while i have the HV battery out of my gen1

Hi Scott,

I had a Battery ECU failure in my Gen1. While waiting for the ECU, I cleaned and sealed the battery terminals and rearrange them such that the highest voltage module pair with the lowest voltage module and the next highest pair with the next lowest. Since the Battery ECU monitors in blocks, i.e. 2 modules, it would see a more balanced blocks. My pack also had higher voltages at both ends than the middle. So I arranged the higher voltages blocks in the middle and the lower voltages at both ends. I had no problem after more than a year until I had to trade in for a Prius C since my COE is expiring.

Vincent

 

It's fine to top off the batteries when it is not hooked up to the Prius.

The Prius will sort of do some balancing itself, but it will not be able to repair a failing pack.

You can do a better job yourself if you spend a lot of time on it and are thorough.
You've got a lot of blocks to go through. Even if it took only a couple of days per block, it could take you a month to do it right.

 

Have you marked each module with their number? You're going to need this unless you record the serial numbers.

If you take the wise advice to physically re-order the modules, wire the remaining modules in parallel . . . there will be sparks and use a fairly heavy gauge wire, 18 gauge. Even so, it will get hot initially as the charges flow from the higher modules to the lower modules. Let them sit of an hour or so.

Make sure the modules are clamped and charge to no more than 8V. Although these modules can go higher in normal operation, 8V is a good upper limit. Measure the voltage before charging with all modules in parallel and rested (i.e., stable.) Then charge and get at least 0.5-1.0 V increase. With 37 modules, you can use a heavier current. Then put a load, say a headlight or 12V bulb on it and bring them down to ~7.5-7.8V and leave them in parallel.

The goal is to raise all module voltage to the same level and then trim discharge them down to the same level.

When the three modules come in, same protocol. I call this 'hillbilly balancing.'

Bob Wilson

 

If you are going to restack the pack, what vincent1449p suggested, you have little choice. Just take a photo of the original end module orientation or put a "+" mark and "-" mark on where the battery ends (don't want to reverse voltage when done.) Don't worry about putting the base screws back in until you're ready to reassemble.

Now I would follow vincent1449p's experience first as I have not done a 'hill billy' charge balance. I did wire six modules in parallel to sustain charge in the past but I didn't worry about the inrush.

For parallel charge/discharge, having all like terminals on opposite sides will reduce the risk of an accidental short (HOLY CRAP ARC!!!). Be sure and put the compression rods back on before starting the charge cycle.

Wire up one side and then start the second side with your voltmeter monitoring the difference between the parallel connected modules and the next module. As you add each module, you're likely to see an initial arc with each module added . . . the inrush charge. To minimize the inrush, get a power resistor from Radio Shack, 1-0.1 ohm or so and 5W, and clip on first. The resistor will handle the inrush heat load. Then wire the module into the parallel bank.

As for amps, after letting them settle, you can up the amps as they will somewhat balance out.

Remember, hill billy balancing.

Bob Wilson

 

Don't these chargers have an option to detect the slight negative voltage slope at the top of the charge and know when they're done that way?

-Chap

 

The way I top up a Prius pack is possible without even removing it from the car, but has high voltage so only do it if you know what you are doing!
I use a high voltage power supply (up to 380V, 0.4A or somewhere around there, it is not precise) and I measure the voltage of the pack. If the pack is lower than 250V then I start with 3 standard lightbulbs (no more than 60W each and all equal wattage) in series between supply and pack. Once the pack is above 250V, I use only a single lightbulb and this will dim while the pack is increasing in voltage to above 330V, then it will stop rising and slowly warm up a little while the voltage drops slightly. That is when the NiMH cells are full. You can keep charging at this low rate for some time to make sure that all cells show the same voltage (you will see all modules creep to the same ~8.7V over time). If you start with a completely depleted pack, it might take 10 hours of charging, since we are using a relatively low and safe current of less than 1/2 Amp. If the pack is already pretty full or it is near worn out (low capacity) then the voltage will reach the reversal point much sooner. If you want to lower the current even more, use lower wattage bulb(s). One great source of rugged 20W bulbs are broken Microwaves that you can pick up for free (on Craigslist). My 380V power supply is a 130W multi-voltage (100-240V) switching supply that I had lying around and which has a PFC front-end, generating that 380V (non-isolated!) for the isolated DC/DC converter that generates the output voltage of that 130W supply. In other words - zero-cost HV pack charger - if you know what you are doing. Volt meter to check voltage and polarity *before* connecting and also powering up the supply *before* connecting the pack are required to avoid blowing up stuff. Success.

 

Stop.
I would not recommend balance charging these packs at such a high rate! (3.5 amps?).
Especially as you near higher SOC it can be dangerous and damaging to these cells.

Notice that EV_cor said his high voltage charger does 0.4amps NOT 4.0amps.
Huge difference.

 

If you have all the modules connected in parallel each module has a capacity of 6.5 AH (discharged to fully charged) so you have a total capacity of 6.5 AH x 38 = 247 AH.
If you are charging at 3.5 amps this will take "given no losses" 78.5 hours to fully charge.
Each module "assuming they take an even share of the current" will be charged at 0.0921 amps (or 92 ma).
To charge at a reasonable level of 0.5 amp per module you need to be charging at 18 to 20 amps. Even at this rate of charge, from discharged to fully charged will take about 14 hours allowing for some losses.
Connecting all the modules in parallel give you one very high capacity 247 AH 7.2 volt battery.

John (Britprius)

 

Double post.

John (Britprius)

 

I believe he is charging the modules in parallel not series so his charge rate is safe but will take forever to charge.

John (Britprius)