GM Volt Forum banner

1 - 20 of 26 Posts

·
Registered
Joined
·
251 Posts
Discussion Starter #1
So I haven't actually had the opportunity to try out a pure range extending situation and I'm not exactly wanting to find the time to play around with that BUT, I would like to know that things are working as intended....

I thought "HOLD" mode would do a good simulation of what a depleted battery would be like. Obviously I've used HOLD on long 75 mph freeway drives but that has been WITH some charge in the battery. I've noticed that going up or down hills or passing at that speed has pulled some juice from the battery, so I already expect reduced performance if I don't have that extra charge saved up.

The part I'm a little concerned about or confused with is around town. I can put the car in hold with about an 80% battery and hear the engine kick on and run while I drive. I'll come to a stoplight and the engine will cycle off (?) or at least the dash shows no power from the engine. As I pull away from the stop light it'll use battery only power, usually for maybe just 100 feet or until I'm up to about 20 mph and then the engine speed ramps up and I'll see battery power drop in relation to engine power increasing. However, occasionally I will slowly accelerate up to 35 mph from the stoplight and it will only use battery power to do so and will then continue to ONLY use battery power (no engine sound or dash indication that power is coming from the engine) for maybe four or five miles at 35 mph. I've actually had to switch it out of hold back to normal, wait 30 seconds or so and then switch BACK into hold to get the engine to fire back up. This worries me some if I don't have the battery power left (in the event of a depleted battery).

Is this how hold mode works? (More like a semi-hold) Or could there be something wrong with the engine restarting feature of the Volt? Do you need to really mash the peddle down (50% or more of the peddle travel) when leaving a stoplight if the battery is depleted to get the engine to run? Or will the engine run 100% of the time and not even shut off at a long stoplight?

I just figured "HOLD" would keep my SOC basically the same (maybe +/- 5%) but I could see situations around town where HOLD allowed my battery to basically drain all the way down, even though the car was in HOLD the whole time.

On the freeway it seems to work perfect and will keep my battery where it should be unless there are a lot of hills.
 

·
Registered
Joined
·
521 Posts
Long story short:

1) Hold mode aims to keep the average charge at the same level as when it is activated
2) That said, it will try to optimize and can delay the recharge while avoiding high revving the ICE
ie: the battery charge will dip below and also exceed the target SoC (State of Charge)
3) When "empty" Gen1 Volts actually have ~30% SoC in the battery, ie: the "buffer charge"

So yes, if you are driving uphill in the snow both directions ;), the battery could theoretically deplete to "empty" even under a hold situation.

Here I am guessing: At "empty" it would switch modes (now allowing high ICE RPMS) to allow for the combination of high-load and low battery allowing you to continue drive up hill like a normal person. With ICE engine being loud and vibrating the vehicle, like a normal person. I live in Texas so... no hills to try this on. Curious if anyone else proven this.
 

·
Registered
Joined
·
2,359 Posts
I thought "HOLD" mode would do a good simulation of what a depleted battery would be like.
No, you are misunderstanding HOLD mode.
http://gmauthority.com/blog/2012/04/2013-chevy-volt-and-the-new-ev-hold-mode-feature-spotlight/

Obviously I've used HOLD on long 75 mph freeway drives but that has been WITH some charge in the battery. I've noticed that going up or down hills or passing at that speed has pulled some juice from the battery.
The Volt is capable of roughly 114KW of power from the battery and roughly 55KW of power from the REX/Generator. HOLD mode does it's best to run from the REX, but keeps the option to pull from the battery (up to the maximum of 114KW) if you demand it. THEN, when demand drops it does it's best to return your internal battery to the same state of charge it was at when you initiated HOLD mode.

<snip> However, occasionally I will slowly accelerate up to 35 mph from the stoplight and it will only use battery power to do so and will then continue to ONLY use battery power (no engine sound or dash indication that power is coming from the engine) for maybe four or five miles at 35 mph. I've actually had to switch it out of hold back to normal, wait 30 seconds or so and then switch BACK into hold to get the engine to fire back up.
This does not sound right. In my car, in HOLD, the REX will stop running at a stop and the initial motion off the line will be battery only, but then the REX always kicks in within 10-20 seconds of motion and I get the same behavior if I have depleted the available battery.

