The making of the BLF UC4 charger: the start of a new venture, INTEREST LIST, UPDATE 7 (Well, ramping stopped :/ )

Hi! I would be interested in one, please.

I am absolutely interested.

I read extensively about proper care of batteries when I was doing a lot of RC stuff since the packs can get very expensive. I don’t have much experience with NiCd cells and I’m not sure about charging currents for them.

The voltage drop when a cell is full is much smaller with a NiMH than a NiCd and charging at very low currents makes it even smaller. Smart -dV/dT chargers use noise filtering to detect the ~5mV drop and if the current is too low, the drop might just get filtered as noise and miss termination.

Extrapolating from this, the best charge current to use for cell longevity would be the lowest current that the charger can still reliably detect a -dV/dT drop. You can charge most NiMH cells safely at 1C but they will get hotter and the overall lifespan of the cells will be reduced.

Here’s a couple resources I found with a quick search:

“It is difficult, if not impossible, to slow charge a NiMH battery. At a C rate of 0.1C to 0.3C, the voltage and temperature profiles do not exhibit defined characteristics to trigger full-charge detection, and the charger must depend on a timer. Harmful overcharge can occur when charging partially or fully charged batteries, even if the battery remains cold.”

NiMH battery slow charging is not to be recommended. Using charge rates of between 0.1 and 0.25C do not provide the indicators needed to detect the end of charge. With voltage changes of only about 5mV at full charge rates, the smaller changes arising for a slow charge are virtually impossible to detect.

Cool thanks. This is good stuff:

Some advanced chargers apply an initial fast charge of 1C. When reaching a certain voltage threshold, a rest of a few minutes is added, allowing the battery to cool down. The charge continues at a lower current and then applies further current reductions as the charge progresses. This scheme continues until the battery is fully charged. Known as the “step-differential charge,” this method works well for all nickel-based batteries.

Interested

Please add me to the list for two units, please.

I totally agree that there should be an easy way to upgrade the firmware using some SPI flasher or TTL serial connector.

If this charger is going to support 21700 and/or 26650 cells then a >3A charge rate would be useful.

So after Rayoui’s informative post, and some more research, I will be charging my cells like this from now on:

0.2 (for recovering an 18650 below 2.5v)
0.7 (for AAA NiMh/NiCd batteries, 14500 li-ion, or recovering a “heater” 18650)
1.0 (for gentle charging 18650, or capacity testing any li-ion)
2.0 (for quality 18650, AA NiMh/NiCd batteries, 21700, or 26650)

Hopefully this is useful to others.

Hi, I’m interested in one, thank you for this project.

I have some suggestions, some sounds probably very niche but it costs nothing to say them :

- Support for LTO , (min 1.8~2V, max 2.6~3V), I imagine it’s just a firmware thing.

- Support for any chemistry (setting any charge voltage allowed by the charging circuit), for futur proofing, if support is dropped at some point for example, or for charging already existing exotic stuff (like LTO, if a setting for it is not added, or even a super capacitor for example, but would need to be able to charge at set current from 0V), may require a more advanced UI though.

- Adding the option to never stop the charge, i.e. floating the cells.

- Ability to easily connect leads for charging any format outside of the charger slots (big cylindrical, wired, non opposite terminal cylindrical etc…), it’s usually easy for the sliding negative contacts with an alligator clip, but not for the positive one against the body, could be with the help of threaded holes, similarly to this charger for example, or by having contacts going higher than the body or rather just having the body go a little lower behind the terminals, or another idea…

- About the fan, the bigger the better, I saw some discussions about it but I’m not sure if it has been decided or not, bigger is better for cooling and noise, it would be great if it was a standard sized PC fan (80,92, 120mm… etc) considering that probably a lot of us have some lying around if original fan fails, and if not there is a huge offering of inexpensive decent PC fans to choose from, also allowing to replace the original fan with a higher quality one. But the voltage of the original fan can be an issue, if it’s 5V then some 12V PC fan might be too slow, at ~7V or above is generally fine depending on the model, if the original is 12V then it can be replaced by a either a low rpm 12V fan, or simply using a resistor on a faster 12V one.
Case in point, I replaced a 35mm noisy 5V fan with a 80mm on a charger and the whole process was annoying, aside from the charger body modification, all 80mm 5V fan that I found were way too fast at 5V, and could not be undervolted without stalling. I ended up adding a small boost converter to step up the voltage to 7.5V and used a standard 12V PC fan.

thanks for reading.

Interested for 1 please

1. This one could be easily implemented.

2. Technically, it’s already been implemented, but only between 3,4V-4,40V. It could be extended to 0-4,50V, but a physical switch connected should be the only way to access this more advanced, and dangerous, mode.

3. That would be great, but this feature will not be included for cost and ease of assembly. However, external leads could be provided, if the user wants to pay for it.

4. In the current design, an 80/92mm fan can be used. I’d prefer going to 92mm, as it would make it very easy to replace it. 120mm would be very large, and would lower static pressure.

2. I think the UI should feel more like a power supply. Set your max voltage, max amps, and termination type.

3. I bet he would be happy with solder-pads on the PCB.

@JoshK

2. Yes of course regarding current(up to 3A) and termination type, but even theoritically, charging voltage will be limited to 4,8V, due to the individual buck converters used needed some room to work.

3. Excellent idea! I’ll actually forward the idea to DLYFull, so we could actually include a special solder pad for the 4th charging slot, and allow charging/discharging for other types of cells.
This is an exception I’m willing to make, probably the only one, but I doubt DLYFull would be keen on that, rather than making custom leads, as it would be easier.

I would also like the ability to attach external leads. Best would be something like the Olight UC Magnetic USB Charger

You could sell it as an add on.

@paetzi, yes, that’s what the pads will be waiting for. Someone will write a how-to, and you will just need to drill a small hole in the case and connect your wires to the solder pads.

1) great.

2) hidden switch for advanced voltages sounds good.

3)

Understandable. About solder pads : ultimately wires can just be soldered where the contacts are soldered in the charger, dedicated solder pads don’t really add anything.

4) 92mm fan sounds great.

Something else, about the UI :

5) Could there be a way to configure several slot at once like on some chargers, for example the zanflare C4 : before 9s have passed since 1st cell inserted, the first button press enable configuration for all cells inserted. (not saying it should be this way, and in this case 9s is actually a bit to short to insert 4 cells)

The solder connection to the battery contactor is dual purpose, it is both an electrical and mechanical connection. If someone were to try soldering a wire to the board at that point, the contact would fall over when the solder became liquid. Maybe that’s no big deal for someone with solder skills and a quality iron, but that’s not everyone.

Interested in two of these.

Dedicated solder pads to anode and cathode battery rail connectors add some value and they are really very easy to set or put, all it takes is a couple spots where the solder mask is removed or unlaid, and maybe positive and negative (+, −) signs. The impact on the charger's cost is absolutely negligible, virtually nothing.

I see the default charging currents' list was modified, plus an additional 2.5 A value was added. Since my list was written with decimals using point/period as separator (learned back in the days of writing computer programs), but the 2.5 A value was added with comma, it looks weird/wrong. I will refrain from judging the new value addition and how it fits in between, but in any case here is the list (whole point 1) fixed with commas (as BlueSwordM did at first):

1. Adjustable charging current: (0,03A – 0,05A – 0,08A – 0,12A – 0,18A – 0,25A – 0,35A – 0,50A – 0,70A – 1,00A – 1,40A – 2,00A – 2,50A – 3,00A).