Yeah your right, I had forget the thread was talking about plug in vs say a FEH, sorry about that ..I was just thinking about standard FEH...what would it do with more battery capacity? Would that equate to higher mpg?

 

This is a great question, and also important to know what happens to mpg when the battery pack capacity is reduced.

For costly components or developments in a product design, it is common to select a (lower cost) component that covers 80% of the need.

This may be the case with ourt batteries!

 

A fully charged Ford pack has about 2 useable miles of EV.
If you stacked two Ford packs ( which wouldn't be exactly easy due to all the communications wires, not just the power wires... also the car is probably not going to understand all of a sudden having twice as many battery sensors, etc... ) you could get 4 miles. If you pluged one, or both in, they would charge in a couple of hours. You would see a slight increase in your normal driving MPG. I'll estimate 3-6 MPG more over short trips... then it would taper down to what you get now, if you have mostly flat roads.

If you live/drive in mountains or hills, here is where you would get 3-6 MPG better ALL THE TIME. With 4 miles of "juice" for the uphills, you would also have room for 4 miles of "juice" on the downhills. If you don't have downhills to use the Regenerative brakes on, then the extra battery is not much use to you after the first 4 miles for example. Plus you will have extra weight all the time.

A larger pack without the plug-in will not give you much boost in MPG if all the recharge comes from gas. You'll see a little gain, but the gain cannot be offset by the cost.

Plug-ins get 100+ MPG because you are recharging with grid power, and use zero gas to recharge the battery. Our FEH always use gas ( just in an efficient maner ) to recharge the battery. -John

 

One major thing is the software is MUCH different. With a higher battery capacity and a wider state of charge range they use a depletion strategy until the battery gets low then they switch to sustain mode like our FEH's. This means the ev is stronger and is used in hybrid mode (ICE and electrics combined) much more, until the battery is drained.

Also dont forget it still needs about $2.00 - $3.00 in electricity to fully charge a battery. So if you used a gollon of gass to go 140 miles and depleted your battery it would really be like 75 to 90 mpg in cost. Still pretty good.

 

I talked with the designers of one of the (Canadian) plug in hybrid companies. Their piggyback battery is connected to the 300V power bus using a virtual diode (FET). That means the charged up piggy back battery provides current to the bus until it's voltage drops below the voltage of the standard FEH battery pack. The diode keeps current from the FEH battery pack or the FEH generator from feeding back into the piggyback battery.

THe designer said they do not modify any software or electronics on the FEH, they only connect the piggyback battery. And the charger only charges the piggyback battery.

 

[quote=DavidH;158260]I talked with the designers of one of the (Canadian) plug in hybrid companies.
quote]

Is this Hymotion? A well known poster raised the question of safety with the piggyback design. I understand it is tucked behind the rear seat when they are up, but what happens if you need cargo room and want to flip the rear seats down?

 

I also heard Hymotion has abondoned plans to make packs for the Ford Escape. Their web page still mentions the Prius.

 

Yes, Hymotion. I talked to one of their designers in April 07.

 

Thanks, gpsman1 and PravusPrime for setting me straight. I stand corrected. : )