battery removal thought experiment

[insightman]

Our Spartan 2,700-lb 2010 Honda Insight hybrid has always disappointed by rarely topping 40 mpg. I'm amazed that our luxurious 4,100-lb Clarity PHEV can easily get 45 mpg or better. What a difference 8 years made. I wish Honda had made an IMMD CR-Z before they abandoned that car. That would have been the right car to call the "Insight," rather than a re-bodied Civic. I expect it could have achieved 60 mpg or better.

 

[nerd king]

The question no one has asked is why do you get such poor gas mpg on your car? I haven't gotten worse than 48 in the last 3 months (drive 100% on gas so lots of data) , do you drive over 80 mph? The only time I hit 40 (and lower) is in winter.

I drive mostly on electric so don't have the data that you do, was just going off the EPA estimate of what gas only fuel economy might look like. Great to hear another voice that shows our cars do better!

 

[Pooky]

I drive mostly on electric so don't have the data that you do, was just going off the EPA estimate of what gas only fuel economy might look like. Great to hear another voice that shows our cars do better!

I would like to chime in as well and mention that on my recent road trips between WA and OR (~600 miles total) I averaged 50-60 MPG when cruising at 65 MPH. On one leg I even managed to get as high as 66 MPG in HV mode. The EPA estimates are very conservative and I have never gone below 45 MPG on any road trip. You don't even need to try to hypermile, just don't drive over 70 MPH because fuel economy takes a nosedive.

 

[rodeknyt]

Two years ago, we did a road trip that was about 4,000 miles total. Started in the L.A. area, went to Lake Havasu, then Flagstaff, Durango CO, Denver, Grand Junction, Salt Lake City, Boise, Bend OR, Corvallis, Crescent City CA, Mountain View and back home. Lots of high mountain driving and lots of ~80 mph speeds (to avoid getting run off the road).

We did the entire trip on HV. We did plug in whenever we found free charging, usually overnight, because some battery always gets used even in HV. I recorded the fuel used from the gas receipts and did the math when we got home. Over the entire trip, we averaged just shy of 44 mpg. I was quite pleased.

 

[Mowcowbell]

I could see pursuing this idea if gas was $5/gal. But at under $2/gal with no future price increases, why bother?

 

[MrFixit]

Over the entire trip, we averaged just shy of 44 mpg. I was quite pleased

@rodeknyt -
Just curious.. Out of the ~4,000 miles on your trip, how many miles would you estimate were derived from the free charging that you were able to do along the way?
This is a very nice trip to evaluate the HV performance of the car, but you really need to discount the free miles you got from the plug-ins along the way. If, for example, you got 400 miles from the free plug-ins (~8 charges), then your real HV mileage would be 10% less, or more like 40 MPG.

 

[cmwade77]

If you stay anywhere overnight, try making sure the hotel has a charging station or at least an outlet you can plug into. 40 miles might not sound like a lot, but it can add up over the course of a long trip. We tend to do this with our CMAX when we take it on long trips. Now that we just got a Kona, those long CMAX trips may be a lot fewer, but that is another story.

 

[cmwade77]

I could see pursuing this idea if gas was $5/gal. But at under $2/gal with no future price increases, why bother?

Gas is at least $3/gallon out here in California and has been increasing (even after accounting for the illegally increased gas tax).

 

[nerd king]

I could see pursuing this idea if gas was $5/gal. But at under $2/gal with no future price increases, why bother?

there wouldn't be any real financial incentive to do it, more about the satisfaction of driving a vehicle that was optimized to what was being asked of it, and being lighter and more responsive, less carbon emissions, and just wondering if it could be done without changing any of the software.

 

[Landshark]

Well, I must have a lemon as far as HV mpg goes. It gets 36mpg at 75-80mph. If you guys are getting 45, and 50-60mpg at 60-65mph that’s a disturbingly high reduction in fuel economy for a relatively small increase in speed.

As a comparison I drove a VW Jetta diesel for 11 years and 140k miles. It got 40-42 mpg at 65mph and 36-38 at 80mpg. Our diesel Grand Cherokee gets 30mpg at 65mph and 27-28 at 80mph. Diesel engines typically suffer a substantial reduction in fuel economy above a certain sweet spot which is usually geared for 65-70mph.

If this thing actually gets the mileage you’ve stated a 65mph compared to what I’ve obtained at 80mph, I’ll have to add that to the “undesirable characteristics” list for this car.

On a positive note, I have gone 55-65 miles in EV numerous times.

