I understand that activating the button in the footwell of the FEH uses the 12v battery to warm the HV battery, thereby increasing its ability to provide power. Since the optimal battery temp is 82 F and having the ability of the HV battery to accept as well as deliver power is an important factor in optimal hybrid performance would there be any advantage to using this function routinely during cold weather operations?

Thanks,
DavidH

And greetings from the burbs of Seattle!

 

Hi David,

Good question, but I don't think the jump start feature would work that well if the battery was not low enough to accept the charge as it would with a low enough battery that could not start the FEH/MMH ICE. Also, a cold battery does not accept charging that well anyway. After starting and dumping the 12V battery, the high DC to low DC converter would need to replace that 12V battery energy quickly from the generators and HV battery.

At any rate, if you leave your HV battery low when parked, the small generator will still heat up the battery during warm-up of the ICE. If my temp here is in the low 50F, the battery will not accept regen in addition to the small generator anyway, till things warm up.

Bottom line, I would not even try it unless I had a HV battery that would not start the FEH/MMH and had no choice.

GaryG

 

Where did you hear this? You can use the 12V battery to charge the HV battery to start your vehcile using the charge switch should you deplete the HV battery and can't start up, but warming it? That's the first I ever heard of doing that.

 

It was on a forum here where this function (warming) was mentioned. If I understood it correctly the jump function doesn't transfer power from the 12v to the HV battery but merely warms the HV battery, thereby allowing it to deliver more energy for starting purposes. I was inquiring not about using the function as a last ditch effort to start a cold depleted HV battery but as a means of getting a cold battery warm ASAP to facilitate optimal FE. I'll look for that forum and give you a link to it if I can find it again.

Regards,
David

 

I've never heard that and I think I've read every thread on here. The closest thing I could imagine to that may have been someone mentioning that as a side effect of the "jump start" the HV battery would be warmer...just like charging any battery warms it up. And another thread talking about how a warmer battery gives off more energy than a cold one. Perhaps a mental merger of two ideas???

 

No he's right.. somewere else in the forum someone has stated that the effect of that switch is to warm the battery not to charge it. I think its in one of the threads on engine block heaters. I don't know if its true or not but someone has posted that "fact"

 

Two things:

#1 The "jump start" button is not even "active" unless your HV battery is below some preset, very low level. Thus you can not warm a "normal" battery, only a nearly dead one.

#2 It sounds counter-intuitive, but in workshop manuals and wireing diagrams, no "step-up" voltage converter can be found anywhere. The DC/DC converter acts as an alternator would, and converts 330v to 14.2v to charge the 12v system. There's no mention that I can find that it works in reverse. However, there is explicit mention in the shop manuals that the "jump start" button warms the HV Battery. Anyone can try this: Put your cell phone battery in the freezer and it won't run your phone. Warm it up in your hands, and it will work again. Did your hands "charge" the cell phone battery? I think you'll agree not. I'm guessing here, but I 'think' the jump start button provided resistive heat to the HV battery pack. The manuals state that your 12v battery should have enough juice for two, 8 minute cycles, but will be nearly depleated after that. I've tried to recharge the HV battery via this route, and it doesn't work. I've never had my HV battery low enough for the button to even activate.

-John

 

How do you know if it is activated John? My FEH stays in my unheated garage so probably didn't get below 35-40 F even in our big freeze here in Seattle last night. When I pushed the button the LED came on and was off when I came out to go to work 10 minutes later. Is there some other indicator other than the LED coming on to say if it has in fact started the warming cycle?

FWIW my 9.6 mile commute had a sub-par MPG on the scanguage. I only have 2K miles on my 07 though and am still learning as well as still breaking it in.

Regards,
David

 

No. There is no "indicator" nor reference in any manual.

I just learned through experimentation with volt and amp meters that repeated button presses did absolutely nothing when parked in my garage at about 40'F.

After 2 hours time, and 8 or 9 "cycles" of 8 minutes each, my HV battery did not improve, and my 12v battery did not go dead.

I doubt many people have done this, so if you wish to duplicate this experiment and see if it turns out the same for you, that would be nice to know.

-John

 

John, where is it stated in the workshop manuals that the 12V jump start button warms the HV battery? I'm sure that dumping the 12V battery charge into the HV battery in 8 min. would have some warming effect, but I couldn't find it in the manuals. Also, you must have overlooked the section that says there IS a low voltage charger that is used during the jump start proceedure. It is contained within the HVTB itself (page 414-03-2 of volume 2).

David, the reason the indicator light on the button went out when you returned to your vehicle after 10 min, is because after 8 minutes, the indicator starts to flash rapidly for two minutes and it then goes out. More than likely, your battery didn't need or could accept a rapid 8 min charge the way the system is designed. Again, a low battery can take a much faster charge. A cold charged battery takes a charge much slower. Anyone can test this out by checking your instant MPG with your econ reset or navi average reset from a low battery till it recharges. Simply reset with a low battery and watch the ICE increase MPG as the battery fills up. The small generator will slowly back off generating power and the ICE will get better mileage as the battery gets full.

Also, I've had first hand experience with a very low (below 40% SOC) battery when I ran out of gas with a low battery SOC and drove a distance further in EV on I-95. My FEH still had enough juice to start, but the small generator was pouring such a fast charge into the HV battery that regen could not add any more at the same time when I fake shifted. I'm sure the design of the Jump start button is only good for a jump start when you need one. Your not going to heat the battery with a 40% SOC or higher I would not think.

GaryG