I could see situations around town where HOLD allowed my battery to basically drain all the way down, even though the car was in HOLD the whole time.
So are you saying you "could" see this happen, or has your car actually run the battery down in HOLD mode before?
 

·
Registered
Joined
·
2,359 Posts
Also
If you actually want to know what "reduced power mode" feels like, set your dash display to show KW being used and don't exceed about 55KW draw. Personally I don't think it's bad at all...unless you got hills.
 

·
Registered
Joined
·
145 Posts
I have 8966 miles on my 2017 Volt, with only 57% EV.

That's because I've driven from eastern Tennessee to Florida and back as well as to Chicago and back. I have no concern when the battery is depleted when driving normal highway conditions.

If I was planning to drive in the Smokey Mountains or the Rocky Mountains, I would keep extra reserve by driving in mountain mode. Never had any issues due to using up the battery charge. That said, I do often drive in Hold mode to save my charge for when I am doing city driving, but eventually run down to zero on long trips. No issues at all, and no concern.
 

·
Registered
Joined
·
1,313 Posts
Long story short:

1) Hold mode aims to keep the average charge at the same level as when it is activated
2) That said, it will try to optimize and can delay the recharge while avoiding high revving the ICE
ie: the battery charge will dip below and also exceed the target SoC (State of Charge)
3) When "empty" Gen1 Volts actually have ~30% SoC in the battery, ie: the "buffer charge"

So yes, if you are driving uphill in the snow both directions ;), the battery could theoretically deplete to "empty" even under a hold situation.

Here I am guessing: At "empty" it would switch modes (now allowing high ICE RPMS) to allow for the combination of high-load and low battery allowing you to continue drive up hill like a normal person. With ICE engine being loud and vibrating the vehicle, like a normal person. I live in Texas so... no hills to try this on. Curious if anyone else proven this.
Your (3) is misleading... that 30% (more like 25% IIRC) is never available to be used. When the car shows as "empty", there is about .5kWh (3-4%) buffer the car can dip into, but that's it, it won't allow you to go lower. If you hit that, you can get into "Reduced Propulsion Mode"... mostly seen by people on steep hills who didn't engage Mountain Mode early enough. I'm not 100% sure, but I think Hold will allow as high RPM as Mountain if your SoC falls far enough below where you set it.

OP said:
I just figured "HOLD" would keep my SOC basically the same (maybe +/- 5%) but I could see situations around town where HOLD allowed my battery to basically drain all the way down, even though the car was in HOLD the whole time.
OP, it will not do this, it will NOT drain all the way down when in Hold (except maybe if going 80mph up Mt Washington). City driving, esp at lower speeds (20-30mph) doesn't use much juice, so the engine will not always be on. It will likely cycle on and off as needed, each time providing some motive power and filling a buffer plus a little. This is normal. You are WAY over-thinking this. It will perform just fine when your battery is depleted, almost the same as when you are experimenting in Hold. It keeps an "invisible" buffer to allow the engine to run as-needed in the most efficient way (which may be cycling on/off, but may not be, depending on several factors). The only time you would have a problem is if you tried to climb a long, steep hill at high speed after depleting the battery. Hard to find that in most parts of Texas, I imagine. But if you do, that is what Mountain Mode is for, just need to engage it 20 minutes-ish beforehand.
 

·
Registered
Joined
·
251 Posts
Discussion Starter #7
No, you are misunderstanding HOLD mode.
http://gmauthority.com/blog/2012/04/2013-chevy-volt-and-the-new-ev-hold-mode-feature-spotlight/



The Volt is capable of roughly 114KW of power from the battery and roughly 55KW of power from the REX/Generator. HOLD mode does it's best to run from the REX, but keeps the option to pull from the battery (up to the maximum of 114KW) if you demand it. THEN, when demand drops it does it's best to return your internal battery to the same state of charge it was at when you initiated HOLD mode.


