Backup/Redundant batteries
 

We recently had an interesting discussion on the NSRCA pattern list concerning backup batteries. The power supply is the first thing we think of when we have trouble so it would be nice to eliminate it as a source of catastrophic failure. I don’t know who should get credit for the concept but I got interested when Chris Moon suggested making up a special voltage regulator that would connect to the balance connector of the motor pack, tapping off the bottom two cells. I suggested just making a simple cable that could be connected to any voltage regulator and these are now available from F3A Unlimited.

The way I configured my system was to build a simplified version of my Perfect Switch Harness that would allow me to connect an onboard voltmeter so I could read the voltage of the two cells when I installed the motor battery. This would assure me I had installed a charged battery. I have been carrying around an Eagle Tree data logger and display to provide this info. You only need to take off once with a perfectly good but discharged battery and come down with a bad battery, to wish you had been more careful. I set the output of this regulator to 6.3 volts so the system would not draw current from my receiver pack which is regulated to 6.0 volts. I then charged my receiver pack to the storage voltage and haven’t charged it since.

Then one of the guys at the field says how do you know you aren’t using up the capacity of the receiver pack so I went home and installed a voltmeter that would read both. The photo shows the results.

Jim O

RE: Backup/Redundant batteries
 

Hi Jim,
Clever !!
Between you and Chris you have come up with a great idea.
I use an Emcotec dual batt,, switch/reg,, . It monitors both batt's and takes from the highest voltage source.
I don't see anything wrong with keeping the rx batt,, charged ,using the emcotec ie, so that the 10s is kept for the motor when capacity is tight. eg using a 4400.
The Emcotec gives a flashing led warning if one or both batt's are low in voltage, separate/different warnings I think - I will check.

Brian

RE: Backup/Redundant batteries
 

Double post - RCU ??? Timeout error ??

RE: Backup/Redundant batteries
 

Brian, one of the greatest considerations when adding a redundant or backup battery is weight. By using the motor battery as the primary source one can use a very small backup receiver pack. The smallest I had was 800mAh but one could go even smaller. Most of us draw less than 100 mAh per flight so even a 300mAh pack would work. You might find that you could go to a larger motor pack with no additional weight if you went to this system. And I don't see why you couldn't use your existing Emcotec device. That is why I recommended just building an adapter cable because most folks already have the other components required.

Jim O

RE: Backup/Redundant batteries
 

Jim,
I routinely fly with a 250 or 370 on their own. I use 45 to 55mAh per P flight.
I have my eye on a 160mAh right now - for comp flights.
This is for a big bi-plane to make weight.
I will be doing this and testing with recharging frequencies, ie; after 1 flight,2 flights,3 flights etc.
Hugs and kisses !! :D

Brian

RE: Backup/Redundant batteries
 

On tap into the power pack as the backup source, just wonder if somebody has experience doing so with CC ice hv. Any chance of interference from the ESC?

RE: Backup/Redundant batteries
 

Are you sure ?
Below is the Emcotec DPSI Micro – DualBat spec.

The DPSI Micro – DualBat serves as redundant power supply in RC models. Redundancy is accomplished through two connected batteries. If one battery fails, safe operation is assured by the second battery. Usually both batteries are equally discharged. Furthermore, due to both batteries being “parallel”, current drawn from the batteries is cut in half; therefore, batteries with lower capacity can be utilized.

RE: Backup/Redundant batteries
 

Jim, can you explain how you would tap in into the 10s batteries to power the rx? Is this something that you are going to sell possibly?


Thanks,

RE: Backup/Redundant batteries
 

''Hint:
For the DPSI Micro - DualBat, two identical batteries must be used, i.e. same
type (NiCad/NiMH or LiPo) and same cell number. The capacity may vary – even
if this does not make sense.''

Another quote from the manual !
It has completely separate pathways for each batt,,.
It will take from the higher voltage source at all times, therefore normally maintaining an equal voltage batt 1 to batt 2.
It has separate and combined low voltage warnings.
The manual is a German to English translation - some quirky phrases result.

Brian

RE: Backup/Redundant batteries
 

I just downloaded the manual here

http://shop.rc-electronic.com/e-vend...=6&c=541&p=541

but did not found the explanations you are mentioning on the french or english version.

The idea to use a DPSI Micro DualBat 5.9V/7.2V or a POWERBOX™ ELECTRONIC SWITCH with one 450 Mah RX batt and 2 cells from the 10S packs looks great.

Due to the bad weather, I can't do some inflight test, so hope somebody will give it a try pretty soon

J-P

RE: Backup/Redundant batteries
 

Robert,
Chris Moon sells the "pigtail" to do it now.
See the F3A Unlimited website.
JLK

RE: Backup/Redundant batteries
 

2 more quotes from the English version;

''Decoupling of both batteries in the DPSI Micro - DualBat and the
electronically switches are completely separated (inclusively peripheral
electronics) and therefore duplicated. No twin diodes (i.e. two diodes in
one housing) are being used. Malfunction of one part does not lead to
a total loss of the system. This circuitry has proven in many thousand
systems already.''

