Justflying1

It's funny how some seem to think it's a no no for running the two batteries in parallel to one ECU. Regardless if you run one or two or 100. If you have a short anywhere in the system which runs that turbine it will most likely shut down. Running batteries in parallel is NOT to prevent a shut down if a short happens.
Thank you all

ira d

I have a Jet Munts and I found with the onboard factory battery it is good for about two starts usually on the third start it will do a hung start. I found that I could plug in a battery in parallel off board for the start and
disconnect once started and get many starts. I make sure its a lipo and that both batteries are always at close to the same voltage.

sidgates

My Feedback: (2)

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I have "Y" cable in 2 of my jets where you plug in the Start battery. With this setup I can plug in a 5000mah lipo in parallel when doing a lot of starts. I have used a diode in series with parallel battieries where I want about a 1/2 volt of voltage drop. This was used on reciever/servo batteries. For a jet start battery the diodes would have to rated at approx. 25 amps which would be very large.

David Gladwin

Running two batteries for each ECU is easy and I do that on that on several of my JetCat installations. It adds an extra layer of safety and extends the number of flights between charges. Emcotec offers a battery sharing device, two battery inputs, one out to the ECU and has an input for simultaneous charging of both packs.

The unit is called the DPSI Ampere.

It is a myth that diodes are required, they are NOT , a dead battery will not be cross charged to any, if any , extent by the good unit.

There is an excellent explanation of this on the Hangtimes battery clinic ( Nobs batteries) and my own experiments confirm that explanation. ( Hangtimes Hobbies) Very well worth a read and the guy obviously knows his stuff.

If if you don't want to use dual airborne batteries, then a Y lead allowing a ground battery connection ( we started Vampire engines, Goblins, in the RAF on cold days like that) is a good solution

I used this this for years on my first kero start engine, a. JetCat 70, when the Duralite LlIon battery could not deliver the amps for the plug during start. Worked, and still works, perfectly.

KISS is all very well, but if adding an extra component can virtually eliminate the possibility of failure of a most critical system, it has to be good practice, which is why it is such standard practice in the fullsize world.

Justflying1

Thank you all for your input.
I personally have never used diodes when running batteries in parallel or series. However each to there own.
I have been flat out working on my A-10 as I got sick of looking at the box. LOL.
I know I'm sounding like a broken record and if anyone is waiting for the specs on the amperage reading just hang on a little longer. I will post the results as soon as I have done it for everyone who mite find it interesting.

mauryr

I went to read this explanation and it seems to me to be specific to nicd batteries. It specifically says that these batteries' voltage drops at full charge, which is definitely not the case for lipos.
Unconvinced this applies to lipos, I went and did my own test just a few moments ago.
One 3s lipo, almost fully charged (12.4v) and a partially discharged one (11.7v). Same brand, same 20C rating, same age and same size (4900 mAh).
After checking the voltage I setup to connect them in parallel with an amperometer and as soon as I connected them, the ammeter registered a 6A current flow between the two batteries.
While this may not seem all that much, it's still above 1.2C and I know people who never charge batteries above 1C for fear of ruining the battery or causing fires.
Considering the voltage difference was only 0.7v and the batteries are both pretty old and tired, I am even more convinced of the necessity of using diodes to uncouple two high powered lipo batteries.
With lipos, the difference between nominal and fully charged voltages is quite substantial, so cross charging seems inevitable to me. Should you forget to charge one battery, or should one become weaker than the other and discharge sooner during the flying day (unlikely, I know, but possible) I really don't like the idea of the other one recharging it (also putting additional load on the good battery, taking it away from the system).

Justflying1

Thank you for the info mauryr.
I wonder what the hundreds of helicopter users around the world do when they connect there batteries in series.
No to mention the 4 WD that are running there new Lifepo batteries in parallel.
Also most good quality lipo batteries can be charged more than 1C. I do understand that if you charge at 1C you are being more kind to the lipo, and you should get the full charge cycles out of it providing you have not drained it to low and kept it at storage charge when not used.
Also when connecting batteries in parallel or series I personally prefer to only use same brand, size capacity as stated before. Batteries should both be charged and balanced.

Desertlakesflying

My Feedback: (28)

Talk about over thinking things.....

David Gladwin

You raise some interesting points. I haven't used nicads for many years,( although in my larger models I did use dual nicads , no diodes, before lithiums arrived) changing to dual Duralites ( lion) for receiver power. These were used with regulators, but no diodes, and that's how I tested many years ago.

I have never tested Lipos in parallel for cross charging, but I have a couple of dead packs, so I will repeat the experiments with them.

That said, dual ECU packs via the Emcotec DPSI unit seems to be a perfect answer.

mauryr

If this can be of use to anyone, a couple years ago I also ran a destructive test on turnigy/hobbywing 8-15 becs, the ones with battery voltage leds on them. These little things are pretty good and I've used a lot of them, but I never knew if I could parallel them safely, so I simply tried. While the 2 of them are both turned on, they work just fine (not sure for how long though). If you turn off one of them while the other is still on, the one you turned off gets destroyed by the other one and does not work anymore if you turn it back on afterwards. This test is specific to these voltage regulators, but could apply to other ones as well, so be mindful of connecting voltage regulators in parallel as they may seem to be working fine just to break when you least expect it. One failure mode of these becs is also pretty scary as they simply stop regulating the voltage and output the full battery voltage as it comes. Since they can use up to 3s inputs, you may end up powering your 6v servos with 12v, most likely not very safe to do