grounding battery

originally i wired my rv12 with the batteries [earthx] behind the panel . after considering an airtight battery box i have decided to remount the batteries fwf. the engine is grounded to a firewall passthru bolt that holds the ground strip terminals for the panel and the engine compartment. the engine has a second ground from another point on the block to another bolted terminal on the firewall.
do i really need to run a cable from the neg. of the batteries to that terminal where the ground strip terminals mount or can i bolt the cable from the battery ground to the firewall by the battery and save the weight of at least 2 feet of cable?
thanks for any advice.

Ground

I would definitely not use the aluminum firewall to conduct electricity. You should run the negative of the battery directly to the post where the engine ground connects. Otherwise full amps attempting to run the starter would be flowing through the firewall. It would hamper starter performance and might cause a fire.

Very simply, dont cheat on your grounds. Ever. The ground is more important that the hot side to get clean and strong. If you short change it in your build, electricity will find a way to complete the circuit, but it wont be through where you want it to go....and drive you crazy chasing electrical gremlins.

Run the extra cable, and save yourself years of headache, worry, and mistrust of your airplane.

bobnoffs said:

originally i wired my rv12 with the batteries [earthx] behind the panel . after considering an airtight battery box i have decided to remount the batteries fwf. the engine is grounded to a firewall passthru bolt that holds the ground strip terminals for the panel and the engine compartment. the engine has a second ground from another point on the block to another bolted terminal on the firewall.
do i really need to run a cable from the neg. of the batteries to that terminal where the ground strip terminals mount or can i bolt the cable from the battery ground to the firewall by the battery and save the weight of at least 2 feet of cable?
thanks for any advice.

Click to expand...

Run your battery ground cable to this bolt.

Energy actually runs from the ground (-) of the battery, to the + terminal of the battery. So the ground is VERY important....

BTW.... the firewall is stainless.... NOT aluminum.

thanks guys,
i guess i will replace that battery to terminal ground cable on the fwf side of the firewall. appreciate the input.

Related question (I think)

My RV7A is having ? xenon strobe light? issues and I?m wondering if I might have a ground problem. My strobes quit working and after talking to a Whelen representative I?ve accomplished the following checks.

1. I disconnected all three plugs to the power supply (left and right wing strobe and tail strobe) and then plugged them in one at a time to see if a strobe light short was the problem. Result: no difference. None of the strobe lights worked separately.

2. Pulled the power supply and took the tail light strobe, placed them on the bench and hooked up an external power supply. Result: tail light strobe fired normally indicating both the power supply and tail light strobe were okay.

3. Reinstalled power supply, hooked up only the tail light strobe that I?d previously checked on the bench and guess what? Nothing!

4. Checked power going to power supply. Voltage was 12.3 volts from the battery, strobe light switch worked and ground showed a good continuity.

I?m at a loss as to what?s causing my problem. However I do remember when I replaced my Odyssey battery last year that my ground cable was attached to the firewall. Also, the aircraft has never had a great tradition of cranking easily. Most of the time I have to engage the starter several times to get it to have a normal starting crank.

My question is: where should the battery ground be connected to the aircraft? If not to the firewall, then where?

i am not the builder but I am the second owner. It?s had several A&P/IAs work on it and a couple of EAA tech reps over the last three years of ownership assist me on maintenance issues and none of them have ever commented on the battery being grounded to the firewall.

Battery is grounded to the same firewall ground lug that you ground the engine.

A couple of things to check:
- Do you ground the engine on the starter ground lug or under some greasy engine bolt? Try the starter ground lug if not there to see if engine start is better.
- Is the battery ground lead and engine ground lead the same gauge (#2 or #4)?
- Do you use airframe ground for your strobes? If so, run a separate ground wire to the firewall ground and see if that solves your problem.

Carl

strobes not working

What you are describing is a poor connection in your electrical system. When you are checking the voltage at the strobes, you need to check it under load. I would guarantee you are getting a significant voltage drop. You are also no doubt getting a voltage drop to the starter solenoid. Check all the connections for the power source to those items.

jask said:

I would definitely not use the aluminum firewall to conduct electricity. You should run the negative of the battery directly to the post where the engine ground connects. Otherwise full amps attempting to run the starter would be flowing through the firewall. It would hamper starter performance and might cause a fire.

