HV Battery Pre-Heat... Anybody tried it?

[Rokeby]

HV Battery Pre-Heat; possibly an overlooked cold weather FE/MPG tweak.

This thread is an attempt to give stand-alone visibility and direct access to
an idea that was embedded in another more general thread. I'll begin by
extracting, and editing for brevity where appropriate, the relevant posts.

Originally Posted by Rokeby

The HSD integrates two power sources the primary being the ICE, the
secondary being the HV battery. Most discussions of maintaining high
FE/MPGs in cold temps invariably include a recommendation to install
an EBH to "preheat" the ICE. All well and good as far as that goes.

But what about warming up the HV battery? I can't remember it being
recommended too. It would seem like a logical next step. And on first
consideration, relatively easily done with some sort of electrical warming
pad, foot warmer, etc.

Or have I missed something... really long warm up time... fire danger... ?

Originally Posted by JimboK

I seem to recall someone suggesting it... And of course, as opposed to the
designed-in capability for an EBH, the car isn't made for it. Many unanswered
questions: What would one use for a heater? How to plug it in? How much of
a pain to install and use? How to keep it safe? Any unanticipated side effects
on battery chemistry or function? Would the fuel savings offset the cost to run
it? Would the fuel savings offset the hassle of installing it and using it on the
few occasions it's really needed? Etc.

On the other hand, if someone wants to experiment on their own car and then
can document safety and effectiveness, I'll consider anything that boosts my
fuel economy by 0.002783 MPG.

Originally Posted by Fred_H

Hi Rokeby, you might find this interesting:
http://www.nrel.gov/vehiclesandfuels...-633_sw_ap.pdf

Originally Posted by Rokeby

...So, the answer is yes, preheating HEV batteries to room temperatures can
make a significant contribution to efficient charge/discharge at very cold
ambient temps. The most efficient method to preheat is direct application of
high frequency AC to the battery terminals. No way I'm doing that!

But there is the suggestion that by preheating with hot air through the
cooling duct will work, although with major inefficiencies. I guess preheat
could be done with a hair dryer... probably a significant fire hazard.

But there is still the possibility of contact heating with a heat pad, etc...

Originally Posted by Fred_H

Good morning Rokeby,
I think the most important thing to keep in mind is that it's important to
keep the temperatures even within the Battery. Uneven temperatures are
bad for the battery.

I would say that we can rule out attaching heat pads to every single battery
module, for most do-it-yourselfers. Using a heat pad on the outside of the
battery pack would probably result in uneven temperatures unless special
measures are taken. For example surrounding the battery completely with
heat pads and heating it very slowly for many hours, or circulating air to
distribute the heat more evenly.

Which brings us to the air heating method. Of course, the Prius already has
a good air circulation system for the battery, so we could just push some hot
air through it. But simply hooking up a forced air heater to one end would be
very inefficient, because most of the heat would be exhausted into the
atmosphere at the other end.

If you could figure out a practical way to recirculate the air without danger
of overheating, then I think you could build a halfway efficient battery
preheater. You have to make sure that air can not bypass the battery
through the heater or recirculate to the battery when the battery needs to be
cooled.

I have thought a little bit about this before, but soon realized that on my
wife’s daily commute, the benefit would be minimal, because the first part
of her route requires no significant battery power, and by the time she gets
to the part that does, the battery is sufficiently warm from the cabin heat.

But for people who start their commute with a long city drive in very cold
temperatures, I can imagine that a preheated battery could make a
significant difference.

If there’s not already an old thread about this somewhere, maybe you could
start a new battery preheat thread in the technical discussion section?

For HEVs battery preheat is not really necessary, but for the upcoming
PHEVs, it will be important, and for BEVs battery preheat will be crucial in
cold weather.

Originally Posted by Rokeby

... I now believe that a recirculating warm air system would be most practical.

Most likely, the system would use a 120V AC fan and heating element.
It would require tapping into both the supply and exhaust sides of the HV
battery ducting, and perhap using the cabin as part of the circuit -- some
synergy there; preheating the cabin would tend to cut down on the interior
windshield icing issues some folks experience. All this is not impossible, but
daunting nonetheless...

Ok, that's the introduction.

Once again, has anybody tried something like this? If so, any pics? Any
comments, suggestions, dire warnings are welcomed.

As a preliminary concept, I'm thinking of something that would have maybe
100-200 watts heating output, enough to get ~75 degF air, and a small muffin
fan to move the air through the existing battery cooling ducting. It would be used
along with a electric block heater EBH for two or three hours before start-up on
cold mornings.

I'm still hunting around for some pics/drawings of the HV battery and the
associated ductwork, especially on the exhaust side. When I find something,
I'll post it.

