Nominal Voltage range of Gen 1 pack

I've seen just over 300 V when in heavy regen mode. Not something I'd recommend. Low voltages, that I remember, are in the 250 V range. These are just fleeting memories and not something that I'm really worried about.

Bob Wilson

 

Actually, ~300V is a common voltage level for a healthy Gen I battery pack at rest. The 273.6 volt rating is somewhat akin to a 12V rating on an automotive battery, which will typically read about 12.7V at rest.

 

ive seen upwards of 7.9 volts on an individual module, its very possible to have 300 volts.

i got a question for jk450, since you seem pretty knowledgable on this, whats the theoretical highest voltage the battery ECU can read?

 

You bet. A quick look at a couple of Gen 1 vehicles with healthy packs would confirm that 300V is quite normal. By chance, I looked at a correctly charging Gen 1 quite recently, and it happened to read exactly 300V at rest.

But the proponent of the "300V is too high" myth is tenacious, and will brook no discord from any Unbelievers, nor let details such as data and logic get in the way.

I've never looked, and I don't know if Toyota publishes that information for the Gen 1. However, it's probably well above any realistic figure. Toyota states, for example, that the battery voltage display range on the Gen II is 0 to 510 volts, and that's a ~200 volt battery.

 

Last night (3-25-10) we took the HV pack out of our '01 Prius and removed the top cover to expose the cells, all of this because of a p3006 code,(well there were other codes and lights also) all cells were at 8.01 to 8.04 except for one at 6.71 volts. Using a good digital VOM, each half of the battery tested at 154 and 155 volts making a total of 309. I'm pretty sure that that is about correct. Nominal cell voltage should be 7.2 with actual voltages at around 8.1, so 7.2 X 38 equals 273.6: 8.1 X 38 = 307.8, so ------. I'm just amazed that apparently one 1 1/2 volt cell has gone bad (causing all sorts of issues) and the dealer wanted $4200.00 to repair it. ON a car that has a book value of $3500. at best!!!!

 

Well done!! Have you got a cell to replace it with?

 

To deal with one bad cell in one module, the others get over charged. Then things tend to cascade. The shorted cell becomes a resistor and heats the adjacent modules.

Bob Wilson

 

The voltages cited do not necessarily reflect overcharge.

The voltage reading of the weak module does not necessarily indicate a short.

 

Any sources? Perhaps some backup data? Opps, I forgot, just another empty opinion.

Doing the experiment improves one's confidence because you know it is real. For example, here's mine with cell-shorted module:


If you have a handy power source, say 9 V DC, and a current limiting resistor, take the VOM a clock and make the measurements on the failed module. Do the experiment and move beyond the nonsense of intimidation postings.

In this case, the ".2C" is the charge rate based on the reported 6.5 Ahr original specification. So at .2C, the current drain would be about 1.3 A. In this case, you might want to use say .1 C, say 650 ma. Even so, you're in the 7*.65 ~= 5 W range. See if you can shake up a 15 ohm, 5 W resistor and you should be able to do controlled charge and discharge plotting.

Bob Wilson

 

Logic should suffice.

As the pack's six-cell modules are, on average, charged to 8 volts, each cell is running at ~1.33V.

A shorted cell (low resistance) will produce little to no voltage.

8.00 - 1.33V = 6.67 volts, or close to the 6.71 volts of the bad module.

However, a cell that has completely dehydrated will also produce little to no voltage. Again:

8.00 - 1.33V = 6.67 volts, or close to the 6.71 volts of the bad module.

In addition, several partially degraded cells in a module can also produce a module voltage of 6.71 volts.

As I said, the voltage reading of the weak module does not necessarily indicate a short.

 

Nonsense, it is simpler than that:

• 1.2 V - nominal NiMH cell voltage

One module of 6 cells is at least 1.2 V low ... Occam's razor, that module has a shorted cell.

