Cold-Temp Salvation

Hi Tmanson,

Where did you hear the series resistance gets worse with cold temps? Metal has a lower resistance at colder temps (including motor windings). But chemical reactions become slower. That implies, and is so documented on the PEVE website that battery power reduces with cold weather. So, to avoid using allot of gas, the accelleration needs to stay out of using the battery much. Braking slower will also avoid the reverse power limitations of the batteries.

I am able to stay in the mid 50's m,pg (just finished the last tank at 57.4 mpg)with morning temps above 10 F, and afternoon temps in the 20's to mid 30's F. But, I am not going very fast on the highway in the morning, and not on the highway in the afternoon. I am using the block heater below about 12 F in the morning only.

Remember that tire pressure varies with temp at 1 PSI per 10 degree F. I have my tires set to 44/42 PSI at 10 F right now. Its going to be about 5 F tomorrow morning here.

 

Did you have to mention this? Brrrrr
I am freezing just reading it

 

Car batteries really don't suffer from ESR as much as say electrolytic caps do and have never even heard of a discusion of car batteries and esr being an issue. Car batteries measure such low esr. BTW, for the money here's the best piece of test gear you can own:

Dick Smith ESR meter Kit:

Dick smith esr capacitor tester or meter can help to test ceramic capacitors in circuit

$100. I built mine and its going on 20 years old & use it almost everyday at work. Very accurate in circuit.

 

First, it helps to understand the temperature effects:

My studies indicate that at urban speeds, the challenge is keeping the engine and transmission warm. But at highway speeds, it looks like the higher density of cold air predominates. The engine can easily maintain 85C at 65 mph in 25F weather but the dense, cold air increases the drag.

Bob Wilson

ps. For our metric friends:

 

The car must also keep the catalytic converter hot, otherwise it's ineffective when the ICE starts.

 

There is still some room in the southern states and Mexico.

 

All this worry about the battery getting cold is premature. It only gets cold overnight, and you don't "loose" energy from that, only the ability to draw energy from it before it warms up.

As soon as you start to drive, the battery quickly warms up. So yes, when you start out, in effect, the battery may be unable to deliver large amounts of energy, or to put it another way, may appear to be down in SOC, but that will change very quickly. Within 5 min. of starting the battery is up to "nominal operating temperature" as it is heated in use from current flow into and out of it. The energy "lost" when cold reappears as soon as it warms up, and was never really lost, just inaccessible.

Poor winter mileage is mainly caused by having to warm up the engine and cabin. To do this the engine must run when otherwise it could be off. The loss of mileage in the Prius IS greater than other non-hybrid vehicles, but that is because there is just not a lot of "waste heat".

For example, Pearl drops from about 4.7 l/100 km summer to about 6.5 l/100 km in winter (short trips both cases, temps in the +25C range summer, -20C range, or just below 0F winter). Once the engine is warm, at idle Pearl burns about 1 l/hr or just slightly less.
The anti-Prius (2001 Nissan Pathfinder) burned 14.5 l/100 km in summer and 17-18 l/100 km in winter. Once warm the anti-Prius burned about 2 l/hr at idle. That's a big difference and most of it goes into waste heat!

 

I am spoiled in sunny los angeles, but I am up in Mammoth now on a trip for a few days. This is the first time my Prius has been in the snow, and I bought her in Dec of 07. The mpg does seem to get a little lower, and I need to remember to check the tire psi.

Has anyone noticed clicking sounds when tapping the brakes? The temp is about 20-30 degrees here and this is the first time I have heard those types of sounds

 

I would like to be able to see the expressions on the faces of the rest of us "Northerners" at this question!

My guess is that you encountered some slippery conditions and your anti-lock brakes engaged for the first time. The sound simply is evidence of the braking system in action.

Thankfully, I don't hear it that often, but it is reassuringly loud when I need the assistance.

 

Evan,

Are you suggesting (is it fair for me to infer) that we will get better performance out of the HV battery by heating up the interior? If so, how does the efficiency gain/loss compare to the "cost" to heat the cabin during the first 5-10 minutes of driving during a cold winter day?

 

I'm with you on that one. My only problem is that I tend to do this even with passengers in the car. It isn't a problem for me to have no heat (until we get down to really cold temps, like 5 or 10), but most people kind of expect heat in a car!

I don't have your extra gauges, so I don't know how long it takes to get to that temp. If I'm going to turn on the heat, I won't typically push the button until I have two 5-minute bars showing (one if it is REALLY cold).

I just completed two such trips in the past four days, and I tried one with the heat full-out (auto set at 70!). I didn't see that the heat setting had any bearing on MPGs (highway driving) for the long haul. In fact, use of the cruise control tended to have a much more noticeable drag on MPGs than have the heat on Auto at 70.

 

I use a EBH and a Coupe warmer(1300W)
I do see a rather big difference on the first 5 minutes on the MFD bar when I have both connected for three hours before I drivo off to work.
It also kinda gets rid off the whole need for the heater on my 15 minute drive.
Oh, and on a side note, the electricity used is from a totally renewable source.

 

I can report similar highway observations. A recent highway trip with a starting battery temperature of 32F and the cabin heat running (not normal for me) in the low 70s showed battery temperature still at 32F after 30 minutes.

On the other hand ....

If a trip provides opportunities for regeneration and electric-only propulsion (after ICE warmup), no question the battery will warm more quickly. It still isn't this quickly, however. On some of our coldest days this winter where the battery has started out in the low 20s (F), it might have been 20-30 minutes into the (urban) drive before I could get the EV switch to work, generally around 35F.

Here is a related thread.