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I have a wall of 8 windows using battery operated motors (8 AA batteries in a long tube). I am looking to run these off a DC power supply instead.

I can't get the exact specs on the motors, but a Reddit user who successfully converted his were 12v with less than 1amp peak draw.

Can I wire these in parallel using three 18/2 runs? The longest run is 47 feet to the power supply (running them through the attic and back down into a furnace closet). Here's a picture from before the wall was finished and the path of the three runs I would take if running multiple motors (wired in parallel):

enter image description here

I am looking at connecting each of these lines to this 12V 20amp power supply:

https://www.amazon.com/dp/B078RTV41D/ref=cm_sw_em_r_mt_dp_U_VbDRDbEWJGRA7

And this wire:

https://www.amazon.com/dp/B01J4E0KO8/ref=cm_sw_em_r_mt_dp_U_6gDRDbEWEBMCN

Or would I need to run 8 separate wires and connect them to an 8 channel power supply like this one?

https://www.amazon.com/dp/B0069MIBLS/

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  • \$\begingroup\$ You can use a supply with significant less amperes if you do not run all your motors at the same time. \$\endgroup\$
    – Oldfart
    Oct 21, 2019 at 15:51
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    \$\begingroup\$ I wouldn't call it a good design even if the battery pack can provide this current. Your wires will be long and will carry relatively high current in your use-case dropping much of voltage. Better get individual supplies near each motor. \$\endgroup\$
    – Eugene Sh.
    Oct 21, 2019 at 16:01
  • \$\begingroup\$ @EugeneSh, oops, I didn't clearly state that the goal is for them to not run on batteries anymore. Edited my post to be more clear about that. \$\endgroup\$
    – spockdude
    Oct 21, 2019 at 16:08
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    \$\begingroup\$ Still better split it off a higher voltage power supply (mains?) and have individual adapters for each motor to minimize the voltage drop on the low voltage wires. I think. Well, and these will be probably cheaper all together than one 20A adapter. \$\endgroup\$
    – Eugene Sh.
    Oct 21, 2019 at 16:10
  • \$\begingroup\$ @EugeneSh, since the wall is now finished with insulation, etc, the smaller low voltage line would be easier to fish through the wall. Also, I don't want to have exposed outlets and adapters in the window openings. It seems like hiding the low voltage lines behind the blinds will be easier. \$\endgroup\$
    – spockdude
    Oct 21, 2019 at 16:37

2 Answers 2

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If you wire it as you have shown, with three individual runs going up to your AC->DC converter, yes, probably.

18 gauge wire has a resistance of about 0.0062 ohms/foot (see this table and convert from ohms/meter). So your 47 foot run will see about 0.6 ohms round trip; that works out to a voltage drop of about 1.2V, which is only 10% of your starting voltage.

Be sure to fuse everything properly and generally make the thing to code so that your insurance company won't have an excuse to deny your claim if a grease fire breaks out on the opposite end of the house. What's "correct" would be a question for the diy stackexchange, and of course varies according to your local laws.

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  • \$\begingroup\$ when you say to "fuse everything properly", does a power supply that says "Safety features: Automatic overload cut-off, over Voltage cut-off, automatic thermal cut-off, short circuit protection" fulfill this requirement? It doesn't say anything about having actual fuses that can be replaced. \$\endgroup\$
    – spockdude
    Oct 22, 2019 at 22:25
  • \$\begingroup\$ Actually, I mean do it to local code, or if you live someplace where local code doesn't mean anything, do it according to your own sensibility or whatever makes your insurer happy. You're probably OK, if the power supply lives up to its promises, but -- code. \$\endgroup\$
    – TimWescott
    Oct 23, 2019 at 0:04
  • \$\begingroup\$ Thanks @Tim. I've been trying to figure out if Utah has any codes for low voltage work, but so far all I've found is that low voltage installers don't require any special business license. But, yeah, definitely trying to go as sensible and safe as possible. \$\endgroup\$
    – spockdude
    Oct 24, 2019 at 3:47
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Just for anyone else searching for this issue, as a master installer of motorized window coverings, I can tell you that you can run it on the smaller wire for the shorter pulls (generally up to about 20 feet), but the longer the wire, the less power to the motor as mentioned by others. The big problem with that is the motors running on the longer wire will be noticeable slower. So your shades up above will go up much faster than your shades below. If the wire run is too long for the size of the wire, the motor will not work properly and will short the memory generally causing the electronic limits to be lost which can cause all kinds of other issues (damage to shade and possible motor). Almost all manufacturers recommend 18g over 15 feet up to 100 feet. Then you need to go to 16g.


I do want to clarify that my above answer was based on your motor running at 1.5 amps which a few manufacturers use. Most battery powered motors run between .8amps and 1.2 amps. In which case you can go further with the smaller gauge wire. For example, old Hunter Douglas motors and smaller Somfy motors run at .8amps and you could run 22g wire for up to 40 feet. I generally use 20g wire for most battery powered motors that are 1.1amps or less and can get up to about 50 foot runs. This helps keep the motors running at full speed. Some motors now have adjustable speeds, so if some are running faster than others, I just slow them down so they are all similar. Hope this helps others.

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