The internal structure of an NiMH battery consists of nickel coated with nickel hydroxide, two versions, and a mass of metal hydride:

The metal hydride has a fiberous, plastic mat that prevents internal shorting. But when the electrolyte loses water, the conductive area between the electrodes shrinks, increasing the resistance. Eventually the resistance gets high enough that ohmic heating melts the separator and shorts the electrodes.

Bob Wilson

 

Again, it may have a shorted cell. Then again, it may not.

And "nominal" voltage is just that: not necessarily corresponding to actual value. Real-world voltages will be higher, as explained in previous threads, and demonstrated in this thread. This is not unique to NiMH. For example, a so-called 12V battery will read about 12.66V at full charge. But a true 12V reading would indicate partial discharge.

And if a code sets before the separator melts, you have a high-resistance, low-voltage module.

But you don't have a short. And there is a reason for this.

Focus on the logic. Pictures and graphs are pretty, but they need to contribute to the discussion, as well.

 

LOL!

The traction battery with the failed module is in the owner's hands. Hopefully, they will find a fix:

• replace the failed module with a working one - possible, I'd bought four good NHW11 modules several years ago before buying a failed pack
• contact "Re-InVolt" and see what they can offer

In the meanwhile, I've got one module reactivated. Tomorrow, I'll start refurbishment, which usually takes 5 days. If the OP wants it, we'll do a swap. I can use the bad module for my studies.

Bob Wilson

 

Not yet, but we found one in LA, and since we're about 60 miles north of there, will hopefully pick it up tomorrow. This forum is great, what a wealth of information!!!

 

Not to hijack this thread, but because we're discussing one cell, I picked up the one cell that I had found in LA, and along with the good one, they gave me the "bad" cell that had been replaced in their HV pack. I got home and attached the good cell to my NiMH battery charger for my model Helicopters and proceded to give it a 20 minute charge at .5 C. When done, the cell measured 8.4 volts and 24 hours later reads 7.88 whereas the HV pack, that last Thursday mostly read 8.01-8.04, now reads about 7.75, so the new used cell obviously didn't get charged very long, and may have been out of a used pack for ???? Anyway, I also put the second "bad" cell on my charger and charged it for about 80 minutes at .2 C.. after 83 minutes, I removed the charger and hooked my DVM to it and watched it drop about .1 volts every second until it got back down to under 7 volts. So it really is bad, but now that I look at that cell, it has a definite "bulge" to it, that I didn't notice before, and I'm thinking we're lucky that I didn't explode it while charging it. Anyone had any experience with using an external charger on one cell? NiMH batteries normally don't have charging issues, (like Lipo's do) but I suppose one can ruin anything if you put your lack of knowledge to it.
Tonight's the night, I think we'll be changing our bad cell, then putting the Hv pack back into the car tomorrow.

 

Excellent!!

Now you may still have 'issues' with module matching but I think you have a Graham scanner. Just monitor the minimum and maximum voltages, locations, and battery temperature.

The Dept. of Energy found in their fleet studies that module capacity had fallen to ~2.5 Ahr after 160,000 miles of Arizona usage. The modules from the bad pack were mostly under 2 Ahr and some as low as 1 Ahr. Still you should be in good shape to diagnose and deal with any issues.

Tonight, I'll start module rehydration. Having gotten the module voltage high enough to see NiMH chemistry, the next step is to increase the active surface area. The internal resistance is still too high but I'm still testing my 'hack charger'. The next week will be the 'acid test.'

I may still have to pulse activate the electrodes with a charged capacitor. The literature discusses 'fracturing' the metal hydride surface with some high currents and David Taylor mentioned a 20 A jolt.

Bob Wilson

 

Just to let you guys know, we replaced the one bad cell in the Hv pack, it went as planned, no issues, re-installed the pack in the car, everything was back to normal, then last evening my daughter-in-law (twas her car) traded it in on a new CHEVY!!!! Said she had no faith in it anymore. So: Thanks for the help/info, it was interesting learning about the car. But back to my normal helicopters and hotrods. Keith.

 

Any pictures?

Bob Wilson

 

A few, I'll try and insert them here. It was very straight-forward.