This does not sound right. In my car, in HOLD, the REX will stop running at a stop and the initial motion off the line will be battery only, but then the REX always kicks in within 10-20 seconds of motion and I get the same behavior if I have depleted the available battery.


So are you saying you "could" see this happen, or has your car actually run the battery down in HOLD mode before?

To you last point, it hasn't actually run the battery down because I haven't given it the chance. Either I want to save the battery charge because I know it would be better used later in the day OR because I want more heat :p

I have however seen at least 3 to 4 miles in zero traffic at 35 mph on battery alone even though I'm in "HOLD". Like I said, usually off the light it'll switch the engine on after a few seconds and when I'm up to 10 to 20 mph. However, every now and then it'll let me climb all the way up to 35 and then I can set the cruise and it'll stay on battery. It does seem that if I push down harder on the peddle it will cycle the engine on. Maybe I've just recharged the battery enough that it has a kW or so to burn to bring it back down to the level where I engaged HOLD? It's hard to tell on the dash because I think each bar is roughly 1.5kW or 1.8kW so I could be at a weird point in-between bars.
 

·
Registered
Joined
·
251 Posts
Discussion Starter #8
OP, it will not do this, it will NOT drain all the way down when in Hold (except maybe if going 80mph up Mt Washington). City driving, esp at lower speeds (20-30mph) doesn't use much juice, so the engine will not always be on. It will likely cycle on and off as needed, each time providing some motive power and filling a buffer plus a little. This is normal. You are WAY over-thinking this. It will perform just fine when your battery is depleted, almost the same as when you are experimenting in Hold. It keeps an "invisible" buffer to allow the engine to run as-needed in the most efficient way (which may be cycling on/off, but may not be, depending on several factors). The only time you would have a problem is if you tried to climb a long, steep hill at high speed after depleting the battery. Hard to find that in most parts of Texas, I imagine. But if you do, that is what Mountain Mode is for, just need to engage it 20 minutes-ish beforehand.
This helps a lot. I wasn't sure how much the engine was charging the battery PLUS driving the wheels but I know there is some of that going on since I can see the regen to the battery. I wish it broke out in kW. Like A yellow 25 kW to show what the engine is producing and then the standard kW usage which might be like 22 kW so I can get an idea how much extra is going into the battery.

Like I said, I haven't depleted the battery yet, just trying to get an idea of what it'll be like the day I do. (And yes I know to try and always save battery if I've got mountains since that's worst case, but rarely something I drive over)

Guess I need to get out there one day and just deplete the battery and drive around and get a feel for how it's like as a "normal" car. On the flip side I guess it's good news that without engaging hold mode I probably could do 95% or more of my driving on battery alone. (And maybe more if I don't do any road trips that year :p)
 

·
Registered
Joined
·
871 Posts
To put it briefly: the Volt will never ever let you run it completely out of battery. If you run out of fuel and battery, it will shut itself off before the battery depletes itself beyond salvage.

When you're in Hold mode, or when the battery is depleted, the computer keeps a fairly large reserve of battery power. It's intentionally keeping the engine off as long as possible so that it saves fuel. If you accelerate slowly up to 30 MPH and the engine still doesn't come on, congratulations! You must have regenerated quite a lot and thus you don't need your engine as soon. The Volt can start its engine in a fraction of a second (nearly instantly), so you never need to worry about running out of juice.

If you run the battery down into "charge depleted" mode and mash the accelerator, you'll still get an impressive amount of power from a stop even before the engine has a chance to start, all because of that buffer the computer keeps.

Basically, if the battery falls below "threshold X", the engine will start and run until the battery charges above "threshold Z", at which point the engine shuts off and the cycle restarts.
 

·
Registered
Joined
·
5,782 Posts
..it'll let me climb all the way up to 35 and then I can set the cruise and it'll stay on battery.
Volt is not a Prius. The engine does not need to fire in all cases where more power is needed.

I'm guessing that the battery had built up extra charge due to regen in some cases more than others. The engine will cycle on and off as the computer determines you need power to maintain the battery SOC set when Hold was engaged. It is not dependent on how much power you call for with the throttle like a Toyota or a Ford hybrid.

