Wire size for big DC current
Garry P. Adkins
Hi.
I need to run a DC cable that will handle about 50A at 12
continuous (an hour or more).
It's to power a big power inverter to run some electronic
equipment. Currently I use Alligator clips to hook it
directly to the car battery. I'm needing a little more
permanent solution in my car (92 Ford Explorer), so I thought
I'd run a big cable from the battery (or starter relay)
through the firewall, and inside the molding to a compartment on
the back of the truck.
I'm concerned, however, about the length of the cable (I estimate
about 20 or so feet because I want to hide it in the molding).
Will a 4AWG copper wire (I'm specifically looking at a spool of
battery cable in a JC Whitney catalog) be sufficient for that
load and that distance?
Obviously I don't want to catch my car on fire from an overheated
cable...
I used to have a book that gave this type of data, but I seem to
have lost it. Any suggestions welcome.
Thanks!
Garry
p.s. I crossposted to rec.radio.amateur.misc and rec.radio.cb hoping
some people there might have experience running big cables for their
transmitter amps.
C.Orlando
On 11 Jan 1997 03:13:19 -0500, adk...@piranha.ianet.net (Garry P.
Adkins) wrote:
Check out the local "car stereo installers" around town, I've seen as
big as 1awg. stranded - for a car stereo amp, they really draw the
power. They might be able to give ya ideas. Might be even cheaper to
buy the wire from them, than to order it.
chris
chr...@airmail.net
Gary Coffman
In article <5b7i2v$i...@piranha.ianet.net> adk...@piranha.ianet.net (Garry P. Adkins) writes:
>I need to run a DC cable that will handle about 50A at 12
>continuous (an hour or more).
>
>It's to power a big power inverter to run some electronic
>equipment. Currently I use Alligator clips to hook it
>directly to the car battery. I'm needing a little more
>permanent solution in my car (92 Ford Explorer), so I thought
>I'd run a big cable from the battery (or starter relay)
>through the firewall, and inside the molding to a compartment on
>the back of the truck.
>
>I'm concerned, however, about the length of the cable (I estimate
>about 20 or so feet because I want to hide it in the molding).
>
>Will a 4AWG copper wire (I'm specifically looking at a spool of
>battery cable in a JC Whitney catalog) be sufficient for that
>load and that distance?
>
>Obviously I don't want to catch my car on fire from an overheated
>cable...
#4 AWG is safe at 50 amps. Temperature rise should not exceed
75 degrees Celsus for continous duty in an enclosed conduit
bundled with other cables of similar ampacity. Voltage drop for
a 50 amp draw across 20 feet of #4 will be 0.253 volt. That may
not be acceptable for your application. It wouldn't hurt to use a
larger wire. I'd suggest #0 or even #00. #0 would have less than
0.125 volt drop at 50 amps for a 20 foot run.
Note that connection losses have to be added to this. That
could add another couple of tenths of a volt drop at each
connection. That starts to become significant for nominally
12 volt equipment, which often becomes "squirrelly" if you
operate only slightly below 12 volts. If you intend to operate
with the engine off (I don't recomend that since you'd rapidly
discharge the battery and car batteries don't tolerate deep
discharge well), this becomes especially critical. Make sure
you choose low resistance connectors and install them properly.
Of particular concern is the type of fuse and fuse block
that you use at the battery (you *must* fuse this line at
the battery). Ordinary fuses and fuse holders can represent
an unacceptable voltage drop at this current draw. That is
especially true after they have been exposed to the elements
for a while. High end audio shops specializing in high power
auto audio installations carry special gold flashed fuses and
holders which will resist corrosion in the auto environment.
Make sure the holder clamps the fuse *tightly*. I'd recomend
the fuse and holder styles which *bolt* the fuse in place
rather than those which depend on spring pressure.
Gary
--
Gary Coffman KE4ZV | You make it, | Due to provider problems
Destructive Testing Systems | we break it. | with previous uucp addresses
534 Shannon Way | Guaranteed! | Email to ke...@radio.org
Lawrenceville, GA 30244 | |
ko4qc
Garry P. Adkins wrote:
>
> Hi.
>
> I need to run a DC cable that will handle about 50A at 12
> continuous (an hour or more).
>
> It's to power a big power inverter to run some electronic
> equipment. Currently I use Alligator clips to hook it
> directly to the car battery. I'm needing a little more
> permanent solution in my car (92 Ford Explorer), so I thought
> I'd run a big cable from the battery (or starter relay)
> through the firewall, and inside the molding to a compartment on
> the back of the truck.
