Battery Discussion Please Help

Excellent post!

Good plan.

Sounds about right. Anything over 8 V. seems to approach overcharge and that is bad.

Given the 60A discharge, no. Weak but not bad. It takes a 1.2 V. drop on a module for it to be bad. If you could, numbering from the control electronics, which modules were low?

Here is my battery study: Prius Battery Photos

You need to check a datasheet on NiMH batteries. They are more of constant current battery versus a voltage device like lead-acid. I believe your charge limit to 8 VDC is 'OK' but I would want to make sure there is a temperature monitor. If it ever goes into overcharge that would be bad.

The ECU monitors the voltage pairs, 19 voltage sets.

I bought a spare NHW11 traction battery but am leaning towards rebuilding it using NHW20 modules. They have lower internal resistance and much better construction. BTW, I've seen two, independent reports that the 'sealant' gook and corrosion on the buss bars can lead to some performance problems. I'm not in that camp but it seems reasonable.

I suspect top-off the traction battery, let it rest, and put it back in and you'll be OK.

Bob Wilson

 

I went through this same thing a few weeks ago. I wasted nearly a week playing with the darned battery. I recharged all of the cells but I found mine were so weak that 3 of them would revert to only 1.5 volts and .75 volts a few hours after charging. I tried re-installing the battery and the engine would turn, but not fast enough for the car to actually start. I spent a lot of time cleaning up the bus-bars too, only to eventually decide to buy a new battery pack and it came with new bus-bars.

Anyway, I believe after re-charging and balancing your pack it sounds like you could probably get the car to start, but I'm not convinced it would last very long. Even if you replaced the failed modules, you'd probably still be back where you are now in a few months so I'd go ahead and look into buying a new battery.

 

A few questions and comments:

- What did your wife do to the car, to cause the traction battery to die? Was this an out-of-gas situation or something more interesting than that?

- I am wondering how you could put a 60A load on the battery for two hours? That implies 120Ah capacity, but the battery modules are rated at 6.5Ah. Further, a 60A load on a nominal 273V battery implies 16KW of power being dissipated, which is hard to believe you could achieve without burning down the house.

- Regarding your voltage measurements, the critical question is what the measurements are while the battery is under load. I would say that a difference of 0.5V between high and low might be enough for the traction battery ECU to log a fault code.

- You cannot buy new G2 modules as they are not for sale to the public, but you can buy salvage G2 battery assemblies, which I would recommend. 2008 would be a good year for a salvage battery.

 

I agree with all above especially Patricks statement "a 60A load on a nominal 273V battery implies 16KW of power being dissipated". I would think a 5 or 10A load for short periods is in order, not for long periods. The strain and heating on the cells will be too much. I own an 03(G1) and an 06(G2) prius, and when the 03's battery goes I will probably get a reconditioned one for under $1500 then install a "plug in" kit which will greatly increase the life of the traction battery, not to mention it will be in EV mode for half or more of the day. The 03 my wife uses now only for around town driving, and the 06 is that and highway. Thats not to say the 03 can't go on the highway! it surely can. But the G2 battery is much better than the G1 as far as longevity of charge and retention overnight. These batteries were not meant to be very powerful, but rather to only "assist" the ICE on accelerations and to run the 12V charging system. In the 03 it seems to pull out of the battery only on accels or up hills, for short times then the system is charging it right back. The sure sign of a dying traction battery is it's inability to hold a charge overnight. Then the end is near. Look for the plug in kits (various co's) those may work very well for a much longer time, but they are also much more powerful! Pay attention to wiring and gauges used.. Oh and I would not replace any cells with a different age or quality of cells. That is why they suggest getting a scrapped G1 or G2 battery and rebuilding with similar in aged cells. This way the chemistry of the cells will be similar and no cell will be overcharged verses the others.

 

BTW, my 03 also needed the throttle body and MAS cleaned recently, it had the DTC's and would not run. As far as the wife driving it until traction battery was dead, that (I'm sorry to say) is potentially a very expensive mistake. A friend of mine had an 01 recently and ran out of gas about ten miles away from the nearest gas station. He tried to "make it" to the station anyway. That killed his traction battery! If the ICE does not run for any reason, do not run in ev mode for any longer than to pull the car over to a safe spot to park. Then fix the problem or have it towed. This will save buku bucks.

