Turning 5s+4s+5s balance cables into two 7s balance cables

[wesnewell]

I've got a 14s pack configured 5s+4s+5s and I want two 7s balance cables instead of the three.
First 5s brick cells Middle 4s brick second 5s brick
+1-+2-+3-+4-+5- +1-+2-+3-+4- +1-+2-+3-+4-+5-

For the first 7s balance cable I wired the first 5s brick balance leads straight to the 7s connector, then from the 4s brick 1- and 2- to pins 7 and 8 of the 7s connector. I tested this and the first 7 cells show up fine. Now I assume for the 2nd 7s connector I need to split the 2- wire (or +3, depending on how you look at it) of the 4s brick and take it to pin 1 of the second 7s connector also, and then continue on down with each cell skipping the +1 of the second 5s brick and ending with 5- as the last connection.

Anyone see anything wrong with this? Looks right to me but thought I better check to see if there's something I'm missing.

 

[neptronix]

Sounds right.

Verify it on a multimeter to be sure.

Each connector will have 8 pins total, first pin on connector #2 is going to be the positive of the previous cell ( which will be the negative lead )

Thus, cell 7 will have two wires coming off of it.

 

[wesnewell]

Got it wired and all is good. Balance gap was .016V after non balance charging for about 5 days. Completed a balancer run and it brought the gap down to .007V. Wasn't hardly worth the time it took to make the adapter cable.

 

[neptronix]

Eh. You'll need to balance it from time to time. And once you get a big parallel pack, you will thank yourself

 

[neptronix]

Oh also, that will come in handy if you ever want to use a pair of celllog 8s's.

Those doohickeys are badass.

 

[dogman dan]

Sounds cool. I've had similar thoughts, about turning 5s packs and 2s packs into handy 7s ones.

 

[GGoodrum]

It's actually pretty easy to combine odd size pacsk. You just need to "overlap" the last pin of the first pack, with the 1st pin of the 2nd one, etc. In your case, pin 6 on the 1st 5s pack is also pin 1 of the 4s pack. Pin 5 of the 4s pack is the same as pin 1 of the 2nd 5s pack. The same thing happens with the two 7s cables, pin 8 on the 1st 7s is the same as pin 1 on the 2nd 7s, and would connect to the junction between the 7th and 8th cells, which in your case would be pin 3 on the 4s pack. Confused yet?

-- Gary

 

[wesnewell]

Sounds cool. I've had similar thoughts, about turning 5s packs and 2s packs into handy 7s ones.

Yeah, If I'd know how much easier that would have been when I bought the two 5s and one 4s pack for 14s, I'd have bought two 5s and two 2s packs and done just that. One of these days hopefully 7s packs will become common at a comparative price. $280 is ridiculous for a 7s pack, when you can tie a 5s and 2s together for $56.

 

[Partycat]

Can you take a picture or something, if you have a moment?

I'm looking at these two diagrams, which, don't seem to be quite the same idea.

So the 5-/1+ isn't actually connected to the balance plug anywhere, or am I mis-interpreting what you're saying?

http://scriptasylum.com/rc_speed/_picture.html?bal_gen_3s3s_wmain.gif~14

http://scriptasylum.com/rc_speed/_picture.html?bal_gen_3s3s_nomain.gif~14

This is a diagram that would make sense to me, as attached, but, it doesn't seem this is the effort you went to.

 

[wesnewell]

Your diagram is correct, although I didn't Y the leads between the packs because the the serial connection between bricks does that already. What's probably confusing is the connector pin numbers. The numbers I used in my post just represent the cells across the packs, not actual connector pin numbers like you have. BTW, I didn't actually use the wires right out of the packs, but plugged them into a pigtailed female connector and used those to connect to the 7s connector. That way I can just use standard parallel balance cables to add up to 5 more 14S packs of 5-4-5. Still, If I was building a 14s pack today, I'd go with two 5s, and two 2s bricks wired 5-2-5-2, making the connection to the 7s connector simpler and easier and leaving parallel expansion easy with standard 5s and 2s parallel charge cables. Come to think of it, any combination 4 bricks would be easier than the combination of 3. 6-1-6-1, 4-3-4-3, etc.