Is adding a second battery possible?

I do intend to reply later, And dont want to take away from the topic. At the end if the day we just want to improve out mighty gen2's. But just wanted to add LifePo4 are taking over the EV industry. I work in mining and am seeing there is a huge industry shift to LFP happening, it will become the dominate EV battery in the short term - mostly for cost effective reasons yes- cheaper and more plentiful materials but the industry also note the safety and far more durable and long lasting aspect of LFP vs lithium cobalt or magnesium They are actually superior in many ways. All the mining magazines are going on and on about this industry shift and EVinsider reporting the same. I think they have come a long way since the early days. and China have been using them for ages now and a lot of data over the years. I think we have also used them in solar long enough to know how to keep them happy and last for 30years. Also the energy and power density has gotten way better then a few years ago have a look at the size of a 280AH CATL cells they are less the half the size of a Winston LFP battery from a few years ago. And some manufacturers of LFP are able to almost match battery pack density of NMC/NCA.

 

Looking at a topographic map, the highest point (not necessarily a road) is about 700m and drops down to sea level in that area.

Where I live going east I go from 2,348m to 3,448m (1,100m) up to the top of Monarch Pass. The Prius or Avalon, going down that, feel full in about the first couple km or miles. The main part is 10 miles or 16km long with about a 6% grade. Now that's what I call wasted energy. This is just one of several mountain passes like this in the area.

Maybe not. I got kids and a wife I got to fill up the car with. On the other hand the Prius needs a battery. I'll probably go with an OEM battery for about $1,500 to $2,000 USD since I don't trust the $600 rebuilt and aftermarket NiMH batteries. But for that much money it would be nice if there were a suitable alternative for not much more that had more capacity for about the same size and weight.

 

Maybe get a Thule roof box. Use it either for the battery or the family.

 

That could work for around town. For highway driving, which would use more of the ICE anyway, it would make the vehicle have worse aerodynamic drag, which is where most of the energy goes already after engine efficiency losses.

But for around town is where having cargo space is less important. Groceries take up space, but not like road trip luggage does.

Maybe a second battery in the trunk that could be removed for road trips? That way the car could be spoofed into EV only for around town but then lose the extra battery and work as an ICE for long trips. I'd need a way to charge it of course.

However, that wouldn't help with gaining more energy on long downhill grades.

Let me put it this way. For road trips making the car more aerodynamic makes more sense. I know lots of Prius owners love their Thule boxes, but knowing the math and physics behind them, I cringe every time I see one on a Prius.

 

Life is full of compromises. Where else will you put Aunt Edna?

 

Ya, but putting more batteries to save fuel in a box that will make the car use more fuel makes zero sense.

The energy to move a vehicle can easily be derived from multiplying the velocity squared by the density of the air by the crossectional area of the vehicle and its coefficient of drag plus rolling resistance. Of the two, air drag is the greatest loss of energy coming from the engine or motors in any vehicle going 60mph except maybe the not-yet-available Aptera. A Thule box will add both a greater crossectional area and also increase the coefficient of drag, both of which mean more drag.

In other words, a Thule box can easily increase fuel consumption by 10% or more. Would a bigger battery make up for that and surpass it?

If I were to make a vehicle with more cargo space, I'd go the Aerocivic route. The aerodynamic tail acts as a bigger storage trunk and improves, not destroys, the aerodynamic shape even if some people think it's "ugly."

 

I'm not a lover of the roof top boxes either, but adding one for the family road trip isn't that bad an idea. The fuel economy is going to be poor anyway, the car is fully loaded after all, but more regen capacity would save wasted energy going into the brakes and wasted as heat friction and brake pad/disc wear .... the added weight needs more energy to get mobile and needs to shed a lot more energy trying to reduce speed.

The increased battery weight caused by increasing the storage capacity does affect fuel economy and probably a waste for a town vehicle in the flat land country. Living in an area with a lot of up and down hills changes that, the '06 Silver Prius, while dragging around the extended range battery (that couldn't store regen or fast charge, so only off assistance for half the city trip) still had better fuel economy than the 2 yrs newer taxi Prius with only the standard traction battery, so the battery weight v the fuel use doesn't mean less fuel economy. My hope is, the improved regen capacity and ability to fast charge while in the city, will mean a fuel economy improvement that will offset the cost of the new LTO battery pack ...... only time will tell I guess, but it's an interesting project I've thought about for quite some time.

