Hack-charging on a generator

[Cottonwood]

This tow-charging makes sense - how can the car know if it's being towed or if it's rolling down a steep hill? However the method is totally contrary to Tesla's very strong warnings about NEVER towing (only flat-bed). Can someone please explain the reasons for the "No Tow policy"?

Don't know, but I have heard (many levels removed, perhaps urban legend) that Tesla themselves have used the tow to charge method on both the R and S when they needed a quick charge on a demo car.

The real issue is where best to connect a tow line safely. The R has a nice screw in eye bolt. The method shown in the owner's manual for pulling up on a flatbed truck does not seem to safe for 30-50 mph charging.

 

[strider]

This tow-charging makes sense - how can the car know if it's being towed or if it's rolling down a steep hill? However the method is totally contrary to Tesla's very strong warnings about NEVER towing (only flat-bed). Can someone please explain the reasons for the "No Tow policy"?

Well, NO car maker will say that you should tow their car w/ a chain behind another vehicle. Typically one would do this because the car is broken down or out of fuel so that means no brake assist. If the tow car needs to stop suddenly you won't have power brakes to stop and you may ram the tow car. Also tow ropes brake all the time and become high speed cutting implements. Now I've done this when I was younger and couldn't afford a tow truck but had a friend w/ the truck. In my case it was the xmission that died so I could run the engine and still had brakes. Not the smartest thing to do but it works.

Now, the prohibition on using a "tow truck" (the kind w/ the hook on the back that lifts up one end of the car - it has nothing to do w/ Tesla or EV's. You will find that all "sports" cars (be them sedans or coupes) will have this same language (my Corvette was the same). It's because of low ground clearance. If you hoist the front or rear end you will drag the nose or tail on the ground.

 

[eledille]

This tow-charging makes sense - how can the car know if it's being towed or if it's rolling down a steep hill? However the method is totally contrary to Tesla's very strong warnings about NEVER towing (only flat-bed). Can someone please explain the reasons for the "No Tow policy"?

If you just want to tow the car, then regeneration might damage the towing car, and if the battery reaches 100% then regen would suddenly disengage, which might cause surprises. The regen creates a very noticeable drag, even at just 8 kW, which would be surprising if you weren't aware of it beforehand. Also, as Cottonwood describes, the rope should be fastened close to the center line, otherwise it would tend to pull the front wheels to one side, which would be dangerous.

I would think the Tesla regen would be able to keep going indefinitely, but that's speculation. I can imagine that the charge curve is less than ideal, also pure speculation.

And all of what strider said while I was writing. But if using a good rope and a rubber snubber, it will not break unless one of the drivers does something really stupid. You have to take it easy and tighten the rope slowly, but the snubber makes that a lot easier. Never tow with a chain only, it's not elastic at all and will break, and that's dangerous.

 

[Cottonwood]

If you just want to tow the car, then regeneration might damage the towing car, and if the battery reaches 100% then regen would suddenly disengage, which might cause surprises. The regen creates a very noticeable drag, even at just 8 kW, which would be surprising if you weren't aware of it beforehand. Also, as Cottonwood describes, the rope should be fastened close to the center line, otherwise it would tend to pull the front wheels to one side, which would be dangerous.

The charging limit is changes slowly as the battery fills and the PEM gets hot. I strongly doubt if there would be any sudden changes. Besides, what happens if the regen level changes, the speed of the two vehicles just speeds up or slows down.

The force at 750 lb is within reason, but probably a 2,000 lb working rating should be the minimum for the tow rope. See below for the calculations. Also, note that in addition to the losses of operating the tow vehicle, there is a 25% overhead in operating and pulling the Model S through the air. This may work as a fast charge in an emergency, but it certainly is not a "green," efficient charging method.

 

[eledille]

The charging limit is changes slowly as the battery fills and the PEM gets hot. I strongly doubt if there would be any sudden changes. Besides, what happens if the regen level changes, the speed of the two vehicles just speeds up or slows down.

If a braking force of 3.4 kN suddenly disappears, then you will certainly notice it. I seemed to remember someone saying that the regen of the roadster would cut out going downhill with a full battery, and that this was uncomfortable. I don't own one, unfortunately, so I don't know how it behaves in this respect. Anyway, agree that this should not cause any problems.

The force at 750 lb is within reason, but probably a 2,000 lb working rating should be the minimum for the tow rope. See below for the calculations. Also, note that in addition to the losses of operating the tow vehicle, there is a 25% overhead in operating and pulling the Model S through the air. This may work as a fast charge in an emergency, but it certainly is not a "green," efficient charging method.

