AGR26

I was under the initial impression that you could peak charge NiMH packs. But; I have read conflicting information on this.

What is the general consensus? What do you guys do?

Thanks!

bhanley

Do it all the time. I use Sirius chargers for fast charges. Then I do cycle them with a slow charge every few
months. Use a Hobbico Elite for that which is also a peak detection charger. Keep my batteries two to three years. Haven't
had a problem yet.

Rodney

You must use good low impedance leads with good connectors. Small gage wire and clip leads will not let the charger properly detect the peak.

3D Joy

EXACT!! In my experience, low impedance cells also seem to help for fast charging, they don't heat up and are more consistent during the charge.

KC36330

i believe the two of you are confusing impedance and resistance. impedance is opposition to current flow in an AC circuit and has nothing at all to do with a DC circuit.

kc

richrd

This the advange of NiMH "hee hee memory" and extra capacity. I only peak charge always top off before going to field, 3 to 15 minute per plane and go.
All new batteries are NiMH soon it's all I'll have.
Rich It's all in the charger get what you pay for.

3D Joy

Nimh DO have some memory effect. It may be less evdent than with Nicad but it is still there. It is the Nickel part of the cells that cristalizes and diminishes overall capacity.

Anyway, Nimh came a long way and are now very rugged, have good capacity and are really easy to get now from lots of sources. That is until we have a good electronic system that works at over 8 volts so that we can get rid of those regulators and plug 2-cell lithiums straight into our receivers and servos.

Rodney

KC36330, Sorry you are in error. Impedance is the impeding of current flow, whether it be pulsed, ac, dc or whatever. It consists of two parts, reactance (due to capacitance or inductance) and resistance (that part of the impedance in phase with the current. To be correct, you should always refer to impedance, not resistance when you are talking about electrical current and the forces impeding that current. When you get into AC current, you also have to worry about phase due to the impedance.

KC36330

same reply i gave to your other comment on the same subject just a few min ago........

you might wanna do a little tutorial reading of your own, I've been doing aircraft avionics (even have a degree in it) for the past 17 yrs and in every book i have on the subject impedance is defined as such:

impedance is only relevant in an alternating current situation. in DC it's purely resistive. when you get into circuits that have both AC and DC you need to know the differences between the two or you'll be lost like a ball in high grass. a coil has no impedance to a DC current, but is dependent on frequency as to how much it has to an AC current, capacitors are just the opposite, to an AC current they are in essence a short (very low resistance), to DC currents they are like an open (very high resistance). this is why each plays a very good roll in filtering between the two circuits when intermixed.

kc

PS: on your reference to worrying about phase shifting, we use the 'ELI the ICE man' for the leading and lagging of voltage to current be it inductive or capacitive.

Jeff9329

KC36330:

You are correct.

There is a lot of misinformation and hearsay on this board, and people want to argue their incorrect points. Very frustrating and misleading.

There is also a lot of good information gained from practical experience.

3D Joy

OK, I stand corrected.

What should we say then when we talk about low impedance batteries? Are they low resistance batteries?

Directly from the NoBS site...

BTW I am not trying to argue, just want to be informed.

Jeff9329

To measure battery impedance you use an AC battery load test.

The AC method measures the phase shift between voltage and current. The battery’s reactance is used to calculate the impedance.

The AC method, also known as the conductivity test, measures the electrochemical characteristics of a battery. This technique applies an alternating current to the battery terminals. Depending on manufacturer and battery type, the frequency ranges from 10 to 1000Hz. The impedance level affects the phase shift between voltage and current, which reveals the condition of the battery. The AC method works best on single cells, not packed.

The AC battery load test is pretty much a QC check of a similar batch of batteries as the values obtained by the test can only be used to determine the quality and integrity of a specific cell batch and not another cell batch with slightly different physical/chemical properties.

To measure battery resistance you use a DC battery load test.

The DC load test applies a discharge current to the battery while measuring the voltage drop. Voltage over current provides the internal resistance.

KC36330

but i do like the way that the misinformed are so hell bent on things they were taught back in the 40s are still current knowns when dealing with electronics, yet they own a 62" plasma TV that is 1/2 the weight of the old AM radio they sat around the cole oil lamp on Saturday night listening to.

kc

Rodney

As an electrical engineer in good standing with some 30 years in the business, impedance is defined as the opposition to current flow rather it be DC or AC. It is just that the impedance for DC is a single point at the beginning of the scale in an infinate number of possibilies and does allow you to ignore the reactance part of the impedance equation when working in pure DC. It is still impedance whether you are talking about the resistive portion for DC or of the full electromagnetic spectrum. As KC36330 says, the missinformed do make erroneous or incomplete statements. I might add that the partially informed make just as many mistakes.

KC36330

How are you liking that Plasma TV Rodney??

kc

Jeff9329

I suggest all us battery geeks read this book on battery technology.

There are many good chapters that are a free internet read.

http://www.buchmann.ca/faq.asp

laryboy

My Feedback: (2)

rodney is 100% right. impedance=R +jwL +1/jwc where w=omega or 2xpie f

Jeff9329

Lary Boy is an idiot.

This once again proves most of the supposed technical information on here is anecdotal or just wrong.

The impedance of a circuit element is defined as the ratio of the phasor voltage across the element to the phasor current through the element:


It should be noted that although Z is the ratio of two phasors, Z is not itself a phasor. That is, Z is not associated with some sinusoidal function of time.

