Is there a guide to how to rebuild the battery pack? How many cells does it need?

It takes 2-3 times the physical number of cells (at a minimum) because you need to find balanced cells or else it will be worthless.

 

I am selling my 22 remaining good, tested and re-balanced modules on eBay from my old battery ($30 each plus shipping, I can do a bit better in a direct sale outside of eBay as this avoids their selling fees). In my battery, there were 27 good modules. Only one had a failed cell when my Prius complained of problems. I was a bit lazy and purchased a rebuilt battery from: http://www.reinvolt.com for $1600. My Toyota dealer agreed to install it for $400! (and I got to keep my old battery which I am parting out on eBay).

You should either get modules from a low mileage, recent model, Prius that lived in a cool climate or get ones from an '04 or later that have been rebalanced and verified to have full capacity (6.5 amp-hour) and a slow self-discharge rate. You probably only need to replace a small number of modules to get your Prius working again. The bad one(s) will have a noticeably lower voltage than the rest.

The re-balancing process is to cycle each module through a careful discharge/slight overcharge three times. The computer controlled units to do this cost about $50 each and can re-balance a module in about 36 hours. This balances the charge on the six NiMh cells in the module as well as determining the module capacity.

As Toaster said above, the 28 modules that you use need to be matched as well. The minimum is to slowly discharge each of them to the same voltage (use either a 10 ohm, 10watt resistor or an appropriate incandescent bulb - pull less than an amp at 7-8 volts) before reconnecting the bus bars. Of course it would be best to also re-balance each of your existing good modules as well to maximize how long your rebuilt battery will last before needing to repeat this process. Note that whenever you are charging/discharging theses modules, they need to be clamped (as they are in the full assembly) to handle the internal pressures that build up in the module. It is also wise to provide plenty of air flow to avoid over-heating the modules.

If you choose to do the job yourself please be careful whenever the bus bars are in place. Even with the safety disconnect relays, there are voltages in this battery that can kill you.

JeffD

 

Re-Involt is one company that will refurb your battery. If you haven't found them:

Remanufactured Hybrid Vehicle Battery Packs

Just my impression from that site: bringing a failing battery back to health is a tricky balancing process. And unless you really know what you're doing: leaving it to a pro, at a set price, is the prudent course.

Have a look, they have some interesting videos on battery restoration, and some other Prius info, like how to deal with unexpected acceleration, for example.

 

There are two "balancing" issues.

1. Each module has 6 cells in series and you want them to all be charged to the same level. This is what my little re-balancer does along with measuring the overall module capacity in amp-hours it took to do each discharge.
   
   After the charging the module voltage is high and then quickly drops overnight to under 8 volts. A good module will then exhibit a very slow self discharge rate of under 0.1 volt per month.
   
   It is the imbalance of the cells in a module that will eventually cause its demise. the weakest cell will slowly deviate from its siblings (those in the same module) and when your battery is asked to discharge to 40%, that weaker cell runs down to zero and gets reversed which is sudden death for the cell. You then have a 6 volt module instead of a 7.2 volt module. The Prius battery ECU detects the voltage variance of the pair and complains bitterly.
2. To keep the battery ECU happy all of the module pairs need to stay equal in voltage (within 0.1 volt) as the battery charges and discharges. This is the module "balance" that was discussed by Toaster in an earlier post. Starting the modules at the same voltage helps, but better is if all of the modules measure at equal capacities as well which can be done if you have a large set of modules, re-balance/measure all of them, and pick those with similar capacities.
   
   Just starting out at equal voltages with a reasonable set of modules will get your Prius running and you won't have to repeat the process for a while.

The full module balancing is what a professional outfit like ReInVolt does. To be to be time efficient you do what good friend Seilerts (Nevada) did, he bought 14 of the re-balancing units so that he can refurbish a battery in 3 days (He also sells refurbished batteries).

I only have one Supermate DC6 charger/re-balancer and a 12 volt, 5 amp power brick to supply the required 12volts to the DC6. I bought the DC6 from a hobby supplier (Dynam Supermate DC6 DC Multi Function Balance Charger/Discharger 1-6 cell Lilo/LiPo/LiFe, 1 to 15 cells NiCd NiMH) on sale for $25 (they are generally available for $40) and the power brick for $10 on eBay ( Power Adapter 12 Volt 5 Amp 12V 5A Supply LCD F1703 | eBay). It is convenient to run the balancing units from a UPS as a power failure causes a loss of data. You do need to do some homework to learn how to set the re-balancing parameters of the DC6 to do a safe and effective job.

