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While Most Owners - use the Volt or ELR’s pre-heating feature to warm the car’s interior for comfort reasons, there are other undisclosed benefits, such as heating the high-voltage batteries and even your cold engine as well.
Greetings forum members, in this article I’ll share numerous aspects with regard to pre-heating and getting the most mileage out of our EV’s battery. We’ll also touch base on correct pre-heat procedures and the role they play in protecting our investment. Most importantly, we’ll cover another cold weather feature most owners mistakenly avoid called; “Engine Assisted Heating”, a feature GM included where we use our engine to both condition our car and extend our winter range.

Winter Commuting - Along with winter comes every EV’s nightmare of losing range, therefore proper “Pre-Heating” procedures for conditioning our Volt or ELR’s cabin as well as the high-voltage batteries are of prime importance to get back some of the lost mileage. I’ve owned my ELR for over a year now and recently added a 2015 Volt to my fleet. While I’ve owned a few other EV’s, I have always been amazed and fascinated with the GM system. It is for this reason; I traded in my BMW I3 RX and bought my second GM Voltec car.





Fortunately For Us - GM incorporated some great features in our EV’s to help cope with cold weather driving. One such feature allows us to “Pre-heat or Condition” our car from our key fobs, or remotely use On Star’s remote app with our smart phone. A typical pre-heat cycle lasts for 10 minutes, however we can perform a second cycle giving us up to 20 minutes of preheating. I’m sure many of you have heard a number of noises coming from your car during one of these cycles, these are the needed pumps, compressor, relays, valves, etc., that are required. Unlike gas powered cars which require the engine to be running when they pre-heat, with the Volt or ELR, we can pre-heat using our high-voltage battery with the range extender engine off.

In This Article - aside from just electrical pre-heating at home, we’ll also cover the Volt or ELR’s engines role in dealing with cold weather as well. While the main reason I decided to write this article is to help current and new owners understand how the pre-heat system works and its advantages, I also wanted to dispute some incorrect rumors that plug-in pre-heating reduces the Volt’s or ELR’s range and only draws the battery down. In retrospect, this article will show there are a number of distinct advantages using correct pre-heat procedures during winter months.
While we have the ability to pre-heat or condition our EV from its own high-voltage batteries, say at a restaurant or while shopping, the real benefits of pre-heating is while our Volt or ELR is plugged in at our home.

Temperature Management System - While the GM Voltec system employs four separate cooling/heating systems to manage vehicle and equipment temperatures, for the most part, pre-heating is accomplished with two separate systems, one for the cabin and engine, and a second system for the high-voltage battery.
Cabin preheating involves a battery powered electrical element, which heats coolant, which is then circulated though a radiator then fan forced to heat the cabin. While not mentioned in the manual, I discovered the same coolant to heat the cabin is also circulated to heat the engine as well. By pre-heating the engine during cold weather start up, it allows to thin the oil as well as allow more uniform expansion of the mechanical components such as rod and crank inserts, pistons etc.

In addition to owner selected pre-heating, the Voltec’s processor (TMS) also incorporates an automatic battery maintenance protocol, which will cool or heat the battery by itself during extreme temperatures, providing the car is plugged in. Therefore, whenever there is a chance of temperatures falling below 32 or above 100 degrees, your Volt or ELR should be plugged in to help condition the batteries for further range and battery longevity. This type of automatic conditioning is called “Stand-By” management.





The Cabin Heater – As mentioned, your Volt or ELR uses a resistive heater to heat the coolant for the cabin. This “Can bus” controlled heater module contains four separate heating elements; there are three elements that can be controlled separately for more aggressive heating, and a forth variable element which is proportionally controlled from “off” to any increment of heat for fine-tuning of the required cabin temperature. This element heater module may require a peak of around 4KW for a period of time. In addition, when we add another 2KW for the battery heater, we can see up to 5-6KW come off the battery when other utilities such as fans, valves and circulation pumps may be running.

Lithium Battery Ideal Temperature - In some respect the lithium batteries in our EV’s are like humans, they perform best at around 70 degrees. In fact, at this temperature, the entire battery can be depleted in the Volt or ELR with no additional required cooling. The batteries temperature management system (TMS) incorporates three separate modes of operation:

1- A winter circuit for circulating element heated coolant to the batteries to bring their temperature to specs.
2- An average weather circuit, which circulates heated or cooled battery coolant to a front mounted radiator for conditioning in moderate weather.
3- An aggressive summer circuit, which additionally uses the EV’s air conditioner system to forcibly cool the batteries using a heat exchanger when the forward radiator circuit is not sufficient.




