to install Piper style ground power receptacle or not?

[gmcjetpilot]

Peter and Randy you all make good points. I never thought about shorting the electrical system with a charger. I always had the rule of NOT leaving the battery charging unattended. The other point about shorts causing damage has me thinking. I never was comfortable running avionics off a el-chepo battery charger. All battery chargers are not equal. Some do have short, reverse polarity and many other protections afforded microprocessors in the better chargers. I guess the lesson is know thy charger.

I am not anti-Jump Plug, just presenting the CON to putting one in. Really the down side is weight and cost. Otherwise I can see IF you needed it, IT could be a real nice to have.

Also if your alternator is weak, it might roll over and die if you demand it charge a discharged battery. Just keep that in mind. A real dead battery will demand as much as the alternator can put out.

One student pilot I had did a solo cross country and made one small boo boo. She forgot to turn the alternator on. It was a mighty C-152 and she just split the master switch accidentally. She noticed it 1/2 way to her destination as the battery discharged and turned the ALT on. However with the battery now charging and drawing A LOT, plus the radio, transponder, lights on, she pop-ed the CB, twice. Well from then on she did everything perfect. She did not try another CB reset, did a 180, shed load and landed back at the departure airport. Of course if she would have shed load first before turning on the alternator, to let the battery charge a little first, before bringing the other stuff back on line, the CB would not have pop-ed. Hey it was part my fault, I did not know to teach her that and never thought the alternator could pop the CB under normal output. It did. I guess the alternator output CB is under sized, which is not uncommon. SO IF YOU JUMP, let the engine run a little time at higher RPM than low idle. Charge the battery before loading on the other stuff.

[f1rocket]

And I think the real risk exists when you don't have a charger attached. At some point, the small wires coming from your plug have to get connected to the battery. Even if you use an inline fuse or circuit breaker, you potentially can unleash all the power of the battery through this circuit should the power wire short. It would create a fair amount of smoke as that wire burns. I think that's why the battery charger solenoid is so important.

[gmcjetpilot]

Originally Posted by f1rocket

At some point, the small wires coming from your plug have to get connected to the battery.

That's a great point and it applies to anything connected to the battery. I DO think 18 awg wire, with an in-line fuse, say 10 amps, is pretty safe. That is what I have. If the 10 amp fuse is right next to battery, you will not smoke the wire (82 amp fusing) since it's whole length 100% protected. Shorts are not good anytime on any wire.


Chargers and charging safety

Charger wires should be fused. Some cheap chargers don't have fuses in their external connector wires, but that's easy to solve, put one in. Many of the new chargers are excellent and now have microprocessors which shut down if there is an internal battery short, which could cause an explosion. Of course they also shut down with a wiring short, but still I would not just leave it hooked up unattended.

Charging batteries do have risks, no doubt about it, but you can mitigate that risk with some care, common sense and good charger. Same with jump starting a plane or car, there are precautions.

Clearly you don't want to run extension cords and wires all over the wing, cowl and canopy. A little common sense is good. The Fire Marshal who inspects the hangers will not allow extension cords to be connected in unattended hangers. You can use them temporarily. I follow the same practice at home I unplug all extension cords in the shop when not there. It is easy to understand why. I know many use trickle chargers and leave them for days on their bikes, cars and planes. probably OK but there is a chance of fire.

Some recommend you remove a battery if it needs to be fully charged. They do blow up on rare occasion. If you bench charge make sure you protect your eyes. I consider charging in a vented plywood box. Here is a good charger that does AGM (absorbed glass-mat or SLA - sealed lead acid) with short, reverse polarity and over load protection.
http://www.batterychargers.com/detai...D1000A&catid=2

The above is a bit of overkill for trickle charger, but if you do get a trickle charger, max volts for a PC680 is 13.6 volts for extended trickle charger. Typically these trickle chargers only put out about 1.25 amps. This is NOT enough to deep charge a battery but just maintain a charged battery. If you have a full charger that does not cut back automatically to trickle charge (13.6 volts) you must manually disconnect it from the battery. It is not suitable to leave connected for more than say 1-2 hours depending on the charger. These chargers can be used to charge but you must monitor them and turn them off manually. Again I would not leave any charger unattended, at least for an extend period. All the above is for new SLA/AGM batteries, not flooded lead acid batteries, which have different requirements. The above charger will also charge your car battery or deep cycle marine bats.



RISK of ELECTRICAL SHORTS

If you install a JUMP PLUG and connect a 2 awg wire to the battery, running it all over the fuselage with no protection that is a welder. A 18 awg with a fuse adjacent to the battery not so bad.

If we really study wiring diagrams of planes, on many there is often a length of unprotected wire somewhere in the wiring. I know many builders run a wire from the master relay to their battery buss with no fuse or CB. There's wire protection for the items branching off the main buss but not the main buss itself? really true story. It's probably OK if the wire run is short and well protected. The saving grace I guess is you can turn the master relay off if you smell something burning or see smoke.


Battery charger wiring:

HOT wire direct to battery is OK, but if you do run a small wire direct to the battery for a remote charger plug/connection, make sure it's fuse protected (6-10 amps is good), 18 awg wire. Protect and shield from shorts, you'll be fine. You are not tyring to jump start, but just charge without removing the cowl. Even though the RV-4/6 battery is in the cockpit it is hard to get at.

Most chargers are 6-10 amps max, and you don't want anything more 6-7 amp charger for a PC680 SLA battery, which is oddysey's recommendation. If you have a larger battery you may need a 10-15 amp charger. There is probably no reason to go to a larger wire than 18 awg, unless you have real long wire run. I recommend you keep it short as possible, at least under 3-5 feet. Besides the battery, even a drained one, will not pull more than the max amps of the charger, except for the first few minutes of charging. Than the current drops rapidly as it charges, say 3 amps, until when charged and the current is a trickle.