>
> I'm concerned, however, about the length of the cable (I estimate
> about 20 or so feet because I want to hide it in the molding).
>
> Will a 4AWG copper wire (I'm specifically looking at a spool of
> battery cable in a JC Whitney catalog) be sufficient for that
> load and that distance?
>
> Obviously I don't want to catch my car on fire from an overheated
> cable...
>
> have lost it. Any suggestions welcome.
>
> Thanks!
>
> Garry
>
> p.s. I crossposted to rec.radio.amateur.misc and rec.radio.cb hoping
> some people there might have experience running big cables for their
> transmitter amps.
should be no problem.
Ko4qC
Gary
adk...@piranha.ianet.net (Garry P. Adkins) wrote:
yada yada yada
You can use #8 if you parallel in a 1 farad cap( found in most car
stereo places)by your amp. It will keep your voltage up between peaks.
"73" Gary KF9CM
Blake Bowers
tur...@wwa.com (Gary) wrote:
>yada yada yada
No, a #8 would be foolhardy. The cap might smoothout the DC a bit,
but it will do nothing for the amps...
L.S.Bradley
Garry P. Adkins <adk...@piranha.ianet.net> wrote in article
<5b7i2v$i...@piranha.ianet.net>...
>
> Hi.
>
> I need to run a DC cable that will handle about 50A at 12
> continuous (an hour or more).
>
>
which is a fine standed wire.( very similar to welding cable ) I have seen
it in sizes from #14 to #2/0.
Lee W1WXS
leeb@islc
SV/FUNDY
Dennis Grindrod
Boy I'd Like to see how your GOING TO FIT a 1 FARAD cap in your car! You
sure you Don't mean a 1 MIRCO-FARAD CAP?
--
Best Wishes & 73
Dennis A. Grindrod WA1EHF
* * * Lead, Follow Or Get Out Of The Way * * *
Gary <tur...@wwa.com> wrote in article <5b90gh$8...@kirin.wwa.com>...
: adk...@piranha.ianet.net (Garry P. Adkins) wrote:
:
: yada yada yada
:
: You can use #8 if you parallel in a 1 farad cap( found in most car
: stereo places)by your amp. It will keep your voltage up between peaks.
:
:
: "73" Gary KF9CM
:
:
:
:
:
Scott Darling
UN93B
Garry P. Adkins wrote:
>
> Hi.
>
> I need to run a DC cable that will handle about 50A at 12
> continuous (an hour or more).
>
> equipment. Currently I use Alligator clips to hook it
> directly to the car battery. I'm needing a little more
> permanent solution in my car (92 Ford Explorer), so I thought
> I'd run a big cable from the battery (or starter relay)
> through the firewall, and inside the molding to a compartment on
> the back of the truck.
>
> I'm concerned, however, about the length of the cable (I estimate
> about 20 or so feet because I want to hide it in the molding).
>
> Will a 4AWG copper wire (I'm specifically looking at a spool of
> battery cable in a JC Whitney catalog) be sufficient for that
> load and that distance?
>
> Obviously I don't want to catch my car on fire from an overheated
> cable...
>
> I used to have a book that gave this type of data, but I seem to
> have lost it. Any suggestions welcome.
>
> Thanks!
>
> Garry
>
> p.s. I crossposted to rec.radio.amateur.misc and rec.radio.cb hoping
> some people there might have experience running big cables for their
> transmitter amps.
Gary,
4 guage will handle 50 amps but you'll still see a voltage drop at 20
feet(a half a volt or so).
Just advice:
Pulling 50 amps from a stock explorer or any other car is risky.
Even though you may have an alternator rated at 100 amps, it will not
hold with a 50 amp load plus the rest of the cars loads. It may
initially but once it gets hot (AND IT WILL) you can expect 50A or so
from it. This is very very hard on the alternator.
Consider a dedicated high output alternator with another battery(deep
cycle).
later , Brett
Stan Aughenbaugh
According to my little referance guide, 4AWG wird has a resistivity of
.235 Ohm/1000ft @77degF......worke out to about .1v loss per 10 ft
+- 77degF. for 50A. That's I^2*R=W or 50^2 * .00235 ohm ~ 5 watts
continuously (if the connections are tight) shouldn't even get truly
warm. but... if you *double* each run, you get half the resistance,
about
1AWG and even less heat..
