# Shoot down my electric car charging solution. **URL:** \ **Category:** Factual Questions\ **Created:** [April 29, 2011, 1:09pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152 "2011-04-29T13:09:42Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Nars\_Glinley](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nars_glinley/32/8177_2.png) [@Nars\_Glinley](https://boards.straightdope.com/u/Nars_Glinley)\ **Post date:** [April 29, 2011, 1:09pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/1 "2011-04-29T13:09:42Z")
TANFL. I get that. I really do. Any energy used to charge the batteries has to come from somewhere. My idea (I’m calling it mine but it’s entirely possible that someone else has already thought of it and figured out why it won’t work) is to harness power from the shock absorbers. As I understand it, they are working all the time due to even tiny fluctuations in the road. Couldn’t some sort of generating apparatus be put at the end of each of these to harness this energy? Since TANFL, the generator itself would help decrease shock which is after all the purpose of a shock absorber. That’s it. It seems simple enough but I’m sure there’s some glaring hole that I’m not seeing. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [April 29, 2011, 1:19pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/2 "2011-04-29T13:19:56Z")
Have you done any calculations as to the maximum recoverable energy from a rough road? Is it worth pursuing? ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [April 29, 2011, 1:27pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/3 "2011-04-29T13:27:29Z")
> [@Musicat](#): > > Have you done any calculations as to the maximum recoverable energy from a rough road? Is it worth pursuing? That’s my thought, other then big bumps, those minor fluctuations are pretty minor. On top of that, you’d need something (a rectifier?) to make sure that both directions charge the battery instead of a dip in the road charging while a bump drains the battery. That’s going to add weight (I assume…unless it’s inherent in the design). If I were the OP, before going any further with this, I’d study regenerative breaking. Just to understand how it works. How is the power captured, how is it “ignored” when the person isn’t breaking, how is the power from all four wheels combined to one source and sent to the battery etc… and see if any of that can be applied to this. Also, what does TANFL stand for? ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [April 29, 2011, 1:35pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/4 "2011-04-29T13:35:25Z")
Also, something else this reminds me of that I would look into is wave energy. On the surface, it seem similar enough that it seems worth a casual look. When people attempt to capture wave energy, they’re trying to capture the energy produced by the vertical movement of the water, similar to what you’re trying to do with the car. Also, I remember something about someone trying to capture the energy of the ebb and flow of the water at shallow depths, again, something I’d look into. He had planted small, errr, things a few feet down in the ocean near the shore and as the water went back and forth he could capture the energy as the water pushed them around. Again, this seems similar to what you’re doing and I’d look into these things and see if they could be adapted (or not) and why they did or didn’t work. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [April 29, 2011, 1:46pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/5 "2011-04-29T13:46:01Z")
> [@](#): > > TANFL presumably “there ain’t no free lunch.” truncation of TANSTAAFL. ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [April 29, 2011, 1:46pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/6 "2011-04-29T13:46:05Z")
TANFL=There Aint No Free Lunch ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [April 29, 2011, 1:49pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/7 "2011-04-29T13:49:03Z")
> [@Joey\_P](#): > > That’s my thought, other then big bumps, those minor fluctuations are pretty minor. On top of that, you’d need something (a rectifier?) to make sure that both directions charge the battery instead of a dip in the road charging while a bump drains the battery. That’s going to add weight (I assume…unless it’s inherent in the design). A rectifier is small, cheap, and not heavy (a diode is one kind of rectifier). Not a significant factor. > [@](#): > > If I were the OP, before going any further with this, I’d study regenerative breaking. Just to understand how it works. How is the power captured, how is it “ignored” when the person isn’t breaking, how is the power from all four wheels combined to one source and sent to the battery etc… and see if any of that can be applied to this. Regenerative braking in electric cars uses the motor in reverse, which makes it a generator (theoretically, that is the only difference). > [@](#): > > Also, what does TANFL stand for? [Let me google that for you.](http://lmgtfy.com/?q=TANFL) ---
