Brushless generator

[solarbot]

Hi all,

I have in mind to build my own generator by bolting a brushless motor onto a fossil fuel engine and rectifying the three phase output one way or another, perhaps even using an existing bldc motor controller in regeneration mode.

My first question: are generators on topic for diysolar? I suspect yes, because there are applications where a generator has to be part of a complete solar system. For example, where power demand somtimes spikes to a level that would rapidly deplete even a large battery bank, even though average demand could be met easily by the solar array. But I have nagging doubts, so please just let me know if it would be better to take this elsewhere.

If this is judged on topic, then what I have found out there on the net so far is just a great lack of information on the topic, and a considerable amount of obvious nonsense. Very little discussion at the engineering level. Perhaps I am just not looking in the right places. What I want to know is, all the reasons an ordinary (controllerless) brushless motor would make a poor generator. If there are none, then yippee, on to the experiment.

 

[newbostonconst]

Questioning what your total system goal is?

Gas generators cost lots to run even recovering all the lost heat they have the highest cost per unit energy(combustion engines at best are 30% efficient). I would guess your best setup might be solar/inverter with some batteries then charge the batteries when needed with your generator concept.

 

[DerpsyDoodler]

Questioning what your total system goal is?

Gas generators cost lots to run even recovering all the lost heat they have the highest cost per unit energy(combustion engines at best are 30% efficient). I would guess your best setup might be solar/inverter with some batteries then charge the batteries when needed with your generator concept.

I suspect that would (hopefully) be the goal. For my planned solar installation, I also have a generator, but it will be used as a backup. No sun and dead battery = no power. I always want a reliable backup solution. Whats more expensive, fridge and freezer full of spoiled food or the temporary cost of fuel? I would further argue that with the money you’re already saving on solar, the fuel cost is offset in the big picture.

That said, I have no idea if what he wants to do is worthwhile. Curious to see if any EEs chime in.

 

[schmism]

I would guess your best setup might be solar/inverter with some batteries then charge the batteries when needed with your generator concept.

You can have spent all the money in the world to build the biggest array on earth, but when the sun don't shine, you have no power. Dark overcast days of northern winter climate = need for generator

As others have found, time and effort are a thing. So yes, if you want to reinvent the wheel you can. However inexpensive brushless 3 phase inverter generators litter Amazon for just a few hundred dollars.

Can you cobble something together out of the parts bin lying around. Likely, Would it be as reliable and efficient as a commercial unit, unlikely.
If you're looking for something to tinker with in the garage as a hobby, the sky's the limit. If you're trying to build something that you intend to use as a serious power producing piece of equipment I think you'll have as much money invested in it as you would a commercial unit.

If you go for it start a thread in the show and tell forum and keep us updated on your progress.

 

[solarbot]

Questioning what your total system goal is?

Gas generators cost lots to run even recovering all the lost heat they have the highest cost per unit energy(combustion engines at best are 30% efficient). I would guess your best setup might be solar/inverter with some batteries then charge the batteries when needed with your generator concept.

Right, that is exactly my system goal: solar-mostly, but able to run on generator when necessary. For example, if I have a two day power outage in the winter. Yes this has happened. Another example: a cabin with small solar array, but I sometimes want to run power tools. Longer term, I am thinking about repowering my boat as DIY diesel-electric, but I better get that sorted out on land first before attempting it on the water.

To put this in more concrete terms, I would like to be able to generate about 5kw for up to two days with diesel, should the need arise, but otherwise never turn on the motor. Emergency generator, if you like. And because I like to make things hard for myself, I want to build my own generator using a standard BLDC motor. I don't know whether that is an incredibly stupid idea or not, I'm here to ask that question.

 

[solarbot]

I suspect that would (hopefully) be the goal. For my planned solar installation, I also have a generator, but it will be used as a backup. No sun and dead battery = no power. I always want a reliable backup solution. Whats more expensive, fridge and freezer full of spoiled food or the temporary cost of fuel? I would further argue that with the money you’re already saving on solar, the fuel cost is offset in the big picture.

That said, I have no idea if what he wants to do is worthwhile. Curious to see if any EEs chime in.

You're right, that's what I want to do. And to make it interesting, I want to DIY it with a BLDC motor instead of just doing the easy thing and plugging a stock generator into a stock charger.

 

[DerpsyDoodler]

You're right, that's what I want to do. And to make it interesting, I want to DIY it with a BLDC motor instead of just doing the easy thing and plugging a stock generator into a stock charger.

Sounds like a fun project! Take your time, learn about it, and do it right!

 

[solarbot]

As others have found, time and effort are a thing. So yes, if you want to reinvent the wheel you can. However inexpensive brushless 3 phase inverter generators litter Amazon for just a few hundred dollars.

