Heating Electric cars

[tjh290633]

I understand that batteries in electric vehicles have to be cooled by some means or other. Why do they not use the heat to provide interior heating, a bit like the VW Beetle did many years ago? I understand that the usual method of heating uses power from the battery.

TJH

[servodude]

I understand that batteries in electric vehicles have to be cooled by some means or other. Why do they not use the heat to provide interior heating, a bit like the VW Beetle did many years ago? I understand that the usual method of heating uses power from the battery.

TJH

Good question.

I think it's down to complexity, cost, weight and need.

The old VWs used air cooling, so there was hot/warm air around that you could redirect easily (vents valves ducts)

Most EV batteries will be liquid cooled for the immediate future - air cooling just isn't sufficient.
That means you'd need another converter to get the heat back out in to the cabin blowers, if the occupants want it, at the temperature they want.
And car AC/climate control systems just aren't set up to accept the heat from a battery's liquid cooling system.
That's not to say they couldn't be (or won't) but a suitable heat exchanger will be heavier (and harder to control) than something like a heating coil and if the balance of concerns comes down on the wrong side of improving the range of the vehicle then it will be ignored.

I keep hoping they can come up with a suitable peltier junction type thing to convert the heat back to electriciy (a thermal alternator?) so that it can be stored and used directly elsewhere (a different smaller battery that drives the vehicle electrics)

-sd

[tjh290633]

I believe the Hyundai Ionic 5 recovers waste heat from its batteries via a heat pump to warm the car.

I would have thought that was a strange way to get what you already have. Unless they are trying to increase the heat, of course. Using electric power to avoid using electric heat does make sense, but avoiding it altogether seems a better way.

TJH

[OhNoNotimAgain]

It is quite amusing to see the predicted range decrease as you increase the desired cabin temperature.

On a different tack has anyone experienced the problem of charging being limited to 80% in conjunction with an Electric Vehicle Systems Alert?
If so have they fixed it?

And yes I have disconnected the 12v battery to give it an Apollo 10 reboot but than made no difference.

Hyundai can't look at until August.

[staffordian]

I believe the Hyundai Ionic 5 recovers waste heat from its batteries via a heat pump to warm the car.

That may be correct, but I believe most higher spec BEVs use heat pump technology to heat the interior in the same way as a domestic heat pump works ie taking heat from the outside air, rather than using excess heat from the batteries, which would surely need a heat exchanger rather than a heat pump.

Whilst using battery heat seems an obvious win, the key advantage of a heat pump in a BEV is that it will heat the interior using less battery energy than the alternative, which is used in cheaper cars, which is the vehicular equivalent of putting a two bar electric fire in the cabin

[AF62]

I think the heat from the batteries is scavenged and boosted by the pump, as you say. The heat pump is also an efficient way to cool the cabin of the vehicle.

Aside from heating or cooling the cabin of the car, the heat pumps in some EVs are also used by the car to warm or cool the battery itself.

In cold weather the range of the car is impacted by a cold battery so warming the battery with a heat pump, preferably whilst it is still plugged in and charging, can improve that.

In warm weather the charging speed of the battery is impacted by heat so cooling it with a heat pump helps solve the issue. If I plug my EV in to charge on a day like this, then when I return to it the heat pump fans are making a significant noise trying to keep the battery cool.

[9873210]

FIrst, not all electric cars are the same.
Some are better designed than others. Some cars are designed, or have options, for different climates. Some are designed for different purposes. At the low end price is king and the "heating" system is designed only to partially defog the windows, the driver can wear gloves and long johns.

You should expect most designs to get better over time as we get a larger pool of experienced designers and OEM parts, and competition drives out ineffective designs.

Not mentioned: there is a tendency to use localized heating such as heated seats and steering wheels. This is usually electric resistance heating but putting small amounts of heat where you need it is more efficient.

[tsr2]

I understand that batteries in electric vehicles have to be cooled by some means or other. Why do they not use the heat to provide interior heating, a bit like the VW Beetle did many years ago? I understand that the usual method of heating uses power from the battery.

While some heating and cooling of the battery may be necessary in electric vehicles it seems unlikely that the batteries will produce enough waste heat in normal use to heat the cabin. In a combustion engined car the typical efficiency is around 20% with most of the waste 80% expelled as heat requiring substantial cooling systems, which can drive the cabin heating. EV efficiency is close to 90% and requires much less cooling. Battery cooling is not sufficient to require a big radiator and coolant run at close to boiling point, so there is just much less heat to extract and it would probably not be viable.

