I've been having some problems running my Arduino-INA219-OLED Wattmeters from zinc carbon 9v batteries. So I thought I'd check the capacities of NiMH, alkaline and zinc carbon versions of these 9v batteries. This threw up some odd results, so I went on to check the internal resistance of the zinc carbon ones.
Useful links:
https://en.wikipedia.org/wiki/Nine-volt_battery
https://www.google.co.uk/search?q=zinc+carbon+internal+resistance
http://batteryuniversity.com/learn/article/how_to_measure_internal_resistance
https://www.experimental-engineering.co.uk/zhiyu-zbp30a1-electronic-dummy-load/
Useful links:
https://en.wikipedia.org/wiki/Nine-volt_battery
https://www.google.co.uk/search?q=zinc+carbon+internal+resistance
http://batteryuniversity.com/learn/article/how_to_measure_internal_resistance
https://www.experimental-engineering.co.uk/zhiyu-zbp30a1-electronic-dummy-load/
zinc carbon and zinc chloride are both zinc carbon cells (!). they use a zinc container as one electrode and a carbon rod as the other. the first zinc carbon dry cells used ammonium chloride as the electrolyte. later improvements led to zinc chloride being used as the electrolyte instead, in an otherwise identical cell. the marketing designation of the improved version was "heavy duty", or "super heavy duty" or similar, a use which persists today. the surprisingly high internal resistance figure comes from the series construction of 6 individual cells required to give 9V, of course the internal resistance is cumulative over the battery. alkaline 9V batteries also have a internal resistance much higher than their single cell counterparts such as AAs, but the single cell value is so low that its not generally an issue even when multiplied by 6.
When it comes to batteries for stuff like this I find you absolutely get what you pay for. I've had dollar store Energizer brand batteries that had a short circuit current of around 100ma fully charged at around 9.3v. Chateau brand are also junk. I can't even use them with 7805 regulators because the voltage drops so steeply if it's even the slightest bit discharged.
Absolute rubbish indeed. Do yourself a favor and splurge on a pack of Duracells or something of high quality. I usually have to chuch the dollar store ones once they're down to 8-8.5v because they'll drop below 7v with any sort of load.
It also helps to find a datasheet for the batteries you're using, as well. I never thought to look up the datasheet for a 9v battery, but they're full of all sorts of useful information like internal resistance, amp-hour rating, discharge curves and such.
I've tried all sorts of store brand, dollar store, and similar cheap batteries, and have pretty much given up on all of them, preferring these days to buy either Duracell or Energizer because they perform better for me. I saw in the comments below where someone mentioned leakage issues, and I did have one problem with that and when I contacted the company they sent me coupons for free batteries to compensate for that, so in the long run no problem. This was leakage while still in the package, not in a device.
i at one point had a whole pile of rechargeable batteries. There were a few different brands, but the only ones that I seemed to have some luck with were Kodak branded, and even those didn't seem to want to hold a charge for as long as I'd like. I was using these in a digital camera, mostly, and sometimes in a 2-AA flashlight that I carry around. The "9V" ones were actually 7.2V when fully charged, and damn near useless for anything that I tried them in. There are apparently some 8.4V rechargeables too, but stuffing more cells into the same size case means lower mAH coming out, so it's a tradeoff. Most of these were nicads, but at one point later on I got some NiMH from Harbor Freight, and those turned out to be utter crap after a while, too, and eventually I quit using them entirely. Gave them to someone I know who uses a wireless mouse and keyboard, and apparently does okay with them, until the device ceases functioning while in the middle of some game where timing is a critical factor. 🙂
Your arduino wattmeter might be happier for longer if you added a capacitor across the battery input terminals, I'd try 100uF to start, see how that works. And of course going with the lower clock speeds, etc. would lessen the drain on that particular battery.
I look forward to more of your homebrew converters, particularly if you can achieve something isolated, which would do away with the need for that 9V battery to run the wattmeter, for example, or perhaps do things like provide high-side gate drive for H-bridge MOSFET circuits or similar…
You could have put those two 9 volts in parallel to only draw 10ma load
They could be put in my old Jade Radio that I purchased with the money I got shoveling snow back in 67 after the big blizzard snowed in the whole town. Funny, the things your mother saves for you, she gave it to me a few months back, she had put it away after I married and left home, and kept it for over 45 years locked away in her old writing desk. I think it would do just fine with that battery, it was just an AM radio 10 Transistors it says on the back what a wonderful product made in Japan in the late 1960's and still plays as good today as it did when I walked around with it glued to my ear listening to the old rock and roll that made us who we are today!
You know there are some folks that aren't even happy if you stab them with a new knife!
Awesome video project~~~^_^ Please feel free to contact me for free samples if you have any interests and free time.:-)
As you see 9V batteries are a great source of AAAA batteries (used in some tablet stylusesesi)
Love these simple practical tests. Thanks!
Those 9v carbon cell were designed for small pocket radios and garage door opener remote transmitters that typically draw about 8-12 milliamps. As you discovered they never were designed for high drain loads. Old style radio B batteries for tube sets were made the same way only with slightly larger cells.
I think that your Buck converter is missing a capacitor at the load