Help cut plug off charger

lasvegas · Occasional Visitor Joined: Dec 28, 2005 Posts: 1

Can you hard wire the tom tom one?
I have cut the plug off my tom tom one so i can hard wire it to my cigarette lighter and found that there is 3 wires.Red,black and white.
Is the red positive,black negative,what is the white wire for and how do i connect it

Andy_P · Posted: Wed Dec 28, 2005 6:38 pm Post subject:

STOP!!!!!!!
What you are trying to do will fry your TomTom!
The TomTom works on 5 Volts, and the supplied cigarette lighter adaptor reduces the 12 Volts from your car battery down to 5 Volts.

What you need to do is rewire it back as you found it, quick.
If you want to do a neater install, buy a cable mounting cigarette socket from Maplins or some car accessory shops, and wire that in parallel with your existing socket. Then plug the complete TomTom adapter into that and hide it all behind the dashboard.

JimmyTheHand · Frequent Visitor Joined: Apr 16, 2005 Posts: 386

Andy_P · Posted: Wed Dec 28, 2005 6:40 pm Post subject:

For more info on how to put it back together, look here:
http://www.satnav-shop.com/index.php?ln=en&pg=6&sec=9

Frazz · Posted: Wed Dec 28, 2005 6:40 pm Post subject:

Not sure why there are three wires, but the adaptor also reduces the votage from 12V to 5V so if you wire it in directly you will fry it Exclamation

Frazz

Frazz · Posted: Wed Dec 28, 2005 6:45 pm Post subject:

Looks like we all got alarmed by this post at the same time - let's hope it isn't too late for lasvegas 8O

Frazz

Andy_P · Posted: Wed Dec 28, 2005 6:59 pm Post subject:

The white wire is a voltage "sense" wire that measures the voltage actually at the input to the TT and sends it back to the circuit which adjusts it's output to allow for loss down the cable.
A common fault (a while back) was that the sense wire broke in the plug so the supply thought the voltage was low and increased it, thus frying the unit.

Oldboy · Posted: Wed Dec 28, 2005 9:59 pm Post subject:

Frazzle · Regular Visitor Joined: Nov 05, 2004 Posts: 66

The white wire, as has already been stated, senses the voltage at the point where it eneters the TTG (the plug) Any voltage drop caused by the current flowing through the thin copper supply cable is detected and compensated for by the switching regulator.

When you remove the TTG from the cradle or power plug you remove the load and no current will flow. The sense wire sees a healthy 5v at the plug so all is well. Voltage drop will only be present when current is drawn.

When the white wire failed I understand that the switching regulator received no voltage sense input from the white wire so "thought" WOW there is a lot of voltage drop along this cable.... I'd better up the voltage a bit at my end to compensate.... this continued until it topped out at MAX volts out, which effectively supplied approx 12V to the TTG connector and TTG = very bad for the TTG.

The sense wire idea is common on high current xcomputer power supplies but if I'm hionest i think it's a bit OTT for a 5V 2A feed to a TTG Smile

The solution to the old "broken sense wire" fault was to connect the switching regulator sense input directly to the 5V supply output and disconnecting the white wire completely. This works well.

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