# Wireless batteryless TPMS

#### YairK

##### New Member
Hello everybody,

I am doing a report about wireless TPMS, and I heard about products (the sensors in the valves) that do not need batteries at all to operate and transmit the data. Is that correct??
there are all sort of energy harvesters mechanisms that generates power from vibrations or pressure (piezo-electric, electromagnetic, active RFID, etc.).

I am trying to understand whether TPMS are becoming battery-less, and if so, with which mechanism?

Yair

#### rjenkinsgb

##### Well-Known Member
I've not seen any batteryless ones, or not so far.
The ones I've seen all have a small lithium cell inside the moulded casing.

The battery life is good and they generally outlive the tyres then get replaced.
Most manufacturers do not want to sell something that will never need replacing!

#### YairK

##### New Member
Thanks for the info.

But it can be a great advantage selling a product that doesn't need maintenance, will probably be lighter, and maybe cheaper.

This company has a product, but it is very expensive: http://www.stackltd.com/tpms.html

#### gophert

##### Well-Known Member
I've not seen any batteryless ones, or not so far.
The ones I've seen all have a small lithium cell inside the moulded casing.

The battery life is good and they generally outlive the tyres then get replaced.
Most manufacturers do not want to sell something that will never need replacing!
The listed lifetime is 6-years so that is about half-way through a second set of tires at the industry average 12k miles/year and 50k per set of tires (those are averages - I don't need to hear how your tire lifetime is better or worse).

#### Nigel Goodwin

##### Super Moderator
Very interesting gophert.
When saying "wireless charging system" you mean that the user will recharge it once in a while? or did you meant that a recharging system will be set on the chassis in front of every wheel?. If you meant the latter, than there is also a solution in the market to recharge/operate the system using RF reader. the sensors will be some sort of RFID tags that will get charged from radio waves.
.
It all seems pretty pointless, the current system with non-rechargeable batteries lasts 6+ years, a rechargeable system is unlikely to reach that age, never mind exceed it, before the batteries need replacing.

#### YairK

##### New Member
Thanks Nigel Goodwin, but are you saying that "energy harvesting" is not effective? we should never use rechargeable batteries?.
What about using Super capacitor? they have longer life span than that of a battery.

#### Nigel Goodwin

##### Super Moderator
Thanks Nigel Goodwin, but are you saying that "energy harvesting" is not effective? we should never use rechargeable batteries?.
It's effective in the right place, as are rechargeable batteries, but the right place isn't in a TPMS where non-rechargeable batteries give longer life.

What about using Super capacitor? they have longer life span than that of a battery.
I suspect you would be sorely disappointed, both in Super caps performance, and in their lifespan.

A non-rechargeable Lithium battery has a nice flat discharge curve, and a long life - Super capacitors have neither.

A good place for a Super capacitor (or multiples) is across such a lithium battery, so as to supply high current pulses which the Lithium can't.

#### YairK

##### New Member
Super capacitors have neither.
Not sure it is correct, SuperCaps can last 10-15 yrs if used properly,
see here https://batteryuniversity.com/learn/article/whats_the_role_of_the_supercapacitor.
also,
The supercapacitor is often misunderstood; it is not a battery replacement to store long-term energy. If, for example, the charge and discharge times are more than 60 seconds, use a battery; if shorter, then the supercapacitor becomes economical.
So maybe it is a good alternative for a battery.

But...after reading the info from the link I shared, I now afraid that if the car won't move for a month or two, the super capacitor will discharge completely, making the entire system drained and not functional anymore. is that make sense?

#### Nigel Goodwin

##### Super Moderator
Not sure it is correct, SuperCaps can last 10-15 yrs if used properly,
see here https://batteryuniversity.com/learn/article/whats_the_role_of_the_supercapacitor.
also,
In practice Super capacitors don't have a great lifespan.

So maybe it is a good alternative for a battery.
In my opinion they are pretty useless as a battery, as they don't provide anything like a stable voltage.

But...after reading the info from the link I shared, I now afraid that if the car won't move for a month or two, the super capacitor will discharge completely, making the entire system drained and not functional anymore. is that make sense?
Yes, it's a bad choice - and while existing battery based are so good why try and change it?

#### YairK

##### New Member
and while existing battery based are so good why try and change it?
I am bringing an answer from the web:
Because the direct TPMS is separated from the computer or the car, it can work with batteries or by a system of electromagnetic induction creating electricity. In addition to solving the battery short life, induction allows the TPMS to generate information faster and it decreases the weight of the sensors.
source: pmctire.com
* I think they mean "faster" then an indirect TPMS, which uses the ABS system to calculate the pressure, and it takes 20-60 minutes to get updated.

#### Cicero

##### Active Member
I bought one from China, cost about £20-25, four external mounted sensors, and a dashboard mounted display with a solar panel on top to keep it charged.
Hmm nice, I'll look into those. Was always too sceptical about them.

#### YairK

##### New Member
Thanks everyone for your answers, but I still can't reach a conclusion about that industry- "battery-free TPMS".... is it just a ferry-tale??

#### Nigel Goodwin

##### Super Moderator
Thanks everyone for your answers, but I still can't reach a conclusion about that industry- "battery-free TPMS".... is it just a ferry-tale??
Presumably you mean 'fairy tale' - and I would say so, particularly for general use. There's no advantage to what you suggested, and it's likely to be more expensive and have a shorter life than a battery.

#### YairK

##### New Member
I knew I should double check "ferry" !!