Right ON!

How can anyone say heating the NiMH battery in 90F degrees weather increase the charge to jump start the engine. The reason I'm getting over 60mpg tanks right now is because the Aux HV battery A/C is maintaining the battery temperature in 90F degree weather, which makes the battery more efficient. Sure, the A/C compressor puts a load on the engine, but the OAT at 90F makes the engine more efficient.

The last two Winter MPG Challenges at http://www.cleanmpg.com/ I won over every hybrid and gas vehicles entered for that matter, because I know HV battery management. A hot HV battery must stay cooled to ~77F degrees to stay in peak performance. Heating the HV battery over ~77F degrees reduces efficiency. I see that every day in both my FEH's while hypermiling. This was one reason I didn't purchase the '10 FEH or FFH because their is no longer a Aux HV battery A/C. My understanding is the new Focus Electric Li-ion battery will have both cooling and heating systems to maintain temperature for efficiency. I bet the new Ford plug-in battery hybrids will have a similar system. Bill Ford just said by 2020, 25% of Ford's made will be Electric and Hybrid vehicles. The HV batteries must be designed with battery temperature control systems for both hot and cold weather.

Thanks for doing the Jump Start testing to prove our point!

GaryG

 

Yes, battery CAPACITY declines with rising temperature. But that fact does not address what happens to the battery's current SOC, or lack thereof, as it is heated.

Only an idiot would believe that battery SOC can be raised efficiently via heating. Just look at the MASS that must be heated vs the ease with which the SOC can be raised via a DC-DC inverter, 12 volts to ~300.

 

I don't understand how the jump starts raised the high voltage battery voltage so much without increasing the temperature or the state of charge. I watched the temp when I drove away and it didn't go up but I noticed the SoC bounced around for a little bit and might have ended up higher than when I started, which I've never noticed before. It usually changes pretty smoothly so something definitely happened from the two jump starts.

 

First, think about how long, or how short really, a non-HSD I4 engine of this displacement's 12 volt starter motor must tyically be engaged for starting. 12 volts at, say, 100 amps (1200 watts) initial current inrush, for maybe 2-3 seconds.

That's the level of watt/second energy the HSD must transfer from the 12 volt battery to the HV battery.

"..I don't understand how the jump starts raised the high voltage battery voltage so much without..."

A fully discharged battery will present a fairly rapid rise in terminal voltage when charging due to the initially high internal resistance.



Since the terminal voltage of a fully discharged battery changes only slightly initially during charging I would be surprised if the voltage derived SOC rose.

And a measureable temperature rise in the bulk/MASS of the HV battery during the transfer of that small amount of energy, just NOT.

 

So the block heater for the HVB exists in all FEH? I though that was only activated with the engine block heater. That would make sense. Anyway, thanks for checking.

 

[quote=FjordHybrid;235363]

However, I did two jump starts and saw the following:

SoC did not change at all. Battery temp did not change at all. HV Battery voltage changed, going from 328 to 338. 12V dropped from 12.7 to 11.7. quote]


What was your SOC and HV battery temperature prior to the first jump start?

 

[quote=Billyk;235392]Prior to the first jump start I wrote down SoC=45.9 and Tav=68.0. The other battery temp xgauge doesn't display anything on my 08.

Over the weekend I did another jump start and saw something interesting. I started with SoC=46.2, Tav=78.6, HVB=332, and VLT=12.9. I did a jump start without a charger and noticed that when I put the key back in (but not starting the car) after the jump start button stopped flashing that for a sec HVB was 335 but started dropping, as did SoC which started at 46.2 but then started dropping. The VLT was briefly 11.3V then jumped up to 13.9 and stayed there. I realized after a second or two that the HV battery was charging the 12V battery. So I think I agree with rperla that the jump start works but you need to have a charger connected or it will kill the 12V battery pretty quickly, which means it's sucking a lot of juice from the 12V battery.

 

[quote=FjordHybrid;235492]And just how many times, where, when would it be that you would have a charger available when a JUMP-START is most typically required.

No, the EXPECTED practice would be to FIRE the ICE immediately after the "jump-start" period expires.

It is highly likely that the jump-start procedure is designed, in extreme cases, to draw the 12 volt battery down to an absolute minimum in order to get the HVB up to a SOC high enough to turn the ICE over. Given that all the solid state components that the 12 volt battery must supply power to during the ICE "cranking" period really only require 5 volts that absolute minimum might be in the range of 7-8 volts.

 

Think of it as a plank and fulcrum device
that is 332 + 12 long or 344. Your trying to
push the long side up by pushing down
on the short side. That will take a lot
of energy. Plus, all electronic systems
are not 100% efficient. Your gonna have
some loses there. Figure 50% loss of
energy.

 

"..figure 50% loss of energy..."

No, more like 5-10% loss for modern day PWM, "switching" type solid state inverters. Inverter input of 12 volts at 30 amps, 360 watts, gets you 330 volts at ~1 amp, 330 watts HV charging rate.

And when it comes to initial ICE starting, turning over, the fulcrum is pretty much centered, with the advantage on the HV side if any.