Heavy Traffic Draining Hybrid Battery

I sacrifice mpg during heavy traffic and allow the ICE to kick on when going slightly uphill to keep the battery charged. Sometimes that can be a challenge. I usually pulse the battery when going slow and then coast when possible. The whole point is mpg while trying to save battery power. Impossible in some situations.

 

This is normal. There are two things that happen. First, you can, and probably were, using battery-only to creep forward. Using the engine to provide a stronger pulse forward might be better. Second, the hybrid battery provides all power for the car's electronics, A/C, headlights, and keeping the 12V battery charged. Even when not moving, the hybrid battery is being drained, and the computers will only let it drain so far without taking action. There are only two ways to keep the hybrid battery charged up: regen braking, or running the engine. Regen braking is basically non-existent in creep-forward traffic, so that leaves running the engine. If the engine is running to charge the battery while forward speed is very low, MPG suffers.

 

Those are exactly the type of traffic conditions where plug-in's and full electric's are going to be an awesome advantage. Sadly though as you've found the normal Prius just doesn't have the battery capacity to deal with an extended traffic jam situation. For the first 5 minutes it's just brilliant, but once you're down to 2 or 3 bars SOC the engine's going to come on pretty much every time you move.

I have a few situations where I can stay in full electric mode in small traffic jams. Like getting in and out of a congested shopping center car park and that type of thing. I also have one small traffic jam where I regularly have to queue on a minor road before getting onto a freeway on-ramp and I travel about 400 yards in about 5 minutes. That one's always full electric.

About the only strategy you can attempt in an extended jam is to try to "ration" the battery power as GWS suggests. A very small amount battery power can go a long way at low speed if you're on flat or slightly downhill terrain. But if you're trying to push up a hill on battery you can drain it all in half a minute, even at very low speed.

What we want to do is to make the best use of the limited battery power to keep the engine off as much as possible. So if you suspect the jam will be too long to completely negotiate in electric mode then try to ration it by only using it where you'll get the best bang per watt, and that's on the easiest flat and downhill sections. If you're trying to pull up hill then hit the go pedal hard enough to force the engine on and save the battery for the easier terrain.

 

CBB, Tony meant that there's nothing to be done about it. It's completely normal. The same thing happens with conventional cars, it's just much less obvious, and of course they don't ever get 100+ MPGs.

 

Yes, it is normal, and yes it can be avoided. Move somewhere lacking heavy traffic.



Tom

 

Slow moving, stop-and-go traffic is ideal conditions for electrical propulsion. If you use a light touch each time you start rolling, you can completely avoid using the gas engine.

The car is designed to do this on an intermittent basis. But with an ongoing stagnation in traffic, stay in "EV" mode long enough, and you will eat up your charge. It's not totally bad: you'll run out of charge, but get great mileage until that happens. Depends on how long the traffic jam lasts. Anyway, if it's looking to be a protracted slowdown:

I'd suggest: accelerate gently at one start-up, ie: keep it in EV mode. Then on the next start-up, accelerate more aggresively, purposely to kick the gas engine on. This will extend the charge, maybe even recharge some, and be closer to normal behaviour for the car.

 

Get a plugin kit, then your battery won't go down

 

I do this as well. It also keeps the engine warm so you don't encounter a secondary warm-up penalty.

 

well, it will still go down, but it will take a lot longer to reach bottom!

 

As everyone else has stated, this is normal.

Just wait until the weather gets hot enough where you have to use the AC.

The battery will drain VERY fast in comparison. I posted about the draw w/AC on at http://priuschat.com/forums/gen-iii...significant-drop-in-mpg-ac-2.html#post1149705. I monitor this via the Bta XGauge (http://priuschat.com/forums/gen-ii-...list-gen-ii-xgauges-scangauge.html#post950412) on ScanGaugeII - Trip Computers + Digital Gauges + Scan Tool.

 

Try to drive at the average speed of the traffic. No stops. This will get the most out of your battery, and maybe make the traffic better as well.

 

Extended period stop-and-go, low speed traffic -- less than 20 MPH or
so -- is a MPG killer, no way around it. However, you will most likely
be getting better MPGs than the other folks so afflicted... a small
consolation at best.

Theoretically, all things being perfect , the Gen II is
capable of ~100 MPG at 20 MPH. (Let's be clear here, this is well
beyond my modest capabilities.) Like it or not, the HSD much prefers
the HV batery SOC to be ~65%. When it's lower, like when you're using
EV in slow traffic, the HSD is doing all kinds of behind the scenes
skullduggery to get it back up. With a ScanGauge, you can see the ICE
being run at overly high RPMs to recharge the HV battery... MPGs
plummet. Drat!

There is some latitude in the ICE algorithms for driver intervention
however. This involves one of the scant few times when an after-
market EV swith for the Gen II can be a useful tool.

The scenario goes something like this (presumably the car is fully
warmed up and in S4, " idle check" completed.):
* Let a space develop in front of you as big as traffic will allow.
* Accelerate "briskly" up to 20+ MPH.
* Use the EV switch to go to ICE-off.
* Go into "no arrows glide" to close the gap, trying to "drive without
brakes."
* Repeat as necessary, or traffic, or your patience/attentiveness
permits.

(You can save a small amount of SOC by shifting in and out of neutral
as well. Remember that you don't get any regen when braking when in
neutral. This is a very difficult sequence to pull off successfully, over
and over again.)

It's a fun exercise up to a point. It's like juggling 4 balls while wearing
boxing gloves...

However, safety and courtesy should always be your primary motivations.

 

If everyone did that, then there wouldn't be any place lacking heavy traffic.

 

I get my best fuel economy in this kind of traffic, but rather than inch forward using the battery, I wait until there's a enough distance between me and the car in front and then gas it enough to use the ICE for a few seconds without any arrows going into or out of the battery.

The caveat is that in cold whether this can be a challenge as the drive cycle can kick out of S4 and drop down to S3 resulting in the ICE running just to warm it back up.

 

Turn the heater off and it won't re-start the ICE until you move

 

I feel your pain. My commute to work is about 5 miles and in the two months I have had my Prius I've averaged about 30 miles per gallon. Of course my average speed during that span is 10 miles per hour in the stop and go traffic. My battery has never been fully charged and usually starts off at two bars. It's gotten close but never full. I've learned to accept it. Leo

 

What I said applies when the heater is off. I never use the heater in stop and go traffic.

 

You folks are talking about how to save gas in a traffic jam.

I had this experience yesterday, caught in a bumper to bumper jam for 30 minutes, and believe me, I wasn't thinking about saving gas. I was thinking about being stranded with a dead battery! I've had this happen to me twice now in 3 years. The battery drained down to two blue bars, and I was praying for the gas engine to come on.

The point is, does the ICE automatically come on to keep the battery from draining dead?
That's a crucial point, it seems, and my dealer will hear from me Monday morning about that question, if I don't see a response here before then. It has probably been covered in other thread for the GenII. Thanks.