Gen II Prius Individual Battery Module Replacement

Ok so mostly top balancing I guess. So would it be effective to use an external resistor bank on the output port of a dual channel iCharger to greatly increase the discharge rate (could go up to 40A while still having the charger keep track the total mA discharged)? Seems like it would greatly speed up the cycling to be able to discharge quickly down to 6V.

 

I have no reason to, so haven't. I think the whole busbar thing is overrated. It may be an issue if you disassemble the battery, but if have never messed with it I don't see how it is ever can be an issue.

The only time you come near the 'full enchilada' is when you install the harness and as long as you follow the correct procedure and do the appropriate checks, it is perfectly safe. After that, there is no more proximity to high voltage than plugging in a 240 VAC appliance which we (here) do every day. In the US and Canada, you're exposed to 110 VAC which I presume you think nothing of doing.

I started off doing it once every 18 months and now probably do a session every 12 months.

Nope, top and bottom balance for the best effect. You can do a top-only balance as an interim measure but the best bang for your buck is to bottom balance too. Bottom balancing is achieved by the discharges to the low voltage cutoff points.

 

First of all, I confirm the wise and excellent advice and explanations given by all the previous commenters to your questions. The swarm intelligence of PriusChat is awesome.

A few of the key points I would emphasize are:

Installing a grid charging harness is normally less dangerous than charging modules individually. To charge modules individually, you need to remove the main battery cover. Even with the service plug removed, there is then still the danger of making contact with one half of the battery circuit, around 100 V.

When installing a grid charger harness, the main battery cover is normally left in place, and only the small electronics and connections cover needs to be removed. With the service plug removed, the highest voltage that you could make contact with is about 13V from the 12V auxiliary battery.


Where I live in Germany, the climate is similar to Vancouver Island; maybe just slightly harsher. I have a fifteen year old 2007 Prius with over 370k miles, still with the original HV battery. I began using a Prolong grid charger about once a year when it was about ten years old. I monitor battery block voltages regularly with an OBDLink, and the battery has never shown any signs of weakness. I do the grid charging just as preventative maintenance.


At first, I did only top balancing with the grid charger, but the last couple years, I have added what I call a "semi-deep discharge" cycle to my grid charging routine: After the normal top balancing, I start up the car and immediately shift to "N", so that the gasoline engine cannot charge the HV battery. While monitoring the battery block voltages, I let the HV battery drain until a low battery alarm comes, and let it continue to discharge until it automatically shuts everything down, which appears to be somewhere around 15% to 20% state of charge as indicated by the OBD monitoring device.

If during the "semi-deep" discharge, I would have seen differences between battery block voltages of more than 0.3V, then I would have stopped the discharge and begun recharging.

After the "semi-deep" discharge, I do another normal top balancing charge.

 

Thanks for sharing your experiences. I'm starting to lean towards grid charging. I've got an OBD II module on the way so I'm going to load test in Dr. Prius and see what that shows first.

Hearing about getting 16,17 years of life while grid charging is certainly a positive review. Maybe the temperate climate is playing a role as well. My Prius hasn't lived it's whole life on Vancouver Island but it's never really seen any really hot weather.

That's interesting about your deep discharge method. Doesn't the Prolong system have a discharger as well? I was wondering the other day, what happens when the car is in maintenance mode and the engine runs constantly? Where does the charging current go if the battery gets full?

 

I feel like the issue with the Prolong charger is that it's just priced a bit too high. The market for these things is probably people who start to worry about their Prius battery at say the 10 year mark. However the price they want is roughly 1/3 the price of a new OEM battery. My battery is probably only worth as much as a Prolong charger at this point. So for a lot of people the math just doesn't make sense.

If they just dropped the price by 50% to ~$300 USD I think they would sell way more of these things. Either that or maybe somehow develop the channels to sell these to people when they buy a new Hybrid. At that point it would be worth $600 to preserve the value of a $20k + vehicle.

 

The car manages the HV battery the same in maintenance mode as it does when it runs normally. You will note that in order to run the battery down Fred put the car in N. Provided the car is in P or D, the car will charge the battery as required.

In maintenance mode? Nowhere. If the battery should be full, it would shut off the generators and waste the excess energy but the car will never fill the battery, it will keep it 2-3 bars.

The charger itself for the Gen 2 is $350 and the light bulb discharger is only $89. I'm not sure I'd pay for the whizz-bang automated discharger, myself.

There are cheaper options if the HA is too much for you. Maxx Volts or DIY.

