extra traction battery?

You haven't said much about your background, but if it isn't at least quasi-EE I would suggest this is not an advisable project. (If you do have a quasi-EE background then I don't even have to suggest it's inadvisable because you'll already see the problems.)

The Gen 2 battery contains a different number of modules than Gen 1, hence their voltages are nearly 100 volts different. You mentioned wiring in series but you can't possibly mean that because nothing else in your car can work with 500 volts from the battery. You could have meant to say parallel but that's no good either because of the voltage difference, and even if you had two identical batteries, managing parallel charge and discharge is difficult engineering. What you're talking about has actually been available to buy in the form of aftermarket "plug-in conversion" kits, which included extra batteries and elaborate electronics to make the combination work without destroying anything. Trying to do it yourself would be essentially giving yourself an EE project of that same scale.

You could, of course, buy one of those systems. But it kind of sounds like what would be your most useful and practical step would be to replace your currently failing battery.

-Chap

 

It is a thing some people have done to buy two Gen 2 batteries (56 modules total) and pick the best 38 modules to replace those in a Gen 1 pack.

Mixing and matching Gen 1 and Gen 2 modules would be iffier (and harder to assemble, because the modules are slightly different sizes). I think I have seen at least one thread where somebody did that, but I don't know much about how it's working out....

-Chap

 

There is always a risk when trying to describe a technology. If too detailed, the reader's eyes glaze over and wanders off. If too simplified, some important technical points may be omitted leading to bad results. But I'll give a try, please be patient.

INTRODUCTION

Batteries capacity is measured in Amp-Hour (Ahr,) the time a battery can provide a given number of amps when discharging between two operating voltages. For Prius owners, a new, single Nickel Metal Hydride (NiMH) cell has 6.5 Ahr between 1.2V and 1.0V. Since the average is 1.1V, a 1.1 ohm resistor drawing about 1 amp would stay hot for about 6.5 hours. An 11 ohm resistor would stay hot for about 65 hours.

Having equal Ahr capacity cells is critical in a series battery pack. If a cell has low capacity, it will fill-up first when charging and its voltage will jump over 1.2V to dangerous values. It will get hot and generate gas. Enough heat and it will melt a small hole in the plastic mesh separator between the electrodes:

Here you see the nickel metal electrodes, the gray plastic mesh separator, and the black hybrid electrodes.

Our Prius battery modules have six cells in series. Here I cut off the top of a Prius battery module:


The electrolyte is a nearly saturated, potassium hydroxide solution. Potassium hydroxide is a strong base used in drain cleaners to 'dissolve' organic material ... like skin, clothing, fingers, and eyes. I had a hose running water, long sleeve shirt, plastic gloves, and safety goggles on. Everything was flooded with water and the parts washed and put in a plastic water bucket.

The six cells in each battery module means their 6.5Ahr capacity is between 7.2V (6 x 1.2V) and 6.0V (6 x 1.0V.) To charge a Prius module up to 7.2V, we have to put a little over-voltage to stuff in the amps. Once a module reaches a little over 8V, there is a 'dip' that signals full charge. It is critical to take this charging voltage OFF because if over charged: they get hot; generates gas and; expand breaking the pack:


This is why I use a computer controlled charger like the ones used by Radio Control hobbyist:

These chargers know how to stop charging when six, series, NiMH batteries, a Prius module, is fully charged. This charger also has a temperature probe to detect thermal runaway. Since normal charging generates a little heat and gas, compression boards and clamps keep the module from ballooning. The battery chemistry will convert the gas back to water in a couple of hours.

Now there are different variations of Prius modules, here the NHW11 and NHW20:

The NHW20 module has thicker plastic on the terminal ends improving the ability to seal in the gas pressure. It also has top and bottom cell-to-cell conductors which reduces resistance heating and distributes the remaining heat between the cells. In contrast, the top-of-cell connectors in the NHW11 module concentrates the heat at the top and near the terminals. The NHW20 silvery material is non-conductive but probably helps in heat dissipation. I understand the ZVW30 modules further reduced the cell-to-cell resistance and may have other improvements.

HOW THEY FAIL

The primary failure mechanism is the electrolyte dries out, the gas normally generated is H{2} and O{2} from the water. The gas is normally kept in by "O" ring seals around the terminals:

Here you see that black smear around the terminal where the "O" ring gasket melted. So the H{2} and O{2} gas leaked out until the electrolyte concentrated the current in a smaller area of the plastic mesh and melted a hole that shorted the cell. BTW, the H{2} and O{2} that leak out takes a little electrolyte out that creates a weak short, a current to the case. This typically triggers a P3009, ground fault code.

Testing has verified that adding water can fully restore module Ahr capacity:

But two problems remain:

1. sealing the hole used to add water (plastic welding because nothing else handles the heat and pressure)
2. repairing the melted "O" ring (no idea here!)

There is no known, practical way to rebuild individual models but it is a puzzle I continue to think about. My latest thought is to take two working modules; drill out the over-pressure vent; add water; charge-discharge to recover capacity; pair two such modules in serial configuration, and; connect over-pressure vent with a vinyl tube securely clamped. It does not cure the "O" ring but the vinyl tube serves as pressure relief buffer with additional head-space to reduce stress on the "O" ring. But this is extremely experimental.

