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EQ5 power supply query


bosun21
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I set up my EQ5 with my Starfield for a nights gazing. I decided to use my Nevada PSU 8A as a change from my Celestron LT power supply. I polar aligned without issue and then parked the scope until it got a bit darker (considering the moon wasn’t that much). I then slew the short distance to Mizar/Alcor to check focus. I spent a few minutes on it then noticed the hand controller was dark. I have a mains extension lead into the Nevada and a 5m Lynx cigarette plug cable to the mount. I could see the power supply was on at the Nevada and found the fuse blown in the Lynx cable (cigarette plug). I quickly just swapped over to my Celestron power pack and spent the rest of my session without issue. Why would the fuse blow when it’s only tracking? Both axis were well balanced and the motors run their full range of motion smoothly. This was the first night using my Nevada and I don’t want to blow the board on my mount. Should I just replace the fuse and try again? The fuse was a 5A  Thanks  

      Ian 

 

Edited by bosun21
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that would suggest that the power supply is ok, but that something in the wiring 'downstream' from the cigarette plug is at fault....  Is the fuse in the Celestron power pack also rated at 5A ?  if not what rating is it ??

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Typically the motors on an EQ5 draw around 1Amp when slewing, so the new PSU will have plenty of headroom and well up to the job of powering the EQ5.  As Julian has mentioned, the fact it blew in the cable from the psu to the mount would suggest that the excessive load would be between the PSU and the mount, but then as you were able to use the old supply for the rest of the night would suggest that the synscan unit / handset is fine.  

If I had to make a guess as to what happened I would say that the fuse is a quick blow fuse, and at some part the slew produced a current surge that momentarily exceeded the 5A fuse rating and it popped.  Now it could also be that the fuse had a wide tolerance and the current it would pop at was below 5A or that the fuse was duff.   Now you could replace the fuse with a standard 5A fuse and it will be fine, but it it keeps popping fuses then further investigation to measure the actual current draw would be worth undertaking. 

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As Malc has said, try replacing the fuse with a 5A slo-blow type, which should allow for any current draw surges....   BTW, the Celestron Overload short protection, is a fuse, just a more complicated version, that is also re-settable..... 

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18 minutes ago, malc-c said:

Typically the motors on an EQ5 draw around 1Amp when slewing, so the new PSU will have plenty of headroom and well up to the job of powering the EQ5.  As Julian has mentioned, the fact it blew in the cable from the psu to the mount would suggest that the excessive load would be between the PSU and the mount, but then as you were able to use the old supply for the rest of the night would suggest that the synscan unit / handset is fine.  

If I had to make a guess as to what happened I would say that the fuse is a quick blow fuse, and at some part the slew produced a current surge that momentarily exceeded the 5A fuse rating and it popped.  Now it could also be that the fuse had a wide tolerance and the current it would pop at was below 5A or that the fuse was duff.   Now you could replace the fuse with a standard 5A fuse and it will be fine, but it it keeps popping fuses then further investigation to measure the actual current draw would be worth undertaking. 

Thanks for the reply. I have ordered some spare glass 30mm 5A 250V fuses to keep as spares. I have other Lynx 5m cigarette plug cables so I’ll swap the fuse over and replace the blown one as i want to ensure it’s not a faulty cable itself. This is unlikely but better to be thorough. It’s the fact that it blew whilst tracking not slewing that puzzles me. I am going to use the same cable and set it up indoors to track for an hour and do some random slewing and see if it blows again. 

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10 minutes ago, Dr_Ju_ju said:

As Malc has said, try replacing the fuse with a 5A slo-blow type, which should allow for any current draw surges....   BTW, the Celestron Overload short protection, is a fuse, just a more complicated version, that is also re-settable..... 

What has it got an internal  rcd? Why put it in an inaccessible place 

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1 minute ago, bosun21 said:

What has it got an internal  rcd? Why put it in an inaccessible place 

It will be a thermal resettable fuse (PCT) type device that looks like a large disk capacitor.  Excessive current causes it to heat up which brakes the connection internally.  Then as it cools the connection is remade. 

I'm no expert when it comes to fuses, but I would have thought that there may be a difference in the voltage ratings. Given these cables are designed to power things via a car cigarette lighter socket and thus run at 12v you would have thought they would be fused with a standard 12v automotive 5A blade fuse rather than a 20mm glass mains fuse. 

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19 minutes ago, malc-c said:

It will be a thermal resettable fuse (PCT) type device that looks like a large disk capacitor.  Excessive current causes it to heat up which brakes the connection internally.  Then as it cools the connection is remade. 

I'm no expert when it comes to fuses, but I would have thought that there may be a difference in the voltage ratings. Given these cables are designed to power things via a car cigarette lighter socket and thus run at 12v you would have thought they would be fused with a standard 12v automotive 5A blade fuse rather than a 20mm glass mains fuse. 

It’s actually a 30mm mains 5A glass fuse. I have ordered quick blow as opposed to slow blow. Are these the wrong ones? I can’t find any slow blow on eBay 

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7 minutes ago, Dr_Ju_ju said:

Thanks for the link, but I refuse to buy anything from Amazon. I have found them and ordered a dozen from Switch electronics 👍

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The function of a fuse is to blow in the event the device it's protecting draws too much current than the rating of the fuse.  Having a quick blow fuse means that there is less chance of damage to the device compared to a standard or slow blow fuse.

From my quick research session it would seem that the voltage makes no difference, and using a 5A 30mm 240v rated fuse on 12v.  Where is does differ is in the wattage rating, being 1200w on mains voltage and 60w with a 12v system.  Amps are Amps

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Well I have been running my EQ5 for two hours now both doing a dummy alignment and tracking mode and it’s working perfectly. I am thinking that it could have been a duff fuse. Thanks again to those who replied to my post.

      ATB  

         Ian 

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