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Gear / Technical Help => Remote Power => Topic started by: stevetoney on August 14, 2012, 11:43:23 AM
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I'm sure there are alot of people here that already know this, but last night I was doing some battery research while considering lightweight alternative powering scheme's for my Oade m118 and discovered that there's not a 9V battery chemistry (the transistor type batteries) out there that actually delivers 9V. They actually put out 8.4V nominal. In my case, 16.8v would probably power the m118 for awhile, but it wouldn't be long before they dropped down to below 16V which is too low...meaning that 9V transistor batteries just aren't a good alternative. In my case, the important discovery is that there's never a situation where using two 9V in series would ever give me a full 18V, but I can't even expect decent run-times between 16-18V before voltage dips down too low using two 9V.
Nevertheless, I thought it might interest people to know that you don't actually get 9 Volts out of a 9V battery, regardless of whether the chemistry is alkaline or any of the various rechargeable chemistries...I checked them all.
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But how does that relate to the gear?
Its not as if there once was some "true 9V" battery...that isnt made anymore.
Wouldnt the gear be designed to run at 8.4? (aka 9V)...?
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But how does that relate to the gear?
Its not as if there once was some "true 9V" battery...that isnt made anymore.
Wouldnt the gear be designed to run at 8.4? (aka 9V)...?
Yes for sure your point is true. I'm not implying that all gear that runs off 9V batteries are being underpowered. All I'm saying is that 9V battereis aren't 9 volts!
For example, if you put a meter on your gear and you expect to see 9V, you'll be surprised. But don't conclude that there's something wrong when you read 8.4, because a '9v battery' is a misnomer...it's actually an 8.4V battery.
EDIT: In the next comment, JD points out that 9V batteries read over 9V when they're new. I should have clarified by saying that the NOMINAL voltage of a 9V is 8.4V. When batteries are new/fresh or newly charged, they'll give a higher voltage reading than the nominal voltage. The nominal voltage is the flat part of a battery voltage discharge curve. In terms of gear design, you want your gear to be able to be powered by a battery that provides a nominal voltage that is higher than the minimum voltage required for your gear to operate. If the flat part of the battery discharge curve is BELOW that voltage, then your batteries aren't going to be a good match for the gear you have because, once the battery starts supplying a load to your gear, your battery voltage will dip down too low too quicly and your gear will shut down quickly on low voltage even though the battery works at first.
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Every new alkaline battery I have ever checked was in the 9.4 to 9.6 vdc range. I just checked 4 energizers that I have here with a calibrated Fluke 179 and they all measure 9.6vdc. Am I missing something?
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The reason I thought this was pertinent information to point out is that I'm familair with 6v and 12V SLA batteries, as well as other. The nominal voltage of batteries, which are also commonly called 'six volt' or 'twelve volt' are above 6V and 12V respectively. Under load, the actual measured voltage doesn't dip below 6V and 12V until the battery is well depleted.
So in the case of a battery we all call a 'Nine Volt Battery', the term is a loose approximation of the voltage, as long as you round upward. ;D
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Every new alkaline battery I have ever checked was in the 9.4 to 9.6 vdc range. I just checked 4 energizers that I have here with a calibrated Fluke 179 and they all measure 9.6vdc. Am I missing something?
You're not really missing anything. It's just that the voltage of brand new, or newly recharged batteries is higher than the nominal voltage after a load has been applied to it. Check out the graphs on this link and I think you'll understand what I'm trying to say:
http://www.powerstream.com/9V-Alkaline-tests.htm
What I'm reading in 9V battery specs is that the flat part of the curve on almost all 9V batteries (alkalines and rechargeables) is around 8.4V. On the batteries that we call Six Volt and Twelve Volt lead, when they're newly re-charged they measure 7V and 13+V respectively, but the flat part of the curve is a little bit above 6 and 12 respectively.
Again, I'm not trying to screw with anybody here, I just thought it was interesting because in my mind a 9V battery really should probably be called an 8V battery if it were to acurately portray the voltage that it delivers over its life.
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FWIW the Powerex rechargable 9V batteries have a nominal voltage of 9.6 but when new, fully charged and without load are between 10.5 and 11.5V. The Nbox doesn't seem to work well with the rechargable 8.4V but does great with alkaline or these Powerex ones. So if anyone needs a batter in the shape of a 9V and needs more than 8.4, it might be worth trying the Powerex.
EDIT: Branding is Powerex, not sure why I was thinking Maha.
EDIT: I just checked again and they are Maha Powerex. I give up. :P
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Hi all,
it helps to know the internals of a 9V Alkaline block: there are 6cells in series. I have opened up some of them, and the construction was interesting: 6 little alkaline cells (AAAA) connected in series via a circuit board (carrying the contacts) and a rubber plate with metal strips. I would not dare to draw high currents with this kind of construction, but for low currents it is sufficient.
Here an "Energizer" datasheet: http://data.energizer.com/PDFs/522.pdf
Rechargeables come in three types: 6, 7 or 8 NiMH cells in series (7.2, 8.4 and 9.6V nominal). Capacity is inversely proportional to voltage, i.e. the batteries with the highest cell number have the lowest capacity. I have seen one with oval button cells inside (Varta Germany).
There are also LiPoly 9V blocks: 8.4V fully charged, 7.4V typical, capacities up to 500mAh. Requires a special charger. I got mine from Conrad Elektronik (Germany).
BTW a properly designed device that operates off 9V blocks has a voltage window from 6 to at least 10V.
Hope that helps.
Greetings,
Rainer
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BTW a properly designed device that operates off 9V blocks has a voltage window from 6 to at least 10V.
Rainer...thanks for the feedback.
Please correct me if i'm wrong, but the significance of your comment about voltage window from 6 to 10 volts is that batteries don't have a constant voltage so a device needs to operate within a range of voltages in order to accommodate receiving battery power at a range of voltages (as the battery discharges).
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FWIW the Powerex rechargable 9V batteries have a nominal voltage of 9.6 but when new, fully charged and without load are between 10.5 and 11.5V. The Nbox doesn't seem to work well with the rechargable 8.4V but does great with alkaline or these Powerex ones. So if anyone needs a batter in the shape of a 9V and needs more than 8.4, it might be worth trying the Powerex.
EDIT: Branding is Powerex, not sure why I was thinking Maha.
EDIT: I just checked again and they are Maha Powerex. I give up. :P
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Just checked 2 fresh 9v Energizer Alkalines and they measure around 9.4 volts :P ;)
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+1 for the maha powerex 9 volt Lithium Polymer rechargeables. Been using them for 4 years with no failures.