DIY Charger - Possible Project

I’m thinking about scratch building an instrumented battery charger. Why? Hobby. I can build exactly what I want.

Some of my projects never get past the back of an envelope. Most of the time, I complete the design but never order parts. Others have made it to working prototypes. I’ve never built more than two or three of anything.

We will see how far this gets.

Constructive comments very welcome!

Step 1 Requirements and design goals:

  • Must be something I can build at home.
  • Must be possible to model in Spice or LTSpice
  • Able to charge 1 to 4 cells.
  • Up to 4 independent charger circuits.
  • Multi Chemistry Li-Ion, LeFePo4, NiMH
  • Programmable or adjustable charge rate.
  • Maximum charge rate of at least 2 amps. 4A preferred.
  • Battery temperature monitoring. Charge termination on over / under temp.
  • V, Current, Ah logging
  • Internal resistance measurement
  • Computer interface. (Serial / BT / Ethernet to be determined later)
  • Modular design.
  • Will operate stand-alone without external computer or controller
  • DC power input

Battery Charger IC Selection

I’m going to use a commercial battery charger IC. No point in making this harder than I need to.

To make selection easier, I am limiting myself to parts from Linear Technology. This cuts down on the number of data sheets and application notes I need to read. More importantly, many of their parts have LTSpice models.

My Long list of candidate ICs:

Buck Switch Mode
LT 1511
LT 1505
LTC 4000
LTC 4008
LTC 4009
LTC 4012
LTC 4013
LTC 8490

Buck-Boost Switch Mode
LTC 4110
LTC 4020

LTC 4000 + Switcher

USB or Wall power

No LT parts meet design goals.

LT 1511 and LT 1505 do not support LiFePO4. I will probably eliminate them early on.
LTC 4000 reference designs have a high parts count. I will probably eliminated it.

That’s all for now. I’m off to read some data sheets.


im Curious now

Updated the candidate list:

LTC 4009
LTC 4012
LTC 4020
LTC 4110
LTC 4020
LTC 4155
LTC 4015

I’ve updated the requirements to explicitly mention independent charger circuits. It isn’t safe to run all four slots in parallel from a single charger. While this is obvious, I thought it was worth a brief explanation.

We don’t know the chemistries or the state of charge(SOC) of the 4 cells in the slots. For example LiIon and LiFePo4 have different CV voltages. The charger would end up over or under charging some of the batteries.

Even if all 4 batteries are identical types, we don’t know the SOC.

Imagine what would happen if a fully charged INR18650-30Q was in one slot and a discharged INR18650-30Q was in the second.
The two batteries would be in parallel. The batteries would be connected together with only about 40m ohm load. I = 2V/0.04 ohm = 50A.

50 amps is a bit more than the recommended 4A rapid charge current. I’m not sure what would happen but it wont’t be good.

Of course we could put a protection fuse or resistor between the charger slots, but independent chargers is much better.

LTC 4015 looks promising.


product video:

I’m going to have a quick look at Maxim, TI and whatever else google finds.

MAX1645 —

MAX1647 —

you look quite lonely, but dont be discouraged and stop posting, keep sharing, i bet there are many people still reading, at least i am

Texas Instruments has too many choices. Lots of reading ahead.

bq24190 Lithium only.


bq25890 and bq25892 Lithium only.


The features look good but it comes in a microscopic DSBGA package. It has 42 pins in a 2.8 x 2.5 mm package. PCB layout and assembly will be challenging. I will probably skip this part because of the package.



For later — I2C keypad scan IC. May be handy if I put a keypad in the device.

PCA9557 I2C and SMBUS I/O expander - 8 bit parallel port

Will do!

I’m surprised no one has jumped in to tell me this It has already been done.

I’ll work on this when I have time.

Analog Devices:


I like the 1.5MHz switching frequency.

5 Channel LED driver. The charger could double as a dim flashlight :slight_smile: It is suppose to be a backlight driver.

Full I2C programmability. I2C fuel gauge and temperature sensor.

AD5062 Linear
Fully programmable I2C.
AC or USB power. USB 3.0 with external USB controller chip.
Limited to 1.5A though.

Of interest for later:
AD7824 Battery monitoring system. Primary use is monitoring series cells in automotive applications. Could be useful.

So far, I like LTC 4015, ADP5350 and AD5062.

The TI parts look like they will be too hard for a one-person DIY.

I never saw this until today. Now I’m watching to see what happens. :GLASSES:

Cool project, Andrew.
Thank you!

Wish I could help in some way but this is beyond me.
Good luck with it, I will be watching and learning.

ADP5350 maxium fast charge current is only 650ma. Otherwise it was looking good. It has a lot of extra functionality that could have been usefull. I’m going to keep that one in mind for future projects.

I will probably go with the LT4015 but am going to look at the AD5062 first.

ADP5062 has great features:

  • Standalone or I2C control. In standalone, basic settings by jumpers
  • Thermal limiting and battery temperature limits.
  • Very low external part count.
  • Battery Isolation FET. Useful
  • USB or external adapter power.
  • Battery short detection.
  • Dead and weak battery trickle charge rates.
  • Optional JEITA battery temperature charging rates —> reduce rate if battery is too cold or too warm. Adjusts CV voltage too.
  • Programmable Charging termination voltage between 3.6V and 4.5V in 0.02V steps. :slight_smile:
  • Programmable fast charge current between 50mA and 1300mA in 50mA steps
  • dead battery, trickle, watchdog and safety timers :slight_smile:
  • programmable LDO for system power - I can use the 5062 to provide power the rest of the device.
  • Good application support including PCB layout guidelines.

Layout guidelines are sooo helpful.

The part is missing a few features. 1.3A charge current is below my design spec of at least 2A. 1300mA just barely covers the standard charge rate for some 18650 cells. I’d like to be able to test and use rapid charge rates too. An INR8650-30Q or 25R can rapid charge at 4A.

Panasonic NCR18650B standard charge rate is 1.625A

1.3A is not enough. I like the ADP5062 but it won’t work.

The MAX1645 and 1647 are primarily meant for use with smart batteries. Not what I’m looking for.

I’m going to give the LTC4015 a closer look.

For those reading along, here is the product page and datasheet again.


I would approach this from a different direction, battery charger ICs are designed for minimum cost low parts count commercial projects and can be fussy to operate outside designed goals. Starting with the goal of flexibility and maximum control I would use something like an arduino with software to control and measure current and voltage with basic power chips instead of battery specific.

I’ve thought about that. I agree that most of the battery charger ICs are designed to be part of a device like a tablet or laptop.

In the end, I may end up going with the flexible option.

Before I do that, I want to explore the more integrated parts to see if there is one I can make work.

I’ve already eliminated quite a few of the low part count ICs so because they don’t meet requirements.

Going the Arduino + power supply route puts the parts count up a lot and possibly the load on the Arduino. It means my code and external hardware is responsible for safety checks.

Some of the charger ICs have programmable temperature, voltage and time checks. They go into a fault mode if when any of the limits are exceeded.

Since I plan to have 4 independent chargers, part count is important.


I’m impressed by just how few external parts the new charger ICs need.

This is an SLA charger I built in 2012. It charges a single 6V battery. Look at the parts count!!