View Full Version : Connecting 22 Amp transceiver with 15 Amp car electricity net

Tue 16th Feb 2016, 04:46
Hello everybody, I would like to connect my brandnew Yaesu FT-957D transceiver to the cigarette lighter connector in my car... potentially with a 20m long cable to set it up on a camping table outside... Dos the amp drag exceed the cars capabilities ??? According to specs the radio might drag up to 23 amps, but the fuse might only allow up to 15 Amps.... Is there a problem ???? Is it wise to upgrade the fuse to a 25 Amp fuse ??? What are your experiences...

Tue 16th Feb 2016, 12:12
Hello sambamarco,

Professionally I wouldn't recommend plugging the YAESU FT-857D into a cigarette lighter connection as the vehicle's wiring will NOT be able to handle the Extra Direct Current drawn by the transceiver and even if your increased the Fuse value, you're setting yourself up for a major failure, i.e. Fire within the electrical harness and vehicle. The Owner's Manual recommends to wire that transceiver directly to the vehicle's battery. The reason the transceiver's fuses are right out at the battery is that when you install the DC cable through the vehicles firewall and you're not careful that wire could short out damaging the cable and the vehicle's electrical system. $$$$$$$ Repair to the vehicle.

Run the DC Power Cable through the firewall and use these Anderson Powerpole Connectors in the interior passenger compartment:


Splice in an Additional 25 Feet of the Red / Black # 12 AWG Zip Cord to extend the reach of your transceiver:

http://www.powerwerx.com/wire-cable/red-black-zip-cord.html $24.05

In the end, this will be a much Safer installation for outdoor camping.


Tue 16th Feb 2016, 16:27
As I recall, the J563 spec for the 12V connector commonly referred to as the "cigarette lighter" calls for 10A at the connector itself. Putting a bigger fuse in the circuit may just cause you a fire unless you're very careful about the amp rating of your wiring *and* that specific connector you're using.

Edit to add:

I was sort of wrong. It's 20A +/- 2A for fifteen seconds on the test cycle, with the wiring and fuse rated to 20A, with the actual current draw of a "cigarette lighter" being 10A. See section 8.4 of the spec: http://autoparts-standard.org/index/images/userfiles/media/SAE%20J563-2009.pdf

Tue 16th Feb 2016, 17:08
Lighter sockets are not positive contact, just friction. This means a lot of power gets wasted in heating up the socket itself rather than running the radio or whatever's plugged in. Run your radio's power from as close to the battery terminals as you can get. Fuse the positive side right at the battery. If the vehicle's grounding system is in good shape, you can then connect the negative wire to a convenient piece of metal like a seat bolt. Use a multimeter to determine whether you have a good electrical connection.

Tue 16th Feb 2016, 20:39
Upgrading the fuse won't upgrade the wiring, and this is the problem.

I run my mobile from the lighter socket in the Grand Vitara, as there is one specifically rated at 10 amps. That said, I only ever run 10W, which draws around 2.5 amps. I have a digital volts amp meter fitted as a bit of a back, so that I can monitor what's going on.

If you are planning on parking up, and running the radio from a table, why rely on the car at all? You could obtain a separate battery or even a small portable generator. Just a thought.

Kind regards,


Wed 17th Feb 2016, 11:29
I can run a 25w 2m mobile rig from the lighter socket in my car, like Phil's it will safely give 10 amps. The car's second lighter socket provides power for a low noise pre-amp.

If I go for HF mobile at 100w or so, then I will have to do as Phil suggests, running a good quality power cable directly from the battery to a fused terminal box in the footwell of the car. I've done it before, the only only issue these days is finding a suitable point to pass the power cable through the bulkhead. Have a look at the in car audio forums for guidance - these guys regularly have to use far more power to destroy their hearing (!) than we might for an HF rig on full power! Their power cables are really thick.

Tue 30th Aug 2016, 06:23
Running electricity at a level too great for the wiring it's going through causes the wiring to heat up. That's why codes specify certain guages of wire for certain numbers of amps. Basically, the more amperage you want to run, the thicker the wire required. You might get away with it if the overload is fairly small and very, very short term, but it isn't either smart or safe. This applies to cars, homes, and electronic (and electrical) equipment; any place where electricity is flowing. Running amperage above what a circuit is designed to handle (the wiring in your car in this case) results in heat, then melting wires, and then often a fire. If you're lucky it might just melt a wire, breaking the circuit and killing the flow. If you’re not lucky, the hot wire could cause something to ignite before it melts, or after melting the live end could spark or contact the wrong thing, again starting a fire. Even if a fire doen’t occur, the heat can destroy valuable electronics.

Fuses and breakers are a safety device, and they insure that you cannot overload a circuit. The amp rsting of a fuse or breaker is chosen specifically for the level of power a circuit can safely handle. The fuse or breaker is a part of the circuit it protects, and if the circuit starts to get hot, the fuse fails or the breaker trips, cutting the flow of electricity before the overload causes enough heat to do any damage.

Years ago houses were built with fuses in the circuits rather that the circuit breakers now common. Most were screwed into a socket in the fuse box, just like screwing in a light bulb. If a fuse failed, a well known temporary fix was to pop a penny into the socket. That always restored the power but, unfortunately, that copper penny could pass a whole lot more power than the circuit could handle, and a lot of houses burned down.

Swapping out a fuse in your car for one with a higher amp rating is the same as putting a penny into one of those old fuse boxes. It doesn’t matter why you’re doing it, you’re creating a situation that could cost you your car. And if it’s at a campsite and you’re at a table a few feet away, it could cost you your life.

“Upgrading” any fuse or breaker, be it in a car, a home, some piece of equipment, or whatever, is just asking for at best a problem and at worst a disaster. Do NOT do it.

Tue 22nd Nov 2016, 20:13
Most cigarette sockets in cars are rated for a maximum of 10 amps, so do not depend on it to run your rig - it will blow the fuse !

Tue 22nd Nov 2016, 21:31
You also need to consider volt drop - 20m of cable capable of handling the full load your radio could (but probably won't) attempt to demand is going to be VERY heavy - and to keep the resistance low, you should really go up in cable size - with 13.8V and 20 odd amps, a few Ohms resistance is going to impact on the voltage drop quite a bit. My view to this would be a proper power tap - like the camping/motor home fraternity use with a properly protected output on a connector type capable of handling the power.

There is another solution though. Here we call them leisure batteries. A battery similar to a car battery that is designed to put out constant lower currents than starting a car. Car batteries nowadays are designed for high starting current in small bursts - they're not good any more at supply constant power at lower currents.

With a leisure battery close to the radio, the shorter cable length isn't a problem, and then you use an inverter to provide mains power to charge the leisure battery.

Sat 26th Nov 2016, 00:22
I would use alligator clips on the power cord and connect directly to the car battery. The accessory (cigarette lighter) plug usually has a 10 amp fuse in the car on it. But some cars have a 15 amp fuse on them though. Years ago when they really put cigarette lighters in the socket using metal and ceramic sockets then they could handle more current. But today the sockets are all plastic and not designed for lighting up cigarettes anymore. Running more than 10 amps though it heats up the connector from the contact resistance it has.

I like to use 3 cell 5,000 mah Lipo (lithium polymer) battery packs myself. You can get a Lipo battery charger and you can recharge the pack fairly quickly. But a 5,000 mah pack will last a long time though. So two packs will work well for most people as you can alternate and charge the packs as needed if you are are handling a lot of radio traffic. The Lipo packs weigh next to nothing compared to a lead acid battery or nicad pack. That way you don't forget and run down the car battery on yourself.