[rangestransform]

This is a stupid idea because you’d have to make fasteners and high voltage interfaces that can survive an order of magnitude more cycles than they have to for a fixed pack. It would also be significantly more difficult to use the pack as a stressed member of the car structure. It’s better to just have less batteries and use them more efficiently through weight savings.

[Earw0rm]

Don't the charging ports already have to do that?

[bcrl]

Do you realize that one of the reasons for the swappable batteries on various Thinkpads is so that you can hot swap batteries without powering down or rebooting?

I've never had an issue with the connectors for the batteries of the ThinkPad, and being able to swap in a spare fully charged battery has been very helpful many times when out doing field working all day long. What is an issue are the little plastic tabs on the batteries that break off over time. However, usually the batteries have already lost a lot of their lifespan by the time that happens, and since the batteries are removable they can be replaced without opening up the system or melting glue with heat as is the case on most modern cell phones. Seems like a win to me!

[sightbroke]

I could be wrong but the currents and voltages for EVs are rather bit more dangerous and taxing than that typically found used in laptops.

Which I think the person you replied was partially attempting to point out.

[bcrl]

My point is that hot swappable battery packs have benefits that outweigh the cost of the connectors for the people that have a use case that needs them, as the grandparent referred to in Thinkpads. Not everyone fits in the constraints of design space chosen for a given product. There's a reason virtually every modern computer has a means of adding expansion devices.

Making a high voltage connector is well understood problem space. Every electrical engineer knows how to deal with ramping up current when a power supply is plugged in or turned on (inrush current specifications are most definitely a thing), and the entire electric grid is based on sizing, insulating, spacing and switching conductors appropriately for the voltage and current being used. Moreover, high voltage battery packs tend to have switches / contactors on the battery pack that keep the high voltage off until the connection is securely made and enabled, hence why even Telsas require a functioning low voltage battery to start the system.

There are also certain use-cases that are likely best served by putting battery packs in a trailer. Take the trucking industry: going by the charging requirements of a Tesla semi (1MW for 30 minutes), replicating your typical truck stop turns into a huge problem for the grid -- you'd need upwards of 50MW of charging capacity to replicate the flow of diesel coming out of a bank of 10 fuel pumps (sorry, I ran the thought experiment on that one back when specs were first released). Having a battery pack attached to the trailer that gets charged at a more leisurely rate at the warehouse while it is unloaded and re-loaded over a couple of hours is far more scalable than charging the truck in a few minutes at a truck stop. Charging overnight while the driver sleeps is fine, but getting the 8-12 hours of runtime for a workday in a semi is a heck of a lot of battery.

The dangers can be mitigated -- that's the entire raison d'etre of the electrical engineering discipline! Otherwise you wouldn't be able to safely charge an electric car at a 350kW rate these days at charging stations all over the world with a connector that is deemed safe to be handled by random humans. It's not like the software industry where we throw half baked shit at the wall and see what sticks when users encounter it by running an A / B test in production....

[sightbroke]

> Moreover, high voltage battery packs tend to have switches / contactors on the battery pack that keep the high voltage off until the connection is securely made and enabled, hence why even Telsas require a functioning low voltage battery to start the system.

These are little bit different than than what a swappable system would entail, aren't they?

> Otherwise you wouldn't be able to safely charge an electric car at a 350kW rate these days at charging stations all over the world with a connector that is deemed safe to be handled by random humans.

Okay maybe I miss read the initial premise but I took it as a home user swapping in-and-out modules themselves.

That would appear to me to be a significantly different engineering challenge and safety issue than what's currently deployed in consumer market EVs...

I'm not even sure the small upside here would justify the added costs and complexity either.

[bcrl]

> These are little bit different than than what a swappable system would entail, aren't they?

From an electrical point of view, swapping batteries is fundamentally the same general problem regardless of whether they are large or small: you want to avoid arcing when the connector is plugged in, and you need to avoid exposing the user to stray voltage. Sure, there's added complexity to achieve that in a safe and cost effective manner when high voltages are involved, but it's a solved problem as the charge port does exactly this today.

> Okay maybe I miss read the initial premise but I took it as a home user swapping in-and-out modules themselves.