360 Volt Battery Heater - During a typical pre-heating session, aside from warming the cabin, should the high-voltage batteries temperature fall below 40 degrees, a smaller secondary 2 KW heater will heat coolant which is then circulated through small thermal passages that are actually between the cells to maintain the entire pack of lithium cells at optimum operating temperature. This heater can increase the batteries temperature about 1 degree every 2 minutes, so in a 10 minute pre-heat cycle, we can bring the entire pack up 5 degrees. There are 16 thermal sensors which scan the batteries 10 times a second which maintains every cell in the EV within a variance of only a few degrees. To conserve battery energy, the TMS has a target at around 60 degrees, even though at 72 degrees the cells produce more range.

Lowe’s Iris Power Management - At my home, I use a “Lowes Iris” system to control my alarms as well as all my EV and RV charging plugs, this way I can enable or disable charging right from my Iphone when I’m out of the house. Fortunately, Iris also provides exact wattage reading so I can monitor how much power it uses when plugged in. In addition, the Iris system also gives me a daily - weekly - monthly and yearly power cost to charge my Volt and ELR, so I know my exact electric cost to run my EV’s. As shown in the image below, the Iris display shows the wattage on the charger as well as the charge required each day. On the right side you can see on Tuesday it took $1.96 to charge my Volt.





High Voltage Battery Location - Fortunate for us, unlike other electric’s such as BMW or Tesla, where their batteries are located in the floor of the vehicle where they have little separation from the elements and exposed to hot or cold thermal temperature changes from air passing under the vehicle, with the Volt or ELR, GM instead designed the vehicle where the batteries are pretty much located in the interior of the heated or cooled car, protected from the elements. GM also provided an insulated exterior battery case, so they can be exposed for an extended period of time with minimal change in temperature.

No Heat Pump For You – Regretfully even in the new Gen 2 Volts, GM did not incorporate a “reverse cycle” heat pump system. While a heat pump system is not very efficient at temperatures below 30 degrees, at moderate temperatures they can operate at 1/3 the power of the existing heating element system used on the Volt and ELR. Since our EV’s already have an electric-powered compressor for A/C cooling, one would wonder why GM would not just add a reversing valve and heat exchangers to improve the system for increased winter mileage.
Presently, the BMW I3 BEV model uses a heat pump system and an element heater to heat the batteries and cabin and therefore increasing the I3’s mileage during moderate cool weather. The use of heat pump systems to warm the batteries in EV’s are documented to gain additional mileage even though they are self-powered from the EV’s own batteries.



Charging - Charging our Volt or ELR at home is accomplished with two different levels of charging, one powered by 110v and the other by 220 volt. For most, the standard 110-volt charger is sufficient since most users commute during the day and charge at night. Lets look at how each level contributes to Pre-heating.

Level 2 Charging & Pre-Heating - If you’re charging and pre-heating on a Level 2 (220v) charger, the shore power will pretty much handle the pre-heating circuit with little to no current coming from the Volt’s battery. While dependent on ambient temperature, a level 2 charger (220v) may require an additional 5-15 minutes after the pre-heat cycle for the system to replenish the power used and re-peak the batteries.

Level 1 Charging & Pre-Heating - If you’re using the standard level 1 -110v to charge, the line will only be able to supply a portion of the current needed to run the heaters, pumps and fans so there could be up to a 2-3KW draw from your high–voltage batteries reserve. Therefore, a simple solution is to make sure that you pre-heat about 30 minutes or so before your departure.
After a pre-heat session, depending on temperature, it could take about 15-30 minutes for your 110v charger to replenish the power lost for heating and to re-peak the lithium cells. If you’re concerned that after 15-30 minutes the car will be cold again, this is really not an issue because 75% of the heating work is already achieved from house current; therefore you’ll have heat almost instantly since the coolant is already pre-heated in the circuit. In addition, since the batteries are insulated, they will retain practically the same temperature for hours.

Typical Level 1 Pre-Heat Cycle - By observing the draw and the charging status lamp on my Volt’s dash, and my Iris system, I have included below a typical pre-heat session at 43 degrees and the time it took to replenish and re-peak the battery using the L1 (110v) charger.