**Author:** ![Nars\_Glinley](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nars_glinley/32/8177_2.png) [@Nars\_Glinley](https://boards.straightdope.com/u/Nars_Glinley)\ **Post date:** [April 29, 2011, 1:52pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/8 "2011-04-29T13:52:50Z")
TANFL - There ain’t no free lunch. At least, that’s the way I remembered it. A little googling shows that I should have used TANSTAAFL. There ain’t no such thing as a free lunch. :smack: Unfortunately, I’m just a computer programmer and have no expertise in the area of recoverable energy. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [April 29, 2011, 1:55pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/9 "2011-04-29T13:55:00Z")
nm ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [April 29, 2011, 2:01pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/10 "2011-04-29T14:01:16Z")
> [@](#): > > A rectifier is small, cheap, and not heavy (a diode is one kind of rectifier). Not a significant factor. I think the key question that needs answering is how much energy is actually there to begin with. Looking at e.g. regenerative braking, you have a relatively tremendous amount of kinetic energy available from the forward motion of the vehicle. with shock absorbers your looking at random fluctuations, with limited displacements. I suppose piezoelectrics could be one way, I don’t really see induction working that well. one other potential downfall is that shock absorbers _move_ so you have to make sure the associated wiring won’t suffer damage from normal operation. also with so many cars using MacPherson struts up front, those have to be able to turn with the wheels so that complicates things even more. oh, also, yes in theory drawing power from them would provide damping like a normal dashpot shock absorber, but what happens when you “don’t need” the power available from them? e.g. you’re already in regen braking and the battery can’t take any more charge at that time. Does your damping go away, or do you burn it off in dummy loads or something? ---
**Author:** ![smithsb](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smithsb/32/12107_2.png) [@smithsb](https://boards.straightdope.com/u/smithsb)\ **Post date:** [April 29, 2011, 3:00pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/11 "2011-04-29T15:00:22Z")
We already have magnetohydrodynamic shock absorbers in some premium automobiles; Corvette Z06 and ZR1, Cadillac CTS-V, and some others. An electric current is passed through the shock fluid (it’s either magnetic or has magnetic particles suspended) to vary it’s resistance to flow through the shock absorber porting. The electronics “stiffen” or “relax” the fluid 100s of times a second to vary the response to road conditions. I imagine it would be possible to have the fluid generate a charge (moving magnets, coils, and other stuff I know exist but am not much up on) but I’m not sure if it would be substiantial enough to recover. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [April 29, 2011, 3:21pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/12 "2011-04-29T15:21:36Z")
Sure it’s a way of recovering some of the energy expended to get the car bouncing in the first place. But just like regenerative braking, it’s not free. It all comes from energy you expend to make the car roll or bounce in the first place. Regeneration is not extremely efficient either. There is loss in the generator, loss in rectification, and loss in the battery charging process, plus all the losses from wiring and mechanical linkages too. On top of that, unlike the regenerative braking situation, you need some of that energy in the shock absorbers to return them to a neutral position. If you rely on a return spring to do that, then you lose all the energy needed to compress the spring. Doesn’t sound like a very effective means of recovering energy, but if it doesn’t cost much or add a lot of weight to the car, why not? Here’s an interesting question to follow: Can a linear homopolar generator be made? This would eliminate the need for a rectifier, brushes, or commutator (although increase the losses from transmission of DC). ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [April 29, 2011, 5:33pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/13 "2011-04-29T17:33:13Z")
