Stirling phone charger

[Tom Booth]

I was inspired by this video:


https://youtu.be/dOKnGouQX6s?si=8dlrUkrONrAw79m_


The video received quite a lot of negative commentary. A lot of skepticism. The most apparently up-voted post at the top of the comments says he has a wireless charger under the table.

Someone gave a helpful suggestion, that a higher gear ratio might help. So I thought I'd give that a try.

I have a couple of the same engines and they are probably a couple of the most powerful of all my small models, especially after some minor modifications, so, I'm not entirely convinced one could not actually charge a cell phone, albeit, at an extremely slow rate.

My first step in this experiment is to increase the gear ratio. I did this by increasing the drive pulley diameter by cutting some rings out of some PVC pipe and fitting.


https://youtu.be/546LT0AnL40?si=huso_MOsPegZZJ8u


So far so good.

Normally these engines require a LOT of heat to run at very high RPM to just barely light the supplied LED. But I found that this is more due to the extreme inefficiency of the little generator at low RPM. It needs to be geared up quite a bit, rather than lack of power from the Stirling engine itself.

Why they supply these engines with 1:1 ratio pulleys I don't know. Gear them up a little and the engine has no problem lighting the LED with just a tea candle rather than a propane torch.

[Tom Booth]

Actually, it was this other video that received a lot of negative comments. More than the other video anyway, but also some positive ones.


https://youtu.be/M3W-o1FU614?si=TFO4Ij4HYOuSdEAV


It is somewhat concerning the number of people who seem predisposed to assuming Stirling engines have no power and so could not possibly even supply the few watts it might take to charge a cell phone.

I have to admit that until very recently, I've had much the same mindset, because I've had at least half a dozen model engines with generators that seemed hard pressed to light up a single LED.

Apparently though, the fault is not with the Stirling engines so much as with the little generators supplied with them that require very high RPM, along with the supplied gear ratio, which is often just 1:1 or not much better.

Of course, some more efficient generators that don't require high RPM would perform even better, but increasing the gear ratio is at least a quick fix.

[VincentG]

Fantastic Tom! I recommend measuring the open load voltage of the generator at the desired rpm of the generator itself. That will give a better idea of the ideal load. In other words, if the generator is spinning at 1000rpm and the open load voltage is 4 volts, the more ideal load would be 2 LED's in series as opposed to just one.

[Tom Booth]

Fantastic Tom! I recommend measuring the open load voltage of the generator at the desired rpm of the generator itself. That will give a better idea of the ideal load. In other words, if the generator is spinning at 1000rpm and the open load voltage is 4 volts, the more ideal load would be 2 LED's in series as opposed to just one.

Not sure what you mean by "the desired rpm of the generator itself". Though I can certainly measure the open circuit voltage with varying heat input and RPM.

If the voltage goes high enough, I may just try charging some old cell phone directly from the generator output, as in the video. I'm sure I have a few old phones with cracked screens kicking around somewhere.

[Tom Booth]

Well this is better than I had anticipated.

https://youtu.be/_cVg3fy6F_c?si=yEsHMSb6w6OWlf5J


No problem topping 5 volts at fairly low RPM.

Lots of extra heat from the blow torch didn't seem to do much.

[Tom Booth]

I dug up a couple of old sacrificial phones and a charger.

The color coding for the cable (the old one I have anyway) is apparently:

Red: +5v
Black: -5v (or ground)
White and Green are data.

Other stuff is just shielding

In the video it appears that he twists the power and data wires together which seems like a really bad idea.

I'll just be using the red and black. (After verifying the polarity with the meter).

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[Tom Booth]

Normal output for the phone charger is, of course 5 volts DC

Resize_20231230_001845_5124.jpg (297.91 KiB) Viewed 2384 times

So, as the guy stated in one of the videos, the voltage put out by the little generators that come with these engines should be just about right.

