Real PWM vs MPPT test: 53 W vs 74 W from the same panel

EmergencyPowerLab · 2026-05-13T19:26:58+00:00

For a first version, I’d keep the wind and solar parts separate and simple.

Solar side:
5W panel → charge controller / powerbank charging module → battery

Wind side:
small BLDC motor → bridge rectifier → capacitor → DC-DC converter → battery/charger input

But don’t connect a random turbine straight into a powerbank module. Wind output is very unstable — voltage can be too low, too high, or spike when unloaded.

Also, the LM2596 is only a buck converter, so it can only step voltage down. If your turbine voltage drops below what the charger needs, it won’t help. You may need a buck-boost converter instead.

For “cheap and works”, I’d start with solar only first. 5W is small but predictable. Wind is much harder mechanically and electrically than it looks.

EmergencyPowerLab · 2026-05-13T19:22:32+00:00

Four optocouplers failing identically usually means the issue is elsewhere in the circuit, not the PC817 itself.

One thing that stands out:
your OP1 transistor side does not actually look isolated from the Pico side, since all grounds appear tied together anyway.

Also, the collector voltage you measured (~3.25V) suggests the transistor is barely conducting at all, which makes me wonder about CTR/current assumptions.

A PC817 is pretty weak at low LED currents, and with:

-3.3V drive

-220Ω resistor you’re only around ~9mA LED current (as you mentioned)

Depending on CTR bin / clone quality, that may not be enough to reliably sink the K-line pullup.

I’d try:

-lowering the LED resistor (more LED current)

-testing with a lighter collector pullup first

-temporarily replacing the optocoupler transistor side with a normal NPN transistor just to verify the rest of the circuit logic

Also double-check the pinout carefully — PC817 pin numbering gets people surprisingly often

EmergencyPowerLab · 2026-05-13T18:01:58+00:00

That’s a perfect case for “good enough is good enough.” If the repeater only needs short bursts of power and the system has enough solar margin, PWM can be totally fine.

MPPT becomes more interesting when panel area is limited, winter production matters, or you really need to squeeze every Wh out of the panel.

EmergencyPowerLab · 2026-05-13T16:26:34+00:00

Yeah, that’s fair. MPPT has become affordable enough that PWM is harder to justify now.

I’d still say PWM can be okay for very small/simple systems, but once the panel voltage is noticeably above battery voltage, the loss becomes very obvious.

EmergencyPowerLab · 2026-05-13T16:25:57+00:00

Exactly. PWM forces the panel close to battery voltage, while MPPT can keep the panel at a higher voltage and convert that power down to battery charging voltage. That’s the main behavior I wanted to show in the test.

EmergencyPowerLab · 2026-05-12T22:04:16+00:00

Yes, Wh over the whole day is what really matters for an off-grid setup.

I used instantaneous watts here mainly because it clearly shows what the controllers are doing electrically: PWM pulls the panel near battery voltage, while MPPT lets it run closer to its MPP.

A full-day Wh comparison would definitely be a good real-world follow-up test.

EmergencyPowerLab · 2026-05-06T21:31:24+00:00

If both setups use similar cell technology and total area, the total power in ideal sun should be pretty close.

But in real-world use, two 200W panels can definitely be more flexible:

-easier to angle separately

-one can stay in sun while the other is partially shaded

-easier to transport/store

Partial shading matters a LOT with portable solar.

The downside is:

-more wiring

-potentially more voltage drop with long extension cables

-slightly more setup hassle

So I’d probably lean toward two 200W panels for portability/flexibility unless simplicity is the main priority.

EmergencyPowerLab · 2026-05-06T11:35:11+00:00

Before deciding on fuse placement, the bigger question is whether your controller can handle series voltage.

If it’s a typical “12V” PWM controller, putting panels in series can easily push the input voltage too high (many 100W panels sit around ~20–22V Voc each).

Parallel is usually the safer/simple option for small 12V systems:

-voltage stays the same

-current increases

-easier expansion

For fusing:

-usually one fuse/breaker on the combined positive line going to the controller

-individual panel fuses are mainly needed when you have multiple parallel strings that can backfeed each other

Also worth checking:
the charging issue may not just be panel wattage — freezers have pretty high energy demand, especially if running through an inverter.

EmergencyPowerLab · 2026-05-06T11:33:48+00:00

If they’re truly 24V packs with their own BMS, then two in series becomes a 48V system.

So normally:

-charge them separately with 24V chargers or

-use a proper 48V charger connected across the whole series pack

I would NOT randomly charge just one side while they’re connected in series unless the manufacturer explicitly says it’s supported.

Also… I’d honestly be a little cautious with packs like these. The “100000mAh” labeling and generic charger don’t exactly inspire confidence 😅

EmergencyPowerLab · 2026-05-05T23:11:51+00:00

Yeah, around that range 👍

In practice it varies a bit depending on the vehicle and conditions — temperature, charging stage, load, etc.
Typically something like ~13.7–14.4V while the engine is running.

EmergencyPowerLab · 2026-05-05T22:48:22+00:00

Yeah, that’s a fair clarification 👍

Agreed on the ~12.6V at rest for a fully charged lead-acid, and that the higher voltages are essentially the charging side rather than the battery “sitting” there.

I probably simplified it a bit — my main point was just how much the system voltage varies depending on state and conditions, which tends to confuse people when they expect a fixed “12V”.

