I was wondering , if longer leads = energy loss , heat = energy loss .. Well
Using my hobby charger to discharge batteries , I use the original leads + the ones from my cradle ..
Thats almost around half a meter of lead , + two different gauges .
Discharging 18650's I found the leads to get some what warm ..
So as an experiment , I went and got some heavier gauge leads , cut them much shorter ...
So now im discharging the Samsung 28A , and wait to see if there is any difference in the results [ any measurable variation ] with the new shorter , and heavier gauge leads .
For my charger setup I used silicone coated 12AWG cable rated at 0.006 Ohms/m, with a cable length of about 7" from the charger to the battery.
I'd love to pretend I planned it knowing that it would help but it's just what I had on hand as it's what I use for my RC battery packs. The length was enough for it to sit next to the charger without too much cable hanging around. Yay! for chance :)
If your battery cables are feeling warm, there will definitely be losses there! Takes a measurable amout of energy to warm up wires.
Things that can contribute to energy loss
1) Bad Contacts - Contacts are the most common failure points in a power system. Dirty or oxidised contacts create significant resistance, and make the contact unreliable, especially with movement.
2) Small surface area - Undersized or point contacts with insufficient surface area (essentially under-rated contacts) are the other common problem. Aligator clips tend to give relatively limited current carrying ability if not positioned carefully.
3) Small wires - another common problem associated with budget equipment. Most of the time small wires dont stop a device working, therefore are common places for materials to be cut back, however there can potentially be significant losses in efficiency.
4) Wire Length - This is related to 3), ultimately its the total resistance of the leads thats important. Longer wires increase resistance, as does smaller wires.
In the case of Lithium chargers that follow a true CC/CV profile, Poor cables (connectors and wires) can potentially slow down charging, by artificially placing the charger into the CV part of the cycle too early due to the resistance of the setup. Chargers that are able to detect cell voltages independent of the power leads (Balancing Li chargers) are able to negate the effects of cable resistance, and can charge at full rate for longer, allowing a quicker and more accurate charge. I find that using a balance lead drops my charging time for my RC batteries from 1.5 hours to 1.1 hours. Im charging my 7.4V LiPo 5.2A batteries at 5.2A. At this current, I'm using 18AWG wires (looks to be 1/8" external diameter including insulation for a easy reference), at about 8" length or so, and there is no detectable warming of the cables.
Solutions:
Shorter and thicker wires that help reduce resistance.
My problem isn't wires, its the conections. I'm using an older CBA II and I have a hard time getting consistant results. I've tried everything: magnets, cradles, and clamps and I'm never satisfied with the consistency. I see noticeable shifts in identical tests. I really need to find a solution thats effective but not too exotic.