Adjustable E-bike Battery Charger

This is a simple and cheap way to make an adjustable E-bike battery charger, that can charge batteries with different voltage rating at the speed you determine yourself.

An old PC where the power supply is still working.

An adjustable CC/CV boost converter, here is mine.

A voltage/ampere-meter, I bought this one .

A contact that fits your battery, mine is XT60.

A switch.

You only need the PC cabinet and the power supply (PSU). The rest can be removed.

If you keep a led to indicate power on, make sure to add a resistor in line with it, to avoid frying it. Smaller or bigger than 1k ohm will make them the brightness you want.

An ATX standard PSU will have black wires as ground, yellow as 12V and green as power on.

Red wires are 5V, and can be connected to any remaining Usb-port, if you want Usb charge ports as well.

Cut only the wires from the PSU that you will use, to avoid any loose wires from making unintended shorts.

I cut the green wire and a black wire and soldered them to an On/off switch, which I mounted on the cabinet front.

I cut 4 black and 4 yellow wires to connect the input side of the boost converter, black to - and yellow to +.

My meter came with bare wires I could solder extension wires to, to be make them long enough to place the meter on the cabinet front.

Connect the - output of the boost converter to the negative (mine is black) wire of the meters input side, and + to the positive (red).

The output wires of the meter should be soldered to the battery-style contact.

Make sure you get the polarity correct.

Connect the PSU to power, and turn the switch on.

The display on the meter should now light up, and show the current voltage output from the boost converter.

My boost converter came with 3 trimpots, where the one near the output is marked CV (Constant voltage).

Turn the tiny screw on the trimpot until the voltage is the max voltage you want to charge the battery to.

My 52V battery can be charged to 58.8V, so I normally set it to 57V to save on battery life.

When connecting the battery to the charger, the PSU might shut down, if the boost converter is set to draw a higher current than the PSU can deliver.

In that case, turn the PSU off, and adjust the trimpot marked CC (Constant current).

I turned mine counter-clockwise as far as it would go, and turned the PSU on again.

Now you can turn the trimpot back again and see on the ampere-meter how many amperes it is charging with.

I have a 4S-battery with cells that the data sheet states charging current 0.5A, so 4S will mean anything below 2A is recommended. I like to charge between 0.8A and 1.5A, to be kind to the battery.