TPMS battery replacement - Maxell CR2450HR EX battery

[Zucca]

TPMS and safety?

There are two tire families: regular and run flat.
Regular: better on gas mileage, in case of puncture you need to stop the journey immediately with the risk of loosing control of vehicle (TPMS does help but does not solve the problem at all here)
Run flat [RF]: tire shoulders are reinforced, in case of puncture you still have 100Km or so to reach the tire shop at low speed. They offers much better handling in case of failure. There is no free lunch, it requires more energy to rotate that tire on the road (bad gas mileage).

Problem is a low leak (or even a high leak sometime, if the driver is a old lady) in a RF tire is not necessary noticeable by the driver --> danger --> TPMS required by law.

What also push the TPMS law was the CO2 emission. If you ever tried a flat tires bike, you know how much tire pressure is important on energy efficiency. TPMS will warn you not only if your tire is leaking but also if it is low on pressure --> that's why in winter with low T a lots of bing "check tire pressure" warning are displayed on cars.

Please note:
- every 10C it means about 0,1 bar variation in the tires.
- a perfet tire with no damages loose about 1 bar/year since it is not a perfect sealed system. (we call it diffusion)

you are smart enough to understand the consequences.

Regarding pairing, a good TPMS should recognize a new set of wheels without any extra tool. In our system we had 8 position in memory for the tires, 4 for sommer and 4 for winter tires for quick detection. If the set was not in memory it took only longer to get accepted by the ECU. You should do a TPMS reset anyway in case of changing tire, should be RTFM.

[DavidAlfa]

"A good TPMS should..." What? .
Remember that the brand usually fu**s it up the most possible to force you going to the dealer stealer and stab you in the liver.

[coppercone2]

I just soldered a 2450 by leaving it in the freezer then soldering one side and then putting it back into the freezer and soldering the other side afters its cold and then putting it back into the freezer. the voltage looks OK but I have no idea what damage I caused.

it is for a coin cell backup inside of something in a thick box that I don't really care about too much so I think it will be ok.

[Zucca]

"A good TPMS should..." What? .
Remember that the brand usually fu**s it up the most possible to force you going to the dealer stealer and stab you in the liver.

Not the one I designed between 2006 and 2011.

[coppercone2]

my coin cell has been in circuit on a RTC for a few hours now after soldering and there is no explosion or nothing

I watched a youtube video on heating a coin cell, he used good solder contact on a big iron for 1 minute before it popped, my solder operation took maybe 3 seconds, you can do it with less also if you scrape it a little bit to activate the metal. I think it will be fine for a while. I don't know if pre-cooling helps or hurts.

On a normal power battery this is a bad idea because it has high surge current, but on a RTC its practically nothing, I don't think its being degraded alot. I think so long its in a metal enclosure you are OK.

[Fraser]

The issue with soldering button cells is that of melting the plastic seal between the positive shell and the negative contact. Any damage to that seal is a possible cause of cell leakage and all that such entails. Explosion of the cell is not normally a risk if the heat is not applied for an excessive period of time. There is also concern about the effect of the high temperature at the contact surface on the internal materials. Excessive heat can degrade those chemicals in the locality of the 'hot spot'

The spot welding of tabs onto cells is the traditional method of 'hard wiring' them into a circuit. The spot welding process does generate localised heat in the casing metals but such is not normally enough to do any harm. Direct soldering is frowned upon by the cell manufacturers and this is understandable as some people may not prepare the surfaces and solder to them quickly enough to avoid damage to the cell.

IMHO, with battery tab welders from China now costing less than £20 in the UK, it is well worth spot welding nickel strips to cells and avoid direct soldering and the issues that can result. The Mini Welder is discussed on this forum. If you want a better battery tab welder, then the KWeld is a good choice. I bought a Mini Welder to play with and, after some important modifications, it works very well off of a 12V car battery.

Fraser

[DavidAlfa]

I tried that years ago.
After 2-3 seconds, when the solder began to stick to the surface, the battery started leaking and bubbling.
I never tried again, bought batteries with soldered tabs when needed.

[oasis2020]

Soldering the battery with a soldering iron requires acidic flux.
Clean the welding surface well and use the least time for welding. I do it all the time, nothing out of the ordinary.