3xAA or 4xAA
- Thread starter Jon__
- Start date
BeanieBots
Moderator
NO IT IS NOT.
4 X Brand new AA can exceed the maximum voltage.
Use 3 X AA.
NiCd & NiMh batteries are lower voltage than regular dry cell batteries, so you can 4 X Rechargeable.
A brand new "Duracell" battery can be as high as 1.62V Four of those would be close to 6.5v
All the way with 3 AAs. The 28X1 is at heart a PIC16F886, so has supply ratings 2-5.5V.
If a project board however calls for 4 x AAs, a series Si diode (or two) in the PICAXE supply line usually does the dropping trick. Si diodes drop ~0.7V when working of course, & this remains pretty constant over a wide current range.
Over the years I've seen diverse circuits even using series LEDs (reds drop ~1.8V, greens ~2.0V) for such regulating tasks. Although load current drain will be limited to the ~10-20mA LED capabilities,the glowing LED(s) can make a handy (& cheap) "what's going on" ammeter.
Diode droppers may seem pretty trivial when 3 terminal 7805s are so well established, BUT the whole 78xx family needs a supply a good 2V above their delivered output voltage. Hence if 5V is needed from a 6V supply, perhaps to run a PICAXE, a 7805 will not be suitable.
If a project board however calls for 4 x AAs, a series Si diode (or two) in the PICAXE supply line usually does the dropping trick. Si diodes drop ~0.7V when working of course, & this remains pretty constant over a wide current range.
Over the years I've seen diverse circuits even using series LEDs (reds drop ~1.8V, greens ~2.0V) for such regulating tasks. Although load current drain will be limited to the ~10-20mA LED capabilities,the glowing LED(s) can make a handy (& cheap) "what's going on" ammeter.
Diode droppers may seem pretty trivial when 3 terminal 7805s are so well established, BUT the whole 78xx family needs a supply a good 2V above their delivered output voltage. Hence if 5V is needed from a 6V supply, perhaps to run a PICAXE, a 7805 will not be suitable.
Last edited:
hippy
Ex-Staff (retired)
The historical confusion comes I believe from the way Microchip used to give their specifications for the PICmicro devices and their evolution.
My Microchip printed datasheet for the 16C5x shows VDD as 2V to 6V, absolute max 7V5. Later, for example the 16F886 (28X1), show VDD 2V to 5V5, absolute max 6V5. In the intervening years as the device range expanded massively there was much confusion as to what was acceptable for VDD and conflicting information around.
The rule now is to not exceed 5V5 ( or whatever the datasheet states ) and generally to keep at or below 5V when possible. Above 5V5 the PICAXE may not operate correctly and its usable lifetime may reduce, above 6V5 it may be permanently damaged. Connect 9V PP3 and it almost certainly will be.
Thus 3xAA is recommended, normally giving 4V5.
4xAA would be acceptable providing the total battery voltage were below the 5V5 or maximum allowed. That would not be the case for 1V5 batteries. Note that recharged batteries may be of higher voltage than their nominal ratings.
The PICAXE can also be used in conjunction with 4xAA batteries ( or more ) providing the PICAXE is powered through a suitable voltage regulator to keep below 5V5 or maximum allowed.
My Microchip printed datasheet for the 16C5x shows VDD as 2V to 6V, absolute max 7V5. Later, for example the 16F886 (28X1), show VDD 2V to 5V5, absolute max 6V5. In the intervening years as the device range expanded massively there was much confusion as to what was acceptable for VDD and conflicting information around.
The rule now is to not exceed 5V5 ( or whatever the datasheet states ) and generally to keep at or below 5V when possible. Above 5V5 the PICAXE may not operate correctly and its usable lifetime may reduce, above 6V5 it may be permanently damaged. Connect 9V PP3 and it almost certainly will be.
Thus 3xAA is recommended, normally giving 4V5.
4xAA would be acceptable providing the total battery voltage were below the 5V5 or maximum allowed. That would not be the case for 1V5 batteries. Note that recharged batteries may be of higher voltage than their nominal ratings.
The PICAXE can also be used in conjunction with 4xAA batteries ( or more ) providing the PICAXE is powered through a suitable voltage regulator to keep below 5V5 or maximum allowed.