I think if you're tow-charging, then efficiency and "green-ness" is probably low on the priority list. If I insisted on environmental friendliness even in emergencies, I would try to maximize regenerative power to reduce speed, which would reduce drag and increase efficiency. Don't do that unless you know for sure that the regen can take sustained max power, though. On the other hand, an ICE is usually at its most efficient at full power near torque peak, so I wouldn't be all that surprised if it turned out that tow-charging the EV and then driving it to the destination would be better than just driving the ICE instead. Just a thought, completely irrelevant really.

I think the really wonderful thing about it is that if there ever is a power outage lasting for weeks, or a shorter one but I want to run my fridge, tv and some lamps off the EV battery, or I need lots of kms in a hurry, or I'm stranded somewhere, or any other scenario that I can't think of now, then charging by towing really does work. Any other vehicle plus a rope is all I need, so I'll never be out of power.

Reminds me of those toy cars that you wind up by pulling them backwards

 

[dpeilow]

This tow-charging makes sense - how can the car know if it's being towed or if it's rolling down a steep hill? However the method is totally contrary to Tesla's very strong warnings about NEVER towing (only flat-bed). Can someone please explain the reasons for the "No Tow policy"?

The cars' electronics can take 40kW regen for a few seconds but I expect sustained regen/charging at that level will fry it.

 

[eledille]

The cars' electronics can take 40kW regen for a few seconds but I expect sustained regen/charging at that level will fry it.

It must be able to regenerate down steep hills, otherwise it would get into trouble in Norway and any other mountainous country. Warning signs saying ">8% - Low Gear" are not uncommon. Those who use their brakes instead of the engine down Måbødalen or down to Røldal run the risk of a nasty surprise halfway down the mountain when the brake fluid starts boiling.

The Roadster weighs 1235 kg. Going down an 8% decline at 80 km/h means losing height at a rate of 1.78 m/s. That's 21.5 kW, then subtract air and rolling resistance. It must be able to regenerate at that rate for several minutes, at least. A big sedan full of luggage, a whole family and their dog, plus ski box on the roof would be far worse. That said, I did not use max regen when I tried this, I even let the car roll freely from time to time just to be sure. It would be interesting to know the real max rated sustained regeneration.

 

[smorgasbord]

I thought this thread was about using a generator to charge an EV.

A lot of the recent posts are about ways to leverage regen to charge an EV - shouldn't they be moved to a different thread?

 

[mknox]

I thought this thread was about using a generator to charge an EV.

A lot of the recent posts are about ways to leverage regen to charge an EV - shouldn't they be moved to a different thread?

Well, the thread is called "Hack-Charging", so it seems any "hack" to get the car charged is fair game

 

[strider]

It must be able to regenerate down steep hills, otherwise it would get into trouble in Norway and any other mountainous country. Warning signs saying ">8% - Low Gear" are not uncommon.

The car will regen at max until the batteries or PEM heat up (or batteries become full). As they heat up (or fill up) the amount of regen will taper off - it will not suddenly stop. It works the other way too. After you range charge you will have no regen. As the batteries run down you will get more and more regen until they have run down enough that they can accept full regen. With the air-cooled Roadster PEM you may not be able to "tow-charge" for very long but the liquid-cooled Model S PEM should be able to do this for longer.

 

[smorgasbord]

Well, the thread is called "Hack-Charging", so it seems any "hack" to get the car charged is fair game

No, it's called "Hack-charging on a generator."

 

[eledille]

The car will regen at max until the batteries or PEM heat up (or batteries become full). As they heat up (or fill up) the amount of regen will taper off - it will not suddenly stop. It works the other way too. After you range charge you will have no regen. As the batteries run down you will get more and more regen until they have run down enough that they can accept full regen. With the air-cooled Roadster PEM you may not be able to "tow-charge" for very long but the liquid-cooled Model S PEM should be able to do this for longer.

So it seems that the car will do the sensible thing and protect itself if someone tries to regen-charge too aggressively - so no possibility of fried electronics?

No, it's called "Hack-charging on a generator."

Hack-charging with a rope?

 

[stevezzzz]

This is an interesting thread, and I don't mind at all that it suddenly veered off from generator charging to tow charging. Just to reassure all of you waiting for your cars, both the Roadster and the S are perfectly happy to provide regen braking when descending steep mountain roads with several thousand feet of elevation loss over some miles. Just last week I descended from 9000' to 5000' in the S starting with an SOC of about 65%, with grades occasionally exceeding 15%. For grins, I did it with the cruise control engaged and never touched the brakes or the accelerator. It's a very comfortable experience, and regen works like a charm.

