Primarily for general aviation discussion, but other aviation topics are also welcome.
By SimonM
#1889945
In answer to the OP

I always thought it was to do with current.

As the voltage goes down (1.5v down to 1.2V), current goes up and hence damages sensitive electronic equipment.



I am happy to be corrected though.
By rdfb
#1889949
SimonM wrote:I always thought it was to do with current.

As the voltage goes down (1.5v down to 1.2V), current goes up and hence damages sensitive electronic equipment.


Typically the current will go down if the voltage goes down. No risk of damage to equipment unless the designer pretty much goes out of their way to make it otherwise. It is possible with a voltage regulator to increase current as the voltage drops and this would result in constant power draw as you describe, but then the regulator would provide stability so no risk of damage.

In any case, as an alkaline battery gets exhausted, its voltage drops to zero (if connected to equipment that's on). So all battery powered equipment has to deal with the voltage dropping anyway.

The only reason to "require" alkaline batteries is that it reduces the number of people complaining about power related issues. For example, the "battery low" alert will be accurate (instead of getting 30 seconds warning as you might with rechargeables when the electronics is designed to predict remaining battery life using the alkaline discharge curve), you'll get the advertised battery life, and when any battery runs low the equipment will start to malfunction (requiring a reset).

There are other complex differences (eg. internal resistance) but this rarely makes a difference.
By mpk
FLYER Club Member  FLYER Club Member
#1889951
Leaving price out of it, the top in tests by Which magazine are Panasonic Eneloop Pro and Ansmann AA. Amazon Basics also did ok. I wouldn't bother with any others nor take advice off 'reviews' elsewhere.
#1889953
I use and have used non-rechargeable Energizer Ultimate Lithium AA 's in my Lightspeed Zulus for probably the last 5years. I change them roughly once a year as a ritual excercise but never had them go flat ever. Totally reliable.
They are not cheap but having never had a problem with them it's happy days as far as I am concerned :D
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By bvq
#1889961
When designing battery powered equipment the designer has a number of options:
1. Use the batteries directly with no regulation.
2. Use a linear regulator.
3. Use a switching converter.

There are pros and cons to each but in answer to the OP, I suspect that they are using option 1 or 2 which means that starting with a cell with a terminal voltage of only 1.2V may not provide sufficient voltage to power the electronics. That would therefore necessitate using primary cells (1.5V) to allow operation of the circuit.

A switching converter would allow the battery voltage to be stepped up to the required level and maintained until the battery voltage is no longer able to power the converter. With rechargeable cells this occurs quite close to when the charge is fully exhausted so it works quite well.

Options 1 & 2 are certainly simpler to design, cheaper to manufacture and more reliable which is why they may have been chosen. That said, option 3 is quite common and generally performs well.

I cannot see any reason why using rechargeable cells would damage the circuit given that a discharged primary cell will end up at about 1.2V eventually anyway. The warning is probably more to do with preventing disappointing performance where the batteries only last a very short while. In addition the low battery warning system will be designed to work with only one battery type.
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By Genghis the Engineer
FLYER Club Member  FLYER Club Member
#1889962
The warning is probably more to do with preventing disappointing performance where the batteries only last a very short while.


That is certainly how my SEHT ANR behaves with 1.2V rechargeables.

G
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By Trent772
#1889963
'Work' Indian headset works off ships power.

Vastly more comfortable, leisure DC One-X's last up to 3 months on 2 Duracells........
By Lefty
FLYER Club Member  FLYER Club Member
#1889966
All these experts are forgetting their fundamental principles of electricity.
A piece of equipment requires a certain “power” to operate .
Electrical power = volts X Amps

Therefore to get the same “power” with a lower voltage (eg 1.2 volt Vs 1.5 volt) requires a higher amperage. In fact 25% more amps (current).
This extra current may cause excess heat - or the electronic circuitry may be “current limited” as described above. If this is the case, there will not be enough power to run the circuit.

Bottom line - if you don’t want risk bug getting it up . use whatever batteries the manufacturer recommends.

My personal opinion Is that Duracells are so cheap in bulk, that it isn’t worth the hassle of trying to remember to charge your rechargeable before each flight.
#1889980
Lefty wrote:All these experts are forgetting their fundamental principles of electricity.
A piece of equipment requires a certain “power” to operate .
Electrical power = volts X Amps


Going very slightly of topic but sticking to explaining the fundamentals of electricity (at least for basic DC circuits), whilst the Power(W)=Volts(V) x Amps(I) equation is correct, it is actually only the calculation for working out the power (watts) consumed by a load drawing a specific current at a specific voltage, which very often leads to the misconception that should either the voltage or current change the other value will vary to maintain the power being used, which is not the case generally, as if this was true, this would result in 'Thermal Runway' until the ultimate destruction of the load due to excessive current....

The load (the headset) in its most simplistic form is just a constant fixed resistance applied across the power source, the battery in this case. Consequently utilizing basic Ohms law V=IR with the formula adjusted for the variables in use I=V/R, as R is albeit a fixed value, as the voltage from the battery decreases so does the current being drawn by the circuit.
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By tr7v8
FLYER Club Member  FLYER Club Member
#1889984
I am told that the reason products don't recommend rechargeable batteries is so they don't need type approval for the two types of batteries. I know from some of our work stuff that type approvals run into big money.
By riverrock
FLYER Club Member  FLYER Club Member
#1889989
If using alkalines, just make sure not to mix types or partially discharged ones.
If you have unbalanced alkalines, there is a risk that one battery will charge the other, causing it to leak.
Similar reason to not store items with batteries in them for extended amounts of time. The cross charging can happen as the charge in both gets very low.
By PA28
#1890010
Hermitageclose wrote:
Lefty wrote:All these experts are forgetting their fundamental principles of electricity.
A piece of equipment requires a certain “power” to operate .
Electrical power = volts X Amps


Going very slightly of topic but sticking to explaining the fundamentals of electricity (at least for basic DC circuits), whilst the Power(W)=Volts(V) x Amps(I) equation is correct, it is actually only the calculation for working out the power (watts) consumed by a load drawing a specific current at a specific voltage, which very often leads to the misconception that should either the voltage or current change the other value will vary to maintain the power being used, which is not the case generally, as if this was true, this would result in 'Thermal Runway' until the ultimate destruction of the load due to excessive current....

The load (the headset) in its most simplistic form is just a constant fixed resistance applied across the power source, the battery in this case. Consequently utilizing basic Ohms law V=IR with the formula adjusted for the variables in use I=V/R, as R is albeit a fixed value, as the voltage from the battery decreases so does the current being drawn by the circuit.

Well done. I was going to write the same.
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