RE: IMAA's Marez speaks out on parallel systems  
View related threads: (in this forum | in all forums)

Tower Hobbies
Enter up to 4 keywords or Tower stock numbers
Logged in as Guest



Users viewing this topic: none
  Printable Version
       

All Forums >> Radios, Batteries, Clubhouse and more >> Batteries & Chargers >> RE: IMAA's Marez speaks out on parallel systems
Page: <<   < prev  1 [2]

Login
Message << Older Topic   Newer Topic >>
RE: IMAA's Marez speaks out on parallel systems - 3/26/2005 4:36:53 PM   
Diablo-RCU


 

Posts: 3208
Joined: 12/19/2001
From: Hammond, IN, USA
Status: offline 		Say Red:
Could you perform the same experiment using a 5-cell pack hooked to a 4-cell pack in parallel?
That should test the scenario (however unlikely) that one pack has a hard dead short in one of the cells. I'm curious how much current would flow during a 15 minute period (flight).

I also use two 5-cell packs in parallel. My thinking is that if I get a hard short during a flight, the minimum pack voltage is still greater than the receiver requires to function. Receivers work on 4-cells, but die on 3-cells.

(in reply to hiramboesky)
       Post #: 26

RE: IMAA's Marez speaks out on parallel systems - 3/26/2005 5:49:36 PM   
Red Scholefield



Posts: 4902
Joined: 12/8/2001
From: Newberry, FL, USA
Status: offline
quote:

ORIGINAL: Diablo-RCU

Say Red:
Could you perform the same experiment using a 5-cell pack hooked to a 4-cell pack in parallel?
That should test the scenario (however unlikely) that one pack has a hard dead short in one of the cells. I'm curious how much current would flow during a 15 minute period (flight).

I also use two 5-cell packs in parallel. My thinking is that if I get a hard short during a flight, the minimum pack voltage is still greater than the receiver requires to function. Receivers work on 4-cells, but die on 3-cells.


I'll hook it up and let you know, but be advised anything we come up with will only be an illusion of the amount of power transfered.


_____________________________

Red S.
AMA 951 Leader Member

(in reply to Diablo-RCU)
       Post #: 27

RE: IMAA's Marez speaks out on parallel systems - 3/26/2005 6:35:30 PM   
Diablo-RCU


 

Posts: 3208
Joined: 12/19/2001
From: Hammond, IN, USA
Status: offline 		Thanks Red:
RC is one big illusion....

(in reply to Red Scholefield)
       Post #: 28

RE: IMAA's Marez speaks out on parallel systems - 3/27/2005 5:59:00 AM   
jvolkes


 

Posts: 44
Joined: 6/17/2003
From: chesapeake, VA, USA
Status: offline
quote:

ORIGINAL: Diablo-RCU

Say Red:
Could you perform the same experiment using a 5-cell pack hooked to a 4-cell pack in parallel?
That should test the scenario (however unlikely) that one pack has a hard dead short in one of the cells. I'm curious how much current would flow during a 15 minute period (flight).

I also use two 5-cell packs in parallel. My thinking is that if I get a hard short during a flight, the minimum pack voltage is still greater than the receiver requires to function. Receivers work on 4-cells, but die on 3-cells.



Diablo, the point of all this is that you won't be aware of when that pack develops a shorted cell, particularly inflight.

Good experiment but the fact is that electical isolation is the only way to accomplish battery redundancy. I agree with the others that shorted cells occur most often.

_____________________________

DOH!

(in reply to Diablo-RCU)
       Post #: 29

RE: IMAA's Marez speaks out on parallel systems - 3/27/2005 1:35:19 PM   
iflyj3



Posts: 969
Joined: 5/18/2002
From: Paris, KY, USA
Status: offline
quote:

ORIGINAL: Diablo-RCU

Say Red:
Could you perform the same experiment using a 5-cell pack hooked to a 4-cell pack in parallel?
That should test the scenario (however unlikely) that one pack has a hard dead short in one of the cells. I'm curious how much current would flow during a 15 minute period (flight).

