Posted on 3 Comments

Chinese “1200W” DC-DC Boost Converter DOA Fix

1200W DC-DC Converter
1200W DC-DC Converter

Ah the curse of the Chinese Electronics strikes again. These large DC-DC boost converters have become very common on the likes of AliExpress & eBay, and this time my order has arrived DOA… On applying power, the output LED lights up dimly, and no matter how I twiddle the adjustment pots, the output never rises above the input voltage.

Boost Converter Topology
Boost Converter Topology

From the usual topology above, we can assume that the switching converter isn’t working, so the input voltage is just being directly fed through to the output. The switching IC on these converters is a TL494,

Control Circuitry
Control Circuitry

The switching IC on these converters is a TL494,with it’s surrounding support components, including a LM358 dual Op-Amp. Power for this lot is supplied from the input via a small DC-DC converter controlled by an XL Semi XL7001 Buck Converter IC. Some testing revealed that power was getting to the XL7001, but the output to the switching controller was at zero volts.

Inductor
Inductor

The 100µH inductor for this buck converter is hidden behind the output electrolytic, and a quick prod with a multimeter revealed this inductor to be open circuit. That would certainly explain the no-output situation. Luckily I had an old converter that was burned out. (Don’t try to pull anything near their manufacturer “rating” from these units – it’s utter lies, more about this below).

Donor Converter
Donor Converter

The good inductor from this donor unit has been desoldered here, it’s supposed to be L2. This one had a heatsink siliconed to the top of the TL494 PWM IC, presumably for cooling, so this was peeled off to give some access.
After this inductor was grafted into place on the dead converter, everything sprang to life as normal. I fail to see how this issue wouldn’t have been caught during manufacture, but they’re probably not even testing them before shipping to the distributor.
The sensational ratings are also utter crap – they quote 1.2kW max power, which at 12v input would be 100A. Their max input rating is given as 20A, so 240W max input power. Pulling this level of power from such a cheaply designed converter isn’t going to be reliably possible, the input terminals aren’t even rated to anywhere near 20A, so these would be the first to melt, swiftly followed by everything else. Some of these units come with a fan fitted from the factory, but these are as cheaply made as possible, with bearings made of cheese. As a result they seize solid within a couple of days of use.
Proper converters from companies like TDK-Lambda or muRata rated for these power levels are huge, with BOLTS for terminals, but they’re considerably more expensive. These Chinese units are handy though, as long as they are run at a power level that’s realistic.

Posted on Leave a comment

De La Rue Coin Counting Machine Followup – PSU Oddness

I did a little more digging into the PSU circuitry of the small coin counting machine, and it’s even more strange than I thought!
The part I originally thought was a transformer on the PSU board is in fact a DC-DC converter module!

DC-DC Converter
DC-DC Converter

Here’s the device after desoldering it from the PCB. It turns out that instead of a transformer, it’s an inductor.

Hiding Control Electronics
Hiding Control Electronics

Underneath is the controller electronics, with an COB controller & the switching transistors are under a protective covering of silicone.

Mains Transformer
Mains Transformer

Driving this whole lot of PSU randomness is the mains transformer, with a secondary voltage of 35v.

The only reason I can think of that the manufacturer went to this much expense with the power supply is stability – a coin counting machine that miscounts due to power supply surges, sags & spikes wouldn’t be very much use. It’s not likely I’ll see anything similar again, unless I manage to get hold of something like medical grade equipment.

Posted on Leave a comment

Totally Wicked Forza / JoyeTech eVIC 60W Teardown

Display
Display

I’ve been a vaper now for many years, after giving up the evil weed that is tobacco. Here’s my latest acquisition in the vaping world, the JoyeTech eVIC 60W. This one is branded by Totally Wicked as the Forza VT60.

18650 Cell
18650 Cell

Powered by a single 18650 Li-Ion cell, this one is a Sony VTC4 series, 2100mAh.

Under the battery a pair of screws hold the electronics in the main cast alloy casing.

OLED Display
OLED Display

After removing the screws, the entire internal assembly comes out of the case, here’s the top of the PCB with the large OLED display in the centre.

USB Jack
USB Jack

On the right side of the board is the USB jack for charging & firmware updates. The adjustment buttons are also at this end.

Output
Output

On the left side of the board is the main output connector & the fire button. Unlike many eCigs I’ve torn down before, the wiring in this one is very beefy – it has to be to handle the high currents used with some atomizers – up to 10A.

PCB Reverse
PCB Reverse

Removing the board from the battery holder shows the main power circuitry & MCU. The aluminium heatsink is thermally bonded to the switching MOSFETs, a pair under each end. The switching inductor is under the gap in the centre of the heatsink.

DC-DC Converter
DC-DC Converter

A close up of the heatsink shows the very slim inductor under the heatsink.

Microcontroller
Microcontroller

The main MCU in this unit has a very strange part number, which I’ve been unable to find information on, but it’s probably 8081 based.