 

I came across a patent that has a lot of detailed information as to the ideal charging / discharging process:

Method for regenerating nimh batteries

"This preferred embodiment addresses a Ni-Mh battery typically marketed in car models such as the Toyota Prius. This battery consists of 28 modules...

This first charge is preferably performed at a controlled current between 0.5 Amps and 5 Amps to achieve a correct module charge, since beyond this range the 6.5 amp modules could be charged incorrectly or be damaged..

Once the step of rapid discharge is completed, the process for the regeneration of a Ni-Mh battery passes through a second discharge step, but unlike the former, it is a slow discharge in which the parameters are varied by significantly reducing the discharge current and cut-off voltage..."

EP3086399A1 - Method for regenerating nimh batteries - Google Patents

 

Just because there is a patent doesn't mean that it works.

JeffD
ps: I have 20 US patents.

 

Is there any consensus as to whether it's damaging to discharge a cell below 1.0 V? Some seem to say it's terrible, but the Prolong System advises to discharge down to 0.8, 0.6 and finally 0.5V!. Aren't the properties of NiMH batteries pretty well known at this point? I don't understand why there is so much debate around all of this.

It's like for some reason in the car world science is out the window and every maintenance routine basically just becomes some magical superstition with various tribal supporters and detractors. Engine oil additives/flushes is another practice that seem like basically buying some brew from a shaman.

 

There cannot be a consensus on whether discharging below 1.0V per cell will or won't damage a cell under all conditions and in all cases. It depends on many factors. Depending on the age and condition of the cell, temperature, discharge current, pressure, and also the condition of the other cells in the module or pack, the results can range from significant benefits, to neither benefit nor damage, to total failure.

The Prolong procedure that you mention balances and rebalances the cells with gentle, non-damaging "overcharging" before, between, and after each discharge to help prevent over-discharging of the cells which might become out of balance with the other cells during the process. And the whole pack is uniformly cooled by the charger using the battery fan. Nevertheless, if there is a cell in the pack which is severely degraded, there is a chance that the deep discharge will push it over the edge to failure despite all precautions. But such a cell might have likely failed anyway within a short time.

 

Are all of the NiMH prismatic modules since 2010 or so functionally compatible? Like the ones in a Highlander or Camry NiMH pack just more of the same type of module that's in a Prius?

 

Yes, I believe so.

 

There are some NiMh modules that have 8 cells (9.6v) vs our Prius NiMh modules with 6 cells (7.2v).

JeffD

 

Ah I didn't know this. A bit of digging turns up some Lexus models - nx, GS450H, RX450H, RX400H

For the RX400:

• Battery Chemistry :NiMH
• Overall Dimensions :43" x 25" x 8"
• Battery Pack Voltage :288 V
• Number of Batteries :30

Lexus RX 400h Hybrid Battery 2011-2013 - Best Hybrid Batteries

 

I have a load tester for 6 and 12v lead acid. It just has a heater in it and a dial. Nothing fancy. Do you think I could use that to test the gen 2 Prius modules? They're 7.2 volts each and there's 28 of them.

 

Measure the current it draws at 6v (or read the specs). Load testing one of our modules would be reasonable at 1-10 amps for a short, timed load test where you compare voltage drops between modules under test.

JeffD

 

i dont know if i set up my charger wrong or not but i got this at the end of the cycles. please help
Thank You

 

This is a myth, because every cell in a module receives the same current! Weaker cells will not keep charging. By definition, weaker cells are those with lower capacity. They become fully charged first and over charging them just generates damaging heat in the (already) weak cells, while the higher capacity cells continue to store charge.

 

Where does the excess current go? The continued low level charging current will be dissipated as heat in the fully charged cells and in the "weaker" cells (not yet fully charged) will allow them to catch up. This slight overcharging balancing is not a myth. It works to improve a module's capacity.

JeffD

 

The excess current charges the cells that are not yet fully charged. The most heat is generated in the weaker cells because they have reached their (lower) capacity and they are unable to store any more charge.

Think of the cells as buckets which are all being filled at the same rate (constant current), the smaller buckets (low capacity) are going to fill up before the larger buckets. When the bucket is full, there is nowhere else for the current to go except over the edge (as heat)

This is why the voltage (potential) of weak (low capacity) modules rises faster than strong (higher capacity) modules during charging. During discharging, the voltage of weaker modules will fall faster than stronger modules for the same reason, lower capacity. Every cell follows the same charging profile regardless of capacity.