Regenerative Braking while Flat Towing

[BigB]

I Flat Tow my Nissan Frontier with my Motorhome using a Blue Ox Patriot 3 Braking system. It uses a sensor on the dashboard to send a signal to a device in my truck that manually presses the brake pedal to Slow The Vehicle..

Wouldn't this charge the truck every time I hit the brakes? I really Want to Enhance the capability Of Regenerative charging While I tow it with my motorhome Period For example Using an app Let's say I wanted to add 10 percent Resistance To charge The slates battery or have an AI app that knows when to regenerate for example going downhill or just taking your foot off the gas Etc

 

[Lynn]

You're right that this is a problem. The Patriot (and others) draw energy from the towed vehicle's battery in order to operate the mechanical foot. But you want the low-voltage (and the high-voltage) system turned off in order to tow the EV four-down.

This will be an issue for the Slate or any any other towed electric vehicle that requires on-board braking. (Not all towed vehicles require on-board braking. It varies by state, however. Here in the four-corners states of the US southwest, the magic number is 3000 pounds US.)

One solution would be to add a simple 12v battery to the EV, and to keep it charged up via wiring from the motorhome's umbilical cord. Not a rocket-science arrangement.

That matter is solvable, but I think the bigger issue is going to be whether the EV is towable at all four-down. If the Slate is not four-down towable, I plan not to purchase.

 

[BigB]

Same Here.. if it cannot be a flat towed I will not buy it it's that simple as far as the regenerative charging that would be absolutely outstanding and that is the car I will buy even if it is not the Slate

 

[BigB]

I think that it can be done somehow. The car would have to be on and put into tow mode and when you hit the brakes on the tow vehicle it will sense the deceleration and apply regenerative braking

 

[Lynn]

I wouldn't count on regen charging at all. Regen braking is handled via the EV's onboard computer, which needs to be turned off during towing. (In my EV, the computer is powered by the low-voltage system, which is turned off during any tow.)

 

[BigB]

The short answer is no. There are currently no small Chinese electric vehicles (or any production EVs, for that matter) available in the US that support flat towing with regenerative charging.
While the idea is theoretically brilliant—using your RV to charge your toad (towed vehicle) while you drive—the current technology and import laws make it impossible.
Here is the technical and regulatory breakdown of why this doesn't exist yet.
1. The Technical Barrier: Permanent Magnet Motors
Most modern EVs (likely including the Slate truck you reserved and the small Chinese EVs you are asking about) use Permanent Magnet Synchronous Motors (PMSM).
* The Problem: In a PMSM, the magnets are always "live." If the wheels turn, the motor spins and generates electricity.
* The Risk: If the vehicle is "off" (flat towing), the cooling system is also off. The motor generates massive amounts of heat and back-electromotive force (EMF) with nowhere for that energy to go. This will fry the inverter and overheat the motor windings within miles.
* Why "Regen Towing" is a Myth: You might see YouTube videos of people "tow charging" a Tesla or Rivian. This is done by putting the car in Drive (not Neutral) with a driver in the seat to keep the systems active. It creates immense drag (like towing a brick wall), putting dangerous strain on your RV's transmission and hitch. It is not a supported "set it and forget it" feature.
2. The Legal Barrier: "Neighborhood Electric Vehicles" (NEVs)
The small Chinese vehicles you see online (like the Chang Li, Kandi, or Minghong) enter the US under a specific legal classification called Low Speed Vehicles (LSV) or NEVs.
* Speed Cap: By law, they are electronically limited to 25 mph.
* Restricted Access: They are only legal on roads with speed limits of 35 mph or less. You cannot legally tow them on the highway behind your Itasca, nor can you drive them on highways once you unhook.
* Structural Safety: These vehicles often use scooter-grade tires and suspension. Flat towing them at 65 mph behind your motorhome would likely disintegrate the wheel bearings or tires.
3. What About Your Slate Truck?
Since you have a reservation for a Slate, you are already on a better track than a grey-market Chinese import. However, based on the preliminary specs for the Slate (Rear-Wheel Drive, Permanent Magnet Motor), you need to be careful:
* Projected Towability: Unless Slate specifically engineers a mechanical rear-axle disconnect (unlikely on a budget-focused $27k vehicle), you likely cannot flat tow the Slate either.
* The Solution: You will almost certainly need a flatbed trailer for the Slate. This solves the wear-and-tear issue and protects the EV's drivetrain completely.
Summary
* Chinese Small EVs: Not highway legal, cannot be flat towed at speed.
* Regen Towing: Technologically dangerous; destroys motors/inverters without active cooling.
* Recommendation: Stick with your Slate reservation, but plan to use a lightweight aluminum car hauler (trailer) rather than flat towing.
Next Step: Since the Slate is still in the prototype phase, would you like me to monitor their engineering updates specifically to see if they announce a "Neutral Tow Mode" or rear-axle disconnect feature?