 

Thanks for providing the clarification. If you had 19 module pairs in parallel, then you would end up with 123.5 Ah of capacity (assuming the modules were in new condition, which would not be the case with your 7-year old battery.)

If you were charging and discharging at the rate of 60A, then on average each module pair would be charging/discharging ~3.2A. That is OK on average. In reality some modules would be carrying a greater load than others, depending upon the relative internal resistance of the modules.

Its good that you were monitoring the module temps. I suppose you know that you must keep the modules under physical compression while they are being charged/discharged, as otherwise the plastic cases may burst?

7.2V is the nominal voltage for a module. I assume that you would like to measure the module voltages on the G2 battery assembly before you buy it? In that case I would say that you should expect the voltages on the modules to be within a few tenths of a volt from the others. If you find a module much lower, then it is bad.

Assuming that you plan to buy two G2 battery assemblies, then you will end up with 56 modules - so you should have enough good modules for the G1 assembly that requires 38 modules.

Although other posters have successfully done this, no one has posted photos - so please take and post photos so that the group can see the results of your project. Thanks!

 

The paralleling NiMH is not a good idea.
Lead acid and NiMH are completely different animal.
You should test the NiMH only in series.

Prius design is 40% SOC (60% DOD) is the lowest and 80% SOC is the highest.

Ken@Japan

 

Realizing that it is not optimal to charge the modules in parallel - but since you're already set up to do this, I'd suggest that you again charge the modules to 8V, using a low charging current, like 20A total, which would be ~1A across each module pair. Keep an eye on module temperatures and terminate the charging if you should find one module beginning to overheat.

The reason for using a low charging current is to reduce the heating loss due to internal resistance which increases according to the square of the current flow: I^2 x R = P.

Then clean the busbars of corrosion, make sure the sense wires are intact, and reinstall the battery. See if it works or not. If it works, then you won't need to embark on the battery rebuild project.

 

For bench charging, it solves a problem of bringing all modules to the same voltage with a lower voltage charger. You'd still need a good, high current regulator but something as simple as an ordinary but well regulated 12 VDC battery charger would work.

Bob Wilson

 

Sounds like a plan.

One of the best things about an NHW11 is the price is low enough one can get over the "newness" of dealing with a hybrid. It remains a useful training and experimenter's car.

Bob Wilson

 

I think the person who swapped his gen1 modules for the gen2 ones had some minor fit problems like the case had to be "adjusted" or cut to fit the batteries.

Also, I believe the nuts that hold them to the lower case did not align exactly. Nothing a good tinkerer couldn't get around.

If you do please take some pics for us!

Anyone have the link handy?

 

Not sure on that link but here's a link to the place on eBay that sells reconditioned battery packs, and I think these will already fit into an 01-03 classic. They also have reconditioned packs for 04-09's.
01-03 Toyota Prius Upgraded HV Hybrid Battery Pack : eBay Motors (item 130359969815 end time Jan-27-10 17:11:33 PST)

BTW, I had the same problem with the 03 recently, the lights came on and hybrid vehicle warning sign showed on the screen and you couldn't drive it. Would start for maybe 10 seconds but then just shut down. I thought it was the traction battery until reading the dtc it was something about the ice not starting in time. It needed the throttle body and MAS cleaned. Overfilling the ice oil level can cause this as well. You were also showing some traction battery codes? Because I was not. Perhaps because the wife drove it in ev mode and ran the voltage down until the dtc's, and the system disabled the car from driving. But after the ice is able to start (throttle body cleaning) it charges right back up. I think the key here is you got to the repair before the point of no return for the traction battery.
Ours runs perfect again now, just like yours but you know I will probably get one of these above reconditioned batteries when the OEM one really finally fails. It's too nice a car to junk. Good luck, Good job, and please post some pics. Thanks

 

"I trailered it to a friends home who has a great shop. I charged both batteries. Cleaned the throttle body. I had to replace the 12battery. Every thing it back to normal. I have learned a lot from all the help here at this web forum." Yup it really helps to have a good place to work on it, especially in winter. I am glad you found some answers here, on this great site. And yup a low 12V battery can cause all kinds of ghosts!
I'm trying to be ready for that next failure on our 03', which is inevitable. On the hv battery, if everything is correct with the ice it should charge it back normally with the system in about 1.0 hours of driving (best way). Do some brisk accels and then go down a fews hills to cycle it well.
BTW The 06 has yet to have a problem..knock on wood.
Good luck and welcome.