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
Join the NSRCA

RE: Backup/Redundant batteries
 

Thanks John. Until we hear of someone doing it earlier you are the guy. As Brian said, it is a brilliant idea. I hope Chris gets rich from it but in the mean time he is doing everyone a great service by providing the adapters. I told him he should charge $10.

Jim

RE: Backup/Redundant batteries
 

Hi Jim,
It is not moving charge from one to the other.
It is monitoring voltage on both separately. If one is higher it takes from that one only , until they equalize. Under normal circumstances (with 2 equal batts,, ) it will keep them at the same voltage, by discharging (using) the higher one first at all times - I believe.
I am already using one ,and have already done a variety of tests. - not with 'your' idea yet but I will for sure.
We are wondering (kicking ourselves) how we missed this one - well done & thanks for sharing.

Brian

RE: Backup/Redundant batteries
 

Talked to Castle Creations customer rep about providing the backup voltage from 2s in a 10s powering HV ICE 80, and was told CC does not recommend it. The reason is that the ESC could be damaged.

Just like to share the info.

RE: Backup/Redundant batteries
 

Sounds like a marketing guy. I'd like to hear a technical explanation how it could damage the ESC. Maybe it can't stand a common ground. That would be important to know.

Jim O

RE: Backup/Redundant batteries
 

Yes. figuring out the common ground is one of the reasons sited. The other is that switching regulators are poor in dealing with two battery sources.

RE: Backup/Redundant batteries
 

The CC ICE2 HV 80 has no physical connection between its battery power connections and the power and ground leads of the throttle connector. For THIS specific ESC, you can pick any two adjacent cells on the balance connectors of the motor battery to power a regulator. I have several hundred flights on this ESC using Tech-Aero regulators without any problems. I make no distinction about which balance connector to use. However you do NOT want to use two inputs from the motor battery on different sets of cells. That will cause a direct short through the regulators and the receiver ground bus bar. Always use a separate backup battery and regulator.

It's been said several times on various threads that you should not parallel swtching regulators or BECs with any other power source. If the regulator says it will accept an input voltage that is substantially greater that 8.4 volts and will regulate to 5-6 volts, it is not appropriate.

If you obey these rules you should not have trouble nor cause any damage to your ESC. An appropriate ESC is one that is labelled optically isolated. Check that it is fully isolated by confirming open circuit between the throttle connector power and the battery high side of the ESC and separately an open circuit of the ground wire and the battery low side of the ESC. If your ESC instructions directs you to cut the power connection in the throttle connector, it is not an appropriate ESC.

You can use non-optically coupled or common ground ESCs but it requires a lot more thought and strict adherence to process when you swap batteries in the model.

John

RE: Backup/Redundant batteries
 

Here is a diagram that should answer a bunch of questions. I used a Jaccio and a Tech Aero regulator just to show both brands will work properly with this redundant set up. You do not need to use 2 different brands. Also, I show a 6V and a 5.7V input but as long as the primary source is higher than the back up source, again you will be fine. The pic shows an 800mah back up pack (all I had available for the pic) but that is way overkill as with this setup the battery will sit idle unless needed and a 300mah should be more than enough since we only use 50-60mah on a typical flight

RE: Backup/Redundant batteries
 

One more thing to consider is that on the JST-XH (Hobbyking) type connectors, there are no clips on the plugs themselves so only the friction of the pins in the connector holds the balance connector to the redundant adapter so you might consider leaving all of the pins in the connector and just covering them with shrink tube. The Polyquest have a good clip and only the 2 required pins need to be in the connector. The TP plug also has a clip. We left all the pin in on the JST-XH and also the TP ones as the pins are rather short and the clip is not as robust as the Polyquest type.

(Sorry just noticed the Polyquest pic has the connector upside down so you can't see where the clip attaches)

RE: Backup/Redundant batteries
 

If you have been running this system for awhile like I have you will be tempted to do away with the backup battery and fly with just the tap off the motor battery. After all, the backup never does anything. Well don't do it. On my first flight of the day yesterday I was off to a great start and then I did the outside snap on the 45 degree downline and I heard a big cracking noise and could see parts flying. I had no idea what had happened but I knew it wasn't good. I throttled back and landed as if nothing were wrong except I noticed the motor had stopped at the end of my rollout. When I tried to taxi back, I noticed the motor wouldn't run. I could see the canopy was gone and when I got over to the plane I could see the battery pack was also gone.

I don't know if I had been distracted when I installed the batteries and failed to secure the velcro straps or if it is possible the straps are worn out. In any case they let go and canopy wasn't strong enough to contain the 2.5 pound pack at who knows how many g's. I found the canopy after a long search and it had a number of tears but I should be able to fix it. I never did find the battery pack but we can feel good that it didn't start a fire after a 400 foot drop.

Moral of the story, always carry a pack independent of the motor power system.

Jim O

RE: Backup/Redundant batteries
 

Glad you still have a plane, Jim.
I agree, a redundant battery system is cheap insurance especially if you tap the motor battery.
John

RE: Backup/Redundant batteries
 

The Dual battery back is in place to bring the plane back if one battery system fails during flight.
Note: We need to also worry about the connectors we are using. The balance plug connectors on the main power batteries are not the best connector. Single point tin plated.
I would replace the jumper wire every 200 flights.

Some folks are not using a switch to turn on radio system. Plugging the battery into a jumper in to the rvcr. You need to check the contact area the pin. Some low cost jumpers are a folded contact this makes a very poor connection. It is ok if the unit is plug in once a day. But using a half dozen times a day is not good.
Replace those with good contacts. And replace those every year. Take the old parts and put then a fun plane.
So the question what is a good contact. The Old 3 pin deans is good. Two contact points on a solid pin.
There are others don’t save 8 dollar’s spend the money here also.

Get the right connector’s and replace them yearly.

See you on the flight line.
Mark

RE: Backup/Redundant batteries
 

[/quote]

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
[/quote]


Just tested this set up last night and it worked well. My only concern is how long do these hold up? I don't have a lot of confidence in those little balance connectors. I have a back up but don't want to test it.