Generating electricity with a Prusa Stepper motor?  

Re: Generating electricity with a Prusa Stepper motor?

Basic principle of electric motor and electric generator is the same. The difference is what energy is on input and what you get on output. Motor = electricity on input, mechanical energy on output. Generator = vice versa. So if you turn electric motor fast enough, you get electricity. Simple physics.

Rambo electronics is powered by 5V voltage regulator. If the power generated by motor raises its output voltage over some level (about 7V I guess), the regulator gets enough power to provide good voltage to 5V rail and the board comes up until you stop the motor.

Re: Generating electricity with a Prusa Stepper motor?

I did not move the bed quickly so they are pretty good at generating. I wonder how well a motor would be on a small wind generator. Might work great for camping. 😎

Re: Generating electricity with a Prusa Stepper motor?

It's funny to see this topic as this is something I started working on last week. I have some Nema 17 Steppers laying around and saw there's quite a few wind turbines on thingiverse, so I started playing around with making a simple circuit with a rectifier to convert the AC to DC and a regulator with a pot to regulate the voltage output. It works well, so the next step is figuring out how to charge some batteries during the day and add night detection to to turn some LED's on at night. It's definitely do-able though, although I'm not great with electronics and the math behind it, so it's a slow process.

It would be cool if anyone on this forum is good with this stuff and would be willing to write up a tutorial that non electricians/engineers could understand, as it's really hard to find good tutorials online that take you through all the steps from turning motor to smart battery charger that won't explode your batteries. If anyone is interested I can contribute what I have so far and it could be a fun project that I bet a lot of people would find useful.

Re: Generating electricity with a Prusa Stepper motor?

Damian

It's actually quite simple do do and there are many ways to achieve what you are looking for (everyone will have their own different ideas...).

Personally I would go down the route of combining wind power with a small solar panel. The solar panel can be used to generate electricity during the day and also can be used as a sensor to determine how much light there is (as in no output = night time).

Combine these with a buck regulator or two an Arduino (with Darlington ICs for output), a few LED strings and some rechargeable batteries (NiCd or NiMH are the easiest to work with; lithium batteries can require more complex charging circuitry) and you have what you are looking for.

Peter

Re: Generating electricity with a Prusa Stepper motor?

Peter, everything is simple when you *know* how to do it 😉

Combining it with a solar panel would be a good option, although I figure if the batteries are charging anytime there's some wind, and the LED's are only used at night, wind power should be sufficient with a 9V battery or 4 AA Nimh batteries to keep a couple LED's lit. Although lithium batteries would be a better choice, you're right, they're more difficult to work with and require more attention so I'm all for Nimh batteries. I have a regulator which is giving me a constant 3.2V for the ultra bright LED's I'm using, but I haven't tested how much current I'm getting out of the stepper yet, something I'll check this weekend. I'm just using a drill to spin the motor as a starting point since I haven't printed the actual wind turbine.

I did look into some ICs which is probably the smart choice for batter management, but I was hoping for something simpler initially such as this http://www.electro-tech-online.com/attachments/nimh-charger-jpg.18731 which I could not find any schematics for. If I can't find an easy solution I might just go the Arduino route and create an entire smart charging system with an LCD screen for better monitoring.

In any case, I still think it would be cool if there was a good tutorial for people who can just order the parts needed and build it by following some diagrams/images instead of trying to figure out a bunch of schematics and combing them all without a good understanding of electronics.

Re: Generating electricity with a Prusa Stepper motor?

Damian

Firstly, you should not power LEDs without some form of current limiter. Generally LEDs draw about 20mA of current and (depending on colour, taking white as an example) need about 3V to work. If you drive 1 LED from a 3.6 Volt (3 x 1.2V NiMH AA cells), you therefore need to drop about 0.6V across a resistor and limit the current to 20mA.

Feed those figures into a calculator and you get a resistor value of 30 Ohms (or nearest standard resistor value, 33 Ohms). With, say 2400mAh batteries, you could run 1 LED for 120 hours or 10 LEDs for 12 hours.

The reason I suggested using a solar panel is that it would allow you to charge the batteries during the day and sense the lack of light at night to turn on the LEDs. Without it you would require something like an LDR (Light Dependant Resistor) circuit which would use a small amount or current from the batteries you are charging.

Anyway, I think we have hijacked this thread, so better to start a new one should you wish to continue discussion...

Peter

Re: Generating electricity with a Prusa Stepper motor?

Damien

Carry on friend. A great idea and just as I had said on the post. It would be a great idea to make a system. The solar panel idea is good but solar panels cost money. A stepper and some printed parts plus some electrical trickery is not super money. Certainly a lot less then 1 solar panel.