 

[BigB]

Well there you have it this is the deal breaker if it cannot be flat towed in neutral I don't want it I will stick to my pickup truck in neutral with the Blue Ox Patriot braking system

 

[GaRailroader]

I would think it would be difficult to have it be regenerative braking without it being regenerative all the time. That would be a lot of extra load on the tow vehicle to have the Slate recharging all the time when it is being towed. I wonder whether they are planning to use an induction motor or permanent magnet motor on the Slate? If they use an induction motor then you just don’t energize the ‘magnetic’ field and the motor will freewheel a lot better than a permanent magnet motor where the magnetic field always exists.

 

[BigB]

That's exactly what AI said..

Nobody not even China has done this yet so that is the golden opportunity for Slate. If they use a brushless motor I think it would work as a braking regen system.

Everyone has been telling me to just get a hybrid 2005 Maverick that has the Flat Towing Function.

I seriously think this can be done but there would have to be an accelerometer in the vehicle which would apply resistance which could regenerate energy

Honestly if they could simply make a way to completely disconnect the transmission from the motor that would be the cheapest way to go and I would be happy with that otherwise I am not going to buy one

 

[BigB]

As an extremely simple solution I think of the Warn 4x4 Locking Hubs

This is a brilliant engineering concept, and you are absolutely correct on the physics: if you can mechanically disconnect the rear wheels at the hub, the permanent magnet motor won't spin, won't generate back-EMF (electricity), and won't fry the inverter while towing.
However, since you want to "engineer" this, we need to look at the specific mechanical hurdles of the Slate’s chassis. It is not a standard solid axle truck.
Here is the technical feasibility analysis of putting "Warn Hubs" on a Slate EV.
1. The Suspension Problem: The De Dion Axle
The Slate truck reportedly uses a De Dion rear axle.
* What this means: The electric motor and differential are bolted rigidly to the frame (chassis). The wheels are connected to the motor via CV half-shafts (like a front-wheel-drive car), but the wheel hubs are connected to each other by a rigid tube (the De Dion tube) to keep the tires vertical.
* The Friction Point: Most modern setups like this use Unit Bearings (sealed hub assemblies).
* The Hub Issue: Standard Warn locking hubs require a hollow spindle design where the axle shaft slides through the center and locks into a splined gear at the tip. A Unit Bearing usually has no room for this mechanism; the CV shaft nut clamps the bearing together.
2. How you would have to Engineer it
To put manual locking hubs on the rear of the Slate, you cannot just "bolt them on." You would need to fabricate a Full-Floating Conversion for the rear end.
The Build List:
* Custom Knuckles/Uprights: You would need to machine new rear uprights (the part the De Dion tube attaches to) that accept a standard 4WD front spindle (like a Dana 44 front spindle).
* Custom Outer Stubs: You would need to take the Slate’s CV half-shafts and machine custom outer stub shafts. instead of a threaded end for a nut, the shaft needs to end in splines (usually 19 or 30 spline) that sit inside the spindle.
* The Hub Body: Once you have a hollow spindle and a splined shaft inside it, you can bolt on a standard Warn Premium hub body.
Result: When you turn the dial to "FREE," the wheel spins on the spindle bearings, and the CV shaft (and motor) stays stationary. Safe to tow.
3. The Easier Alternative: Axle Disconnect (The "Remco" Approach)
Since machining custom knuckles is a major project, the alternative engineering path is a Half-Shaft Disconnect.
* Concept: Install a sliding spline collar (dog clutch) in the middle of the rear CV shafts.
* Mechanism: You crawl under the truck, pull a pin, slide a collar over to disengage the wheel side from the motor side.
* Pros: You don't have to mess with the wheel bearings, brakes, or ABS sensors.
* Cons: It introduces a weak point in the axle shaft that has to handle 100% of the EV's instant torque.
4. Why Slate might do this for you
Slate has publicly confirmed they are working on "Flat Tow Capability."
Since they use Permanent Magnet Motors (which generate electricity even when "off"), they cannot just use a software "Neutral" like a Tesla induction motor could.
* Prediction: They will likely install an electromechanical dog clutch inside the gear reduction box. When you select "Tow Mode" on the screen, a solenoid will physically disconnect the motor from the output shafts.
Summary:
Your idea is the Gold Standard for protection (physical disconnect at the wheel = zero risk). But because the Slate likely uses Unit Bearings, you are looking at a full custom machine shop project to adapt a "Ford/Jeep style" locking hub to a modern EV suspension.

