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Old 08-04-2017, 04:05 PM
  #3026
Joystick TX
 
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Default GSS NIMH to LiFe battery upgrade

I had to edit this a lot, I messed up. Chemo brain?


I've been watching the progress of the LiFe batteries for a couple of years now and haven't seen any "single" batteries that have failed in flight due to "opens or shorts", so it looks like they are doing pretty well.

Seems like it is time to replace my NIMH two 5 Cell battery system for a LiFe one battery, 2 Cell, system.

The LiFe 6.6V receiver battery comes with two "universal" receiver connectors. Instead of using a Y connector and single on off switch with one connection to the receiver I'm using two switches and two connectors to the receiver for redundancy.

If one of the LiFe cells opens, since they are in "series" to get the 6.6V, there will be no voltage going to the receiver, so this is not as good as the two battery solution that I used to have. The good news is that the LiFe batteries do not seem to be as susceptible to that failure mode as the old Nicad and NiMh batteries were, so for me it is worth the risk.

I still like the two switch installation. Mostly for redundancy, the switch is the least reliable right now.

The LiFe battery will need to be taken out occasionally to balance the cells, or an extension lead will need to be attached.

See diagram for my installation:
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Last edited by Joystick TX; 08-06-2017 at 04:02 AM. Reason: Totally messed up.
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Old 08-04-2017, 06:47 PM
  #3027
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Please excuse my ignorance. What is the advantage of using a single LiFe battery? I'm currently using a two battery system. 2x NiMH 6V 2000mAh. What seems to work for me (in my mind) is that I like the engine has its battery, and the Rx and servos has its own battery. I've had a 5 flight (15 minutes each) day and all seemed well. Don't get me wrong here, I'm amazed how you simplified your battery needs. I just feel (maybe ignorantly) secure about having two different systems. Obviously you are ahead of me in the battery game. Thanks for sharing. Tom
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Old 08-05-2017, 03:48 AM
  #3028
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Very nicely done Steve!
Steve's drawing represents a setup I've been talking about for several years now. It's light, simple, inexpensive, offers twice the amperage capability to the entire flight pack over what a single switch system offers, and complete power redundancy from the battery to the receiver. A bonus for those flying acrobatics requiring heavy use of the rudder, is that the rudder, when wired per drawing, has a direct feed from the battery, without having to go through the receiver.

I also agree with his thoughts regarding the LiFe battery technology. They seem to be doing REALLY well, especially when compared to NiMh.

LiFe batteries are capable of delivering incredible amperage - enough where a single switch becomes a choke point in a high performance system using digital servos. In a plane the size of a Giant Sportster, or really any plane flown hard that's equipped with digital servos (even 20cc stuff!), the servos are often capable of pulling so much power that voltage to the receiver may drop enough where the receiver drops off line - with predictable results (this varies by receiver, some are more prone than others). The double switch/LiFe plan pretty much eliminates that potential. That was my original reason for going with this setup. After going this way, "bonuses" kept popping up as I realized just what it's capable of when wired per the diagram.

As far as the necessity of providing the ign. module with a stand alone battery pack, go for it if it lets you sleep well. Just know MANY are using the same battery the receiver is using - without incident. There have not been ANY reports of problems using that method. -Al

Last edited by ahicks; 08-05-2017 at 10:43 AM.
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Old 08-05-2017, 04:25 AM
  #3029
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Quote:
Originally Posted by Tom Nied View Post
Please excuse my ignorance. What is the advantage of using a single LiFe battery? I'm currently using a two battery system. 2x NiMH 6V 2000mAh. What seems to work for me (in my mind) is that I like the engine has its battery, and the Rx and servos has its own battery. I've had a 5 flight (15 minutes each) day and all seemed well. Don't get me wrong here, I'm amazed how you simplified your battery needs. I just feel (maybe ignorantly) secure about having two different systems. Obviously you are ahead of me in the battery game. Thanks for sharing. Tom
It is mostly a matter of preference. There are pro's and con's with every setup.

I used two batteries for years. Post #3016 shows the two NiMh batteries and two switches (ignore the charging note). That solution gave true redundancy. If one battery fails open, the plane can fly with no problems. I only used my NiMh batteries for two years before I replaced them, but I put over 500 flights a year on each one of my planes. I never lost a plane that had two NiMh batteries with the way I had them connected.

