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DIY Smart Ni-mh High Current Charger

After trying to source a good quality smart charger that could recharge large Ni-Mh or Ni-Cd packs, I found none were at a reasonable price that had the features that I required. Prices started at USD$300 for quality units. Cheaper chinese made so called smart fast chargers that I own seem to turn the battery pack into a heater for the entire charge, which is a sure sign that the charger uses a very aggressive (and not so smart) charging algorithm. After months of working on this charger and many more months testing many prototypes in the feild I'm pleased to announce its ready for release in a kit form. You can build your own rapid universal smart charger in around half an hour, better yet its customized to perfectly suit the battery pack and your requirements with some very unique features to safely charge both nimh and nicd battery packs.

Smart Charger Features:

  • Fast Charging is possible with to up to 5 amp charge rates allowed due to smart design.
  • Trickle charge automatically selected after main charge is complete. Battery pack can be left on the charger so its always topped up and ready to use. Handy since Ni-mh looses 10% of its charge in the first 24 hours if not left on a trickle charger.
  • Boost Button for those times when you need the battery quickly, or for a second charge rate to suit a wider range of packs. Can be setup for either task.
  • Health Checks to ensure the battery is in good condition to be charged and that the charger is also healthy before connecting your expensive battery. The charger goes into an error warning mode if anything goes wrong and protects the battery.
  • Cell Equalizing stage to make sure all cells are evenly charged to help prevent bad cells. Sadly not many chargers have this great feature to extend the life of your battery pack.
  • Pulse Charging to prevent heat in the batteries from occurring with fast or rapid charge rates.
  • LED Indicator to show the status of the battery charger.


Charger Specs:

  • Recharges: Ni-mh and Ni-cd, 7 to 30 cells or 8.4 volt packs all the way to 36v.
  • Charge rates: Passive cooling gives up to a 3 amp rate, fan cooled allows up to 5 amps.
  • Size: PCB with all components measures 85mm x 50mm x 20 mm
  • DC Input: Requires 1.5 * number of cells plus 3 volts. Ie for 14 cell pack 24v or more is needed.
  • Max DC Input: 46 volts
  • Charge termination: Max voltage, Delta V and safety timer.

Here's a picture of the charger fully assembled mounted on the case which also doubles as a heat-sink. The professional PCB's are available right now in one of my kits. Kits include any email support you need to build the charger as well as any minor customizations to how the chargers works to suit your battery pack and personal requirements.


Power Supply Requirements

The total cost of building this charger can range greatly depending on how much current you need and if you wish to build a charger that can travel overseas. A basic transformer will start at around USD$10, I recommend the ones with a range of voltage outputs so you can fine tune the AC voltage output from the transformer under load. I would encourage you to look at switch mode power supplies that can be used on any voltage between 100 - 240 volts AC as this means you can use it anywhere in the world if you need to travel with your new DIY charger. Batteryspace carry a switch mode supply that's suitable for USD$30 and can make a charger up to 3 amps.

Example of a multi output mains transformer.

Example of a Switch Mode power supply.

You need to select a power supply that is 3 volts higher than the voltage of the battery pack when fully charged. For Ni-Mh and Ni-Cad packs this will be 1.5 times the number of cells in the pack plus 3 volts extra, for example a 14 cell nimh pack will need a 24 volt power supply. This extra voltage is due to the internal resistance of the pack.

If its an AC transformer then you will need to use a bridge rectifier to turn it into DC, as well as making sure the voltage of the transformer under a load is not below the required voltage. This is greatly simlified if you purchase a transformer with multi voltage tappings so you can select the output which gives the right voltage at the load your going to use.

Ordering Information

When you place an order for a DIY charger kit I need to know the following information to customize the smart charger to your battery and requirements. I also use this information to give you advice on if something should be changed.

  1. The battery pack details that you wish to charge, ie 14 cell Ni-Mh 5ah pack.
  2. How fast you want to charge the pack on the normal rate and the optional boost rate. ie normal rate of 0.5 amps and boost rate of 2 amps.
  3. The specs for the DC power supply or AC transformer you wish to use to power the charger.
  4. Your postal address.

Payment is made via www.paypal.com which allows for credit cards to be used securely. Contact me if you have any questions regarding the ordering process.


Full kit with all parts and PCB, requires you to supply case and power supply (see above for power supply requirements). USD$68 Free Shipping.
Kit with 24 volt 100-240 auto switch mode power supply and case supplied. email for Price


The finished product housed in a case with a switch-mode power supply to support auto mains selection from 100 - 240 volts. This setup allows me to power it anywhere in the world when traveling overseas, or with the use of an inverter to power it from a cars cigarette lighter. Inverters are now very cheap and allow other devices to be powered in the car hence why this feature was not added to the chargers list of features to help keep the size and price down as well.