REBUILDING PRIUS PACK

All modules need to be close to identical Ahr and equal state of charge at ~60%. Equal Ahr capacity is needed so at the charge and discharge limits, the modules won't fail. Over charged, the module generates too much heat and pressure causes leaking out the "O" ring. At discharge, there is a risk of running a voltage so low the cells are reverse charged which also kills them.

In normal operation, the Prius seeks a 60% charge level +/- 20%. So as a pack, it will charge up to 80% and discharge down to 40%. So it is important that all of the modules be equally charged to as close to 60% as possible. This is called "balanced charge." Since it is nearly impossible to find salvage modules with the same Ahr capacity, a "balance" charged is critical. But equal charge on the high-side is much more important because 'heat is the enemy' and we don't want to blow-out more modules.

For the home rebuilder, parallel charging up to a voltage in the 7.8-8.0 range ensures all of the modules are at an equal state of charge. Starting at say 7.2-7.4V individually, they are wired together and when they stabilize, charged up at least an additional 0.3V. BTW, the Prius detects a 0.3V offset as another P-code indicating unbalanced module pairs.

The 38 modules are grouped into 19 pairs for the battery controller. So the best approach is to pair the weakest and strongest modules. Place the pairs with weakest modules on each end which are the coolest areas.

TAKING THE BATTERY APPART

Numbered from the control electronics, 1 to 38, carefully inspect the buss bars for corrosion. The electrolyte 'eats' copper and corrodes them badly. Carefully take the buss bars off one side first to prevent any potentially high voltages. Thereafter the highest voltages are ~15 voltages. Remove the other side and measure all module voltages. For example:

There are small, voltage sense wires on the long buss bar and the electrolyte can eat the copper yet leave the insulation. Be sure and test these wires to make sure they are not broken.

Any modules that are 1.2V or lower have a failed cell and should be taken to a battery recycler. The others might find a future, a useful life so save them for a couple of years before taking them to the recycler. Alternatively, honestly state their history, voltage, and offer on Ebay. Note that the modules closest to failed modules are likely heat-stressed and likely to fail next.

GENTLE BATTERY DRIVING

The traction battery normally has a lot of small charge-discharge cycles passing very little energy. But if the battery is consistently discharged, the subsequent charge will "heat pump" the battery to a higher temperature. This increases the pressure and weakens the "O" rings. A little gas escapes and the weakest modules are headed to oblivion. The fix is easy:

• minimize driving where power is drawn from traction battery
• use "B" when descending tall hills, 500 ft or taller

Highway speeds of 65 mph or less lets the engine handle pretty much any condition. With a tail-wind, a little faster. Following a loaded semi-trailer truck works great because their power-to-weight ratio keeps their speed range in a Prius-happy range. Do not tail-gate, just use them as a pacing vehicle and your Prius battery will be happy ... and I find it a calm, almost boring drive ... have good tunes or audio book. In hilly areas, climb following a heavy semi-trailer truck so the engine provides all the energy and it does not draw on the traction battery. Then on the descent, shift into "B" to minimize over charging the traction battery.

SPECIALIZED BATTERY REBUILDERS

These folks have the inventory to match modules and experience and tools to test and rebuild a usable traction battery pack. Individuals can and have rebuilt packs with longer service going to those who paid attention to the details. But rebuilding a traction battery pack is as much fun as rebuilding an automatic transmission ... a lot of time to do it right so midway you wonder if the time is worth while.

In 2009, I upgraded my NHW11 with an NHW20, rebuild pack from Taylor Automotive, now Dorman. I kept the old modules and the weakest one eventually failed. I may use the modules for a rehydrate and re-stack pack for an electric moped. Replacing the 48V lead-acid battery will reduce weight and provide equal or more range. But this extremely experimental. So hopefully this write-up gives a clue.

GOOD LUCK!
Bob Wilson

 

It's been discussed several times on here; please do a bit of searching.

But....forget it. Even if it would be possible or practical, you don't wire additional battery capacity in SERIES.
That doubles the voltage and things go up in smoke.
Ideas like that are why they STRONGLY try to discourage owners from messing with the HV battery.

And did you try to send the wrong battery back.....I mean REALLY ???

 

I am more worried about the health of your current battery from your first posting. Please take a peek at any posting about the miniVCI and/or Scangauge II (still struggling with the Android/torque.)

The miniVCI will easily show the voltages of the 19-pairs and temperatures at the end of a typical drive. These metrics let us know the status of the traction battery. A Scangauge II can show the same but requires XGAUGE programming (see stickies.)

GOOD LUCK!
Bob Wilson

 

No need for name calling......man.
So please answer the question:
Did you ASK the seller if he would take it back ??
If not, you might be surprised.
No need to be a dumb nice person man.

 

There is a difference between giving a direct and blunt honest answer and being intentionally "rude".

When asking questions in a public forum, you will get ALL KINDS of different styles of communicating answers.
Getting upset because you don't like the wording doesn't do anybody any good.
Chill.