Gen II Prius Individual Battery Module Replacement

Please what's the black stuff you've got on the table close to the DVM?

 

Looks like an ammeter hooked up to the headlight for a basic resistive discharge circuit.

 

Im in the middle of replacing bad modules in my Gen 2. Ive got five DC6 chargers running the modules through discharge and charge cycles. The DC6 charger is set at it's max of 1.0 amp discharge (but max is actually 0.7amp). The 0.7amp discharge is driving me nuts, its going to take a week just to do 3 discharge and charge cycles. Ive read through the thread and see that most have spent about a week balancing the battery, but there has got to be a faster way to discharge these modules.

 

You get what you pay for. You can buy some awesome electronic loads like a Kikusui for about $2K. I've got a few of those, they work great. Also have some larger load boxes and supplies. We can charge batteries at about 30kW with the 480VAC utility connection and discharge at about 10kW. You too could do this with about a $30K minimum investment.

Or just live with the slow cycling, and put that money towards a whole new Prius...

 

Discharge at 10kW...youre killing me!

I guess I'll let the DC6's whimper along while Im at work.
If I have to do it again, I'll probably end up with a resistor setup something like this to at least be able to discharge around 30 amps....

 

Isn't the discharge current going to b

Isn't the discharge current going to be much on the modules?
Your realtor seems to be 30A. I thought that would be much(maybe 4-5A would do).

 

Thats a good point, I'll have to read up on the maximum discharge rate for the modules.

 

Try a 55W headlight bulb

 

Your Prius will momentarily hit 100 amp charge and discharge currents (130A for 2006+). These modules are quite robust.

JeffD

 

So that's 100 amps / 28 modules = about 3.5 amps per module? I bet 2k1Toaster knows how fast is safe to discharge

 

No, the modules are wired in series, so the current is equal through all of them. 100 Amps means 100 Amps through each and every module.

 

Wow thats impressive! Now I dont feel bad about really wringing the modules out on a discharge down to 6.0 volts.....if I can find a faster way to discharge.

 

I think it was mentioned that 100 amps is instantaneous current, not steady state. I doubt you could pull 100 amps through these cells for a long time. The cells inside a 7.4 volt unit are also wired in series, so they also experience 100 amps of current. Now imagine a AA type of cell having 100 amps going through it. Wouldn't take long to fry. This is why the cells are wired in series to form over 200 volts' worth of potential. That high voltage reduces the current required to develop the same power (in Watts) as with lower voltage and higher current. P = V * I, so if you increase the V (volts) you decrease the I (amps) for a given P (watts), which is the actual measure of ability to do work (turn wheels of a car in our case).

As to your problem of draining the battery, what about investing into a Hybrid Automotive smart discharger? It can do the whole battery at once in a few hours. Not sure if that's helpful in your case.

 

I considered the Hybrid Automotive discharger, but it only discharges at 1.5A-200mA.

 

Yes, but it does the whole battery all at once. Still may be faster than doing a few modules at a time.

 

Thanks, I'll have to look into it a bit more then. Since the whole battery is done at once, I wasn't convinced that the Hybrid Automotive discharger would be able to discharge the individual modules as well as doing them all separately.

 

Keep in mind the modules are also only used at between 40-80% state of charge so as you approach the extremes of SOC you need to be alot more careful not to damage them (as 0% SOC is approached voltage begins to drop off exponentially, with large loads this happens VERY fast).



Hobby RC chargers all basically discharge around 0.7A even though they may be rated at 1A, very normal, they all do that. I would start with one cycle on each to see where you stand on capacity and then do additional cycles if you have some that have fallen behind. Don't do more cycles than you need to and if the modules don't come back into the range of the rest within 3 cycles then replace them. As always, load testing is the most important part so don't forget to do that as well.

 

As VFerdman pointed out, what one cell sees current wise, all cells see because they are in series. The actual battery is a tiny 1.2v cell, and then they are all just chained together. That 1.2v cell can see 100A all day long. 120A is actually very common in heavy Prius acceleration.

If you want a relatively cheap load box, I recommend the B&K 8500. I use this work-horses everywhere. Has great resolution and is good for 300W. Really, 320W, but you shouldn't do more than 300W continuous. I am discharging one of my new modules right now on it pulling 300W out. It's pretty cool because I just set the lower voltage value and the power draw and it just does it. As the voltage drops, the current increases (up to 30A) to maintain the 300W I programmed it to draw. As it gets closer to 12v (my programmed off limit) it backs the current draw down variably.



If you are doing individual original cells, they are half the voltage, so it could do the full 30A no problem. 180W-240W

These are my babies though. Got a few of these Amrel PLA800-120-150E's. They do 800W up to 150A. On an 8v individual battery, that means you could do the 100A draw all day long with one of them. With the 2 of them I can do my modules at 100A. Woohoo!



Here's a 20A load and charge going through this module for many hours.

 

I'm drooling!

 

Keep the photos of equipment coming. Such good stuff!