12V Rail Sag from heaters?

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12V Rail Sag from heaters?

Postby DavidYon47 » 2017-Jun-Mon-18-Jun

Now that I have FAN2 connected up for my 13S, I notice that when the heaters are active, the fan slows down. Most noticeably when the bed heater is on (duh), and to some extent when the hot end is heating up.

Is there such as thing as bringing in a second 12V rail from the power supply that's dedicated to the bed heater? Seems doubtful but figured I'd ask.

I don't notice anything awry besides the subtle fan speed change, but it makes me wonder what else happens when +12 sags.
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12V Rail Sag from heaters?

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Re: 12V Rail Sag from heaters?

Postby RetireeJay » 2017-Jun-Mon-20-Jun

There are many posts about using a separate power supply for the heated bed. But if your power supply has enough watt capability (more than 350 watts) and if you have connected it to the Printrboard correctly, the voltage sag should be very minimal.
"Connected correctly" depends on what kind of Printrboard you have (Rev D or Rev F) and exactly what kind of power supply you have. The typical case these days is a Rev F board, which has a 6-pin connection for power. In that case, you should be using the 6-pin connection from the ATX supply.
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Re: 12V Rail Sag from heaters?

Postby DavidYon47 » 2017-Jun-Mon-21-Jun

Interesting. I ordered the 4-to-6 pin adaptor cable from Printrbot, and got a cable with 6 pins on each end. Even worse, the positional polarity of the new board's 6-pin connector is reversed from what's on the 4. I have the printer connected with the extension cable they (at least used to) sell that allows you to easily get the power supply out of the way. I don't have a similar cable for 6-pins.

So I ended up cutting/soldering/heat-shrinking the original 4-pin from the printer end to the 6-pin at the board end, making sure the polarity was correct. Killed a good 90 minutes sorting all that out.

The supply is the 400W ATX that Printrbot sells. I guess I'll put a 6-pin extension cable on my low-priority to-do list. If I can buy one that would be great, worst case I can fabricate one.

For the moment the printer seems to be working fine.
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