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Old Feb 18, 2008, 01:57 AM
runcyclexcski@gmail.com
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RC airplane gasoline engine as an electrical generator

I've never posted on this group, and I am apologize for rushing right
it with a specific question.

I have an idea of building a tiny generator for an electric R/C toy
which is supposed to output ~300W of electrical power, with a capacity
of, say, 5 Amp-hrs. Is it too crazy of an idea? A portable battery
pack of that power/capacity weighs about 20-30 lbs, and I would like
to reduce the weight as much as I can. It appears that R/C airplane
gasoline engines fall into my desired power/weight category, so I was
thinking to hook up such an engine to a generator. I tried to google
wattage ratings of RC gasoline engines and did not have much luck.
Oh, and a relatively quiet operation would be a plus (say, not more
noise than from a scooter/moped).

I am not an RC person, so I apologize in advance for my ignorance.
Old Feb 18, 2008, 04:58 AM
The Natural Philosopher
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n/a Posts
Re: RC airplane gasoline engine as an electrical generator

runcyclexcski@gmail.com wrote:
> I've never posted on this group, and I am apologize for rushing right
> it with a specific question.
>
> I have an idea of building a tiny generator for an electric R/C toy
> which is supposed to output ~300W of electrical power, with a capacity
> of, say, 5 Amp-hrs. Is it too crazy of an idea? A portable battery
> pack of that power/capacity weighs about 20-30 lbs,


What? a 300watt capable pack runningat 5A/h.. No way. Not lithium

Ive got a 3.6Ah÷300W pack and that weighs about 10oz...


> and I would like
> to reduce the weight as much as I can. It appears that R/C airplane
> gasoline engines fall into my desired power/weight category, so I was
> thinking to hook up such an engine to a generator. I tried to google
> wattage ratings of RC gasoline engines and did not have much luck.


It's 750 watts per horepower. probably what you need is a 40 class glo
motor coupled to a cooling fan and a 300w class brushless motor (e.g.AXI
2826/12 and 6 silicon diodes to make a three phase rectifier,and you
should be able to produce 300w at around 12-16v as long as the fuel is
there,.

> Oh, and a relatively quiet operation would be a plus (say, not more
> noise than from a scooter/moped).
>

Forget it. Use teh LIPO battery instead.

> I am not an RC person, so I apologize in advance for my ignorance.

Old Feb 18, 2008, 07:20 AM
Robert Roland
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n/a Posts
Re: RC airplane gasoline engine as an electrical generator

On Sun, 17 Feb 2008 22:57:59 -0800 (PST), runcyclexcski@gmail.com
wrote:

>I have an idea of building a tiny generator for an electric R/C toy
>which is supposed to output ~300W of electrical power, with a capacity
>of, say, 5 Amp-hrs. Is it too crazy of an idea?


Not crazy, but probably impractical. To do the math, we need to know
how much energy you need to store in the battery. If you specify what
voltage you need, we can start calculating.

>A portable battery
>pack of that power/capacity weighs about 20-30 lbs, and I would like
>to reduce the weight as much as I can.


A 22V 5Ah LiPo battery at weighs less than a tenth of that. Power
output of a couple of kilowatts is no problem. You will need a motor
and a regulator as well, but they don't weigh much.

Since this is a toy, LiPo may not be safe enough, but NiMH will still
be well within your weight limit, and depending on voltage, will most
likely be able to provide enough power.

>It appears that R/C airplane
>gasoline engines fall into my desired power/weight category, so I was
>thinking to hook up such an engine to a generator.


When you include the weight of the generator and the fuel tank, I bet
you will come out at a higher weight than electric.

>I tried to google
>wattage ratings of RC gasoline engines and did not have much luck.


RC combustion engines, like all other combustion engines, are usually
rated in horsepower. One kilowatt is about 1.36 horsepower.

>Oh, and a relatively quiet operation would be a plus (say, not more
>noise than from a scooter/moped).


If noise is any issue at all, electric is the way to go.

BTW: Most small and medium model engines run on a methanol based fuel.
This fuel is much more expensive than gas. You can get gas powered
model engines as well, but they are normally larger, normally about
20cc and up.

The combustion engine has only two advantages left, compared to
electric power these days:

1: Recharge time. Filling the tank takes a minute or two, while
charging the battery takes at least half an hour.

