2001 Prius Battery

Actually, the primary air inlet cannot be seen in your photo, because it attaches to the end of the battery that is out of frame. Open your trunk and look at the underside of your package. Follow the black plastic air duct and you will see where it connects to your battery pack.

 

Yes, at the sides, too. You can plainly see it in Toyota's diagram.

 

I was not aware of Monoco EVS 21 which happened about six months before I bought our first NHW11 Prius. I've only scanned a couple of reports but am impressed with:

EVS 21 Monaco Report

Well more good stuff to read.

I especially appreciate the thermal graphs of the old and new style traction battery modules. I'd seen postings about the difference in the past but this really brings it home. It also explains the melted "O" ring material found at the terminals and the trends seen in NHW11 battery failures:

• warmer climates - higher failure rates because the traction battery is already starting hot
• hills - the best way to get peak charge and discharge rates

It is great to see hard data, empirical measurements, being brought to the forum. This also explains a curious pattern I'd seen in some of the old modules:


I had noticed the modules had a curious triangular, surface pattern which parallels the thermal model showing hot-spots. Literally the modules have been 'cooked' and the smooth sections are where the heat has released the original stresses on the case.

Thanks,
Bob Wilson

 

That taper could be expanded with a press and some sheet metal work. Great photo! BTW, if you blow up my photo of the NHW11 and NHW20 module, you'll notice the terminals extend out ~1/4" (~6 mm.)

What might make sense would be to replace the metal cover with a glass-epoxy case. Make a mold of the existing case and fillet out the taper. Then use a glass-epoxy, vacuum formed replacement. Homebuilt aircraft and boats have been using this for decades. It could be made stronger, lighter and non-conductive.

Bob Wilson

 

"What might make sense would be to replace the metal cover with a glass-epoxy case."
That is an excellent idea.. wonder why no one thought of that yet? How about making the whole case fiberglass epoxy resin?
That potential metal case electrolyte short under the back seat is always in back of my mind.
The only thing that may be wrong is the fact that the 38 modules in a classic prius are quite heavy and upon a crash they may come right up to the front seat with you, so it may break the safety standards a bit unless lots of crash testing went on. Ah who cares -I'll take one.:rockon:

 

No, it couldn't, at least not without creating additional problems. The entire case is somewhat corrugated. Expanding the taper at that point would first require flattening the corrugated sections and further compromising the physical integrity of the case. But even if you choose to ignore that issue, pushing the case out at the sides will lower its height and create another clearance issue. Presses are for shaping metal, not stretching it.

Just for kicks, measure the height of a Gen 1 module as well as the height of a Gen II module, and post your results. I think you'll see the problem more clearly that way.

You have said that you once helped someone install a battery pack in a Gen 1. If so, then you will recall that the battery pack is tied into the frame with reinforcing brackets. Those brackets were secured with fairly large, high-strength fasteners. Had an engineer observed the installation, he or she would have noticed that the battery pack is actually adding significant structural integrity to the rear of the vehicle. So we really don't want that battery pack to flex much, do we?

Yes, and that's all that is needed to create an engineering problem. We don't want the gap between case and terminals to be too much, because we're trying to force air past the module's sides to carry away heat. At the same time, we need to have enough clearance so that the terminal covers won't chafe during battery flex, and so that there is a bit of crush space in the event of a collision. Sticking used Gen II modules in a Gen I case does away with the terminal area crush space entirely.

By the way, forum member oldnoah's assumption that the battery bus bars block air flow from the ends of the modules is incorrect. Air can easily flow around the busbars, and will run into the black busbar covers, which are closed at the top, open at the bottom. The air is therefore forced downward along the surfaces of the module ends, carrying away heat, before making a U-turn and transporting that heat to the case itself.

in other words, Toyota's description of the intended airflow around the battery pack is correct. I think you'll see the problem more clearly if you mount 38 Gen II modules in a Gen 1 case than if you look at individual modules on a bench.