In my experience with battery charging generally, over voltage is not normally a problem because the battery itself tends to absorb that, at least until the battery gets up near to being fully charged, then the power has nowhere to go and the voltage starts to spike, so I wouldn't recommend trying to give any phone anyone cares about at all a full charge by this bare wire direct from the generator method

[Tom Booth]

According to my meter, when plugged into the wall socket, the phone charger is only putting out 4.88 volts

That's kind of encouraging actually. The engine was putting out that just running on residual heat after the flame was blown out.

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Of course, amps may be a different story, as well as actual voltage under load.

[Tom Booth]

It looks like it most certainly puts out enough power to at least light up the charging icon:


https://youtu.be/QRs-ex8Y4TA?si=aRrLw-4P5PJ9y78B


And I'm not pushing it. So nobody needs to hide a wireless charger under a mat or whatever to do at least that.

The engine also did not slow down much.

I forgot to show it, but the voltage also dropped a bit, to just under 5 volts.

If the voltage drops much under five volts, though, I noticed the charge icon won't appear at all.

It took a lot of time and frustrating effort to get that short video because the wires and/or meter probes kept falling off or the very fine wires slipped off or shorted out against the generator or did not make good contact.

I finally ran the engine relatively slowly to avoid the vibration that kept shaking the wires loose.

I had also tried another old phone which also appeared to be charging.

I'll have to do more testing when I have more time to see if the percentage of charge actually goes up over time, but I'll need to solder the wires on or something.

This engine is also one I have not done much to. It still has the original steel displacer for example, so the general performance could be better.

[VincentG]

Not sure what you mean by "the desired rpm of the generator itself". Though I can certainly measure the open circuit voltage with varying heat input and RPM.

You pretty much got the idea already. "Ideally", the gearing would allow the peak power of the engine(under load) to coincide with the minimum necessary rpm of the generator(under load), which should be putting out roughly the voltage needed by the load. Tons of variables but that's the basic idea for the most efficiency.

There is an app called "Ampere" that allows you to roughly measure the charging rate of your phone. That would be a pretty simple way to do some testing as you mod the engine.

Eager to see more results. I've been developing a small low rpm permanent magnet generator after being disappointed by the efficiency levels of available units. I think a modified version of your engine will charge a phone effectively.

[Tom Booth]

....

There is an app called "Ampere" that allows you to roughly measure the charging rate of your phone. That would be a pretty simple way to do some testing as you mod the engine.

That's fantastic!

Already downloaded it on this phone to check it out

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I'm trying out a few similar apps while I'm at it.

I found one so far that records the rate of charge both with the screen on and the screen off, which might be useful.

Eager to see more results. I've been developing a small low rpm permanent magnet generator after being disappointed by the efficiency levels of available units. I think a modified version of your engine will charge a phone effectively.

Well, this should speed things up a bit and take a lot of the guesswork out of things. Thanks!

Don't have to wait for hours now to see if the charge % goes up or calculate what that might mean,just read the charge rate (or discharge rate) and compare it to that of a wall charger almost instantly.

Fantastic!

Now I just have to see if I can get it installed on that other phone.

[VincentG]

Keep in mind they say its not accurate down to the mA but it's good for comparison and a rough estimate.

[Tom Booth]

Keep in mind they say its not accurate down to the mA but it's good for comparison and a rough estimate.

https://youtu.be/X825itoQn_I?si=WX2p7KPOk-okv9js


The setup is certainly less than ideal. Endless loose connections. I'm using an old charging cord that was put in a "junk drawer" years ago because it had a short or something. There was a long segment I cut out of the video because right as I plugged in the engine charger the wires came loose and I'm just trying to get them reconnected for several minutes, but I think in the end I finally got a steady charge and a good reading from the Stirling engine.

[VincentG]

That seems too good to be true lol! What is the rated output of that wall charger? Maybe you have a 2 amp fast charger to try as well?

Even though the little dc generator is not efficient, there's no loss from a rectifier or charge controller like other setups use so the overall efficiency is higher than other efforts online. It could probably benefit even more from a capacitor to smooth the output ripple.

[VincentG]

I have to suggest putting an ice cube on the cold side to see the power change. Pretty cool how fast it reacted to the torch. I bet it will pick up even more from just the ice and the candle. But then again, there's a reason I don't bet!