8:25 Check Status – (blinking) Full Charge 45 miles
8:30 Start Pre-heat Cycle
8:40 Pre-heat cycle Complete (cars running lights off)
8:40 Check Status – Now 43 miles & Charger re-engaged (1465 watts)
8:57 Charge Complete – Status Full (blinking) - Charge 45 miles


Battery Head Charge – Now let’s discuss a second benefit of pre-heating your Volt or ELR. Aside from the advantages of heating the batteries for improved mileage, pre-heating has an additional benefit since it forces a second “re-peaking” of the high-voltage batteries charge. Dependant on temperature, this re-peaking can provide another 3-8 miles of range. Keep in mind, at the end of any charging cycle, practically all batteries acquire what I call a “Head Charge” this is a chemical change (balancing) that occurs in the cells at the end of any full charge. This in turn provides the benefit of extra mileage. On our Volt or ELR, when we pre-heat, the energy management processor otherwise “forces” another charge cycle to re-peak the cells to replace the current used for heating.
Proof of this “Head Charge” is shown in the two images below – while we all know the average miles per kilowatt, this example shows my Volt’s stats after a pre-heat cycle where I forced the battery to be re-peaked just prior to departure.
I left home with 45 miles on the battery indicator, when I drove to town, which is 13 miles away, the dash battery display still showed 39 miles remaining. While we all know the mileage display is not dead accurate, when we look at the energy monitor display on the stack, it confirms those numbers.
In this example, I only used 2.7 KW of battery to travel 13.5 miles; this is 5 miles per KW and I was driving 45-50 mph it was in the 40 degree range when I left home. This clearly shows the improved results of re-peaking the cells with a head charge. In retrospect, if I charge my battery and it kicks off at 2-3 am in the morning and I leave some 5 hours later, I cannot achieve any where near this initial performance.







Pre-Heating Heats Your Engine As Well - Aside from heating the cabin, there are other advantages when pre-heating since a portion of the heated coolant circulates through the engine block. When performing your first start of the day in cold weather, the engine is at a more uniform temperature. The two images below show how my engine temperature increased during a pre-heat session on my ELR. As shown, the engine temperature was 64 degrees, in just 10 minutes of pre-heating; it raised the engine temperature from 64 to 87 degrees, a 23-degree increase.







Engine Auto Start Feature – Another great comfort feature incorporated in your Volt or ELR is a GM protocol called “ERDTT” (Engine Running Due To Low Temperatures) if temperatures get around freezing, your engine will “auto-start” then cycle on and off at a high-idle speed. While most owners think this feature is to only assist in heating the cabin, it also provides other important functions. ERDTT is a great feature since it keeps us comfortable while driving and most importantly, maintains the high-voltage batteries at a more optimum temperature and even charges the battery. When the Volt or ELR’s processor auto-starts the engine for cold weather reasons the display below will appear momentarily to notify the driver this heating mode is activated.



Starting & Stopping Our Engine - Regretfully, there is another false rumor out there that ERDTT will damage our engine with often starts and stops during cold weather. This is purely rumor, there is absolutely no documented evidence that constant starting and stopping of the engine is harmful in any manner. In fact, the only past known problem was the age-old starter with its metal grinding mechanical Bendix and flywheel. Fortunately, the Volt and ELR do not depend on a starter motor since it starts smoothly with the same motor that drives our car.


Cold Weather Starting – Even with no pre-heating, our Volt or ELR, like every other car made will have the same initial cold start in the morning, so there is no difference between our EVs and the millions of car engines in use today. In fact, we have a cold weather advantage over other vehicles because our engine only idles when starting. Another advantage of the GM “auto start” is the fact that when your battery is depleted and the engine starts to power the car, it’s already at operating temperature with oil circulated on the internals.


Engine Start & Stop Technology - In order for car manufacturers to achieve the future 50+ MPG requirements, practically every car manufactured in the future will have to incorporate start and stop technology. Cars like the new GM Malibu already have this technology in use today where in city driving the engine starts and stops hundreds of times a day. US Postal Service has delivery vehicles presently using a start and stop feature that cycles the engines thousands of times a day to conserve fuel.
On some vehicles they use a special none-mechanical belt-driven alternator, which doubles as a starter to avoid the mechanical problems. In the UK, a newly released water-cooled alternator-starter has been designed with a life cycle of over a million starts. If all that's not enough, Mazda has developed a new starter-less designed direct injected engine that carefully stops the pistons at a precise position, when a start is required, the processor injects fuel in the cylinders, then ignites the fuel with the spark plug, which starts the engine. Hopefully this will dispel rumors that ERDTT is not good for our engines.