T1 Terry

 

Doing some math, a 10% loss in aerodynamic drag is a loss of almost 1,500 Wh. per hour at around 62 mph or 100 kph. But weighting a Prius up to its maximum GVRW and climbing 3,000 ft (almost 1,000 m) up incurs a loss of about 790 Wh, which even with a good regen system you can't recouperate all of.

This is why I cringe at Thule boxes. I might get one to add more cargo space, but not to house a bigger battery. A trailer actually could cause less of a loss than a thule box and if designed aerodynamically enough could actually improve fuel mileage.

 

This is a good thread on another roof feature
Story of the weird Prius roof ? | PriusChat

 

Agreed, makes no sense to put the batteries on the roof, keep the centre of gravity low. My point was more toward the advantage of the bigger battery for round town and a bolt on roof box to carry the added stuff on the roof when taking the family on holidays .... or a good aerodynamic trailer for the holiday trip might be an even batter idea, as you say ....

T1 Terry

 

It would be interesting with a single wheel castor type set up under the back and a quick hitch assembly onto the rear of the Prius to increase the load carrying capability of the Gen 2 unit

T1 Terry

 

Decided to try a different layout for the 84 LTO cells today, standing as many as possible on their ends in the spot where the traction battery was mounted and the remained in the spare wheel well.
I think this will improve the weight distribution with the majority of the weigh over the rear axle and retaining the flat floor in the rear so the plastic tray can go back in to house the spare tyre, jack and other assorted stuff that needs to be carted around in the vehicle.

It will create a hump behind the back seat and before the plastic tray, but I reckon I can live with that or make a work around like raising the floor in the rear section to improve under floor storage and create a flat floor to where the seats lay down, then stuff will need to be layered if that whole length needs to be flat for what ever I'm carrying

T1 Terry

 

Look forward to your progress with the LTO cells Terry. I've decided to stick with LFP i just bought 70x of these 40AH cells. Yep i know what your thinking. 40AH is too small. But the data sheet says they are rated for 6C continuous and 10C for 30seconds. I estimate i would only be at around 3Cmax with the Prius. So will see how i go.

 

Did you get the threaded piece welded on top of each terminal? Don't try to drill and tap the solid block if you didn't, it's not very think.
Be sure to add an insulating sheet between each cell, the outer aluminium case will become active linked to the negative terminal, if it isn't already, and that plastic film on each cell will not offer much protection.
I had a 5mm threaded rod buckle and it scrubbed that plastic film off and shorted 4 of the 55Ah cylindrical cells I'm using for the Prius upgrade .... very exciting stuff and 4 destroyed cells that had never actually been used.

A member of our local electric vehicle association built an extended range battery using those cell and used those BBQ mates between each cell. Unfortunately, he didn't strap them tightly to stop them from bulging resulting in the case of a cell that was potentially at 240vdc, touched the aluminium battery box he had made ..... the arc blew a hole through the base of the aluminium box and metal floor of the Prius opening an air supply for the resulting fire, the plastics and carpet etc ..... they were lucky they heard the bang and pushed the car out from under the house ..... the car was destroyed.
His wife was ok with it as it was her car, she bought a new EV with the insurance $$ .... and a dip into the responsible persons wallet .... and he now has instructions not to touch it :lol:

T1 Terry

 

I did get the laser welded studs, as really not keen to try drilling and tapping those myself. And i know what you mean with these thin aluminium cased cells with the thin blue heat shrink wrapping. I've gone through the rigmarole with the larger 280AH CATL cells with the same challenges.(keeping each cell from touching each other, and keeping them clamped to avoid bulging.) But your warnings from your own experience are valid especially at 250VDC!! and that's crazy what happened to that member and a reminder how serious safety and careful design is for these projects.

Looks like i will be going down the darn expensive route with an orion2 BMS and an Elcon PFC2500 Charger. I couldn't really find any alternatives. Besides more convoluted and expensive systems like batrium etc(having to daisy chain modules to allow 70S). But would be open to other suggestions!