 

[Robert.Boston]

Just last week I descended from 9000' to 5000' in the S starting with an SOC of about 65%, with grades occasionally exceeding 15%. For grins, I did it with the cruise control engaged and never touched the brakes or the accelerator.

What was the final SOC?

 

[FlasherZ]

This is an interesting thread, and I don't mind at all that it suddenly veered off from generator charging to tow charging. Just to reassure all of you waiting for your cars, both the Roadster and the S are perfectly happy to provide regen braking when descending steep mountain roads with several thousand feet of elevation loss over some miles. Just last week I descended from 9000' to 5000' in the S starting with an SOC of about 65%, with grades occasionally exceeding 15%. For grins, I did it with the cruise control engaged and never touched the brakes or the accelerator. It's a very comfortable experience, and regen works like a charm.

I was considering posting another thread in the local (to Colorado) forums to see if anyone had done just this. My concern would be descending the mountains and then SOC reaches 100%, causing regen to shut down, so you have nothing but service brakes to slow you. Given that much weight, I can imagine how red those rotors would be glowing by the time you hit the bottom.

I've heavily relied on engine braking before to assist with mountains...

I'm ok with this question being moved if required.

 

[stevezzzz]

I wouldn't worry too much about reaching 100% SOC on a downhill run unless, like Cottonwood, you start at the very highest point of the descent as you leave the garage with a full, Range mode charge. Interestingly, the drag losses and other drains on the battery are such that even at, say, 40-45 mph on average, you won't gain much SOC during any reasonable descent. In the downhill segment, 48.4 miles dropping a net 4000', the S consumed[/] 6.9 kWh, roughly 143 Wh/mi. During the steepest part of the descent I once saw the Rated range jump by three miles, from 175 to 178 over a five mile stretch. The Projected range went through the roof, touching 2400 a mile or two after reaching the bottom of the descent, but that's just wishful thinking.

I hope these are the right cell phone pix to document what I claim here: it's hard to pick them when you get to see only some dozens of thumbnails on an iPad. Note that there is a battery draw shown in the first three photos, even though it was a net downhill run. I threw in the last one just to show that it does go into the green sometimes. :biggrin:

 

[mknox]

No, it's called "Hack-charging on a generator."

Okay, I though it said Hack Charging on a Re-Generator

 

[strider]

So it seems that the car will do the sensible thing and protect itself if someone tries to regen-charge too aggressively - so no possibility of fried electronics?

Correct.

 

[cinergi]

My sister has a new Troy-Bilt 6kW (8.25 peak) generator. Runs the house well. I'm hunkered down here at her place for the storm so I thought I'd try charging from it. And not just 120.
I created an adapter so I could plug one end into the L14-30 on the generator and have a 14-50 on the other. I plugged in the car, set the amps to 5, and let it rip.
Long story short, it wasn't stable over 6 amps with HVAC off (set point; actual was +2) -- voltage was fluctuating around the 250v point (sometimes a few volts higher). It would stop charging, try again, rinse-lather-repeat 3 times and then give up. If I set it to 6 amps or lower, it continued to charge fine.
Not sure why it stopped but it may have been the >250v. Under no or light load, voltage was under 250. I gave up at that point (didn't feel like tuning the RPM a little lower or trying to plug other stuff in to effect a change in power factor or reduce voltage) ... thought I'd share.
I have a video of it that below.

The troy-bilt genny is the cheaper alternator type (vs. something made for electronics (not necessarily inverter)) so I'm not terribly surprised.

 

[FlasherZ]

Not sure why it stopped but it may have been the >250v. Under no or light load, voltage was under 250. I gave up at that point (didn't feel like tuning the RPM a little lower or trying to plug other stuff in to effect a change in power factor or reduce voltage) ... thought I'd share.

Thanks for the video... It's probably not the > 250V -- the chargers are actually rated for up to 265V. It's likely either the crazy voltage fluctuations, but my guess is actually that the car doesn't like the frequency fluctuations. My home's UPS's don't like the cheap gensets and refuse to charge at all, and it's because the frequency variation is too wide based on these generators' governors.

I find it odd that voltage increases under load in your test, generally it drops, and especially when it comes to the cheaper components used on these generators.

What's also odd is that your car shows it is charging at 1-2 amps over the target.