EMRG has selected a standard DC power connector that will be installed on all equipment used by EMRG. The purpose in standardizing on a connector is to allow any radio to work with any power supply, battery or DC adapter cable.
Individual EMRG members are encouraged to use the connector, but are not required to do so. Each member receives one connector to build an adapter from their personal standard to the EMRG standard. The support from EMRG members and other amateurs in the community, has been tremendous.
The standard connector was selected after careful review of current recommendations and common connectors used by amateurs. Availability was an important consideration, but there are few options available locally, so connectors are typically ordered from outside the area anyway.
The connector that was selected, is the Anderson PowerPole. PowerPole connectors are made up of individual housings and terminals. The small housing accepts terminals for 15A, 30A and 45A. This allows the same mating housing to be used with large or small wire sizes for high and low current equipment.
The PowerPole connector are not available locally so, EMRG keeps a supply of connectors for sale to amateurs at meetings and hamfests. For more information, please send an e-mail to VE3IHI@rac.ca.
Each connector comes with a Red and a Black housing, plus two terminals, either 15A (16-18ga wire) or 30A (12-14ga wire) rating. The same shell fits both 15A and 30A terminals. Extra terminals are also available.
The red and black housings slide together, side by side. EMRG has selected the recommended orientation as shown in the picture on the left.
At least 3 manufacturers now sell power distribution equipment using PowerPole connectors.
Fuses are a critical safety and equipment protection device. Every piece of equipment that uses DC power or that supplies DC power, should have a fuse rated for its capacity.
The fuse should be rated at 1.5 times the expected maximum current flow. If the fuse is rated right at the maximum current flow, then it will usually blow after a period of time as it becomes warm. Fuses come in specific sizes, so you may need to select the next nearest size.
For example, if your radio is rated for 9 Amps maximum, then the fuse should be 9 x 1.5 = 13.5 A. Since there are no 13.5A fuses, use a 15A fuse.
The wire that the fuse is attached to, should be able to support at least 2 times the maximum current flow, so the cable does not become a fuse. Wire that supports more than 2 times the maximum current flow is often used, to reduce voltage loss due to the wire.
The most critical aspect of fuses, is the fuse holder. Many fuse holders are cheap plastic, so they do not stay locked together well and in some cases, if the wire moves that attaches to the fuse holder, the power is momentarily disrupted.
An excellent choice for radio equipment, is the automotive ATO style fuse and fuse holders. The fuse holders are typically made with a rubber holder and cover for the fuse, plus the fuse sits tightly in the holder. These fuses are plastic, so they don't break and are readily available. Check with specialty radio or electronics suppliers or a local automotive parts supplier.
It won't hurt if you install a fuse on the negative lead, and the wiring harness that ships with most Amateur mobiles has two fuses.
The fuse on the negative (ground) lead is only really required on installations that connect directly to the vehicle battery. The fuses should be installed close to the battery.
The reason for the fuse, is that if the vehicle grounding from the battery to the car frame/engine should fail, either partially or completely, the radios negative lead "could" in some cases become the return path to the battery for the vehicle, causing the wire to burn.
This is not an issue for radios connected to power supplies, the vehicle chassis or batteries not in a vehicle.
ALWAYS FUSE THE POSITIVE LEAD!
Selecting the correct wire size is important for two reasons;
| AWG (1) | Wire Diameter (Inches) |
Wire Diameter (Centimetres) |
Ohms /1000 ft |
Ohms /1000 m |
Maximum Current (2) (Amps) |
|---|---|---|---|---|---|
| 24 | 0.020 | 0.051 | 31.223 | 102.407 | 2.1 |
| 22 | 0.025 | 0.064 | 19.636 | 64.404 | 5.0 |
| 20 | 0.032 | 0.081 | 12.349 | 40.504 | 7.5 |
| 18 | 0.040 | 0.102 | 7.767 | 25.473 | 10 |
| 16 | 0.051 | 0.129 | 4.884 | 16.020 | 13 |
| 14 | 0.064 | 0.163 | 3.072 | 10.075 | 17 |
| 12 | 0.081 | 0.205 | 1.932 | 6.336 | 23 |
| 10 | 0.102 | 0.259 | 1.215 | 3.985 | 33 |
| 8 | 0.128 | 0.326 | 0.764 | 2.506 | 46 |
| 6 | 0.162 | 0.412 | 0.481 | 1.576 | 60 |
You want to install a new mobile in your car. The specifications for the radio shows that the maximum current is 9 amps. Looking at the wire size chart, #18 wire will support a maximum of 10 Amps, but we want to have a wire that is rated for at least 2 times the required current. This means that the radio must use at least #14 gauge wire.
The wire has resistance, so there will be voltage drop along the length of the wire. The longer the length of the wire, the larger the voltage drop. The wire may be rated to handle the current, but the voltage drop because of the length of the wire may be more than you want. This is not typically an issue if you use a power supply or your car is running. The supply voltage will be about 13.8 volts DC, so a bit of loss in the wire is not an issue. When you run on battery, such as when you turn the car off, the battery voltage drops to less than 13 volts, so the voltage at the radio will be even less than the voltage at the battery, which may be an issue.
The wire from the battery to the radio in you car is 3 metres, about 15 feet. The #14 wire has a resistance of 10.075 ohms per 1000 m. So how much will the voltage drop be in the wire?
E = I x R [E = Voltage drop across the wire, I = Current in the wire, R = Resistance of the wire]
We know the maximum current I for the radio is 9 amps and the resistance R for #14 wire is 10.075 Ohms/1000 m, which is 0.010075 ohms/m
The voltage drop E = 9A x (3m x 0.010075 ohms/m) = 0.3 Volts This is not going to be a problem!
If the wire was 10m (about 33 ft), the voltage drop E = 9A x (10m x 0.010075 ohms/m) = 0.9 Volts If you were running from a battery, dropping almost 1 volt in the wire would not be good. Using a larger gauge of wire will reduce the voltage drop.