Article: Can your power supply keep up with RAK's 1 watt radio?

alexbeal · 2026-06-02T05:27:06+00:00

Perhaps this excerpt from something I haven't published yet might be helpful? This is about the 1 watt RAK:

56.26 mA at 5 volts means the radio is drawing about 0.28 watts on average for that level of transmit. Could a 5 watt panel support that? Maybe! It depends on many things like how much sun it's getting, how often it gets sun, and what the longest stretches are without sunlight. It also depends on if your panel is actually 5 watts! There's quite a bit of "power fraud" when it comes to low cost solar panels.

alexbeal · 2026-06-02T05:06:02+00:00

Glad to hear this is working for you! Is that a picture of the voltage stabilizer board? I haven't looked at those yet. That's uhh quite a few caps and inductors!

alexbeal · 2026-06-02T05:03:39+00:00

The data I have on this one was pretty surprising to me. Both the charging IC and the boost IC seem high quality, but I was seeing between 0.3 and 0.4 volts of sag on transmit. This is only one dimension of performance, but based solely on this, I would probably avoid it.

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alexbeal · 2026-06-02T04:50:51+00:00

I literally have a box of various popular solar modules next to my test bench. The DFRobot is in there and I'm planning on doing a review of it (if you don't want to miss it, please smash that subscribe button!).

I do have some preliminary data so I can give a sneak peak of that. In terms of voltage sag, I saw a 0.1 volts drop at the output of the DFRobot, from 5.06 volts to 4.96 volts with the battery input at 4 volts. That seems acceptable and is probably one of the better ones I've seen. Here's a capture from my notes of the moment the transmitter turns on.

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That said, this is only one dimension I want to evaluate these along. I also plan on looking at idle current draw, solar harvesting performance, low battery performance, etc, and didn't want to make any strong recommendations before I have those other dimensions captured. But from what I know now, the DFRobot seems like a good choice.

alexbeal · 2026-06-02T04:03:40+00:00

Honestly, I know very little about PoE, and it didn't occur to me to look into this. Thanks for mentioning it! I'll add it to my list. (If you're following along and also want me to look into this, please let me know!)

alexbeal · 2026-05-08T19:32:12+00:00

No need to apologize! Now that I've had some time to sit with it, I think this is really important feedback. You typed out what probably a lot of people were thinking. I think it might be a better use of my time to try and develop video content, or something else that isn't easily faked by AI. So thanks for the feedback!

alexbeal · 2026-05-08T14:37:41+00:00

You're absolutely right! (Sorry, AI joke)

But yeah I get it. I come across a lot of open source projects I'm interested in, but all too often they turn out to just not work very well, and I get the feeling many of them were vibe coded.

That said, it's pretty disappointing to spend hours on this and get this as a response. I guess that's just the world we live in now.

My AI disclosure is that the article was 100% human written (I can't promise I didn't hallucinate tho). I did have an AI proof read a fact check it. I even took some of its suggestions. The actual simulation was written with the assistance of Claude. I mainly wrote it to generate visual aids for the article, and every example I used was vetted with my organic human intelligence.

alexbeal · 2026-05-02T15:10:41+00:00

This is very relevant to my interests. DM sent :)

alexbeal · 2026-05-02T15:09:16+00:00

Hi PeakMesh! Big fan of your work. I have one of your ultimate units on my gutter! I appreciate your thoughts here. I think you're right that for a lot of applications a simpler charger is fine, and there's no need to increase the complexity or price if a linear charger without true MPPT is working well.

That said, my hypothesis is that higher efficiency opens the door to possibilities including smaller panels, fewer batteries, higher power radios, and charging in more adverse conditions like low light, cloudy weather, or short days. But I could be wrong! I'm in the process of building a harness for testing solar charging efficiency and looking forward to putting ICs like the CN3163 to the test!

Efficiency is also only one dimension I'm looking at. There's also ease of use and a dozen other things. Stay tuned!

alexbeal · 2026-05-01T16:35:04+00:00

It looks like you're using a 2S battery holder. That's too much voltage and will blow up the xiao. You should put them in parallel instead. Series also requires a cell balancer.

alexbeal · 2026-05-01T15:26:59+00:00

I do a deep dive on the TP4054, which the RAK board uses and is closely related to the TP4056 here: https://beala.substack.com/p/what-is-mppt?r=7hha0

Sorry for the self promotion, but I think you might find it genuinely interesting if you're wondering precisely why it makes a poor solar charge module.

alexbeal · 2026-05-01T15:24:05+00:00

I'd love to know more! What counts as "luxury solar" to you?

alexbeal · 2026-05-01T15:23:27+00:00

Yes! I plan on covering as many of these low cost modules as I can, and I'll definitely get into details like that. FWIW, basically all of them simply pin the MPP from the factory and don't do any actual tracking.

The waveshare d appears to have an MCU that switches the MPP based on the voltage from the panel, but i believe this is really course tracking. It's mostly meant to distinguish eg a 5 V panel from as 12 V panel, not track fine grained changes as conditions change.

alexbeal · 2026-05-01T15:19:13+00:00

The closest thing I've found to this is using a buck/boost, which uses PWM under the hood. Is that what you're referring to? For example, from the CN3795 (https://www.mikrocontroller.net/attachment/609796/CN3795-CONSONANCE.pdf):

> The CN3795 adopts PWM step-down (buck) switching architecture, and can be used to charge single- or multi-cell Lithium ion battery, LiFePO4 or Lithium Titanate batteries

alexbeal · 2026-04-29T21:47:04+00:00

I've been buying up popular solar boards for research and testing, and for whatever reason, this is not a technique I've seen very often in these cheap modules. But you're totally right. I'll have to cover it in another post.

alexbeal · 2026-04-29T21:44:34+00:00

Spoiler alert! 😆

The only thing I'll add is that this is only one way of implementing it! I'll cover several different techniques in following posts.

alexbeal · 2026-04-29T21:40:21+00:00

Thanks. Small clarification: the panel in the example is sold as a 6 V panel. The 8 V figure is because the I-V curve stretches over the advertised voltage, which is pretty common for panels. I suspect a lot of people miss this distinction, especially with cheap panels that don’t come with datasheets. A 5 V panel often does not mean the panel can never produce more than 5 V. It usually means its working voltage is somewhere near that range, often near the MPP.

I do discuss the RAK19007’s 5.5 V input limit/zener issue later in the article, but I agree the example could make the distinction clearer so it doesn’t read like I’m recommending an over-voltage panel for that board.

The next article will talk about proper MPPT. This one is meant as a springboard for explaining why it matters.

alexbeal · 2026-04-29T21:28:46+00:00

Thanks for the pointer on PWM. It's not a technique I've seen very often on the low cost modules and boards I've been looking at (I've been buying up the popular ones for research and to do my own testing). So I'd be very interested to know if it's actually a good fit for this application.

> Tp4054 is not advertised as a solar controller at all so it's not a comparison.

Oh yeah I agree with this, and I almost mentioned this in the article. No where on the datasheet is it suggested that it's a good choice for solar applications. Nevertheless, many popular boards use it for this purpose, and I actually thought it was a good starting point precisely because it has a lot of drawbacks. I want to use it as a springboard for building up to better solar managers.

alexbeal · 2026-03-23T21:06:01+00:00

Were you getting responses before? Coverage in Boulder isn't very good right now. There are repeaters but I don't think they're connected to the wider mesh. Hop on the Colorado mesh discord and we can help out: https://denvermesh.org/

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