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Old 29th February 2020, 22:43   #1
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Default Some technical questions on Electric Vehicles

We all know EVs are the next big thing. And, as an evolving technology, this subject raises several questions to us enthusiasts who have, up until now, grew up on a diet of ICE cars. Suddenly, words like displacement, bore, stroke, BHP, torque, turbo, N.A. are giving way to watts, volts and amperes. Not all of us can run back to physics books. I have, therefore, created this thread to raise questions pertaining to EVs. Needless to say, I have a few questions myself and I would benefit immensely from answers from EV-knowledgeable readers here on tbhp.
Note: If mods think a separate thread is unwarranted, please merge it under an appropriate thread.

Without any further ado, I will get into the questions I have. These are all I could think of right now. As we get deeper and deeper into EVs and as we come to drive/own, more and more questions may pop up down the line.

1. Charge Retention. This is not to confuse with battery degradation which happens over a period of years. By charge retention over a period of unused time, what I mean is, if I charge up my EV 100 per cent, leave on a vacation for 15 days the very next minute and when I return on 16 th day and turn on the engine, what would be the status of charge in battery? Will it be 100 per cent or would it have lost some of it even when car was unused. This happens in cell phones. I have a second cell phone which I do not use much. If I full-charge that cell phone and immediately turn off for 7 days and turn it back on on 8th day, I find 25-30 per cent of charge lost, even though the phone had remained turned off all through the week. And this, in a brand new phone. Do EV batteries also behave this way?

2. EV Transmission. We know about TC, CVT, DSG. AMT in ICE cars. We also know EVs have AT as default. Can we assume it to be a CVT or something similar, because we do hear about single gear AT in almost all EVs? Very few high-end EVs have 2nd gear to bump up top speed.

3. Conventional battery. When you throw open the bonnet, you see a conventional battery sitting up there. Whyyy? The whole floor of the car is battery anyway, albeit a different kind. Is this conventional battery provided to run lights, horn and aircon? If yes, then a follow-up question.

4. Assuming that conventional lead-acid battery runs aircon, can we run aircon in a parked car without "firing" the main engine? In an ICE car, you can't turn on AC without turning on engine because AC compressor runs off engine power. In a parked EV, the conventional battery may run the AC till that lead-acid battery dies. And, when this happens, we can start the main engine which will charge up the conventional battery. Since there is no self motor in EV, unlike an ICE car, a dead lead-acid battery makes no difference as the EV can start at the press of a button off power from main Li-on batteries. This seems to be my understanding of it. Am I wrong here?

Any replies in this regard would be much appreciated. Also, I hope I will not be laughed at or made fun of because these questions may sound childish to experts. Thanking one and all.
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Old 1st March 2020, 01:00   #2
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a) The battery of an EV, even if not being used, will still experience some chemical activity inside the cells, unless frozen to zero kelvin Also the battery continues to power some functions in the vehicle.

b) I had similar questions reg transmissions when the Formula e series started. The single-seater cars use a 3 speed transmission. The Taycan has a 2-speed unit for additional top speed, which is north of 250 kph. Benefits include better top speed and marginal increase in overall efficiency. Mind you the transmission needs to be small to be really beneficial (should not take out more energy and should weigh less as it needs to be carried along with electric power)



Source: https://www.cnet.com/roadshow/news/z...electric-cars/

c) I've seen conventional batteries in mild hybrids where they're utilised for engine start-stop function along with some other functions and the small lithium ion battery provides torque assist and stores regen-energy. In which EV did you notice the conventional battery?
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Old 1st March 2020, 07:33   #3
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2) An EV motor is always connected to the wheels through a fixed transmission. So when you turn on an EV the motor does not run, the motor starts working only when the accelerator is pressed or brake released if the car has creep mode. Even Tesla's used 3 speed transmission on their roadster 1 which was always locked in gear 2. Except for Porsche taycan all EV have this direct drive, Porsche tatvam changes to gear 2 at 75kmph.

3) LA battery is used for lights, electronics and from what I read to start the car( to bring the main battery live). LA battery is cheaper to have as a 12v battery then a Li battery. In case of your main battery and LA are drained completely it is easy to charge a LA battery at a local garage and turn your electronics and charge your main battery. Also do note that the main battery charges the LA battery by DC to DC conversion.

4) EVs aircon is run by the main battery. One of the advantages of EVs is you can sit in your car for hours with your aircon turned on. This is how Tesla is implementing their dog mode & camp mode. With dog mode the car keeps the dog comfortable while you go shopping unless somebody breaks your car to save the dog .

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In which EV did you notice the conventional battery?
All EVs including Tesla's, kona...
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Old 1st March 2020, 08:41   #4
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Default re: Some technical questions on Electric Vehicles

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1. Charge Retention. This is not to confuse with battery degradation which happens over a period of years. By charge retention over a period of unused time, what I mean is, if I charge up my EV 100 per cent, leave on a vacation for 15 days the very next minute and when I return on 16 th day and turn on the engine, what would be the status of charge in battery? Will it be 100 per cent or would it have lost some of it even when car was unused. This happens in cell phones. I have a second cell phone which I do not use much. If I full-charge that cell phone and immediately turn off for 7 days and turn it back on on 8th day, I find 25-30 per cent of charge lost, even though the phone had remained turned off all through the week. And this, in a brand new phone. Do EV batteries also behave this way?

