Jump Start Receptacle

[rv8gibbo]

I'm going to run a jump start receptacle about 4-5 feet from my battery on the firewall, would 6AWG be enough to carry the starter AMPS? I can do it in 4AWG but I'd like to make it as light as possible.

Many Thanks

[David Z]

I'd be cautious jump starting an airplane. Even the bigger planes with ground power connectors and nearly always start on ground power have minimum battery states required even to plug in the power.

If there's a dead/weak battery, charge it first. Ground power is generally used for lessening wear on the battery during start, or running electrics with the engine off. Both of those situations will need different wire sizes than starting the engine solely on ground power.

[HFS]

If you are not using this chart already for wire sizing, you might want to consider it.

HFS

[bjdecker]

The longer the wire run, the larger the voltage drop and thus the slower the starter will spin.

The longer the starter spins, the hotter the wire will become.

Consider the wire size used in some of these LiFePo+ "Jump Packs" -- the cable provided is ~5ft and 10ga and should only be used for 4 minutes.

With that in mind, you should be fine at 6ga -- just keep the cranking in this case to under a few minutes (4? 6?)

[Carl Froehlich]

I suggest you consider ANY option other than a jump start. If you abused your battery to the point it no longer cranks the engine, charge it. If you abused your battery to damage reserve capacity (e.g. left the master(s) on), replace it.

Jump starts are a relic of the past when flooded batteries sat in corroding battery boxes.

Carl

[rv8gibbo]

Thanks guys,
It'll only be used in situations where the battery is dead and access to help is minimal or no existent. I'm going to have a lithium jump pack in my tool kit which are very light weight, small and are more then capable of starting and engine safely. I'm also going to have a ground receptacle so it's plugged in and not clamped on.

[MK77]

After close no-start situation with a cold temp start at an airport away from home base, I'm also planning to add emergency jump capability. I have a Nocco jump pack and they sell an extension cable that you can attached to the battery that can also be used to connect their battery charger/maintainer. It's an 8ga cable and only 18 inches but I think it will be long enough to reach out through the oil filler door in case I needed to use it with the pack.

Years ago, a DA42 was jumpstarted due to a dead battery and took off shortly after. The battery hadn't had a chance to recharge enough and when they retracted the gear, the electric motor drew enough current to pull the system voltage so low that the ECUs went offline. Result was a dual engine failure after takeoff and crash. They redesigned the system after that, but one reason why some planes have minimum battery charge levels.

[jcarne]

Originally Posted by MK77

After close no-start situation with a cold temp start at an airport away from home base, I'm also planning to add emergency jump capability. I have a Nocco jump pack and they sell an extension cable that you can attached to the battery that can also be used to connect their battery charger/maintainer. It's an 8ga cable and only 18 inches but I think it will be long enough to reach out through the oil filler door in case I needed to use it with the pack.

Years ago, a DA42 was jumpstarted due to a dead battery and took off shortly after. The battery hadn't had a chance to recharge enough and when they retracted the gear, the electric motor drew enough current to pull the system voltage so low that the ECUs went offline. Result was a dual engine failure after takeoff and crash. They redesigned the system after that, but one reason why some planes have minimum battery charge levels.

I too have thought about something like this. Those jump starters are quite effective and light. I often fly with mine because my personal courtesy car battery is often drained when I land. (really old truck)

Wasn't aware Nocco had an extension. I may just have to copy that idea.

Something like this.

[Carlos151]

I installed a ground power receptacle on the aft baggage floor of my RV8. This was not done to “help” a weak battery but mainly to provide some cheap insurance in the event that the battery master was accidentally left on at a remote location, discharging the battery and preventing a normal start. I chose the aft baggage floor so that no one is near the prop during start, and because it’s near the rear battery location reducing the necessary wire runs. A vehicle parked aft of the wing line can safely provide power with standard jumper cables. I used Bob Nuckolls diagram and instructions and carry a jumper plug in my travel tool kit. This is no different than jump starting your car to get you home IMHO.

[David Z]

Originally Posted by MK77

Years ago, a DA42 was jumpstarted due to a dead battery and took off shortly after. The battery hadn't had a chance to recharge enough and when they retracted the gear, the electric motor drew enough current to pull the system voltage so low that the ECUs went offline. Result was a dual engine failure after takeoff and crash. They redesigned the system after that, but one reason why some planes have minimum battery charge levels.

This is exactly the accident I was thinking of when reading the OP. My memory tells me it was a brand new airplane undergoing factory test flights prior to delivery. My memory might be wrong, so don't quote me. While we don't have a landing gear motor, instantaneous loads can sneak up on an alternator and cause problems with a very weak battery. I'd hate to move the flaps, transmit on the radio at the same time a strobe light decides to flash and cause a problem.

Relays and contractors also take a minimum volts to close. If the battery is too low, that may not happen. Then an electrical system starts to do weird and unsuspecting things.