[dtbaker]

I am in the middle of my initial pre-install cell top-balance with cells wired in parallel and charging to 3.7v with my mastech power supply. Its been chugging away for two days now at 7+ amps and dropping a little, and I expect a couple more days...

I connected the cells using my bus bars on every other and 16ga wire between. After discussion in a different thread about my final design to use 16ga wire to monitor/balance cells after installed from central, or at least easy access, terminal blocks.... I checked the voltage drop from the 'first' cell the power supply is connected to the 'last' in the string.

Turns out that there is not a LOT of drop, only about .1v, but some for sure I guess from the 16ga sections adding up to *some* resistance.

MY QUESTION is... as the cells come up closer to my final voltage (set to 3.70), will they balance out across the whole pack in parallel? I am assuming the cells closer to the power supply will reach the target first; and the whole idea of a parallel setup is that the charge will essentially skip over the cells at the final voltage and the amp draw drops off to nothing once all cells are at the setpoint.... right?

just checking!

I want to make sure that the batteries at the end of the line won't be ending up lower than the earlier ones by virtue of the voltage drop in the wires?

or, do I need to 'finish' each cell individually with a fixed length of wire to be certain they all 'finished' at the same top voltage?

 

[Overlander23]

I did the same procedure with my Mastech... but then ended up disconnecting it and letting the whole thing sit overnight just wired in parallel with no external input.

The closer the cells become balanced, and the less current that flows into them, the lower the voltage drop will be. If you just let them balance amongst themselves without the supply attached you don't have to worry about a voltage difference between the supply and the last cell.

You could also hook up multiple "trunk" lines... say between the Mastech and the other end of the parallel string. I hooked the Mastech to the middle of my group of cells... and also ran another set of wires to each end. As long as it's all parallel you're good.

 

[dtbaker]

aha. I did hook mine in the middle-ish, but didn't run multiple trunk lines say to the other ends of the strings. hhhmmm, might be worth the extra couple minutes I guess. I also did not pre-charge in series with big charger, I've just been letting the power supply chug along while I am dismantling my FLA system...

 

[Overlander23]

You'll be fine... at the end of day, the cell can't accept more voltage than you set with the Mastech. The end cells will come in line as the cells that hit first just sit there.

aha. I did hook mine in the middle-ish, but didn't run multiple trunk lines say to the other ends of the strings. hhhmmm, might be worth the extra couple minutes I guess. I also did not pre-charge in series with big charger, I've just been letting the power supply chug along while I am dismantling my FLA system...

 

[dtbaker]

...at the end of the WEEK, not the day. glad to hear I am on the right track with this one.

 

[Tesseract]

Hey Dan - just connect your power supply up to the paralleled cells at opposite ends and the path length - and therefore the voltage drop - will be the same for each cell. Something like this:

 

[dtbaker]

Hey Dan - just connect your power supply up to the paralleled cells at opposite ends and the path length - and therefore the voltage drop - will be the same for each cell. Something like this:

cool, I can do this!

.... just changed where my power supply is wired in, and the amps going in dropped from 7.2 to 5.7 . Looking at the kWhr that have gone into the pack over the last couple days (about 5kWhr measured with a Kill-a-watt meter at the plug) I am guessing I've got another day or two of charging to go if the pack was roughly 50% charged when I started ...