A good price on the DL24MP load and a quick review

AliExpress is having a sale right now, and I spotted a good price on the DL24MP load. People often ask me about it, but I haven't reviewed it yet, so I decided to kill two birds with one stone: share the good price, give it a quick review, and compare it with the DL24EW along the way.

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The current price is $25.87, which is genuinely pretty good. Coupons can bring it down even further, and Atorch's page has discounts too, though it costs about a dollar more there.

As I said, I haven't reviewed this version. When it came out, I had other things to worry about. And since I don't have the time or energy for a full review, I decided to at least give you a quick rundown. To get ahead of myself, this is my favorite version of the load, although it has its share of issues too, which I'll talk about as well.
As for a full review, I'll say this: there's simply no point, because 90% of it is the same as the DL24EW, which I've already reviewed. The 24EW has two key differences: charge control, and the fact that the display is mounted on the main board (along with the controller). The rest are mostly cosmetic changes. The 24EW also has WiFi and USB but no Bluetooth, while the 24MP has Bluetooth and nothing else.


I took these photos when another order arrived. Since I order them in pairs at a minimum, I'll show them together.


The load and the module come already connected, so you can basically just plug it in and use it.


By the way, there are two versions of the connection: one has colored wires like the one in the photo, and the other has a white ribbon cable. Sellers ship them at random, so if you get the colored wires, consider yourself lucky. The ribbon cable is problematic: you have to handle it very carefully, or it's easy to end up with a bad connection and glitches. At least the previous 24M had this problem quite often.


The menu is fairly simple, at least compared with the 24EW, but it has all the essentials—and then some. One important difference from the old DL24 is that calibration has been removed from this menu, so you can't accidentally mess it up.
It uses four buttons, but you can also connect an encoder. There's a catch with the encoder: on the 24M and 24MP it works perfectly, even though it isn't installed by default. On the 24EW, which comes with one, it acts up—when you turn it quickly, it can skip steps.


The power board contains only the power stage itself and the analog section; the controller is in the display housing. That's why a poor connection in the ribbon cable can cause problems setting the current.


Here's the analog section. In my 24EW review, I wrote that CV mode was implemented in software. That was a mistake: on the 24MP and 24EW, it's implemented in hardware and works quite well. The board has two op-amps and a switch that selects between them depending on the operating mode. CR and CP modes are software-controlled, of course; nobody bothered to implement those in hardware, and making CP mode work in hardware isn't all that simple anyway.

On both loads, the temperature sensor now measures the temperature of the air coming out of the heatsink, rather than the temperature of the board near the transistor. As a result, it shows complete nonsense, and with an absurdly long response time to boot. I once wrote about seeing someone brag about the low temperature of... something. Not sure what.


As on the 24EW, the power stage balances the load current between the transistors, measured across four resistors. As you can see, the resistors have different values. The manufacturer says this is intentional, to keep the current equal. In simple terms, we couldn't route the board properly, so some resistors ended up with longer traces and others with shorter ones. We compensated by changing the resistor values.



There are four MOSFETs on the underside, just like on the 24EW.


The transistors are all the same type, but have different markings and even different packages. After assembling electronic loads, I've ended up with quite a menagerie of them....
Since these transistors aren't designed for linear operation, I don't recommend applying high voltage and maximum power. It's better to keep the power below 100 W when the voltage is above 50–60 V.


I took it apart not for this article, but to modify the boards for assembling loads.


There's an important detail about the heatsinks: the ones on the 24EW are almost twice as tall, and therefore noticeably more effective. The 24MP and the additional power modules have low-profile heatsinks, so I strongly recommend replacing them. The heatsink dimensions are 40 × 40 mm.


There's no point in replacing the thermal paste (unless you're replacing the heatsinks); it's usually fine.


By the way, once you remove the thermal paste, you can see that the transistors also differ on the back: some are matte, others glossy.


For my further modifications, I desolder them altogether, along with the protection diode, shunts, and a bunch of other unnecessary parts.


By the way, there's also a bad change. It appeared fairly recently: a third 2 mΩ resistor was added to the board.
Originally, a pair of 2 mΩ resistors serve as a current-sense shunt. I replace them with resistors of the same resistance and size, but with a higher power rating. But there's now a third resistor, which means the load is essentially three-wire, since this resistor connects the current negative and voltage negative. I suspect the measurement inputs were often getting burned out, so the manufacturer essentially connected their negative terminals together.
I recommend increasing the value of this resistor by at least a factor of 100.


Interestingly, this resistor has also appeared in a new revision of the DL24EW. So far, I know of three versions:
1. The original, from my review.
2. The same hardware, but with an option to set the current at which charging stops. This was added specifically in response to my comment.
3. The same firmware as version 2, but with hardware changes: the resistor shown above has been added, and the linear regulator has been replaced with a switching regulator.


It turns out the displays differ slightly too, though fortunately only in appearance. By the way, if you need to remove the display, as I do, be extremely careful. I ended up buying a few spares just in case, because it's very easy to damage.
Also, on the older version, the ribbon cable was additionally secured with acetate tape; the new version doesn't have it.



Next, I modify the control board, cut off the excess, add my own power modules, and end up with an electronic load. But as they say, that's a whole other story.


That's about it—at least everything I can think of off the top of my head. So if you have any questions about this topic, ask away.
In my personal opinion (I've worked on almost all of Atorch's loads), the 24MP offers the best balance of price, quality, and features, so that's the one I recommend buying. Choose the 24EW only if you definitely need charging.