I also use two 5-cell packs in parallel. My thinking is that if I get a hard short during a flight, the minimum pack voltage is still greater than the receiver requires to function. Receivers work on 4-cells, but die on 3-cells.


I did this type of test with a 4 cell and 3 cell packs hooked in parallel to satisify my self about four years ago. I observed an 80 ma transfer at about 4.1 volts. This satisfied me that I could continue the curent flight and lad at the end of it. The shorted cell pack would be caught with a loaded voltmeter before the next flight.

A five and four cell test should come out similar. I await the results of Red's test.



_____________________________

Dan Thompson (Long live the ACE MicroPro 8000)
Visit www.groups.yahoo.com/group/mp8k for support

(in reply to Diablo-RCU)
       Post #: 30

RE: IMAA's Marez speaks out on parallel systems - 3/27/2005 3:10:49 PM   
Red Scholefield



Posts: 4902
Joined: 12/8/2001
From: Newberry, FL, USA
Status: offline
quote:

ORIGINAL: jvolkes


quote:

ORIGINAL: Diablo-RCU

Say Red:
Could you perform the same experiment using a 5-cell pack hooked to a 4-cell pack in parallel?
That should test the scenario (however unlikely) that one pack has a hard dead short in one of the cells. I'm curious how much current would flow during a 15 minute period (flight).

I also use two 5-cell packs in parallel. My thinking is that if I get a hard short during a flight, the minimum pack voltage is still greater than the receiver requires to function. Receivers work on 4-cells, but die on 3-cells.



Diablo, the point of all this is that you won't be aware of when that pack develops a shorted cell, particularly inflight.

Good experiment but the fact is that electical isolation is the only way to accomplish battery redundancy. I agree with the others that shorted cells occur most often.


In the 50 years I have been flying R/C and the 30 in the battery business I have never seen a cell short during flight! It may be shorted BEFORE the flight, and that should be picked up in the pre-flight ESV check. Shorts [other than by physical abuse] cannot establish themselves in a fully charged pack! If one finds after a flight (crash) that a cell is shorted it is most likely he took off with a shorted pack. A system will operate on 3.9 volts (the voltage of three fully charged cells) long enough to get you in the air.


_____________________________

Red S.
AMA 951 Leader Member

(in reply to jvolkes)
       Post #: 31

RE: IMAA's Marez speaks out on parallel systems - 3/27/2005 10:47:43 PM   
hiramboesky


 

Posts: 54
Joined: 9/26/2003
From: brooklyn, NY,
Status: offline 		Red, with all due respect, no fair bringing age and longevity into this conservation! I’ve been flying R/C since single channel radios, Bonner Escapements and Kraft tube receivers….My first airplane was a Midwest Esquire with an Enya 15… It had a whopping 36"+ w/s as I remeber. Very big for its time.......

Your observations are anecdotal and not fact. There’s no dispute that the scheme you promote will cover one instance of failure, but not all…….If you’re flying anything larger than a .60 size airplane and your battery drops to 3.9 volts, you’re airplane is most probably finished. If you happen to be flying a .40 sized airplane when the battery drops to .39 v you probably have another 2~5 minutes before your airplane is finsihed…..What’s the point? One way or another, if the second battery fails you won’t know since you’re flying it at the time of failure….If not, then why add secondary onboard battery???

It’s been my experience, in my R/C “career”, that I’ve had more packs go bad that had shorted cell than open cells. , Batteries whose cells usually start with the symptom of low capacity and eventually end up with one shorted cell.

I think to put forth the notion that this is not true is to do everyone in these forums a disservice. The fact is most of my power tools that utilize batteries fail in the same manner.

To rationalize adding a second onboard battery in the event that you forgot to charge, or that the wall charger wasn’t plugged in, or that it was bad, etc. is well, sort of counter intuitive. Why not carry a field charger or an extra battery in your field box? This is certainly not the reason why most R/C’ers add that second pack, particularly onboard.