[scrumpyjack]

On the hottest day of the year I've had an email from VW inviting me to bring my car in for a software update that will improve performance in cold weather!! (plus a free replacement of the 12v battery with a better one). (ID4)

[staffordian]

On the hottest day of the year I've had an email from VW inviting me to bring my car in for a software update that will improve performance in cold weather!! (plus a free replacement of the 12v battery with a better one). (ID4)

I hadn't realised until reading it recently, but the 12v battery can be an issue with some BEVs. If it goes flat, the car won't go even if the traction battery is full, as it is instrumental in getting everything up and running.

Some but apparently not all BEVs constantly monitor the health of the 12v battery, whether or not the car is in use, and keep it topped up using some electrons from the traction battery. I'd have assumed all do this, but it seems not, so some can leave you stranded.

[9873210]

On the hottest day of the year I've had an email from VW inviting me to bring my car in for a software update that will improve performance in cold weather!! (plus a free replacement of the 12v battery with a better one). (ID4)

I hadn't realised until reading it recently, but the 12v battery can be an issue with some BEVs. If it goes flat, the car won't go even if the traction battery is full, as it is instrumental in getting everything up and running.

Some but apparently not all BEVs constantly monitor the health of the 12v battery, whether or not the car is in use, and keep it topped up using some electrons from the traction battery. I'd have assumed all do this, but it seems not, so some can leave you stranded.

The 12V system in BEV is a legacy from ICE cars. Since it works well enough in ICE there was and is no strong reason to change it. As long as the DC-DC convert that charges the 12V battery is at least as reliable as an ICE alternator (and it will be) there are no new failure modes. You can do things that make a BEV 12V system more reliable than an ICE 12V system, but it's not the low hanging fruit so it will be a few years for most manufactures.

Long term I'd expect BEV to forgo a 12V battery in favor of robust DC-DC converter, it's now industrial BEV have worked for decades. But not for a while. You really need a lot of work to make sure it never fails or you get pilloried in the telegraph.

I can also say from personal experience that jump starting a Prius with a flat 12V battery does not take much. You only need a few watts at 12V to boot the electronics. It does not need to turn a starting motor. You can "jump" the car directly from one of those lighter-to-lighter trickle chargers with 20 gauge wires. This should be similar for a BEV, unless the 12V battery is so badly damaged that it's a dead short rather than simply not holding charge very well.

[AF62]

I hadn't realised until reading it recently, but the 12v battery can be an issue with some BEVs. If it goes flat, the car won't go even if the traction battery is full, as it is instrumental in getting everything up and running.

For my BEV the manufacturer’s service schedule indicates replacing the 12v battery every 3 years, presumably to avoid this issue.

[Arborbridge]

I hadn't realised until reading it recently, but the 12v battery can be an issue with some BEVs. If it goes flat, the car won't go even if the traction battery is full, as it is instrumental in getting everything up and running.

For my BEV the manufacturer’s service schedule indicates replacing the 12v battery every 3 years, presumably to avoid this issue.

Another hidden cost of EVs. I can't honestly remember the last time I replaced my battery on an ICE, but it's more than three years ago. I'm not sure I ever have, and the car is 8 years old.

[Arborbridge]

On the hottest day of the year I've had an email from VW inviting me to bring my car in for a software update that will improve performance in cold weather!! (plus a free replacement of the 12v battery with a better one). (ID4)

I hadn't realised until reading it recently, but the 12v battery can be an issue with some BEVs. If it goes flat, the car won't go even if the traction battery is full, as it is instrumental in getting everything up and running.

Some but apparently not all BEVs constantly monitor the health of the 12v battery, whether or not the car is in use, and keep it topped up using some electrons from the traction battery. I'd have assumed all do this, but it seems not, so some can leave you stranded.

The 12V system in BEV is a legacy from ICE cars. Since it works well enough in ICE there was and is no strong reason to change it. As long as the DC-DC convert that charges the 12V battery is at least as reliable as an ICE alternator (and it will be) there are no new failure modes. You can do things that make a BEV 12V system more reliable than an ICE 12V system, but it's not the low hanging fruit so it will be a few years for most manufactures.

Long term I'd expect BEV to forgo a 12V battery in favor of robust DC-DC converter, it's now industrial BEV have worked for decades. But not for a while. You really need a lot of work to make sure it never fails or you get pilloried in the telegraph.

I can also say from personal experience that jump starting a Prius with a flat 12V battery does not take much. You only need a few watts at 12V to boot the electronics. It does not need to turn a starting motor. You can "jump" the car directly from one of those lighter-to-lighter trickle chargers with 20 gauge wires. This should be similar for a BEV, unless the 12V battery is so badly damaged that it's a dead short rather than simply not holding charge very well.

