Parallel batteries

[rifleman_btx]

My question here is, because I'm eyeing to get the f7f, if I were to use 2 2700 batteries in parallel, vs using one battery per side of 3000-3500, would I get better battery performance? Or will it run about the same as having a single battery power the single side. I just have a ton of 2700s and would like to use them vs buying more batteries just specific for this plane. And if I'm gonna need to do so, I just want to be sure I do this one right so I don't run into a bad situation

[fhhuber]

Pretty close to the same when using 2 in parallel vs 1 big one with same C rating. The extra connections add as much (or maybe a tiny bit more) resistance as you "remove" by having effectively fatter wire. In a power system of 1000 watts the difference would be in the last digit before the decimal.

[rifleman_btx]

That makes since, thanks!

[fhhuber]

"playing with" parallel-serial batteries instead of a single pack can cure the battery placement for CG issue in some models.

I plan to use parallel packs as a sort of trick to deal with very long wires from battery to ESC in my big Me262. No room for the packs needed near the nacelles. So I'll put 4 small HIGH C rated 3S around the EDF, then the long battery leads to the main packs. The small packs will act like huge capacitors to reduce the spikes that can develop with long battery leads. Those spikes can bur out an ESC if not absorbed by capacitors or some other method.

Parallel packs need to be the same voltage.

Series packs need to be the same capacity and C rating.

[rifleman_btx]

That about volts and c rating I did know, but I like the idea of using the small packs for capacitors. My reasoning for this is I know there's not much option in the flight line f7f to run a large capacity battery, and I don't want to have a chance of one battery giving up before another if I use the one per side method. So I feel setting them up parallel is my best option for safety and battery stress.

[fhhuber]

Charge and balance the packs separately.

[rifleman_btx]

Always do my friend :)

[OV10]

That about volts and c rating I did know, but I like the idea of using the small packs for capacitors. My reasoning for this is I know there's not much option in the flight line f7f to run a large capacity battery, and I don't want to have a chance of one battery giving up before another if I use the one per side method. So I feel setting them up parallel is my best option for safety and battery stress.

Response to red
How big a batt do you want to run??
Am running 2 4000's in parallel and am getting 7-8 minutes mixed throttle

Response to bold
I've always detested this practice of using the one per side method for exactly the reason you said.
All my twins are wired so the 2 ESC's power leads are Y'd (blk/blk & red/red) together into one blk/red pin connector.
I then have a Y adapter for the two batteries.
Plug the batts into the Y adapter and then plug the Y into the connector for the ESC's that were Y'd.
With this set up you will lose both power plants at the same time if you have one battery that decides to collapse.
No fear of losing one motor during low level flight or landing and watching it graveyard spiral in.
In your case of the 2700mAh 4S you would have 2 parallel sets which is a total of 4 of those 2700's in the F7F.
You would be using 3 battery Y adapters in place of one that I referenced above when I parallel my two 4000's.
A Y on one pair(2 batts) and a Y on the other pair(2 batts). Then you connect the two Y's(4 batts total) with another Y and then that gets plugged into the ESC connector.
The total system mAh that the two motors see simultaneously at full charge rating is 4 x 2700 = 10800mAh.
That's 2800mAh more than my 4000's in parallel. :Cool: You'll easily get 10 minutes of flight time.
Plenty of room in the Tigercat to do that but you can't get it done with the P-38.
Just giving you an option. Hope this helps brother.;)

[rifleman_btx]

I like that idea, I will have to see what it all looks like when it comes in. Lots of combinations

[Ole-Timer]

https://www.rcgroups.com/forums/showthread.php?952523-too-long-battery-wires-will-kill-ESC-over-time-precautions-solutions-workarounds

One thing to avoid on any model you’ll run batteries in either parallel or series is making battery connections to the esc too long. My solution is to now make simple plug connectors to join wires together. The attached picture is a plug that will join two 6s batteries together for my 12s PC-6. When you read the manual for aftermarket esc’s they normally list a maximum wire length from battery to esc! Making plugs instead of wire harness’s ensures you’ll keep the lengths down to a minimum.

[fhhuber]

https://www.amazon.com/Parallel-Battery-Connector-Adapter-Serial/dp/B01NBEQY6Z

Short plug parallel Y

They are available in parallel or series.

Part of the choice of how you do it is making the wires not turn into a pile of spaghetti that wont let you close the hatch.

*************

The long wire lead issue is serious. I'm surprised at the length of wire between battery and ESC in the FW Tomcat without big capacitors added. VERY LONG wires. It is FAR better to have the extensions between ESC and motor than between ESC and battery. So in modifying the Tomcat to Castle ESCs, I put extensions between ESC and motor and cut the length between ESC and battery in half.

And this is why I want high C small packs in the big Me262 right at the EDFs. Long wire run to put the main packs in the fuselage and the ESCs are built into the EDFs I have for it. 2000 mah 50C+ at each EDF and 15,000mah (20C would be enough) in the fuselage. The high C packs will take about the same room as the capacitors I'd need.

[rifleman_btx]

Yeah that is one thing I wish to avoid. I don't want the inside to look on the inside like it's hooked to an EKG. I will probably be going eith those adaptor style plugs to keep things tighty.

[fhhuber]

I was using the 4mm in red plastic connectors because they use the female on + and male on - which makes daisy chaining packs in series really easy. Just cut the web in the middle of the plastic housing to allow separating the wires.

[rifleman_btx]

Yes indeed, and it's foolproof, easy to be assured that everything is correct the first time everytime.

[fhhuber]

no... not when putting 4 packs in series.

Have to be VERY careful not to loop the batteries

[rifleman_btx]

True, if you just throw it together could still screw the pooch. I was figuring go a lead at a time I guess

[rifleman_btx]

Would the f7f fit 2 5200 packs? I would like to parralel those

[Alpha]

I can't imagine that it would fit a 5200, rifleman_btx. The height of the Admiral 4000mAh already requires a slight shave off the cockpit foot. Although double check the measurements of your 5200, whichever brand that is. Hopefully it's longer in length and shorter in height than the Admiral 4000 and 5000, if you're to have any chance of it fitting.

[rifleman_btx]

How much of the foot can be safely shaved off?
if I got to I'll glue magnets up front for the extra flight time. The hight and with of the packs I'm looking at are 1.89" or 48mm, I also thought I could sit the batteries farther back since they would weigh more so go cg the front battery wouldn't have to slide into the pocket, also the hight of the lower battery could support the overhang. Just thinking out loud now...

[rifleman_btx]

If they don't work out, I always have the 2700 to load up and fly with. Either way I'm good with it.