I am trying to design a "Gravity Battery" using a single DC Motor. Motor coupled to a spur gear gearbox and a rope reel to lift a concrete weight.
The goal is to use the unit as a moto to lift a weight with surplus solar power. Then to act as a generator when weight drops.
My question is how cold that be wired on a 90V DC 10A 4700RPM Permanent Magnet Motor so that the DC input power doesn't pass directly to the DC outputs when acting as a motor and also the output power doesn't back feed the motor controls when acting as a generator.

There are other considerations on the mechanical side that I am working on (decent speed control, etc.) But this are a separate issue. I need to know that I can wire it this way first! I don't believe simple resistors would be sufficient to block 10A @ 90V DC. Maybe I'm wrong...

Any help would be greatly appreciated!

 

Diodes.

 

I get using diodes to prevent back feed into motor controls when the unit is generating power. But what about when it is acting as a motor, How to I prevent power from being sent out through the output? I was thinking I could use a relay that is NC and when power is applied to the motor control it switches to Open. Wasn't sure if there was a more practical solid-state way.

 

I suppose I could simply use a DPDT relay and have the motor connected to the commons and the input and output connected to the switched pairs. That would solve all issues I think...

 

A full FET bridge is used for bidirectional control or a DPDT switch and then return energy back to the battery if it fails to reach the limit switch.

Can you compute the stored energy in the battery and the energy to raise the concrete to make sure you can finish what you start? Otherwise it stalls then falls down. This can be done with good batteries by measuring Vbat.

You will also need to minimize all friction to overcome stall/start torque with switches at both ends. You may also want to regulate falling speed to avoid the gravitational acceleration and rising voltage. All energy states and losses must be defined as well as dynamic power curves.

 

My goal is to charge a bank of lithium's batteries I already have tied to my solar system. I would need a charge controller to regulate voltage and allow amperage to vary. That part should be simple enough.

What I've calculated already is the following:
The concrete block weighs 525lbs(238Kg). The total lifting height is 17ft(5.1816m). This gives me a PE of 12,092.46J.

As for braking and descent control I was thinking of having a Rope Brake (for locking in any position manual or automated). Then for descender I was thinking a fan blade flywheel that offers resistance to acceleration, or a magnetic brake using Aluminum and a magnet. Even a "fall arrest/Controlled Descender" (https://www.safety-height.co.uk/web...s/kratos-lift-res-q-rescue-evacuation-device/) would be ideal. Although these options are very cost prohibitive. Anything I do to slow it down is going to cost me in terms of friction losses. I will be using surplus solar (after batteries are at 100% and the panels are still collecting power) to "charge/lift" so any charge gain I get from the decent is essentially "free" so I can accept some considerable friction losses.

Reel: https://www.surpluscenter.com/Miscellaneous/Other-Miscellaneous/19-Dia-Cable-Reel-1-1632.axd
Gearbox info: https://drive.tech/en/stream-content/dc-motors-as-generators

I could use a rope pully or gearbox to get the speeds I desire, or even a combination there of. For example: If using a gearbox it should be Planetary (1 or 2 stage) or Spur Gear so that it can handle being fed AND back fed rotational force. Spur is ideal as it very efficient and highly suited to this task. A gearbox is necessary I believe due to rope speeds at the reel.
A 60:1 would give me a significant advantage (4700RPM motor / 60 = 78.33 RPM)
Then if I used a 7:1 rope pulley and the reel spec'd above has a circumference of 15.5" about 92 rotations of the reel is sufficient to lift the block 17ft (17ft*7 = 119 ft * 12 = 1428") 1 Revolution of the reel being 15.5" or rope gathering... (1428/15.5 = 92 Revolutions). So about 1m10s (92R/78.33RPM = 1m10s) to lift at "full rated motor speed" (4700 RPM).
But in reality with this DC motor max efficiency is about 2000 RPM so (2000/60 = 33.33 RPM @ reel) 2m 45s total lift time.
So about 1.25" per second * the weight which doesn't seem dangerous to me.
At the reel the rope speed would be 8.6" per second which still doesn't seem unreasonable (1 revolution about every 2 seconds).
Stop switches are needed at both ends of stroke length of the weight. (floor and ceiling)
Some kind of Arduino or Hero board to control everything (my Victron Solar System has dry contact and low volt contacts that can be programmed to tell the control board when to charge the gravity battery (lift) as well as when to release the brake for the weight to generate power for the battery bank charging.
I know this isn't everything but it seems fairly straight forward and definitely feasable!

 

"" I know this isn't everything but it seems fairly straight forward and definitely feasable! ""

Unfortunately, it is not even remotely feasible.

What You are leaving out of the equation are the
gross inefficiencies involved in every single step of the process,
and there are a lot of wasteful steps in your proposed setup.

One of the worst inefficiencies is using a Motor as a Generator.

Every time Energy is "altered", or "controlled", or changed from one form to another,
there will be substantial losses which can not be efficiently recovered.
.
.
.

