need help with Resistors.

**Rob Withey** · 06-20-2007, 04:45 PM

Originally Posted by psyrex

Yes, the power will fluctuate too much. Actually, just had a thought. Take the 12v and 5v from your PSU and you'll have your 7v. I don't recommend it, but it's been done. Don't blame me if you screw up your PSU, though!

DO NOT DO THIS...!

If your hub ground is actually 5v, then you just shorted out your power supply's 5v line to 0v through the usb cable between the hub and the pc.

**keatonreckard** · 06-20-2007, 04:49 PM

im pretty sure my computers grounds are all the same....(connected)...so that wouldnt work.

**2k1Toaster** · 06-20-2007, 04:50 PM

Originally Posted by Rob Withey

DO NOT DO THIS...!

If your hub ground is actually 5v, then you just shorted out your power supply's 5v line to 0v through the usb cable between the hub and the pc.

Well a simple chopping of the hub's usb cable to take out the ground and +5v, and leave data +/- only fixes that.

But yes, dont do this unless you are extremely lazy.

**v8 scimitar** · 06-20-2007, 04:51 PM

Like the other guys said resistors are the wrong way to do this. A resistor is a current limiting device not a voltage limiting device. It only drops voltage once you have reached the circuits current limit. You cant guarantee the same load all the time so you wont get the same voltage.
Options are buy a proper regulator or buy a new hub.

**Curiosity** · 06-20-2007, 05:11 PM

It's possible that the first component off the 7.5v is a 5v regulator. If you could identify it, you could rip it out and tap in there. But that may not be the case.

**turbocad6** · 06-20-2007, 05:15 PM

stupid question, but have you tried running it off 5v? I've had some 6.5v hubs run fine off 5v...

**keatonreckard** · 06-20-2007, 09:08 PM

Originally Posted by Curiosity

It's possible that the first component off the 7.5v is a 5v regulator. If you could identify it, you could rip it out and tap in there. But that may not be the case.

good idea....ill look in the morning...

**nobb** · 06-21-2007, 09:38 AM

Yea you cant use resistors in this case to drop the voltage. Your hub may be rated at X watts, but it does not always draw that much power. You only use resistors to drop voltage from a device that has a constant resistance, like a light bulb or another resistor. You might want to consider building a voltage regulator. Search up schematics for a lm317, as you can easily build a regulator with that chip.