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How to connect 5V USB heated pads in series Answered

Hi all,

This is my first post here. I ride a motorbike and would like to do a DIY heated trousers and jacket. I found these pads 30cmx30cm that run off 5V usb sockets. I want to put 4 in my trousers and run them in parallel so I only have one connector to plug in whenever I ride. Is this even possible with USB ports or would I need another connector?

Heated pads: https://www.aliexpress.com/item/32963771423.html?spm=a2g0s.9042311.0.0.78504c4dTlpjMr

Thanks,

Discussions

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Orngrimm

22 days ago

Serial would be best as you could wire 3 in serial and hook up to your 12V of the bike and get 4V instead of 5V to each pad. They would run on 80% capacity. Normally thats enough.
Alternatively, you could DC/DC-Buck it to get 5V from your 12V and go all in parallel.
The Ali-Listing does not state what wattage or amperage they are. So i go with 2.1A as this is what a guy in the comments noted he used to drive them.
4x2.1A + Headroom = 10ish Amps...
something like the 15A-Version of https://www.aliexpress.com/item/4000086535439.html... should do the trick.
However, i would NOT suggest to run 10 Amps thru a cheapo chinese USB-plug. Take a proper industrial conenctor which is rated for 12+ Amps.

So basically you have:
[12V-Plug to bike]-----[12-24V to 5V DC/DC]---|---[Pad 1] left leg
..........................................................................|---[Pad 2] left leg
..........................................................................|---[Pad 1] right leg
..........................................................................|---[Pad 2] right leg
or
[12V-Plug to bike]-------|---[Pad 1]-------[Pad 2]-------[Pad 3] left leg
.....................................|---[Pad 1]-------[Pad 2]-------[Pad 3] right leg

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Jack A LopezOrngrimm

Reply 22 days ago

In the comments, on AliExpress's page for this item,

https://www.aliexpress.com/item/32963771423.html

did you notice the one with pictures from someone who put a meter on this thing? It was posted on the fourth of July, "04 Jul 2019 12:04"

Two measurements, made via one of those little USB power measuring gizmos:
{5.28 V, 1.58 A} and {5.26, 1.83 A}

Divide to get a quantity with units of resistance. Or multiply to get a quantity with units of power.

(5.28/1.58) = 3.34 ohm, (5.28*1.58) = 8.34 W

(5.26/1.83) = 2.87 ohm, (5.26*1.83) = 9.63 W

By the way, the expected power de-rating for a resistive heating element, depends on the square of the voltage. For example: use 4 volts instead of 5, and get 0.64 = (4/5)^2 = (16/25) times the power dissipation.

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OrngrimmJack A Lopez

Reply 21 days ago

Ah. Didnt see the picture. Thanks for this. My assumed 10ish Watt in that case werent so bad then ;)

Yes and i am ashamed by the error i made with the 80%. As an el-ing thats shamefull for me :) Of course thats wrong and your calc is correct. Thanks for pointing this out.

However, i stand by my point: I have a USB-heated west myself and drive it with 3.8V normally to stay cozy warm. Thats why i stated that even 4V would be propably enough in this case as its still 2/3 of the heating power. 5V was really on the hotter side of things and i had to DC/DC it down for longer term use...


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Jack A LopezOrngrimm

Reply 21 days ago

Yeah. I read what you're saying. It is still turning electricity into heat, at any non-zero voltage.

Actually, for any of these electrically heated garments, it is probably a good idea to include a DC-to-DC converter, so the user can sort of throttle the power (as heat) output to level that is comfortable, or to a level matched to how cold it is outside, or even just using less power to make the battery last longer.

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Downunder35m

22 days ago

No specs, no requirements, so I have to assume the pads won't use more than 500mA each.
If you get a 5V buck converter that is capable of 3-5A you can plug them in there.
Might be worth though to use a different type of connector or a slightly modded USB hub.

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OrngrimmDownunder35m

Reply 21 days ago

1.5A-Range each. See the comment of Jack A. Lopez.

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RichyA1

23 days ago

My motorbike runs off 12v