Avalon hybrid. What to mod?

[Isaac Zackary]

Just doing a little math here.

The Avalon's battery is made of 34 7.2V (nominal) modules which in turn are made of 6 1.2v (nominal) NiMH cells. At full charge (1.4V per cell) the total voltage would be 285.6V. If you charge Li ion batteries up to 4.2V per cell that would be the exact equivalent of 68 Li ion cells. (Of course keeping it down to a more reasonable 4.1 or 4.0V max per cell wouldn't be hard to do the bigger the battery is.) Coincidentally the minimum and nominal voltages are exactly the same too.

However, NiMH batteries can be charged at a higher voltage than their max voltage (due to battery resistance, kind of like charging a lead acid battery to 14V and taking it off the charger and seeing 12.8V). So in reality the Synergy drive system could possibly put out up to 326V! That would fry a Li ion battery of 68 cells connected in parallel, expecially if it were near full charge (like in a plug-in hybrid)! Some sort of battery management system would have to protect the Li ion battery under regen near full charge.

According to Car and Driver, the Avalon's battery is capable of delivering some 141hp. That puts us at around 500A. Of course the Li ion and NiMH batteries would be helping each other. But it would be best to match the current since the Li ion battery may have less resistance than the NiMH battery.

So for a parallel LI ION battery, we need 68 in series capable of delivering close to 500A. Maybe 1,700 of 20A rated 18650's? It seems like I've seen some 1300mAh 20A cells on eBay before for some $150 per 100 box. That would put me at some $2,550 for just the cells (if I could find them for that price) but would add nearly 8kWh. I need to check out the Chevy Volt battery specs too.

[cRiPpLe_rOoStEr]

Not sure if increasing the voltage while keeping this very same battery pack would be worth the endeavour. Eventually looking at larger-capacity cells with the same voltage, even though they would naturally become bulkier, might not harm the overall durability of the system. But you should always keep an eye for temperature and other factors that might affect them.

[COcyclist]

Isaac, After following your other thread I think you arrived at a great choice in vehicles. My recommendation of “what to mod?” would be to start with low cost/best return mods. It looks like Toyota has done a good job with aerodynamics but the underside may be an area to clean up. I have a full, front to rear coroplast belly pan, side skirts and rear diffuser, with extra insulation under the engine to retain heat when parked. You may be able to block the upper grill and still stay cool enough, especially in winter. (Make sure you have a digital temperature gauge to monitor temperature.) I use a tank style engine heater and a stick-on Katz heater on the oil pan. On cold mornings I will use both. The Katz was added later and I was amazed how quickly it warmed the whole engine compartment.

A small ice chest with multiple pre-dampened “cooling towels” can help you run longer without A/C in summer. Tint as much of the glass as you can.

To retain efficiency and handling on our mountain roads, adopt the Lotus philosophy and “add lightness”. I have removed the rear seats and spare tire to take over 100 lbs from my car.

[Isaac Zackary]

Ok. So my first mod to the car. An OEM cartridge style block heater. Installed and ready to use and used already.

I do need a thermometer for monitoring before blocking the grill. I'm not sure how good of an idea that would be with all the mountains I have to climb and descend. I would love to do automated grill shutters. Not sure how easy that would be though.

Belly pan and wheel skirts are on the list. I also want to weld up my own tow hitch. The ones I've seen ready to purchase hang down and would affect aerodynamics. I want one that comes through the bottom of the bumper.

[redpoint5]

Yeah I'm surprised there isn't more competition for "hidden" hitches (Hidden Hitch the company makes regular hitches that aren't hidden). The only outfit I know of is Torklift, and they have a limited selection, as well as 2.5x the cost of a normal hitch. You'd think with heavy competition for normal hitches, and the prospect of making 2x more for the same amount of steel and fabrication, there would be a market for hiding the hitch behind the bumper. Maybe most people simply don't care if there is a steel bar hanging below their vehicle.

[Isaac Zackary]

I just uncovered the traction battery for the first time. (Cover is held on by Velcro!) Anyhow, there seems to be a lot of space around the battery where I could add some sort of heating pads. On those -40° days it would be nice to start out with a warm battery and engine.

I also just threw a space heater in the trunk that I will be using to warm the cabin before driving. Some of my drives are very short.

