Laptops, Standby and USB Power Idea

matthewtoney · 06-16-2005, 11:56 AM

Can anyone give me their opinion on why this idea wouldn't work?

I'm designing a carputer around a new laptop - it has very good standby time and I'm planning on simply using the remote on/off switch I've wired up to start the laptop manually whenever I want to use the CarPC, and letting the loss of power and XP's native power management to put the laptop in standby after I've turned off the car. Like many here it would seem though, I've noticed the annoying behaviour in USB where in standby mode on the laptop, it continues to supply 5v power to anything on the USB bus whether I want it to or not. In my case, I have a number of USB devices all going to a small USB2 hub thats externaly powered through an inverter. (in fact, what it does in my case is that the darn hub immediately turns into "self powered" by the laptop when it no longer has external power after I turn the car off)

I REALLY don't want it to act this way as I don't know how much power draw there really is on the laptop's battery by powering the USB devices in standby, but ANY draw is more than I want - I want the standby time on battery to be as much as possible to give me the maximum amount of time that can go by between using the car. (and recharding the laptop again)

Could I not simply take a spare USB laptop-to-hub cable and cut the line used to pass the 5v power? Doing this would mean no devices on the USB bus of the laptop would ever get power but in my case that's what I want since the hub itself is powered by the inverter when the car is on.

Anybody tried this or know of why it wouldn't work??

Matthew

KyleYankan · 06-17-2005, 10:25 AM

could you not throw a relay on that usb cable's 5v? It would allow current to flow when the car is on.

Also, if you disable the USB devices does it stop power? If so, you might be able to rig up a small program.

matthewtoney · 06-17-2005, 10:38 PM

The thing is, although I could put a relay in there, if I am powering the hub externally, you wouldn't think that I would need current to flow on that cable at all.

Yes, I have tried the enable/disable device trick that has been mentioned in other threads on here (and that does seem to work) - I just would like to do this without having to count on that trick.

At this point, it seems like it's worth a try. I'll post back with my results after trying this.