I never liked a separate battery for the ignition and receiver, that solution did not provide any redundancy. In the "old days" it made sense to have a separate battery when the ignition voltage was different (lower) than the receiver voltage. Now the new ignitions can use the same battery voltage as the receiver. With the separate ignition/receiver battery setup, if the receiver battery failed, there would be total loss of control and the engine could continue to run if the the fail-safe was not set correctly. About half of the ones I've checked at our field were not set right. If the engine battery failed, the second battery would allow control with a dead-stick ASAP. Also, the new ignitions only draw about one-fourth of the power of the old ones, so a high-capacity battery for them is no longer required. A 2100mAh battery would run my ignition for almost 20 hours.

The only problem I have now with two LiFe batteries is cost. I have four airplanes to support. The initial cost is high, also like ahicks mentioned in post #3013, if you forget to turn off your system it may trash your batteries and that could be very expensive. The NiMh batteries could recover, with the LiFe batteries that is not guaranteed and I would not trust them if they did appear to recover.

Since the each 6.6V LiFe battery only has two cells and does not seem to be susceptible to the single cell failure like the Nicad and NiMh batteries I'm willing to take the risk and use a single battery now. has two cells which is the equivalent of two separate batteries, I like the redundancy that provides, so I don't need a separate battery.

I don't fear deadsticks with the GSS, I've had hundreds of them and have only peeled off the landing gear a few times. The fuselage mounted gear is great.

Last edited by Joystick TX; 08-05-2017 at 03:47 PM. Reason: A little messed up.
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Old 08-05-2017, 02:21 PM
  #3030
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OK, be patient with me, I'm trying to understand this and I'm fascinated with it. Almost got it. But you say " The only problem I have now with two LiFe batteries is cost". Are you using two batteries per plane? I don't think you are.
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Old 08-05-2017, 02:48 PM
  #3031
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Removed.

Last edited by Joystick TX; 08-05-2017 at 03:07 PM.
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Old 08-05-2017, 02:52 PM
  #3032
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OK, thanks. Could be me too. I study the written and compare to the diagram, and just kind of get confused in it. I'll stay tuned. Thanks
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Old 08-05-2017, 04:00 PM
  #3033
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That's pretty slick. I looked at that battery on Tower and it goes for about $35 a piece. Isn't that actually a savings? Weighs less too than two NiMh batteries.
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Old 08-05-2017, 04:16 PM
  #3034
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Quote:
Originally Posted by Tom Nied View Post
OK, be patient with me, I'm trying to understand this and I'm fascinated with it. Almost got it. But you say " The only problem I have now with two LiFe batteries is cost". Are you using two batteries per plane? I don't think you are.
No problem Tom, thanks to your question, I found a big boo boo in my diagram and had to correct it and some of my posts.

The LiFe batteries cost me more than the NiMh types. If I forget to turn off my plane and fry the LiFe battery, it will cost about $35 instead of $70 with the two battery setup. The cost of forgetting to turn off a plane with the NiMh battery was zero.

I'm in the process of modifying one of my planes tonight to have just one LiFe battery. Hope to have them all done by next week.

Your two NiMh (five cell) battery installation is great except I don't recommend the separate ignition battery due to the loss of redundancy, but that is up to you.

The most common failure mode for the NiMh type of battery is an open cell, and since they are in series, that gives zero volts output. The one battery that I had with a shorted cell killed the ignition, but with a second one in parallel it still gave me enough voltage to power the servos and receiver and get back to the field and land safely.

I've been flying RC planes since 1971 and have had many switch failures and only a handful of battery failures. I fly all year and a lot, so I've had way more failures than most people. I was also an Avionics and Weapons engineer before I retired, so I like redundancy and for things to work well.

I almost forgot. With a single battery, I only have 2100mAh available for flying, which is half of what I used to have with my two battery setup. I also used to fly 8 to 10 flights a day, all about 15 minutes each. Now I only fly four or five flights with 10 minute flight times, so that gives me enough of a safety margin to feel good with only one battery.

