diy solar

diy solar

Wind Turbine PMA for Backup Human Powered Bicycle Generator. Looking for advice on volts, cooling, manufacture, charge controller, ect.

Y

YahwehIsMyEl

New Member
Joined
Jan 16, 2023
Messages
26
Location
New England
Hello,

I am fairly new to world of pmas, and wind powered devices in general.

I will first describe what I am doing, then I will divide my questions into a few separate parts.

The concept is simple. I live off grid with solar in an aria that is known for having lots of cloudy days in the winter time. I am trying to find a way that I can produce enough electricity to charge a battery bank that I have enough to use a laptop, the internet router, and perhaps a light (about 50w/h total) on days where the solar is not producing enough.

I also do not live in an aria where hydro is an option, and I live in a valley that has barely any wind. So, as I am young and strong enough to bike for hours at a time, I turned to the idea of constructing a bike powered generator.

The actual construction of what I am making is already accounted for.

The problems I am having now come from trying to find the right motor and charge controller to use in my system.

Goal: 100w/h - 300w/h generation at decent speeds.

I will now state my questions.

A: After my research, I concluded that PMAs were the best option for efficiency in creating electricity with low "winds." I felt "low winds" were the best comparison to human power that I could find. My goal is to be as efficient as possible, so if I am using the wrong motor, please let me know.

B: AC I think is right for me, as I want to be able to have a wire running quite a distance to my battery bank with the rectifier near the batter bank, but how many volts? I have my battery bank in 12 volts, but I have heard of people getting a 24 volt pma for a 12 volt system. What are the benifits and drawbacks of doing this?

C: How large of a PMA should I get? I see multiple companies producing 7 magnet pmas, and also 14 magnet pmas. How much harder is a 14 magnet pma to turn then the 7 magnet? Would a 7 magnet be sufficient for my needs? (trying to cut costs a bit here)

D: Cooling. I have heard it said and seen it written that the stators have a habit of overheating and ruining themselves. At what point is this an issue? Would me biking have the ability ruin my stators without a cooling fan on the alternator? I expect to get decent rpm with the gearing that I have.

E: What company should I go with? I was originally considering the MW&S 7 magnet pma, however looking at Youtube reviews, and sensing the general feeling of the room, I am a bit uncomfortable going with MW&S. I want to make sure I am actually getting the most power that I can out of the pma I get. The other two companies I have been considering are Hurricane and Thermodyne. However, I have been unable to find any recent reviews on youtube regarding any of these companies, not to mention that MW&S has by far the best looking and most professional website, while Thermodyne has the least, however Thermodyne seems to get the best reviews?? I was wondering if anyone has personal experiences or recommendations regarding any of these companies, or any other company that I should consider. My main question is, will the MW&S 7 magnet pma actually produce power? Have they fixed their cogging issues I have seen them have in reviews? Why is it half the price of the competitors 7 magnet PMAs?

F: Charge controller: What should I go with for this? Would an MPPT really help me, or is a generic charge controller suitable for my needs. Also size, how would you recommend I size the controller for this single pma?(i.e. what amperage do I need) Also, is a dump load necessary for my application? I feel that as I will be right there monitoring the battery voltage the entire time the pma is running, a dump load does not seem necessary. In fact, I have wondered if I could use a solar charge controller, as I would feel as soon as it disconnected my batteries from the pma, and I could adjust my biking speed accordingly. It's not like it's in wind where the charge controller has to keep a load on the pma to keep it from burning up... but I feel like I am missing something on this one. But Solar mppt charge controllers are much a bit less even on Amazon then MPPT wind charge controllers, and even less then some normal wind charge controllers like the MW&S "440 watt digital charge controller"

Summery:
A: PMA right motor?
B: Voltage?
C: Size (7 or 14 magnet)?
D: Cooling
E: What manufacturer?
F: Charge controller and dump load?