2: Cost. High-performance batteries are quite expensive, and they do
wear out.
--
RoRo

Old Feb 18, 2008, 12:29 PM
Tim Wescott
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n/a Posts
Re: RC airplane gasoline engine as an electrical generator

On Sun, 17 Feb 2008 22:57:59 -0800, runcyclexcski wrote:

> I've never posted on this group, and I am apologize for rushing right it
> with a specific question.
>
> I have an idea of building a tiny generator for an electric R/C toy
> which is supposed to output ~300W of electrical power, with a capacity
> of, say, 5 Amp-hrs. Is it too crazy of an idea? A portable battery pack
> of that power/capacity weighs about 20-30 lbs, and I would like to
> reduce the weight as much as I can. It appears that R/C airplane
> gasoline engines fall into my desired power/weight category, so I was
> thinking to hook up such an engine to a generator. I tried to google
> wattage ratings of RC gasoline engines and did not have much luck. Oh,
> and a relatively quiet operation would be a plus (say, not more noise
> than from a scooter/moped).
>
> I am not an RC person, so I apologize in advance for my ignorance.


As mentioned elsewhere, you haven't specified a voltage, and hence don't
have enough information to know how much energy is to be stored.

To figure out wattage, multiply horsepower by 700 (it's really 730 some-
odd, but 700 will get you well within the ballpark). The gasoline weed-
whacker engines that get converted to RC use generate over a horsepower,
if I'm not mistaken. Then figure that your generator is going to impose
an energy conversion tax of between 5 and 30%, depending on the generator.

You probably _don't_ want a weed-whacker engine that's been converted,
though -- an RC engine doesn't need fan and shrouds for cooling, but a
stationary generator set certainly does. So what you really want to
start with is probably an unconverted engine from a weed-whacker or chain
saw.

Figure you'll need some way of transmitting power from the engine to the
generator -- a belt is probably a good way, if the side loading doesn't
trash the bearings on either the engine or the generator. Then figure
out how you're going to gear things so the generator spins fast enough
and the motor at a good speed. Finally (heh heh heh) figure out how to
regulate the speed of the engine and what comes out of the generator so
you can do something useful with it.

You could make this all smaller with an RC glow-plug engine, but you'll
find that the fuel will be less available, the engine will be harder
(possibly much harder) to start, and you'll have to rig the blower and
shrouds to adequately cool the engine.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
Old Feb 18, 2008, 01:40 PM
Doug McLaren
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n/a Posts
Re: RC airplane gasoline engine as an electrical generator

In article <1203328705.18224.0@damia.uk.clara.net>,
The Natural Philosopher <a@b.c> wrote:
| runcyclexcski@gmail.com wrote:
....
| > I have an idea of building a tiny generator for an electric R/C toy
| > which is supposed to output ~300W of electrical power, with a capacity
| > of, say, 5 Amp-hrs. Is it too crazy of an idea? A portable battery
| > pack of that power/capacity weighs about 20-30 lbs,
|
| What? a 300watt capable pack runningat 5A/h.. No way. Not lithium
|
| Ive got a 3.6Ah÷300W pack and that weighs about 10oz...

I'll bet he just meant that this would provide 300 watts for 5 hours
and accidently stuck in the `amp' unit.

Assuming that your 3600 mAh pack is a 3s (just a guess), that means it
could provide 300 watts for about 9 minutes. To make that last 5
hours, you'd need 35 of them, and that would weigh about 22 lbs.

| It's 750 watts per horepower. probably what you need is a 40 class glo
| motor coupled to a cooling fan and a 300w class brushless motor (e.g.AXI
| 2826/12 and 6 silicon diodes to make a three phase rectifier,and you
| should be able to produce 300w at around 12-16v as long as the fuel is
| there

Sounds appropriate. You could also use a similarly sized brushed
motor and skip the rectifier, but then you'd have brushes to wear out.
(What do small, commercially made DC generators usually do? I guess
I'd prefer the brushless version just for the reduced maintenance.)

I wonder how long a R/C engine would last being run non-stop before
just plain wearing out? They're meant to be small and powerful, not
necessarily to last for a long time. Maynard got his to run for
around 40 hours non-stop, but he's a God among men ...

(May not be a concern. I'm just rambling ...)

| > Oh, and a relatively quiet operation would be a plus (say, not more
| > noise than from a scooter/moped).

A four stroke engine would probably be quieter than a two stroke. It
would also cost more, weigh a bit more, but be a little more
efficient.

Don't forget that glow fuel is a lot more than gasoline -- around
$12/gallon US here. You could use a gasoline engine, but generally
they're a lot bigger than 300 watts.

| Forget it. Use teh LIPO battery instead.

Or 35 of them, if I understand what you're asking for better than TNP.

Certainly, a lead acid battery would weigh a lot more. I've got a 100
Ah 12v battery that weighs around 40 lbs. In theory, it could put out
300 watts for around 4 hours -- too heavy, not quite long enough, but
a whole lot cheaper than the LiPo solution.