Of course, if you have something ready-at-hand, your posting it is welcomed.

[statultra]

My 2001 Prius has a issue where the battery gets hot and the fan stays on almost all the time, ( i live in florida ) the gas mileage is pretty amazing to say the least, hopefully one day when I drive it ill post a video of my speed vs mpg

[Celtic Blue]

From what I gathered in the recent regeneration discussion the best way to preheat it is probably to charge it--as in plug in charging. It would seem to be considerably more efficient than external heating.

An ideal system would do this on some sort of timer. It would be nice to hit a switch and start a warm up sequence (perhaps running the car's electric heater and blower as well to warm the interior.) After ~5 minutes, disconnect the plug, start the car and drive off with warm interior and happy battery.

[Flying White Dutchman]

yes
this would be nice

[PaulHS]

Somewhere on PC is a thread (not found by search) where a guy had posted an arrangement (with pictures!) in which he placed a flat yellow heating pad of some sort on top of the battery pack. Don't know how he powered it. So it has been done and reported here.

I had bought a small ceramic heater intending to install it between the grille and the radiator to provide additional heat to the engine. But since the weather is too cold to be tearing apart the front of the car, I've gone with a more low-tech setup. The electric heater sits on the floor on the front passenger side of the passenger compartment facing the driver's side. The power is adjusted to about 600 watts and the power cord is fed out the passenger door. Closing the door leaves the cord snug but not overly tight. I run an extension around to the grille where the EBH plug is located. Power is fed from the EBH timer to a double socket to the EBH and to the ceramic heater so that both turn on at the same time.

The primary purpose here is to pre-warm the passenger compartment. This way the ICE does not need to provide heat for passenger comfort. This works surprisingly well. On 25 degree F days, on my 8-mile commute, the passenger compartment stays toasty without turning on the console heater at all.

Secondly, the preheat will melt frost or light ice which may have accumulated on the windows overnight. And seriously, if this were the only benefit, it's well worth not having to scrape the windows.

Thirdly, I believe that, as a bonus, the circulating heat provides some warmth for the HV battery, though I have taken no measurements yet. Efficiency? No idea. But it's great to step into a warm car in the morning!

[Flying White Dutchman]

i think the energt lost in heating the pack is more then just keeping the charger cycling a charge to the battery pack!

so maybe just charging it during the night and when its full let the charger connected do the moment it just drops a little bit the charger begins charging again!

then the energy is not a total loss

[Celtic Blue]

Originally Posted by Flying White Dutchman

i think the energt lost in heating the pack is more then just keeping the charger cycling a charge to the battery pack!

so maybe just charging it during the night and when its full let the charger connected do the moment it just drops a little bit the charger begins charging again!

then the energy is not a total loss

The key is that charging the pack should be part of the warm up sequence...prior to actually starting the car. Keeping it warm all the time makes little economic sense to me as it is wasting electrical power. But using the grid to warm the battery just before driving makes good sense.

[Rokeby]

Shawn Clark and Flying White Dutchman,

Thanks for your posts. But, I have a sense that you guys are going off in a
different direction with the charging and heating idea. Interesting, but not
readily do-able on a garden variety Gen-I or Gen-II car.

I'm hoping to get info/ideas on HV battery warming ideas that are doable on
the cars and HV batteries that we have now.

[firepa63]

Originally Posted by PaulHS

... I had bought a small ceramic heater intending to install it between the grille and the radiator to provide additional heat to the engine. But since the weather is too cold to be tearing apart the front of the car, I've gone with a more low-tech setup. The electric heater sits on the floor on the front passenger side of the passenger compartment facing the driver's side. The power is adjusted to about 600 watts and the power cord is fed out the passenger door. Closing the door leaves the cord snug but not overly tight. I run an extension around to the grille where the EBH plug is located. Power is fed from the EBH timer to a double socket to the EBH and to the ceramic heater so that both turn on at the same time.

The primary purpose here is to pre-warm the passenger compartment. This way the ICE does not need to provide heat for passenger comfort. This works surprisingly well. On 25 degree F days, on my 8-mile commute, the passenger compartment stays toasty without turning on the console heater at all.

Secondly, the preheat will melt frost or light ice which may have accumulated on the windows overnight. And seriously, if this were the only benefit, it's well worth not having to scrape the windows.

Thirdly, I believe that, as a bonus, the circulating heat provides some warmth for the HV battery, though I have taken no measurements yet. Efficiency? No idea. But it's great to step into a warm car in the morning!

I hope the fire station is just around the corner...

[PaulHS]

Originally Posted by firepa63

I hope the fire station is just around the corner...

What exactly is your concern? Or is this just a smart alec remark?