Refit of Rex/more batteries
- Thread starter osaland
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noakey
Well-known member
osaland said:
Hi.. i have exactly the same query. .. an extra 30 miles range for me would suit 99% of journeys in my BEV. Have always wondered why they didn't fill the Rex save with another few kwh of batteries.
jadnashuanh
Well-known member
The cost to retrofit the REx is likely to be huge...WAY more than the factory option...there's just too much that needs to be added, and it's not just drop in the engine and generator - you've got a new fender for the fuel flap, the gas tank, the muffler, the gas line, the sensors, cooling provisions, rear bumper cover, and probably LOTS more stuff.
Throwing in more batteries as an option isn't likely to happen, but is a bit more possible. The computer logic would need to know about the extra capacity, but keep in mind, the actual batteries aren't 360vdc...they're made up of a bunch in series parallel. You can't just add more without changing, then the cooling/warming for the extra/optional batteries would likely over tax the existing system, and making it bigger means more weight and complexity.
In reality, I doubt you'll see either of those options. Down the road, as battery tech improves, you'll likely see more range available, but the cost to swap that battery pack will probably not make it viable, at least not until the existing one dies.
What could happen, is to let the area where the REx is, maybe become a storage area, but for strength, I'm not sure you could make a hole safely to access it without compromising the integrity of the passenger CFRP frame.
Throwing in more batteries as an option isn't likely to happen, but is a bit more possible. The computer logic would need to know about the extra capacity, but keep in mind, the actual batteries aren't 360vdc...they're made up of a bunch in series parallel. You can't just add more without changing, then the cooling/warming for the extra/optional batteries would likely over tax the existing system, and making it bigger means more weight and complexity.
In reality, I doubt you'll see either of those options. Down the road, as battery tech improves, you'll likely see more range available, but the cost to swap that battery pack will probably not make it viable, at least not until the existing one dies.
What could happen, is to let the area where the REx is, maybe become a storage area, but for strength, I'm not sure you could make a hole safely to access it without compromising the integrity of the passenger CFRP frame.
Boatguy
Well-known member
A REx is about 120kg heavier than a BEV. 60% of i3 owners choose REx and a little less performance. Say you got another 100kg of batteries, and 20kg more cooling, charging, etc. how much range would be added and would it shift the BEV/REx mix?
At 100w / kg, 100kg is 10kw or a 50% boost in i3 range; say 40 miles for a total range of 120 miles (192km).
Who would switch to BEV?
Or is my math just totally wrong?
At 100w / kg, 100kg is 10kw or a 50% boost in i3 range; say 40 miles for a total range of 120 miles (192km).
Who would switch to BEV?
Or is my math just totally wrong?
ultraturtle
Well-known member
According to the BMW i3 Service Managers Workshop document, the 8 current i3 battery packs each weigh 55 lbs each for a total of 440 lbs (200 kg), making mass specific energy density 49.1 wh/lb, or 108 wh/kg. Your math is correct. A 100 kg increase in battery capacity would result in something less than a 50% increase in range, since we all know the extra weight results in a loss of 5% (as measured by BMW) to 6% (as measured by the EPA) efficiency.Boatguy said:
Cramming the volume of not only the additional battery space, but its supporting coolant system into the tiny space occupied by the REx is the greater challenge, so I would propose that (assuming the unlikely probability that the battery modules in their current form factor, and the coolant system would fit) a two module, a 25% increase in battery capacity might be the more realistic suggestion. This might inch range up from its current EPA rating of 81 miles to 98, taking into account a 3% reduction in efficiency due to the additional weight.
Not me!Boatguy said:
mindmachine
Well-known member
ultraturtle said:
Not me either!
I have opted for the BEV, but I would like a removable battery(s) in the space where the REX goes. That way if you need to go longer distances you only pay for the weight when you need it (unlike the REX). Also, I don't think you necessarily have to have those modules cooled the same way the main batteries are. Nissan and VW don't temperature regulate their batteries. Swapping these would be easier than the method Tesla employs with their battery swap technology and would add a lot of flexibility, where they could be traded and swapped along longer routes. The total weight of the extender batteries would not weigh more than the REX. Each module would be light enough for anyone to lift them. Only problem I see, is you might have to remove items out of you trunk to replace a battery. This definitely could not be retrofitted into current BEVs.
noakey
Well-known member
possen said:
Hi possen,
It has been one of those hard to understand design decisions as to why bmw chose to leave the rex space empty instead of packing in another 5Kwh (just a random number). It would make a huge difference in the usability of the BEV... by the way.. my BEV is awesome and I am glad I opted for this model. 23,500 miles later and every drive is as great as the first.
Have fun
Neil
