About Toyota internal power battery balance method

I believe the battery ecu monitors balance, but there is no current shunting etc employed to actively re-balance the pack. Balance is maintained by using high quality, matched cells, and by very strictly enforcing limits of charge / discharge over SOC, temperature, etc to avoid conditions that would be prone to unbalance the pack. The most common failure mode seems to be the eventual aging of the weakest cells leading to increased resistance / decreased capacity and manifesting as imbalance. Given the pretty exceptional reliability / longevity of these packs its pretty remarkable how well this passive approach seems to have worked.

You may be able to get a little more life out of them by re-balancing, but these weak cells will eventually have to be replaced.

I am not an expert in this area, and have no first hand experience. Hopefully someone with more direct experience will chime in.

Rob

 

Rob,
You did a good job of explaining things.

As you noted, in the car the pack operates withing a predefined SOC range, which is good for longevity.

When you do a manual balance you are able to go far below and above those ranges.

 

Very well said, couldn't agree more.

When using mini VCI with Techstream to look at the voltages the key is to watch and see if the same battery block always ends up min under load and switches to max when being charged. If so then you would probably benefit from rebalancing the modules. If the min and max seem to be relatively random, then your pack is in good shape and probably doesn't need to be done.

 

I too believe this, without any real proof. I drive my car over the same terrain, with very consistent temperatures, every time I go out, and I watch the SOC at various points along the way. I notice that on some trips the battery SOC will go much lower than what is normal, and some times it will be noticeably higher. It is conceivable that the battery ECU has some sort of exercise mode that it uses from time to time. There is no circuitry for singling out one module from the others for balancing purposes, so it would have to be done as a gentle equalization charge.

I imagine that most cars spend most of their time on the highway, more or less at high speed on fairly level roads. Under that condition, the battery does not see large swings in SOC, and there would not be much opportunity for the battery ECU to do any balancing. In my case, with large elevation changes, my battery sees all green bars for extended periods, with the (small) attendant temperature rise, and I can only expect that there is going to be some balancing effect from that.

But as mentioned, if the internal resistance of the modules begins to diverge significantly as a result of aging, then it is "game over" and error conditions are set.

 

We tried this repeatedly and did not have any success. The volt signal cable cannot handle even a small sustained load without blowing the fuse. Our Hybrid Battery Rebalancer (Grid Charger) attaches to the main terminals behind the ignition disconnects. The is the only way to safely charge the HV battery as a unit with the vehicle powered off. For the 04-09 Prius, the entire battery cover does not have to come off - just the small end cover.

The Hybrid Automotive Prius system is done. It's going to be released in just a couple weeks - Memorial Day weekend - if you want a quality sub-$400 Hybrid Battery Rebalancer system that will restore your cells as much as possible without requiring pack disassembly.

 

Where does one get the Hybrid Automotive Prius system? Is that different than the Grid Charger re-balancer?

 

Hi Mike,

You can purchase them here on the PriusChat Shop or directly on our website

 

Jeff, 1) How can I be sure they work? 2) How much does it cost to send it to south africa?

 

We can ship anywhere in the world for $60 USD. The vast majority of customers report significant improvements when using a charger. With regular charging and occasional deep cycling, poor battery performance can be eliminated and battery life significantly extended. If the car is in the early stages of failure (recalibrations, decreased MPGs) then the odds of significant improvement in battery performance are very good. If you have already experienced the red triangle multiple times, then odds are a module or two will need to be replaced.

Unfortunately, in any one specific case, it is not possible to say for sure how much the charger will help. The amount of improvement depends entirely on the condition of the underlying battery pack itself. If a few charge only sessions do not help the battery, performing a few deep discharge/charge cycles will often shock the battery back into proper performance.