Effect of preconditioning on range?

[user 3172]

Forgive me for this cathartic and slightly rhetorical post but....

I have been trying to establish what the effect of preconditioning actually is on range because I seem to get some readings that are not that intuitive. Not the cabin preconditioning which I understand will pre-heat the cabin and therefore reduce battery usage on the journey but simply the effect of the battery preconditioning.

The way I figured I could do this simply was to take an update from the app this evening (the car has been sitting outside stationary for ages at between 3c to 5c so should be at ambient temperature). It is plugged into the EVSE but on the off peak charge setting so no charging going on at all at this point.

Screenshot of the app shows 100% charge and 99 mile EV range. The car is at 100% as it was charged Saturday night and not used on Sunday. FWIW, the reason the range is relatively low is that the last journey I did was very inefficient. As I understand it, nothing in the range algorithm should change in that regard until I pull off tomorrow morning on the daily commute.

The off peak charge period is set to 1am to 7am and the charge settings are L2 Max on a 7.4kwh EVSE with preconditioning set and a departure time set of 7.40am.

Questions.....

Will the car know in the morning that the battery has been preconditioned and therefore change the result of the algorithm and show an increased range?

Will the car keep the range the same and simply factor the preconditioning in real time once I get underway on the commute?

Will the car actually precondition the battery at all given that the departure time is outside the off peak charge period?

If it does precondition, what time will it start the process given that it doesn't need to charge much if at all?

Any educated guesses welcome in advance of tomorrow morning but I'll report back what happens in due course. I'll screenshot the app at 7.40am before I pull off. I'll check my meter data after 24 hours to try to establish approximately when the EVSE cuts in. I'm not convinced there is much in the way of battery preconditioning going on at all which is the reason for this post. Is there any other way of knowing?

 

[justanotherdrunk]

http://bmwi3.blogspot.com/2015/03/bmw-i3-understanding-how.html

 

[epirali]

My experience with preconditioning is that the range displayed is still completely not on target, even with preconditioning. There is actually a bug for me that during the preconditioning window the range will jump by 10 miles, then settle back to what it was after preconditioning is complete.

But on very cold days preconditioning WILL increase the range (I have tried with and without). On the standard battery my guess is anywhere from 5-8 mile more range at around 30f. So that's almost a 10% gain.

 

[jadnashuanh]

A cold battery cannot source as much current as a warm one. So, warming the battery before leaving on a cold day will increase your actual range, but may not show on the estimated range display. Warming the cabin while connected to an EVSE also will save on range especially if you have a REx. The only way the REx can warm the cabin is via resistance heaters, so one watt in, one watt of heat. The BEV has a heat pump standard in the USA, and you can get 2-3W of heat from 1W input, so it is considerably more efficient. But, if it's really cold out, the heat pump becomes less efficient and the car can supplement the heat from its resistance heaters.

I've seen my i3 drawing as much as 20A during the departure time/cabin preconditioning period. Much better to do that while pulling power from the grid than from the battery's capacity! I put a meter on the input to my EVSE so I could visualize the power draw.

 

[user 1096]

YMMV--certainly applies, and with zero thanks to that last software upgrade that allegedly gave us new range calculations...for a couple of miles anyway.
Right now, outside my window, in addition to a frozen Hudson River with Albany beyond, we have a foot of new snow with high winds whipping it around and 25F, but with the wind, it feels like 8F. While the i3 can't "feel" the wind, it certainly reacts to headwinds by further reducing the already-reduced battery capacity. In sum, the last voyage I want to make today is 30 miles up the Adirondack Northway (I-87) into headwinds and gusts on a cold battery...I might make it there, but will surely rely on gasoline to get me home.
In sum, I pre-condition whenever possible, but considering how long that process is, (several hours) especially below 20F, I'm never sure how much benefit to expect.

 

[user 3172]

Thanks for the responses, I just read through the blog.

http://bmwi3.blogspot.com/2015/03/bmw-i3-understanding-how.html

The first thing to say is that superficially based on the following Q&A, battery preconditioning just isn't happening for some reason.

Q. How early before the departure time will the vehicle begin to precondition?
A. When using the vehicle preconditioning menu, it will depend on temperature, but generally 30-40 minutes prior to the set departure time the cabin preconditioning will start, and the battery preconditioning will start 150 minutes prior to that.