3. Low Voltage Battery 2: ⎯ ⎯ ⎯ ⎯⎯⎯⎯⎯ ⎯⎯⎯⎯⎯
DualBat ONLY error signal: LED blinks 3 x 0.05s on with 0.05s
breaks each, then 2 x 0.8s on with 0.4s break
If the voltage of battery 2 drops below a certain value, this blinking
code is output. The capacity of the battery usually suffices for one
more flight before recharging is necessary. This error code is also
repeated in a sequence of 6 seconds. If the error is qualified once, it
stays active until turning the DPSI off.
If both batteries of the DPSI Micro - DualBat indicate low voltage, both
error codes are output alternatively.

Take time to read the manual - it is a translation - could be worse, could be French to English ! :)

Brian

RE: Backup/Redundant batteries
 

I used the male half of Futaba extension and spliced it to a balance connector adapter. The Black wire attaches to the pin with the black wire on the balance connector which we'll call pin one, and the red wire then attaches to pin three. Perform a test before you connect it to anything. The output should look exactly like a 2s LiPo.

Jim

RE: Backup/Redundant batteries
 

Here is another shot.

Jim O

RE: Backup/Redundant batteries
 

Thanks Jim, how are you,regulating the voltage from the motor battery.
Good to see that your back JLK:D

RE: Backup/Redundant batteries
 

Jaccio Perfect Switch Harness set to 6.3 volts. See first post in thread.

Jim

RE: Backup/Redundant batteries
 

Thanks Jim, just re-read the first post and it all makes sense now.

Thanks

RE: Backup/Redundant batteries
 

Sorry, but I didn't found these explanations on the Emcotec site.
Maybe you have a link .....

http://www.rc-electronic.com/downloa...ro_2009_EN.pdf
The DPSI Micro – DualBat serves as redundant power supply in RC models. Redundancy is accomplished through two connected batteries. If one battery fails, safe operation is assured by the second battery. Usually both batteries are equally discharged. Furthermore, due to both batteries being “parallel”, current drawn from the batteries is cut in half; therefore, batteries with lower capacity can be utilized.

RE: Backup/Redundant batteries
 

J-P,
Yes that's the one.
My quotes are from the same document. Just check carefully. - See page 10 first paragraph, see page 20 first 'hint' and see page 24 'Error Indication'
I think you have focused on ''parallel''.
Where they say ''parallel'' it's in '' '' because they are speaking metaphorically (or it's a simile).
In your quote ,which is in the same pdf file, they also say 'If one battery fails, safe operation is ''assured'' by the second battery.
If the batteries were in 'parallel' this would NOT be possible.
Hope this helps

Brian

RE: Backup/Redundant batteries
 

It's not really clear ....
And what about Hint @ page 20 ?

Hint:
Supply of a DPSI Micro – DualBat with one battery and a BEC-Supply as second battery instead is not possible!

RE: Backup/Redundant batteries
 

Hi J-P,
Sometimes we see what we want and do not see the rest.
That 'Hint' says a 'bec' !!
The guys are talking about a 2nd battery , all be it a BIG one or in fact 2 cells from a BIG battery.
I will leave you to work it out.

Edit; I believe that the Emcotec Dual batt unit is the ideal way to use Chris's and Jim's idea - which is just brilliant for anyone that may be tight on the weight limit - like me.

Brian

RE: Backup/Redundant batteries
 

Well actually, the idea has been around a little while longer than you may think,but that's OK:

http://www.rcuniverse.com/forum/m_94...tm.htm#9485156

RE: Backup/Redundant batteries
 

I had started writing a post to ask someone to jump in and tell us who really came up with the idea. The "idea" is to tap the pack at the balance connector. I quickly reviewed the referenced thread in RCU but still don't see a reference to tapping the pack at the balance connector. Maybe I missed it but I still don't know who to give credit to.

Jim O

RE: Backup/Redundant batteries
 

This is the post I had started when I was interrupted by a phone call:

We need someone to jump in and tell us who came up with the idea originally to tap into the balance connector.

Regarding the Emcotec Dual Battery unit. It sounds as though the batteries are isolated from each other somehow but it is not clear how the one that is at a higher voltage will charge the one at the lower voltage. It sounds like it does and that could be a problem. If the motor battery gets too low the small receiver pack will try to recharge it. If this is so, it seems almost certain that the receiver pack would end up at 7.5 volts or so at the end of flight. Maybe that is okay as it is close to the storage voltage but if it goes much lower it won't provide much margin. What do you think?

Jim O

RE: Backup/Redundant batteries
 

Jim,
We all know that good ideas are often developed independently but Keith Hoard and I both developed a balance plug redundant system on our own and used it at the Nats. But who knows, it was probably done earlier by others....
See the thread on the NSRCA website for a discussion and description of potential problems:

http://nsrca.us/forum/index.php?topic=167.0

John Gayer
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