Adding a Charging Jack

Changing to rechargeable batteries offer the advantages of lower long term costs, longer run times and more power for the servos. In order to take advantage of rechargeable batteries, it is convenient to add a charging jack to the radio box. This is particularly useful in older Savage models where removal of the radio box top cover can be bothersome.

This article is comprised of three different, yet similar, ways to install a charging jack. As the reader may decide to use different connectors and hardware, exact dimensions are not shown and the reader is encouraged to rely on the figures for implementing the same, or similar modifications.

Contents 1 The Simplest Modification 1.1 Parts Required 1.2 Tools required 1.3 Procedure 2 Professional Modification 2.1 Parts Required 2.2 Tools required 2.3 Procedure 3 Alternate Connector Modification 3.1 Parts Required 3.2 Tools required 3.3 Procedure 4 Safety Warnings 5 Tips

The Simplest Modification

This modification is the simplest to embody with thanks to Savage-Central member HPISavageRC for his idea and picture. See the section on Tips for charger plug adapter ideas.

Figure 1

Parts Required

Hobbico Switch Harness with Charge Plug, P/N HCAM2400

Figure 2 - Switch Harness

Tools required

Dremel-Tool and cutting bit, or small round file

Procedure

1. Mark the Radio Box cover edge for a convenient place for the charging jack to exit.
2. Remove the cover and disconnect the switch wiring at the receiver and at the battery holder.
3. Remove the existing ON/OFF switch complete with wiring harness.
4. Install the new switch with wiring harness and connect the wiring to the battery holder (or new battery pack) and the receiver.
5. Check that your marked area for the charging cable exit does not interfere with any of the components inside the Radio Box and then make a small cut-out in the edge of the Radio Box cover.
6. Install the cover with attention that the charging cable is not pinched during this operation.

Professional Modification

This modification gives the most professional appearance, uses a standard charging jack and has a dust cover to keep the inside of the Radio Box free from debris. Thanks go to Savage-Central member Stew for his original concept and pictures.

Figure 3

Parts Required

Hobbico Switch Harness with Charge Plug, P/N HCAM2400 Ernst Charge Receptacle, P/N 124

Figure 4 - Ernst Kit

Tools required

Dremel-Tool and cut-off wheel, or fine blade saw Portable Electric Drill and drill bits X-Acto knife Small Phillips Screwdriver Nut-Driver or Pliers File or sandpaper

Procedure

1. Remove the Radio Box cover and disconnect the switch wiring at the receiver and at the battery holder.
2. Remove the existing ON/OFF switch complete with wiring harness.
3. Install the new switch with wiring harness and connect the wiring to the battery holder (or new battery pack) and the receiver.
4. Using parts from the Ernst kit as a guide, cut-out the Radio Box cover as shown in Figure 5. File or sand down the edges for a smooth finish.
5. Again, using parts from the Ernst kit as a guide, drill two holes for the lit mounting screws. Clean any flash from the edges of the holes with an X-Acto knife.
6. Trial fit Ernst kit and trim the clamping plate as required. Figure 6 shows a typical trimmed clamping plate.
7. Finalise the Ernst kit installation.
8. Click the switch harness charging plug into the back of the Ernst kit connector.
9. Re-install the Radio Box cover.

Figure 5 - Modified Cover

Figure 6 - Modified Clamp

Figure 7 - Installed Ernst Kit

Figure 8 - Closed Dust Cover Closed

Alternate Connector Modification

This modification allows the use of a coaxial DC Power Jack that is often required when using small wall chargers. It also represents an alternative method of mounting charging jacks as compared to the Ernst kit. A commercially made switch harness could be used, however this modification reveals an alternative that uses the existing HPI switch harness.

Figure 9 - Coaxial Power Connectors

Figure 10 - Mounted Connector

Parts Required

Appropriate Charging Jack, commonly available from electronics parts stores Sheet Aluminum, 20 gauge, or similar Insulated wire, AWG 22 or similar

Tools required

Dremel-Tool and cut-off wheel Drill Press and drill bits Soldering Iron and Solder (resin core) Jeweller’s Screwdrivers X-Acto knife Small Phillips Screwdriver Nut-Driver or Pliers File or sandpaper

Procedure

1. Remove the Radio Box cover and disconnect the switch wiring at the receiver and at the battery holder.
2. Remove the existing ON/OFF switch complete with wiring harness.
3. Manufacture an aluminum bracket as shown in Figure 11. The template in Figure 12 may be used as a guide, however exact dimensions and hole size and location must be done by trial fitment of the charging connector to be used and the existing HPI switch.
4. Carefully pry off the plastic switch cover by inserting a Jeweller’s screwdriver against the locking tabs.
5. Using Figures 13, 14 and 15 as a guide, solder a new positive wire from the positive charging jack terminal to the unused switch terminal and splice another new wire from the negative charging jack terminal to the existing black wire that is routed thorough the bottom of the plastic switch case. See the section on Tips for more information regarding switches and polarity of connections.
6. Using the screws that came with the charging connector, fasten the connector to the aluminum bracket. Note that the heads of the screws may need to have a flat spot filed on one side to obtain the required clearance.
7. Install the switch harness complete with bracket onto the radio Box Mounting Plate. The tabs from the mounting plate should be between the switch front bezel and the aluminum bracket.
8. Connect the wiring to the battery holder (or new battery pack) and the receiver.
9. Carefully measure and mark a spot in the Radio Box cover for the charging plug to connect to the charging jack. Drill a suitable sized hole in the cover. Trim the edges of the hole with an X-Acto knife.
10. Re-install the Radio Box cover.

Figure 11 - Aluminum Bracket

Figure 12 - Bracket Template “Guide“

Figure 13 - Switch Wiring

Figure 14 - Switch Cover Removed

Figure 15 - Wiring

Figure 16 - Assembly Ready to Install

Figure 17 - Cover Hole for Connector

Safety Warnings

• Always wear Safety glasses when working with any power tools. Dremel cutting discs are particularly prone to breaking with resultant pieces traveling at very high speeds.
• Do not charge batteries at a high charge rate as the Radio Box cannot vent significant amounts of heat that may be given off by the batteries.

Tips

• Ensure the ON/OFF switch is set to OFF during charging.
• One alternative to a rechargeable battery pack is to install 4 NiMh or 4 NiCd AA batteries in the existing AA battery holder.
• Unfortunately the polarity of Wall Charger Coaxial DC Power connectors is not standardized. Some have a positive center female pin and some have a negative one. It is imperative that the polarity of the wall plug be verified. Frequently, the information is printed or embossed on the charger, but in the event it is not, a voltmeter will have to be used to determine polarity.
• Many internal receiver switches are DPDT where one side is not used. Better reliability can be achieved if both sides are wired in parallel. To do this, simply solder a short jumper across each set of adjacent switch terminals. Three jumpers will be required. When adding a new positive wire for the charging jack, it may prove easier to insert the stripped end of the wire through the more exposed terminal and down to the terminal underneath and solder the wire to both terminals.
• You may wish to shorten some of the wiring as the Radio Box can become quickly cramped, especially if a FailSafe is installed. Rather than attempting to re-terminate the connector ends of the switch harness, it may be easier to de-solder the wires internally at the switch, cut them back, re-solder the wires to the switch and then re-assemble the switch.
• Many chargers are available and not all have mating connectors suitable for the newly installed harness. An adapter cable may be made from commercially available RC harnesses (such as servo extensions) and connectors typically found at your Local Hobby store. An example can be seen below:

Figure 18 - Adapter Cable