Hitchcocks Forum

This is driving me nuts. I had a problem with the GPS switching off while riding the bike. Changed the settings on the GPS to not switch off when power is removed seemed to solve the problem and the cause was put down to vibration. The GPS works OK now.

New problem. When running the GPS it drains the battery after about 30 miles meaning that Thumper runs out of power and stops. Battery is drained.


I have measured the GPS power usage, using a mutimeter. It draws 6,8 volts and 0,6 amps with the GPS' internal battery fully charged. About 4 watts.

Could that really be enough to drain my battery while running the bike with lights on (as the law here demands)..?



It happened the other day. I was lucky enough to find a boat yard with a charger and they very kindly helped me out. I rode home with both lights and GPS turned off and got home with a still fully charged battery.

Thumper is a classic 500 bullet from 2003, the GPS is a Tomtom Rider.


Any ideas lads?

Now I'm no electrics whiz but you can't draw less than 12 v from a 12v battery can you?

I don't get the 6.8 volts ? with sat nav off what voltage do you get from the battery with the engine running lights off, and what voltage with lights on

If the 6.8v is being measured at the end of the charging lead that plugs into the unit then that might well be correct. The cigarette plug on the lead might well reduce it to that, in common with standard USB chargers. The voltage on the socket on bike that the plug fits into should be 12v.

Ah, I see, transformer in the cig lighter socket plug.

OK. Simple circuit diagram:





Measurements taken across the switch. No cigarette plug. Voltage at the battery is 12.7v (fully charged).

In your diagram the GPS is getting 12.7v. How are you measuring 6.8?

If the plug that goes into the back of the GPS is a micro USB, as most are, and it is connected across the battery as per diagram then I would say it is being over powered. USB charging/ power is a nominal 5v but on your set up, when the bike is running, you will be putting in more like 14v. You need an adapter/ transformer normally contained in the charging plug. If the voltage at the switch with the GPS connected is 6.8v then the GPS is severely pulling the battery down hence your problems. There also ought to be a fuse before the switch.1 amp should be sufficient. I would make certain the GPS is being supplied with the correct voltage and not being over cooked.

Do you have the correct cigarette lighter outlet with the correct plug?

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Thanks Frank and Leon. I'm going to rewire and refit with a cigarette lighter plug and see if this helps. I'll fit a fuse too..


Let's leave it there for now and I'll get back to you all at a later date.

Many thanks to all of you above.