Click to expand...

Could you elaborate on how a frame ground can cause a fire? Millions of cars have been produced that use frame grounds. Many ground to the block, but a good percentage ground directly to the frame. There is a separate ground strap from the frame to the block. Also, Aluminum is a very good electricity conductor, no less efficient than steel. Assuming your firewall is aluminum. Mine and most other aircraft are stainless steel.

Also, did you realize that a primary ground path for your starter runs through your aluminum engine block?

Larry

Tankerpilot75 said:

My question is: where should the battery ground be connected to the aircraft? If not to the firewall, then where?

i am not the builder but I am the second owner. It’s had several A&P/IAs work on it and a couple of EAA tech reps over the last three years of ownership assist me on maintenance issues and none of them have ever commented on the battery being grounded to the firewall.

Click to expand...

Like Carl and many others, I have a ground lug on the firewall. The Battery, Engine Ground strap and airframe gound terminal strip and firewall all are directly connected to this lug. I have a Whelan strobe setup using an airframe ground with no issues. I only used dedicated ground wires for avionics and intstruments or anything directly connected behind the panel, where I used shared grounds.

Larry

Ground

Larry, If you have a poor connection to ground anywhere at all, when current is flowing, the voltage drop that occurs over the bad connection goes into developing heat at that connection. If there is a flammable substance present and the current flow is large enough to generate enough heat, a fire will ensue. Also, when you make any ground connection to aluminum, I suggest using a conductive paste to both surfaces prior to attaching the electrical connector. If you are not aware, poor connections with aluminum wiring used in homes during the 1960's was the source of many fires.

The word thats missing from this Aluminum electrical discussion is "Corrosion", and almost all of that is from dissimilar metals ie your crimped connectors. We all know Aluminum is a great conduction; but Aluminum Oxide is a great insulator.

However, the key here is its not an immediate issue, but an insidious one (those '60s houses took a good few years before issues arose).

+1 on the single grounding bolt on the firewall for avionics, panel stuff, and Firewall fwd stuff.

+1 on paste for far away grounds - nothing wrong with that.

+1 on remembering when you have weird electrical issues that you didnt have just before, thinking ground connection first.

Bob,

I wanted better grounding for my RV-12 so while building (E-AB) I decided to purchase grounding blocks from B & C. I chose GB24/24 grounding blocks and installed them on both sides of the firewall. In addition to having a lug for the high current connections, it also has grounding terminals on both sides of the firewall ... so it great for creating a common grounding point to help with unwanted electrical "noise".

Having all those connections available was a little overkill so I cut down the B&C unit to make it a little smaller (could have made it even smaller for the RV-12). FWF the ground from the battery runs directly to the grounding lug as well as a ground for the engine. The links below are photos of what I did prior to adding the wiring.

http://2.bp.blogspot.com/-Rw--9hkOb40/VpCmiksL53I/AAAAAAAAK10/fRSUKOY7Bx0/s1600/DSC01226.JPG

http://4.bp.blogspot.com/-N_Zy3GZjsNY/VpCm0hxAJkI/AAAAAAAAK18/T5s58uzK7Cw/s1600/DSC01227.JPG

Happy building,

Screw posts vs fast tabs

FWIW, I decided I'd try to stay away from fast tabs as much as possible, and went with screw posts for everything I could - not totally possible, and just my choice for a totally secure connection.

As such I couldnt find grounding blocks with screw posts anywhere, so I made my own. New 1" copper pipe and some new 6-32 all thread from Lowes aviation aisle. Choose your length of pipe and flatten it; then tap it in as many places as you want and thread in the allthread, cut to the length you want (I used 3/4" so I can put a couple of terminals on each post). Soft solder the ends of the pipe and the backside of where the all thread is just shy of flush. Drill some bolt holes to secure it to the firewall and done. $10 and plenty of pipe and allthread left over for other projects. Buy beer with the left over money.

