1.5V AA batteries - real voltage? Wireless thermostat.

Noting that it is now working with new batteries. However I am not convinced that the batteries were the issue as the display still showed plenty of battery life.

Can't be bothered to change back and do further tests.

Cheers

Dave R

In or out of the unit? What is the voltage with the batteries under load in the thermostat?

It depends on the temperature, the load (amount of current drawn by the load) and the age of the battery within the equipment.

See a typical data sheet for a alkaline AA battery (the graphs at the end of the document)

Often there a pairing process you have to perform - consult the instructions.

A new Alkaline cell can have an open circuit Voltage ( strictly EMF) of up about 1.6 V if it is of better quality - purer chemicals, especially manganese. Allow for you meter accuracy and ….

Once in circuit and under load, the current through the cell internal resistance will cause a drop in the reading - depending on the load, condition of the cell etc.

The actual zero-load voltage of a new alkaline battery ranges from 1.50 to 1.65 V, depending on the purity of the manganese dioxide used and the contents of zinc oxide in the electrolyte."

"A cell is considered fully discharged when the voltage drops to about 1.0 V"

Paul

Almost no appliances can run on cells of 1.1v. Most die around 1.3 - 1.2v. Some clocks go lower.

I'd have thought modern devices should be able to cope with Rechargeable at around 1.2v per cell. In your case the real test is what the batteries measure on load. Most partly used dry cells go back to full volts off load as the issue on load is less electrode in contact with the electrolyte, or internal resistance. Brian

Maybe its the battery connectors then, getting tarnished. This happens even when the current is minimal, either due to dissimilar metals or oxidisation. How many old torches did you have to bang to get the bright light back, after all, a lot. Brian

Although my wireless mouse surprises me every time I change the 2 AAA batteries - they each measure about 850mV no load.

I once saw a 'battery saver' circuit, for extra low consumption items, where a sort of charge pump circuit boosted the input to output voltage. It would squeeze the last bits of charge out of a battery.

Joule Thief

Very few old style zinc carbon or even managenese dry cells ever exceeded 1.5v. Their nominal 'flat' point is around 1v.

Wot de man is saying is that 2 x 850mV = 1.7v which is well within range. Silicon transistors give up at about a volt, really.

Its hard to design any electronics that will work below 1V. Above that you can pump to kilovolts if you want..

What type of transistors do you have in mind?

Bipolar silicon transistors had a base threshold of 0.7V Germanium transistors are still available but I suspect at a cost.

MOSFETs can have a tailored threshold, even negative (depletion type) thresholds so there is really no ultimate limit.

Yes, hence Electronic design engineers do still command a modest remuneration despite a diminishing demand.

It depends on your speciality. Someone versed in low voltages might struggle to design a HV transmission system.

There is quite a jump, from a volt of so to kilovolts, so not very comparable.

Electronic flash units manage it. 6V (typically four AAs) to many kV.

Quite, and how would you start to design a source of "many kV" to drive a few LEDs?

My assertion/question was more about comparing the designing of a power supply with say a 1V source and one of a few kV as per TNP claims.

That's it, thanks..

I used to design large FPGAs where the core supply voltage was 0.7V. Only the interfaces to the outside world ran at higher voltages.