Eliminating Bearing Noise in XS 900 Cooling Fan

[Anonymous user]

Recently the cooling fan in my XS 900 Back-UPS started making a noise which I suspected was the beginning of bearings wear. The fan in my unit is produced by Y.S. Tech, and is a 40mm square X 10mm thick 24-volt DC version, their model no. FD244010HB. Initially I thought this fan was one which used a sleeve bearing, but after reviewing the Y.S. Tech spec sheet for this particular model, I learned that in fact it has two ball bearing assemblies, with the expected life of the fan to be 75,000 hours when run at 40 degrees C. This puzzled me since my UPS has been in operation for much less than 75,000 hours since purchased new.

I decided to go ahead and look at the fan with the assumption that it would have to be replaced. Upon opening up my XS 900 UPS (see my previous thread, Opening up the Case on an XS 900, elsewhere in this forum for details on how to do this), I saw that the fan was mounted on a small bracket facing the heat sink assembly (Aluminum bar stock) for the power MOSFET's. The fan is easily removed from its mounting bracket via 4 Phillips-head metric machine screws, which screw into flanges on the mounting bracket, making this fan's removal very easy. The power connections for the fan are made with a pair of wire leads terminated in a 2-contact shrouded socket connector which mates to a corresponding 2-pin connector on the PC Board. Again, this is also easily disconnected after disengaging the small plastic latch on the body of the connector on the wire leads.

Once the fan was completely removed, I decided to further inspect it to see if there was anything I could do to possibly lubricate the bearings, and hopefully cure the audible noise without having to buy a replacement fan. By the way, I'm not sure if APC sells a replacement fan and would allow me to install it myself, so I resigned myself to potentially buying a new fan of equivalent size and performance. However, after looking at the fan more closely, I found I could remove the small circular identification label covering one of the bearing assemblies, and the plastic snap ring for the fan's shaft. I did this by taking an Xacto knife and carefully lifting an edge of the label until I could gently peel it back with a pair of tweezers. Once I did that and placed the label in a safe place, I had full access to one of the two ball bearing assemblies and the shaft's plastic retaining disk. The retaining disk is a small white circular piece of plastic, about 1/8 of an inch in diameter, with a small hole in its center which allows it to be slipped over the end of the fan shaft. A tiny radial slit extends from the edge of the disk's center hole out to the outer edge of the disk itself, and allows the disk to be separated and snapped into an undercut of the shaft, thus retaining the fan shaft in the bearing assemblies on both sides of the fan housing.

To remove this disk, I took the Xacto knife again and carefully inserted the blade under the outer edge of the disk near the slit, and worked it up over the end of the shaft being careful not to cut or otherwise damage the plastic material. This disk is fairly rigid, and once one edge of it was out of the groove in the shaft, it can be worked around the end of the shaft until it pops free. I was very careful to keep one of my fingers gently resting on the disk during this operation so as not to allow it spring free and fly out of sight since it's a snap fit.

Now with the fan shaft and the impeller no longer captivated in the fan housing, I was able to pull the impeller free noticing that it has a small concentric coil spring slipped over the shaft and resting against the impeller's body. This spring keeps axial tension on the impeller body and the second bearing assembly opposite the other bearing in the fan housing where the plastic disk is mounted.

Taking some light, high-speed "turbine" oil (from my local ACE Hardware store), I placed the end of a round toothpick in the oil so as to develop a extremely small drop at the end of the toothpick. *(If you try to do this, be aware that if you can easily see the drop of oil on the toothpick point, you've got too much. You will have the right amount when you can just barely see the oil's film bulging near the end of the toothpick.)* I then touched the area between the inner and outer races of each bearing assembly and noticed that the oil was immediately "captured" and flowed around the middle circumference of each bearing. I did this twice for each bearing, making sure the oil went into the bearings' themselves and not down their center holes or on the outer race and wall of the fan body's bearing mounting hole.

Next, I reversed the disassembly procedure making sure the plastic retaining disk was securely snapped back into place into the groove at the end of the fan shaft. This was actually very simple and I went slowly about the task. Again, if you attempt to do this, just keep in mind you will be working with extremely small parts, so a light touch is all that's required.

Finally, reinstalling the fan and powering up the UPS showed that the noise problem was solved and the fan now runs quieter than ever before. I'm guess that the fan or bearing manufacturer didn't adequately lubricate the bearings, or the fan is being used outside of its recommended operating parameters.

[Anonymous user]

I have rejuvenated cooling fans in this manner numerous times - your mileage may vary depending on how worn the races are by the time you notice it breaking down.

Be advised though you must avoid "penetrating" or "WD-40" sorts of oils as they are:

A. Too thin

B. Contain solvents/rust dissolvers that break down whatever factory lubricants were there to begin with, and and basically evaporate over time.

I always cringe when I see kids using these on their skateboard bearings as I know it does more harm than good !

[voidstar_apc]

Very interesting!

[Anonymous user]

Thanks so much for your very informative post. From your instructions, I was able to disassemble, lubricate, and reassemble my UPS. I lubricated using some CLP. So far it is very quiet. I will post back if I have anything new. Hopefully I was able to salvage my ups and save it from the landfill. Seems like a dumb design by APC.

