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#1 (permalink) Old 03-02-2010, 09:34 PM
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Default Battery Cell Test and Replacement

Hi,
I have reciently purchased an '01 Prius with problems. I'm a electrician in an ethanol plant and we consider ourselves green plus I have been curious about the hybrids so what better way to be green but to have a hybrid and save on gas to as I commute 100 miles a day. I purchased the Prius for a reasonable price as it has several warning lights on but I want to learn how to make the repairs and I have found this to be a great site for information. I've been reading throught the posts and have learn alot given I didn't have a clue. I have a friend with a shop to scan it for me although I haven't got it there yet to get the codes. First I'm doing preliminary checks and tests. I've pulled the battery and tested the cells. Rest assured I have all of the equipment and training not to electricute myself. Can anyone tell me how much the cells can very before the battery computer senses the imbalance and sets a code? I have one cell reading 1.4 volts lower then the rest. I pulled the battery because it would go from full charge to 20% in just a few seconds. Then the motor would speed up to charge it. I haven't driven it enough to get a good handle of the systems but on the way hom (50 miles) I had to stop, shut it off and reboot it 4 times to get home. The check engine light was on, the main screen light and the triangle then the break light would come on the engine would flair and I would lose foward drive. After reboot it would drive good for awhile. Any ideas? All input would be appreciated while I rassel this out.

Thanks
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#2 (permalink) Old 03-03-2010, 12:04 PM
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Default Re: Battery Cell Test and Replacement

We are talking about the 273V main traction battery, right? I'd start by checking one easy thing: there was a recall a few years back regarding corrosion on the battery terminals. That could cause fluctuations in state of charge. How are you measuring "full charge to 20%"?

There is a lot of buzz these days about places that claim to service or rebuild a battery pack--just Google "prius battery rebuild". I'm not sure how reputable these places are, but I have heard intelligent things from a Prius owner named Bob Wilson, so you might want to get his advice first. If it were my Prius facing a significant battery problem, I would first try to buy a salvaged battery pack from a totalled Prius, and just replace the whole thing. (You could sell the bad one to Bob, who will find the usable cells and put them into someone else's car.)

If you're serious about learning how to do this yourself, I recommend you post this on the "Prius_Technical_Stuff" Yahoo group, because most of the people who have been tinkering with the NHW11 "Gen 1" Prius can be found over there, not here.
For example: http://autos.groups.yahoo.com/group/Pri ... sage/28945 (I think you must be logged in to the group to view messages.)

Douglas (2002 Silver, Wisconsin)
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#3 (permalink) Old 03-03-2010, 02:11 PM
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Default Re: Battery Cell Test and Replacement

It would really help if you could get the fail codes. The error screens that you describe can be caused by several things; and without the codes, we are just shooting in the dark.
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#4 (permalink) Old 03-03-2010, 10:22 PM
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Default Re: Battery Cell Test and Replacement

Thanks for the response. I have seen Bob wilson's posts on here and will try to cautch him. Also, I'm off the check yahoo groups.
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#5 (permalink) Old 03-08-2010, 03:03 PM
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Default Re: Battery Cell Test and Replacement

Update,
I have been doing research on this and follwing everyones link suggestions and it has been very helpful. I found that at full charge the cell will be approximately 14% more than rated voltage which mine at 8.1 to 8.2v and rated for 7.2v means there at full charge. The cell in question was at 6.9v so I'm sure it was causing problems. I'm in the process of replaceing it with a used one and will post how that turns out. My nest question is what should I be checking other than connections while I'm there? I read somewhere about check the acid level? They were talking about drilling a hole, topping off the acid and sealing the hole back. I have the Gen. 1 model.
Thanks
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#6 (permalink) Old 03-09-2010, 02:39 PM
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Default Re: Battery Cell Test and Replacement

I think I may be confused...

Are you checking individual cells in the high voltage battery pack that sits approximately over the rear axle and weighs about 120-140 pounds? Or, are you talking about the 12v battery that is under a cover at the far left of the trunk, that looks like a motorcycle battery?

I have never seen any posts about drilling a hole in either of the batteries and filling them with acid, which sounds extremely dangerous. Also, the cells in the high voltage battery pack are NiMH and look kind of like D-cell flashlight batteries (the early ones were cylindrical, and the later ones were octagonal, I think).

I'm not sure the NiMH batteries even use regular battery acid. I suspect that the electrolyte is some kind of paste, although I know absolutely nothing about the actual internal construction. In any case, I think you would probably swap these out. I really don't think one should open these for any reason.

Perhaps, you could be a little more specific on exactly what you are doing...
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#7 (permalink) Old 03-10-2010, 01:05 PM
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Default Re: Battery Cell Test and Replacement

Phoenix,
Dave1956 is clearly talking about the 273V main traction battery, because he says the cell voltages are reading around 7V or 8V. Each cell of a 12V battery is only about 2V.
For details about the procedure he's using to recondition individual cells, you should log onto the Prius_Technical_Stuff Yahoo group, where they've been really delving into the guts of the main traction battery. The phrase "topping off the acid" was probably a little misleading; I believe they are actually adding distilled water to cells that appear to have dried out.

Dave1956,
I don't think you'll get much help on this board. Most of the people involved with disassembling the main traction battery read/post only on Prius_Technical_Stuff. I lurk there occasionally, because they're doing some really interesting stuff, but I don't have spare time to do it myself, so I can't really contribute.

Douglas (2002 Silver, Wisconsin)
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#8 (permalink) Old 03-11-2010, 09:54 AM
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Default Re: Battery Cell Test and Replacement

That's right Doug and thanks for clarifying what it was I read. I haven't had time to find and review it yet so now I know where it was at.
Thanks
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#9 (permalink) Old 03-31-2010, 10:11 AM
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Default Battery Cell Test and Replacement

Yep, thats the idea.
Should handle 16 of those fine. Not sure about how long balancing will take, and we are working on a higher current version for large cells.
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#10 (permalink) Old 04-02-2010, 04:52 AM
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Default Re: Battery Cell Test and Replacement

Update.
I decided not to worry about the water in the cells at this time and proceded with the cell replacement. It had been 2 wks since I had been on the project so I retested the cell voltage. I was now showing lower voltage across the cells with 4 more lower than the others and 2 that seemed lower than normal. I disassembled the pack and removed them, used a 12v smart charger to bring the to 8.2v or so while I watched closely, then load tested them with my small 12v load tester. The 2 lowest seem to charge faster and the load would take them down to 6v or so in a hurry. The other 2 took longer to charge and to 8,2 and would bounce back to 7.2v after being loaded for 10 seconds or so. I concluded the first 2 must be weak and purchased replacements for them also and a spare. I have the pack back in the car but still setting codes. I have made arrangement to borrow a scan tool for the weekend to pull the codes. I will post my findings when I can. I should mention that now, after clearing the codes, I can drive about 16 miles and everything seems to work perfect then the codes come back and I have to stop and reboot. I'm thinking something is getting warm. We'll see.
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