--
Doug McLaren, dougmc@frenzied.us Connection reset by peer pressure
Old Feb 18, 2008, 01:41 PM
runcyclexcski@gmail.com
Guest
n/a Posts
Re: RC airplane gasoline engine as an electrical generator

Thank you, all, for the great responses.

Ideally, I would want an AC 120V output wave and 1.6 Amps,
respectively. But if a sine AC wave is not an option, 24V DC and 8
Amps should would work.

While waiting for the responses, I did some reading in LiPos. 5000 mAh
batteries indeed should do the trick. But I am a total dummy in
electronics, so safely integrating the battery (and generating a 120V
sine wave?) without shorting it and blowing everything up would be a
challenge. In addition, I found numerous LiPos blowing up videos on
UTube (even with mechanical stress), and all those were 2-5 times less
powerful than the 5000 mAh battery that I will likely need. Just how
mature is the LiPo technology?

But all around it looks like my generator idea still loses compared to
the LiPo idea. So, I am totally for the LiPo idea, as long as I can do
it safely.
Old Feb 18, 2008, 01:57 PM
runcyclexcski@gmail.com
Guest
n/a Posts
Re: RC airplane gasoline engine as an electrical generator


>
> Or 35 of them, if I understand what you're asking for better than TNP.
>
> Certainly, a lead acid battery would weigh a lot more. I've got a 100
> Ah 12v battery that weighs around 40 lbs. In theory, it could put out
> 300 watts for around 4 hours -- too heavy, not quite long enough, but
> a whole lot cheaper than the LiPo solution.
>



Thank you, Doug, you made many things clear.

There was a typo in my OP - I need 200W instead of 300W, but it's not
a huge difference. Need about 2 hrs of continuous power output.

I apologize for the vague specs on what I need. Ideally, I need a 120V
AC sine wave at 1.6 amps. Or 24V DC would work, too.

Here is a link to a 16 Ah LiPo battery:

http://www.all-battery.com/index.asp...OD&ProdID=2152

It outputs 22V, so for 200W it's ~9Amps, so it technically should last
for ~1.5 hrs - is that right?

It weights 3 lbs.

But me making this battery pack work would be equivalent to trying to
deactivate a TNT bomb,
Old Feb 18, 2008, 02:04 PM
Morgans
Guest
n/a Posts
Re: RC airplane gasoline engine as an electrical generator


<runcyclexcski@gmail.com> wrote in message
news:49449560-4353-41d1-939d-c3deb19ae862@d21g2000prf.googlegroups.com...
> Thank you, all, for the great responses.
>
> Ideally, I would want an AC 120V output wave and 1.6 Amps,
> respectively. But if a sine AC wave is not an option, 24V DC and 8
> Amps should would work.


You would be money ahead to get a commericial inverter, and if you want 300
watts, get a 500 constant, (and some other higher number, whatever they say)
peak watts. They are a square (modified) sine wave, but they do OK for
nearly anything you want to run.

> While waiting for the responses, I did some reading in LiPos. 5000 mAh
> batteries indeed should do the trick. But I am a total dummy in
> electronics, so safely integrating the battery (and generating a 120V
> sine wave?) without shorting it and blowing everything up would be a
> challenge. In addition, I found numerous LiPos blowing up videos on
> UTube (even with mechanical stress), and all those were 2-5 times less
> powerful than the 5000 mAh battery that I will likely need. Just how
> mature is the LiPo technology?


As long as you don't physically damage them, and don't push them too hard,
in amps draw and in charging rate, and keep them cool, they are pretty darn
safe. Violating one of the three above can get you in trouble.

> But all around it looks like my generator idea still loses compared to
> the LiPo idea. So, I am totally for the LiPo idea, as long as I can do
> it safely.


The generator is cooler, though! <g>
--
Jim in NC


Old Feb 18, 2008, 02:20 PM
Tim Wescott
Guest
n/a Posts
Re: RC airplane gasoline engine as an electrical generator

runcyclexcski@gmail.com wrote:
> Thank you, all, for the great responses.
>
> Ideally, I would want an AC 120V output wave and 1.6 Amps,
> respectively. But if a sine AC wave is not an option, 24V DC and 8
> Amps should would work.
>
> While waiting for the responses, I did some reading in LiPos. 5000 mAh
> batteries indeed should do the trick. But I am a total dummy in
> electronics, so safely integrating the battery (and generating a 120V
> sine wave?) without shorting it and blowing everything up would be a
> challenge. In addition, I found numerous LiPos blowing up videos on
> UTube (even with mechanical stress), and all those were 2-5 times less
> powerful than the 5000 mAh battery that I will likely need. Just how
> mature is the LiPo technology?
>
> But all around it looks like my generator idea still loses compared to
> the LiPo idea. So, I am totally for the LiPo idea, as long as I can do
> it safely.


