Oh come on !! Where is an electrical engineer to talk WHOLE or is it HOLE flow when you need one !!! You know when that little electron moves it leaves a HOLE !! or is it WHOLE !! Thay never can seem to explain that one to me !!!

Hmmm, Edison and Ford huh? Didn't know that. And here I had always respected Edison and his accomplisments...



AV8TOR

A three phase DC motor? Thats a new one on me.

The Edison Menlo Park, N.J. lab is at Greenfield Village in Dearborn, Mi. It was reconstructed from old pictures there in the '20's as the original had been closed 40 yrs before in NJ and the original buildings had calapsed.

There are a lot of pictures of Henry Ford and Thomas Edison camping together and doing various other consolidated ventures. There was most probably a business relationship but a publicity/advertising relationship also.

Its muddy the water time
Ignitions do NOT have a smooth current draw. They take a really big bite of power just after the plug fires and the cap is empty. As the HV cap charges the current decreases. Now all this happens in milliseconds and most MA meters won't show it, but an O'scope will. This makes a big noise spike on the battery leads that is equal to engine rpm. This is one of the major "RFI" sources and why we say to separate your batteries.
Also this power surge can swamp a cheap regulator, the regulator can't react fast enough at high rpm and the voltage available to your ignition is effectively reduced and you develops a high speed miss.

Now why did you do that the fun was about over.
BCCHI

There is no point in the agrument. Everybody is right in their context. We are referring to to three different situations.

Ohm's law states that : For a linear divice, and under constant physical conditions (such as temperature and pressure), current flowing through that device is directly proportional to the voltage difference across it. The coefficient of proportionality (voltage in Volts divided by current in Amps) is defined as the resistance of the device in Ohms.

Devices such as receivers, servos and motors behave very closely to a linear device. So higher voltage will result in higher current and higher power consumptions.

Devices such as switching regulator is highly non-linear. So it is possible that as the input voltage increase, the current consumption actually decrease (to keep the power consumption at the load constant). Because of the design of the circuit, the loss internal to the voltage regulator is negligible.

Devices such as linear voltage regulator is non-linear but not to the extent of the switching voltage regulator. As the input voltage increases, the output voltage will be kept constant and so power consumption at the load is constant. The input current will also be constant, however the heat loss internal to the voltage regulator due to the increased voltage drop will increase.

So to sum up, as voltage increases, the current can increase, be constant, or decrease, depending on whether it is a linear, non-linear, or highly non-linear devices respectively.

CKN

Aw come on why do you think brushless motors have three leads and reverse if you switch a pair. You should have be doing this tutorial.

Absolute BULL PUCKY. Grab a scope at any point of time for any given load at that point of time if you increase the voltage across that load the current will increase. I don't care what the load is and I don't care at what frequency you are talking about. Ohms law is true - you cannot deny the math. Millions of engineering students each year try to inlabs all over the country - world. It holds true. With AC you have to take into acount inductive or capacitve loads - BUT Ohms law still holds true. I do not care if your load is constant is non linear.

John

EDIT -> I'm talking of external loads we use as hobbists. I'm not talking of internal loads within a switching regulator. I'm simply trying to get some basic principals taught so that most people can understand the relationship between volts, current, and resistance.

Thanks for the education. I've run ignitions with some pretty lousy high impedance battery packs and haven't had a problem.

I know the current spikes that digital servos generate are of longer duration and a high impedance battery sucks when you are trying to drive two or three at a time. You can feel it when you are flying.

John

TKG,
I should have asked if you feel using very low internal impedance batteries are worth the additional costs for ignition sources. Or can garden varity packs be used relaibly if they are in good shape.
John

Helio all
Was in the electronics field for 59 years beforing retiring. Mr Norton is correct in his explanation of ohms law, period. I went to Devry Technical Institute, after an Air Force stent in electronics, for a couple years. Am using high impeadance Enloop 4 cell packs for ignition In my 40% Laser with no problems so far. Just for about two IMAC flying seasons. So we will see if they work out as claimed, The claim that hold their charge is valid. Have them in my transmitter (Airtronics RD) and checked them for a first flight of the Laser, after storage over the winter, after an IMAC contest in Ft Worth, and the battery was 10.4 volts.
Just some input from an (oldtimer)
Regards to all

Jack

Ok I'll explain it to you. When electricity flows electrons move from atom to another atom. As the electrons moves it leaves a hole where it was and the atom becomes positively charged, attracting another electron. The holes you are talking about is simply that, the absence on an electron.

