Balancing the blades

[k4kyv]

The 52" Hunter Original I'm trying to restore is running now, very quiet, but it has an unsatisfactory amount of wobble. I tried switching the blades around but I couldn't get much improvement regardless of combination.

I did a search on all the fan forum websites and could not find ANY results on the subject. I would have thought this would have been a popular topic, since wobbling is such a common problem with ceiling fans.

I would be interested in hearing about anything anyone else has been able to do to successfully balance the blades for minimal wobble at all speeds.

The problem with ceiling fans relates to the speed of the fan rotation and the length of the downrod. When the period of the motor rotation exactly matches the period of the swing of the motor and downrod, it becomes like a resonance effect and even a slight unbalance in the blades makes the fan wobble.

The best solution to this problem is to use a long downrod, to give the pendulum formed by the motor and downrod such a slow period of swing that the fan rotation won't make it swing back and forth. But this fan will go into a room where the ceiling is too low for a long rod. The blades need to be only about a foot below the ceiling. At that length, the fan's natural swing is at about the same rate that the blades turn at medium speed.

[Deleted]

Here you go:

www.ceiling-fans-n-more.com/blade-balancing-issues.php

[bds72]

The link above gives good advice to first check for any bent blade brackets. If the fan still wobbles after all the blades are straight, then you need to balance the weights of each fan blade. The suggestion to move weights around can be time consuming, frustrating, and often make results worse. A better approach is to remove the blades and weigh them individually with a scale that measures in grams or fractions of an ounce. If you don't have access to one, go to the post office when it is slow in there, and the postal worker might be able to let you use their scale. Some post offices now have a kiosk where you help yourself.

Step 1 - weigh each blade, and add weights until all blades weigh the same. Use pennies or washers... cheaper than using quarters.

Step 2 - now that each blade has equal weight, you want to adjust the center of gravity of each blade, or the "tip weight". Support the bracket end of the blade on the table next to the scale. Use a small rod, pencil tip, or knife edge out close to the end of the blade as support. The tip end of the blade should rest on the center of the scale, so that only the tip is touching the scale. Measure the blades which have no weights added to them first (from step 1). Note the tip weight. Now weigh the blades that have weights added to them. If the tip weight is too low, slide the weight towards the tip, or slide the weight away from the tip if the tip weight is too high. Do not add new weights in this step, or you will screw up what you achieved in step 1. If you have more than one blade with no weights on it at all, and they have different tip weights, then you'll have to add more weight to ALL blades. Simply add an equal amount of weight to all blades so that the total weight of each blade is equal. IE, add one more penny to all 5 blades. Go back and repeat step 1 to be sure that all blades weigh the same, and then perform step 2 to adjust the tip weights. Now that you have pennies on all blades, you will be able to make an adustment for the tip weight for every blade. Once the pennies are in the right spots, then just tape them in place.

It is true that there is a relationship between the speed of the fan rotation and the "period" (the time it takes to swing) of the pendulum or downrod. If you still have a wobble after balancing the blades, and the wobble occurs only at one speed, then you can try to shift the frequency of either the fan rotation, or the period of the pendulum. Search elsewhere on this forum for how you might slightly change the fan rotation speed by changing the capacitors. To change the period of the pendulum, you can either change the length of the downrod (longer or shorter), or change the mass of the fan. You could add weights to the fan housing itself (not to the blades as described above). Adding weight will shift the natural frequency of the pendulum swing. It may require considerable weight to make a noticeable difference. If the fan weighs 20 lbs for example, then it might take about a pound of weight... a few pennies won't make a difference here. You'd need to use a section of steel plate, or tubing filled with BB's or sand, or any other kind of dead weight. The heavier your fan, the more mass it will take to shift it's frequency. Personally, I like the idea of adjusting the capacitor value and/or lengthening or shortening the downrod first. When changing the downrod, it may only require about a 10% adjustment in length. So change it from 10" to either 9" or 11", for example.