I am curious as to the best way to connect to the power terminals. I have soldered my power connections to header pins and use them inserted into the screw terminals. I have used stranded wire tightly wound and used that as my subsequent connection. I am redesigning the power for my project and could use some guidance in the connection, wire type and wire gauge.
But both have suffered from problems. Neither connection method was stable.
I’ve reviewed the manual and it does not provide any recommendation, particularly as to wire size and gauge. There were some postings that cautioned against using an inexpensive battery holder, as he connecting wire was too small. I don’t remember a definition as to what too small is.
I am thinking of twisting the stranded wire and soldering it lightly; just enough so the strands wick the solder applied. But my past experiences leave me unsure. I have a wire gauge of 18AWG for the servo power. I am taking power from a DC-DC boost circuit via a modified servo cable (to allow removal of the crcuit for testing and tuning) and thinking of soldering it to a small section of the 18AWG wire, to connect to the terminals with. I also am considering soldering the wires to pins from a male DB25 D connector… and inserting the pins into the screw terminals.
Male DB25 pins shouldn’t be to bad, and using .025" wirewrap posts as I’ve mentioned before works. Really not enough room for tinning wires and inserting. Some boards have dual servo power connectors, you can use two pairs of power wires to aid connections.
Servo wires might be a little light for powering any more then one servo. Is #20 or #22 gauge wire available?
I’m thinking of using the servo wire only for VL. Servo power is from a short section of 18 AWG connected to a 14AWG feeder - same as the 5VDC feed in a PC.
If you use a 18 gauge wire for 15 cm (about half a foot) or less and connect directly to the screw terminal, you should be good for up to 24 A @ 6 V DC with little power loss. As for how to get a reliable connection, we recommend simply twisting your wire unto itself into a small ball or flat circle and insert it directly to the screw terminal. You can use solder if you wish but please note that solder has an electrical resistance of at least one order of magnitude higher than copper and aluminum wires and this is not ideal for power connections.
If you do use a male pin header, you should be ok for currents up to a few amps (maybe 3-4 A). Could you tell us more about how many servos you wish to use with this setup and their current draw (no load, average, peak)?
If the metal connectors touch the pads directly and then solder is applied to connect them together then there is no concern since the solder is there to ensure a proper connection is held.
In the above example, a problem may happen at higher currents if the solder used to hold the wire strands together on the 18 AWG wire was covering the entire connection. Therefore, the connection would go from copper/aluminum 18 AWG wire > solder > screw terminal. This would mean a x10-x50 high resistance between the 18 AWG wire and the screw terminal leading to a higher voltage drop and extra heat at higher currents.
I plan on applying a tiny bit of solder to the end of the stripped, twisted wire to keep the strands together. Not the entire end. I am running 11 servos, but don’t know their current draw. What I do know is the supply will server up to 8A and I have had no problems running in the past. BTW, the length of 18AWG wire is measured in inches - 2" to 3" at most.
I am hoping that the servo wire (2" - 3") can supply enough current to VL to run the SSC-32.
That should be fine then. You may even want to try connecting to both VS1 and VS2 and splitting your servos on both sides equally (5 on one side, 6 on the other) to even out the current use and reduce possible heating of the solder on the strands (if any).
Are you using a regular SSC-32 or the SSC-32U? The SSC-32U includes as an improvement some large capacitors to prevent brownouts that can be cause by large power draws from many servos starting simultaneously. If you are using the older SSC-32 (with a DB9 serial port) and the same power source to power both VS and VL, we recommend that you use a capacitor to prevent brownout. Also, make sure the voltage is at least 6V or it may not be enough for VL, since it has its own 5V regulator.
I figured a tank capacitor is a good idea, any suggestions on adding it to the SSC-32 (DB9), that is the version I have currently split up my motors on both sides of the board but I am only using one 6V 2800 MaH NiMH battery. I actually have two of these batteries (one in better condition than the other). I wanted to use two batteries but these things are heavy and I was planning on switching to LiPos.
Actually, I think the tank capacitor is required. I’ve noticed some strange behaviors during the current spike when turning the robot on. One of the things for me was the screw terminals on the SSC32 terminal were difficult to connect to reliably. Using 16 gauge wire, I twisted the ends and tried to compact it as much as possible. I didn’t add any special connectors.
