Battery bus bars

The lithium packs pump out more amps than NiMH... So crappy bus bars aren't as much of a concern with lower amp NiMH.

 

Wait, more peak amps? I thought these were just greater capacity, so same peak amps for longer. Never mind the bus bars, how do we know that the rest of the circuit can handle that extra current on a long term basis without damage?

 

The capacities are fairly similar because the packets are designed to match what the Prius hybrid battery ECU expects in terms of the power curve, but LiFePo4 chemistry is 30 years more advanced than NiMH chemistry so as you accelerate from 0-60 for example you'll feel the initial fully charge NiMH power drop off, whereas the LiFePo4 stays constant all the way to 60mph.

Basically these Lithium packs are going to give an amperage signal of a fully charged NiMh all the way down to two or three bars... And now that we're in hot Summer weather those extra amps does wonders for the air conditioning. Also as time goes by and the pack design is refined they've been able to add a few amp-hours of capacity without throwing warning codes for too much power.

Here's my affiliate link if you want to buy one with it I can offer you unlimited tech support: https://projectlithium.com/?ref=9qLPw

 

Hybrid Assistant can graph these current values and block voltages during acceleration. It will even graph an entire road trip. It would be interesting to see what current curve could be obtained (full chart) when going from a stop, pedal to the floor acceleration to 60-70 mph.

Did anyone already post this when all the 'test' batteries were put out for trials?

 

We had one guy on here who said he got the data that you're referring to before & after project Lithium and he said he was gonna post it soon. Soon as I remember his username I'll see if he's got it yet. I'll also make sure to send a notification your way once it's posted.

 

Again, if the aftermarket busbars have higher resistance, would it not show up in higher internal resistance data on the scantool? The HV battery ecu uses voltage measurements from the sense harness and amps from the current sensor to calculate IR.

The HV pack is a series circuit, so extra resistance should affect the voltage readings.

Posted via the PriusChat mobile app.

 

Well, YOU have a lithium pack. Couldn't you log some block voltage and amperage data from some hard driving and post it? HA, Techstream, Dr Prius, something? Add in vehicle speed (& I think Techstream data has a timestamp PID), and you will have scientific, repeatable data.

Posted via the PriusChat mobile app.

 

Oh yeah, that's right, I do... Even have brand new pack in a box I've been meaning to deal with. But it's Summer and got so many gardens I take care of. But valid point. Let's design a test... The app creates a huge amount of data on just a short test drive but sounds like the first test would be a freeway onramp from a stop up to 60mph at same time of day, same temperature and no traffic. What other tests should we add to this to make it more interesting?

 

Yes, more than once over the years Jack has raised concerns about bad HV cables and bus bars is an extension of that. And in some ways I have a hard time accepting that so much metal in most any type of conductive metal is going to be a problem. But if I put myself in his shoes and think of all the time and major investment into developing these packs I can understand why any unexplained anomalies could default back to that. Of course trying to explain an anomaly is to overthink it... Unless of course it's not an anomaly.

 

I'd also be interested in seeing one of these nickel plated stainless steel bus bars, the cross section after cutting in half and the seller information.

 

Maybe. The bus bar resistance for copper is going to be on the order of 0.1 mOhm (my estimate), so 4.5 mOhm for steel. I have seen posts which say that Dr. Prius shows resistances like 24 or 25 mOhm. Adding the resistance of the copper bars will be in the measurement noise, but 24-25 vs 28.5-29.5 should be evident. The thing is, this assumes all the battery cells are still optimal, the resistance probably goes up as they age, and by how much? So is 28 an old cell or a steel bus bar?

Why is the small resistance sometimes a problem when the much larger resistance of the battery cell is not? I think probably it is because of the available surface area for dumping the heat. The bus bar is very small and all the heat is concentrated there. The battery cells are bigger and they can shed heat outward over their entire surface, excluding those faces which are pressed up against another cell, where the heat flow in both directions would roughly cancel out.

 

Regarding the current, here

https://projectlithium.com/

it says:

I had missed that before, thought it was just more AH, not more A. The issue then is that one of the power formulas for heat due to resistance is:
P = R* I^2

That is not "2.6X more power", that is 2.6*2.6 = 6.76X more power, as HEAT.

That said, I'm not even sure what this statement really means. (Elsewhere in the faqs it lists 210A and 506A at different temperatures, probably maximum current of a shorted battery.) I doubt that pack resistance is the sole determining factor for maximum battery current, the inverter circuitry is going to have its say too.

 

On the other hand, the current that flows in real life will be what the (unchanged) HV control ECU programming selects: sometimes up to 90 amps charging on heavy deceleration, as far as maybe 160 amps on heavy acceleration, as long as it isn't for long enough to blow the (unchanged) 125 amp fuse.

 

Just a couple screen shots from a couple earlier full throttle/full brake episodes...Toyota battery.
156 amps discharge on acceleration / 98 amps regen on braking
172 amps discharge on acceleration / 104 amps regen on braking

 

Something like 0-60-0, maybe charge it up to 7 bars and EV glide at just under 40 for as long as possible on a flat road.


Posted via the PriusChat mobile app.

 

Back to the original purpose of this thread... Looks like @jacktheripper did a youtube video using a super expensive machine to measure internal resistance of the various busbars that are available for Prius packs. He was able to confirm there is a difference. But how significant? Doesn't seem very significant, but solid copper bus bars are still the best:

 

Interesting video indeed, in that it concluded the plated/unplated difference was essentially a wash, but there was a bigger difference associated with the kind of nuts you use (with vendors supplying yucky serrated ones instead of Toyota's flat ones).

 

I'm a believer in copper and try to stick with using only new wire frame #2 assemblies. Every now and then, I reuse an original, but all those bars get dipped in muriatic acid and polished.

So far, from what I've seen in core batteries, is nothing beats the nickel plated bars on the subject of corrosion resistance/buildup. Even with that being said, I'll stick with the copper!

 

I wonder if those minor differences in internal resistance somehow translate to much bigger differences at higher amp loads? Would be fun to take a thermal camera to each set of bus bars after heating up the pack on an aggressive drive?

 

The nice thing about that is that Ohm's law is just math. It's so totally just math that if you know the amps and you know the ohms, you don't even have to leave your chair to figure it out.

It looked like the differences he was seeing between busbars was somewhere in the ballpark of a hundredth of a milliohm. So if there are going to be 14 busbars, that's a difference of 0.00014 Ω in total for all of them. Run 200 amps through it and you're looking at a difference of 5.6 watts of heating, spread across all 14 bars.

That's a darned small fraction of the total dissipation going on in the battery, which at that current would be supplying 40 kilowatts of power and dissipating 3400 watts of heat (going again by his expensive machine's readings).