Using serial cables for balance charging

[Philistine]

I have seen a few folks using what look like printer serial cables to achieve a one plug solution for balance charging lipo (ie, they have all the balance wires and the two charge wires put into the serial plug, so they just plug one plug in for balance charging. I think the members I saw doing this were El Steak and Aussie Jester, but I could be wrong.

I am building a 10S battery for a friend who I would like to be able to have them just plug one plug in, and balance charge. But my question was, when you run the main power/charge leads into the serial port plug, how big does the wire you use for the charge lines need to be (if say you are charging 10S at 10amps)? I would have thought that there would be too much resistance with the + and - charge leads going through such a small pin, or is 10amps not such a big deal? Could the wire you use leading up to the pin be the same kind of thinnness as balance leads?

 

[SamTexas]

Serial cables have either 16 or 17 pairs of tiny wires. Each pair can handle up to 2A.

For a 10s configuration, you would need a total of 11 pairs. You can use 3 pairs for the two main leads (+ and -) and 1 pair the each of the rest. So the max tolerable current is 6A. 10A would not be a good idea.

I have used serial cables for my home built 1.5A charger. I have tested each pair of wires for current capability. They are cool at 2A but get warm at 3A.

However, instead of using prebuilt serial cables, you can always make your own using heavier wires to support higher current.

 

[Philistine]

Thanks SamTexas, much appreciated. I had suspected that 10amps might be too much, they looked too thin but thought I would check.

 

[SamTexas]

You're welcome.

Here's a robust alternative. A 14 pin military quality connector. Use 2 pins for each of the main leads and 1 pin for the rest. Should not have any problem handling 10A.

http://www.ebay.com/itm/1-Military-14-Pin-Twist-Male-Female-Connector-14PF-/260560280062?pt=LH_DefaultDomain_0&hash=item3caa9a59fe#ht_1164wt_849

 

[Jozzer]

I've tested some serial cables that turned out woefully bad for balance leads. 1v drop at 2A balance current. Also, many leads don't come with all the pins poplulated I found. I don't know if I just got unlucky (I ordered randomly from 3 suppliers).
A similar (cheap) cable that has been working out OK for me are the OBD2 leads. Much heavier duty..

Steve

 

[Ypedal]

I've done a few of these :
http://ypedal.com/Cyclone/cyclone4.htm

8)

 

[nicobie]

I used a military plug that I got off ebay. Works great, but takes time to solder up.

Check out the link to pics of it in my build thread below

 

[El_Steak]

I have seen a few folks using what look like printer serial cables to achieve a one plug solution for balance charging lipo (ie, they have all the balance wires and the two charge wires put into the serial plug, so they just plug one plug in for balance charging. I think the members I saw doing this were El Steak and Aussie Jester, but I could be wrong.

Yes, I did it and Aussie Jester did it as well.

I didn't use a prebuild cable, instead I bought a bunch of DB25 connectors with solder cups off ebay and build my own cable.

Inside the connector, the balance pins are connected with 22AWG wire. This is small but I haven't noticed any significant difference in voltage readings right at the battery or at the end of the DB25 wire. Balancing is also precise and accurate.

The main leads are connected with 20 AWG (largest that fits in the solder cups). There are 4 short wires for the positive and 4 short wires for the negative. They are connected to a single 14 AWG wire right after the connector (4 x 20 AWG is the same cross-sectional area as 1 x 14 AWG). I haven't noticed any heat on the connector while charging. As for the DB25 pins, I've seen ratings anywhere from 2A to 7.5A continuous per pin. 5A seems to be the most common value I see.

I charge with a 1420i limited to 350Watts (limit of my PS) so its only about 7A. The connectors and wires stay cool while charging.

I think prebuilt DB25 cables use very small wires to keep the total diameter small and I don't know how good the connection is between the pins and wires. With solder cups you can use larger wires.