Can you cobble something together out of the parts bin lying around. Likely, Would it be as reliable and efficient as a commercial unit, unlikely.
If you're looking for something to tinker with in the garage as a hobby, the sky's the limit. If you're trying to build something that you intend to use as a serious power producing piece of equipment I think you'll have as much money invested in it as you would a commercial unit.

If you go for it start a thread in the show and tell forum and keep us updated on your progress.

I want to tinker, not necessarily with parts lying around. I want to put numbers and reasons to the "reliable and efficient as a commercial unit" question. And I don't mind making things hard for myself if I learn something.

I am not sure what you mean by "brushless 3 phase inverter generator", did you mean brushless generator? Or DC generator? A link or two would be helpful.

(edit) I found this one, which just looks like an ordinary BLDC motor to me:
https://www.amazon.com/Permanent-Generator，400W-Vertical-Horizontal-Turbine/dp/B07ZDDM1FY
3-phase Permanent Magnet Generator (600W48V)

I'm not quite at the show and tell stage on this project, I'm now in the research phase. Specifically, how do the electrical characteristics of a BLDC motor differ from a brushless generator, if at all?

 

[newbostonconst]

You may want to calculate the fuel usage....I am guessing around a gallon an hour and at $3 a gallon that will around $70 a day... Every two days you can buy another panel or an other battery.

 

[solarbot]

You may want to calculate the fuel usage....I am guessing around a gallon an hour and at $3 a gallon that will around $70 a day... Every two days you can buy another panel or an other battery.

The cost of fuel is not an issue here because I assume that the average case is handled within the solar envelope. Adding panels doesn't help if the sun isn't shining or you ran out of space for panels. Sometimes there is just no getting away from the generator, that's not the question. The question is how to do ithe generator elegantly.

 

[solarbot]

Here is one from Central Main Diesel, in the wild:

www.centralmainediesel.com/order/Kubota-4500-Watt-Diesel-Generator.asp?page=Kubota_4500

Things we can tell from a quick peek:

* This is an aftermarket mod of the much-loved Kubota OC60-E4 single banger diesel
* That seems to be an air-cooled BLDC motor bolted on
* A rectifier/inverter assembly is bolted onto that. Very compact.
* From the factory the OC60-E4 is pull-cord start
* They use the BLDC as a starter motor, so that answers the question "can you do that?"
(edit: I erred here, the OC60-E4 has 12v electric start, so the question "can you use a BLDC as a starter" is still open)
* The BLDC must be at least 120v, maybe twice that, so they don't have to boost it
* Runs 6 hours on 3.5 liters (.92 gallons) at "half load"
* A lot more expensive than your typical Costco generator
* Lots of vibration and noise!

I can only speculate what that motor actually is. All I have gleened from my web searches about the electrical constraints so far is that it has to have enough stator windings to produce the desired voltage at relatively low RPM. So what is the difference between what I see here, or imagine I see, and what I want? Well I would rather generate 48vdc than 120ac, or maybe generate 48v 3-phase and convert it elsewhere.

I am not fixated on diesel, but I see some distinct advantages. Around a liter per hour fuel consumption would be hard to beat, if true. Reliability is reputed to be very high and maintenance very low. This is really a simple motor, I love that. There are disadvantages too. Look how it jumps around at low rpm, and significant vibration at operating speed too. That's because of the single cylinder. This is very much an acquired taste. If quiet is a major requirement then this is not the way to go, a four cycle gas engine would be better.

But enough on the engine, it's the generator I'm primarily interested in. Maybe something like this:

48 Volt 5KW BLDC Motor Air Cooled

Great selection of Hub Motor Kits. Our sine wave controllers deliver strong, smooth, silent power and are programmable with Bluetooth or Windows.

www.goldenmotor.ca

Going back to the video link above, you get a clear look at the housing that had to be fabricated to marry the motor to generator. Engines typically use SAE bellhousing standards and electric motors use NEMA mounts, so there is roughly zero chance of finding anything suitable off the shelf. If I attempt a build, fabricating that mounting will be a major part of the effort and expense, likewise the shaft coupler. After this research, I really appreciate what Central Marine has done there, I can see how much effort that housing was to engineer and I can imagine they had to lay out a fair amount of cash to manufacturer it, most likely in small volume. So yeah, that detail gives me pause. But it's not a stopper, my take on it doesn't need to be pretty, it just needs to work.

And back to the electrical questions. I'm currently working up a test setup using a smaller BLDC motor at 440 watts, and drive it with another, low tech brushed e-bike motor, cheap from Amazon. It looks like suitable three phase rectifiers are readily available off the shelf and are also not hard to build, but I am really more interested in what happens when I use a motor controller as a rectifier. For this, I don't have much hope of getting joy from the controllers that came with the motors from China because of zero documentation, and a high likelihood of the controllers being "too helpful" about being motors, and thus getting in the way of being a generator. Luckily, there is a healthy e-skateboard open source motor controller scene out there that might be able to provide me exactly the hardware I need, in a form I can hack at the micro-controller level. That's where it starts to get comfortable for me, because that's what I am, a software engineer.

