Paralleling additional OEM Traction Batteries

If you search some more on PC, you will find people that have put in up to 4 packs. I warn you, that it is not a simple endeavor as you might think. The Prius only uses about 40% of the capacity of he pack. This does two things, it extends the life of the pack, and it lets Toyota get away with not having much of a BMS. I have tested the car with its 1 pack in EV mode, and the range is limited to 1 to 2 miles at most on level terain. One of the hills I need to climb will use up the battery in 0.1 miles. If you just add 3 more batteries, your range will be 4 to 8 miles on level ground. Now, if you use 80% of the battery instead of the 40%, you would have decent range. However, you would need to fool the Prius battery cpu to allow you to increase the higher voltage end and decrease the lowest voltage before it recharges, so you can get at that capacity, and add a good BMS to insure you balance the cells properly when you charge them. You will also need to disconnect all the extra batteries when the car switches out of EV mode, or it will burn a lot of gas trying to charge them up, unless you can reduce the effective capacity in the BMS to make the not waste a lot of gas trying to recharge your batteries.

 

I'm new at this, having bought my '06 Japanese import Prius a week ago. I did it for the fuel economy, as gas is expensive and I have a long commute - (spending <$5K p.a. on gas was starting to rankle). The commute isn't only long, but is over some pretty serious hills - highest point is 1200 feet over lowest point (near sea level). This is the issue - not sure if it's a big one or not, but the last hill home is a 3 mile, 1000ft, drop, and doesn't really exploit the battery regen system very well, since it shows a full charge about 1/2 way down the hill. It would be really nice to "capture some of this energy" for the return journey on the way TO work in the morning, not to mention for the other hills on the journey - there are several more, not quite as high in a single and as short a climb as this one.
Hence the interest in this particular thread.
Also, I'm in New Zealand, so don't have access other than through ebay to a lot of the resources a lot you guys in the US have. Gas price here is a tad more than the US at NZD2.01/L (NZD =0.837USD) & (3.78L/US Gal).

 

Unfortunately, you can't really do anything about it since it's a big descent, bro. Just let the car do it's thing in keeping the HV batteries healthy. You can probably assist it beforehand by going into B mode earlier than it will need to. Another strategy is to use just enough juice in coasting towards crest so that by the time you start your descent, the state-of-charge should be no less than 48-50% (3-4 blue bars). Once you're over the crest, let the car pick up speed using gravity. About 5kph before you reach the speed limit, put it in B and use that to control your speed going in and out of B without touching the brakes. Perhaps another thing you might want to do is turn on your aircon to full blast (fan on high and temp to the lowest you can go to make sure the the compressor is always on) including lights/fog lights to at least draw a couple of amps out of the battery for that stretch of descent. You can also open all the windows while you're at it to increase drag.

Another (costly) alternative is to use the above plus starting the coast down in neutral to enable the use of just the slight amount friction brakes to control and limit your speed to a safe and steady 40kph for say the 1st kilometer or until gravity eventually pulls you down faster and you have no choice but to go faster. Just make sure that you should engage D or B before you reach 67kph or else the speed will over-rev the motor generators (can't remember if it's MG1 or MG2).

I hope this helps...

 

Hi Agent J. Well, that's that then. I started trying to get the state of charge of the batteries down a bit so the regen has something to do on the way down. But it's not easy, as the approach to the steep part of the hill is about 5-6km of less steep (300ft elev) undulating winding down hill, which is just fast enough to not use EV mode on, although some of it is, so I do take advantage of that, and try to glide the rest of the time.
Hey look on the bright side, the battery is at fully 100% at the bottom of the hill, so should be doing it some good to keep it fully charged - although the engine still starts up for a warm up in the morning.
The last part of the journey at the bottom of this hill is about 1km (1/2 mile) of flat, so gets to discharge a little. The economy of the warming up engine is rock bottom though, on the ascent in the morning, like 4.5km/l, luckily only for about 3km! I still manage to average 22.7km/l (52mpg) so can't complain really!

Hey maybe I'll get a PHEV when I can afford one, that'll "use" the hill more efficiently.

Cheers bro! Hope you're not burning or swimming! Jeesh, you guys get all the fun.

 

Sydney was pretty much caught in the middle of those two but the bushfires have eased off already with heavy downpour expected to come in a few hours.

Towards the bottom of the hill when the bars are all full and green and the engine starts to burn off excess energy, it seems 100% but it's really 80% for longevity reasons. The same goes on the opposite end where the limit is 40% when it looks empty. It's good what you're doing staying away from continuous and heavy EV mode going uphill is not good for the HV battery's health in the long run.

52mpg net is not bad considering the climbs you go through but it can still be improved if you follow a simple counter intuitive technique --> accelerate down, decelerate up. This just means to judge your right amount of speed going down to gain momentum and maintain that momentum during the climb. As you approach the crest, try and get your speed to decrease slowly by lifting your foot in really minute increments. It will take lots of tries but you'll soon find the right formula to tackle the hills in your area.

 

It hits "all bars" about 1/3 of the way down, with about 600 ft of elevation to go, so may be more than 80% by the time I get to the bottom...
I bought a little OBD-II bluetooth dongle on ebay in the weekend, so may be a little more enlightened when I get this going. I've seen a fair bit about the Kiwi branded OBD-II dongle on here, so may be upgrading to that yet...
I've been doing something like the up hill decelerate etc even when I had my old car, and have pretty much gotten into the habit of doing it. I imagine a rail car on hilly terrain, it accelerates down the hills and decelerates up them, using a minimal amount of energy in the process - just gravity basically. It really screws up when PC Plod is doing speed checks in the dips though...
This is going to take a while to perfect I think.
Also, all the kids went back to school after the summer holidays today adding to the traffic volumes.
Felt kinda smug hardly using any petrol when the going got really slow. This is kind of where the pay-off is I guess - or one of the pay-offs anyway.
Only just started on my second tank, so have some way to go yet...

 

That's a great purchase if you can use Torque or any application that can monitor vital signs. It's a fun and informative way on trying to understand and get familiarised with the car.

Yeah, the speed traps don't help at all if that's the case. School here started today as well so it's back to a 6mpg or 0.3L/100km hit for me on my commute. But I'm still happy because we're still 150-200% better than most of the cars on the road in terms of fuel saved.

 

Yep. I'll get Torque when the time comes. 0.3L/100km is pretty impressive! I'm doing about 4.4L/100km, and i thought that was pretty good. What's your secret?

 

Sorry, what I meant by .3L/100km is the difference between the mileage during the holiday season and the normal rush hour traffic which started today. So from December to January, I was able to do 3.3 L/100km but now it's back to 3.6.

 

Still pretty damned good!