Getting back to our topic – It’s important that owners are not afraid to use their Volt or ELR’s engine the way GM intended. Keep in mind; it costs no more to run your engine now than it does to charge. We all paid thousands of dollars for great engine option; we surely don’t want to waste fuel hauling this hunk of steel around and not be using it!

Auto Start Heat Cycle – As I mentioned, this ERDTT engine-assisted heat cycle will quickly heat the cabin and batteries with the advantage of not running continuously. This feature cycles the engine at high-idle speed to heat the engines coolant to around 150-degrees, then shuts the engine back down. When the engine cools back down to 125-degrees, it will restart again to bring the coolant back up to 150-degrees. This cycle will continue as long as the temperature outside remains under 37-degrees. On the Volt, you have two engine-assisted heat selections, one at 37-degrees and the other at around 15-degrees. On the ELR it’s set at around 37-degrees as well. On my Volt I use the higher 37-degree setting. This great comfort feature barely sips fuel since the engine is running only at high idle for a short period of time. On a typical trip to town I use only a 10th of a gallon of fuel.

The default display on my Volt is the amperage graphic, since it shows me a number of stats regarding what’s happening with regard to my engine and battery. The image below shows this display, the small yellow line on the right shows the engine running in its high-idle, auto-start sequence. As the yellow bars climb on the right, they represent increased engine rpm and work. On the left side are the battery stats. Around center position the motor is at idle, as you require more energy the graph bars will climb. From center position down, the bars are green, which represents regenerated power going back to the battery.




Center Stack Display – GM gave both the Volt and ELR great graphic displays. Using the Volt’s center stack display you’ll find plenty of accumulated electrical and engine data such as; fuel usage, MPGe, and other data. The display with 3D car with spinning wheels, offers a quick glimpse as to the immediate status of our engine and battery system.

Driving 35 mpg Using Only the Engine - I recently discovered that when the engine is idling during an ERDTT auto-start cycle, I can actually drive the car around 30-35 mph with only the current provided by the engine generator at idle and use no battery energy. When we balance of power generated from the engine with the load, the display will show “Engine Power”, which means the power output of the idling engine matches the speed you’re driving. If you happen to add throttle, the display will show the “Engine and Battery Power” to show you’re using more current than the engine is producing. If you let off the throttle too much, the display will change to; Regen Power Recovery.
This shows that even though the engine is only idling, it still produces a substantial amount of power generation. The image below shows the four energy displays on the center stack of the Volt – the upper right display is where the motor is producing just enough power to drive the car at speeds around 35 mph while at idle as we discussed.
What a great system when you can own a car for over a year and continue to learn new things about it, it’s pretty amazing!





Auto-Start Also Charges Your Battery – I also discovered another fact that when the engine is idling during a ERDTT cold weather “auto-start”, it charges the Lithium batteries, as well.
The other day we went to breakfast at Merciers Apple Orchid, in Blue Ridge, Georgia. After breakfast, when I got back in the car, the temperature was still in the 30’s, so as we began, the engine came on automatically. When I started my short trip to Mc Caysville, I noticed there were 13 miles of remaining battery. We then drove 11 miles to Mc Caysville. When I arrived in town, I glanced at the battery indicator expecting to have only a few miles remaining, much to my surprise, the short cycling of the motor on my trip recharged my battery all the way up to 20 miles!
As we look more closely, in 17 minutes, I drove 11 miles and added 8 more miles to my 13 miles of range. So this is a total of 18 gained miles with the engine idling maybe 4-5 minutes on the way to Mc Caysville. Somebody slap me, because I feel we just discovered the “third” engine-running mode that GM needs to add to the Volt & ELR, we’ll call it “Intermittent Mode” or something like that - this is nothing short of amazing!

Use That Generator - Now I know a lot of you guys are totally against running the engine in the Volt for any reason at all, since it lowers the life-time mpg. And I can understand that to a point, but when it’s cold, it’s cold! I’ve even seen guys modify their Volt’s electrical system to prevent the engine from self-starting in cold weather. I also witnessed others traveling in a freezing cold car so they don’t have to start the engine. We all paid good money to have a great range extender / generator in our EV’s, use them proudly. The Volt’s generator is one of the best features you can add to an electric car, it enables us to commute more comfortable, avoid range anxiety and have benefits of greater distances and the ability to charge in the safety of our home.