Unfortunately, that would create a safety issue. If leaking electrolyte creates a significant conductive path between the battery modules and the top case, and the case is conductive, then the vehicle's high-voltage current leakage detection circuit would be unable to detect the leak.

Another problem is that a glass-epoxy case is likely to shatter rather than deform upon impact. The case needs to be able to deform and thus absorb some of the energy of a catastrophic impact.

 

Actually carbon-fiber epoxy would be a great start. User "oldnoah" has already confirmed that a sufficiently high, MEGGER will 'poof' the electrolyte trace . . . probably driving off the water and layer of whatever salt the KOH has become.

Before going too far down that path, it would make sense to verify KOH does not attack the epoxy although most are know to be fairly resistant to most chemicals. Still, it would need testing.

Would you have the NHW11 internal resistance data handy? I can use Auto Enginuity to read it out later tonight and compare it with the note vincent posted.

Bob Wilson

 

I looked for this quite carefully last night while I was taking the photos.There is a ridge that forms a seal along the short edges of the modules, preventing air flow in this direction. The passage that is outside of the seal line on the top and bottom of the batteries is open to atmosphere on one end, but there is no air flow through that passage.

I don't have any gen II modules to play with, but it looks like the other side of the case has a little room to play with. A simpler solution might be to elongate the holes in the bottom plate to allow the modules to move away from the tapered side. I think we're only talking about a millimeter or two of clearance.

 

BTW, I'm travelling on business this week, so I don't have access to the battery parts in my garage. Everything I'm saying here is either from memory or conjecture.

 

You are correct about the airflow around the modules. The airflow has no defined inlet or outlet to the sides of the modules where the busbars reside. Although one could assume that air could get to that area, it definately does not have a flow path, but is actually blocked off by foam insulation and the module end caps.
It really does not matter how many diagrams are presented to the contrary, as you have pointed out in the actual photos of the pack, Toyota has made no provision to cool the sides of the cell modules since all cell material is inside the normal path of airflow.

 

I'm happy to say that although I noticed the discoloration in Bob's photographs of the modules, I didn't notice similar discoloration on the modules from either of my battery packs. I will look again when I get home, to see if I just missed it, but it certainly didn't make itself obvious.

 

I'm not sure I'd call this a safety issue so much as an informational one. As long as no short occurs, safety isn't an issue, but you certainly would like to know if the modules are leaking.

That said, my old battery had obvious signs of leakage from the terminal to the metal pan, but this battery didn't give a p3009 code.

The newer battery gave a p3009 code, but didn't have obvious signs of an electrolyte trail to the pan, and there was an obvious leak that percolated upward to the top of the buss bar. I'm not sure where it found the voltage leak, but it might see it from between the terminals of two adjacent blocks.

 

The worn-out pack I picked up was in South Carolina ... nice warm climate. But it was below freezing that January day when I drove over and back. At 4:00 AM, it was 17 F leaving Huntsville and about 18 F when I got back shortly after midnight.

Bob Wilson

 

It does.

No. While the most efficient air cooling will have an entry and exit path, secondary cooling can be achieved without an exit path. As long as you can get air to absorb heat from a surface, move, and transfer that heat to another surface, you have achieved a cooling effect.

Consider the Prius transaxle. In addition to two different fluids, it is cooled, in part, by air.

Where is the entry? Where is the exit?

I disagree. The airflow diagram that vincent1449p posted is from Toyota's hybrid diagnosis course 071, which was developed by Toyota to train their own technicians. If you read the entire document, you will see that flow is indicated at the sides of both Gen I and Gen II battery packs.

I think you have some learning to do. Start with fluid dynamics. And yes, air is a fluid.

 

The diagram in question suffers from the effect that made M.C. Escher famous, namely, that a 2 dimensional representation cannot accurately convey three dimensional information. The diagram may appear to show flow in the space alongside the modules edges, but those arrows are actually showing the gas rising THROUGH the pack, not alongside it.

