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Delivering ~12v? 12.2? 12.3? DC from a battery?

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#1 mtc

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Posted 27 October 2020 - 01:27 PM

I'm looking at building a portable power supply using a 12V DC battery..

 

On my AC/DC power blocks, my volt meter readings show:

12.01 VDC for my ASI533

12.22 VDC for my Sirius EQ-G Mount

12.38 VDC for my accessories 

 

What's written on each of these bricks is simply '12V' or '12.0V'

 

I plan to use synchronous buck boosters to keep the voltage constant, but what voltage level should I set it at where it would be safe for all of these?

 

Thanks!


Edited by mtc, 27 October 2020 - 01:34 PM.


#2 jdupton

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Posted 27 October 2020 - 01:59 PM

mtc,

 

   You should be good with setting the output of the regulator to anywhere between 12.6 and 13.4 volts. I do the same thing with my battery box which has two synchronous regulators. One is set at 12.8 volts and the other is set at 13.2 volts.

 

   The only consideration is whether you will be using any "12v" computer accessories powered by your battery. Those most often have specs of 12v +/- 5% or 10%. That means a maximum of 12.6 or maybe 13.4 volts. You can run them at the top of the range or a little more but their lifespan can be reduced quite a bit due to internal heat build-up. (These computer devices often use 5 volts internally and dropping the input voltage with their internal regular generates heat. The higher the input voltage, the more heat they generate internally in normal use.) This usually applies to USB Hubs (non-industrial) or power for USB Hard drives or SSDs and such.

 

   All astronomy equipment is usually good to at least 14 volts although there are a few exceptions. Some astronomy equipment is rated up to 15 or 16 volts. In general, your cameras, mounts, and so forth will be quite safe at anything up to 13.8 volts. (My battery box outputs 13.5 - 12.5 volts unregulated directly from the LiFePO4 battery, 13.2 volts regulated, and 12.8 volts regulated.)

 

 

John


Edited by jdupton, 27 October 2020 - 02:02 PM.

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#3 markb

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Posted 27 October 2020 - 02:01 PM

Many power supplies 'float' to a higher voltage if not under load. You may get different figures if you measure voltage when the devices are plugged into the power supplies and running under power.

 

If a device is rated for 12v, that should be the ideal voltage.

 

Please remember auto batteries run about 13.8 voltage and may charge over 14 volts.

 

Most devices made for astro use may tolerate the car voltages but some may not. For example, early Vixen drive controllers emitted the magic smoke hooked up to cars and a particular slew rate was selected, even if the opposite-of-normal polarity was corrected.

 

If using lead acid batteries without regulation to 12.0 volts, ask the device manufacturer.



#4 sg6

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Posted 27 October 2020 - 02:01 PM

You will likely find that anything of 13.2v and less is fine, for the mount maybe higher.

The Skywatcher mounts are stated as 12v, then you find you really need a good 13 volts, and the Sirius is a derivative.


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#5 mtc

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Posted 27 October 2020 - 02:07 PM

ok, so if I set to 12.5V or 12.6V, it will be fine for for these? (being extra cautious here)

12.01 VDC for my ASI533

12.22 VDC for my Sirius EQ-G Mount


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#6 jdupton

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Posted 27 October 2020 - 02:13 PM

mtc,

 

   Yes, 12.5 to 12.6 volts will work for your camera and mount. The mount may sometimes complain (by blinking the power LED as user sg6 implied) when slewing but it will work OK.

 

   When slewing, the connectors and sheer wire length in the power cabling can result in the voltage seen by the mount's motor drivers dropping below 12.0 volts. It blinks the power LED as a warning that you may have marginal power but voltage levels will recover once the slew stops and it goes back to only tracking and guiding.

 

 

John



#7 e7FvPDZR

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Posted 27 October 2020 - 02:16 PM

I'm looking at building a portable power supply using a 12V DC battery..

 

On my AC/DC power blocks, my volt meter readings show:

12.01 VDC for my ASI533

12.22 VDC for my Sirius EQ-G Mount

12.38 VDC for my accessories 

 

What's written on each of these bricks is simply '12V' or '12.0V'

 

I plan to use synchronous buck boosters to keep the voltage constant, but what voltage level should I set it at where it would be safe for all of these?

 

Thanks!

I always set a "12 volt" power supply to 13.8 volts.



#8 mtc

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Posted 28 October 2020 - 07:12 AM

The context provided here is very helpful - thanks!



#9 mtc

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Posted 29 October 2020 - 06:48 PM

Hmm, I'm wondering. Do I need a step-up converter or step-down converter?
A fully charged 12V battery may push 13.x volts but over time may drop to say 12.0 volts..
If I want to target output at 12.6V, I'd need voltage stepped down, but as the battery voltage drops, I'd want it stepped up..

Should a step-up or step-down converter be used?

Thanks!

#10 jdupton

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Posted 29 October 2020 - 07:12 PM

mtc,

 

   You need both. I suggest you search for a synchronous buck-boost converter with seamless zero drop-out voltage operation. 

 

   Many converters (either step up or step down) can only regulate properly when the voltage is either 0.5 to 1.5 volts higher (in the case of step down) or lower (in the case of step up). This is called the drop-out voltage.

 

   In my own field battery box, I use regulators based on the LTC3780 controller chip. These work well and can regulate up or down from the input voltage and exhibit no drop-out range. Amazon has a good selection of such buck-boost converters from a number of suppliers. A couple are linked below. There are others available. Just look at the specs to find that they use the LTC3780 regulator control chip. There are other control chips that also do seamless buck-boost regulation but I have used these and found them to work pretty well.

 

https://www.amazon.com/JacobsParts-Synchronous-Converter-Step-Down-Efficiency/dp/B078KQ63HZ

 

https://www.amazon.com/HiLetgo-Constant-Automatic-Step-Down-Regulator/dp/B082KPGLVQ

 

 

John


Edited by jdupton, 29 October 2020 - 07:13 PM.

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#11 mtc

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Posted 29 October 2020 - 07:38 PM

Perfect - thanks for clarifying!

#12 HxPI

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Posted 07 November 2020 - 12:06 AM

Also cable diameter is a factor. I use 6ft 18 gauge cables that cause a .5v loss. Need to use shorter/thicker gauge cable and/or find a voltage regulator to boost the voltage. YMMV.


Edited by HxPI, 07 November 2020 - 12:08 AM.

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#13 HxPI

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Posted 07 November 2020 - 12:09 AM

I always set a "12 volt" power supply to 13.8 volts.

I do the same and all my astro equipment works just fine. Loss through the cables actually deliver less voltage to the equipment.


Edited by HxPI, 07 November 2020 - 12:10 AM.



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