Same Cost To Charge or Gas - With the advent of lower gas prices, it’s now become just as cost-effective to run your Volt’s generator, as it is to charge at home. Looking at the math . . . the average cost for a gallon of gas is $2.00 or less, which gets you 35-40 miles of range - about the same distance as a full charge at the national level of 12 cents a KW, which costs around $2.00 as well.

Manually Starting Your Engine - If the temperature is over 37-degrees and you have over 20 miles of charge on the battery, neither the Hold nor Mountain Mode will allow the engine to start for heating the cabin. If you have no “plug in” capabilities and would like to pre-condition your ELR or Volt, here’s a work-around. By pulling the hood latch with the ignition on will activate the “service mode,” which will start the gas engine and retain it at Idle. By using this feature before starting out on your trip, it’s possible to quickly heat the cabin and high-voltage batteries, as well. When you’re ready to depart, carefully pick the hood up a foot or so and release it to lock it again and the engine will shut down. I recommend hanging a reminder on the mirror that the hood is unlocked.
Engine Start Switch - I’m in the process of installing a switch on the dash that will override the “hood closed” switch. A special hood switch, which tells the processor it’s OK to start up, is located right by the hood release - by tapping into this circuit, I’ll be able to start the engine right from the cabin anytime I wish. I’ll put up a post when I complete the mod.




Heated Seats - I would like to briefly touch base on the heated seats. As you know, this feature can be operational during pre-heating cycle. Heated seats draw very little current and since they are touching your body, they have the ability to heat your core, which is very effective. You’ll find that during milder weather, just running the seat heaters can make for a very comfortable drive, which really preserves battery when compared to running the resistive heater curcuit.
For safety reasons, the Volt and ELR seat heaters run on 12 volts rather than the 360 volts used with the car heaters. Since the KW reading is primarily the same for any seat setting, I feel they obtain the different levels of heat by pulsing the voltage at different frequencies to obtain the different heat levels. Regardless, the seat heaters of the Volt and ELR are some of the best I’ve felt. They are very economical as well and only draw 40-50 watts when running.





Setting your Charge Time – Another tip that will provide a few extra EV miles during cool weather can be achieved by delaying your charge cycle just prior to your departure. There are two benefits; first, you’ll you have the advantage of a “head charge” since you’ll be using the battery immediately after a full charge. Secondly, as your batteries charge, there is heat created within the cells which raises their temperature, resulting in additional performance and range. Therefore, when you shut down you car the night before, look at the charging time required and set a timer so the charger stops about 30-minutes prior to your departure.

In Conclusion – I hope this article answered the many questions about pre-heating and using the engines assisted heating features. GM built a wonderful product which addressees the many variables of temperature so we can enjoy driving our electric vehicles regardless of the elements. We all paid extra money for the security of having an engine in our cars, don’t just haul it around and save it for the next owner. ERDTT cold weather running is actually a benefit since it exercises the engine, injectors, pumps, etc. and equally important, it helps keep fresh fuel in our tanks. Don’t sacrifice your comfort and mileage by not running your RX, enjoy your Volt or ELR as GM intended, it is an amazing piece of transportation technology.

Regards- Mike Mas
www.rotory.com









 

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Very nice post, thank you. I have only had my Volt for a month and we've had ALL kinds of weather in VA during that time so I've been able to experiment here and there. This week I've been running with the ERDTT setting pushed to the lower temperature and....I'm putting it back to the higher one. As you say, gas is cheap right now and I'd rather be warm, and as I keep noting, I came from a Jeep with 18 MPG so the Volt at its worst MPG is still a miracle to me!
 

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My only input on this write up is that it's known among Volt owners to not just "push down on the hood" to latch it. It should be lifted to a height of 6 to 8 inches and allowed to drop. This is because the hood is very thin and some folks found out the hard way how easily it can be dented by simply pushing on it to latch it closed.
 

