How do the tire pressure transmitters stay powered?

[Iowa4Runner]

After reading about the tire pressure monitoring system on the latest 4Runners, it appears that each tire periodically sends a signal to the mother ship that the pressure is OK. So, if you leave the spare in the garage does it really turn the warning light on?

Somebody said the pressure sensors use lithium ion batteries, which strongly suggests there is a system in place to recharge them. Anyone know how that works? I suppose the sensors could include some kind of bump / rotation powered magnet and coil assembly. Interesting...

Mike

 

[NoDak]

there is a thread way back about the sensors with pick of the actual sending units attached to the rim. they are just a the valve with an extra end piece that contains the battery sending unit attached to it.

if you read in the owners manual, whenever you replace the tire, you are suppose to replace the valve stem/senosr unit according to a table of scenarios.

 

[Iowa4Runner]

I read all the pressure monitor theads I could find, but didn't see any pics or anything that explained how the batteries get recharged.

 

[dcampen]

TPM batteries

but didn't see any pics or anything that explained how the batteries get recharged.

They don't get recharged. When they run down they have to be replaced. It is like the coin battery on the motherboard of your PC.

 

[Iowa4Runner]

Lithium batteries would make more sense because Lithium Ion batteries have a much higher self-discharge rate and are not used as primary cells.

Does anyone know how long the batteries last and what happens when they get weak?

 

[leftyrb]

Does anyone know how long the batteries last and what happens when they get weak?

I read on a different site that the batteries used in many type of tire pressure monitoring systems are said to last 10 years.

 

[Iowa4Runner]

10 years is pretty impressive.

 

[aj884runner]

Tire Pressure Sensors

I`ve seen the tire pressure sensors on the Caddillac CTS. They are a small unit attached to the valve stem on the inside of the rim. If you get new tires at a tire shop make sure you tell them the tires have this feature since they can be easily broken. The Caddy`s have a display monitor which shows the pressure of each individual tire and is very accurate. This being said, I assume that the sensors constantly send a signal to a computer (body computer?)via radio signal. The computer probably looks for a signal at certain intervals.

 

[ToolmanJohn]

How about-

Some kind of magneto driven power source similar to the kinetic wristwatches now available? They could dispense with the batteries altogether, and the stem would not have to be replaced unless damaged. Every time the wheel rotates it could send a signal to the reciever "I'm still ok".