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Back up battery

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Old 03-10-2018, 02:27 PM
  #1  
427jimmy
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Default Back up battery

I want to use LiFe batteries in my aircraft, a 3000 Mah and a back up 1100 Mah .
My feeling is to separate the two and have the smaller battery isolated until needed. Two switches?
I have looked at several websites but cant seem to locate exactly what I'm looking for. Booma, MPI, Scorpion,etc.
Separate isolated batteries of different capacity but otherwise identical.
Also would like an LED to show it's on.
Anyone have a suggestion?
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Old 03-10-2018, 04:08 PM
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Well, depending on what radio system you use they may have receivers that will provide dual battery redundancy.

Otherwise use a switch like the Booma, MPI, Battshare, etc...
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Old 03-10-2018, 08:42 PM
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All Day Dan
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Smart-Fly Engineered to Exceed your Expectations

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Old 03-13-2018, 01:34 PM
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427jimmy
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I have been doing more research on the subject of redundant battery systems and I now believe an isolator is definitely called for. I'll post more as the research progress.
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Old 03-14-2018, 03:06 AM
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Why add another device that could fail? I simply use two battery packs and two switches plugged into the receiver.
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Old 03-14-2018, 03:22 AM
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427jimmy
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I posted this question on a couple of sites and got conflicting answers. Consensus seems to be as you say, "why add another device" . I believe as one gentleman said "An isolator is a solution to a problem that doesn't exist"
It was previously my belief that one battery could affect the other. Apparently that's not the case. KISS !!
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Old 03-14-2018, 07:00 AM
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All Day Dan
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Oops 427 it is the case. When you connect two batteries in parallel without an isolator you complete the circuit between them. The weaker battery will always be a load on the stronger battery. And, if one of them fails as a short circuit it will take down the other one. Dan.
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Old 03-14-2018, 09:20 AM
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Mr. Dan That was my belief in the beginning too. I put this question on another forum and more than one pointed out that one battery cannot affect the other. Also that isolators were not necessary.

Maybe we could put it up for a vote? To isolate or not to isolate? At this point I will vote....Maybe!!
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Old 03-14-2018, 10:07 AM
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Don't put it to a vote. I'm an electrical engineer by trade. My father spent a fortune making sure that I got my degrees. Notice the "s". It all involves electrical circuitry.. There is only one way. Don't put batteries in parallel. Ask any EE. Thanks for everyone's replies. Dan.
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Old 03-14-2018, 10:53 AM
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Yawn

The batteries don't affect each other and isolators are nonsense.

I have degree(s) too if such things matter.
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Old 03-15-2018, 07:50 PM
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Western Robotics Ltd. Battery Buffer This will do exactley what you want.
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Old 03-16-2018, 05:06 AM
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427jimmy
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All the responses got me to thinking about whether or not an extra isolated battery is necessary. Here's my reasoning, let me know what you think.
The reason to isolate one battery in a dual battery setup is in case of some type of catastrophic failure of one battery.
Worst cases would be a larger than normal internal resistance developing or a massive resistance (open circuit) or a dead short (both primary leads touching).
The receiver power circuit is bussed together (thus allowing you to plug into any port)
If my limited electrical knowledge is correct one battery with large resistance would limit current flow, not a problem. An open circuit would do absolutely nothing. (you would just run off the remaining battery)
Now we get to shorted leads, which would be a problem in my opinion. If you short one battery, current flow would max out , fed from the second battery and that would affect total system voltage.
I'm thinking this would be like placing a jumper across power and ground pins of the receiver (dead short) high current flow, heat , fire, etc. Not a good thing.
There have been replies on both sides. Is my thinking here not right?
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Old 03-16-2018, 05:58 AM
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Be sure to add dual batteries to your transmitter along with isolation because if your single transmitter battery fails you could crash.

How far do you want to take this?
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Old 03-16-2018, 07:35 AM
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Originally Posted by BarracudaHockey View Post
Be sure to add dual batteries to your transmitter along with isolation because if your single transmitter battery fails you could crash.

How far do you want to take this?
+++++++++1
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Old 03-16-2018, 09:42 AM
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427jimmy
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I'm done.
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Old 03-16-2018, 12:54 PM
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hangtimes.com has a QnA that offers a recommendation that no one here will believe. But, hey give it a shot
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Old 03-16-2018, 03:14 PM
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All Day Dan
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Thanks Aww, something to think about. Dan.
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Old 03-16-2018, 04:21 PM
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Originally Posted by AwwNaww View Post
hangtimes.com has a QnA that offers a recommendation that no one here will believe. But, hey give it a shot
I'll post the link. BTW.been flying this way since the late 80's..Parallel Packs
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Old 03-17-2018, 11:24 AM
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Been doing the same as well. No problems.
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Old 03-20-2018, 07:00 AM
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Steve Collins
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I wonder why guys put themselves through all this worry about battery pack failures. In 35 years of flying R/C, everything from helicopters to turbine jets, I have never had any battery have a failure of any kind. Currently I use A123 packs in all of the turbine jets. They have been great.

As long as we don't use any battery that is suspect, like something peculiar going on with one or more cells, or no longer holding a charge like it once used to, you should be good to go.
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Old 03-20-2018, 08:10 AM
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Yep, same thing I told him on the thread in Flying Giants. Most people that recommend battery isolation gadgets are selling them and those stuck in 1950's tube technology
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