I have two patents dealing with fluid dynamics. The majority of my expertise is not electrical, but deals with fluid flow and heat transfer. And there is NO provision for gas flow in the space outside of the sealed plenum chambers that force air to flow between the modules. The space is open to atmosphere at one end, so while there is some possible convection going on, it is minimal. Even it if was, the buss bar holders and covers obscure access to any gas flow that might provide cooling to the top of the module where the interference problem resides, and the lower portion of the case has ample room for air flow along the exposed part of the module edge.

 

Thank you for pointing out the common sense logic. This is the key difference between someone who has done a ton of reading and someone who actually has had hands on experience.
As you have pointed out, Toyota went to great lengths to seal this area from the forced air of the battery cooling fan. They did not do this just because they had extra material laying around that they needed to dispose of. Just ordinary common sense. Thank you.

 

Let's go with your assertion: a two-dimensional representation cannot accurately convey three-dimensional information. Do we, then ignore the two-dimensional photos that you posted? Or do we ignore only any photos and diagrams that do not support your hypothesis?

Of course, folks can be fooled by an image. For example, forum member bwilson4web posted a photo to this thread that purported to show that the battery pack air inlet was on the drivers' side of the vehicle. In truth, the inlet is on the opposite side (it's pretty hard to miss), and wasn't even in the picture. But you didn't catch it, and I'm sure you know that's not right. Is it possible that, rather than seek to find out how the battery is cooled, you have focused on "disproving" the question that has been raised?

By the way, I would like to thank bwilson4web for correcting his error.

A diagram of air flow in the Gen II battery pack can be found in the same document that contains the diagram of air flow in the Gen I battery pack. Do you draw the same conclusion from the Gen II diagram? Do you think the Gen II battery is cooled in a similar manner to the Gen I?

That's great. I'm sure your knowledge will be a welcome addition to this thread. My advice to study fluid dynamics was, however, directed to forum member hybriddriveguy.

Okay, let's work with that.

This contradicts your previous statement.

And how minimal is "minimal", especially on a day where ambient temperatures are high?

Why do you think the covers are closed at the top, and open at the bottom?

 

Who has done a ton of reading, and who has hands-on experience? And how did you determine this?

But I think you are getting ahead of yourself. In this forum, you have done a fair bit of marketing the battery packs that you sell. That's fine, and I wish you all the success in the world. In doing so, however, you have made several statements that have cast Toyota's battery packs in a poor light, and by comparison, made your used battery packs looked better.

In return, you have been invited to substantiate those statements—a logical request—but have not done so. I think is is reasonable to expect you to either lay out the logic behind your claims, or withdraw the claims altogether. Fair enough?

The claims are:

1. that Toyota's replacement battery backs are "definitely not" designed any differently than they were during Gen 1 production

2. that you have decoded Toyota's battery pack serial numbers, and have used that information to establish that replacement packs you have seen have been produced in 2008 or earlier.

By the way, I am also curious as to your opinion about the loss of crush space in your battery packs. How does that affect vehicle safety? How much pressure can the case exert on the modules during chassis flex? What kind of testing did you do prior to installing these packs in customers' vehicles?

 

Whoa! You're criticising me for identifying a caveat to my own assertion? No. My assertion is that there is no PROVISION for gas flow. That is not contradicted by the statement that convection can occur anyway. And to answer your question, minimal means not significant.

He has. You haven't. Have you withdrawn your claim yet? It's been disproven.

As for these:

This is what's called a strawman argument. You misstate your opponents claim in order to make it appear weaker. If the gen II redesign had been deployed in the gen II modules, the change would be obvious. Have there been any changes in the gen I modules? No obvious ones.

But your position implies that there HAVE been changes in the gen I modules, but you have provided no evidence of this change.

Do you have reason to believe that this decoding is not accurate? What is your reasoning behind making this statement at all?

Now that the "cooling the sidewall" conjecture has been refuted, let's just move the goalposts, shall we?