They add a second pack for REDUNDANCY, and for no other reason.

You cannot have redundancy without electrical isolation, period!

Now for those of you that worry about bad switches you can purchase batteries with two power connectors, but adding a second pack is, well, of questionable use. Sort of a coin toss……..

(in reply to Red Scholefield)
       Post #: 32

RE: IMAA's Marez speaks out on parallel systems - 3/28/2005 4:22:12 AM   
Forgues Research



Posts: 3411
Joined: 12/15/2001
From: Glen Robertson, ON, CANADA
Status: offline
[/quote]


Branded -

If we're going to throw around titles, I'm an EE PhD, electrical and aeronautical engineering with a minor in mechanical. I have extensive experience in power system design, including battery subsystems. I have performed very sophisticated ESS and HALT tests on many types of battery cells. In the majority of "in use" failures cells increase in resistance or fail open - far more often than they short. You see this in reduced capacity or a slow degradation of the batteries ability to deliver current (i.e. hitting the wall) Without getting technical - Red's explanation above explains it perfectly. This holds true in the batteries used in full scale aircraft, automotive, cellular phones, back up power inverters, rechargeable consumer devices and just about everywhere else batteries are used. Perhaps there is something special about the cells in our flight packs? Doubt it.

In mechanical battery banks (i.e. assembled packs) the prevailing failure mode was an open pack (not an open cell) due to failure of the mechanical bond (i.e. weld) of the tabs or wiring.

While I agree I may have used a blanket statement above without offering any data - I have found no merit whatsoever in using a battery backer or sharing device as long as both packs are routinely checked, in the same capacity, and charged in a similar fashion using a gang charger. I have in fact seen them create more problems than they solve, hence my statement.

If you want to use different capacity batteries or different technologies, then maybe I can see using it.

I wasn't trying to start a p'ing match, just trying to offer up a biased opinion - how's that for piling it higher and deeper!

DP





[/quote]

I have a question here that I hope you can help me with on this subject.

I also have used Nicds ever since I have been in the hobby which is longer then I would like to remember. I also think that with good preventive maintenance, which I do, battery failure is quite rare. Soooo, why even go to two battery packs in the first place. The only failure point that I can see is the switch. I use only one battery pack for the servos with two switches on the same pack. I also have a battery pack for the receiver which is totally independent of the servos (read opto isolated)

I also use only one receiver even in my recent 52% Edge. Receivers didn't break down with small airplanes so why are they more vulnerable in larger airplanes mostly when you have no servos connected to them in the first place. Hell, my receiver battery is a 500ma pack.

So any coments from you would be welcomed.

Regards
Roger


_____________________________

Evo Engines
http://forgues-research.com

(in reply to famousdave)
       Post #: 33

RE: IMAA's Marez speaks out on parallel systems - 3/28/2005 5:37:34 AM   
Flying Geezer



Posts: 1024
Joined: 4/12/2003
From: Bowling Green, KY, USA
Status: offline 		I am a little amused, and somewhat disgusted with the lack of tolerance for the opinions of others in this thread. One distinguished, veteran hobbyist wrote an article, and expressed an opinion. The opinion was not even on RC UNIVERSE. He was attacked in a mean-spirited manner in the first post of this thread.

Since then there has been a steady flow of undocumented "facts", none of which takes away the right of any person to have an opinion. I don't care if you have an EE, PHD, or the biggest, overblown ego in America. Humbly accept that "All the knowledge lies in no one man".

I have seen a lot of absurd advice on RCU by those claiming EE's, PHD's and more. And, I have seen a lot of good advice from some who have had little or no electronic training.

When my car doesn't run, I don't want an engineer or an auto executive. I want a practicing auto mechanic with at least a GED, some technical training in auto repair, and some on the job experience. Remember, engineers design them, technicians point the mistakes out to the engineers, after correcting them.

