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FreeTrack Forum > FreeTrack : English Forum > Support : Tracking System > Can't find PTC's anywere.

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Blindasabat #1 02/10/2011 - 16h57

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Hello,

Since I got my new headset and have a new camera on order I want to build a usb powered clip like the one Ben Meijer made.

http://forum.free-track.net/index.php?showtopic=1856&page=2

I found most of the stuff I need, even those plantsupports at the local gardencenter, but I can't find PTC's anywhere, at least not the ones with the correct values (Ihold=  75mA, Itrip= 250mA). Farnell has PTC's that come close, but they don't deal unless my order exceeds €50,-.

Is there anyone who has those PTC's so I can buy a few from and mail them to me? I only need 3 or 4 of them, I live in the Netherlands.
Edited by Blindasabat on 02/10/2011 at 16h59.
Steph #2 03/10/2011 - 16h04

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Hi,

you don't need PTC's for the mount. It's an additional security.
To be on the sure side use a USB charger. You can get them for less then 10€.
Blindasabat #3 03/10/2011 - 19h07

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Hi,

I have thought about that, but my headset is usb too and I want to make a nice and practical setup with my pointmodelcable right along with the headset usb cable connected to the front usb ports of my computer. If I'm going to use a charger I need to separate them and use a longer cable. And not using a PTC seems risky. Would a normal fuse work also?
Edited by Blindasabat on 03/10/2011 at 19h09.
dewey1 #4 03/10/2011 - 20h56

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Fuse are to slow reacting. By the time a fuse would "blow" the damage to the PC may already have been done.

A PTC is basicically a thermistor that has a Positve Temperature Coefficient.
Hense the PTC acronym. Basically a temperature controlled resistor.
The resistance increases with temperature as a result of the current rising.

They are also known as Poly Switches.
See here;
http://en.wikipedia.org/wiki/Resettable_fuse
Steph #5 04/10/2011 - 15h40

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When using the USB port on motherboard you better get them.
Although I'm not a great friend of that kind of USB handicrafts:

Some non-standard USB devices use the 5 V power supply without participating in a proper USB network which negotiates power draws with the host interface. These are usually referred to as USB decorations. The typical example is a USB-powered keyboard light; fans, mug coolers and heaters, battery chargers, miniature vacuum cleaners, and even miniature lava lamps are available. In most cases, these items contain no digital circuitry, and thus are not Standard compliant USB devices at all. This can theoretically cause problems with some computers, such as drawing too much current and damaging circuitry; prior to the Battery Charging Specification, the USB specification required that devices connect in a low-power mode (100 mA maximum) and communicate their current requirements to the host, which would then permit the device to switch into high-power (up to 500mA max.)mode.

Wikipedia

Therefore even a PTC doesn't prevent of problems.

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