 

[Lynn]

Mine is an EV conversion, not a production vehicle.

The BMS controls a lot of functions, including regen, which is also switched.

A toggle on the dashboard disables regen. It also has a manual low-voltage switch and a manual high-voltage switch.

When all systems are switched off, the Hyper9 motor spins freely.

An idiosyncratic matter with this car is that the manual transmission prevents towing in neutral. Very unusual, but it happens. (It's the five-speed transmission made by Mazda for the MX-5.) In order to flat tow the car, the following must obtain:

1. Transmission in a high gear (4th or 5th, just to slow down the motor)
2. Regen off (just to make sure)
3. Low-voltage off (which turns off the BMS computer)
4. High-voltage off (so no charging of the battery packs is possible)


Lynn

 

[BigB]

Mine is an EV conversion, not a production vehicle.

The BMS controls a lot of functions, including regen, which is also switched.

A toggle on the dashboard disables regen. It also has a manual low-voltage switch and a manual high-voltage switch.

When all systems are switched off, the Hyper9 motor spins freely.

An idiosyncratic matter with this car is that the manual transmission prevents towing in neutral. Very unusual, but it happens. (It's the five-speed transmission made by Mazda for the MX-5.) In order to flat tow the car, the following must obtain:

1. Transmission in a high gear (4th or 5th, just to slow down the motor)
2. Regen off (just to make sure)
3. Low-voltage off (which turns off the BMS computer)
4. High-voltage off (so no charging of the battery packs is possible)


Lynn

I was looking at just converting my current truck by using a used Nissan Leaf full stack the only problem is where to put the battery but I wouldn't even care if I just put it in the bed of the truck but it would raise the center of gravity

I'm going to have to look at what you did for your conversion do you have a YouTube or Facebook Maybe

 

[Lynn]

There are a bunch of pictures of the conversion on my Flickr site. Most of the pics were done by Nick Bradley, the proprietor of the company that did that part of the work:

pictures of conversion

I did part of the job (removal of ICE and all related equipment), and Nick did the rest.

 

[BigB]

I'm getting NOWHERE
Your logic regarding induction motors is technically sound in isolation: unlike Permanent Magnet (PM) motors, an induction motor does not generate Back Electromotive Force (Back-EMF) when it spins in a de-energized state. Theoretically, if a Tesla had only induction motors, you could spin the rotors without frying the inverter voltage clamps.
However, you still cannot flat tow them for three specific technical reasons:
1. The Lubrication System is Electric, Not Mechanical
This is the primary mechanical failure point. In a traditional internal combustion vehicle with an automatic transmission, the transmission fluid pump is driven by the input shaft (engine rotation). In a Tesla Drive Unit (both Large Drive Unit and Small Drive Unit), the lubrication is managed differently:
* Modern Units (Model 3/Y/Raven S&X): Use an electric oil pump (12V) to circulate fluid (Pentosin ATF 9) through the heat exchanger and onto the gears/bearings. When the car is "off" or in a passive Neutral state, this pump is not active. Flat towing would spin the final drive gears and motor rotor at highway speeds (up to 15,000+ RPM) with dry bearings and gears, leading to rapid catastrophic failure.
* Older Units (Legacy Model S/X): Relied largely on "splash lubrication" (gears dipping in oil). While this might theoretically survive low-speed towing, it lacks the active cooling required to dissipate the heat generated by the gearbox friction over long distances.
2. Thermal Management Systems are Inactive
Even if the induction motor is not generating electricity, the mechanical friction of the rotor spinning at 10,000+ RPM creates significant heat.
* Tesla’s cooling loops (glycol-based) actively pull heat from the stator and the inverter.
* During a flat tow, the vehicle's high-voltage contactors are open (battery disconnected). The coolant pumps and radiator fans are off. The drive unit effectively becomes a sealed, uncooled box generating friction heat, which will eventually cook the stator insulation and seal rings.
3. The "Dual Motor" Trap
You must be certain the vehicle is purely induction.
* Legacy Model S/X (pre-2019): Often used dual AC induction motors.
* Model 3/Y & Modern S/X: Almost all Dual Motor configurations now use a Permanent Magnet Switched Reluctance (PMSRM) motor in the rear (for efficiency) and an AC Induction motor in the front (for boost).
* Even if the front induction motor is safe to spin, the rear PM motor will instantly generate high-voltage Back-EMF, overwhelming the inverter's DC bus capacitors and likely destroying the power electronics.
Summary
While you are correct that a de-energized induction motor doesn't act as a generator, the lack of active lubrication and cooling (due to electric pumps being off) makes flat towing mechanically fatal to the drive unit.