Jake Ruddy

My Feedback: (40)

No one is sponsoring me either... but consideirng the abuse I put foamies through including crashes if the battery is installed properly I dont see what the problem would be. I also have a friend flying lipos in an high end 2m pattern plane.. while electric is smoother.. those negative 1.5 snaps are pretty darn violent amoungst other things

People do more damage running them harder than they are designed to run, running them down too low, and improperly charging them than anything.

rmh

If you call and ask the ignition guys you shoud get a definitive answer
but --one more time ----------
when yo reduce the voltage lower than the design input ---
you automatically INCREASE the amperage into the ignition - this MAY overheat transisters and cause premature ej- excuse me, failure.

Jake Ruddy

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haha dick

the ignition he is using is stated it can run at 3vs

3d-aholic

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I don't understand this...

V=IR
Voltage is directly proportional to Amperage. Voltage goes down, Amperage has to go down as well.

Bob Pastorello

My Feedback: (198)

http://www.the12volt.com/ohm/ohmslaw.asp

I think 3d is right, Dick.... how come we think the current drawn will go UP with lower source voltage?

rmh

ah screw it -

Jake Ruddy

My Feedback: (40)

just to clarify.. I was laughing at your joke

3d-aholic

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I was just asking for a clarification.....

I have studied electronics and I don't understand how you can squeeze more amps out of a closed circuit with resistance held constant and you actually have less voltage to work with. Its kinda saying that you going to keep the hose the same size, turn the water flow down and somehow the water pressure is going to go up.

I'm just figuring I'm missing something.....[&o]

Scott Ellingson

My Feedback: (146)

OK, The CH version of the Rcaxl will run on a 1 cell lipo. A single A123 I am not sure because of the lower voltage. Josey is testing that right now to see how much of the capacity it will use before starting to miss. If the voltage gets too low it will simply start missing at higher RPM's and you should land imediatly.

Bill at CH has been flying 2 planes for a couple of months now on a 1 cell Lipo. I also have been flying mine the same way. I have bench tested the setup at 10,000 rpm and it went for 2 hours 15min on a 1550 1 cell LiPo pack. Current draw was about 680 mah. The same as when it is run on a 4.8v pack at that high of an RPM. The higher the RPM, the higher the current draw. There was NO current draw increase with the lower voltage pack. On the bench I did not get a miss until the voltage was just below 3v. So the A123 should be able to run it at most of its capacity. Further testing is needed on that, but it should. The key to this EI running at that low of a voltage is not the EI itself, it is the hall sensor. The Panasonic hall sensor used by most EI builders will not run at that low of a voltage. The Allegro hall sensor the Rcaxl EI uses does. It is not supposed to go down that low either, but it does for some reason. I have tested multiple Allegro hall switches and they all seem to preform the same.

Scott Ellingson

My Feedback: (146)

3D, You are correct. If the CH version of this EI is run at 6v, it heats up because of a higher current draw at the higher voltage. Not the other way around. That is why CH says 4.8v max, even though the manufacturer says 6v.

rmh

I was looking at watt requirement - lower the voltage -you have to increase the amperage to get same watts
but not ignitions are done the same way - what may be a problem tho is that LiPos as they run down drop to under 3 v as the primary stage of the ignition is "loaded " the A123 holds voltage under load right ondown to about 80% of charge

also the IC(if they have one) may have a threshold which is close to 3 v
anyway run what you like-- if it quits - you will know the test did not work.

3d-aholic

My Feedback: (7)

Ok thanks for explanations..
I understand the thought process now.

dirtybird

My Feedback: (5)

Keep studying. You will find that reactive components don't act the same as resistive components

rmh

like a girl friend or wife -
some resist --others react---

Bob Pastorello

My Feedback: (198)

And *neither* follow Ohm's (or anyone else's) Law, for that matter....

rmh

Today's secret word is --- capacitor
here is a little stiry about ignitions
If you want "x" amount of energy out of a ignition -- you have to put "x" (plus a little) into the ignition s
If you reduce input -what happens to output?
The time required to fill up the ignition primary stage is greater than the time it takes to discharge the spark -- so --that helps
However -there are limits to all things .
One thing more -- the faster you extract power from a battery -- the voltage you get will become lower
How cum?
batteries have internal resistance -this is resistance to change -either charge or discharge - so you can slowly extract power and the battery will deliver higher voltage-
or you can do it in a nanosecond and it will be lower -
so if you start with a low voltage and you rev things up - what happens?
next week we look at persnipitors.