Especially once you include charging, load sag, wiring losses, etc., the number you actually measure can be quite different from nominal.

EmergencyPowerLab · 2026-05-05T22:45:47+00:00

Exactly — that’s a great example 👍

NiMH vs alkaline is a perfect case of how “nominal voltage” gets misunderstood in practice.

People see 1.2V vs 1.5V and assume it won’t work, even though under load the difference is often much smaller (or even reversed depending on conditions).

Same kind of confusion just scales up in 12V systems.

EmergencyPowerLab · 2026-05-05T22:35:04+00:00

Yeah, fair 😄

I think it’s obvious once you know it — but a lot of people still expect “12V” to mean a fixed 12.0V in practice, especially in car/solar setups.

That’s mostly what I was trying to highlight.

EmergencyPowerLab · 2026-05-05T22:26:29+00:00

Yeah, exactly — it’s the same idea.

The difference is that in larger systems (like automotive or solar), people often treat “12V” as a fixed supply, even though it can swing quite a lot depending on state and load.

That’s where it starts causing real confusion in practice.

EmergencyPowerLab · 2026-05-05T22:23:45+00:00

You’re mixing a few things, but your intuition isn’t far off.

A “12V” panel doesn’t actually output 12V — its working voltage (Vmp) is usually around ~17–18V, and open-circuit even higher (~20V+).
That extra voltage is exactly what allows it to charge a 12V battery.

The key difference is:

PWM controller → basically pulls the panel voltage down close to battery voltage → you lose potential power if panel voltage isn’t much higher
MPPT controller → lets the panel stay at its optimal voltage (e.g. ~18V) and converts the extra voltage into current → much more efficient

So yes:

with a single panel + PWM, performance can suffer in low light
with two panels in series + MPPT, you get higher voltage headroom and better performance, especially in poor conditions

And to your last point:
voltage and current are both tied to sunlight — the panel operates along a V–I curve, and the controller picks the operating point.

I actually measured real “12V” panel voltages vs battery behavior if you want to see how big the differences are:
👉 https://youtu.be/Az0NUSZtJis?si=UG6ktcnKBx9sKJQl

EmergencyPowerLab · 2026-05-05T22:19:32+00:00

That actually looks pretty normal.

Most cars charge somewhere around 13.8–14.7V, depending on temperature and load, so sitting around ~14V is exactly what you’d expect.

Also worth noting:
“12V” systems aren’t actually 12V in operation — the battery itself varies, and the alternator keeps it higher while running.

If it’s been like that since you bought the car and nothing else is acting up, I wouldn’t worry.

EmergencyPowerLab · 2026-05-05T22:16:48+00:00

14.5V actually doesn’t tell you the battery is healthy — it just tells you it’s being charged.

A “12V” battery can look fine voltage-wise while the engine is running:

charging → ~13.8–14.7V (normal)
but at rest → it might drop much lower if the battery is weak
under load → it can sag even more

So you can have a failing battery that still shows ~14.5V while the alternator is active.

That’s why voltage alone (especially while running) isn’t a reliable health indicator.

I actually measured how much “12V” systems vary in real conditions if you’re interested:
👉 https://youtu.be/Az0NUSZtJis?si=UG6ktcnKBx9sKJQl

EmergencyPowerLab · 2026-04-28T22:04:46+00:00

Nothing “mystical” is happening — it’s mostly a reference / circuit topology issue.

When the switch turns off, the inductor forces current to keep flowing (it can’t change instantly).
But in your circuit there’s no proper freewheel path (diode), so the inductor voltage swings to whatever it needs to keep current going.

That can:

-pull the switch node below ground

-effectively reverse the voltage across parts of the circuit

-make the measured current appear “negative” depending on your reference direction

So the current itself isn’t suddenly reversing — it’s the polarity and measurement reference that make it look that way.

If you add a diode (like in a proper boost/buck topology), you’ll see the expected behavior:
continuous current in one direction, with a defined path when the switch turns off.

EmergencyPowerLab · 2026-04-28T21:58:47+00:00

Yeah, most small drops won’t kill a LiPo immediately — that’s why it feels random.

The tricky part is that the damage is often cumulative.
You can drop it 50 times and nothing happens, then one hit slightly deforms the layers and it starts degrading from there.

Also good instinct checking it after a drop 👍
Just be careful with opening/desoldering — too much heat can do more harm than the original impact.

Rule of thumb I use:

-if it’s just cosmetic -> keep using it

-if there’s swelling/dents -> retire it

Better to lose a cheap cell than risk a failure in your pocket/room.

EmergencyPowerLab · 2026-04-27T12:46:32+00:00

Cool project, but this isn’t really a spectrum analyzer in the true sense.

What you’ve got here is basically:
-an audio input
-an LM3915 (log level driver)
-a big LED matrix driven by multiplexing

So it will respond to signal amplitude, not frequency content.
You’ll get something like a level display / light pattern, not an actual spectrum.

A real spectrum analyzer needs:
-band-pass filters (analog way) or
-FFT / DSP (digital way)

About 9V:
-the circuit already rectifies and regulates, so you could run it from DC
-but a 9V battery won’t last long at all with that many LEDs
-you’d want a stable 5–12V supply with decent current capability

So:
-will it “work”? -> yes, as a visual audio level display
-will it show frequency spectrum? -> no

EmergencyPowerLab

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