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-   -   Cons for installing redundant receiver batteries ? (http://www.rcuniverse.com/forum/rc-jets-120/11267425-cons-installing-redundant-receiver-batteries.html)

rcfun2005 10-19-2012 09:44 AM

RE: Cons for installing redundant receiver batteries ?
 
"the genuine A123's are capable of being charged at 10amps without a problem"


so for everyday charging , what is typical charge rate ?


sounds like they get full charge in 15 min .

tks

BaldEagel 10-19-2012 09:53 AM

RE: Cons for installing redundant receiver batteries ?
 
If they are in the workshop I balance charge them at 2Amps on the field I give them a charge at 5Amps after a couple of flights, 10mins and they are 90% charged again, but first you have to find a charger that can charge at the rate you want, contrary to popular opinion they do need a balancing charge occasionally if you want them to last.

Mike

Sparhawk 10-19-2012 09:58 AM

RE: Cons for installing redundant receiver batteries ?
 
Why even bother with switches? Just another failure point in my eyes. Unless your batts are buried, I use the Deans to connect to my receivers.
In the past, I used the Smartly failsafe regs with the pin and flag switches when I used 2c LiPo's . Now, with LiFe packs, I just use a Deans wire harness from the receiver. Battery - wire - Deans F - Deans M - wire - Receiver.

Doesn't get any simpler than that.

Dan

BlueBus320 10-19-2012 10:33 AM

RE: Cons for installing redundant receiver batteries ?
 

Quote:

ORIGINAL: Sparhawk

Why even bother with switches? Just another failure point in my eyes. Unless your batts are buried, I use the Deans to connect to my receivers.
In the past, I used the Smartly failsafe regs with the pin and flag switches when I used 2c LiPo's . Now, with LiFe packs, I just use a Deans wire harness from the receiver. Battery - wire - Deans F - Deans M - wire - Receiver.

Doesn't get any simpler than that.

Dan

Simpler & Cheaper.. I think I like it

DrYankum 10-19-2012 10:45 AM

RE: Cons for installing redundant receiver batteries ?
 
Since almost all our switches are internal in jets, and the canopy has to be removed anyway to get to them, their is no advantage to using a switch. Deans to Deans without switch. Also has the advantage of not draining battery when not in use, since many switches have a slight current draw

basimpsn 10-19-2012 10:51 AM

RE: Cons for installing redundant receiver batteries ?
 
1 Attachment(s)
I go alittle bit farther.. Two battery, two switch and two receivers ;)

mr_matt 10-19-2012 11:01 AM

RE: Cons for installing redundant receiver batteries ?
 
I like the idea of a RX connector (in fact I am going to try to go to that, but I am not sure if that process (pushing and pulling) is more reliable that a good switch. It certainly could be, at least I would think.

In my aerospace days, I heard a lot of arguments between competing reliability guys, so to me reliability estimates are not always intuitive.

I think that the referenced NoBS write up about parallel batterys is one of the best ones (I run his batteries whenever I can). IIRC, he does not argue that these effects do not occur (one battery effectively "charging" the other), rather he argues that the effect is so slight it can be ignored.

A lot of it depends on the real world failure modes of the batteries and the regulators and of course the frequency of the failures (ugh I hear those reliability engineers arguing again!).

edh13 10-19-2012 11:14 AM

RE: Cons for installing redundant receiver batteries ?
 
Honestly when was the last time you heard of a RX battery failing in flight? Dying in flight yes, but failing(?) And if you’re out of juice you’re out of juice, dual batts aren’t going to matter. I’ve quit running dual batts, waste of weight. For those who say you can just run two smaller batts to make up for the weight penalty you’ve just doubled your chances of failure. If your plane needs 1400mah and you run two 700mah batts, if one quits you’re still crashed.

Dr Honda 10-19-2012 11:14 AM

RE: Cons for installing redundant receiver batteries ?
 

Quote:

ORIGINAL: BlueBus320

Thanks Dr Honda!.. I was hoping someone would chime in quick, as I am Finishing up my cart with Dreamworks as we speak. From my research on the Wolverine this morning, it appears that the 2 switches share a common circuitry board, so I agree 100%. 2 switches seem to be the only way to truly have 2 independent power sources.

