03 Prius

We're currently using 5 of those IMAX chargers that I share with a friend... They're awesome chargers and the more of them you have the faster things go, but the resistance design for automatic discharging, as well as measuring that discharge kinda sucks, varies between IMAX chargers/not to be trusted.

Instead use one or two headlamp bulbs from your car with a cheap multi-meter and a kitchen timer. This set up will give you:

1) exact time it takes to discharge module down to the threshold of your latest discharging cycle,

2) the dimming of the light towards the end of the discharge will alert you to the exact moment when the threat of discharging too far is about to occur,

3) allows you to monitor multi-meter for sudden voltage drops during discharge, which might indicate where a bad cell is before it goes totally bad,

4) a much less error prone testing process/more clear sense of which modules are stronger, which are weaker...

 

Yes, you understand and have accomplished the basic process correct.

What you're missing is that you want to measure the voltage drop on the multi-meter, not just the light bulb.

What you did with your module would be the third stage of discharge and recharge. The second stage would be dropping it down to 6v and recharge. The first stage would be dropping it down to 6.5v and recharge.

Each module gets discharged and recharged three times. The concept is that you're gradually discharging and then recharging then discharging even deeper and recharging then discharging at the very deepest and recharging.

The folks at Prolong say you can discharge a module as low as 0.6v, but most think that dangerously low because if you discharge to 0.0v you've ruined the module.

 

They can't possibly mean that ... that would be a daringly low discharge voltage for a single cell, and there are six of those in a module. That would mean 3.6 volts for the module. I've seen 1 volt or 0.9 volts suggested as reasonable discharge limits for a cell, which would be 6 or 5.4 volts for a module.

-Chap

 

I don't use the IMAX for discharging, it's not reliable... So I don't know what you mean by setting the Imax to .1 volt for an hour but I already clearly said Prolong says absolut limit of discharge for a fully balanced module is .6 volts, because their are 6 cells in each module. Hope you didn't just kill a module? Did you recharge it before you started discharging? I sure hope so!

 

Yes, the electrical engineers at Prolong recommend doing manually, or via their automated discharge system a third level discharge to 17 volts on the whole pack, which divided by the 168 cells in pack calculates out to .1 volt per cell... Many of folks on Prius chat think that number is too low in terms of risk and I tend to agree. But as far as Prolong is concerned, they're the ones who handle the liability on their product, not us, so it must work pretty well... Having a balanced and full charged pack is key before you push that level of discharge though!

 

If you have known 3 bad cells, why don't you just replace then??

 

Yea... "Fixing" a confirmed bad module with charging and discharging is probably not going to work, but the process of "confirming" that the module is bad could include this process. I'm not sure what OP means by "bad" module in this instance, but figure they'll figure it out if they keep at it long enough and didn't want to offer up too much info for the sake of simplicity.

 

I've had the experience of putting in a crappy ebay module that didn't make it 10 miles before it failed... I've had the experience with buying really top notch high quality modules that threw error codes because the remaining pack modules weren't as good as them. The former is something you can't do much about other than get a refund... The latter, sometimes battery pack reconditioning can get the old pack's modules to be restored to match up close enough to newer better ones. But in general I'll do all I can to avoid breaking up a pack and adding a different module.

 

6.5v? Bad.
5.8v? Trash.

 

If you need to do it kinda on the cheap, buy more old modules and keep at it. It's not going to be straightforward, and you will probably go through multiples of what you need to find compatible modules. If you want to rebuild to a better battery, check every C/L within a day's drive and try to find a later Gen2 or a Gen3 battery to mine for newer modules and then buy some individual modules to make up the difference. They aren't mix or match, you'd have to replace all of the old ones with new generation ones Something out of a totaled out Prius is what you're looking for.

Replacing modules in your old battery is probably a losing proposition. As you know, they've got to match up pretty closely, and as they're all kinda old, you'll replace a bad one and another will pop up.

 

Did you recharge the modules after the load test?

I thought you were conditioning, not load testing... Load testing needs to be done once you've recharged, not after you discharged.

 

That's true with Honda, but Prius is much more flexible with replacing modules, which is why there's so many hacks on Craigslist making good money selling sloppily "rebuilt" packs that last for a while. And if you're super thorough and do everything right a module replacement can last a year or longer.