I have zero electrical knowledge but would be up for playing with idea. I have a few steppers lying around now. How much the stepper produces is what is going to be the key here. If its not going to do enough its not going to be worth it. It would be a good idea to see if we can produce a system that will run the printer for instance. What is required for a printer? I guess if the bed was off it would not be half as much?

Re: Generating electricity with a Prusa Stepper motor?

Ben

6V 4.5W solar panel £8.56 delivered: http://www.banggood.com/6V-4_5W-520mA-Mini-Epoxy-Solar-Panel-Photovoltaic-Panel-p-987805.html

Something like that would be ideal for use as a secondary power source and day/night detector.

You would also need a couple of buck regulators: @ £1.42 delivered: http://www.banggood.com/DC-DC-Adjustable-Power-Supply-Buck-Converter-Step-Down-Module-p-922049.html an Arduino, some LEDs, batteries and battery holder, a Darlington IC and a few resistors.

Then you would need to print some blades and a head for the motor, a pole, some wire and off you go.

The buck regulators are goon in that they preserve about 90% of the power generated; they reduce the voltage but increase the current output. Using a 4-pack of NiMH batteries, they could also be used to power the Arduino.

Peter

Re: Generating electricity with a Prusa Stepper motor?

Wow thats cheap 😮 I must have been asleep the past year as I though solar panels were still expensive and pretty crap.

Has anyone used Banggood in the UK and have they actually got what they ordered from them?

Those Buck regulators sound like a dam good idea especially when every little counts in this setup.

This is added to my list of things to do. Been looking at some fan designs on Thingiverse for some time now. Some have done a few different designs and tested them with success.

Re: Generating electricity with a Prusa Stepper motor?

Ben

I have been using Banggood regularly for over 6 months now. Placed over 80 orders (over 100 different items) and I have never had a parcel go missing and only 1 item damaged, which they sent a replacement for straight away.

The only issue for me here in Slovenia is that any parcel over €20 is subject to VAT and clearance fees. The good news is that I can get items shipped to here via DHL quicker than from the UK and at a small fraction of the price.

I prefer to buy from Banggood rather than eBay nowadays; much cheaper and more reliable than many eBay sellers.

Peter

Re: Generating electricity with a Prusa Stepper motor?

Yeah most of the stuff Peter listed is cheap to buy, which is why projects like this are possible for hobbyists. Actually I ordered an IC, 2 small solar panels, 5 buck converters, and 10 battery holders the other day from ebay for around $30. It will take a few weeks to arrive, but worth it IMO. I also tried a simple light sensor circuit on my breadboard and it works well, I just have to figure out how to put it all together now.

Peter, you've got me thinking, what happens to the current when a regulator is used to reduce the voltage, does it stay the same? I assumed a regulator basically does what a buck converter does, but it seems I'm wrong. Also to your point about having resistors for the LED's, I did have plans to do that, but I figured if the regulator is supplying them exactly the voltage they require they shouldn't need resistors for testing... although maybe that's why I fried a couple of them already 😳

Re: Generating electricity with a Prusa Stepper motor?

Damian

Linear regulators (like the 7805) work by dropping the voltage and dissipating the dropped voltage as heat. The output current is limited to the input current. Buck/boost regulators are very much more efficient and when dropping the voltage they increase the current with very little heat generated (depending on the efficiency at the required/input voltage).

Buck regulators can therefore be used to output a higher current than linear ones, mainly due to lower heat dissipation requirements.

A regular arduino board uses linear regulators, whereas the RAMBo board uses a buck regulator for the 5V circuit.

If you want to power LEDs directly from a power source, you need a current-limited power source, otherwise you will burn them out. All LEDs are different and even 2 from the same batch will require slightly different voltages. At the top end of the working voltage, one tenth of a volt increase will see the current draw increase by 100 times or more (ie not linear).

As a hobbyist, I prefer to include a resistor to limit the current rather than blow up the LED. And also remember that an LED passing 15mA will last significantly longer than one passing 20mA and the difference in light output will hardly be noticed.

I agree that including a resistor is wasteful as far as the heat output by the resistor is concerned, but for me it is better in the long run.

Peter

Re: Generating electricity with a Prusa Stepper motor?

Hi all,

Stepper motors are not an ideal design to be used as generators. This comes from my experience working on motor-generators in the military and teaching about generator design while getting my PhD in Physics. For generators you want minimal resistance and to work at low torque/high speed. Stepper motors care mostly about accuracy and are designed toward high torque/low speed.

This is not to discourage, just to point out a limitation of doing this. It sounds like a fun project.

