i have 2 -700 mah packs and i'd like to make a nice 6 volt pack for a 40 sized US and i need some help please, i think ive had one too many beers because i have done this once before

Both drawings appear to be the same. Separate the positive line of the plug at the pack and solder to the new question mark cells positive. Solder a jumper from the question mark cells negative to the packs positive cell where you remove the positive plug line, Done

Remember this is a seris circuit and increases the packs voltage but not the capacity. You will not get the same endurance as the 4.8 pack but you probably already know that.


John

Here's how it should look.

Ken

yes i accidentally posted two of the same pic

thankyou Ken

The battery manufacturers (Sanyo, Panasonic etc) recommend that all cells in a battery be of the same brand, same type and of the same capacity. Otherwise, all cells will not charge optimally and may not produce their full rated capacity.
The life of your complete investment - airplane, engine, radio, etc. depends on good batteries, it is not a good idea to experiment or gamble with them. Batteries are cheap, airplanes etc are not.

You are probably right, but this isnt for a high profile model, the 4 cells are(JR) Sayno, and the 5th cell is also a Sanyo and are all 700 mah, i will do a cycle before i try it out tomorrow.

I just want the added security of having a 5th cell. Not too long ago on one of my 5 cell packs, i lost a cell, if that would have been a 4 cell pack i would have lost the plane, thanks to my Voltwatch II i saw it in the red zone, and immediately took that bad pack out. It read about 5.56 v which is what a nicely charged 4.8 pack should yield.

An important thing to keep in mind is that the solder tabs will not hold up of movement of the cels for very long. A good heat shrink covering is a must. If the batterys can wiggle around in the pack, the tabs are going to fail. I know from experience.

I've built a few packs, and I'll tell you, you are money ahead to purchase pre-assembled packs. There are a few companies on Ebay and the Web that sell packs very cheep. I just picked up four 2500 mah NiMh packs, the same physical size as the Futaba pack for $40 including shipping. I've had the same companys TX packs in my transmitters for several months now and they are awsome. A charge on Sunday night using the Futaba Wall Wort. is good for four days flying. The key is to NOT use a field charger and if you do limit it to less than a 1 amp charge rate. THe NiMh don't like to be overheated and I've got a dozen of the individual cells I got for my Digital camera that I basicly killed with charging them to fast. THe first charge wasn't very impressive and it went down hill from there. These last packs had tiny print saying to limite the charge rate to less than 1 amp. My field charger said to charge them at 2.5 amps. Believe the battery.

Don

If/when I build my own packs I will also lay down a bead of hot glue between each cell to keep the pack together and not wiggle. I then heat shrink the entire pack.

Ken

Ken, do you use the fabric type that is somewhat rubbery and low temp, or the higher temp stuff. Sounds like a good Idea, it would probably saved my last plane.

Don

I use the lower temp stuff.

Shoe Goo is a great glue for making batt packs. Much stronger that hot glue.