[solved] USB 5V 1A LiPo battery charger with load sharing and protection

Hej,

I have 3.7V 5000mAh Li-Ion pouch cells with no built-in protection circuit.

I want to be able to charge them from USB also while the load is connected, without using a switch.

I gather that this is called "load sharing".

Are there affordable small charger PCBs around that have this feature and protect the battery from going under 3V (some write 2.7V or 2.4V but I don't know what is "right").

Many thanks!

Edith: I found these things here based on the TP4056 that suggest load sharing capability, but there's never a specification sheet.

There are two basic types of TP4065 boards available. The ones without and with protection circuitry. The image you posted has got the "protection parts" (two chips on the right). One is a voltage detector, and slightly larger one is the mosfet switch.

Google "TP4065 datasheet" to learn how the charging chip works.

An easier way is to buy a 5Ah powerbank. They have all the features you're asking for. Leo..

With load sharing, the USB V+ source automatically takes over powering the load circuit when it is plugged in, and the battery charging proceeds to completion independently. This is necessary to prevent continuous charging of the battery, which could lead to smoke and flames.

The module in your picture doesn't appear to have load sharing parts, and I haven't seen a module that has charging, protection, and load sharing. But load sharing requires just three parts - a P-channel mosfet, a Shottky diode, and a resistor.

Here are two links that tell you all about it. I think they use different charger ICs, but the principle is the same. You just have to be careful to orient the mosfet so the body diode is pointing the right way.

http://ww1.microchip.com/downloads/en/AppNotes/01149c.pdf

http://blog.zakkemble.net/a-lithium-battery-charger-with-load-sharing/

Wawa: There are two basic types of TP4065 boards available. The ones without and with protection circuitry. The image you posted has got the "protection parts" (two chips on the right). One is a voltage detector, and slightly larger one is the mosfet switch.

Google "TP4065 datasheet" to learn how the charging chip works.

Hej Wawa,

thanks, that helps a lot as I was not aware that some of these come with protective circuitry.

ShermanP: With load sharing, the USB V+ source automatically takes over powering the load circuit when it is plugged in, and the battery charging proceeds to completion independently. This is necessary to prevent continuous charging of the battery, which could lead to smoke and flames.

The module in your picture doesn't appear to have load sharing parts, and I haven't seen a module that has charging, protection, and load sharing. But load sharing requires just three parts - a P-channel mosfet, a Shottky diode, and a resistor.

Here are two links that tell you all about it. I think they use different charger ICs, but the principle is the same. You just have to be careful to orient the mosfet so the body diode is pointing the right way.

Hej ShermanP,

thanks, I was not aware that the part I found had no load sharing or "power-path".

So, in a nutshell, one has to solder one's on circuit, as I understand the Zak site. I, obviously wrongly, thought that - because there are so very may Li-Ion products out there these days that one can use while plugged in to charge - I could buy such a "charge-while-use" PCB off the shelf.

Lagom: Hej ShermanP,

thanks, I was not aware that the part I found had no load sharing or "power-path".

So, in a nutshell, one has to solder one's on circuit, as I understand the Zak site. I, obviously wrongly, thought that - because there are so very may Li-Ion products out there these days that one can use while plugged in to charge - I could buy such a "charge-while-use" PCB off the shelf.

I too would expect that such a module would be widely available, but apparently they are not. However, the Adafruit PowerBoost 1000C might work for you. It appears to include everything. But it's $20.

No reason why this kind I thing shouldn't be available from the East for a few bucks.

Thanks ShermanP,

yeah, true. I seached more with “load sharing” and “power path” and found a knock-off that seems to have received not many buyer complaints and does not have the unnecessary voltage boost function. It is also based on the “go-to IC” MCP73871.

Let’s see how that works once it arrives…

s-l300.jpg

ShermanP: No reason why this kind I thing shouldn't be available from the East for a few bucks.

But they are not, unless you can provide a link ?

So what do you think is the reason (or explanation) why they are not available for a few bucks ?

About $2.50 . . .

https://www.aliexpress.com/wholesale?SearchText=MCP73871

Thanks, dochawk. It’s hard to tell anything from the photos, but the description says it has load sharing. But I don’t see a USB port.

Those are cheap, too, :). I don't know if this one has a spot on the board, but there might be others.

I have some of these waiting to use, but I plan on charging from solar in the garden, and using serious power management, so I'll be using battery holders and pigtails, not usb.

Thanks,

I ordered the one in the above image, the type dochawk also mentioned; since they are said to be 1:1 derivatives of Adafruit's, one can solder the USB socket and JST connector on, if one wants Adafruit's plug'n'play functionality.

Have anyone tested this module already? I don’t see any component on the board that would look like a mosfet. I doubt this module provides proper load sharing, unless I’m missing something obvious.

Works just like Adafruit's. It's a copy, using the same MCP73871 IC. There ain't no MOSFET on Adafruit's board either. See the EAGLE schematic.

The load sharing circuit is built into the MCP73871 charger chip. The schematic of the chip shown in the datasheet shows the mosfet. So this looks like the real deal. Thanks for finding it, dochawk.

Are you sure you need all of this. I have a standard (set to 1A) TP4056 board connected to a ~2Ah LiPo, with and a ~60mA load permanently connected to it. The battery stops charging @4.2volt, and starts again at about 4volt.

I suppose there could be a problem when the load draws more than the final charge current. But is it in this case. Leo..

Leo, the TP4056 terminates the charging function when it's in constant voltage mode and the charging current falls to 10% of the programmed charging current. So with charging current set to 1A, it will shut down at 100ma. Since your load current is 60ma, charge termination can still take place when the actual charging current is 40ma. So in your case, everything will work without needing a load sharing circuit.

But the danger is that as the load current approaches or exceeds the termination current, the charger will never shut down. And that will eventually destroy the battery, with possible resulting fire or explosion. So it's really a safety issue. But as long as nothing happens that significantly increases your load current, you should be ok.

But note that if you decided to change the Rprog resistor so you could charge at a more gentle 500ma, that would actually be unsafe.

I understand all of the above, but OP didn’t say anything about the load connected to the battery.
Leo…

The load in my case is an LED driver and LED (1000mA and 2.95V).

Adafruit's charger and the no-name copy work well (so far).

I have not used the no-name TP4056 charger yet.