 

Not impossible.

You are trying to use potential energy as a storage device when there is surplus power during the day.
You calculated a PE of 12,092.46J . Let's round that to 12 kJ To power this up and deplete a fully charged battery lets start with 15% more for losses and round up to 14 kJ = 14k W-s or 3.9 Wh of battery energy or up to 10A for say up to 170 seconds is 14kW-s /170s=82W If the motor impedance starts at 0.7 to 0.9 ohms or whatever DCR coil resistance, this impedance then rises with BEMF with speed means you need to supply 82W/0.9ohms= V^2 or V~ 10V to power the PMSM motor.

This will have more winding loss and less efficiency so 15% loss will not be enough. Perhaps 5x rated current for starting is a better starting point for acceleration.

We need the motor efficiency curves with power input to compute better values of efficiency.
This also assumes it is cheaper to use all this gravity energy storage than to use surplus lead acid 2V batteries from a TELCO that is decommissioning their POTS service, where each 2V cell weights as much as your concrete. Or you could get really creative and lift the batteries for both electrical and gravity storage (lol)

Chat GPT3.5 says to lookup... (maybe on archive.org)

1. Permanent Magnet Motor Selection:
   • Reference: "Permanent Magnet Motor Technology: Design and Applications" by Jacek F. Gieras, Rong-Jie Wang, and Maarten J. Kamper.
   • Details: Consider motor specifications, efficiency, and size. Brushless DC (BLDC) motors or permanent magnet synchronous motors (PMSM) might be suitable.
2. Energy Controller and Power Electronics:
   • Reference: "Power Electronics: Converters, Applications, and Design" by Ned Mohan, Tore M. Undeland, and William P. Robbins.
   • Details: Understand bidirectional power flow control, use inverters or converters for bidirectional energy transfer.
3. Mechanical System Design:
   • Reference: "Mechanical Engineering Design" by Joseph E. Shigley and Charles R. Mischke.
   • Details: Focus on mechanical aspects, including lifting mechanisms, safety features, and braking systems.
4. Control System Design:
   • Reference: "Feedback Control of Dynamic Systems" by Gene F. Franklin, J. David Powell, and Abbas Emami-Naeini.
   • Details: Implement control algorithms for optimizing energy conversion and ensuring stable system operation.
5. Energy Storage Calculation:
   • Reference: "Energy Storage Systems" by Richard E. Sonntag, Yogi Goswami.
   • Details: Calculate the energy storage capacity based on the mass, height, and gravitational potential energy formula.
6. Grid Integration and Standards:
   • Reference: IEEE Standards (e.g., IEEE 1547 for distributed energy resources).
   • Details: Understand grid integration requirements and compliance with relevant standards.
7. Environmental Considerations:
   • Reference: "Sustainable Energy – Without the Hot Air" by David JC MacKay.
   • Details: Consider the environmental impact of materials used, and try to design for sustainability.
8. Safety Measures:
   • Reference: "Introduction to Safety in the Chemical Laboratory" by James A. Kaufman.
   • Details: Implement safety features and fail-safe mechanisms to prevent accidents and handle system malfunctions.
9. Monitoring System:
   • Reference: "Instrumentation and Measurement in Electrical Engineering" by Roman Malaric.
   • Details: Implement sensors and a monitoring system to track parameters like position, speed, and other relevant data.

 

https://www.wired.com/story/battery-built-from-concrete/

The concept is sound. And even being done in large scale.
It isn't about efficiency. It's about utilizing power from solar that otherwise goes unused to lift the block. We call that "free" input.
My system already have 12v 400AH of Lithium batteries. Not much, but minimally sufficient to run my needs.
The gravity battery is mean to expand that capacity.
If my math is right I'd only gain 6ah @12v which clearly isn't great.
Using a DC motor as a Generator is straight forward. No additional wiring or rewiring needed as they are one in the same. Just depends if you are applying electrical energy to generate rotational mechanical energy (motor) or if you are applying rotational mechanical energy to generate electrical energy (generator). DC generators are nice in that they produce power across a large range or RPMs. Unlike their AC counterpart (car alternator) that requires a high cut in speed and an additional motor to do the heavy lifting.
I could double the power storage by doubling the weight. My limit would be the weight capacity of the garage structure so I would have to look at my truss designs on that. I already know that I'd need to span multiple trusses with a heavy beam.
The overall goat if for it to be Automated, Safe, Practically functional.
6AH probably is the killer of the Practically functional part. Unless I had a way to stack blocks like in the above linked video. Which I don't

 

You will need a degree in EE to make the MPPT and synchronous mot-gen electronics to match the battery voltage and be cost-effective and efficient.
The driver must be synchronous using complex math on voltage & current or rotational Hall sensors. 3 Phase is best.

https://www.researchgate.net/public...ion_on_Elevator_Energy_Regenerative_Unit_EERU

https://www.directindustry.com/prod/dongguan-hobiba-technology-co-ltd/product-4567491-2583782.html