Not a prob. I don't always have the perfect answer... but I think a lot of what goes on... on this end of the hobby... is overkill. BUT... because of the issues with fires, and/or injury if there is a failure... it's good to have some redundant safety. And... since a switch is mechanical... and could fail... it's good to double up on that. (I direct plug in is good too) Also... since you now have 2 batteries... you don't have to worry about drawing too much power, and having a brownout. (Rx resetting)

Now... what they guys are saying about genuine "A123's" is true. It's probably the best LiFe battery out there... but fast charging any Lithium battery will shorten it's life. So... I charge at 1c always. Personally... I don't own any because of the price tag. The Life Batteries from Tower are fine... and I even have some "Import" versions that work fine. The nice thing with the new chargers is that you can cycle a battery to see exactly what capacity it has.


Finally a word on an "Isolator."

Without a doubt... an isolator would be great if you have a pack short internally. BUT... when was the last time you heard of that happening on an Rx battery??? Right... never. If an Rx battery fails... it's normally that it looses capacity, or a solder joint gives up. you can make a simple isolator by putting a rectifier diode in the feed wire... but you will get a voltage drop across the diode. Depending on they type/size... it will be 0.5 to 1v.


As normal... just my 2 cents... take it for what it's worth.

flyinfool1 10-19-2012 11:31 AM

RE: Cons for installing redundant receiver batteries ?
 

Quote:

ORIGINAL: Sparhawk

Why even bother with switches? Just another failure point in my eyes. Unless your batts are buried, I use the Deans to connect to my receivers.
In the past, I used the Smartly failsafe regs with the pin and flag switches when I used 2c LiPo's . Now, with LiFe packs, I just use a Deans wire harness from the receiver. Battery - wire - Deans F - Deans M - wire - Receiver.

Doesn't get any simpler than that.

Dan

Initially it will be more reliable.
Gold plated connectors do NOT make reliable switches.
Gold is a very soft metal and will wear off the connectors very quickly leaving a less than optimal contact surface.
A quality switch has contacts designed to repeatedly make and break a circuit. Typically the contacts in a switch will be coin silver with a geometry to provide for a first contact and then slide to the final current carrying position for a solid clean connection. The switch will also slide away from the current carrying position before breaking the circuit to again keep the on position clean. Very few connectors have this arrangement. Deans and standard servo type connectors do not have the geometry to be self cleaning. On my electric powered aircraft that use Deans I have to replace the connectors every 30 - 40 flights because the contact resistance is starting to rise. There are connectors that do have the proper wiping action like the Anderson Power Pole connectors. As my Deans fail I am switching over the the APPs for this very reason. The APP also have a locking feature to keep them from accidentally coming apart. Many of the available systems use Deans because they are popular, not because they are better. Deans was once the gold standard for electric powered aircraft.

You are going to be more reliable in the long run using quality switches over using plugs as switches.

David Gladwin 10-19-2012 11:31 AM

RE: Cons for installing redundant receiver batteries ?
 
John, I used to do what you did, use two batteries isolated via diodes etc. Worked well. However, when I got really serious about power supplies, BVM F4, AMT Pegasus arrived 14v years ago, , (and its still around !) it was Tony Fradiowack, then working in NASA's model dept who suggested I just connect two Duralites straight onto the RX bus. This I did, still do, but being a nerd I wanted to test it for myself. Never did I find a battery that discharged into the other at any significant rate, with or without regulators and I tried flat batteries and some which were completely dead, wouldn't even take any charge. That is the conclusion on the NOBS battery site too where the author is a battery expert from the industrial field(GE). Its worth a read. I also thought it logical to connect the two batteries to opposite ends of the bus, turned out that doubles the current capability of the bus. Can't hurt even if there is no real practical advantage.

I agree that a standby battery in a tx would be of benefit but after gathering a LOT of data via my Weatronics systems , I can see that tx batteries have a very easy life compared with those in the Rx. If one produces a graph on Weatronics software of Tx batt voltage its almost a straight line with a gentle decline indicating a near constant small current. On the other hand the current (the voltage stays very stable) in the rx primary battery shows considerable fluctuation, varying between 3 amps with spikes upto 10 amps on an AirWorld Hawk. Do these variations increase the risk of battery failure, I don' t know but its very reassurring to have TWO battery circuits EACH independently capable of running the system.