Bob Pastorello

My Feedback: (198)

Damn!!!!!!!! I had one of them thar persnipitors once.... dang thing got all wound up in the p-factor, shorted out the decalage generators, and the vapor un-locked. Man, it was UGLY..... persnipitorforesence was dripping off the airplane EVERYWHERE.....(and it glowed in the dark afterward)

rmh

those were the early ones - they now are improved -- actually they crosslinked a persnipitor with a persnickity which is of course , intolerant of "*vascular obfuscating".

It cost my folks a lot to put me thru electriciti school and soon I will grajewate.
It will be a shock too many.

* bloody confusing

Scott Ellingson

My Feedback: (146)

Actually the larger the engine, the harder and more spark energy it takes to run it. I am running my 60 on the single Lipo. It is a 20c lipo so the EI will never draw enough current to even effect it. Who says it takes 4.8v to run an EI system? They are only set up to run on that because that is the batteries we run. I can not give all of the technical reasons why a 3.7v battery works. I just know it does. I fly, it runs, top RPM are the same on the 3.7 as a 4.8 pack. Idle is the same. Transition is the same. It works and that is all I care about. Also a 1.4oz battery for over 2 hours of flight is kind of nice. Who care what it SHOULD do on paper. What it DOES do in reality is what matters. In reality, with that EI and hall, it works, and works well.

Bob Pastorello

My Feedback: (198)

I agree, Scott. The proof is always in the performance, or lack of it.

I do have one question - maybe someone can 'splain.... this business of "larger engine needing more spark energy".... theory says that is absolute hogwash. The spark, whatever size, simply STARTS the burn.... the amount of spark shouldn't make a difference. The DURATION (dwell) may.... but on a two stroke, I don't think I understand why we think we need greater spark with bigger engine....

Anyone??

Scott Ellingson

My Feedback: (146)

I do not know how to explain it correctly either. I do know more compression makes it harder to spark. The higher the compression, the higher the resistance of the fuel/air mix. I know a weaker EI will work on smaller engines, but not larger. It may just be because of compression. I am not sure. That would be a good question for TKG.

Josey Wales

My Feedback: (61)

I sent a PM to TKG--hopefully he will drop in give us some techno-talk about this--

Bob Pastorello

My Feedback: (198)

Cool.
Joe - did you do some flying today with the single A123 on ignition??

Josey Wales

My Feedback: (61)

No..not since Friday but I will be flying tomorrow again with the A123 on the ignition....I was reading CH's website and they will adjust your ignition to run off a lipo without needing a reg if you want to...If TKG says not to run the low voltage cell that may be another option depending on how much it will cost..then we could run it like you have....

rmh

FWIW--- the pressure in the cylinder determines the amount of current needed - not the cylinder displacement.
When I had a special system made years back for a 1.4 cu in engine - we tested on SUN equipment the spark - it was 15000 volts - this was and still is typical VOLTAGE - the AMPERAGE required changes again with pressure and spark desired . (some ignitions are 20000 volts but if you can't tell the difference who cares .)
as I tried to explain earlier - you can't get more out than you put in - sorry- it just is not possible
If it is enough for YOUR engine - fine -most of these have extremely low , effective compression --especially the converted industrial stuff.
I am not saying it is bad -it isn't - these make great little engines but they are not power tuned high performance engines and quite frankly 90% of the users will never want a highly tuned set up. It would just be a pain in the ask for them.
however - just because the engine does not miss --does not mean the spark supplied is enough for max performance
Those guys who have been thru CDI/ and mags and other racing setups and measured performance (speed, acceleration etc., know what I mean.
Before a lot of flyers were born - a really hot ignition was a set of dual points and dual coils -used to ensure full saturation etc., at higher rpms. Now, this is all museum stuff
The present ignitions range from the inexpensive and good imports from China to the really fancy stuf from MVVS and lots of othe types in between
All of them that have published specs I have seen, are 15000-20000 v and run on 4.8 - 8v -input
who publishes a lower input voltage?