I'd like to add more engine heating/insulation. One idea I have is to install a tank type heater, but with a pump. Normally the problem I have with tank type heaters is that it's hard to install them just right so that they draw water from down low and perculate up high. And usually when you do them right then the flow is backwards from what the engine pumps while running, so they're useless if you're trying to use them with the engine on. But with a pump that problem would be solved. Plus, if I get enough heat, I could turn on the car and heat the interior at the same time. If there's enough heat coming from the tank heater then the engine should not turn on, or not stay on for very long, while I defrost the windshield and heat the interior. I'm not sure if it can be done, but since the engine apparently already uses electric pumps, I wonder how hard it would be to wire it up to turn on the pump that goes to the heater core and put a tank type heater inline with that.

[S Keith]

Max battery discharge current is about 150A. Not sure where you got that 141hp number, but that's just not the case.

Heaters that aren't forced-convection based aren't likely to be very effective as you're trying to heat an 82# insulated block of mostly nickel. If you installed some sort of forced air heating that pushes air in from the trunk and exits in the cabin, it would be double plus good as you'd heat the interior as well. This also increases the surface area you're heating by about 30X.

Think multi-speed/multi-heat hair dryer (maybe not strong enough from an airflow perspective).

The thermistors are on the bottom of the pack, so they will be the first to be heated even if the pack itself is notably colder. I suspect it would need to run for quite a while to ensure the pack is truly above 50°F at which point the hybrid system is pretty much unrestricted.

[Isaac Zackary]

Originally Posted by S Keith

Max battery discharge current is about 150A. Not sure where you got that 141hp number, but that's just not the case.

Heaters that aren't forced-convection based aren't likely to be very effective as you're trying to heat an 82# insulated block of mostly nickel. If you installed some sort of forced air heating that pushes air in from the trunk and exits in the cabin, it would be double plus good as you'd heat the interior as well. This also increases the surface area you're heating by about 30X.

Think multi-speed/multi-heat hair dryer (maybe not strong enough from an airflow perspective).

The thermistors are on the bottom of the pack, so they will be the first to be heated even if the pack itself is notably colder. I suspect it would need to run for quite a while to ensure the pack is truly above 50°F at which point the hybrid system is pretty much unrestricted.

Thanks! I was wondering about that current rating too since 141hp didn't make all that much sense.

Anyhow, one problem I'd have with blowing hot air through the battery is that I don't want to overheat it. It's one thing to set a heating element or light bulb next to the battery all night with a thermostat on the case to shut it off if it ever gets too warm and another to blow high power hot air through the battery and somehow set it up to shut off before it gets too hot.

Plus I got to think about how much electricity I'm using. If I got 200W in the block heater plus another 1000W for a tank heater that leaves me with about 200-300W for heating the battery, unless I shut off one heating system to turn on another.

But I still like the idea of heating the battery more efficiently and quickly. The same with the engine. Ideally it would be best to heat these up quickly right before taking off instead of wasting heat all night through "trickle heating."

[S Keith]

The issue is the complete waste of effort with radiant heating. It will be grossly inefficient and slow. You are heating sheet metal radiantly, which then radiates externally (wasted) and internally onto PP/PPE plastic with very low thermal conductivity and a cavity that permits heat escape out the inlet. Furthermore, the temperature sensors are on the outside, which will react relatively quickly even when the cells are bone chilling code. This could permit the car to use full hybrid function on a very cold battery. That will kill it in no time.

I linked a multi-speed, multi-heat dryer. High fan and warm heat is highly unlikely to get the battery too warm. They LOVE to be 90-100°F, and it will likely take many hours to get there.

30-60 minutes prior to start would probably suffice.

[Isaac Zackary]

Originally Posted by S Keith

The issue is the complete waste of effort with radiant heating. It will be grossly inefficient and slow. You are heating sheet metal radiantly, which then radiates externally (wasted) and internally onto PP/PPE plastic with very low thermal conductivity and a cavity that permits heat escape out the inlet. Furthermore, the temperature sensors are on the outside, which will react relatively quickly even when the cells are bone chilling code. This could permit the car to use full hybrid function on a very cold battery. That will kill it in no time.

I linked a multi-speed, multi-heat dryer. High fan and warm heat is highly unlikely to get the battery too warm. They LOVE to be 90-100°F, and it will likely take many hours to get there.

30-60 minutes prior to start would probably suffice.

Thanks! I'll look into it. I'll have to look and see where the air normally comes out. I assume somewhere on the right side, opposite of where it normally enters on the left side.