I think it was David Searles who published the fact that JPO found that the MAIN cause of crashes in jet models was battery failure, dual batteries will virtually eliminate that risk. Its easy to do so why not do it ?

We cannot remove ALL risk in aviation, a 747 has only one fin, one came off in Japan, years ago, but they still fly with one fin, but at least we can go a long way to improve safety by eliminating obvious and serious risk, particularly when the solution is easy and cheap. A failure of a single battery and its all over, with a dual battery installation failure of a single battery is a non event.

and may I ask why Xairflier changes his batteries every year, worried about failure perhaps ? Some of my batteries in Dual installations are years old, I will change them only when they start to show a deterioration in service , confident that the risk of a dual simultaneous failure is negligible.

Regards,

David.

erbroens 10-19-2012 11:32 AM

RE: Cons for installing redundant receiver batteries ?
 
Quote:

ORIGINAL: edh13

Honestly when was the last time you heard of a RX battery failing in flight? Dying in flight yes, but failing(?) And if you’re out of juice you’re out of juice, dual batts aren’t going to matter. I’ve quit running dual batts, waste of weight. For those who say you can just run two smaller batts to make up for the weight penalty you’ve just doubled your chances of failure. If your plane needs 1400mah and you run two 700mah batts, if one quits you’re still crashed.

Failing a batt is not real issue. However year ago saved a jet of mine due to redundancy as I found a broken wire on one of the batts.


And about someone who might use two 700 mah batts when 1400 mah are needed, deserves to be tarred and feathered.

gooseF22 10-19-2012 11:32 AM

RE: Cons for installing redundant receiver batteries ?
 

Quote:

ORIGINAL: rcfun2005

''the genuine A123's are capable of being charged at 10amps without a problem''


so for everyday charging , what is typical charge rate ?


sounds like they get full charge in 15 min .

tks
4 amps

Chris Smith 10-19-2012 11:39 AM

RE: Cons for installing redundant receiver batteries ?
 
Quote:

ORIGINAL: Stobe777

The real question is: why don´t we have 2 batteries also in the transmitter? : )

TP.
The transmitter battery is a failure point, however the enviornment is fairly stable in the transmitter. We should not forget that amp loads and power draws in the airplane can vary and challenge the reciever battery. Especially in jets, the airplane is more likely to experience a "brown" out condition with amp spikes and low voltage. We are less concerned with the odds of a total battery failure. These brown outs are the largest issue dual batteries can fix. The dual switches help keep the amps from choking on wires that are inadequate.

Not a real issue for the transmitter.

gooseF22 10-19-2012 11:56 AM

RE: Cons for installing redundant receiver batteries ?
 

Quote:

ORIGINAL: BlueBus320

If the wolverine fails, do you loose both ports? It seems like it may be better to go with 2 individual high quality switches.
My story on the wolverine: The wolverine output is on a common output bus but it has in essence 4 redundant paths with isolation on the input side... I have seen a direct short on the output side that caused a FIRE on the switch circuit board and while it was putting out a blue flame on the edge of the circuit board, the aircraft was still powered.. one of the transistors was burned totally, but the other three were working fine. Once I removed battery power on that failed sw, (which was still on), it would not re latch, but thats as designed.. the direct short was my fault, I pinched a servo wire under the switch and didn't see it.. could have been disaster, but ..... pretty interesting seeing a blue fire inside the canopy, smoke coming out the wheel well.

so the switch would have to fail all 4 transistors to fail totally.. something I have not been able to do in testing up to 40 amps back when..

So if you want isolation and sharing, wolverine is a great candidate, regardless whats on the output side (regs or rx direct)..





David Gladwin 10-19-2012 01:06 PM

RE: Cons for installing redundant receiver batteries ?
 

[
[/quote]

. Especially in jets, the airplane is more likely to experience a ''brown'' out condition with amp spikes and low voltage. We are less concerned with the odds of a total battery failure. These brown outs are the largest issue dual batteries can fix. The dual switches help keep the amps from choking on wires that are inadequate.