JeffD

 

As someone with a computer science degree (but NOT EE) and puts together his own PCs, even I would likely not want to attempt mucking w/the pack myself. I have no experience in working w/high voltages. If you don't, I'd suggest you don't either.

 

Here's a link to discussion about rebuilding a Gen1 battery: http://priuschat.com/forums/generation-1-prius-discussion/84114-prius-battery-rebuild.html

 

That's a really good deal. It should give you several years of faithful service. As far as balancing cost vs. hassle, this is a clear winner. I do think that you could drop in a pair of Jeff's cells and fix the old one, but it would take a little time to do the quick fix that might last a year or two, or a lot of time for the full reconditioning.

 

What parameters need to be set in order to use the DC6 Charger / Discharger?

 

You need to set the max charge to 7500-8500 mah (some debate there), safety timer to 720 minutes if using discharge mode, 6 cell nimh with 5 amp charge, 1 amp discharge, discharge -> charge, 2 cycles minimum (will take 24 hours). Modules must be kept under compression else the -dV/dt peak will not happen and the module will swell/vent. Highly recommend running a fan over both the DC6 and the module being charged.

 

Thanks! I would think the best way to charge the packs under compression would be to take the bus bars off but leave the battery packs installed in the case?

Also, if Nominal Capacity is 6.5 Ah, wouldn't it be safer to set the max charge to 6000 - 6500 mah?

Thanks,

Mylar

 

That's the debate. Due to the charging inefficiency, it takes more than 100% for a full charge. Charging inefficiency increases significantly beyond 75% SoC, which is when the battery begins to heat up. I have seen sources suggest that 150% (9.75 Ah) is required to make the module fully charged and internally balanced. I have seen them take 9 Ah, and terminate charging by reaching the charge limit rather than -dV/dt. I do not believe there is a need to set the charge limit any higher than 8500 mah, however.

Leaving the modules installed in the case is an excellent practice.

 

Read your posts with interest and thanks, will be trying to build a usable pack from three less than perfect packs--will be using a thunder t6 multi [4 x dc6 ] when it arrives and thinking about the best parameters to set--to cycle test to balance ,est capacity and charge equally. My first thoughts are to set the cut off v drop high to ellimintate it, set total charge to 125-150% and set the safety timer to 109 min as the manual suggests. 720 min seems a little high-is the limit for each charge cycle or total run time? will use three d-c cycles,at 3A ,about C/2 as I do not think these chargers can deliver near 5A. I think a goal of equal state of charge from module to module is the key,and only a min of maybe 60% soc to start the car is needed. Your thoughts, I will keep up with my progress.

 

The Supermate DC6 discharges through a 5W power resistor, so the discharge current is about 700 mA. Looks like yours T6 is the same. So you'll need to set the timer high to get a full discharge. The way I read the specs for your T6, it will do 50W of charge power. They give 11V, 4.5A as an example. If there is no current cutoff, you could see current as high as 6A-8A. But there may be a hard limit of 5A like the DC6.

Your mission now will be to find a 250W 12V (or 15V) DC power supply to power the T6, for the case when you have 4 modules charging at once. A battery charger + 12V battery (i.e. stuff already at hand) might be able to do it. A wall wart or laptop supply will not.

 

Yes,thanks,I will be using a pc ps of 30A to power. Are you thinking a stand alone discharge to below 1v per cell, then to c-d cycle? I think the safety timer is for the charge cycle only, if I read right. Also,think you can discharge to any v without a time limit. The calc in manuel would be 6500/4.5/11.9=120 or 2 hrs. Guesss I will need to do a little experimenting . Open to all ideas for a plan,both tested and in theory.

 

I can't give away all my secrets, but you are on the right track. Good luck.

 

hi JeffD,
do you have any prius battery cells remaining? I believe 1 of my cells went bad giving me error codes p0a80 and p3017. Thanks, kevin.