Running on Electric Motor

Yes it will run and, depending on the SOC, it may be a mile or so.

DO NOT consider this to be a "lifeboat" in case you run out of gas. This is BAD for the battery.

 

Yes, it will, but the length entirely depends on the SOC of the battery, current speed, and terrain conditions. The most you'll generally get is about a mile of EV.

Keep in mind, that doing something like this will drain your battery a lot, potentially lower than it would like to go, which may cause problems with longevity - the best bet is to just stop where you are when your gas runs out and call AAA.

 

<div class='quotetop'>QUOTE(eagle33199 @ Oct 30 2006, 12:16 PM) [snapback]340751[/snapback]</div>

Ya know, I doubt this to be true. I've done a lot of research on batteries lately with an eye towards doing some battery mods. One thing I discovered is the supposed fact that the Prius (and other hybrids too, presumably) only use about 33% of their battery capacity. Doing this makes sense for several reasons (which is why I believe it):

1) Rechargeable batteries lose capacity over time, and by using such a small amount to begin with allows the batteries to "wear down" over time without you noticing because of the spare capacity.
2) Ni-MH batteries are prone to "polarity reversal" if drained completely empty. This happens when one cell in a pack drains before the others and starts drawing power from the neighboring cells to recharge itself. In doing so, the cell effectively reverses polarity, potentially damaging the entire pack. To avoid this, you never want to drain the batteries completely dead.

Using only 33% of the capacity nicely takes care of both problems. I don't think it's possible to drain them lower than that, the electronics won't let you. So, I doubt running the battery down (on the SOC anyway) will cause any long term effects, though there's only one way to be sure.

 

<div class='quotetop'>QUOTE(Mr. Zorg @ Oct 30 2006, 12:46 PM) [snapback]340825[/snapback]</div>

Did your research include any of the horror stories of people who actually ran their cars as far as possible on battery?

Several years of reading these "Out Of Gas" posts lead me to believe otherwise. This is not only a longevity issue, it can also affect the fuel pump. Some people have ended up with some expensive repair bills to get their Prius back on the road after running out of fuel.

It just ain't worth it, just fill up at 1 or 2 pips and you won't have to worry about it.

 

<div class='quotetop'>QUOTE(efusco @ Oct 30 2006, 02:37 PM) [snapback]340882[/snapback]</div>

I would imagine that those 40% and 20% SOC levels are relative to the 33% overall capacity. If the SOC measures the "usable charge", not the full battery capacity, that would equate to thresholds of 19.8% and 26.5% overall. If that's true, that's well within any safety tolerances. Is there evidence to the contrary? I'm not sure how we could know for sure, and I'll wager Toyota won't tell us.

 

The 20% figure comes up because the traditional thinking appears to
be that a "safe" range for NiMH was 20 - 80 % of charge range. It
is what the controllers in the Insight allow, for example. Toyota
seems to have decided to carve a bit off the bottom of that in the
interest of longer-term cell chemistry life, limiting safe discharge
to 40% instead, probably on several industry-experience cues that
maybe 20% is pushing it just a little too far. That's one reason
Insights are forever having the dreaded "recalibrations" all the
time after the battery is pushed a little bit -- the controller is
sensing a steeper voltage dropoff, possibly coming a little too
close to reversing a cell for comfort, and frantically resets the
condition to "empty" and does a full charge cycle. At the expense
of a lot of MPG.
.
_H*

 

The original poster said he wouldn't allow his car to run out of gas, but as the discussion has taken that tract...

The traction battery in the Gen 2 Prius is a series connected set of 168 NiMH cells. There are 28 sets of 6 cell modules.

The cells may be matched (I would expect they are anyway), for equal capacity. The modules may be coded to indicate this.

Discharge:
Whenever you deal with a series string of NiMH or NiCad cells, you have to worry that the lowest capacity cell will be completely discharged before the others. That is why they are matched, although the matching isn't perfect, and cell capacity will change with age, and not all cells will age the same. If one cell discharges first, continued discharge then charges that cell backwards. This can happen to more than one cell at a time. If allowed to occur repeatedly, this will quickly result in a nickle "whisker" shorting out that cell. With 168 cells it would be hard to tell this is happening, just watching the battery voltage. You COULD tell by watching the pack voltage of each of the 6 cell packs. My experience with hand held two way radios is once you start to reverse charge a cell it is damaged beyond repair and must be replaced, as even if you "burn out" the whisker, it will quickly regrow.

Charge:
When charging, you will also have a problem with the lowest capacity cell(s). They will charge up first, and with 168 in series, it will be hard to detect this happening. When they do charge up before the others, they will then be overcharging. NiMH cells charge well up to about 80% capacity, converting a large percentage of the power to chemical charge, then they start to convert a lot of the charging current to heat. This is why the chargers for commercial packs will switch them to "trickle charge" at about 80% charge - most often detected with temp. sensing circuitry - the pack will start to heat up and so is switched to trickle.
Anyway, the lowest capacity cells will be overcharged and overheated. They may vent to prevent explosion and they will then loose electrolyte. They will loose further capacity, making the original problem worse (lower capacity than the other cells).