 

[KClark]

On several trips from LA to southern UT driving pure HV I've seen 39mpg pretty consistently. Speed limit on I15 ranges from 65 to 80 but real world speeds are 75-85. I drove about 77mph. On one trip I purposely drove about 67mph, braving the wrath of everyone, including semi trucks, behind me. On that trip I saw about 42mpg.

 

[Landshark]

there wouldn't be any real financial incentive to do it, more about the satisfaction of driving a vehicle that was optimized to what was being asked of it, and being lighter and more responsive, less carbon emissions, and just wondering if it could be done without changing any of the software.

If the Honda engineers participated on this forum they would be lining up to give you a pants down spanking. They are quite proud of the efficiency of this vehicle.

Apparently, you believe it is not efficient and doesn’t perform as designed.

 

[Pooky]

Well, I must have a lemon as far as HV mpg goes. It gets 36mpg at 75-80mph.

This is normal behaviour for the Clarity.

that’s a disturbingly high reduction in fuel economy for a relatively small increase in speed.

Absolutely, and it is a flaw of Honda's i-MMD system by nature of its design and single-ratio electric motor/gear ratio. The same issue persists with Honda's other i-MMD hybrids, such as the newest generations of the Insight, Accord Hybrid, and CR-V hybrid. Fuel economy is great for all of them, granted that you are driving slower than 75-80 miles/hour. It's like driving 80 mph in fifth gear when you really should be in sixth. Single-speed xEVs of all types suffer from this design flaw. Porsche has made and attempt to mitigate this problem by providing separately-geared traction motors for the Taycan, where it has a lower gear ratio for low speed driving/high acceleration and a high gear ratio for higher speed driving. I am uncertain as how that translates into real-world efficiency, but it does make the Taycan feel like it has a geared transmission when accelerating.

 

[Tek_Freek]

I guess I look at it differently. I get in and drive it. I get the mileage I get. {shrug}.

Drove to Mt. Charleston again today and used HV on the way to. Because of a couple of odd things happening (as usual) we ended up with less than 50% charge. On the way back down I gained 32 miles of charge.

What do I receive? A smooth, comfortable ride in a car that is ridiculously quiet.

 

[Tek_Freek]

I got a kick out of the OP #1. How much gas/electricity could you buy for the cost of doing all that work and the parts to buy?

 

[nerd king]

If the Honda engineers participated on this forum they would be lining up to give you a pants down spanking. They are quite proud of the efficiency of this vehicle.

Apparently, you believe it is not efficient and doesn’t perform as designed.

If you don't have anything intelligent to add to the conversation please refrain from posting here or on my future posts.

 

[nerd king]

The questions I asked were:
What would the MPG effect be on removing the traction battery and replacing it with a much lighter pack at the same voltage?
and
Could this be done without freaking out the battery management systems?
Insightman thought the answer to the first question would be around 47mpg, which I appreciate. I didn't ask if this was a good idea, or if it was cost effective to do so etc. I even titled it "thought experiment" in the hopes that people wouldn't get confused as to my intentions. I'm mostly asking because I'm curious about engineering parameters. I've built an electric car and did a lot of research and design with balancing range, efficiency, power- it's a topic that interests me, that's all. Does anyone have an opinion as to whether the car would "know" if it was hooked up to a lower capacity back that is at the same voltage? Yes? No?

 

[MrFixit]

This is just an opinion, but...

I suspect the characteristics of the battery are so embedded into the design of the vehicle that it would be virtually impossible to alter it without "inside information" which would never be available publicly. I think the BMS is distributed within the battery assembly itself, but intimately coupled with the engine computer and the display computer, the inverter, charger, etc. All of these systems are highly proprietary and filled with software that without source code and technical hardware details would be next to impossible to reverse-engineer.

In summary, this is not like a flashlight where you could remove the Eveready and plug in an Energiser !

 

[Landshark]

If you don't have anything intelligent to add to the conversation please refrain from posting here or on my future posts.

It’s an open forum. You don’t own the thread.

If you disagree with a statement or opinion, say so. Comments about someone’s intelligence generally don’t lead to a constructive conversation.

 

[ClarityBill]

Does anyone have an opinion as to whether the car would "know" if it was hooked up to a lower capacity back that is at the same voltage? Yes? No?

You seem to have much more knowledge about batteries, and electric vehicles than I do... but I would vote yes.

It does seem the BMS is built into the battery module, so the easiest way to do this would be just remove cells from the battery, and cross tie the appropriate voltage lines to feed information back to the computer. The BMS obviously handles a lower capacity battery as the cells degrade. Success would hinge on if the system would accept a 'step-change' in capacity, or requires gradual degradation.

A more interesting way to do it would be to remove the battery pack, and install a computer to intercept the communications and respond with the messages that would keep the system going. This would really involve information from the belly of the beast.