Current EVs on the market suffer from decreased maintainability compared to traditional ICE vehicles. The battery swapping skill set needs to be more widely available so that we don't see EV owners being dinged $40k for a battery swap. There are videos on Youtube showing people doing a battery swap themselves, and while it is challenging, it's not all that hard to do safely when the battery is not damaged given that the battery packs don't expose high voltage on the connectors when not enabled. Of course a damaged battery pack means that all bets are off on the safety front depending on the nature of the damage.

> That would appear to me to be a significantly different engineering challenge and safety issue than what's currently deployed in consumer market EVs...

> I'm not even sure the small upside here would justify the added costs and complexity either.

It a solved problem!!! Just put the charge port at the back of the vehicle and then use it for the add-on battery pack like the existing signal light connectors for trailers. You're done. The only added design constraints on the EV are on the location of the port and verification that it works while the vehicle is being driven. The F150 Lightning fails this today since the charge port is just in front of the driver side door, but relocating the charge port is not exactly rocket science.

Many EVs have already taken the step of making the charge port bidirectional so that the expensive battery in an EV can be used to provide power during an outage or to balance the load on the grid, and that is a far, far more complicated problem than accepting power from an external battery pack through the charge port while the vehicle is operating.

[sightbroke]

> From an electrical point of view, swapping batteries is fundamentally the same general problem regardless of whether they are large or small: you want to avoid arcing when the connector is plugged in, and you need to avoid exposing the user to stray voltage. Sure, there's added complexity to achieve that in a safe and cost effective manner when high voltages are involved, but it's a solved problem as the charge port does exactly this today.

The arcing is the problem AND generally when handling battery packs/modules requires high voltage safety equipment and precautions.

The charge port uses a low-voltage connection to "handshake" as I understand it before the high voltage is being supplied.

You can't, without a good bit more complexity to the battery module itself do that as the batteries terminals will just have the voltage of the battery itself (depends on their state of charge).

Plus the bus bar the module is connecting to also will have a voltage if there's existing modules connected to it.

You're down to having contactors and BDUs at every individual module.

> Current EVs on the market suffer from decreased maintainability compared to traditional ICE vehicles. The battery swapping skill set needs to be more widely available so that we don't see EV owners being dinged $40k for a battery swap. There are videos on Youtube showing people doing a battery swap themselves, and while it is challenging, it's not all that hard to do safely when the battery is not damaged given that the battery packs don't expose high voltage on the connectors when not enabled. Of course a damaged battery pack means that all bets are off on the safety front depending on the nature of the damage.

I'm not saying it can't be done. I am saying it's harder to make it actually safe for the average normal consumer to do as simply as plugging a battery into a power drill for example. In part because of the higher voltages involved.

> It a solved problem!!! Just put the charge port at the back of the vehicle and then use it for the add-on battery pack like the existing signal light connectors for trailers. You're done. The only added design constraints on the EV are on the location of the port and verification that it works while the vehicle is being driven. The F150 Lightning fails this today since the charge port is just in front of the driver side door, but relocating the charge port is not exactly rocket science.

This is a different concept than adding/swapping individual modules in the vehicle itself.

But regarding the concept of a trailer, I suspect that the high cost for the product for the minimum gain it not justifiable for the average consumer. That is you're trying to solve a problem in an inefficient and not profitable manner. (Who wants a trailer of batteries parked in their garage 99% of the time just to have a slightly lighter car?)

> Many EVs have already taken the step of making the charge port bidirectional so that the expensive battery in an EV can be used to provide power during an outage or to balance the load on the grid, and that is a far, far more complicated problem than accepting power from an external battery pack through the charge port while the vehicle is operating.

I understand that, but either you want a trailer or you want internal swappable/addable modules which both economically in my opinion seem of little benefit over engineering better cars with newer/better battery technology and stronger/lighter material.

Additionally, I didn't even mention the annoyance of engineering integrating the heating & cooling system for the modules themselves.

Better energy density batteries & better materials (or smarter manufacturing) make more sense to me than trying to make individual modules for a car swappable or asking people to drive around with a trailer they would use so infrequently that it would not justify the cost to them (not to mention most people don't know how to drive with one properly anyways).