Ok, there's my brain dump for today, I hope there are a few bits and pieces in there worthy of comment/criticism.

 

[Hedges]

BLDC would typically be a permanent magnet 3-phase motor.
Maybe drive electronics provide electronic braking and recovery to DC power rail, maybe not.
The 3-phase VFD I'm familiar with synthesize a sine wave of current to drive motor. They may do as nicely for braking.
Typical 3-phase diode rectifier used on 3-phase alternator just clips the top off sine waves, which generates harmonics. Probably causes more loss in the magnetic core.
Ideal rectifier corrects PF to 1.0, drawing sine-wave current while delivering DC. That is found in some inverter/chargers.

Typical stand-alone generator head has bearings, and you would use a shaft coupler. Some generators, like some pumps, have rotor bolted to crankshaft and stator is supported by bracket. No extra bearings or coupling.

Once you've got a generator, you have to decide how to manage it's electrical output, charge battery (or AC couple), avoid generating harmful voltage transients.

As was said, about 30% efficiency from ICE, so you should do CHP, combined heat & power, recovering waste heat for domestic use.

 

[WoodsieLord]

I remember this generator. Is smaller in scale and aimed at something else, but It was very neat and well tested:

 

[MattiFin]

There are couple of open source firmwares for R/C controllers and e-bike controllers. Rcgroups.com and SimonK firmware ahould give you some pointers.
For ebikes there is open source firmware for the cheap chinese KUnTeng controllers https://endless-sphere.com/forums/viewtopic.php?t=87870

With suitable firmware you can also boost the bldc output voltage.

BLDC output waveform is not sine wave and you should account for this if you want to maximize your efficiency.

 

[MattiFin]

As was said, about 30% efficiency from ICE, so you should do CHP, combined heat & power, recovering waste heat for domestic use.

Could be waste of time depending on usage scenario. If you need the generator power only for ”emergencies” or something like 100kwh per year CHP doesn’t make sense.
Then on the other hand if you live 67N like some members you would need generator power for 3-4 months if you go off-grid.

 

[MattiFin]

Design and implementation of a low-cost maximization power conversion system for brushless DC generator

This paper presents a simple and low-cost method to capture maximum power throughput of permanent magnet brushless DC (BLDC) generator. Conventional m…

www.sciencedirect.com

 

[Hedges]

Design and implementation of a low-cost maximization power conversion system for brushless DC generator

This paper presents a simple and low-cost method to capture maximum power throughput of permanent magnet brushless DC (BLDC) generator. Conventional m…

www.sciencedirect.com

I have difficulty reading patent-speak and much academic writing.
Glad to see they did a physical implementation and measured it as well.

I would condense the entire article to, "Emulate a resistive load."

 

[MattiFin]

I would condense the entire article to, "Emulate a resistive load."

Essentially that. Tricky part is the emulation.
Sensorless field orientation control or direct torque control probably gives mire reading for OP..

 

[Hedges]

Essentially that. Tricky part is the emulation.
Sensorless field orientation control or direct torque control probably gives mire reading for OP..

KISS

You get 90% of the way there with 6 diodes to rectify the 3-phase output.

Conclusion of the paper included,

"Simulation results show an increase of 11.6% in the output power. Therefore, the weight and volume of the generator can be reduced by 11.6% by using the optimal control method."

If MW or GW scale, then we would be talking real money.

Don't think the paper quoted absolute efficiencies, just relative. So can't be sure how much heating was reduced. Could have been 50%, could have been 90%. Copper losses I^2R improved with PF. Core losses could improve dramatically with reduced harmonics, or not.

Good PF correction becomes more important for applications that would otherwise impair system performance or interfere with communications. (Things like the instruments I deal with, and EMC to meet regulatory requirements.)

 

[solarbot]

I remember this generator. Is smaller in scale and aimed at something else, but It was very neat and well tested:

Great find! So we have proof by example that DIY brushless generator is not a stupid idea, thanks much. Plus so many valuable tips. One I paid particular attention to: he says the generators operating range should be twice the target DC voltage. I hope it's not quite that bad because it suggests rather severe inefficiencies. I conceived of a 48 volt motor/generator feeding into 48 volt battery rails. Well, now I better think about what voltage the generator actually needs to produce. I suspect this is about the quality of the rectifier. Fortunately, the higher power BLDC's I see on offer tend to span a comfortable voltage range, to 96v and some a bit higher. The question: how many amps under full load at engine's ideal RPM? I will attempt a decent guess before ordering, but the only way to be sure is to try it.

The video... worth watching just to see the the gigantic resistors cooled with a spray bottle.