Thank you for any help you may have.
 
diysolarforum.com

Wind Resources

Rule 1: The power rating of a wind turbine has NOTHING to do with the amount of power you'll get. The amount of power you get depends on the size and efficiency of your wind turbine, and your wind. The power rating of a wind turbine is just its...
diysolarforum.com diysolarforum.com
 
sunshine_eggo said:
diysolarforum.com

Wind Resources

Rule 1: The power rating of a wind turbine has NOTHING to do with the amount of power you'll get. The amount of power you get depends on the size and efficiency of your wind turbine, and your wind. The power rating of a wind turbine is just its...
diysolarforum.com diysolarforum.com
Click to expand...
All good information, thank you for sending it to me. From what I can gather, this seems to answer my question that I would be perfectly fine going with the 7 magnet pma. However other than that it seems to be focused on the placement of wind turbines and wind conditions. Thankfully for this situation I don't have to worry too much about that, as I will be providing the driving force myself.
 
Sunshine is quite right.
You are not looking to build a large powerful expensive system, so you might do much better by repurposing something you can get for free, or very cheaply.
How about a salvaged treadmill motor ?

There will be a rating plate attached which should tell you three things, the voltage, the maximum current, and the rpm (when used as a motor).

It might say for instance 5 amps, and that will be the maximum current the windings can handle without overheating, regardless if its being used as a motor or as a generator.

Now when used as a generator, there will be no fixed voltage. The faster you turn it, the higher the voltage output will be.
The rating plate might say 180 volts at 5,000 rpm for example.

When used as a generator the output voltage will be proportional to rpm when unloaded, and slightly less when fully loaded.
If you turn it at one tenth of the speed, you get one tenth of the voltage, say 18 volts at 500 rpm, or maybe 14 volts at 390 rpm.
Those are usefully low speeds for a human powered generator, or a small wind machine.
You can safely get only the rated maximum 5 amps continuous output from it though.

That is not a huge amount of power, only 70 watts or so, but its about all you are going to get from a human powered generator for any useful length of time without rapidly exhausting yourself. A 70 watt wind machine over 24 hours would be 168 watt hours.
Some of the larger treadmill motors are 8 amps or 10 amps, and the rpm varies a lot too. So see what you can find.

If it works as expected, no reason why two treadmill motors could not run together doubling the power if you find you need more.....

Don't overestimate what you can do human powered, even a very fit trained athlete looks pretty weak compared to the power of an electric motor over anything more than a few minutes.
 
Warpspeed said:
Sunshine is quite right.
You are not looking to build a large powerful expensive system, so you might do much better by repurposing something you can get for free, or very cheaply.
How about a salvaged treadmill motor ?

There will be a rating plate attached which should tell you three things, the voltage, the maximum current, and the rpm (when used as a motor).

It might say for instance 5 amps, and that will be the maximum current the windings can handle without overheating, regardless if its being used as a motor or as a generator.

Now when used as a generator, there will be no fixed voltage. The faster you turn it, the higher the voltage output will be.
The rating plate might say 180 volts at 5,000 rpm for example.

When used as a generator the output voltage will be proportional to rpm when unloaded, and slightly less when fully loaded.
If you turn it at one tenth of the speed, you get one tenth of the voltage, say 18 volts at 500 rpm, or maybe 14 volts at 390 rpm.
Those are usefully low speeds for a human powered generator, or a small wind machine.
You can safely get only the rated maximum 5 amps continuous output from it though.

That is not a huge amount of power, only 70 watts or so, but its about all you are going to get from a human powered generator for any useful length of time without rapidly exhausting yourself. A 70 watt wind machine over 24 hours would be 168 watt hours.
Some of the larger treadmill motors are 8 amps or 10 amps, and the rpm varies a lot too. So see what you can find.

If it works as expected, no reason why two treadmill motors could not run together doubling the power if you find you need more.....

Don't overestimate what you can do human powered, even a very fit trained athlete looks pretty weak compared to the power of an electric motor over anything more than a few minutes.
Click to expand...
I had been considering the treadmill motor, however my thought was "There must be a reason that micro-turbines use PMAs." There is also the issue that the treadmill motor is in DC, meaning I would have to either have large wires and/or have the batteries close to the bike, which is not something I am planning on doing. Is the treadmill motor really efficient enough though? PMA's are built to produce power, it seems like even though the cost is greater, the power produced would be larger for the same amount of effort put in, due to the efficiency factor. If the treadmill motor would allow me to get 75 watts for instance, but the pma would let me get even 125 watts for the same amount of effort, I would rather go with the pma. as those extra 50 watts would make a huge difference in my system.
 