If you think about it, the more cells you have in series the worse this condition will be, and the more difficult it will be to detect, if you only have access to the terminals at the ends of the string of cells. One or even five cells lost can be "buried" in the normal battery voltage variation. NiMH cells exhibit about 1.2 V just before being emptied of charge, 1.25 V in their "operation range", and 1.5 V fully charged. The 168 cell pack can vary from 201.6V to 252 V! How could you tell if one cell was in trouble?

Because of this, Toyota engineers apparently made the reasonable decision to operate the pack between 30% and 60% charge, with emergency discharge to 20% and emergency charge to around 70% permitted. This would avoid fully discharging the pack and reverse charging a cell(s) and fully charging the pack and overcharging a cell(s).

Having said all this, if you ran out of fuel and "limped" the car as far as it would go, you will still have about 20% charge left (the system will "shut you down" at about this point). If you did this once, I doubt you would cause any problem. If you did this once a month, I suspect you would perhaps halve the life of the battery (just a guess).

At any rate, you can "limp" the car typically a mile or so, and some have actually gone a bit further. I think, based on the above, it would be prudent to limp it to a safe place and call for fuel. Be aware, from reports of others who have run out of fuel, you need at least 3 gal to get the engine going again if you run out while moving due to fuel pickup issues.
Also, running out of fuel is not a good idea. The electric fuel pump is fuel cooled, and even if it shuts off as soon as the ICE quits, it will have to dissipate any heat energy it will contain in air. Not a good situation!

 

<div class='quotetop'>QUOTE(eagle33199 @ Oct 30 2006, 02:16 PM) [snapback]340751[/snapback]</div>

Let me add that you should get your car out of the traffic lane!

 

Thank you all for the clarification, I love learning new stuff.

Most of the time when I see people referring to SOC around here, it seems to in reference to the little battery gauge on the MFD so I assumed that's what it was in reference to (is there a glossary of terms anywhere?). I imagine THAT only shows what Toyota deems in the usable range (40% - 80%) not the whole battery, is that right? Or does it indeed show the whole battery range? In which case, it certainly seems to go beyond 40% and 80%...

As for where the 33% figure came from, I read that somewhere while studying up on batteries. But, it's really not out of line with the numbers you guys are quoting. If toyota limits the charge to between 40% - 80%, that's a 40% range, which is pretty close to the 33% I read...

 

Where are you getting this 30 to 60 percent nonsense? There are
NUMEROUS pieces of Toyota documentation that explain how the system
is always *seeking* a 60% SOC under normal operation, and regen
braking or electric propulsion will allow SOC to drift away from
there within carefully monitored limits. Please do not throw
numbers around that are different from what are well understood
long-term around the community under the guise of "explanation".
.
And you totally forgot to mention how every pair of modules [12
cells worth per block] are independently monitored to try and
help detect capacity drift. Battery pack builders are well aware
that you can't just throw a bunch of stuff in series and trust it.
Some controllers [but alas, not in the Prius] even use the mid-string
monitor leads to inject or pull out a little charge to help equalize.
.
_H*

 

<div class='quotetop'>QUOTE(hobbit @ Oct 30 2006, 10:31 PM) [snapback]341137[/snapback]</div>

OK, you win. I'll crawl back under my rock now. I'm glad you're such an expert who has both the access to and the time to read every piece of Toyota technical documentation, PLUS every post on this forum -- it sure helps put mere mortals like me in my place. You'll note that nearly every one of my statements were prefixed with "I imagine", "I think", "I doubt" and "supposed fact". I never once presented my word as gospel and there's no reason for you to treat me like I did. The others who were correcting me did so in a more educational manner...

By the by, for anyone else reading this, I never meant to condone running with no gas -- I have no doubt it can cause overheating, gas pump issues and all the other things people are talking about. I merely meant to question that it would damage the batteries...

 

<div class='quotetop'>QUOTE(Mr. Zorg @ Oct 30 2006, 11:18 PM) [snapback]341148[/snapback]</div>

Another problem, other than damage, is the cost of recharging the main battery if it's down too low. I've heard that not every dealer has that and it costs a few hundred to do so.

 

<div class='quotetop'>QUOTE(efusco @ Oct 31 2006, 05:52 AM) [snapback]341178[/snapback]</div>

If that's the case, I retract my sarcasm laden rant. This is why quoting is a good idea.

 

<div class='quotetop'>QUOTE(aaf709 @ Oct 30 2006, 01:16 PM) [snapback]340750[/snapback]</div>

Forget it. My points have been made many times over in this thread.