Friday, September 16, 2011

Reliability and repair of the solar gearmotor

I had specified what I had hoped to be a readily available, inexpensive and reliable gear motor for the actuator of my DIY tracking parabolic trough solar heater. Having bought and used several of these over the last five years, I had one that needed repair or replacement. It was not turning well and smoke was coming from the motor. So yesterday I did a bit of work to see what had failed and whether it could be repaired.

This Dayton 2L008 from Grainger priced at US$58.30 has worked well here for five years in my own solar collector. Probably it has operated for several hundred hours in all sorts of temperature and humidity conditions.

It is not essential to use this particular gearmotor. There are all sorts of gearmotors. I wrote about alternative sources here.

Granger has branches and representatives worldwide. Here in Canada, Grainger is represented by Acklands-Grainger. I called them yesterday to check price and availability and was told that I could have one tomorrow but the price was C$97.92! Wow! I thought the C$ and the US$ are about the same? I ordered one and I will argue with them about their rip-off Canadian pricing tomorrow when I pick it up. I need to have a spare new one. Then I turned back to looking at the one that had failed.

(click on any picture here to enlarge it) By removing the four screws at the corners, I was able to split the gearbox. I wasn't surprised to see the caked old grease flung into the corners of the gearbox. What pleased me was seeing that the final three gears in the drivetrain (yellow arrows) are metal gears. In a gear reducer, it is the final gears that take most of the punishment. The gears all seemed to be in good condition. The two orange arrows point to flat washers that I might have missed while cleaning out the old grease. Look for these when you split the gear case as they may come off their shafts and be stuck where you might not see them.

Here is another view with the final two drive gears removed. The flat washers on the cloth go on either end of the final drive shaft. The yellow arrows point to another smaller flat washer that I almost missed while cleaning out the old grease and where it belongs.

This view shows the heads of the motor mounting screws. These fit a Torx T-9 driver. Dayton used thread lock on assembly so they are a bit tight to remove but they will come out easily.

With the screws removed, the small DC motor just comes out the back. The motor looked very familiar to me. It seems to be a very commonly used motor in small appliances, like printers. While there might be many variations like operating voltage, shaft diameter and length, I optimistically went to my bin of small motors to see if I could find somthing that might fit.

As luck would have it, I found a very similar motor (the one on the right). I think this one was from a salvaged HP printer. It was the same size, had the same mounting holes and the shaft diameter was the same. I hooked it up to 12 volts and it spun quietly.

Armed with a possible replacement, I took the end cap off the defective Dayton motor to see what was wrong. I did this by bending four small tabs that were holding the end cap and forced the armature against the end cap by pushing it down on a hard surface. The end cap popped out and I could see the cause of it's distress. The wear to the armature was pretty obvious in the grooves that had been worn into the copper fingers. So much wear in fact, that part of a commutator finger was missing. This motor was toast.

I removed the small plastic gear from the Dayton motor by using a large flat blade screwdriver as a pry bar. The gear came loose fairly easily. If you look closely, the shaft of the Dayton motor has been grooved to increase traction with the gear.

When I tried the same process to remove the gear from the replacement motor, I found that it would not budge, even with a fair amount of force. The gear I found was a metal gear and of course, not the same size or number of teeth as I needed. It had to come off. Not wanting to damage the motor bearings, I needed a better way. I needed a small gear puller but didn't have one. By trapping the gear in the nail pulling notch of a pry bar and using a very small drift pin, I tapped on the shaft with a small hammer until it came loose. Success!

Here I have soldered the lead wires from the Dayton motor to the replacement. The wires are substantial, 18 gauge. I cleaned the motor shaft and the gear with isopropyl alcohol and here I am ready to glue the gear onto the shaft. I found that the nylon gear fit too loosely on the motor shaft so thought that gluing it was the best solution.

I then mounted the motor in the gearbox. I checked the placement of the motor gear against it's mate to see that I had placed the gear correctly on the motor shaft. The shaft of the replacement was a bit shorter than the original but fortunately long enough to fit completely through the gear and align correctly.

I assembled the gears making sure that all the washers and shims were in their original positions and then liberally dabbed each of the gears and shafts with white lithium grease.

After reinstalling the gearbox screws, I checked the operation of the gearmotor with a 12 volt power supply, running it in both directions for several hours.

Given the relatively high cost of the Dayton 2L008 gearmotor, it is comforting to know that it is sturdily built and gives good service in the DIY Tracking Parabolic Trough Solar Heater. Even better to know that it can be repaired if necessary.

Since there are a few of us using this gearmotor, it will be useful to know of a source for the replacement electrical motors since they are likely to fail before the gearbox does. Here is a sketch of the motor that we are looking for. Any advice about sources would be appreciated.

An update: Acklands-Grainger gave me a "break" on the price of the Dayton 2L008 I bought today - C$82.04. Still pretty high I think. The best thing, if you are buying one of these in Canada, or anywhere non-US, is to take in a copy of the Grainger webpage for 2L008 showing the US price or make it clear on the phone that you know the US price. Put them on the spot.

Another update 2L008 is part of a series of 12 volt gearmotors from Dayton with varying gear ratios and RPMs. In case the information in the post is useful to others using one of the the series, I have listed them here for the search robots: 2L003, 2L004, 2L005, 2L006, 2L007, 2L009, 2L010, 2L011. Page 110 of Grainger Catalog 402 about this series is here.

No comments: