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I've been following this tutorial on Arduino's, for the one's that are interested it's this one (https://www.youtube.com/watch?v=5bHPKU4ybHY&t=575s)

Yesterday I was struggling to get a servo moving, sometimes it made small twitchy kind of movements, other times it wouldn't move at all. So I did some research on what the reason for this could have been.

The most common answer was : Don't use a 9V battery for a motor

So I ended up buying 6xAA batteries, which do very well in moving the servo.

But in the tutorial he IS using a 9V battery, so what are the differences that matter here? (Quality, more mAh, alkaline vs non-alkaline, ...?)

My knowledge regarding batteries is still very poor, so I've put three images at the bottom that I would like to compare if possible.

  1. What's the difference with my 9V battery and his 9V battery?
  2. Why are 6xAA batteries (1.5V) recommended over a 9V battery?

Thank you!

Images:

  1. My 9V Battery
  2. His 9V Battery (I believe it says 'Radioshack Enercell 9v Alkaline Battery')
  3. My 1.5V batteries

My 9V Battery His 9V Battery 1.5V Battery

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    \$\begingroup\$ Simple, higher current output from 6xAA batteries. \$\endgroup\$ – Shibalicious Aug 11 '18 at 13:26
  • \$\begingroup\$ @Hypomania I see, thank you. But what are the differences between the two types of 9v batteries I'm showing then? \$\endgroup\$ – Tobias Heuts Aug 11 '18 at 13:28
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    \$\begingroup\$ The difference is probably not the comparison of your 9V battery and the one you saw in the video. Instead it is far more likely a difference of the amount of load being applied to the battery. The servo in the video may very well be a lower current demand servo. \$\endgroup\$ – Michael Karas Aug 11 '18 at 13:38
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    \$\begingroup\$ The Panasonic NEO that you're using is a Zinc-Carbon battery. The Enercell is an Alkaline battery. And THAT's the difference. 'Alkaline delivers more energy at higher load currents than zinc-carbon' \$\endgroup\$ – MartinF Aug 11 '18 at 13:41
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    \$\begingroup\$ If you monitor the voltage, this will tell you if the ratio of load resistance to total resistance including battery . Servo Motor’s have very low DCR when the position error is high dropping the input voltage such that it fails to switch. FETs conduct when Vgs is 2-3x times the threshold Vt . If Vt is 2-4V (std) it may not conduct at 8V or less. Thus a twitch response as battery drops then recovers slowly. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Aug 11 '18 at 19:03
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What's the difference with my 9V battery and his 9V battery?

The difference is the chemistry of your "Extra Long Life" (Zinc-Carbon or more likely Zinc Chloride) 9V battery vs. video battery.

Not sure what is inside your 9V battery. What is known is your "Extra Long Life" has less energy capacity than alkaline. You would need to look at an zinc-carbon or zinc chloride datasheet to see the discharge characteristics.

This is only a 50 mA discharge curve for 9V batteries.

enter image description here

Why are 6xAA batteries (1.5V) recommended over a 9V battery?

This is not totally correct. One might say use AA alkaline rather than AAA or AAAA alkaline. Or use alkaline rather than zinc carbon. I suspect that 6 AA may still be better choice than 6 AAAA or 9v alkaline.

There are 6 AAAA alkaline batteries inside a 9V alkaline battery.

This is a 9V Energizer alkaline battery.

enter image description here
Source: 9 Volt Battery Hack!



From Wikipedia

The zinc chloride cell is an improvement on the original zinc–carbon cell, using purer chemicals and giving a longer service life and steadier voltage output as it is used. These cells are usually marketed as heavy-duty, extra-heavy-duty, or even super-heavy-duty batteries, and offer about twice the service life of general purpose zinc–carbon cells, or up to four times in continuous-use or high-drain applications.

Alkaline batteries offer up to eight times the battery life of zinc chloride batteries, especially in continuous-use or high-drain applications.


From Battery University.

Zinc-carbon, also known as carbon-zinc or the Leclanché battery, is one of the earliest and least expensive primary batteries. It delivers 1.5V and often come with consumer devices. The first zinc-carbon invented by Georges Leclanché in 1859 was wet.

Alkaline-manganese, also known as alkaline, is an improved version of the zinc-carbon battery and delivers 1.5V. Lewis Urry (1927–2004) invented alkaline in 1949 while working with the Eveready Battery Company laboratory in, Ohio, USA.

Alkaline delivers more energy at higher load currents than zinc-carbon. Furthermore, a regular household alkaline provides about 40 percent more energy than the average Li-ion but alkaline is not as strong as Li-ion on loading. Alkaline has very low self-discharge and does not leak electrolyte when depleted as the old zinc-carbon does, but it is not totally leak-proof.

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What I found on the web is that the 9V batteries have about 500 mAh, While AA batteries vary from 1.8 - 3 Ah. So in short it's because of the higher current.

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    \$\begingroup\$ The available energy of a battery is measured in Ah (current * time) but that does not neccesarily have anything to do with the current which it can supply. Perhaps you could find out something about the internal resistance of the cells in question and revise your answer. \$\endgroup\$ – Andrew Morton Aug 11 '18 at 13:41
  • \$\begingroup\$ Incorrect assumption. \$\endgroup\$ – winny Aug 11 '18 at 13:43
  • \$\begingroup\$ @AndrewMorton Yeah I see, I messed up things together. \$\endgroup\$ – Mohamed Abduljawad Aug 11 '18 at 13:44
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    \$\begingroup\$ While this isn't directly the cause it is highly correlated. Generally speaking, a higher capacity battery will be able to delivery higher current than a lower capacity battery of the same type. Alkaline 9V batteries are generally made of 6 cells just a bit smaller than AAA's. Carbon Zinc ones are often in a different physical configuration, but still multiple small cells. \$\endgroup\$ – Chris Stratton Aug 11 '18 at 16:22

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