Find a video of the explosion and fire you can get from a quart of
gasoline, and ask yourself which is safer.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
Old Feb 18, 2008, 02:21 PM
The Natural Philosopher
Guest
n/a Posts
Re: RC airplane gasoline engine as an electrical generator

runcyclexcski@gmail.com wrote:
> Thank you, all, for the great responses.
>
> Ideally, I would want an AC 120V output wave and 1.6 Amps,
> respectively. But if a sine AC wave is not an option, 24V DC and 8
> Amps should would work.
>
> While waiting for the responses, I did some reading in LiPos. 5000 mAh
> batteries indeed should do the trick. But I am a total dummy in
> electronics, so safely integrating the battery (and generating a 120V
> sine wave?) without shorting it and blowing everything up would be a
> challenge. In addition, I found numerous LiPos blowing up videos on
> UTube (even with mechanical stress), and all those were 2-5 times less
> powerful than the 5000 mAh battery that I will likely need. Just how
> mature is the LiPo technology?
>
> But all around it looks like my generator idea still loses compared to
> the LiPo idea. So, I am totally for the LiPo idea, as long as I can do
> it safely.


LIPOS are pretty good, and an be seriesed and parallelled pretty safely

Best deal on high capacity I have found yet is www.maxamps.com

Check them out. They do 10Ah stuff..

as long as you don't run them flat, short them or charge them beyond
their rated voltage, ort leave them in te sun too miuch, they are safe.
Its really the fact that we perate them without any safety circuits to
get the most power out that means that carelessness can cause accidents.

I would say you should investigate a small UPS or caravan type inverter
if 120VAC is what you want, and run from 12v (3 or 4 series cells) at
about 20Ah

The generator option is amusing, but you will have to DIY it a lot more.
Old Feb 18, 2008, 03:12 PM
runcyclexcski@gmail.com
Guest
n/a Posts
Re: RC airplane gasoline engine as an electrical generator

Thank you guys, you are the best.

Yes, a quart of gasoline blowing up would make a pretty good fireball,
too, wouldn't it?

I did not realize that RC airplane engines are not meant to be run
long. I guess I would need a toy semi-truck analog, if you know what I
mean - low RPMs. But then the size and the eight go up - and I am in
the 4-stroke category.

At any rate - looks like the LiPos are the way to go. Instead of do
the wiring myself I could indeed get an inverter. I still need to
figure out a way to limit the discharge rate. E.g. the 12 Ah LiPo
battery I found (btw it's $500) is rated at 20V and 6A max discharge.
That gives me 120W, and it's already at max output (safety?). OK, I
could put two of these in series, I guess... but I still need to
understand how to make a circuit to limit the discharge rate. Would an
AC inverter have such a circuit pre-installed?

Old Feb 18, 2008, 04:10 PM
Doug McLaren
Guest
n/a Posts
Re: RC airplane gasoline engine as an electrical generator

In article <36e3a17a-5b65-4884-8b73-b49f2a1ae5ac@i29g2000prf.googlegroups.com>,
<runcyclexcski@gmail.com> wrote:

| There was a typo in my OP - I need 200W instead of 300W, but it's not
| a huge difference. Need about 2 hrs of continuous power output.

200 W for 2 hrs is a lot easier than 300 W for 5 hours.

| I apologize for the vague specs on what I need. Ideally, I need a 120V
| AC sine wave at 1.6 amps. Or 24V DC would work, too.

Ultimately, the form of the electricity doesn't matter _that_ much,
because converting isn't too difficult. But if you need AC rather
than DC, that does make an engine powering a generator a little more
attractive.

| Here is a link to a 16 Ah LiPo battery:
|
| http://www.all-battery.com/index.asp...OD&ProdID=2152
|
| It outputs 22V, so for 200W it's ~9Amps, so it technically should last
| for ~1.5 hrs - is that right?

Well, at 22 volts it's time to stop. But it starts at 26 volts fully
charged (according to the page, though most R/C chargers would only go
up to 25 volts), so the average is around 24 volts, and that works out
to 8.3 amps, and so you last 1.92 hours -- very close.

(Perhaps you could go to 7 cells and get the extra power that way? It
depends on the load, on how easily it can be adapted to slightly
different input voltages.)

Also note that this limits the discharge rate to 6.5 amps, if you buy
this pack as-is. (Looks like the individual cells are good to 1C, so
they should be able to do 16 A if you make your own harness.)

| It weights 3 lbs.