All batteries will lose charge even in unused due to the chemical properties of the batteries.

Plus, the batteries in car are always powering one or the other functions namely the BMS(Battery Management System) to control charging as well maintain the SOC(State of Charge), door lock/unlock, car firmware upgrades etc... So they are never completely idle(This may be true even in case of mobiles,especially which has smart batteries).

However the power consumption in car will be very negligible compared to its capacity. It will take very long idle parked time(in months) to lose considerable amount of charge.
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Old 1st March 2020, 08:50   #5
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Default re: Some technical questions on Electric Vehicles

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All batteries will lose charge even in unused due to the chemical properties of the batteries.

Plus, the batteries in car are always powering one or the other functions namely the BMS(Battery Management System) to control charging as well maintain the SOC(State of Charge), door lock/unlock, car firmware upgrades etc... So they are never completely idle(This may be true even in case of mobiles,especially which has smart batteries).

However the power consumption in car will be very negligible compared to its capacity. It will take very long idle parked time(in months) to lose considerable amount of charge.
Yes, typically Tesla loses around 15% of charge every month. So after a three month vacation, you can expect your parked Tesla to be at 150 miles, rather than the 300 miles full charge you leave it at
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Old 1st March 2020, 08:59   #6
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The Cheapest EV Conversion Ever Seen and it is a Maruti 800!

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Old 1st March 2020, 09:23   #7
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Originally Posted by pgsagar View Post

1. Charge Retention. This is not to confuse with battery degradation which happens over a period of years. By charge retention over a period of unused time, what I mean is, if I charge up my EV 100 per cent, leave on a vacation for 15 days the very next minute and when I return on 16 th day and turn on the engine, what would be the status of charge in battery? Will it be 100 per cent or would it have lost some of it even when car was unused. This happens in cell phones. I have a second cell phone which I do not use much. If I full-charge that cell phone and immediately turn off for 7 days and turn it back on on 8th day, I find 25-30 per cent of charge lost, even though the phone had remained turned off all through the week. And this, in a brand new phone. Do EV batteries also behave this way?

.
Thank you for starting this thread. EV is a topic I am very interested in. I believe this to be the future together with another disruptive technology in clean energy production. Don't know what that would be but I feel we are not far.

Coming to your this particular point, normally when batteries are fully charged but still connected to the mains (for eg your inverters), there is something called trickle charging wherein the charging current still flows but just enough to balance the discharging happening at idle.

So my question, are EVs disconnected from the mains when you are away for long periods? If no, then probably the trickle charging will take care to ensure 100% charge availability when you are back.

If they are disconnected, then of course this could be an issue, but I don't think it would be a big proportion of the total energy storage. In order for the battery to be completely discharged, it would perhaps need months of inactivity.

Comparing with ICE cars, we should remember that for long period storage it is recommended to drain off the fuel tank to prevent deterioration of fuel inside.

I have another question to those who intend to buy EVs but stay in apartments. I assume you will have to draw in cables from your main supply to set up a charging point near your parking place. How do we ensure that power theft does not happen in such cases. I mean anyone can drive up and charge their car when you are not around. Or is it under lock and key?
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Old 1st March 2020, 15:11   #8
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Default re: Some technical questions on Electric Vehicles

Thanks a ton guys for prompt reply. It took me more than one reading to grasp some points. I'm an EV dummy, you see. Question mo.1 was most important to me. Now it's clear that a fully charged EV loses power even when parked unused. As, tsk1979 has pointed out , a Tesla loses 50 % in 3 months. Now, that's Tesla which is at the pointy peak of EV pyramid. I'm sure budget-end EVs will lose more charge. Now, this is a matter of concern as an additional cost. A fossil fuel car hardly loses any fuel to evaporation in 3 months. Even petrol, which is more volatile than diesel, doesn't deplete because of hermetically sealed fuel cap. I think it evaporates in the heat of the day and condenses back to liquid again inside the tank in the night. Right?

Coming to EVs, isn't there any way around this battery charge depletion? Can't they provide a kill switch which isolates charged battery from every system of the car? You hit that switch when you go outstation for long periods of time.

I think while calculating per KM running costs of an EV, we need to factor in this charge depletion which just vanishes into thin air. Not everyone uses his car on a daily basis. There are retirees and frequent flyers who have their cars sitting parked for a week to a month(s) or more. The lost charge in such scenario adds to the running costs. And, lastly, thanks once again guys.
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Old 1st March 2020, 17:55   #9
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Default re: Some technical questions on Electric Vehicles

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3. Conventional battery. When you throw open the bonnet, you see a conventional battery sitting up there. Whyyy? The whole floor of the car is battery anyway, albeit a different kind. Is this conventional battery provided to run lights, horn and aircon? If yes, then a follow-up question.