John

PS Its a little negative logic like digging a series of holes in the ground and tossing the dirt forward, but claiming you are moving backwards in the direction of the holes instead of forward with the dirt.

The smaller the battery in MAH the better quality it must be. We had some bad times with the first generation 6-700mah nimh batteries. A 600mah nicad worked just fine.
The newer 7-900 mah nimh also work just fine. I power most of my ignitions with them, no sense hauling around sub-c's when AAA's will last for 2hr.
We never had any trouble with any of the sub-c nimh batteries of any generation.
quote]
TKG,
I should have asked if you feel using very low internal impedance batteries are worth the additional costs for ignition sources. Or can garden varity packs be used relaibly if they are in good shape.
John
[/quote]

One of the most common misconception of Ohm's law by first year engineering students is that it applies to all loads. No. It is only true for linear devices such as resistors, inductors, capacitors etc. Strictly speaking even for these linear components Ohm's law still require that some physical conditions be met (such as constant temperature and pressure). Also for inductors the magnetic permeability of the core can introduce non-linearity. For capacitors the dielectric constant can introduce non-linearity.

For a linear device, Volt across device divided by current through device is a CONSTANT defined as the resistance (in case of DC) or impedance (in case of sinusoidal AC) in Ohms. You double the V and you will get double I.

For non-linear device, V divided by I will not be a constant. That is, doubling the V may not result in double I. In other words, the R seem to be changing with voltage.

Diodes and transistors are typical non-linear devices. Systems building out of them are even more non-linear.

So to sum up, it is not strictly correct to assume that when V increases across a load you will certainly have I increases as well. A typical example is the universal voltage adaptor that comes with the mobile phone. They are rated for a wide range of voltage to suit 90V to 260V ac. They are in fact a switching power supply. For that electronic system, as V increases, I actually decreases.

CKN

I understand everything you are saying. But in what way does it help the average person understand ohms law?

This posting certainly isn't for engineering grads. If you remember back that far a Tunnel diodes exhibited reverse conductance also but it is an active device not a load we see as hobbist.

I stand by my words as written.
John

Thank you Terry.

ckn, Thank you for your educational post!!

On that note I'll say good bye. I cannot explain the frustration I am experiencing. Kurt did you even try to understand the math?
Later,
John

Don't need no stikin math, LOOK at a MA meter when the ignition is running. Then change battery pack voltage and look again. Theory is wonderful, but facts is facts.....

I've been following this thread and I can tell there are some VERY intelligent people giving many fine examples of their side of the argument. I am no electrical engineer and have no idea who's winning, what I do know is that the argument has almost nothing to do with how voltage supplies and current consumption are reflected in the ignition systems we use on our toy airplanes, at least in any way that the general modeler could understand. It doesn't even matter what type of ignition system it is, if the discussion, examples, and test findings were to stay focused on DC ignition systems, as TKG explains, it is so simple to prove with a simple MA meter connected to and ignition, the bigger the battery used to power it, the bigger the number is on the MA meter.... everytime..... what more is there to prove?</p>

Nothing like getting out there and doing it?

It gets better. Our ignitions only develop a full capacitive charge in the lower rpm bands. As the rpm increases that re-charge is reduced so that the faster our engines run the lower the amount of voltage will be delivered through the spark plug. The charge cycle can't work fast enough. It's called post delay. That's where a weak battery really starts to show up. It could be a 20v battery but if it's low in amperage or charge state you'll have a missing engine.

I agree with Jack about the Eneloops. Been using them for ignition batteries for about 2 years now. They retain a charge quite well and none of mine have ever let me down for a day's flying with a twin. 4.8v, 2,000 ma and they work out very well. Thanks for the original heads up Jack. They have worked out quite well.

And meters have tolerance and internal resistance issues which can and usually do affect their readings. Understanding the basics in theory results in a better understanding of what facts are facts. How often have you seen someone use a VOM on a resistance range to measure voltage?

All I was trying to do guys is give a simple explanation of basic DC OHMS law to help the average modeler understand why increasing voltage will increase current on a load, or what to expect for battery life given an average current draw. I thought providing simply math as a proof would be the final word on the subject.

I forgot that engineering is held in contempt by the average guy. He doesn't want to see math. Engineering has made such progress in the last century that the results are now expected and treated as if they were magic. Understanding theory is not necessary and it's not possible to understand anyway. Add to the mix of political correctness where everyone should be treated equally and a mathmatical proof becomes just someone elses opinion.

Thanks for the entertainment guys it's been an interesting thread.
John