I think you're underestimating how often you need to brake and the amount of power that's added to a system here. If I only get one brake every few minutes before you heat soak the wire, it's next to useless. I'd say at minimum you need to be able to handle 30 seconds of braking before any sort of 'cooldown' period.
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Heat battery while braking?
- Thread starter taraquin
- Start date
I think you're underestimating how often you need to brake and the amount of power that's added to a system here. If I only get one brake every few minutes before you heat soak the wire, it's next to useless. I'd say at minimum you need to be able to handle 30 seconds of braking before any sort of 'cooldown' period.
Why would it need to be a POINT of contact?
My old waterbed used to have a heater.
It never boiled.
The issue here is that regen braking is disabled when the battery is low.
No problem at all to have a heating element to dump the power so as to maintain regen braking AND warm the battery as a bonus.
You are deliberately being obtuse like my 7yo.
By "point" I don't mean a tiny point, I mean the surface of the heating element, if that area is a reasonable size and you try and dump a huge amount of energy you will have boiling across the surface. If the S\X heater is 6kw and you want to dump 60kw of energy in you are going to want a heater with 10X the surface area so the temp of the coolant at the contact AREA is not getting too hot. This is aside from the fact resistance heaters don't do well with fast cycling. You can see this using an electric range(not induction), they don't use a rapid cycling it is slow probably 10-15 seconds on/off. A lot of regen events are just a few seconds.
Another way to look at my point about area the power is applied to think about a magnifying glass and the sun, now the area the energy is applied to is much more than 10X reduced but the concept still works. The sun hitting 8sq in warms the area nicely, but apply that same total amount of energy to .1sq in and you can burn wood.
The heaters in the S/X are also a known point of failure so they need to be changeable with relative ease, start making the heater bigger to absorb more energy fast and you impact battery architecture and ease of part replacement.
Another thing I don't get is why so many random people think they know more than an engineering group numbering in the hundreds, the engineering group certainly can figure out something but they have an accounting group they need to work with and between them they decided what we get is the best balance.
100kW = 134hp.
deceleration times with 100kW braking power is equal to acceleration times with a 134hp motor.
One can decelerate from 125mph to 15mph in 30 seconds using 100kW of braking power.
From 80mph to 15mph it takes 12 seconds.
Braking slowly or hardly doesn't make much difference since the kinetic energy that transforms into heat is the same. So braking from 80mph to 15mph in 12 or 24 seconds means the same from heating point of view (except the rolling resistance losses).
And of course once the wire reached a limit temperature, it can be disconnected.
I understand how to convert between units. I also understand that it doesn't actually take 30 seconds to stop in almost any circumstance.
The problem is that drivers may do a lot of accelerating and braking repeatedly (stop and go traffic, just aggressive driving, etc), so you need a lot of extra margin to account for that. If the wire just 'gets disconnected' when it heats up too much, then you're back to inconsistent braking feel and weird results.
If I only get regen-like braking for the first 10 seconds of a stop over a 1 minute period, then it immediately goes back to freewheeling you have an unpredictable system that is garbage to drive. This is about consistency. Pulling away all of that heat from the wire quickly is going to be a bear.
Not sure if you noticed but regen doesn't work all the way down to 0mph. Every system (all models) has a transitioning period from regen to rotor braking.
Obviously. Although it does work down to 0mph on some cars, just not Tesla vehicles. That still doesn't invalidate any of my points, though. If you're in traffic and you regen repeatedly because of cars cutting you off or lots of acceleration/braking, then you'll hit a limit on this really really fast.
Why do you think you know better than teams of engineers that I guarantee have looked at this problem? This would offer Tesla an enormous boost in efficiency during the winter time compared to competitors, so I'm sure is something they'd be properly motivated to do if they could.
Why would the limiting be a problem? I don't see any of your points being valid. I already have a wire sitting at 50 deg C in the battery pack. Keeps heating the batteries. If its temperature drops, it will be raised back by the next braking.
Don't assume engineers are the ones making decisions. Tesla decided to leave out the electric heater from the Model 3. Why? Because it has to be a $35k vehicle.
I think you're glossing over how easy this would be to transfer the heat properly, keep things linear, not burn out the coils from the quick cycling, and have braking feel emulate the regen we get today. I'm sure SOME solution could be devised if cost was no object, but your suggestion that this is maybe a few hundred dollars in cost I think is wildly inaccurate.
If all of this is so simple, I suggest you start a battery pack manufacturing company, since there will be plenty of people clamoring to have cold weather range reduction solved.
"braking feel emulate the regen we get today"
good thing about a simple resistor is that it doesn't care about the shape of the waveform. So whatever went into the regen can go into the wire as well. And I doubt it would run into limitations in usual driving. Even if it does, it can be managed.
It isn't more difficult than the current system with the cooling ribbons currently used in the battery pack. Most likely these systems can be combined. But it adds cost and weight. Control systems are easy and cheap so the heat management you worry about is a non issue. Seat heaters have no issues with cyclic heating. This source here rates copper up to 100 deg C. Wires for Heating Applications | Delta T
I only calculated the cost of the raw material based on today's prices, so not sure what's wildly inaccurate there?
If this was implemented, they would use some cheaper solution with lower weight and limited to ~50kW.
But there are alternatives, like battery cell self heating.
diamond.g
Active Member
Bjorn has complained that the 7kw heater isn't fast enough to heat the pack enough to accept fast charging (for a short trip), so why include it in the 3 if they can get similar heating power from running the motors/inverters inefficiently?
Heater replacement in the S is $400 including labor, meaning wholesale purchase price is cheap enough it could have been included.
Seeing as it is a known point of failure that has already been updated I suspect warranty exposure is a big reason it was left out of the 3.
Heater failure immobilizes the car because it is a high voltage system problem, as such the car will not recharge the 12volt, since it can't recharge the car tells you "it may shut down at any moment" not an exact quote but you get the idea.
Who knows maybe they have battery chemistry in testing that improves cold weather chargeing so they chose to skip a separate heater for now knowing it would be redundant soon.
Again I think it foolish to presume we know more than the company.
Every penny matters in the automotive industry.
Is it still there in the new Raven? That will answer this.
By the way, older Model S had less efficient motors. So it already had a "built in" battery heating which the Model 3 achieves with suboptimal motor control.
?? Never said so.
My whole point is that it can be done in a reasonable way. And I think it is more expensive than the electric heater however more efficient.
I'm going to give you this tip for free. It would serve your own interest to specify which side of that "or" statement you are saying yes to.
Daniel in SD
(supervised)
60kW! I'm hired: Heavy Duty 60kw Commercial Electric Water Heater From Factory - Buy Electric Water Heater,Commercial Electric Water Heater,60kw Commercial Electric Water Heater Product on Alibaba.com
Resistors are very simple circuits. I am also curious why they didn't dump regen into heating the battery. I'm still getting limited regen warning, at 80% charge, in San Diego, in May!
And that is meant to be pulse width modulated not run for minutes at a time?
AlanSubie4Life
Efficiency Obsessed Member
Specifically talking about this device, and not about the feasibility/applicability for Model 3, it's an instant hot water heater, so presumably it can be run for very brief intervals.
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