[Anonymous user]

Recently the cooling fan in my XS 900 Back-UPS started making a noise which I suspected was the beginning of bearings wear. The fan in my unit is produced by Y.S. Tech, and is a 40mm square X 10mm thick 24-volt DC version, their model no. FD244010HB. Initially I thought this fan was one which used a sleeve bearing, but after reviewing the Y.S. Tech spec sheet for this particular model, I learned that in fact it has two ball bearing assemblies, with the expected life of the fan to be 75,000 hours when run at 40 degrees C. This puzzled me since my UPS has been in operation for much less than 75,000 hours since purchased new.

I decided to go ahead and look at the fan with the assumption that it would have to be replaced. Upon opening up my XS 900 UPS (see my previous thread, Opening up the Case on an XS 900, elsewhere in this forum for details on how to do this), I saw that the fan was mounted on a small bracket facing the heat sink assembly (Aluminum bar stock) for the power MOSFET's. The fan is easily removed from its mounting bracket via 4 Phillips-head metric machine screws, which screw into flanges on the mounting bracket, making this fan's removal very easy. The power connections for the fan are made with a pair of wire leads terminated in a 2-contact shrouded socket connector which mates to a corresponding 2-pin connector on the PC Board. Again, this is also easily disconnected after disengaging the small plastic latch on the body of the connector on the wire leads.

Once the fan was completely removed, I decided to further inspect it to see if there was anything I could do to possibly lubricate the bearings, and hopefully cure the audible noise without having to buy a replacement fan. By the way, I'm not sure if APC sells a replacement fan and would allow me to install it myself, so I resigned myself to potentially buying a new fan of equivalent size and performance. However, after looking at the fan more closely, I found I could remove the small circular identification label covering one of the bearing assemblies, and the plastic snap ring for the fan's shaft. I did this by taking an Xacto knife and carefully lifting an edge of the label until I could gently peel it back with a pair of tweezers. Once I did that and placed the label in a safe place, I had full access to one of the two ball bearing assemblies and the shaft's plastic retaining disk. The retaining disk is a small white circular piece of plastic, about 1/8 of an inch in diameter, with a small hole in its center which allows it to be slipped over the end of the fan shaft. A tiny radial slit extends from the edge of the disk's center hole out to the outer edge of the disk itself, and allows the disk to be separated and snapped into an undercut of the shaft, thus retaining the fan shaft in the bearing assemblies on both sides of the fan housing.

To remove this disk, I took the Xacto knife again and carefully inserted the blade under the outer edge of the disk near the slit, and worked it up over the end of the shaft being careful not to cut or otherwise damage the plastic material. This disk is fairly rigid, and once one edge of it was out of the groove in the shaft, it can be worked around the end of the shaft until it pops free. I was very careful to keep one of my fingers gently resting on the disk during this operation so as not to allow it spring free and fly out of sight since it's a snap fit.

Now with the fan shaft and the impeller no longer captivated in the fan housing, I was able to pull the impeller free noticing that it has a small concentric coil spring slipped over the shaft and resting against the impeller's body. This spring keeps axial tension on the impeller body and the second bearing assembly opposite the other bearing in the fan housing where the plastic disk is mounted.

Taking some light, high-speed "turbine" oil (from my local ACE Hardware store), I placed the end of a round toothpick in the oil so as to develop a extremely small drop at the end of the toothpick. *(If you try to do this, be aware that if you can easily see the drop of oil on the toothpick point, you've got too much. You will have the right amount when you can just barely see the oil's film bulging near the end of the toothpick.)* I then touched the area between the inner and outer races of each bearing assembly and noticed that the oil was immediately "captured" and flowed around the middle circumference of each bearing. I did this twice for each bearing, making sure the oil went into the bearings' themselves and not down their center holes or on the outer race and wall of the fan body's bearing mounting hole.

Next, I reversed the disassembly procedure making sure the plastic retaining disk was securely snapped back into place into the groove at the end of the fan shaft. This was actually very simple and I went slowly about the task. Again, if you attempt to do this, just keep in mind you will be working with extremely small parts, so a light touch is all that's required.

Finally, reinstalling the fan and powering up the UPS showed that the noise problem was solved and the fan now runs quieter than ever before. I'm guess that the fan or bearing manufacturer didn't adequately lubricate the bearings, or the fan is being used outside of its recommended operating parameters.

[Anonymous user · Accepted solution]

I have two such units that were purchased in January 2009 and I followed a similar procedure prior to finding your posting, but I used a penetrating/lubricating oil on the one that had seized. Mine ran fine for about 6 weeks before the fan started making noise again. Turns out the label came off and there's not much hope of getting that to go back on and stay on.

Early last week the other unit started to do the same thing, but this time I used 3-in-1, so hopefully it will work better. I'm currently doing the same to the unit I described above.

If I hadn't thrown out the receipt, I'd be able to RMA them both, but the warranty won't be honored because I don't have that and they are going off the date of manufacture (December 2006).

Message was edited by: LoneWolf3574