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Tesseract · #31 09-01-2011, 04:44 AM

Quote:

Originally Posted by powerhouse

Hmm... I don't understand how the 10ah battery pack with more internal resistance has the same voltage sag, thus power, as the 8ah battery pack ?

I wouldn't place too much faith into calculations of what the sag *should* be based on these Chinese cell manufacturer's datasheets. To paraphrase Mark Twain, there are lies, damn lies and battery datasheets.

From the PM you sent to me, you wish to construct an 8p112s pack (note the order of p and s - that helps to clarify that you are first paralleling the cells then putting them in series) and the claimed internal resistance - Ri or R[int] - is 6 milliohms per cell.

The Ri in milliohms of a group of 8 cells in parallel would be:

1/((1/6mΩ)*8) = 0.75mΩ

And 112 of those in series would be 112 * 0.75mΩ = 84mΩ

To calculate the voltage drop due to Ri you simply multiply the battery current and the total resistance of the pack while to calculate power *lost* to Ri you multiply by current again:

1000A * 84mΩ = 84V; 1000A * 84V = 84kW
2000A * 84mΩ = 168V; 2000A * 168V = 336kW

The maximum power occurs when the load impedance (or resistance) matches the source impedance (or Ri here) because at that point half of the voltage is lost to Ri and half to the load. In other words, when voltage sag from Ri is half the nominal pack voltage (assume 3.2V per LFP cell, so 358.4V total) then trying to draw more current results in less actual power being delivered. In this case we want to find the amount of current that results the pack dropping to half of 358.4V, or 179.2V:

179.2V / 84mΩ = 2133.3A
179.2V * 2133.3A = 382.3kW

If you need more convincing this is true, the voltage drop and total power at 3000A and 4000A:

3000A * 84mΩ = 252V; (358.4V - 252V) * 3000A = 319.2kW (63.1kW less)
4000A * 84mΩ = 336V; (358.4V - 336V) * 4000A = 89.6kW (292.7kW less)

But all of this is the *theoretical* performance of your battery pack. You won't actually know what the voltage sag of your pack is until you have built it and measured the actual difference in voltage at two non-zero currents (as I did previously in this thread).

Bowser330 · #32 09-01-2011, 10:30 AM

Quote:

Originally Posted by Tesseract

From the PM you sent to me, you wish to construct an 8p112s pack (note the order of p and s - that helps to clarify that you are first paralleling the cells then putting them in series) and the claimed internal resistance - Ri or R[int] - is 6 milliohms per cell.

Can you help me with the Formulas if instead of having the pack setup in 112 clusters of 8 cells each it was setup with 8 clusters of 112 cells each (112s8p)? I am assuming since you specified that previous arrangement that there is an impact to the IR of the pack as a whole.

dladd · #33 09-01-2011, 04:14 PM

Quote:

Originally Posted by powerhouse

I don't think theres any difference between the 112s/8p or 8p/112s
theyre both the same, however you're supposed to put parallel first.

physically, there is a difference, right? 112s8p means you have eight strings of 112 cells in parallel. 8p112s means you have 112 sets of battery packs consisting of 8 parallel cells, which are then put in series. Do those two configurations behave the same?

Bowser330 · #34 09-01-2011, 04:33 PM

112s8p = 112 Series 8 Parallel

Cells in Parallel add Amperage
Cells in Series add Voltage

so no matter is you write 112s8p or 8p112s they mean the same thing, right?

112p8s is what makes things crazy, as you already described.

I was just wondering if you had to make battery modules because you couldn't fit one huge brick of cells...which would be better?

Eight modules in series, each 44.8V & 64A (14s8p) 8*14 = 112s

or

Eight modules in parallel, each 358V & 8A (112s1p) 8*1 = 8p

Any difference?

x88x · #35 09-01-2011, 04:44 PM

Quote:

Originally Posted by Bowser330

so no matter is you write 112s8p or 8p112s they mean the same thing, right?

The difference is in how you physically build the pack. 112s8p would be 8 strings of 112, paralleled at the ends. 8p112s would be a single string of 112 blocks of 8 paralleled cells. Building them the latter manner is supposed to be better for the batteries.

powerhouse · #36 11-06-2011, 02:49 PM

Back again!

Well this build is going slower than I had hoped :/
My father insists that we order one component at a time, since he isn't in any rush, but I was really hoping to finish the vehicle by the end of the year. Oh well, better safe than sorry.

Approximately 4 weeks ago I ordered the motors from Rebirth Auto, hoping they would arrive within the week, however they still haven't arrived which is upsetting but understandable. I ordered a transwarp 9 and a warp 9, which I intend on coupling together. I don't fully know how I am going to couple them together, but I hope for it to be rather straight forward.

Once the motors come in, I will post pictures of them for you guys to see. I also plan on picking up some small little tid bits while I am down in Tampa picking up the motors. Wire, connectors, contactors...

Once the motors arrive, I plan on ordering a 3 or 2 speed gear vendors transmission to finish off the drive train. I know that Ron (Team haiyan) and John Metric (DC plasma) are using the gear vendors, so I know I am purchasing a tranny that has some proof in the pudding.

The transmission!!

Since my last update, I have disassembled the car to the bare engine and transmission. I Have yet been able to remove the drive shaft, which is the only thing stopping me from extracting the drive train. Its STUCK on there, since the dumb honda engineers decided to use 6mm, galvanized steel hex nuts to hold the driveshaft in place. So of course they stripped out, and now have to be cut off.

These pictures were taken a while ago, since then many more components have been removed

My Zilla 2k EHV also arrived too! The first thing I noticed was how heavy it was. It came nicely wrapped in a cardboard cocoon, ensuring it would get to me safely. Manzanita Micro made the process very quick and easy, something I applaud them for.

The hair ball has so many inputs, so many possibilities

Hopefully, next weekend I will be down in Tampa picking up my motors and a bunch of other components. Once I get the motors installed in the car, the batteries will be ordered, something I cant wait for.