Voltage Quest

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Voltage Quest

Postby bdring » Wed Dec 19, 2012 2:41 am

As I have been adding higher current extruders and bed heaters, I have noticed my voltage is dropping. It has dropped to as low as 10.50 volts with everything on using my mini ATX power supply. I decided to stop by Fry's to see what was on sale.

They had several big ones on sale but they were all basic models. The problem with many ATX power supplies is that they have more than one +12V "rail". You might have a 600 watt power supply, but no one 12V rail can deliver all the amps you want. Overloading one of the supplies can cause the voltage to drop.

I found one Antec 400W Extreme Gamer Partially Modular supply that had one common 12V rail rated to 30amps on sale for about $40. I thought the modular concept might work well for me too.

The wire used on the cords looked to be about 16 awg. When I hooked one of the modular cord to my printer I still got almost a volt of drop. This was due to the resistance in the wire. I found one of the cords had 4 common 12V lines and 4 common ground lines. I tied them all together into one cord and my voltage was now 11.8V with everything on. Because the 12V was all coming from a single source I was able to tie them together. Unfortunately it was not on a modular cable. If I get a mating connector and pins, I think I can go modular.

HCG-400M_1.jpg
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Re: Voltage Quest

Postby orcinus » Wed Dec 19, 2012 3:36 am

Just a heads-up, i had some not-quite-good expriences with Antec PSUs.
Not suggesting yours is going to fail, but keep in mind that it might (there used to be whole batches of them with "counterfeit" capacitors that popped like popcorn within a year).
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Re: Voltage Quest

Postby bdring » Wed Dec 19, 2012 3:42 am

They brag about the quality of their "Japanese" capacitors on the box. Maybe the had a bad experience with non Japanese caps.
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Re: Voltage Quest

Postby nismobg » Wed Dec 19, 2012 6:38 am

I am using CORSAIR TX750M for about 2 months now and its dead on 12V on the rail, It's rated 12V-62A and it's been a god send for now. It's a little pricey at 120$ a pop but well worth it. You can use the other rails too for various tasks.

P.S. The constant 12V is at the RAMPS Terminal.
Last edited by nismobg on Wed Dec 19, 2012 6:28 pm, edited 1 time in total.
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Re: Voltage Quest

Postby bdring » Wed Dec 19, 2012 12:56 pm

My voltage is about 12.2V at the power supply, but 11.8V at the end of the cable under full load. The cable is about 3-4 feet long. It is 4 parallel conductors of 16-18awg for about half the way then about 14awg after that.
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Re: Voltage Quest

Postby nismobg » Wed Dec 19, 2012 6:30 pm

@bdring I used to have a 350W and it was way under performing, My voltage drop was about 0.6V at the end of the line.
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Re: Voltage Quest

Postby r691175002 » Wed Dec 19, 2012 7:17 pm

I have had very good experiences using the Chinese switching supplies. Shipping can take a while so I keep a stack of them around.

You can get 12V/10A for 15$ shipped, http://www.ebay.ca/itm/12V-10A-120W-Swi ... b44&_uhb=1

12V 30A is ~30$ shipped. I've found that a lot of computer supplies don't actually deliver as advertised, at least not when most of the power is being drawn from the 12V lines. I have a 400W supply that for some reason drops below 10V at only a few amps of load.

You can also go up to 24/36V at very low cost with the chinese supplies for higher acceleration.
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Re: Voltage Quest

Postby bdring » Wed Dec 19, 2012 8:00 pm

The nice thing about many of the single output power supplies is you can easily dial up the voltage a few percent to deal with the drop on the power cable. The drop in the cable is basic physics, it does not matter how good your 12V power supply is. Realistically I am not going to hang 12Awg cables off the back of my portable printer.

The stepper motors can run higher, but you will quickly destroy other parts on a controller if you try to run it much above 12V. They have parts sized to the 12V. You might toast your heaters too.
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Re: Voltage Quest

Postby nixtacy » Wed Dec 19, 2012 9:03 pm

r691175002 wrote:You can get 12V/10A for 15$ shipped, http://www.ebay.ca/itm/12V-10A-120W-Swi ... b44&_uhb=1
12V 30A is ~30$ shipped. I've found that a lot of computer supplies don't actually deliver as advertised, at least not when most of the power is being drawn from the 12V lines. I have a 400W supply that for some reason drops below 10V at only a few amps of load.


Not to take away from Barts post;

Of course, While I would not recommend the 10a, I too chose the 30a for about $30 shipped.
Once it got in, and what I really liked about it, was the fact that I can bottom mount it as part of the printer, and that I didn't have to rewire it at all. The body of the power supply has several threaded inserts on the bottom, and sides, to allow me to mount it. I had to clearance the washers to prevent them from interfering with my V-wheels. (minimal at best) Electrically, the only thing I have done is used a common 120v/30amp wall light switch to be my master/emergency power on/off.

PS, don't make fun of my printers legs. Even unpowered, there was far too much wobble, so I created L-Angle legs with rubber adjustable feet.

Image

Image
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Re: Voltage Quest

Postby BenJackson » Wed Dec 19, 2012 10:25 pm

bdring wrote:The stepper motors can run higher, but you will quickly destroy other parts on a controller if you try to run it much above 12V. They have parts sized to the 12V. You might toast your heaters too.


I run my RAMPS board off of an old Dell laptop power brick (4.5A at 19.5V). The only downside is that I have to be diligent about holding the duty cycle of the hot end heater below 38% whenever I build a new firmware. The heated bed is run off a different supply (it was a later addition) which is supported by RAMPS.
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