Unfortunately, VW got this wrong on the ID3 and the traction battery does not seem to top up the 12v in a reliable way, neither was the 12v man enough for the job. It's something which is being addressed through a software update and a new "technologically improved" battery.

We'll wait and see. So far, VW software updates have sometimes cured one known fault, only to create a further glitch.

Arb.

[AF62]

I hadn't realised until reading it recently, but the 12v battery can be an issue with some BEVs. If it goes flat, the car won't go even if the traction battery is full, as it is instrumental in getting everything up and running.

For my BEV the manufacturer’s service schedule indicates replacing the 12v battery every 3 years, presumably to avoid this issue.

Another hidden cost of EVs. I can't honestly remember the last time I replaced my battery on an ICE, but it's more than three years ago. I'm not sure I ever have, and the car is 8 years old.

I have a few times on ICE, usually around five years old, but then my cars then did live a hard life of a cold start with a three mile drive where they were left all day to a cold start three mile drive home.

[Hallucigenia]

Another hidden cost of EVs. I can't honestly remember the last time I replaced my battery on an ICE, but it's more than three years ago. I'm not sure I ever have, and the car is 8 years old.

You're probably on borrowed time then - both cars I've kept that long have needed a new battery after around 5 years IIRC.

[Arborbridge]

Another hidden cost of EVs. I can't honestly remember the last time I replaced my battery on an ICE, but it's more than three years ago. I'm not sure I ever have, and the car is 8 years old.

You're probably on borrowed time then - both cars I've kept that long have needed a new battery after around 5 years IIRC.

I'm sure I am! Probably in the first cold spell this winter. However, whatever happens it's considerably longer than the 3 years mentioned previously.

[Hallucigenia]

You're probably on borrowed time then - both cars I've kept that long have needed a new battery after around 5 years IIRC.

I'm sure I am! Probably in the first cold spell this winter. However, whatever happens it's considerably longer than the 3 years mentioned previously.

You're comparing apples with oranges though - a manufacturer's "replace so that you don't have problems" time is going to be shorter than the "keep until there are problems" time. I wasn't replacing them on the offchance they might go wrong, they were properly knackered at 5 years, not holding charge at all.

Halfords see rather more batteries than either of us and they say :
This question doesn’t have an easy answer, but it’s generally recognised that most car batteries last between 3 and 5 years.
There are several factors that can affect a car battery lifespan including temperature extremes, taking regular short trips, long periods of inactivity, vibrations from rough journeys and the number of electronic devices like sat navs and smartphones that join you on your drives.

Telegraph points to higher loads in modern cars being one reason for shorter life - and EVs tend to be tech-heavy in other areas.
of all the perishable components on our cars, we probably neglect batteries the most. And with technology placing increasing pressure on modern cars' electrical systems, batteries – which have barely changed in the history of the automobile – seem to be dying young. A good ballpark figure for car battery life is five years, but there are a number of reasons why you might find yourself replacing your battery much sooner. Depending on the types of journey you tend to take your car on, you could find your battery starting to show signs of age at three years, and become practically unusable after four.

So I don't think it's particularly anything to do with EVs per se, although a flat battery may have more impact in an EV than an ICE car and so it makes more sense to play safe by aiming to replace it before it goes badly wrong.

[88V8]

There are several factors that can affect a car battery lifespan ....the number of electronic devices ...

Yes, it doesn't take much to run a battery down.
In our 205, the radio had a habit of switching itself on when the car was parked, and used to flatten the battery.

In my 74 Land Rover, for reasons of expediency I installed a GPS speedo, and if left switched on it's constantly looking for a GPS signal, even that can run the battery down, not flatten it but the starter turns over noticeably slower.

In the 205, I cured the problem by removing the radio, and in the Landy I make sure to remove the master key so the battery is totally disconnected.

I gather that it is not practicable to disconnect the battery of a modern car.

V8

[Hallucigenia]

In my 74 Land Rover, for reasons of expediency I installed a GPS speedo, and if left switched on it's constantly looking for a GPS signal, even that can run the battery down, not flatten it but the starter turns over noticeably slower.

In the 205, I cured the problem by removing the radio, and in the Landy I make sure to remove the master key so the battery is totally disconnected.

I gather that it is not practicable to disconnect the battery of a modern car.

I guess the other option would be one of those solar trickle chargers for the Landy? Of course if a Landy is being used correctly, it will also be experiencing a lot of vibration which is not good for batteries. The final straw for my batteries has generally been a week in Scotland playing Colin McRae on forestry tracks. They'd make it home just fine - a long run on motorways - but then they'd be flat a week or two later.