 

Also Terry, A you running a hybrid interfaces BMS canbus spoofer for your prius conversion? or something else?

 

Ummm..... more information please I plan to link the module cables that sense the voltage to the equivelant number of cells to make up the same voltage. Did that with the 1S70P LFP cells that made up the extened range pack when the NiMh went bang and the flames came out. I needed to move it from the rear of our house through a very narrow zigzag path and with no traction battery sense, it wouldn't release the park pawl. When I connected it up and turn the system on, the ICE started so I drove it to the workshop .... well half way, a big dip in the road between bitumen and dirt resulted in a wire falling off and it all rolled to a stop .... but the park pawl didn't engage so we winched it onto a trailer and moved it the rest of the way that way.

T1 Terry

 

More information? I'm not sure what more information there is, just wanted to know what method you will be using so that the Prius will make use of the extra battery capacity?(or what are you already running should say? a can bus spoofer?) or will you be using the stock Toyota system and merely replacing the NiMh with LTO's and keeping the voltages the same)

That's unfortunate what happened with the NiMh yikes!

 

I'm hoping I can get away with running the original Toyota system, that is part of the project to see if the traction battery capacity has any affect on the toyota BMS system as long as the voltages remain within the Toyota parameters .... time will tell I guess. Almost finished the last pack that make up the behind the back seat battery pack. Then I have to make an enclosure that is liquid tight so I can do the E Fluid experiment .... then build the box and battery that goes in the spare wheel well hole.

In a previous post, you were looking for a BMS system for the 70 cells, two come to mind, the ZEVA BMS system that can be linked to other modules of the same system to add cells to the number required, the catch is you either have to build it yourself or get someone the build it for you. The man quite the pressures of being a manufacturer and put the design and build instruction out there for anyone to use ....

The other is the EV Power BMS Lithium Battery Management Systems – EV Power Australia Pty Ltd that uses cell top modules. I would recommend adding a remote heatsink per module wired to the cell negative and the negative end of the module to keep the balance discharge heat out of the cell. They make, or at least did make and I don't know if they still do, cell top modules for 200Ah and bigger cells. These can burn off 2 amps, but they nake enough heat in the negative end to burn the pattern into the finger and thumb if you try to hold on to one when connected across a high voltage cell .... and that quick the burn happens before the reaction to let if go reaches the brain ....
I use them for the first stage balancing of big house battery pack to assist the active cell balancer we use, but mount them on 100mm x 3mm square pieces of aluminium with very light gauge wire for the connection to the negative terminal. They do have a high cell voltage cut signal and I believe a low voltage cut signal that daisy chains across the modules, so if a cell goes really high voltage (I think they use 3.8v) then you can use that to stop the charge until it brings it back down to 3.6v ..... there is a small red LED that lights up when it is trying to pull the voltage down across the cell and goes out at around 3.6v mark.

The idea was that the signal told the charger to drop the current to what ever the discharge capacity was of each balancer, the idea was to set the end of charge voltage at the point that all the cells would register a high voltage a high voltage cut.
I've removed them from all the battery packs I've inherited in EV etc because I don't like the damage the heat into the cell does to cell cycle life and prefer to use active balancers and monitor cell voltages dependently, so the draw of the balancer doesn't affect the cell voltage reading.

The member of the Electric Vehicle Association that had the unfortunate Prius battery fire, had made a cell top board that active balanced and reported lots of information back to a central control but also held some of the processing work within each module .... the hive mind principle, the idea was it could work around any glitches, montor the cell voltage and temp on the cell either side and the system would compare that to the information received from each module, that was it could detect any abnormalities and report it to the users phone as an alarm if they became serious enough to interrupt the smooth operation of the BMS .... that was how he was notified his Prius had a problem and managed to save his house from burning to the ground along with the car.

A brilliant system, but he lost interest when the car went up and he was told he could not experiment on any more of his wife's vehicles ...... I've been trying for a yr or so now to get him to make them for me and I'd be a long term market for him .... no luck yet, but maybe one day ......

T1 Terry