4. Assuming that conventional lead-acid battery runs aircon, can we run aircon in a parked car without "firing" the main engine? In an ICE car, you can't turn on AC without turning on engine because AC compressor runs off engine power. In a parked EV, the conventional battery may run the AC till that lead-acid battery dies........ This seems to be my understanding of it. Am I wrong here?

3. The main battery system ( called as High Voltage (HV) Battery ) is at much higher voltage rating ( typically either 48V or in the range of 300 - 500 V DC ). In current vehicles, all the accessories ( coolant pumps, lights etc) and controllers are designed to run @ 12 V. So we need a secondary battery rated at 12 V ( called low voltage , LV circuit) . This battery is usually a Lead acid battery and is charged by the High voltage battery whenever the battery charges level drops below a threshold.



4. In a ICE, the compressor is mechanically driven by engine . In a EV, the compressor is a electric compressor and is run by the high voltage battery as the compressor voltage rating is higher that 12V . Hence in parked condition, the AC will draw power from main battery and not the conventional low voltage battery.

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Old 1st March 2020, 18:05   #10
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Coming to your this particular point, normally when batteries are fully charged but still connected to the mains (for eg your inverters), there is something called trickle charging wherein the charging current still flows but just enough to balance the discharging happening at idle.

So my question, are EVs disconnected from the mains when you are away for long periods? If no, then probably the trickle charging will take care to ensure 100% charge availability when you are back.

Trickle charging a lithium ion batteries should not be done. The lithium ions will not tolerate overcharge and will result in irreversible damage.
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Old 1st March 2020, 20:38   #11
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Coming to EVs, isn't there any way around this battery charge depletion? Can't they provide a kill switch which isolates charged battery from every system of the car? You hit that switch when you go outstation for long periods of time.
I have had my Model3 for 2 years now, and I occasionally travel for long periods of more than a week. I always leave the charger cable connected to the car. With connected cars you control when and how much you want to charge. So I schedule for the charging to begin the night before I arrive.
When I forgot to connect the cable, I have had to call my kids to go connect the cable. Unfortunately, the app can't do that.
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Old 1st March 2020, 22:30   #12
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3. The main battery system ( called as High Voltage (HV) Battery ) is at much higher voltage rating ( typically either 48V or in the range of 300 - 500 V DC ). In current vehicles, all the accessories ( coolant pumps, lights etc) and controllers are designed to run @ 12 V. So we need a secondary battery rated at 12 V ( called low voltage , LV circuit) . This battery is usually a Lead acid battery and is charged by the High voltage battery whenever the battery charges level drops below a threshold.


4. In a ICE, the compressor is mechanically driven by engine . In a EV, the compressor is a electric compressor and is run by the high voltage battery as the compressor voltage rating is higher that 12V . Hence in parked condition, the AC will draw power from main battery and not the conventional low voltage battery.
Thanks for clearing that up. And, let me see if I got this right. In an ICE car, we do have to keep the engine running as AC runs off engine power. In EV, AC will run off the main battery without the motor running. And, motor kicks in only when we step on the accelerator. Niiice.

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I have had my Model3 for 2 years now, and I occasionally travel for long periods of more than a week. I always leave the charger cable connected to the car. With connected cars you control when and how much you want to charge. So I schedule for the charging to begin the night before I arrive.
When I forgot to connect the cable, I have had to call my kids to go connect the cable. Unfortunately, the app can't do that.
Gutsy, when I said a way around charge depletion, I didn't mean how to replenish lost charge. Sure, you can leave the car connected to power source. What I meant instead was, how to prevent battery from losing any percentage of charge, however minuscule. Because the lost charge adds to per Km cost of EV. Being from SoCal yourself, not sure if are aware of "kitna deti hai" math we run here. Hence my question about any battery isolation switch. Like in ICE cars, when we go away for 3/4 months , we pull out the battery connectors to keep the battery from going dead.
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Old 1st March 2020, 22:38   #13
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Trickle charging a lithium ion batteries should not be done. The lithium ions will not tolerate overcharge and will result in irreversible damage.
The car knows how much to charge, in fact you can limit the charge percent. Many owners do komt to 80% charge percent, check Mohan's post in kona ownership review he limits charging to 80%. The rule many EV owners follow is 'Always stay plugged' , Gutsygibson a TM3 owner following same practice from above post.
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Old 2nd March 2020, 04:37   #14
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Gutsy, when I said a way around charge depletion, I didn't mean how to replenish lost charge. Sure, you can leave the car connected to power source. What I meant instead was, how to prevent battery from losing any percentage of charge, however minuscule. Because the lost charge adds to per Km cost of EV. Being from SoCal yourself, not sure if are aware of "kitna deti hai" math we run here.
Vampire drain is for real. The battery management system is up and running depending on ambient conditions. There is no real solution for vampire drain.
I still do the "kitna deti hai" on the gasoline powered motorcycle and my second car. The EV is mostly powered by home solar. Sending any excess power back to the grid, the tariff per kW is much less than what they sell it to us at. We are better off using all of what we produce.
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Old 2nd March 2020, 09:28   #15
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All EVs including Tesla's, kona...
Thanks, where is it packaged? I took this photo from a Kona info kiosk in a Hyundai outlet sometime back. Didn't mention the lead acid battery.
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