Oh yeah, make sure you clean up any residual solder flux as its corrosive, and clean up the copper block by dropping it in a glass of Coke for a few hrs.....

Bob, if you haven't read the Aeroelectric Connection, I'd strongly suggest getting and reading it before proceeding. Single point ground systems, while not absolutely required, can cure a host of ills.

More generally, misinterpreted anecdotes can lead to less than useful conclusions. A couple have surfaced in this thread. There isn't, and never has been, anything wrong with aluminum wire. In fact, it's a virtual certainty that your house (all our houses) has/have main feeders that are aluminum. The problem was contractors using the wrong *connectors*, either through ignorance or simple greed. (The outlets & switches that install fastest aren't compatible with aluminum, due to the attachment method.) Another is favoring screw terminals over (quality) Faston style terminals. Either will work and both are 'approved' method's, but with both properly dressed, some environments can actually put a screw terminal at greater risk. (Sorry, Mani.)

Charlie

charlie,
including my warrior had alum. wire to starter. after i replaced it with copper i didn't need a jump every time. but anyway............
i have read aero lectric many times and originally i built a battery tray fwf and i had my cables from batteries to grounds strictly by the book. then the question of operating temps of the earthx came up [several years ago] lipo was new and i didn't want heat so i moved the batteries and fat cables to the avionics bay, again all cables connected by the book.
THEN it turned out lipo is rated higher than lead acid , and finally the smoke issue with the batteries became a concern. an airtight box was way harder than moving the battery tray fwf AGAIN.all the holes are already there for mounting.
just thought maybe the way i had been doing it was overkill but apparently not so it will go back together the way bob n. would want it.

I feel your pain. Changing from al to copper was probably a good idea. But you could have had undersized al wire, or (more likely) corroded, high resistance terminators on the ends of the wire. Same thing happens with copper, but we're so tuned to 'conventional wisdom' that we blame the al, & dismiss the same problems with copper as 'time to replace the cable'. Not unlike an alt engine failure being blamed on inadequate auto engine quality, but we seem to just accept burned valves, worn cam lobes, defective crankshafts, etc, if they happen in 'aircraft' engines.

Resistance Wins

Jask, you were right. I checked both wires (positive and negative) going from the panel switch to the strobe power supply. Continuity on the ground side was excellent indicating my ground was good.

Power voltage on the positive side showed 12.6 volts with no load. It was obviously dropping significantly when I turned on the strobe and put current to the strobe box. Checked continuity on the positive wire running from the switch to the strobe and discovered 26 ohms resistance. . I bypassed that wire running a temporary wire from the switch to the strobe power supply (had no resistance) and IT WORKED!

That proved the positive wire from the switch to the power supply was the problem. Now comes the hard part - running a new wire from the switch on the panel to the strobe power supply behind the cargo compartment panel. Ugh!

Why it waited 8 years to have this problem I don’t know. I HATE RUNNING WIRES!!!

I apologize to Bob Noffs for borrowing his thread. I honestly thought my problem was ground related.

Tankerpilot75 said:

Jask, you were right. I checked both wires (positive and negative) going from the panel switch to the strobe power supply. Continuity on the ground side was excellent indicating my ground was good.

Power voltage on the positive side showed 12.6 volts with no load. It was obviously dropping significantly when I turned on the strobe and put current to the strobe box. Checked continuity on the positive wire running from the switch to the strobe and discovered 26 ohms resistance. . I bypassed that wire running a temporary wire from the switch to the strobe power supply (had no resistance) and IT WORKED!

That proved the positive wire from the switch to the power supply was the problem. Now comes the hard part - running a new wire from the switch on the panel to the strobe power supply behind the cargo compartment panel. Ugh!

Why it waited 8 years to have this problem I don’t know. I HATE RUNNING WIRES!!!

I apologize to Bob Noffs for borrowing his thread. I honestly thought my problem was ground related.

Click to expand...

Before running new wire why not try new connectors on each end? Do you have a connection mid-stream? It may be corroded.

no problem sam. i am almost done already fixing my rearrangement.