I3 Rex Auxiliary power and 8000 Feet Elevation

BMW i3 Forum

Help Support BMW i3 Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

EVMan

Well-known member
Joined
Feb 25, 2017
Messages
340
Location
USA, DC
I love to take the Rex on long trips, specially over mountains
All i carry is a 2.5 gallon additional gas tank , which fits in front

All ICE cars and trucks were speeding each other and the slow RVs , over the passing lanes
But i observed, that changed quite suddenly , at above 8000 thousand feet of elevation.
Now the cars , Trucks and the Jeeps were no longer hurrying up to pass the slow RV's at the first chance.
Instead they were decently giving way for others to pass

With no deterioration of pickup speed, it was easy to accept that.
I am guessing with that elevation, they did not have the quick pickup . i believe traditional ICE will have around 30% power reduction at that elevation

The last time , i was driving a Ford explorer V6 automatic above 8000 elevation, i remember , it just would not pickup above the 55 miles , so i could not pass. it was not a choice.

I am sure my Rex also lost power, but with my buffer , it did not matter. I could care less
I like to call Rex - Auxiliary power. I use it every time , at uphill , to help reduce load on battery ( and be within 2C discharge rate) and shut-it off otherwise
I love this multiple power sources like in star-trek . :)
 
EVMan said:
i believe traditional ICE will have around 30% power reduction at that elevation
Definitely true in the past. However, many newer vehicles have turbocharged engines which should eliminate or at least reduce this power loss at high altitude.
 
Power definitely decreases at altitude on a normally aspirated engine. As noted, though, that should not happen at typical altitudes you can drive with a turbocharged car, and may not happen if it is a supercharged one as well. Using regular on a car optimized for premium will also be much more noticeable at altitude since the cut back in timing required and with less oxygen available, also decrease the power available.
 
I can't wait to get a Tesla or other long range BEV and drive it on mountain passes.

Air density, and power, drop about 3%/1000 feet elevation above sea level. Normally aspirated engines can use lower octane fuel at high elevations. Why they sell 85 octane. Turbos or supercharged vehicles should not, they often work the turbo harder at high elevations to lose less power. MPG should go up due to less air drag.

Growing up at 7,200 feet, anything with more than 25 lbs/hp at sea level was pretty miserable to drive up hills. Most modern cars have no problems driving 80 mph up mountain passes though.
 
Its mostly the pickup , trucks which are racing. I have no idea if they are diesel or what ever they are. They do have lot of power
Many of these vehicles are not new, and may not be turbo.

Also i suspect , even a 15% drop in power , may mess up the gear ratios and optimizations, that driving uphill performance is effected more than 15%

While coming down, you literally loose no charge. That's the best part.
 
Climbing up and higher speeds is brutal on the batteries.
While i did not notice any loss of power due to overheating, it may or may not be, due to rex helping the batteries , and keeping the discharge rate lower.

I saw a parked tesla model 3 and the peak. Its was running its AC to cool the batteries. Tesla's cool batteries , even when parked, when not at home , anticipating more drivig.
 
The i3 cannot exceed certain power draws continuously...the batteries will overheat and to prevent that, the computer will, after awhile, limit the maximum power output. IOW, you cannot use 170HP constantly. But, the good thing is, you rarely need full power, so may not reach that upper limit requiring it to throttle down. This is independent of the SOC limitation.

The i3 is better than the Leaf in that aspect. The reason the Leaf cannot be DC fast charged repetitively on a trip is that their rudimentary air cooling cannot keep up with both high speeds (high discharge heats the battery more) and the accumulated heating caused by DC fast charging the thing...as a result, you must take an extended break to allow things to cool down before you can charge it again. Their maximum (with no intermediary stops) DC fast charging is two cycles. The i3's, unlimited. WEll, maybe if it's like 110-degrees out. Current both in or out is limited when the battery is outside of the optimum temperature range.

WIth a turbocharger, the input fuel charge is always about the same, so to get maximum power out of the vehicle, lower octane won't work whereas, an atmospheric system, a lower octane will work. It was worse back when we had carburetors...many of them did not have barometric compensation for the mixture, and lacking forced induction, there was less air available.
 
Back
Top