Charge pumping on the Mohawk trail with the prius prime

Speaking in broad generalizations, HV mode tries to maintain the battery charge.


iPhone ? Pro

 

As for calling this "charge pumping," two thoughts:

First, "charge pump" is a term for a certain general type of DC-to-DC converter circuit -- essentially the DC equivalent of a transformer for AC.

Second, on my Gen-2 Prius, I refer to nonchalantly (not!) driving in very-cumbersome ways trying desperately to prevent computer from turning on the engine, "battery surfing"! Perhaps this is an ever better application for that term?


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I don't have hills here but I use this same method (switching from HV to EV when applying regen braking from high speeds and then back to HV) on highway drives in my Energi. I call it EV banking.

 

First off, kudos for being curious and performing the experiment:

The initial drive to the New York border shows what we call in the BMW i3-REx world, "charge sustainment mode." Once put in HV mode, the car tries to keep the battery SOC at a constant level. But in an area of tall hills, there can be a substantial change in battery charge that averages out.

You noticed an increase in battery charge on the return. I would recommend using Google Earth to measure the starting and ending altitude of your drive. In my case, I used "Brindley Mountain" (34.518141, -86.593270) a 525 ft (160m), 8% grade, 1.5 mi section of US 231. Climbing at 55 mph, I burned ~0.08 gal. and on the descent, added 6% to the traction battery. But you've suggested an interesting experiment:

• Climb at 55 mph on 0% battery
• Descend at 55 mph to gain 6%
• Park car and READY cycle
• Repeat

If the 6i% is maintained climbing the hill, the descent will add another 6% to bring it up to ~12%. Of course it might be easier just to use the 'charge mode.'

Bob Wilson

 

My PiP does the same. We don't have hills here, but we have lots and lots of opportunities to slam on the brakes from 60 mph. I sometimes switch to EV as I'm slowing and then back to HV. I can gain 2-3 miles of range in about 15 miles of travel that way. I call it ratcheting the battery voltage. I haven't decided yet how much it actually helps. I suppose there are lots of possible terms for the effect. I wonder if we'll ever come up with a standard term.

 

What you are suggesting is cycling between EV and HV can be used to trick the charge holding mode to racket up the SOC. Interesting idea.

Bob Wilson

 

It definitely works for me, but as I said, I haven't tried to figure out if it is really any advantage in the long run since the energy you store while stopping isn't all available once you're back in HV. Then again, the car does not have a problem with borrowing from that stored energy when it needs to, so maybe it is a net gain. Finding out would seem to me to require a predictable and repeatable set of circumstances. Something I can't do in the high traffic random stoplight environment here.

 

That's exactly what it does. I use a scangauge in my Energi and see I usually pick up 2-3% SOC during each stop from high(er) speeds. The trick is to not forget to switch back to HV. Depending on conditions, I can usually pick up 4-6 miles of range during my 80-90 mile out of town trip. I use those EV miles once I reach my urban destinations where they are most efficient.

Now the question is: would that regen energy be better used (most efficient) for blending in HV while still on the highway or ascending hills vs banking that surplus for pure EV driving at slow speeds.

 

Yup! I wonder the same thing. Sounds like just the kind of experiment @bwilson4web might enjoy. I know I'd enjoy it if I had a good place to do it and a day or so to play with. The only place around here where I could have repeatable conditions is my local neighborhood with 20 mph speed limits. Not very "real world."

 

I strongly suspect it only averages out if your starting and ending points are at the same altitude.

 

It would really help if Prime owners would post the mileages obtained using the various surfing/banking/sustaining modes. While using and charging the battery is important, it is the actual mileage changes that the various modes cause that determine their usefulness. Keeping a certain charge level in the battery is not necessarily the best high mileage strategy.