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Cabin preheating involves a battery powered electrical element, which heats coolant, which is then circulated though a radiator then fan forced to heat the cabin. While not mentioned in the manual, I discovered the same coolant to heat the cabin is also circulated to heat the engine as well. By pre-heating the engine during cold weather start up, it allows to thin the oil as well as allow more uniform expansion of the mechanical components such as rod and crank inserts, pistons etc.
The same coolant is used, sort of. When only the electric heater is being used, the fluid is pumped through a much smaller loop, bypassing the engine, radiator and larger coolant loop that the engine would use. A much smaller volume of coolant is used to heat the car when the engine is not in use, and this is discussed in one of the stories here on GM-Volt.com: http://gm-volt.com/2010/12/09/the-chevrolet-volt-coolingheating-systems-explained/

Haven't had time to read the rest yet, but beware of inferred conclusions. A lot of what you're discussing has been hashed out here, and is in the FAQ's. With many of the items, it is easy to be convinced of something that isn't true.
 

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Kudos for a detailed post with lots of detail. I know this sort of 'blog' takes ages to pin together. (Also love the pair of red cars!)

In the cycling ERDTT mode, does the engine speed run up to a fixed speed and stay there, at a speed irrespective of accel pedal position, or does it vary in speed in response to the pedal position, like it does in hold?

I also think you are not quite accurate with the coolant circuit. I think they should have enabled a feature to allow block engine heating when plugged in, but it doesn't seem they have. If your engine does heat up then it might have a defective distribution valve, which controls exactly this function.

I also do not believe you gain '3 to 8 miles' from any additional top-up charging. This is an extra kWh or two, 10% to 20% extra SOC? I don't think so. When it is very cold, thick ice on the window, I will start mine up an hour before use and just leave it 'running' and plugged in. This method (as ari_c found out) adds a wee extra by filling up the 'buffer', but it amounts to 1 mile or so, max. If you are finding a difference between recharging for a while after pre-heating compared to not 'recharging' then this is because the preheating uses more electricity than the charger lead can supply, and it gets the extra form the battery. So immediately after 'preheating' the battery will be discharged and will need a top-up. You are probably comparing the depleted battery with the topped-up battery, rather than a topped-up battery with a 'super-topped-up' battery.
 

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Hmmm, why don't we see the "Chevy engineers are Gods, how dare you question their wisdom" replies when you post about modifying the car to burn more gas than Chevy intended? Those of us who hate ERDTT get a ration of crap all the time for wanting to be in control of our engine... but you want to pre-heat in warm weather using the gas engine and nobody jumps on you for it! This is not a negative comment on you, I think you have every right to take full control of your cars engine, just surprised the "oh my god your warranty is void!" alarmists haven't jumped all over you yet.

Philosophical differences on engine use aside, the post is very well written and informative of the Volt systems, and I applaud your efforts to take control of your engine to make it do as YOU wish it to. :D

Keith
 

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A nice looking writeup, but there are some errors.

While most owners think this feature is to only assist in heating the cabin, it also provides other important functions. ERDTT is a great feature since it keeps us comfortable while driving and most importantly, maintains the high-voltage batteries at a more optimum temperature and even charges the battery.
ERDTT does absolutely nothing to maintain the condition of the batteries. It is a completely separate coolant loop and heater.
Heat from the engine cannot physically pass to the battery coolant loop.

And to avoid beating the horse that is why people don't want ERDTT with a full battery - I'll jsut say:
A lack of evidence showing failure does not prove ERDTT short cycling and low temp operation is good for an engine.
It also does not prove it is bad. But you cannot make conclusions that because nothing has failed yet, it must be ok.
In fact, there have been engine failures. People speculate as to what the cause might be (regular vs premium gas?)
The fact is, we just don't know.
 

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GM should add a new feature

ERDTT does absolutely nothing to maintain the condition of the batteries. It is a completely separate coolant loop and heater.
Heat from the engine cannot physically pass to the battery coolant loop.
I'll start by saying that you are correct when it comes to the mechanical loop (based on something I read on this site) but I also know that a small idling engine produces very little heat. You need to load the engine and you do that by generating electric power. It will generate more waste heat when loaded which is picked up by the coolant and the electric power generated can go to the battery heater and cabin heater. The engine and cabin temperature can ramp up quicker this way as well. The article also mentioned that charge was added to the battery, probably to get the most out of the fuel that's burned as I'm sure the engineers have determined the most efficient operation since they state this many times as they created 5 different driving modes for the 2016.

