Batteries and Connecting in Parallel

[bunnygirl80]

Hi guys,

Using a 4000mah 4s 20c my hex has a total air time of about 5 minutes, but is perfectly capable of lifting the weight.

So, I would like to add a second battery!

How do I connect them? I think it';s parallel and not serial?

Is it also okay to mix two Zippy 4s 4000ma 20C and 45C? OR is this not a good idea?

Thanks.

[SimonS]

Parallel keeps the S rating the same but doubles the mAh. Serial doubles the S rating and keeps the mAh the same.

I';m sure someone will have used mixed packs but I would always use two identical packs.  Same make/S/c/mAh. You don';t want one battery trying to charge the other.

[Ross]

Think someone showed this recently when on about soldering the wires.
See New Lipo below your query
http://www.multi-rotor.co.uk/index.php?topic=3215.0

[peter_a]

i would say capacity is more important than C rates , If each battery was the same capacity I would hope that each battery would take half of the load and discharge equally ?.

[guest325]

When I';ve paralleled packs I';ve always used identical packs if you use mixed C ratings there is the potential for the lower rated pack to attempt to discharge beyond its specified rate which could result in catastrophic failure.

[rsmith21]

Funny thing, I just decided to do that too. I had a good look about the web and was satisfied with the information that the 2 Batteries should be twins as much as possible. Charge them individually and keep a watch full eye on the cell voltages after charging ( as you always should I suppose ) , so I made up a Y lead and enjoyed a much longer flight time :) .

I was in the process of changing connectors to XT60s I was fed up of the sparking the deans type did, great move simple connection positive polarity every time, failing eyesight needs all the help it can get :)

[peter_a]

I got a pair of zippy 5800s to power by hexacopter , which I`m thinking may be a little overkill .

The fun is try to fit xt60s on a battery with 8swg wires , I cut the 3.5mm plugs off to had to make a adapter to bring it down to a size I could solder in the xt60.

[bunnygirl80]

Hi guys,

Thanks for all your inputs and making me a little more knowledgeable about mixing batteries. The general consensus seems to be to keep the C rating the same.

Many thanks,

Stef

[MOFO64]

C rating of pack doesn';t matter, they can cope with higher amperage draw....batteries don';t force amps out. As long as the capacity is the same on both lipos then you';ll drain them equally and won;t have any issues. If you use different capacities and one lipo runs lower than the other (therefore having a lower voltage level) then that';s when the stronger lipo will effectively begin to re-charge the weaker lipo.

[guest325]

I think I have a possible answer to this problem, but would need someone with better practical knowledge than me to confirm that I';m on the right track.
If you were to make a change over circuit using a low voltage alarm triggering a solid state relay with the one battery through n/c contacts and the other through n/o contacts this should work without the need to parallel up 2 batteries.
That';s the idea now I need someone with the knowledge of the components needed to make it work!

[rsmith21]

I think I have a possible answer to this problem, but would need someone with better practical knowledge than me to confirm that I';m on the right track.
If you were to make a change over circuit using a low voltage alarm triggering a solid state relay with the one battery through n/c contacts and the other through n/o contacts this should work without the need to parallel up 2 batteries.
That';s the idea now I need someone with the knowledge of the components needed to make it work!

OR, maybe diodes connected to allow the batteries to deliver without getting flow beck to the batteries, a bridge rectifier . The downside of the change over relay would be that you would not get the benefit of the two batteries at the same time, the rectifier would. There  would be a voltage drop over the diode so that may be too much, one for the electronics gurus :)

[peter_a]

The problem I could see with a voltage alarm is that it would keep oscillating between the two batteries until the first battery is below the trigger voltage off load.

AND

That would happen to the craft if it goes from 10 volt to 12.4 volt without your control , when ?

[rsmith21]

The best (and safest) way of doubling your battery capacity, is to buy a bigger battery!

Yeh! I tried that too http://www.multi-rotor.co.uk/index.php?topic=3184.msg25588#msg25588

[bunnygirl80]

Thanks for all your comments. Yeah, I';m kinda in agreement with some of you that it';s dangerous to mix the batteries. I flew with a 4000 4s this morning and got 7 minutes out of it and the alarm still hadn';t beeped. So, I';m starting to think now that I will use the left tray to hold a battery for the gimbal and the right tray to hold a battery for the motors and everything else. 7 minutes should be enough at which point I can land and swap batteries and think about my next move.

[guest325]

The only other thing that has occurred to me is that if you can go for a higher cell count this is another way of improving flight times, higher voltages are more efficient (if your motors will take a higher cell count) and the power density is generally better. Zippy compacts are one of the best batteries for improving your power density plus they are very reliable.

[ChrisH]

I understand the power density vs cell count and sounds a nice idea. Trouble is the external dependencies - Video Tx, gimbal, etc., that would probably need a voltage control module. Nice idea though.

Maybe install a module anyway, swap battery cell counts at a whim!

[guest325]

This is another good reason to go for a higher cell count, higher volts means less amps means less heat, it';s high current that kills motors and esc';s not higher voltages. I';ve been running a 3D profile foamy (Twisted hobbies Crack Yak) on 3S instead of the intended 2S even though the motor is only rated at 2S for a while now and the esc and motor are always cooler than when I ran it on 2S plus it is quite a bit more entertaining and gives longer flights. The only downside was that I had to move the battery - which proved to be a pain in the a55 because a servo was in the way 

[guest325]

Quite agree with what you say, simple high school physics but the motor will be running at higher rpm with a smaller prop and it seems that there are less losses as heat than with a lower voltage larger prop combination - I can';t say as I completely understand why but can speak from the experience of doing it and seeing the results. Perhaps it is dependant on the current load?

[guest325]

OK but I don';t think it';s quite that simple - the fact that higher voltages incur lower losses as heat is clearly demonstrated by the national grid, not saying it';s the same but.....

[guest325]

So how could it be that I';ve experienced a difference?
I had been quite careful with my assessment and have measured flight times and temperatures of components fairly accurately - initially I only bought one battery to trial and on the strength of the results I got bought the full compliment of packs I wanted.

[peter_a]

So it looks like they should be a forum rule about sex religion politics and batteries in parallel !!!

[guest325]

Sorry not the best thing to have done, hopefully something good might come out of the protracted exchange! 

[KK1W]

So how could it be that I';ve experienced a difference?
I had been quite careful with my assessment and have measured flight times and temperatures of components fairly accurately - initially I only bought one battery to trial and on the strength of the results I got bought the full compliment of packs I wanted.

I have to agree. Besides the power consumed by the motor and absorbed by the propeller there is power consumed by the I2R losses in the motor windings and connecting wires. That resistance does not change when you raise the voltage but the power losses because of resistance go down by the square of the current. If you reduce the current by 50% the power loss is reduced to 25% of the original. How much a part of the overall system those losses are I have no idea and/or desire to calculate  ::)

And yes, parallel battery discussion go on forever, and ever, and ever   

Jim

[ChrisH]

So it looks like they should be a forum rule about sex religion politics and batteries in parallel !!!

Nooo...

I';m learning with every post! 

Keep the information flowing!!