Prius II HIV battery module change

The vents that allow the battery to dry out can clearly be seen in the picture kindly provided by Usnavystgc They are connected together by the black tubes.

 

By the way Stu the cells are filled with a strong alkali (KOH) not acid. It is basically caustic soda.

 

Do not assume this. Gas will not vent quickly and swelling will def occur if not charged under compression and cooled. If the modules vent, they will also lose fluid. The vents will pass fluid and gas. You don't want them to swell or vent. Venting causes a loss of capacity and corrosion. From what I've read/researched, it takes an extremely high pressure to cause them to vent (that's why they swell).

 

Sorry I could have made it more clear, the voltage quoted is cell voltage not module voltage. So minimum module voltage would be 5.1v.

If the vents do vent the gasses given off are hydrogen and oxygen (water) this is how the cells dry out. Remember in use the battery can be subject to charge and discharge rates in the region of 80 to 100 amps. The venting may not be large amounts but over time non the less drying out does happen.

 

Sounds like you have everything tide up.

The DC6 charger has the same function as the Hitec and detects the so called nee of the charging curve then shuts off the charge lets the battery rest then discharges it lets it rest the recharges and does this for the number of chosen cycles.

Keep everything you do logged numbering each module and marking with the final capacity. As I said before takes time but is worth the effort. Any questions I will answer if I can and I'm sure other people will help if I cannot. Best of luck.

John (Britprius).

 

best to buy a powerlab charger/discharger.

looking at your dealer price for replacing these ~200 dollars devices can help a lot
they can be connected with a USB adapter and so on your PC you can see a graph and a capacity calculation.

this way you can match cells and find the failty one with far less cap.

 

Hi Stu, I would go with a slightly higher charge limit of say 6750mah.

The modules should start to warm up when the charge capacity limit has bean reached. This is because the good cells in the module cannot absorb any more charge so that any current through them is given off as heat, it is this stage that allows cells with a lower charge to catch up and become fully charged, thus balancing the cells in that module.

You are obviously going in the right direction as the modules are shown to be improving in capacity, close to 1 amp/hr. I do not see anything to gain by discharging further than the present limit although this may show up as more capacity it also runs the risk of reverse charging any low charge cells within a module. It is the top of the charge cycle that gives these cells the chance to catch up.

The problem you have with the discharge rates is well know and as you say it is governed by the discharge resistors within the charger. I did not have the problem as I had 10 chargers "bought in an auction of bankrupt stock probably for little more than you paid for one charger" speeding things up dramatically. It may be possible to add external resistors but not having a charger now I cannot look into this, but I did warn you it took time and patience to balance a complete pack.

Hope this is of help and not disheartening.

John (Britprius)

 

Stu,
Yes it is painfully slow. Adding a larger load to the battery will discharge it faster but, I don't think your charger would be able to measure the capacity accurately. You could easily put a 6v lightbulb in parallel w/ the charger. This would discharge it faster but, you would likely get a lower ah reading from the charger. I'm thinking if I was in your shoes, I would charge/disch w/ charger only (for baseline), charge/disch w/ charger and light, and charge/disch w/ charger only to get a final reading. This would speed it up a little.

Alternatively, you could do all 3 cycles w/ the light and simply match cells to those readings (knowing the capacity is actually higher).

What do you think John?

 

The idea in its self is sound.

The problem is that the charger is programmed to do the charge/discharge cycles unattended making it difficult to know when to attach extra load for discharging.

Unless all modules are treated and balanced in the same manner the amp/hr readings become meaningless. In other words the load needs to be switched on and off by the charger. This may be possible just by bridging the internal resistors as long as the path for the current through these does not run through any solid state components (transistors diodes ect) that cannot handle the extra load.

 

Sounds good as long as the treatment is exactly the same for all modules, otherwise the figures will be meaningless.

Do not worry about the amount of heat you are noticing the important thing is that you see improvement in the amp/hr capacity of the modules as you slightly over charge them.

The heating wattage would be .7 amp (your charge current) x about 8.5 volts the end voltage charge (may be higher than this), about 6watts spread over the module, but you can get into a situation of thermal runaway when charging so do not try to push things in this area.

Keep up the good work I know it can be tedious but worth the effort

PS. what area are you in the UK.

John (Britprius)

 

I'm wondering if the sense wire might be loose or making intermittent contact. The KOH electrolyte 'eats copper' and I've seen photos of one sense wire that 'looked OK' but it was just the insulation. The copper inside the sense wire had been corroded away by the KOH.

Bob Wilson

 

Yes, I agree with Bob. The most likely cause of this problem is the sense wire. You proved beyond a doubt that the module was stable . The symptoms you describe I've never seen a battery vary in voltage by that much not to mention that quickly. So in essence, the module is not the problem. Your sense wire is either loose or corroded away. This is an easy, cheap fix.

I don't recommend you use/sell this unit for spares because you will have the same problem with a new pack.