Hold is different than when the battery is at the lower SOC (The forum calls it Charge-Sustaining (CS) mode). Hold will use more of it's buffer since it has more to use.

In either Hold or CS modes:

- The engine will not always turn off at a stop. If the buffer is not high enough, it will continue to run. This usually happens if you do a jack-rabbit start and then have to stop at the next light. One can learn when this happens to avoid it if it is annoying.
- The engine may turn off at any speed if enough extra battery power was build up such as a hill descent or a lot of other regen happened.
- The computer will use all of the battery first and then fire the engine unlike some other hybrids like Ford or Toyota. In the case of Hold mode, 'all of the battery' is down to whatever SOC was when Hold was engaged.

As previously noted: Don't over think this. The car knows what to do to maintain it's battery and engine.
 

·
Registered
Joined
·
132 Posts
If you're worried about power on big hills, this is what Mountain Mode is for.

I've depleted the battery just to see what it's like. In city driving it seemed to build it a slight capacity so it wasn't constantly changing RPM. My best guess is there is an optimal point for efficiency that it runs at. It will regenerate a surplus of power so the engine can shut off for a few miles. If I'm on the interstate it doesn't do that. Engine is on while on flat ground or going up hills. Engine is off coming down hills and exiting ramps.
 

·
Registered
Joined
·
1,539 Posts
Assuming it is basically the same strategy as Gen 1, then yes it is perfectly normal.

HOLD seeks to preserve the SOC +/- ~0.4kWh. If you do not exceed 10kW in accel and remain at relatively low speeds (as you describe) the battery will pull lower and allow it to reach the limits of that range. If you whack the pedal then the engine will cut in immediately in anticipation of your power-hungry driving style.

I often use this if I misjudge the trip home. If I get to within a few streets and the gauge flips to 'engine running' then I will back off completely and very cautiously tip-toe home and keep it under 10kW. I have done over a mile before now even though the battery was at 0 miles, as it will let you dip into the reserve it keeps below that 0 miles (which is also +/- ~0.4kWh around '0' SOC).

In this state, the instant you pull more than 10kW the engine cranks over instantly.

Of course there is a limit and you need worry not about anything at all. Once it goes over that margin, whether you are pulling 10kW or not then it'll crank the engine. In fact, very annoyingly a few times I have made it home by the skin of my teeth only to forget I have the AC on still and as I pause and exit the car, the engine cranks because the AC has just tripped the final extreme SOC it will tolerate.
 

·
Registered
Joined
·
871 Posts
Assuming it is basically the same strategy as Gen 1, then yes it is perfectly normal.

HOLD seeks to preserve the SOC +/- ~0.4kWh. If you do not exceed 10kW in accel and remain at relatively low speeds (as you describe) the battery will pull lower and allow it to reach the limits of that range. If you whack the pedal then the engine will cut in immediately in anticipation of your power-hungry driving style.

I often use this if I misjudge the trip home. If I get to within a few streets and the gauge flips to 'engine running' then I will back off completely and very cautiously tip-toe home and keep it under 10kW. I have done over a mile before now even though the battery was at 0 miles, as it will let you dip into the reserve it keeps below that 0 miles (which is also +/- ~0.4kWh around '0' SOC).

In this state, the instant you pull more than 10kW the engine cranks over instantly.

Of course there is a limit and you need worry not about anything at all. Once it goes over that margin, whether you are pulling 10kW or not then it'll crank the engine. In fact, very annoyingly a few times I have made it home by the skin of my teeth only to forget I have the AC on still and as I pause and exit the car, the engine cranks because the AC has just tripped the final extreme SOC it will tolerate.
In Hold and C/S mode in the Gen 2, you can pull more than 10 kW of power without it firing up the ICE. It's a bit smarter with reading the buffer. I was driving in C/S mode and was driving at a fairly high speed (~50 MPH) before coming to nearly a complete stop with the regen paddle at a light. I was able to accelerate at a decent rate up to about 35 MPH from that light before the ICE came on again, which definitely drew more than 10 kW. The battery must have been towards its upper buffer boundary before I started to regen, so it had a surplus of power for taking off again.
 