Impressive.

| But me making this battery pack work would be equivalent to trying to
| deactivate a TNT bomb,

LiPos aren't _quite_ that dangerous. But yes, you'd have to be
careful, you'll need a charger, etc.

Doing 200 watts for 2 hours makes batteries look a lot more attractive
for this than 300 watts for 5 hours does.

--
Doug McLaren, dougmc@frenzied.us
On the other hand, you have different fingers
Old Feb 18, 2008, 04:31 PM
Doug McLaren
Guest
n/a Posts
Re: RC airplane gasoline engine as an electrical generator

In article <044f7de1-03aa-4a24-bfdc-630894395804@i12g2000prf.googlegroups.com>,
<runcyclexcski@gmail.com> wrote:

| I did not realize that RC airplane engines are not meant to be run
| long.

Well, that's just supposition on my part, but certainly getting one to
run for hours might be tricky, and I don't know how long it would last.

The analogy would be a 3.5 liter V8 Indy car engine making 650
horsepower -- compare that to a 3.6 liter engine in your truck that
puts out 250 hp. But the Indy car engine only needs to last one race
....

I guess I would need a toy semi-truck analog, if you know what I
| mean - low RPMs. But then the size and the eight go up - and I am in
| the 4-stroke category.

For R/C engines, two and four stroke engines are a little different
than the rest of the world.

For R/C engine, 2 and 4 stroke means just that -- 2 and 4 strokes. It
has nothing to do with the lubrication system, for example, and most
R/C engines, 2 or 4 stroke, have the oil mixed in with the fuel.

It's not like the small engine world, where `four stroke' means not
only four strokes but also a closed lubrication system. Most R/C
engines will create a slime of oil at the exhaust.

You can get a big 2 stroke R/C engine easily enough, much bigger than
200 watts. 200 watts is perhaps on the small side ...

| I still need to figure out a way to limit the discharge rate.

Your load should do that for you. You certainly don't want to hit any
load limiter on an inverter, because then it just shuts off.

| E.g. the 12 Ah LiPo battery I found (btw it's $500) is rated at 20V
| and 6A max discharge.

If that's the link you gave, the 6A limit came from the way the cells
were put together. Individually, they can do 16A. So you just have
to wire them up yourself.

There are other battery options, and you can have places make you a
custom pack set up exactly the way you want it. But it'll cost you
....

--
Doug McLaren, dougmc@frenzied.us
`Mate, this parrot wouldn't VOOM if you put four million volts through
it!' --Monty Python
Old Feb 18, 2008, 05:11 PM
Morgans
Guest
n/a Posts
Re: RC airplane gasoline engine as an electrical generator


"Doug McLaren" <dougmc+usenet-20080218@frenzied.us> wrote

> Well, at 22 volts it's time to stop. But it starts at 26 volts fully
> charged (according to the page, though most R/C chargers would only go
> up to 25 volts), so the average is around 24 volts, and that works out
> to 8.3 amps, and so you last 1.92 hours -- very close.
>
> (Perhaps you could go to 7 cells and get the extra power that way? It
> depends on the load, on how easily it can be adapted to slightly
> different input voltages.)
>
> Also note that this limits the discharge rate to 6.5 amps, if you buy
> this pack as-is. (Looks like the individual cells are good to 1C, so
> they should be able to do 16 A if you make your own harness.)
>

If it figures that close, it will never do it. Inverters are only around
50% efficient. You will need a battery twice as big, I would guess.
--
Jim in NC


Old Feb 18, 2008, 05:48 PM
The Natural Philosopher
Guest
n/a Posts
Re: RC airplane gasoline engine as an electrical generator

Morgans wrote:
> "Doug McLaren" <dougmc+usenet-20080218@frenzied.us> wrote
>
>> Well, at 22 volts it's time to stop. But it starts at 26 volts fully
>> charged (according to the page, though most R/C chargers would only go
>> up to 25 volts), so the average is around 24 volts, and that works out
>> to 8.3 amps, and so you last 1.92 hours -- very close.
>>
>> (Perhaps you could go to 7 cells and get the extra power that way? It
>> depends on the load, on how easily it can be adapted to slightly
>> different input voltages.)
>>
>> Also note that this limits the discharge rate to 6.5 amps, if you buy
>> this pack as-is. (Looks like the individual cells are good to 1C, so
>> they should be able to do 16 A if you make your own harness.)
>>

> If it figures that close, it will never do it. Inverters are only around
> 50% efficient.


90% plus for larger ones.

You will need a battery twice as big, I would guess.
 


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