LAPTOP ADAPTOR: 4-6 cell charger up to ~5A

This device has been designed for use between 15 and 24v. This suggests it should be suitable for charging between four and six lipos directly at pretty substantial currents. This would make it one of the world’s cheapest and easiest DIY lipo chargers. I’ve only used it to charge a test pack of six lipos so far, but initial impressions are very encouraging.

To charge lipos direct there are a few mods to consider:
1. A trim pot is needed to replace the switch to adjust voltage accurately.
2. It will be necessary to adjust the current sensing wire if the current is not appropriate for your cells.
3. The device needs extra cooling (probably less of an issue with the 120W version).
4. Input and output diodes are needed for reverse polarity protection.
5. Higher voltage output capacitors are recommended if used to charge six or more lipos.

It is necessary to bypass the switch and the resistor array beneath it and use a multi-turn trim pot to set the voltage accurately. This is because lipos need a slightly different voltage than provided by the sliding switch. For six lipos you need 25.2v (4.2 x 6) for which a 1k trimmer is perfect (a 1k5 or larger pot is needed for 4 or 5 cells). The first photo shows where I glued my trimmer and drilled two holes to route the wires. In the second photo, the green arrow shows where I cut one trace on the board, and the red and blue arrows indicated where I connected the leads to the pot. The charger needs a load to regulate accurately. Set the output voltage first with no lipo connected and then check it with a fully charged one connected (you are likely to need to reduce the setting slightly; no load may be about 0.2v higher).