I recently received a “TOP 5A CC CV LED Drive Lithium charger Power Step-down Module W/ USB Voltmeter” which I purchased for shy of $7 from ebay seller alice1101983 who operates the TxHang Electronic store on eBay. My order was shipped from Shenzen China promptly, and arrived via international post in just over a week.
I wasn’t sure exactly what to expect.
Specifications
From the listing I knew it was a switch mode DC-DC power supply built around a buck converter. Also:
- 5-36VDC input range
- 1.25-32VDC output range, adjustable
- 0-5A output current, also adjustable, with output short protection
- Max output of 75W with thermal shutdown
- Up to 96% efficiency
- A display that can be switched between showing: input voltage; output voltage, current and power.
The listing also included detailed application notes for use as a step-down, current limited power supply, a constant-current LED driver, and battery charger.
Review
I purchased the device because the adjustable constant voltage and constant current features, and the way it transitioned between the two were enough to make it useful to do supervised, one-off charging of lithium ion battery packs that had multiple cells per series, something I needed to further investigate getting data from old laptop battery packs.
The device has three LEDs to facilitate use as a battery charger. The LEDs indicate whether it is voltage or current limited, whether it is “charging” or whether the battery is full.
I knew that it determined that the battery was full the way most lithium chargers do, by monitoring the current during the constant voltage phase and noting when it dropped to 1/10th of what it was during constant current phase. Real chargers stop charging at this point. It wasn’t clear whether this one did, or whether it just lit the light.
I can now report that this isn’t suitable for unsupervised charging of lithium ion batteries, because it doesn’t terminate the current once it determines the battery is full. This is bad for the health and safety of lithium ion batteries.
I’ve noticed another quirk as well. If the output of the device is connected to a battery and the power is removed from the input, the display, and voltmeter end up being powered by the battery, which seems to me to be less than ideal.
There are also issues with the USB output connector on the board. First, it appears that while there are resistor pads for indicating available, output current to USB devices, they are all unpopulated. Second, and more concerning, the USB output voltage isn’t fixed at 5V, but instead varies with the output voltage setting. As a result, there is a very real possibility of frying a USB device if one doesn’t know about this quirk, or you do, but don’t remember to adjust the output voltage. I’ll probably fill in the socket with hot glue, or desolder it and remove it from the board all together.
Conclusion
Good
- Inexpensive
- Quick shipping
- Constant Voltage and Constant Current options
- Built in volt and amp meter
- Useful for supervised one-off battery charging
Bad
- Doesn’t automatically terminate battery charging. Dangerous for un-supervised charging.
- No safeguards against non-standard voltage on USB port.
- Drains battery when power input is removed.
All in all, not a bad module to have on hand, if you know its limitations.
Teardown
A brief look at some of the key components on this module
Buck Converter IC
The heart of this module is an XLSemi XL4015, which is described as a 5A 180KHz 36V Buck DC to DC Converter. It is marked “XLSEMI, XL4015EI, 4032R.”
One thing stands out immediately when I look at the english language datasheet:
Wide 8V to 36V Input Voltage Range
I’m not sure what to make of the fact that the seller claims that this device has a 5-36V input voltage range. Its possible that the input has enough resistance to cause a 3V drop, but that seems rather unlikely. It may also be that the datasheet is out of date. More likely though, I think someone along the way either made a mistake in drafting or copying the spec for the module, or the converter is intentionally being used outside of its specification.
Speaking of intentionally using the IC out-of-spec, Julian Ilett reviewed a similar module using a different XLSemi buck converter IC, the XL4005, and noted that when he set the output voltage to 0, it no longer limited current properly. Not entirely surprising, since that IC has a minimum output voltage of 0.8v. I haven’t tried the same test with this module, but I suspect that it will also allow you to set the output voltage below spec, and that similar behavior will result.
Bottom line is: Check the specs! Don’t count on the designers of these modules to put in safeguards.
More Information
Thanks for the review: not getting much input on YouTube; probably because the chip has not been identified til now.
(devices generally searched on YouTube by main chip)
there is an identical board less the meter and that useless USB,
on Ebay “Alice” has both.
The question I have with this board; is the output regulated.
If I’m running off a battery (which drops in voltage), will my LED
lights on the output side have constant voltage, or will they sag with the battery ?
Sorry not to reply sooner. If the battery voltage drops, the output voltage should remain constant, provided that certain operating conditions are met: The battery voltage must be at least 8v, and at least 0.3v above the output voltage, and the battery must be able to deliver enough current to supply the power demands of the LED load + the conversion inefficiency of the converter.
Thanks for the response;
The system here is 24v LED lighting, running on paired 12v batteries; which top out at 28.2 volts charged and can sag to as low as 23 volts. But with solar panel trickle charging I suspect that the norm is above 24 volts all the time. So I guess what you are saying is that below 24.3 volts one will notice the lights start to dim.
……and I suppose that is a good thing, considering it is the bottom 25% of the charge cycle and the solar panels will probably keep the batteries above that.
I was really hoping to use one of these on a solar test panel charging a series of 18650’s. Could you figure out why it kept applying current? Been watching a few videos myself and from what i seen the first pot’ voltage which you need to treat it as float voltage cutoff so set it below the actual max voltage and from there it will curve the current down untill its fully charged. “that’s what it should do. I’m not exactly sure but dose this display amps aswell?
Right button selects display of input voltage, output voltage, output current, output power or auto-cycle between all.
Left button toggles display on/off
Hi there,
I appreciate your review. The problem I’m having is that the board’s output terminals have now become shorted.
Until recently, was using it to charge a 3s Li-ion pack with input supplied from a 36v LifePo4 with no problems and am curious what caused it to fail. Do you think increasing the voltage to 42v (fully charged LifePo4) could have caused the damage?
Do you have a circuit diagram of this board? Do you know what failed component could be causing the short?
Oh, and one more point worth mention… this module also has a feature to adjust the input voltage readout by holding down the right button while the display is set on input. Would this function have any value in controlling max input voltage?
Many thanks!
I bought 2 of this module and for me it looks like crap already.
I wanted a 5 volt in and 3.3 volt out.
That works fine but don’t try to fix the correct display precision.
Put 5 volt in: display in is 7.2 and can not be set to 5 volt in.
When you try to step down (with left button in the input voltage calibration mode), it steps from 6.2 to 8.2!
The same is with the output mode. It’s not possible to adjust to the right value.
Ibought one module and it work fine about 40 min than the display work no more !
probably lm317 overheats and shuts down. it regulates 5v for meter circuit from input and gets pretty hot if input is over 30V
“it doesn’t terminate the current once it determines the battery is full.”
— But the Voltage trimmer lets you set the “full” voltage. Are you saying this charger will overcharge the battery to a higher voltage than the “full” voltage you set?