There is an old adage, "never discuss religion or politics". We may have to add batteries to the phrase.

So let the expert here who is willing to claim he knows it all, step up and say so, whether he has a PHD, EE, or GED. I'll pay his tuition to charm school, ( or help him get a refund if he has already been).

I don't care how you wire your airborne pack. It's your airplane and your opinion. I think you have a right to it, and so does Eloy Marez.

Hope this helps,

_____________________________

Flying Geezer
Hughes RC

(in reply to Forgues Research)
       Post #: 34

RE: IMAA's Marez speaks out on parallel systems - 3/28/2005 5:52:35 AM   
jvolkes


 

Posts: 44
Joined: 6/17/2003
From: chesapeake, VA, USA
Status: offline 		Hey, how about technicians that have evolved into engineers?

Is that ok with you, Geezer? Take some elixer and go to bed. You're getting cranky!

Back on topic- Aerografix- Your setup makes sense to me and I have a couple of my airplanes similarly wired.

I always (on an aerobat) use two batteries, one for servo supply, one for reciever. I don't follow the redundant switch philosophy. It's just my preference, I'm not saying its a good idea or bad- just that I've never had a switch failure and I'm not sure of the usefulness.

As for the second "redundant" battery pack....I would never do this as it makes no sense to me. If I wanted this "redundancy" I would electrically isolate the batteries (EE-101)......

JMO


_____________________________

DOH!

(in reply to Flying Geezer)
       Post #: 35

RE: IMAA's Marez speaks out on parallel systems - 3/28/2005 10:55:26 AM   
JNorton



Posts: 3134
Joined: 1/29/2002
From: Montague, MI, USA
Status: offline 		Flying Geezer,
quote:

I have seen a lot of absurd advice on RCU by those claiming EE's, PHD's and more. And, I have seen a lot of good advice from some who have had little or no electronic training.
Yah know that statement is just wrong. I've seen more myths perpetrated by those who have little electrical knowledge.

quote:

One distinguished, veteran hobbyist wrote an article, and expressed an opinion. The opinion was not even on RC UNIVERSE. He was attacked in a mean-spirited manner in the first post of this thread.
And what if what he is expressing is wrong? Just another myth being spread. If you really need to isolate the packs use 2 Schottky diodes in series. Heck of a lot cheaper.

My 2 cents.

John

_____________________________

Have desk ... Will Fly....
Saito Member #467

(in reply to jvolkes)
       Post #: 36

RE: IMAA's Marez speaks out on parallel systems - 3/28/2005 11:24:33 AM   
Flying Geezer



Posts: 1024
Joined: 4/12/2003
From: Bowling Green, KY, USA
Status: offline 		TO: JMO and JOHN, I respect and tolerate your right to your opinion. Doesn't mean I agree, doesn't mean I don't.

_____________________________

Flying Geezer
Hughes RC

(in reply to JNorton)
       Post #: 37

RE: IMAA's Marez speaks out on parallel systems - 3/28/2005 1:40:19 PM   
JNorton



Posts: 3134
Joined: 1/29/2002
From: Montague, MI, USA
Status: offline 		Flying Geezer
I'm chuckling over your reply - I especially like the word tolerate. If you lived closer we could go out have a flight or two then go out for for a beer!
John

_____________________________

Have desk ... Will Fly....
Saito Member #467

(in reply to Flying Geezer)
       Post #: 38

RE: IMAA's Marez speaks out on parallel systems - 3/28/2005 2:01:22 PM   
Red Scholefield



Posts: 4902
Joined: 12/8/2001
From: Newberry, FL, USA
Status: offline 		It appears this thread as run its course. I hope the technical information provided will give those that comprehend it enough to make an intelligent choice regarding power systems in our models.

The thread is now locked.

_____________________________

Red S.
AMA 951 Leader Member

(in reply to Red Scholefield)
       Post #: 39

Page:   <<   < prev  1 [2]
All Forums >> Radios, B