I always set the departure time via the app in the evening more than 3 hours earlier than due (as stated in the blog) and the precondition setting is switched on. I generally hear my EVSE open about 30-40 minutes before departure suggesting this is only for cabin preconditioning. Examination of my meter consumption readings generally confirms this. No evidence of significant power usage in the 2 1/2 hours prior to when I first hear the EVSE opening. What generally happens is that at 1am (commencement of the low cost charging window) the EVSE opens and charges the car then switches off charging when 100% complete.

Back to my test, I turned on the Start button this morning and the range had increased from 99 miles to 102 miles (a 3% gain) so it's obviously factored in some new information but is that battery temperature or cabin temperature given that it had raised it from the ambient 5c to the 20c I was due to drive at. For the record, external temperature hadn't moved from 5c so that wasn't a variable which changed.

I won't have meter figures until tomorrow so will post back on that to confirm power usage.

As I said at the outset, I just don't think battery preconditioning is happening for my car. I am usually awake for an hour and a half before leaving and whenever I hear the first clunk of the EVSE opening, I check the time and it is always around 30 minutes prior to the set departure time suggesting cabin only.

Any ideas at all welcome please ??? Either in respect of other tests / settings to try or why it may not be apparently working.

 

[jadnashuanh]

Set your departure time for when you actually wish to leave...the car will then start things early enough to optimize its benefits. If you say plan to leave a 7am, and tell it 4am, it will then have nearly 3-hours to cool off again, negating most of the benefits.

 

[user 3172]

Sorry if I've misled somewhere Jim. That's what I do. I leave at 7.40am so I programme departure for 7.40am with precon set. Nowt much happens it appears though until about 7.10am when cabin starts.

I've just been pawing over previous posts on related subjects and found reference to 10c as perhaps the battery temperature the car is working towards.

I suppose it's possible that getting from 5c ambient to 10c could be relatively quick and not require a 3 hour lead time. Maybe if it was colder I would see an earlier kick off of power consumption.

I've also dug up your post on the hidden system menu to show battery temperature. I think I'll try a "before and after" on that to see what it shows.

PS I can't see instructions to exit the hidden menu. Does it just disappear after a time delay or restart or something?

 

[alohart]

PS I can't see instructions to exit the hidden menu. Does it just disappear after a time delay or restart or something?

Just press the Start/Stop button to shut the car down.

 

[user 3172]

Okay, some good news I guess. I've been out this morning at the departure time and despite the ambient temperature being 3c, the battery temp was showing as 10c so it appears to be doing something.

I've just checked the power consumption for the previous night/morning and it shows about 0.75 kwh burned at around 4.30am and then another 1.25 kwh between 7am and 7.40am (set departure time).

The surprising bit for me was the energy consumed at 4.30am. I hadn't seen any appreciable consumption on previous occasions but maybe I was looking for more over a prolonged period and maybe I was expecting the battery to get warmer than 10c given the previous things I had read about 20c being the optimum temperature.

I'm going to keep an eye on the battery temp on various days and journeys to see what it does in use.

Thanks for all the input by the way. Just the App to get working again now :roll:

 

[jadnashuanh]

The electric heater for the battery compartment is a 1Kw element. So, when on fully, you should see 1Kw/hr usage. Depending on the actual temperatures, it may not run full time. The cabin heating/cooling can easily hit about 2Kw/hr, depending on options/version/temperatures.

The act of charging the batteries will heat them some, so for maximum efficiency, rather than telling the car to charge immediately, you could setup a low-cost charging time window nearer to when you expect to leave, and it would then not likely need to run the heaters. Well, it might, if they are too cold, but maybe not. It can get confusing!

 

[user 3172]

Good point, my car mostly charges from 50% + SoC so on the 7.4kwh EVSE it shouldn't take more than about 2.5 hours to charge. I suppose I could set my low cost window to commence at 3am instead of 1am and then the battery should be warmed up more as a result of the charging activity.

 

[wilcovh]

What I do not understand is why BMW made the preheating of the battery only possible when plugged in. The consuption of the 1kW heater is very low compared to the cabin preheating which is possible without plugging in and can draw about 6kW. The 6kW heater costs you range but increases comfort and even cost you more range on a cold battery.... The battery heater increases the range. And if you look at the capacity /temp graph capacity conciderably increases the range when it is really cold with just a little bit of energy.
Or do i miss something here.

