Electrics questions
Duncan Mould - 2/2/10 at 11:38 PM
Wondered if anyone could give me some quick definitive answers to the following questions.
Explain the term Earth return and its advantages?
Explain the term Insulated return and its advantages?
And what are their limitations.
In lay man's terms.
This is the place to gain common sense answers I find.
Madinventions - 3/2/10 at 12:08 AM
In a car scenario:
Earth return: 12V feed from battery to headlight (for example), the other side of the headlight bulb is connected to chassis (earth) which is
connected to battery negative. All the current flows through the chassis.
Insulated return: As above, but other side of headlight bulb is connected to the battery negative with a separate insulated wire instead. The chassis
is normally connected to the battery negative terminal but all the current flows through the wire - not the chassis.
Everyone knows about specifying the correct size of wire to carry the current on the positive side, but remember that this current also flows through
the negative wire/earth as well. Therefore, earth (chassis) is generally used for large current items. Low current items (ECU, stereo etc) are often
connected with insulated earths directly back to the battery as this can help minimize interfence from the large currents flowing through the
chassis.
That's a simple take on it anyway. Earthing becomes a bit of a black art when it comes to very sensitive items like audio recording studios....
Ed.
Edit: Picture, thousand words etc etc:
Earth types
[Edited on 3/2/10 by Madinventions]
Fatgadget - 3/2/10 at 07:41 AM
Interesting questions.Soo which system is the most efficient?
Or is it a case of 6 of one, half a dozen of the other?
[Edited on 3/2/10 by Fatgadget]
Angel Acevedo - 3/2/10 at 08:04 AM
No Fatgadget,
You misunderstood, itīs the other way around.
On a serious note though,
A large load return still may carry enough punch (Voltage Differential or drop) to cause damage so you short it ASAP to Gnd to minimize risk.
AA
Fatgadget - 3/2/10 at 09:13 AM
^^
Is that what's refered to as a 'crowbar'?
BenB - 3/2/10 at 12:17 PM
quote:
Originally posted by Fatgadget
^^
Is that what's refered to as a 'crowbar'?
Nope, a crowbar is an over-voltage protection device for a PSU.
I'd just attach everything to earth via the chassis (unless it's a GRP monocoque 
), if you're installing sensitive ICE your engine
isn't loud enough
Now if we're talking black magic we're presumably talking ground loops..... They suck big time.
Madinventions - 3/2/10 at 01:47 PM
I found that my Megasquirt ECU was less tempramental when the grounds were connected directly back to the battery.
In car entertainment for tintops usually show up bad earths as whistles and clicks - the entertainment in the Mojo is the right foot (although I do
use an iPod now and again!).
Recording studio earths can be a total PITA although it's getting easier now - I just rewired mine with fibre optic cables and it's now
totally digital Just don't get me started on RF earths...
Ed.