73,
--
Stan KF0NC
"90% of all statistics are made up"
Gary
bbo...@townsqr.com (Blake Bowers) wrote:
>tur...@wwa.com (Gary) wrote:
>>adk...@piranha.ianet.net (Garry P. Adkins) wrote:
>>yada yada yada
>>You can use #8 if you parallel in a 1 farad cap( found in most car
>>stereo places)by your amp. It will keep your voltage up between peaks.
>No, a #8 would be foolhardy. The cap might smoothout the DC a bit,
>but it will do nothing for the amps...
I run #8 wire on my amp( in conjuntion with a 1 Farad cap) it's about
500 watts out(SSB)....no probelms for 3 years.
Gary
Gary
"Dennis Grindrod" <D.Gri...@worldnet.att.net> wrote:
>Boy I'd Like to see how your GOING TO FIT a 1 FARAD cap in your car! You
>sure you Don't mean a 1 MIRCO-FARAD CAP?
NO!.....
>--
Trot your self down to your nearest car stereo store and you will find
one their about the size of a Fosters beer can.
> Best Wishes & 73
> Dennis A. Grindrod WA1EHF
>* * * Lead, Follow Or Get Out Of The Way * * *
>Gary <tur...@wwa.com> wrote in article <5b90gh$8...@kirin.wwa.com>...
>: adk...@piranha.ianet.net (Garry P. Adkins) wrote:
>:
>: yada yada yada
>:
>: You can use #8 if you parallel in a 1 farad cap( found in most car
>: stereo places)by your amp. It will keep your voltage up between peaks.
>:
>:
>: "73" Gary KF9CM
>:
>:
>:
>:
>:
Garry P. Adkins
>GPA>Obviously I don't want to catch my car on fire from an overheated
>GPA>cable...
>
>Slowly breaking the cable, hot terminations, and disappearing insulation
>is more likely to cause a cable fire.
Thanks to everyone for giving me good advice! Several people
mentioned things that I had not thought about.
Here's a summary for those interested:
1) Visit a car stereo supply store for cable, etc. They're cheaper
than most places, and are familiar with this type of install.
2) Make sure the cable doesn't flex, a flex point can cause a fire.
3) Run both pos & neg cables, don't depend on the frame for high current
4) Fuse BOTH leads near the battery connection point (if the ground strap
were to break, my starter's 200 amps will go through my cable and
my car will become a smoldering heap of melted plastic)
5) use some sort of quick-disconnect near the end so that I can rapidly
disconnect if I have a catastrophic failure of some type.
All very good advice, and I hadn't considered #1, #3 & #4.
Thanks!
Garry
Tony Antoniou
Garry P. Adkins <adk...@piranha.ianet.net> wrote in article =
<5bf5gs$h...@piranha.ianet.net>...
> >GPA>Obviously I don't want to catch my car on fire from an overheated
> >GPA>cable...
> >
insulation
> >is more likely to cause a cable fire.
> Thanks to everyone for giving me good advice! Several people
> mentioned things that I had not thought about.
> Here's a summary for those interested:
> 1) Visit a car stereo supply store for cable, etc. They're cheaper
> than most places, and are familiar with this type of install.
Very true.
> 2) Make sure the cable doesn't flex, a flex point can cause a fire.
Not true. As long as the cable is not coiled up or have any kinks around =
sharp corners, there is no reason why the flexible cables aren't safe. =
I've been running 8 gauge in my setup for my 2 audio amps (about a 4m =
run I think) and I haven't had any problems at all (the amps draw 45A =
all together).
> 3) Run both pos & neg cables, don't depend on the frame for high =
current
Not true again. The ideal grounding for any equipment is the shortest =
(and therefore, closest) point on the vehicle's chassis. Therefore, it's =
unnecessary to run both pos & neg to the battery. I've done many =
installations for people, as well as my own vehicle of course, and have =
never experienced any problems. Anything over 45A would result in me =
using 4 gauge cable instead to supply power to the amplifiers and once =
again, using the vehicle's chassis as an earthing point. Don't know how =
well/poorly made the American cars are up there but I'd imagine that =
they're every bit as good as the Australian and other imported cars! =
This is perfectly safe, and there's no chance of any failures as such.
> 4) Fuse BOTH leads near the battery connection point (if the ground =
strap
> were to break, my starter's 200 amps will go through my cable and
> my car will become a smoldering heap of melted plastic)
In the case of just wiring the pos lead only as I suggest, just fuse the =
positive lead. That fuse is definitely imperative so that point is well =
suggested and should be well heeded.
> 5) use some sort of quick-disconnect near the end so that I can =
rapidly
> disconnect if I have a catastrophic failure of some type.
Yep.
--=20
Adios,
LarZ
----------------------- TAMA - The Strongest Name in Drums =
-----------------------
Blake Bowers
tur...@wwa.com (Gary) wrote:
>bbo...@townsqr.com (Blake Bowers) wrote:
>>No, a #8 would be foolhardy. The cap might smoothout the DC a bit,
>>but it will do nothing for the amps...
>I run #8 wire on my amp( in conjuntion with a 1 Farad cap) it's about
>500 watts out(SSB)....no probelms for 3 years.
Congratulations.
I have Sheriff offices that have run #12 wire for light bars, sirens,
and radios, for years. When they finally burn up, they come to me,
and have our people do the installs from then on.
Do something professionaly, do it right, the first time, and you will
not have problems.
Run #8 wire, for a 50 amp load, 20 feet, and you WILL have
problems.
The Cap makes no difference.
Gary Coffman
In article <5bepmh$o...@kirin.wwa.com> tur...@wwa.com (Gary) writes:
>bbo...@townsqr.com (Blake Bowers) wrote:
>>tur...@wwa.com (Gary) wrote:
>>>yada yada yada
>>>You can use #8 if you parallel in a 1 farad cap( found in most car
>>>stereo places)by your amp. It will keep your voltage up between peaks.
>
>>but it will do nothing for the amps...
>
>I run #8 wire on my amp( in conjuntion with a 1 Farad cap) it's about
>500 watts out(SSB)....no probelms for 3 years.
Is that 500 watts continous single tone or PEP? The application for which
wire gauge was requested was for an *inverter*, not an amplifier with a
speech waveform duty cycle. That's a very different thing. The difference
between speech PEP and single tone is typically 8:1, so what works on
your 500 watt PEP amp would only serve a 62.5 watt single tone continous
load such as an inverter. The capacitor would serve no purpose since the
peak to average ratio is 1:1.
Gary Coffman
In article <01bc019b$28ab39c0$772574cf@353135824worldnet> "Dennis Grindrod" <D.Gri...@worldnet.att.net> writes:
>Boy I'd Like to see how your GOING TO FIT a 1 FARAD cap in your car! You
>sure you Don't mean a 1 MIRCO-FARAD CAP?
No problem fitting a 1 farad capacitor in a car, even a model car.
Panasonic will sell you one about the size of a lithium watch battery.
My camcorder uses one instead of a memory battery.
It won't do anything to keep a 50 amp current from burning up a too
light gauge wire, however.
Gary
ga...@ke4zv.atl.ga.us (Gary Coffman) wrote:
I used #8 wire because as a Ham I use SSB. 500 watts peak (@50%
eff=1000 watts DC input peak )1000 dc watts = 73.52 amps @ 13.6VDC.
Now if I were to use CW with a brick on the key, granted those wires
will get little toasty even though #8 wire is rated at 73 amps
countinous current in individual runs.
I use a 1 Farad cap to keep the voltage up to 13.6. The cap is located
only a few inches from the amp and has the same basicly the same
effect as mounting a battery in the same location.
Using the 8 to 1 comparison it still runs cool.
"73" Gary KF9CM
Michael White
> >Boy I'd Like to see how your GOING TO FIT a 1 FARAD cap in your car! You
> >sure you Don't mean a 1 MIRCO-FARAD CAP?
1 farad, 1 volt caps are available off the shelf. Fill up the trunk of
your car and off you go!
My opinions are my own, not my employer's.
Thomas Brockdorf
>
>I need to run a DC cable that will handle about 50A at 12
>continuous (an hour or more).
>
>It's to power a big power inverter to run some electronic
>equipment. Currently I use Alligator clips to hook it
>directly to the car battery. I'm needing a little more
>permanent solution in my car (92 Ford Explorer), so I thought
>I'd run a big cable from the battery (or starter relay)
>through the firewall, and inside the molding to a compartment on
>the back of the truck.
>
>I'm concerned, however, about the length of the cable (I estimate
>about 20 or so feet because I want to hide it in the molding).
>
>Will a 4AWG copper wire (I'm specifically looking at a spool of
>battery cable in a JC Whitney catalog) be sufficient for that
>load and that distance?
>
>
>I used to have a book that gave this type of data, but I seem to
>have lost it. Any suggestions welcome.
>
>Thanks!
>
>Garry
>
>p.s. I crossposted to rec.radio.amateur.misc and rec.radio.cb hoping
>some people there might have experience running big cables for their
>transmitter amps.
Garry:
I posted a reply here, but for some reason, it did not show up.
I am a State of Wisconsin Certified Master Electrician.
I work with sizing wire for the load it will carry, almost every day.
If I was making this installation in my car, I would use #8.
The National Electrical Code says #8 can carry 50 Amps, no problem.
If you are worried about voltage drop, use the #4.
Some battery cables, as original equipment on the car, are only #4.
Just be sure to make a good secure connection. Don't use alligator type clips.
73 de Thomas W9FL
Elite
In article <32DAC0...@wwdc.com>, sdar...@wwdc.com says...
> &
>
Anything bigger will last longer, be safer, work better, and
cause less problems. When in doubt, use bigger wire, it will
never hurt, smaller will. End of story.
Tony Antoniou
Blake Bowers <bbo...@townsqr.com> wrote in article =
<5bfv1q$p...@tofu.alt.net>...
> I have Sheriff offices that have run #12 wire for light bars, sirens,
> and radios, for years. When they finally burn up, they come to me,
> and have our people do the installs from then on.
>=20
> Do something professionaly, do it right, the first time, and you will
> not have problems. =20
Agreed.
> Run #8 wire, for a 50 amp load, 20 feet, and you WILL have=20
> problems.
Only in terms of voltage drop and a warm cable. The latter isn't a =
really big problem but I'd go the #4 cable anyway for safety's sake. I =
usually limit the cable's rating by 10% less than rated for the sake of =
safety. So in the case of #8, 45A is the most I'd put through it, for =
example. It's more paranoia than anything, as I'm sure they wouldn't put =
a 50A rating on the cable for a joke.
> The Cap makes no difference.
True.
Gary Coffman
In article <5bgki0$l...@kirin.wwa.com> tur...@wwa.com (Gary) writes:
>ga...@ke4zv.atl.ga.us (Gary Coffman) wrote:
>>In article <01bc019b$28ab39c0$772574cf@353135824worldnet> "Dennis Grindrod" <D.Gri...@worldnet.att.net> writes:
>>>sure you Don't mean a 1 MIRCO-FARAD CAP?
>
>>Panasonic will sell you one about the size of a lithium watch battery.
>>My camcorder uses one instead of a memory battery.
>
>>It won't do anything to keep a 50 amp current from burning up a too
>>light gauge wire, however.
>
>eff=1000 watts DC input peak )1000 dc watts = 73.52 amps @ 13.6VDC.
>Now if I were to use CW with a brick on the key, granted those wires
>will get little toasty even though #8 wire is rated at 73 amps
>countinous current in individual runs.
#8 bare copper is rated at 73 amps in *free air*. Insulated wire
in a confined space, IE a conduit or wiring channel (as the orginal
questioner said he was going to run it), is rated at 46 amps continous.
But that rating is the current for which the wire won't exceed 100 degrees
Celsus. Now that's the temperature of boiling water, and I don't suggest
running thermoplastic insulated wire that hot for long periods. The
insulation will get brittle, and you'll wind up with a short and a fire.
Because of the duty cycle of your HF amp, you're only drawing an average
current of about 10 amps, so #8 is fine for your use. What we should be
more concerned about is voltage drop in a mobile setup. For a continous
load, using #4 is the right way to deal with that. For a load which only
needs a transient high current, such as your amp, the capacitor can deal
with peak demands.
>I use a 1 Farad cap to keep the voltage up to 13.6. The cap is located
>only a few inches from the amp and has the same basicly the same
>effect as mounting a battery in the same location.
Well not quite, but for supplying energy during brief voice peaks,
it does keep the voltage from sagging much, and is a good solution
for your installation. It doesn't help at all for a continous load.
>Using the 8 to 1 comparison it still runs cool.
You bet, and that's *why* it runs cool. Your time averaged draw is
only about 10 amps.
BTW, the Panasonic 1 farad capacitor I mentioned above wouldn't be
a good choice for your installation. It has too high an internal
impedance to supply the peak current demand of your amp (though it
is great for supplying microamps to keep a memory alive for weeks).
The beer can size units have a low enough internal impedance to work.
(And don't ever short a charged one, the fireworks are spectacular.)
alc...@ix.netcom.com
Gary Coffman wrote:
> #8 bare copper is rated at 73 amps in *free air*. Insulated wire
> in a confined space, IE a conduit or wiring channel (as the orginal
> questioner said he was going to run it), is rated at 46 amps continous.
