The LXD-75/LXD-55 HEAT Problem Page

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LXD-75/55 Heat Problem:

I like to take pictures of sun spots and noticed that while I was tracking the sun looking at the sun spots on my monitor getting ready to take a picture the suns image just drifted off the screen.

I checked everything and couldn't find anything wrong. I noticed that Autostar didn't contain positional data for the sun and thought that it might have some form of protection in the software that wouldn't allow the sun to be observed. I know how ridiculous that sounded but nothing else I could come up with sounded any better. So in desperation I called Meade.

Meade never intended their products to be used in the day time (according to a customer service representative I spoke with in March of 2005). Even though their manuals indicate that you can use their equipment on terrestrial objects in the day time they don't warranty their equipment for day time use or problems thereof.

This came as quite a shock to me as I generally check for sun spots in the day time and there are times when I like to photograph the moon and bright planets late in the day to get the blue sky as back ground.

I continued to experience this problem and then one day I stumbled on the problem. It was HEAT!!! I live in Phoenix where it regularly hits 115 degrees F in the summer time. However, it was only spring and the days were sunny and clear with a mild temperature of 75 degrees F. So where was the heat coming from?

Meade in all their wisdom had just introduced a brand new mount, the LXD-75. It was a cool off-white color and looked really great. However, they had not updated their motor boxes. These were still housed in two black plastic units. A black object in the phoenix sun, even in the spring, gets real hot. So I used a laser temperature gun to measure the box temperatures over the course of a day. At the same time I ran a tracking test periodically to see how well the mount was tracking.

What I found was astonishing. The unit performs well until the control box (the bottom motor box where all the cables plug into) temperature exceeds 112 F and then the tracking rate would slow down. The table below shows the test results:

     Control Box         Tracking Rate 
     Temp. (F)          (% of Sidereal)

      90                     100
     100                     100
     110                     100
     112                     100
     114                      95
     116                      90
     121                      78
     126                      65
     130                      55
     136                      40
     143                      23
     147                      13

The temperatures on the black boxes reached a maximum about 2:00 P.M. then the temperatures started to drop following the sun's departure. The temperature of the 115 VAC transformer (providing power to the mount and the Autostar hand box) reached 162 degrees F, while the temperature of the Autostar hand box didn't exceed 132 degrees F. The temperature of the Dec. box stayed about ten degrees F above that of the control box. The day time air temperature, at 2:00 P.M., was 74 with 28% humidity on the day the above temperatures were recorded.

Heating of the Dec. motor box and the Autostar hand box didn't affect the tracking rate. The problem was isolated to the main control box - the lower unit where all the cables plug into. As the control box heated up the R.A. tracking clock's pulse rate decreased.

The Autostar hand box software had provisions to change the tracking rate. With this you could change the rate from -999 to +999, where 000 = 100% sidereal. At -999 the tracking rate went to zero and the mount didn't track - terrestrial mode.

At +999 the tracking rate increased to 200% sidereal. This would then compensate for proper operation up to 132 degrees F, at which temperature the tracking rate would have slowed down by half.

The problem was that if a cloud went over then the temperature cooled a few degrees and the tracking rate went up a bit and you would have to change everything again. So changing the tracking rate to compensate for the temperature problem was a losing battle.

The Solution:

So I decided to paint both of the motor boxes with Gloss White enamel paint. I put a small piece of masking tape over the name plate on the control box so I could read what all the little plug holes went to. I put tape over the cords so I wouldn't get them painted as well as the black boxes.

Be sure to paint the Dec unit, as well as the control unit, as there is a cpu and a clock rate generator in it as well. Paint both sides, the top and the bottom. Use Gloss White as this reflects the most heat.

This has solved my problem for now. But summer isn't here yet. While this fix will keep the mount from absorbing the sun's radiant heat I am not sure what will happen when the air temperature, in the shade, exceeds 112 degrees F as it does each summer. Maybe I'll stay in on those days...

I expect this is a problem for all of Meade's mounts especially their older LXD-55 mounts as I didn't see where the control boxes had been changed.

Disclaimer:

This modification is for Meade's LXD-75 or LXD-55 Mounts ONLY!. These modifications are not intended to be used with other mounts, although other mounts may also suffer from the same problem.

We/I will not be responsible for any problems that arise from anyone using the information provided herein. While we have taken great care to ensure that everything set out here is accurate, we will not share in any responsibility for any damage(s) that may result if this information is used in any way.