I don’t t think the machine you use to generate matters too much, you just want to consider the speed it has to turn to generate the voltage you need.
For my human powered generator I ordered a Chinese wind alternator which claimed to be “low speed” but required me to get it spinning pretty fast for my 48 volt system.
I don’t think you’ll overheat anything! Getting 100 watts into my batteries is something I can’t do for very long.
I ended up using the wheel (less tire) to drive a chain which drives a sprocket I installed on the alternator to get the rpms high enough. I just covered it with a thin layer of rubber and use a gravity tensioner. The wheel is so big it works fine.
I also used a Genesun boost controller. They are a fantastic company. They can custom program the boost controller to withstand a continuos source of high current and not burn up. Not needed for this project, but I did it just to be safe.
the problem with the MPPT controller is that it’s constantly changing the current, looking for the best point, which slows down your rotation.
 
DougfromdaUP said:
I don’t t think the machine you use to generate matters too much, you just want to consider the speed it has to turn to generate the voltage you need.
For my human powered generator I ordered a Chinese wind alternator which claimed to be “low speed” but required me to get it spinning pretty fast for my 48 volt system.
I don’t think you’ll overheat anything! Getting 100 watts into my batteries is something I can’t do for very long.
I ended up using the wheel (less tire) to drive a chain which drives a sprocket I installed on the alternator to get the rpms high enough. I just covered it with a thin layer of rubber and use a gravity tensioner. The wheel is so big it works fine.
I also used a Genesun boost controller. They are a fantastic company. They can custom program the boost controller to withstand a continuos source of high current and not burn up. Not needed for this project, but I did it just to be safe.
the problem with the MPPT controller is that it’s constantly changing the current, looking for the best point, which slows down your rotation.
Click to expand...
I see, if you were to chose a different controller that was not mppt, what would you recommend?

And yes, I had planned on doing a similar thing with the bike wheel to provide a gear ratio large enough to spin the motor fast enough.

Thank you for the advice!
 
My next step is to eliminate the controller. I am swapping in a new chainwheel which should give me the speed I need.
The power an individual can generate is so small compared to the battery bank that I’m just going to rely on the fuse and breaker for protection. My inverter draws more power for itself than I can generate for long.
 
PMA has no brushes and the output is AC. At low voltages you will lose one to two volts through a three phase rectifier with a PMA.
That is nothing at 48 volts or higher, but at 12v the rectifier losses start to become really significant.

A dc brush type motor/generator may actually be more efficient at 12v than a pma + rectifier.
 
DougfromdaUP said:
My next step is to eliminate the controller. I am swapping in a new chainwheel which should give me the speed I need.
The power an individual can generate is so small compared to the battery bank that I’m just going to rely on the fuse and breaker for protection. My inverter draws more power for itself than I can generate for long.
Click to expand...
Very interesting! Thank you for the advice!
 
Warpspeed said:
PMA has no brushes and the output is AC. At low voltages you will lose one to two volts through a three phase rectifier with a PMA.
That is nothing at 48 volts or higher, but at 12v the rectifier losses start to become really significant.

A dc brush type motor/generator may actually be more efficient at 12v than a pma + rectifier.
Click to expand...
This is quite interesting. I had not considered that maybe quite as much as I should.
 
The cheapy diode rectifier bridges drop about almost a volt per diode.
Half a dozed really nice Shottky diodes perhaps about 0.4 to 0.5v per diode.
There will always be two diodes in series, and that adds up to a significant voltage drop.

With commutator brushes, the losses should be negligible.

Even with a dc machine, you will still need one Shottky diode in series with the battery to prevent the generator from motoring, unless you can do something really clever with a power mosfet.
 
Basically when pumping those pedals, there is an efficient cadance, a sort of natural rhythm that is most comfortable for a human.

The cyclists sometimes have something lika a 16 speed gearbox to maintain a constant rhythm over a very wide range of road speeds.