I think the main reason people want to modify (disable) the ERDTT is that they have a short trip to their next charge and see it as a waste of gas. The car doesn't know how far you are going and that you intend to charge at the end. This is where GM should add a new feature as a software upgrade. The car could continuously estimate time and distance that you could go with electric heat and heat reservoir with the battery alone while presenting the driver with the option of disabling ICE assisted heating with a "I think we can make it now" option. If you misjudge, the engine will come on when the SOC drops otherwise you finish your trip and plug in knowing that you minimized the gas use.

I'm sure someone at GM is aware of this based upon all the related posts on this topic but maybe this desire hasn't found the right ears yet.
 

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Discussion Starter · #14 ·
Thanks for all the reply's and links guys - I'm not in any way trying to tell any owners how they should use or operate their EV, these procedures are pretty much GM protocol - the information is there for reference and to help new owners understand and take advantage of the amazing technology used in the Voltec system.

With the engine running a few minutes at a time, it maintains or RX in a safe operating temperature and we benefit with more range since our battery is not taxed trying to heat the vehicle. In addition, the RX also charges our battery to a level of 20 miles, all the while just sipping fuel. Most important; we use the normally wasted bi-product of "Free Heat" so the battery can concentrate on mileage.

Myself- I feel that ERDTT is our best weapon for winter use. We have an engine we paid a lot of money for, so why not use it, it plays an important role to the whole EV package. If my Volt or ELR didn't have an engine, I would not have bought them. If you're not going to use the engine, you would be better off with a "battery only" car - there's no sense hauling this engine around every where we go if we're not going to use it.

Regards!
 

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With the engine running a few minutes at a time, it maintains or RX in a safe operating temperature and we benefit with more range since our battery is not taxed trying to heat the vehicle. In addition, the RX also charges our battery to a level of 20 miles, all the while just sipping fuel. Most important; we use the normally wasted bi-product of "Free Heat" so the battery can concentrate on mileage.
In general this makes sense, but if I know I can cover the entire range I'll drive until the next charge on electricity alone, then I'd rather not burn any fuel. With temps in the low-mid 20s, I'm finding that I can easily cover my commute, and with ERDTT threshold set at 15 degrees, no gas at all is used.

For longer trips in this sort of weather, it sounds like it makes sense to set the threshold at 35 degrees as that would maximize efficiency. And even for shorter trips with passengers in the back seats (which, in my model, do not have heaters), I'd probably run the climate control in "max" mode as it simply doesn't get warm enough back there in eco mode. I assume this would cause the engine to turn on even if the ERDTT threshold is set at 15 degrees, but I'm not sure. I've only had my '16 Volt for 2 days! :D
 

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In general this makes sense, but if I know I can cover the entire range I'll drive until the next charge on electricity alone, then I'd rather not burn any fuel. With temps in the low-mid 20s, I'm finding that I can easily cover my commute, and with ERDTT threshold set at 15 degrees, no gas at all is used.

For longer trips in this sort of weather, it sounds like it makes sense to set the threshold at 35 degrees as that would maximize efficiency. And even for shorter trips with passengers in the back seats (which, in my model, do not have heaters), I'd probably run the climate control in "max" mode as it simply doesn't get warm enough back there in eco mode. I assume this would cause the engine to turn on even if the ERDTT threshold is set at 15 degrees, but I'm not sure. I've only had my '16 Volt for 2 days! :D
Agreed. The solution for me would be driver control of ERDTT. Let me turn it on/off and set the temperature like I do my Nest thermostat. The problem for me isn't ERDTT (it can be useful), the problem for me is I can't control it. I don't always need it, yet it still comes on.
 

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Agreed. The solution for me would be driver control of ERDTT. Let me turn it on/off and set the temperature like I do my Nest thermostat. The problem for me isn't ERDTT (it can be useful), the problem for me is I can't control it. I don't always need it, yet it still comes on.
Right. Of course, where I live (near NYC) it rarely gets below 15 degrees - sometimes at night, but usually I'm not driving then. So the 15 degree threshold amounts to the same as turning off ERDTT under most conditions - and if it's really below 15, I'd probably appreciate the extra heat anyway.
 

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Discussion Starter · #18 · (Edited)
Kudos for a detailed post with lots of detail. I know this sort of 'blog' takes ages to pin together. (Also love the pair of red cars!)

In the cycling ERDTT mode, does the engine speed run up to a fixed speed and stay there, at a speed irrespective of accel pedal position, or does it vary in speed in response to the pedal position, like it does in hold?

I also think you are not quite accurate with the coolant circuit. I think they should have enabled a feature to allow block engine heating when plugged in, but it doesn't seem they have. If your engine does heat up then it might have a defective distribution valve, which controls exactly this function.

I also do not believe you gain '3 to 8 miles' from any additional top-up charging. This is an extra kWh or two, 10% to 20% extra SOC? I don't think so. When it is very cold, thick ice on the window, I will start mine up an hour before use and just leave it 'running' and plugged in. This method (as ari_c found out) adds a wee extra by filling up the 'buffer', but it amounts to 1 mile or so, max. If you are finding a difference between recharging for a while after pre-heating compared to not 'recharging' then this is because the preheating uses more electricity than the charger lead can supply, and it gets the extra form the battery. So immediately after 'preheating' the battery will be discharged and will need a top-up. You are probably comparing the depleted battery with the topped-up battery, rather than a topped-up battery with a 'super-topped-up' battery.
Thanks for your reply - When the engine runs on a Auto-Start it is controlled solely by temperature and only runs based on keeping the engine between two pre-set temperatures, so it is not related to throttle position - since it also charges, it follows the protocol of the mountain Mode with regard to charging to 45% SOC.

Since the Pre-heat function does heat the engine - there would be little need for a block heater. In addition - There is a dedicated means of heating the engine, its not a defect in any manner.

Regarding the extra 3-8 miles on a re-peaking of the cells - the two images substantially show 15 miles on 3 KW, this is not obtainable at least to me (with my driving habits) without re-peaking - this head charge is common on all types of chemistries such as ni-cad, Nickel, etc.

I did cover in my Level 1 & 2 charging the required charging times to re-peak the cells.

Thanks - Mike
 

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Discussion Starter · #19 ·
A nice looking writeup, but there are some errors.


ERDTT does absolutely nothing to maintain the condition of the batteries. It is a completely separate coolant loop and heater.
Heat from the engine cannot physically pass to the battery coolant loop.

And to avoid beating the horse that is why people don't want ERDTT with a full battery - I'll jsut say:
A lack of evidence showing failure does not prove ERDTT short cycling and low temp operation is good for an engine.
It also does not prove it is bad. But you cannot make conclusions that because nothing has failed yet, it must be ok.
In fact, there have been engine failures. People speculate as to what the cause might be (regular vs premium gas?)
The fact is, we just don't know.

Thanks for your reply - regarding your comment; "ERDTT does absolutely nothing to maintain the condition of the batteries" is not actually correct.

During a ERDTT cycle, the high-voltage batteries heater is activated which heats the cells providing the cells temperature is below their specified range. While the protocol of ERDTT is to start and stop the engine to maintain temperature, it also assumes the same electrical responsibilities as our Mountain Mode to charge and maintain the battery at 45% SOC. along with this responsibility is to control the batteries operating temperature as well.

Regarding your comments on start & stop operation, I can truly say in all my years in automotive, I never heard any concerns about starting our cars engine to often. Keep in mind, the Volt's engine is at around 100 degrees when started with the oil already circulated. This is the same temperature as starting any cars engine in the summer!

As an example, if we take a typical trip to town, if our Volt's RX had to start as many as 20 times for ERDTT, this would only duplicate maybe 3-4 days of starting of a conventional cars engine. If you're running errands around town it's not uncommon for us to start our cars engine 5 times a day or more. As you can see, there really is no concerns about constant starting, nothing has really changed!

Thanks - Mike
 

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"During a ERDTT cycle, the high-voltage batteries heater is activated which heats the cells providing the cells temperature is below their specified range. While the protocol of ERDTT is to start and stop the engine to maintain temperature, it also assumes the same electrical responsibilities as our Mountain Mode to charge and maintain the battery at 45% SOC. along with this responsibility is to control the batteries operating temperature as well. "

We'd need WOT to weigh in, but, this is pretty much wrong. ERDTT does not maintain SOC like mountain mode. The battery is drained to it's lower SOC as normal. And AFAIK, ERDTT has nothing to do with "the high-voltage batteries heater is activated". The batteries maintain their optimal temperature using a heater or the car's A/C as needed independent of any ERDTT event.

Basically, the only thing ERDTT does to save some battery energy is by using ICE heat to maintain cabin temperature instead of resistive coil heat.
 
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