For DC circuits, the resistance is defined by Ohm's law to be the ratio of the DC voltage across the resistor to the DC current through the resistor:


where the VR and IR above are DC (constant real) values.

Also, Rodney you are not an electrical engineer, most likely some kid.

kx250ryder

Resistance: Opposition to flow of electrical current.

Impedance: Resistance of a component for a given frequency.

Calling it impedance, when the frequency component is essentially null and void works but its like calling water by its chemical name, dihydrogen monoxide, which is just overkill.

Ross Kean

How about dihydrogen monoxide (H2O)??

Sorry, I just couldn't resist (or should I say impede?)

Ross

kx250ryder

Sorry, I put that in as a filler, and was working on verifying that when you posted. I usually edit almost all my posts at least once.

EDIT: Whether or not you couldn't resist (or impede) depends on whether or not this thread is direct or alternating at some frequency.

EDIT AGAIN: It can also be called Hydrogen Oxide.

Ross Kean

Thats OK. I was just trying to inject a little humor into an argument that people are getting far too excited about!

"EDIT AGAIN: It can also be called Hydrogen Oxide."

My EDIT: Since we have blown the original topic right out of the water (dihydrogen monoxide), we might want to clarify that Hydrogen oxide might also refer to H2O2 - Dihydrogen Dioxide - AKA Hydrogen peroxide.

I think I'll stop now before this gets even sillier!

Cheers

Ross

laryboy

My Feedback: (2)

jeff............the problem with going to trade school is that you never learn to express anything mathematically. this might help.

"Resistance is a force that tends to resist the flow of electrical current. Resistance is usually created deliberately by a resistor, a device used to create resistance in a circuit. Resistance is pretty straightforward: The more resistive a resistor is (i.e. the more ohms it's rated for), the more it restricts the flow of electricity through it. Perhaps the best news of all is that if you're working with DC (Direct Current), resistance is the only thing you need to concern yourself with; the slightly more complicated concepts of reactance and impedance only exist in the world of AC (alternating current).

Reactance, unlike resistance, is usually undesirable in a circuit. Whereas resistance is created by a resistor to achieve some effect, reactance is an unfortunate by-product of certain electrical components. There are two basic types of reactance: Capacitive reactance and inductive reactance. Appropriately enough, capacitive reactance is created by capacitors, while inductive reactance is created by inductors. Using either of these device types in an AC circuit will introduce some reactance. Like resistance, reactance is expressed in ohms, and it behaves in much the same way as resistance, in the sense that it tends to restrict the flow of current through a circuit.

The formula for calculating inductive reactance is as follows:


XL = 2*pi*f*L

XL is the inductive reactance. X is the general electrical symbol for "reactance", and L is the symbol for "inductance" or "inductor", so put them together and you get the reactance of an inductor.

pi is, as you probably guessed, the famous ratio of a circle's circumference to its diameter, to wit: 3.14, etc.

f is the frequency of the AC flowing through the circuit.

L is the inductance of the inductor, in henries.

So you see, when you muliply 2 by pi, by the frequency of the AC, by the inductance of the inductor, the resultant value is the inductive reactance of the circuit.

The formula for capacitive reactance is similar, but there's a twist to it:

1
XC = --------
2*pi*f*C

XC is, as you might have guessed, the capacitive reactance, and C is the capacitance of the capacitor (in farads).

The two formulas for inductive reactance and capacitive reactance create interesting counterpoints. Notice that for inductive reactance, as the frequency of the AC increases, so does the reactance. Higher frequencies result in lower current. The opposite is true of capacitive reactance: The higher the frequency of AC, the less reactance a capacitor will present.

Similarly, a more inductive inductor will present more reactance, while a capacitor with more capacitance will yield less reactance.

Once you know the resistance and reactance of a circuit, the impedance is actually the overall opposition to current presented by the circuit. The impedance of a circuit is also expressed in ohms; Unfortunately, you cannot simply add the resistance and the reactance to get the impedance. The formula is a bit tricker than that, but for those who learned the Pythagorean Theorem, well, you'll finally have a place to use it here.

The total impedance of a circuit is the square root of the sum of the squares of the resistance and reactance. In other words, impedance can be represented as the hypotenuse of a right triangle. Resistance can be one of the shorter sides of the right triangle, and reactance can be the other shorter side. The longest side, the hypotenuse, is then the impedance. If you learned (and remember) the Pythagorean Theorem, you know that the square of the longest side of a right triangle is equal to the added squares of the other two sides. This formula is sometimes expressed as a squared + b squared = c squared, with a and b being the shorter sides of the triangle, and c being the longest side. Impedance, then, is:

Z = sqrt( (R^2) + (X^2) )

That is, impedance (which has a standard electrical symbol of Z, for some warped reason) is the square root of (resistance squared plus reactance squared)."

hands without shadows

Hydrogen oxide might also refer to H30, heavy water, dont drink any You people are way off topic. I peak charge my packs, why wouldnt you?

Ross Kean

Heavy water is D2O where "D" is heavy hydrogen or deterium. (one proton and one neutron for deterium and just a proton for hydrogen).

I also peak charge both NiCd and NiMH packs - mostly because I forget to slow charge before I get to the field. I try to do a good slow charge at least every 4th or 5th cycle. Don't know whether it helps but I don't frequently have to replace batteries.

Ross