Another EE question - - grounding

[[email protected]]

Using three batteries, I have three "-" battery wires running to a negative terminal strip all "jumped on the terminal input side. Is it also best to ground the "-" terminal strip to the largest metal mass in the glider such as the elevator/aileron yoke?

Thanks.

Ben

[Tom Gardner[_2_]]

wrote:
>
> Using three batteries, I have three "-" battery wires running to a negative terminal strip all "jumped on the terminal input side. Is it also best to ground the "-" terminal strip to the largest metal mass in the glider such as the elevator/aileron yoke?

I'm not going to answer that question since it is based on a
fallacy: the concept of "ground" is, except in important but
limited circumstances, a mere concept not a reality.

Arguably the most useful technique is to consider where the
current will flow and where voltage drops will be apparent.
And answering that requires knowledge of not only "what's
connected to what", but also the detailed wiring loom between
each component.

Note that the answers will be different depending on both
the magnitude of the current and also how fast the current
is varying. The latter is most clearly apparent when
considering antennas, RF and transient spikes caused by
pulsed loads.

I'm sure others will give you a more helpful answer.

[JJ Sinclair[_2_]]

Hi Ben,
Well, I'm not an EE, but I have been working on our glass toys as an A&P since '76. It won't hurt anything to ground all batteries to the yoke. Glasflugal did just that to help prevent noise in the radios used back in the day.. Make sure the ground wires are big enough. I once traced the ground in a 2 place glider to a single 20 gage wire. Also, I don't like crimp-on terminals, solder is better, but secure all leads close to the terminal because floppy wires will eventually break at the end of the solder joint. This happened to me in out ASH-25 because the factory battery plug & fuse was loose and failed after 2 years flying. We were left with nothing, not even a vario. If you don't think you rely on all our modern instruments, try turning everything off and fly 50 miles in silence. The thing I missed the most was my vario audio. Good reason to have 2 batteries, one big enough to last 4 hours with a smaller backup wired through their own master switch.
Hope this helps,
JJ

[Eric Greenwell[_4_]]

On 4/30/2013 5:54 AM, JJ Sinclair wrote:
> Also, I don't like crimp-on terminals, solder is better, but secure
> all leads close to the terminal because floppy wires will eventually
> break at the end of the solder joint.

Learning to make a good crimp connection is easier than learning to make
a good solder connection, and the crimp connection will be more
reliable. The wire breaking on a soldered wire is common, as the solder
makes a high stress area where it stops, even it done properly.

In a "pure" glider, however, the vibration is generally so low, you
might not notice the difference. In a motorglider, you will notice the
difference.

Even if the reliability were the same, I'd prefer the crimp method for
it's speed and ease.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

[JJ Sinclair[_2_]]

On Tuesday, April 30, 2013 3:47:47 AM UTC-7, wrote:
> Using three batteries, I have three "-" battery wires running to a negative terminal strip all "jumped on the terminal input side. Is it also best to ground the "-" terminal strip to the largest metal mass in the glider such as the elevator/aileron yoke?
>
>
>
> Thanks.
>
>
>
> Ben

If you use crimp-on terminals, get a good crimping tool that holds the outside radius constant while forcing a prong into the crimp and rolls the split into the joint forcing it against the outside radius with the wire in between. Don't use the cheep Wall-Mart crimpers that just smash top and bottom together.
JJ

[Eric Greenwell[_4_]]

On 5/1/2013 5:45 AM, JJ Sinclair wrote:
> On Tuesday, April 30, 2013 3:47:47 AM UTC-7,
>> Ben
>
> If you use crimp-on terminals, get a good crimping tool that holds
> the outside radius constant while forcing a prong into the crimp and
> rolls the split into the joint forcing it against the outside radius
> with the wire in between. Don't use the cheep Wall-Mart crimpers that
> just smash top and bottom together. JJ

What he said. It's worthwhile spending $30-$50 for a good crimping tool
like that. It will serve you well for your glider, trailer, car, and
other wiring uses.

This advice applies to other connectors you might use, like the
Powerpole type many people use on their batteries. The larger the
contact, the more difficult it becomes to make good soldered connection.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

[[email protected]]

On Tuesday, April 30, 2013 6:47:47 AM UTC-4, wrote:
> Using three batteries, I have three "-" battery wires running to a negative terminal strip all "jumped on the terminal input side. Is it also best to ground the "-" terminal strip to the largest metal mass in the glider such as the elevator/aileron yoke?
>
>
>
> Thanks.
>
>
>
> Ben

Ben,

'Grounding' the minus wires to metal structures was (and still is in some cases) used as a way of saving wire and reducing circuit resistance. Back in the day when most electronics devices were built on metal chassis, it made a lot of sense to eliminate half the wiring by using the chassis itself as the 'return' portion of the circuit. However, this practice has no relevance in modern gliders, as there is very little metal anyway, and what metal there is is not usually located conveniently.

The very best way of handling multiple battery setups is to use a twisted-pair cable from each battery to a common location, where the minus/return wires should be tied together to the minus side of the power distribution bus.. The plus and minus wires from each battery should be sized the same, as any electrons going out of a particular battery must come back to the battery via the minus wire. In general, the larger the wire size, the better off you are (up to the point where wire size/weight/flexibility become an issue, of course). The twisted-pair technique is a very effective way of suppressing RF noise problems, and twisted-pair cables can be fabricated very easily using regular wire and a cordless drill (a good twisted-pair cable will consume about twice the wire for a given length though).

Hope this helps,

Frank (TA)