speed, I oil both bearings but realize the end is near. There are small resistors to provide some reduction of conducted RFI in the 12V feed. When the bearings get really bad the resistor will sometimes overheat. Trying a couple midified with a common mode ferrite choke. Tried several other brands, but just like the quiet, two speed, low current, reasonable air movement. Everything but those sleeve bearings looks like good quality, but they are a real weak link.

Frankly

wingssail · 02-07-2020, 15:43

Quote:

Originally Posted by Frankly

I have 11 Hella turbos on Cbreeze, I am convinced the slight speed modulation is usually the bearings (battery voltage can also produce speed variations). When mine start to change speed, I oil both bearings but realize the end is near. There are small resistors to provide some reduction of conducted RFI in the 12V feed. When the bearings get really bad the resistor will sometimes overheat. Trying a couple midified with a common mode ferrite choke. Tried several other brands, but just like the quiet, two speed, low current, reasonable air movement. Everything but those sleeve bearings looks like good quality, but they are a real weak link.

Frankly

These Hella Turbos are quiet and use little power and they are the "standard" fan on Wings. We have 7 installed and about 4 of those are operating at most times in the tropics. You cannot get more than 48 inches from a Hella fan in our boat. We have used Hella fans for about 25 years. When I go on other boats as navigator I take my own Hella and alligator clips. The ones we have now are at least 5 years old and running fine.

The key is to keep the bearings lubricated with very light oil, WD40 works well, and keep the oil off of the circuit board. The resistors are delicate and overheat easily, and then are soon fried. Even a little heavy oil, like 3in1, can put a drag on the bearings and cause overheating. Cleaning the speed control sliders is also useful, use alcohol. Taking the fans apart to clean and lube them is just a little tricky, but once you learn how to do it, it is quick and easy.

Computer fans are also good, but the installation is not as elegant.

Sternwake · 02-07-2020, 18:55

Recently my Dremel brushes wore out and I was getting wild fluctuations in speed. Shaved down some mystery tool extra brushes to fit and it works perfectly again.

A few years back I lost a halogen headlight bulb. I was not happy with the products available in the town I was in, and bought only one. When I plugged it in and walked around to the front of the vehicle to check, the other one burnt out in front of me.

If modification of your hella fan is doable for you, Look into computer fans from Delta. Most of them respond beautifully to voltage as a speed controller and have dual sealed ball bearings. Some are ridiculously powerful.

a 5 amp XL4015 based voltage bucker only drops 0.19v across it. I attach one of thse to the body of delta fans and use a remote potentiometer for infinite speed control. Most slow to nearly silent at about 7 volts and consume about 0.1 amps down there.

The Silverstone FM121 and its larger FM181 and AP182 come with built in speed controllers. The AP182 does not like battery charging voltages.

Put a glob of Dielectric grease where the power wires enter the hub and are soldered to circuit board. This requires lifting the hub's sticker slightly on most fans, but a few require removal of the C clip and removing the impeller.
I use 'amazing goop' as a conformal coating.

So much more engineering has gone into computer fans in terms of noise made for air moved and amperage consumed, and hardening them for marine use is not excruciatingly difficult.