Something else I just thought of as I was driving my (hybrid) Insight. A system like this would be installed on a hybrid car. Hybrid cars tend to be very very light. Unless it has very spongy shocks ISTM that there’s going to be very little vertical movement to get this energy from. I know my car has a pretty stiff ride, on par with a Civic. ---
**Author:** ![Nars\_Glinley](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nars_glinley/32/8177_2.png) [@Nars\_Glinley](https://boards.straightdope.com/u/Nars_Glinley)\ **Post date:** [April 29, 2011, 5:36pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/14 "2011-04-29T17:36:32Z")
> [@Joey\_P](#): > > Something else I just thought of as I was driving my (hybrid) Insight. A system like this would be installed on a hybrid car. Hybrid cars tend to be very very light. Unless it has very spongy shocks ISTM that there’s going to be very little vertical movement to get this energy from. I know my car has a pretty stiff ride, on par with a Civic. Some are, some aren’t. There are hybrid SUV’s, medium size sedans (like the Fusion and Camry) and pickups. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [April 29, 2011, 5:47pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/15 "2011-04-29T17:47:03Z")
> [@runner pat](#): > > TANFL=There Aint No Free Lunch Hybrid braking/charging systems disagree. ---
**Author:** ![Enilno](https://avatars.discourse-cdn.com/v4/letter/e/58f4c7/32.png) [@Enilno](https://boards.straightdope.com/u/Enilno)\ **Post date:** [April 29, 2011, 5:59pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/16 "2011-04-29T17:59:55Z")
I think a similar topic has come up before. Anyways here’s what wikipedia says about [regenerative shock absorbers](http://en.wikipedia.org/wiki/Regenerative_shock_absorber). And from one of the [cited articles:](http://www.physorg.com/news188035494.html) > [@](#): > > “For typical driving conditions, we are predicting the ability to harvest approximately 64 watts per wheel, for a total of approximately 256 watts,” Zuo told [PhysOrg.com](http://PhysOrg.com). “This value increases considerably when the system is used on irregular roads.” ---
**Author:** ![spifflog](https://avatars.discourse-cdn.com/v4/letter/s/c5a1d2/32.png) [@spifflog](https://boards.straightdope.com/u/spifflog)\ **Post date:** [April 29, 2011, 6:02pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/17 "2011-04-29T18:02:12Z")
> [@Philster](#): > > Hybrid braking/charging systems disagree. It’s still not a free lunch. You’re just getting to eat one that you’ve already paid for. ---
**Author:** ![BubbaDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bubbadog/32/333_2.png) [@BubbaDog](https://boards.straightdope.com/u/BubbaDog)\ **Post date:** [April 29, 2011, 6:05pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/18 "2011-04-29T18:05:20Z")
The shock absorber by its design is already a device which receives, stores, and releases energy. I doubt if there is much excess energy available to take out of that system without compromising its intended purpose. Think of it this way, regenerative braking makes sense because you are capturing the energy instead of letting it dissipate via waste heat. Conventional brakes will overheat if used too much. But conventional shocks already capture energy (compressing), store it (kinetic), and release it to do desired work (expansion). Very little energy is dissipated via heat. And that would be the only energy available for charging batteries. You need the rest of the energy to keep the car from becoming a low rider. ---
**Author:** ![Folly](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/folly/32/3219_2.png) [@Folly](https://boards.straightdope.com/u/Folly)\ **Post date:** [April 29, 2011, 6:11pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/19 "2011-04-29T18:11:24Z")
> [@spifflog](#): > > It’s still not a free lunch. You’re just getting to eat one that you’ve already paid for. Actually, you puke some of your lunch back up, ruminate on it awhile, and then eat it again. …ewwww ---
**Author:** ![Darth\_Panda](https://avatars.discourse-cdn.com/v4/letter/d/ee7513/32.png) [@Darth\_Panda](https://boards.straightdope.com/u/Darth_Panda)\ **Post date:** [April 29, 2011, 6:15pm UTC](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152/20 "2011-04-29T18:15:40Z")
> [@Folly](#): > > Actually, you puke some of your lunch back up, ruminate on it awhile, and then eat it again. > …ewwww Sounds at least half way kosher to me. [Next page](https://boards.straightdope.com/t/shoot-down-my-electric-car-charging-solution/580152.md?page=2)