The efficiency will be limited. If you intend to drive it using a wind turbine, you will likely need to use some reduction gears. It may also be fun to play with the Archimedes style turbine:
http://www.thingiverse.com/thing:1067856

Good luck! Let us know if you have good results.

Re: Generating electricity with a Prusa Stepper motor?

Ok, well I might as well post my fritzing diagram if anyone is interested in helping me figure this out (don't judge me, I can't read schematics properly lol).

So I guess in my head it would work like this:

Stepper produces AC
Rectifier converts to DC
Buck regulator replaces the reducer circuit in the diagram (to provide steady voltage/current to battery charger)
Bought a MAX713 IC off ebay yesterday so I'll make a charging circuit using it later when it's delivered
4 NIMH batteries get charged whenever there is wind and energy is stored until the light/dark detector kicks in when it gets dark out
LED's get fed from the batteries at night

Does this seem to make sense? I'd use the online resistor calculator here http://led.linear1.org/led.wiz for the LED's (2-4 probably). Here's the diagram I have so far.

Re: Generating electricity with a Prusa Stepper motor?

There are a couple of things I would change:

Immediately after the bridge rectifiers, drop one of the electrolytic caps, but keep the ceramic cap. I really don't see a need for a battery charger IC if you are using a buck regulator.

4 x 1.2V NiMH batteries = 4.8V, not 6V as written; use 3 batteries to give 3.,6V nominal (4.5V max). The fourth battery is wasted - you will need to drop the voltage to 3V for the LED.

You will probably require a Darlington pair instead of single transistor so you get a "full on/full off" situation. You will then be able to drive at least 5 LEDs. You will need 15mA (average) per LED, so the resistor value with (say) 4V supply will be 66 Ohm - nearest standard value is 68 Ohm.

A 68 Ohm resistor will pass 22mA at 4.5V and 8mA at 3.6V. The LEDs should be fine with these current draws. and will dim very gradually as the battery level reduces. 2200mAh batteries should last about 30 hours with 5 LEDs driven. However I doubt you will get that sort of charge in a day - maybe 1000mA max.

Please note that these figures do not take account of voltage drop across the transistor (about 0.2V).

Peter

Re: Generating electricity with a Prusa Stepper motor?

Thats good Damian thanks for sharing 😉

Is it safe to say the motor will output at at least half of input? I am thinking along the lines of a slow trickle charge of a 12v battery. Slowly charge that up or keep it charged.

Re: Generating electricity with a Prusa Stepper motor?

Peter, that's some great info, thanks!

I had 2 electrolytic caps because my reference didn't use a battery so it made sense, but you're right it's not needed in this situation. I could probably even drop both caps before the ceramic one, but I guess it can't hurt to leave one.

When you say the fourth battery is wasted, do you mean because it would provide more voltage then I need? Does that mean the batteries should be connected in series? or do you mean keep the fourth battery but it will never be needed because the LED's only need about 3V?

While I was looking through my parts I found I do have a pair of buck regulators after all like this one:

If I don't make the smart charging circuit as you're suggesting, I should have all the parts I need to assemble this. The main reason I wanted a smart charger is to not overcharge and destroy the batteries, but if that happens I can always go back and add the IC to the circuit later. I'll revise the diagram and post it up for scrutiny when I get a chance.

Ben, no problem, if this thread inspires or helps others to try making a wind turbine then that would be great. I'm curious as to how much energy the motor will produce realistically as well, but I have only tried some quick tests turning the motor with a power drill so far. I think trickle charging a 12V battery should be pretty easy, it's the part about keeping it charged once it's already charged that gets tricky and requires a smart battery charger circuit of some kind, especially with Lipo batteries but less so with NiMh, NiCd, or lead acid batteries. I would think a motor should output about 80% of it's input though, but I'd be guessing at this point.

Re: Generating electricity with a Prusa Stepper motor?

Damian

As the LEDs don't require the voltage, there is no point in having it as it will only be wasted energy. 3 batteries in series will be fine.

Your buck regulator has the variable resistor to set the output; set that to between 4.2 and 4.5 Volts and you will not be able to over-volt the batteries.

Peter

Re: Generating electricity with a Prusa Stepper motor?

Ok, that makes sense Peter.

I updated the diagram, but I never made a Darlington pair circuit so here's an attempt on it. There's 2 variations, not sure if either one of them makes any sense, and I'm at work so I can't breadboard it for testing. The online LED resistor calculator give me 22ohm resistors for the 5 LEDs that I would be using (3.2v/20mA), but I'm not sure how to connect it properly.

Here's the diagram: