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12v regulator available?

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#1 Thrifty1

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Posted 24 May 2022 - 06:04 AM

I have different 12v batteries I use with various ETX telescopes.  I measured the output of them and 2 are around 11.7 - 11.9 volts. The third one I recently purchased is a higher capacity 12v battery and output measures 13.7 volts when fully charged. 

 

if I use the larger voltage one with my ETX105 the alignment / go-to’s are way off. If I use it with my ETX125, it doesn’t seem to have this problem. Not sure if the ETX125 has some sort of regulator inside while the ETX105 does not. Is it correct to assume I’d have to train drives / calibrate motors to use the larger voltage one with the ETX105?  

 

To keep the voltage regulated closer to 12v is there some sort of a DC regulator that could drop down the one battery from 13.7v to 12v?

 

In the research I’ve done on some power regulators, I’ve seen comments like “voltage regulation gets complicated when the source and the output voltages are closer than about 2 volts, because regulators need some headroom to work with.”  I need a drop of about 1.7v so not a lot of drop needed. 
 

The batteries I use are Talentcell lithium batteries.  My primary questions would be:

 

1. should I worry about using a battery putting out 13.7v?  Can it harm the electronics?

 

2. can I somehow easily regulate the battery so it outputs closer to 12v?

 

 



#2 dcaponeii

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Posted 24 May 2022 - 06:09 AM

Is your 13.7 voltage when the battery is loaded (powering the scope) or just the battery itself?  I don't think your scope would balk at 13.7V nor cause a tracking issue even if that is the voltage when loaded.  The battery is almost never going to be at 12V as you operate the scope the battery voltage is going to be decreasing during the night in any case.


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#3 Thrifty1

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Posted 24 May 2022 - 06:22 AM

I measured all 3 batteries at no-load.  When using all 3 batteries on the ETX125 and doing an Easy alignment the telescope slews correctly to both stars. 
 

When using the batteries on the ETX105, the higher voltage battery slews past the position of the 1st alignment star and I have to turn off the telescope before the OTA moves too far down in DEC and hits the mount base. But switching back to the 11.7 battery and it works fine. So it seems the higher voltage is somehow regulated in the ETX125 but not in the ETX105. 



#4 OzAndrewJ

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Posted 24 May 2022 - 06:49 AM

Gday Randy

The ETXs all use raw voltage to the motors at max speed.

The encoders and PICs are all fed by a regulated 5V supply

but the motor runs much faster at max speed with higher voltage.

You dont need to do a drive train, but you should recalibrate the motors

if you change power source, so the encoders can set the best

current to suit the high encoder speeds

( The encoders are exposed LED/Reciever units with slotted disks

so the LED brightness affects how they read at high speeds )

 

Andrew Johansen Melbourne Australia



#5 Thrifty1

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Posted 24 May 2022 - 07:07 AM

Thanks Andrew.  I will calibrate the motors with the higher voltage one on my ETX105 and see if that solves it. 
 

Should I be concerned at all using a 13.7v battery?



#6 Thrifty1

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Posted 24 May 2022 - 07:21 AM

Andrew - calibrating motors made no difference unfortunately with the higher voltage battery. 
 

When I use the smaller Talentcell battery and a test alignment inside  the telescope moves to where Arcturus is in the sky (first photo). 
 

When I use the larger Talentcell battery and do the exact same alignment (even after calibrating motors) the telescope keeps moving past where Arcturus would be and I turn off the telescope before the OTA hits the base ((2nd photo). 
 

if I get a chance later today I can try to train drives with the larger battery and see if that makes a difference. 
 

 

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#7 Thrifty1

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Posted 24 May 2022 - 07:56 AM

It may just be my ETX105 has an issue with its voltage regulator or something inside. When I do the exact same experiment with both of my ETX125 telescopes they slew to the exact same position with either battery.

I’ll just have to remember to use the batteries closest to 12v with my ETX105.

#8 astrokeith

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Posted 24 May 2022 - 08:16 AM

You could use something like this...

 

https://www.amazon.c...0NsaWNrPXRydWU=

 

There are cheaper ones, but these are good.

 

You would always have the same 12V for your various scopes, regardless of which battery you are using. It will also mean you can drain more from the battery as it will work down to 10V



#9 Thrifty1

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Posted 24 May 2022 - 09:11 AM

Thanks Keith - I’ve looked at similar ones and saw comments that you need at least 2v of drop down for them to work properly. Maybe my 13.7 to 12v drop is close enough?

#10 astrokeith

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Posted 24 May 2022 - 10:52 AM

Thanks Keith - I’ve looked at similar ones and saw comments that you need at least 2v of drop down for them to work properly. Maybe my 13.7 to 12v drop is close enough?

The old fashioned linear type regulators did need some head room.

 

This is a switching type, and needs none, indeed it even steps up! Any input voltage between 10V and 36V will work.



#11 Thrifty1

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Posted 24 May 2022 - 01:04 PM

The old fashioned linear type regulators did need some head room.

 

This is a switching type, and needs none, indeed it even steps up! Any input voltage between 10V and 36V will work.

Awesome - thank you.



#12 Rayh

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Posted 26 May 2022 - 05:20 PM

Amazon sells a cheap little device called a Drok Buck Boost converter that will hold a battery voltage constant from 5-35 volts input to 5-35 volts output.  It only handles about 5 amps but that should be enough for a Meade.



#13 Thrifty1

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Posted 28 May 2022 - 09:20 AM

Amazon sells a cheap little device called a Drok Buck Boost converter that will hold a battery voltage constant from 5-35 volts input to 5-35 volts output. It only handles about 5 amps but that should be enough for a Meade.


I saw those and they have mixed reviews. I’d rather pay more for a good high quality one to protect the telescope electronics.
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