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Author Topic: 13.7 volt power supply?  (Read 1300 times)

Phil morgan

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13.7 volt power supply?
« on: January 16, 2018, 17:41:32 »

I've been doing the setup and testing of my astroeq and converted CG-5 with a 12 volt Gel battery and everything seems to be working fine 😀
I have a 13.7 volt 3 amp power supply which I'd like to use when setup in the back garden.  Is 13.7 volt ok for the astroeq,  or will I need to step down to 12v with a buck converter or something similar?

Cheers

Phil
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TCWORLD

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Re: 13.7 volt power supply?
« Reply #1 on: January 16, 2018, 17:48:13 »

Hi Phil,

13.7V will be fine.

The AstroEQ is nominally rated for 12V, but will happily run with a supply of 9V to 15V.

Kind Regards,
Tom.
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Tom Carpenter (AstroEQ)

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Re: 13.7 volt power supply?
« Reply #2 on: March 17, 2018, 07:03:43 »

Hi . I would like to ask you for a separate power supply option for the stepper motor and ASTROEQ unit. Can be used one 20 Volt adapter for motor ( for pin "VMOT" and it will be disconnected to ASTROEQ board ) and the other one 12 Volt adapter for the ASTROEQ board thru standard 5,5/2,1 mm connector at the board ?
I need to add some power for my stepper motor because it seems to be weak at low temperature ( gear box oil viscosity in -16 C , my own fork mount ). I am using just 12 Volt power supply and 1,4 Amp per phase settings and DRV8825 drivers. I just think that if the DRV8825 use an optocoupler it can works with independent power supply but I am not sure . Will it be helpfull, will it works ? Sorry for my english.

Peter
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TCWORLD

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Re: 13.7 volt power supply?
« Reply #3 on: March 17, 2018, 09:48:02 »

Hi Peter,

It's technically possible to do that, yes.

You would have to isolate the VMOT pins from the 12V rail, and connect them to the higher voltage. Which traces to cut would depend on which AstroEQ version you have as the PCBs vary version to version.

Furthermore, the 100uF caps on the VMOT pins would have to be uprated. They are currently spec'ed for 25V which gives a nice overhead when operating at up to 15V. For running at 20V, I would swap them out for 35V rated capacitors.
The 0.1uF ceramic caps are already rated for 50V, so those wouldn't need changing.
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Tom Carpenter (AstroEQ)

passing

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Re: 13.7 volt power supply?
« Reply #4 on: March 17, 2018, 11:57:23 »

Thank you for your immediate response. I was planning to isolate the fully stepper motor circuit from the board (by removing the 100uF capacitor). I also do not want to interfere to the board by the cutting of the trace. I wanted to isolate the circuits by bending the pins on the rail. But by replacing the capacitor I will not destroy anything.
The sidereal speed also works at low temperatures. Only with GOTO speeds and low temperatures the stepper motor was no longer in operation. Last night, I tested the functionality with a 2 A setting per phase and 12 volts and all worked at temperatures around 0 C. For the time being, I'm probably not going to deal with it, but with the coming of winter I probably will have to.

Thank You for help and good luck with study !

Kind regards, Peter.

« Last Edit: March 17, 2018, 12:00:23 by passing »
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TCWORLD

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Re: 13.7 volt power supply?
« Reply #5 on: March 17, 2018, 19:56:29 »

Ah, ok, it's the V4.7 you have. For this version the electrolytic capacitors are already rated for 35V, so wouldn't need to be changed.

The regulator on the V4.7 board can handle up to 25V safely, so it should be possible to feed 20V directly in to the 12V input without modification.

The only potential issue is C10 (top left corner by the power connector). That is rated for 25V only, so would have to be replaced with a 100nF 35V 0603 ceramic (or higher voltage rating).
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Tom Carpenter (AstroEQ)

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Re: 13.7 volt power supply?
« Reply #6 on: March 18, 2018, 05:09:17 »

Hi, that's great for me! That capacitors are rated at 35 volts I noticed after sending my post. I'm not a skilled electrician but I can replace the SMD C10 capacitor. I will let you know the result after the replacement and testing. But I can not guarantee ambient temperature -16 C :)

Thank You again for this informations!

Kind regards, Peter.
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passing

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Re: 13.7 volt power supply?
« Reply #7 on: March 26, 2018, 13:07:47 »

Hi. So after testing I can say that my fork mount works well. After increasing the supply voltage to 19,5 Volt (the current is set to 1.6 Amps), not only do not miss the steps of the stepper motor, but I can also achieve a higher GOTO slew speed. The ambient temperature was -6 C. I can recommend the adjustment I made. More power for the stepper motor has solved my problem.

Clear sky for all, Peter.
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