 

[jadnashuanh]

The battery heater is a 1Kw device, but it can take three hours to raise the temperature enough to make it worthwhile, so it's not one, it's 3Kw, or nearly 20% of the available capacity BMW allows you to use.

Preheating the cabin has a peak draw of about 2.5Kw, if I remember correctly, but it only runs for about 1/2-hour and only at max at the start, or possibly a bit over 1Kw. The cabin preheating is in the order of 7-8% of the available capacity. Some people are fine with a heavier coat and maximizing their range, so cabin preconditioning can save some energy, but if you want maximum range, you don't want to be doing it by using battery capacity, which decreases it...you want it coming from the power grid. On a luxury car, people are more interested in comfort than maximum range, so they allow you to precondition any time.

I did read about one company that has a prototype battery cell that has built-in heating capabilities where they claim the effect is useful - more energy available if you preheat verses leaving the battery cold, but the battery design we have did not have that tech available when implemented, and it uses (like everyone else that does it), an external heating element, which isn't as efficient. Plus, it's one more thing to go wrong as there would be an additional circuit in each cell. MTBF rates are heavily affected by the number of components, and throwing in nearly 100 more gives you a worse MTBF, not something most people are looking for.

 

[user 3172]

The battery heater increases the range. And if you look at the capacity /temp graph capacity conciderably increases the range when it is really cold with just a little bit of energy.
Or do i miss something here.

Surely Newton's laws apply. You can't get more energy out than you put in, so the heating element must burn at least as much energy as it releases in extra range?

 

[Kristian]

Taking readings from the hidden battery temperature menu I'm getting around 5 to 6 degrees C increase in battery temperature when preconditioning. This is off a slow 10amp 240v charger. I try to precondition the batteries when the outside temperature drops below 10 degrees C. I've no real need to charge overnight as have free charging at work but there is no option to just warm the batteries.
I had also been wondering how much the batteries get warm in use. I left the temperature menu on while driving this morning. Ambient was 10. Batteries warmed to 15. Battery temperature went up to 16 and stayed there over 28 miles of steady driving at 45mph (A420 to Abingdon). I was expecting them to get warmer than that.

 

[jadnashuanh]

The amount of warming varies by the current draw. The higher the current, the more heat generated by the internal resistance of the battery (think of it like a heating element...the more current, the hotter it gets). Ideally, there'd be no internal resistance in the battery, and thus, no losses, and no heat generated. Cruising along at 40-45 isn't stressing the batteries. A few full-throttle starts and cruising at high speeds, then, you'll see the temperature rise more (until the cooling turns on, anyways).

 

[CharonPDX]

Relatedly, does anyone know a way to make preconditioning use the defogger setting instead of standard cabin preheat? I'd much rather come to my car in the morning with the windows able to see out them than have it warmer...

 

[jadnashuanh]

Relatedly, does anyone know a way to make preconditioning use the defogger setting instead of standard cabin preheat? I'd much rather come to my car in the morning with the windows able to see out them than have it warmer...

Is the HVAC on AUTO? I've not had your issue. The HVAC system will engage the a/c to dry the air if it is enabled. Another big deal is if there was some snow on it, it's MUCH easier to remove from the windows than if you don't precondition unless it's really cold, dry, fluffy stuff which we don't see all that much of here!

 

[CharonPDX]

Is the HVAC on AUTO? I've not had your issue. The HVAC system will engage the a/c to dry the air if it is enabled. Another big deal is if there was some snow on it, it's MUCH easier to remove from the windows than if you don't precondition unless it's really cold, dry, fluffy stuff which we don't see all that much of here!

I've tried HVAC on AUTO, and manually turning it to just the window defogger before shutting it off. No matter how long it preconditions before I get out to it, the windows are still very fogged up. I get in, manually push the front window defog/defrost button, and it's defogged within a minute.

Not snow, just morning dew. (Although it will be far more important when we get Portland-usual-Winter "dew that freezes in to a layer of ice on the windshield." That requires either hard labor scraping off, or run the defog/defrost for a few minutes. I'd love it if the precondition could do that for me, so I don't need to scrape the window.)