Charging a battery, the voltage does not change by very much, and neither should the generator rpm.
A bit of experimentation may be required to convert maybe 50-60 pedal rpm to about 13v to 14v generator rpm.
But once you have that right, its just a case of pedaling harder (but not much faster) for more current.

All you need is a battery voltmeter and an amp meter for encouragement !
No other control system should be necessary, once you have the gearing set up right.
Most efficient gearing will use largest practical diameters, especially on the generator.
 
Last edited:
Warpspeed said:
Basically when pumping those pedals, there is an efficient cadance, a sort of natural rhythm that is most comfortable for a human.

The cyclists sometimes have something lika a 16 speed gearbox to maintain a constant rhythm over a very wide range of road speeds.

Charging a battery, the voltage does not change by very much, and neither should the generator rpm.
A bit of experimentation may be required to convert maybe 50-60 pedal rpm to about 13v to 14v generator rpm.
But once you have that right, its just a case of pedaling harder (but not much faster) for more current.

All you need is a battery voltmeter and an amp meter for encouragement !
No other control system should be necessary, once you have the gearing set up right.
Most efficient gearing will use largest practical diameters, especially on the generator.
Click to expand...

once you have that right, its just a case of pedaling harder (but not much faster) for more current.
Click to expand...
I'm not really sure I understand what you mean here, how do I control how hard I have to pedal?
I think I understand that the goal is to convert the cadance speed to the correct rpm to generate 12vt through gearing, but how do I control amps? This is something I don't understand about generators / alternators in general. It seems like a higher speed will produce a higher voltage, but what produces more amps a set voltage? Is it just the load you have on it?

Another way to put it would be to say, why is a 12 volt motor a 12 volt motor? Is it 12 volts at a given rpm? If so, how does wind power work where the speed is variable? Is that what the charge controller regulates?

Also, I would be curious if getting a 24 volt motor would be more efficient as from what I understand you can spin it slower to generate 12 volts. What would be the drawbacks of doing this?
 
How fast you pedal controls the generator voltage.
How HARD it is to pedal decides the current.
Below some pedal speed it will be really easy to turn, requiring almost no effort at all. There will be no charging current either.

Once you are going fast enough to reach the actual battery charging voltage, it will progressively become much harder to pedal, like going up an ever steepening hill, and you will start to see an increasing charging current..
If you really lean into it and try to go even faster, the hill becomes very steep indeed, and the charging current much higher.
Torque is where the current comes from, the harder you push on those pedals, the higher the charging current.
If you back off a bit, it will become easier, but the charging current will also be less.

So how fit are you, how long do you want to pedal, it can be set up any way you want by altering the gearing.

It could be really easy, like going for 45 minutes while watching TV.
Or maybe a maximum effort for five minutes, where you get off that bike sweating and gasping for breath, your heart pounding and can hardly stand up.
When I was younger I could do 1/2 Hp for five minutes which is reasonable for an untrained healthy person in their prime.
That might be about 300 watts or something ? Dead easy for a couple of minutes, but that last fifth minute is a real killer.

A very serious champion cyclist should be able to hit 1Hp for several minutes.

The guy that flew the human powered Gossamer Albatross across the English Channel trained at about 1.5Hp for twenty minutes.
That is an incredible feat of strength and endurance by any standards.

So think in terms of designing for perhaps 100 watts max or less, or you will never be able to keep it up for long enough to usefully charge anything.
 
Last edited:
You must log in or register to reply here.

Similar threads

L
Charge and dump load controller for DIY wind turbine
Replies
3
Views
329
Hogheavenfarm
Hogheavenfarm
L
Appropriate generator characteristics for small wind turbine
Replies
1
Views
300
Hogheavenfarm
Hogheavenfarm
cubish
Thermodyne System for Sale!! 1200.
Replies
2
Views
415
cubish
cubish
S
LG Smartdrive 36 Pole PMA
Replies
1
Views
346
OzSolar
O
D
Diesel Powered Wind Turbine
Replies
14
Views
670
Rednecktek
Rednecktek
Back
Top