Battery balancing

Not exactly. The HV battery is assembled using brand new modules that are typically less than a month old. Panasonic/Primearth manufacture the modules under strict QC programs. They're as close to being perfectly balanced as they'll ever be. I'm sure the final assembly has some random testing performed prior to shipment/installation. I'm sure some of the QC testing during the design phase demonstrated that the majority of the HV batteries would be fully functional until at least the end of the car warranty. After that, it wouldn't really matter to Toyota. It wouldn't make $$ sense for them to invest in a balancing system (and raise the car price more) if it's not needed to reach warranty expiration.

 

yeah, but the chemistry of nickel metal hydride is not like that of lithium varieties, -- having had their pre gen in Japan (which had a plug in charger!) and the gen 1 that made it to the US, you would think enough would have been learned that 1.2 volt difference could happen and the ECU should be able to rectify that since it is already probing 14 pairs ... --- geeze , a little trickle charge function for a block that is getting 'close' just seems like asking alot of toyota battery management engineers and software / firmware, after all, it's only the best selling (or was) car (corolla?{) and car of the year (prius ) in the past decade or 2 ....?

 

Why spend the expense if the battery rarely fails during the warranty period?

From business (and planned obsolecense) standpoint, it seems to makes sense forgo adding a balance function.

 

they went to so many efforts to literally give these away , even to the point of losing money because of low price ...
but ... no .. we dont want them to last toooooo long, just long enough ...

is it even really an expense ? (maybe a 50 thousand dollars in computer programing /testing manhours I'll bet several tens of millions went into the various research , engineering and testing starting from the 1999? Japanese only pre-gen1.

( all lithiums must be balanced to get full utilization )..

- with such a narrow 1.2 v differential toleration,
one would think a simple 'getting close to max delta' routine of the ECU block sensors would then implement extra current/voltage to the blocks that are say 1volt lower than the highest block for 30 min (be it split up over a few trips or one, it can count and keep track) - and keep doing that routine until the lowest block was say <0.5 volt less than the highest block. .. I'm certain they balance on the newer lithium pack cars !!!

 

You seem to be pretty upset that Toyota did not include a top end balancer. I suggest you purchase a Prolong kit for your car. Then you can balance out your pack whenever you want.

 

Actually you can purchase balancers for about $10 apiece from Asia. Generally will do 4 cells each.

 

4 cells or modules? How would you wire that out without removing the buss bars?

 

it is upsetting that toyota kept an ancient battery technology like nickel metal hydride when they could be using a more stable and longer lasting and higher power density LITHIUM (yes with higher cost) - but at least more cars would be on the road instead of becoming paper weights after 130k+ miles due to no one really wanting to invest several thousand more or gobs of time with DIY to put more ancient tech back into the old thing ....

 

do u mean 4 modules ? each module has 6 cells in it -- so theres 7.2v nominal for those 6 series cells ... or 14.4v nominal for 6S + 6S (2 modules in series)= 1 block pair.

 

If you purchase a system that can do the correct voltage you could treat the module as one cell.
So if it handles 4 inputs then wire it asy would any cell balancing system.
A lead to the negative.
The next wire to the positive of the module
Continue to each positive of the next 3 modules.
The trick is finding or making a system that handles the voltage.
There isn't a way to access individual cells in a Prius module.

 

another way to balance (as has been listed elsewhere in these forums) is to connect all the positives together in parallel and all the negatives in parallel .. or connected all the battery modules together in parallel (using a bunch of alligator clip wire leads ) so that the whole thing becomes the same potential and change ... the tabs are removed from the front and back of the pack before doing this.

 

I doubt a Prius with only 130,000 miles will become a paperweight. They get sold to people who can repair or replace the battery and use or sell the car. It’s akin to someone selling their mini when they get a 7000 dollar estimate to rebuild the transmission. It happens with many different cars for many different reasons.

 

The trick is finding or making a system that handles the voltage.
There isn't a way to access individual cells in a Prius module.[/QUOTE]


Yes but the battery charger doesnt know that, it thinks you have 6 batteries in series when you just have 1 module connected or 12 with a block (pair) and that seems to be an issue with many chargers, as a standard 12v battery LA has only 6 cells ...

 

What whole pack charger do you use or recommend? Im looking for a low priced one.

Thanks.

 

Would this require a heavy-duty (and potentially expensive) charger, since charging all 28 modules simultaneously draws a lot of current?

 

Depends. Balancing is done with a small current. Often "C" is used for the capacity, which is 6.5Ah for the Prius batteries. Charging *indefinitely* can be done with NiMH batteries with 1/20C or 1/20th of 6.5Ah, so 325mA (note I dropped the "h"). So if you have a 250Vdc 300mA powersupply, you could use that (but they are rare and you have to know what you are doing).

But if you want to cycle it, then you need something that can charge faster (unless you don't mind waiting for a day before the battery is full again) and you need a method of discharging it as well (usually done with 230V~ lightbulbs or two identical 120V~ bulbs in series).

 

A Prius module is a NiMH battery containning 6 cells inside They balanced by themselves as you charge the module full. More often than not, a "dead" module can be regenerated to work like new, no need to replace, waste of money. I only consider a module as "dead" if I cannot regenerate it after, say 5 cycles and it still can only store up to 2500 mAh or below, which is rare.

 

most people do a couple blocks at a time since 2 blocks is 4 modules ( 6cells* 4 = 24 cells, at 1.2v per .. ) this is about the limit of many hobby chargers, something special and usually pricey to do all the modules at once , over $150..

 

Most hobby chargers I have seen can charge up to 15 cells max, which would mean only one block (two modules in series) would be possible.

So if a person wanted to charge more than a block at a time, they should carefully peruse the specifications of any charger at which they were looking.