Look at most “9V” rechargable batteries and you’ll find that they only produce 7.2V.
I don’t think so. While “9V” is a nominal value in the same way as “two by four” describes a pine stud that is not two by four inches, most consumer-grade batteries off the shelf produce slightly more than the nominal value. Spot-checking a pair of 9v Duracells on my shelf, purchased about a year ago and never used, they each measure 9.46 D.C. volts with a digital Fluke multimeter.
Of course that value will be slightly lower if measured under useful load; the Fluke presents a nearly-infinite resistance.
Just where did you get that “7.2V” figure? From a run-down battery?
smack Read the psot again. He said rechargeable 9 V batteries. Take a NiCd 9 V battery, for example. Most of these also use 6 cells, just like alkaline ones do. However, since NiCd cells are nominally 1.2 V, a 9 V battery will be 6 x 1.2 V = 7.2 V, whereas an alkaline cell is nominally 1.5 V, making a true 9 V battery – 6 x 1.5 V = 9 V. I’ve also seen lead-acid 9 V batteries, which are usually 4 x 2.0 V cells = 8 V. I have seen 9 V NiCd batteries which use 7 cells for a nominal 8.4 V “9V” battery, but these are less common.
Check out Energizer’s datasheet for their “9V” rechargable offering.
There are some real 9V rechargables out there now–as I was informed in another recent thread. They’re not easy to find, though. If you buy a rechargable at the local Wal-Mart, you’ll wind up with a 7.2v.
If this charger was designed to work with standard “9V” rechargable batteries, it’s quite possible that it’s putting out 8V by design.
Sorry – entirely my fault for mixing chargeables with non-rechargeables. Yes, they do have actual values different from nominal ones, and rechargables are typically lower even when fully charged.
However, everything I have said about waveforms, AC/DC, scopes, meter measurements, etc. still stands.
No. Canada and the US both use 60 Hz/120v AC power.
It used to be 50. Has that changed in the last 40 years, perhaps to sync up with regional power grids? I must have missed that memo.
No, it didn’t. The US began trading electric power with Canada in 1901, something which would have been impossible with different frequencies.
I should know better than to try correcting an authority of Q.E.D.'s stature. Still…
According to at least one clock history site, line frequency wasn’t tightly regulated until at least 1918. There wasn’t much need until the first Telechron clocks (which used the line frequency as a time base) were developed.
If a stable frequency wasn’t essential to the early power grid, it seems that a standard frequency might not be essential either.
The exact frequency need not be tightly regulated for grid sharing to work. Generators naturally synch with each other when wired together. From MadSci.org:
To limit strain on the interconnected generators, the frequencies should be fairly close, however. I’m naot sure of the exact effects of connecting a generator operating at 60 Hz to one operating at 50 Hz, but I suspect the more powerful generator would attempt to “swing” the weaker one to whichever frequency it is outputting, and the final result would be a frequency somewhere between the two, weighted towards the stronger generator.
Well, Hell’s bells. I just realized that quote I posted above came from our very own bbeaty. Heh.
Q.E.D., the phrase “60 hz, 50 hz in Canada” seems to be so ingrained in my memory that although I haven’t given this a thought for decades, I would like to find out if my memory is faulty. To avoid hijacking this thread, I have started a new one, What is the frequency of consumer-grade A.C. powerlines in other parts of the world than the U.S.?
The effect would be for circulating currents to pass between the two generators with each generator trying to run the other as a motor when they were not in phase. I’m pretty sure that the effect would be to destroy one or both of them unless there was considerable line impedance between them.
Right, but assuming the two generators are indestructible, would they eventually sync up in phase at some point?
I’m not sure. I think it would depend upon they relative power of their respective prime movers. If the generator with the weaker prime mover is forced to sync with the stronger, then its prime mover would also have to be indestructible and we’re sort of getting into never-never land.
just measure the resistance of those mysery elements both ways ( both polarities ) if its the same its a resistor, if one way the resistance is much higher than another - its a diode.
also what is that bigger thing connected to a piece of metal there ? could be another diode ? and the piece of metal could be its heatsink ?
regardless, i use a $40 MAHA battery charger that puts each battery on a separate microprocessor controlled circuit, and does a full charge in 100 minutes. and because the circuits are independent i can put a fully drained battery next to an almost-full battery and they will both charge to perfection. when its done a light next to each battery changes from red to green and the charging of that particular battery stops, others keep going.
your batteries last longer if you treat them well.
Yes and no. David Simmons answer was pretty much spot on.
First, let’s assume a steady state operating condition.
Remember that there is a control system on each of them that targets a particular frequency. On one, it’s 50 Hz, on the other it’s 60 Hz. The control systems only control the throttle, there’s no brake.
If the 60 Hz generator was powerful enough to supply the entire load at 60 Hz, then it would do just that. The 50 Hz generator would just motor along at 60 Hz (3,600 rpm), and supply no power at all.
If the 60 Hz generator was not that powerful, it’d slow down to some lower frequency. The power that the load absorbs is frequency dependent, because it includes things like synchronous motors which use less power at lower frequencies. That lower frequency could be, say, 53 Hz. The 50 Hz generator would still be supply no power whatsoever.
The 50 Hz generator would only begin supplying power once the frequency got down to close to 50 Hz. Then the two generators would begin to share load.
So there are two stable frequencies, 50 Hz and 60 Hz. In between, the frequency would float up and down depending on the size and composition of the load.
Now, that’s assuming indestuctable machines, and it’s what would occur in practice if you connected two small 50 Hz and 60 Hz internal combustion generators - like those little Honda things. Big gas turbines or steam turbines will have overspeed protection, and will trip off at something like 53 Hz, because they simply aren’t capable of running at speeds higher than that without suffering damage or even flying apart.
Next, let’s consider the instant when the machines are first connected together. The 60 Hz machine will attempt to supply an enormous accelerating torque to the 50 Hz machine, with a correspondingly enormous current through both machines and the transformers and transmission lines connecting them together. In practice, that would trigger overcurrent protection everywhere, and whichever had the fastest response time would interrupt the current and separate the two machines.