Not a real issue for the transmitter.
[/quote]


and thats another point, Chris, there should NEVER be a significant voltage drop if the battery(s) and cables are adequate for the job in hand. The voltage , logged at every.1 seconds on my Weatronics system shows that my voltages never vary by more than .2 volts at most and under the biggest load, and rarely at that. Clearly the batteries have the capability to meet worst case demands but the Wea gives you the data at analyse that aspect, invaluable.

Regards,

David.

BlueBus320 10-19-2012 01:16 PM

RE: Cons for installing redundant receiver batteries ?
 
OK so I'm thinking a great/cheap/simple solution would be 2 batteries direct to opposing receiver ports (no switches), utilizing Anderson Power Pole connectors would be a very reliable setup. Goose, that's great info on the Wolverine, if I decide to use switches I'll have to make a choice between Wolverine, 2 Badgers, or 2 JR switches with built in charging ports.

Boomerang1 10-19-2012 02:17 PM

RE: Cons for installing redundant receiver batteries ?
 
I've used Anderson Power Poles (also known as Sermos connectors) for many years on my electric
models without ant problems at all. I've standardised my jets, too, using them, without switches,
for connecting the ECU battery.

I don't use them for reciever batteries, no real reason, I just don't use them for that application.
For the reciever I just run two batteries through two switches to the reciever, as many others
have mentioned in this thread.

As for the myth that one faulty RX battery would drag the voltage of the other down how many
people have ACTUALLY done a test?

In a very old RC Jet Int (Feb/Mar 2001) a gent named Paul Mitchell actually did the tests for most
scenarios & published the results.

Apart from a simultaneous failure of both power supplies (improbable) or EVERY cell in one of the
battery packs short circuiting SIMULTANEOUSLY (extremely improbable) just two packs will do the
job.

It's a myth. - John.

BarracudaHockey 10-19-2012 02:28 PM

RE: Cons for installing redundant receiver batteries ?
 

Quote:

ORIGINAL: rcfun2005


Quote:

ORIGINAL: BlueBus320

Thanks Dr Honda!.. I was hoping someone would chime in quick, as I am Finishing up my cart with Dreamworks as we speak. From my research on the Wolverine this morning, it appears that the 2 switches share a common circuitry board, so I agree 100%. 2 switches seem to be the only way to truly have 2 independent power sources.
''2 independent power sources'' but if you plugging them into one reciever bus ,,, your 2 sources are now connected on the one bus ... so depending on way a cell fails it can draw down the other batt being connected on one bus with no isolator circ...
so what is going to be the failure your protecting against ? ....

no right answer ... just pros and cons both ways...

interesting



That myth was busted a long time ago.

What method of failure do you suppose will pull the other battery down?

BaldEagel 10-19-2012 02:31 PM

RE: Cons for installing redundant receiver batteries ?
 
For the switch also worth considering is the Boomer RC BRC_IS1 Intelliswitch, it is a dual switch that also reads the Mah used during operation from each battery, very useful when using A123's as you can then measure the amount put back into the packs and compare the results.

Mike

Dave 10-19-2012 02:54 PM

RE: Cons for installing redundant receiver batteries ?
 
Running two battery packs in parallel is a bad idea since their voltage is not identical. Therefore, they oppose each other constantly as one voltage bucking another. This is called buck voltage. The battery share circuit eliminates this problem.

The link in post #7 is WRONG.

mr_matt 10-19-2012 03:20 PM

RE: Cons for installing redundant receiver batteries ?
 
Here we go.....

BaldEagel 10-19-2012 03:22 PM

RE: Cons for installing redundant receiver batteries ?
 
Pop corn, peanuts get them here, best value on the site. ;)

Mike

Dr Honda 10-19-2012 04:19 PM

RE: Cons for installing redundant receiver batteries ?
 
Yep... cooking the pop-corn.


Was this supposed to be a debate... or a simple answer to a question? I'm out........ :)

mtnflyer14 10-19-2012 04:29 PM

RE: Cons for installing redundant receiver batteries ?
 
Wow. I'm not an expert, but I would be very hesitant to take on the NOBS battery expertise. I follow their advice and run two 6.6v LiFe batteries through a Miracle switch into the battery input in the receiver and another unused channel. No problems.
Regards,
Gus


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