·
Registered
Joined
·
488 Posts
I have traveled Michigan to North Carolina numerous times in the Volt. You don't need Mountain mode on any interstate highways. The engine may rev up quite a bit but I've never had reduced propulsion. I77 up from the piedmont to Fancy gap is probably the longest climb with most grade, no problem, 70 mph average speed, plenty of power. The closest I ever came to wishing I had used Mountain mode to build up some buffer was in the mountains east of Phoenix AZ. Those grades had the ICE screaming and I did slow up a bit, but nothing wrong happened. People make too much of an issue about using the Volt as it was designed, it's a car like any other, which just happens to not burn any gas for the first 35-40 miles of a trip. It's actually a nice highway car the 700 pound battery parked smack in the center lends to great stability and nice handling.
 

·
Registered
Joined
·
871 Posts
The Gen 2 doesn't need Mountain Mode. It would be very unlikely to need the full 150 hp for longer than the battery buffer can sustain it. The engine's 100-or-so hp is plenty for any grade the average driver is going to climb. The Gen 1, from what I hear, definitely needed it because of weaker engine cooling and a weaker engine in general, but the feature is superfluous on the Gen 2.

EDIT: Although, I did use it once as I was almost at an empty tank (and empty battery) so that I could use up nearly the last of my gas right as I got to the gas station, and then have a sufficient charge to get home from there without the ICE. I got to the entrance to my neighborhood and the ICE kicked in...ugh. Should have started MM a mile earlier.
 

·
Registered
Joined
·
418 Posts
I have always climbed mountains in Hold mode. Not sure why anyone would want to use the electricity up so quickly. It's not terribly efficient for the ICE either, but I think it's probably more efficient.

Am I wrong about this?

Thanks,
Rick
 

·
Registered
Joined
·
2,634 Posts
I thought "HOLD" mode would do a good simulation of what a depleted battery would be like. Obviously I've used HOLD on long 75 mph freeway drives but that has been WITH some charge in the battery. I've noticed that going up or down hills or passing at that speed has pulled some juice from the battery, so I already expect reduced performance if I don't have that extra charge saved up.
I think others have already answered your question, but a point to make here is with the 55 kw generator motor and gas engine (called generator set, or genset from now on) has enough power to drive approximately 100 mph on flat ground.

If you have a drained battery and forget to use mountain mode, and go to drive up a steep mountain pass, you have about a 1 kwh of reserve buffer before the battery is actually drained (to the point the car cuts it off to protect it). After that, you rely solely on the genset's 55 kw. This is still a fair amount of power (a bit less than 80 hp). It is not enough to maintain high speed (like 75 mph) on a steep mountain pass, but still enough to maintain speed on flat ground with no wind (up to the max rated speed). There are passes like this on I-80, I-24?, I-70, etc.

So unlike the BMW i3, it isn't really an issue of running on reduced power mode, except in the rare circumstance of a steep mountain pass at high speed. A hard acceleration from 70-90 mph to pass is fine, as the 1 kw buffer will cover that. The BMW i3 has the issue of only having 25 kw or something much too low to maintain high speeds. The BMW is suitable for low speed highway (55 mph), but not interstate travel, a headwind or something would really cut the speed. The Volt was designed to sustain high speeds anywhere (remember to use mountain mode 15 min prior to a mountain pass, or hold mode on the highway will serve same purpose if done before it drops too low).
 

·
Premium Member
Joined
·
14,156 Posts
Note that if you expect to do some climbing and have forgotten to put the car or mountain mode (don't ask me how I know this but it has to do with stopping for fuel), you can put it in mountain mode and the car will add some SOC to the battery, insuring you don't run into a "propulsion reduced" situation.
 

·
Registered
Joined
·
45 Posts
FYI we took our 2016 Volt from Los Angeles to San Fran up the coast highway and got 40mpg and had zero issues with the hills along the way. In gas mode, it's not a high powered car but it works fine and I never felt like the lack of power was an issue.
 
1 - 20 of 26 Posts
Top