Last edited by Joystick TX; 08-05-2017 at 05:56 PM.
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Old 08-05-2017, 04:23 PM
  #3035
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Quote:
Originally Posted by Tom Nied View Post
That's pretty slick. I looked at that battery on Tower and it goes for about $35 a piece. Isn't that actually a savings? Weighs less too than two NiMh batteries.
It is not a "savings" if you have a LiFe battery and you forget to turn off your receiver and trash the battery. If you have two LiFe batteries you may even cry.

Fortunately, I don't do that very often. I'm more likely to forget my wing, or transmitter when I go to the field.

As far as the weight difference, with the GSS, you probably won't notice any performance difference.

Last edited by Joystick TX; 08-05-2017 at 04:26 PM.
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Old 08-06-2017, 03:57 AM
  #3036
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Might be worth pointing out as well, is the fact that as airplane size and power are increased, the weight and size advantages of a single battery system decrease considerably for most of us. In that case, this same wiring diagram (post 3026 above) can be used equally as well by substituting 2 batteries feeding the 2 switches, rather than the one as shown.

As far as battery removal to balance charge, nope. There's a way around that too. It requires that you modify the battery slightly. Using the standard J type connectors, you can use the white/3rd wire as your balance wire. This mod in place, you can make an adapter for your charger to allow the use of the switch's charge port to balance charge. The one "gotcha" to this plan is the need to cut the white wire on the output side of the switch. The receiver has no use for 3.3 voltage on the signal buss. -Al.

Last edited by ahicks; 08-06-2017 at 04:04 AM.
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Old 08-06-2017, 06:17 AM
  #3037
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Whew, I better stick with my two NiMh batteries for awhile. It has some advantages for me.
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Old 08-06-2017, 10:19 AM
  #3038
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Here is a diagram to help with a dual battery setup:
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Old 08-06-2017, 10:26 AM
  #3039
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Quote:
Originally Posted by Tom Nied View Post
Whew, I better stick with my two NiMh batteries for awhile. It has some advantages for me.
Are you going to use one battery for the ignition and the other one for the receiver, or are you going to set them up to do both so you have a backup in case one fails?
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Old 08-06-2017, 05:14 PM
  #3040
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I have it setup as two independent systems. One battery for the ignition, the other for the receiver. If I have a deadstick, I've got plenty of practice at that, and I'm not going to worry about that. Losing power to the Rx shouldn't occur, I check that battery every flight. Flawed thinking? My ears are open. I studied your diagram for a two battery system. The most flights I've ever gotten in one day only amounted to 5. I do utilize a DLE Engines Opto Gas Engine Kill Switch (RCEXL)
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Old 08-06-2017, 06:41 PM
  #3041
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Quote:
Originally Posted by Tom Nied View Post
I have it setup as two independent systems. One battery for the ignition, the other for the receiver. If I have a deadstick, I've got plenty of practice at that, and I'm not going to worry about that. Losing power to the Rx shouldn't occur, I check that battery every flight. Flawed thinking? My ears are open. I studied your diagram for a two battery system. The most flights I've ever gotten in one day only amounted to 5. I do utilize a DLE Engines Opto Gas Engine Kill Switch (RCEXL)
Your system will work okay. You just don't have any backup for the RX system when something does fail. The flights per day does not enter into it, unless the number of flights is zero.

Since you already have two batteries, your system can easily be changed to give you almost double the reliability, with very little effort and only a couple of dollars for a Y connector.

Don't confuse "reliability" with "life expectancy." When you say "Losing power to the Rx shouldn't occur"; I agree, but stuff fails. The two highest times for failures are when things are new and when things are old. A dual system takes care of those two times.

I quit using the Opto Kill Switch a few years ago due to failures. I see about five failures a year at our club. The good part is they hardly ever fail in flight. They just cause a lot of heartburn when trying to restart the engine since they are the last thing people check.

Last edited by Joystick TX; 08-06-2017 at 06:46 PM.
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Old 08-06-2017, 08:00 PM
  #3042
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Yeah, I get it now. Now I see how the Y connector makes the difference. Will consider that. And yes, I've already done the failed restart when another flyer distracted me from my starting checklist and the kill switch on the Tx was thrown to "kill" from the previous flight engine shutdown. Thanks for the enlightenment. I will have to keep a keen eye on this part of the system.
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