> But that rating is the current for which the wire won't exceed 100 degrees
> Celsus. Now that's the temperature of boiling water, and I don't suggest
> running thermoplastic insulated wire that hot for long periods. The
> insulation will get brittle, and you'll wind up with a short and a fire.
>
Amen. I worked on a project where power lines were routed under flooring in a shelter.
A faulty circuit breaker did not open when the current exceeded its trip rating. About
50 amps. flowed though the wire; current was limited by the source impedance. No fires
started, but....the insulation decomposed and created cyanide gas. A technician working
in the area was overcome, but was saved. Needless to say, all of the wire was replaced
with insulation which did not produce toxic fumes under such conditions.
Al
Garry P. Adkins
>I sure hope you have a dedicated high output alternator with another
>battery.
Nah. Just a regular alternator.
>Pretty soon junction temps will get critical and GAME OVER.
>After this its time to buy a new alternator.
I'm hoping that the connection direct to the battery will help
ease this burden a lot. When I was testing it on my explorer,
firing up the inverter (when connected directly to the battery
vi big clips for testing) didn't have any noticible effect on
the car's idle over a several minute time period.
i.e. I had the car running, fired up the inverter, and then
put a 450W load on the inverter. The idle didn't appear
to drop any at all.
Anyone else try this?
Thanks!
Garry
Jason Lavoie
"Dennis Grindrod" (D.Gri...@worldnet.att.net) writes:
> Boy I'd Like to see how your GOING TO FIT a 1 FARAD cap in your car! You
> sure you Don't mean a 1 MIRCO-FARAD CAP?
I see the humour, but yes, you can fit a 1 farad cap in a car.. I used to
have three of them, they were about the size of coffee cans.
a micro-farad will fit on your finger tip..
Jason Lavoie
--
DJ/Car audio tech/electronics nut
Jason Lavoie
Scott Darling (sdar...@wwdc.com) writes:
> Alot of bs on this one, foresure.
>
> Acording to the Ontario Hydro electrical safety code book. You need #6
> this will do @ 50 amps for a 23.4 feet. #8 is only good for 14.7 feet
> but because all wire is at least 15% over rated you could probably get
> by with it for a non continuous load. But why take the chance? Use #6
> and sleep well. Any bigger wire is overkill and a waste of money.
> end of story
keep in mind that this is DC and usually requires thicker wire.
Jason
Brett Collins
I sure hope you have a dedicated high output alternator with another
battery.
a stock charging system is just asking for trouble. Just because
an alternator is rated at 100 A doesn't mean it will deliver 100 A
for an hour. If you try this it will get REALLY hot, as it does
output current will drop due to the increased resistance in the stator
and the rotor windings.
Pretty soon junction temps will get critical and GAME OVER.
After this its time to buy a new alternator.
Later, Brett
Gary Coffman
In article <5bm78e$e...@piranha.ianet.net> adk...@piranha.ianet.net (Garry P. Adkins) writes:
>>I sure hope you have a dedicated high output alternator with another
>>battery.
>
>
>>After this its time to buy a new alternator.
>
>ease this burden a lot. When I was testing it on my explorer,
>firing up the inverter (when connected directly to the battery
>vi big clips for testing) didn't have any noticible effect on
>the car's idle over a several minute time period.
>
>i.e. I had the car running, fired up the inverter, and then
>put a 450W load on the inverter. The idle didn't appear
>to drop any at all.
With modern computerized engine controls, idle shouldn't change.
It isn't like the old carburetor days when there was a mechanical
idle screw. The computer just lengthens the duration of the fuel
injector pulses to compensate for the extra loading.
But if the alternator can't make up the charge you're drawing
from the battery, you'll eventually totally discharge the battery,
even with the engine running. So the battery can only help for
*short duration* discharges. For a continous load, the alternator
ultimately has to supply all the current. Operating the alternator
flat out *continously* is beyond its design specification. It will
overheat, and it will fail.
Modern vehicles have higher cpacity alternators than only a few
years ago when 35 amps was a standard alternator rating. Production
vehicles typically have a 65 amp alternator today. But it isn't
intended to supply 65 amps *continously*. The manufacturers still
offer "police" packages with higher capacity alternators, often
90 amps. That's large enough to handle a continous 50 amp load.
Try your test for a few hours, with headlights on, air conditioner
running, radio blaring, etc, and see if the alternator gets hot
and if the battery retains full charge. If the battery stays up,
and you can hold your hand on the alternator at the end of the
test, then things should be Ok (though you should really run the
test in July so that cooling air for the alternator will be at
summer ambient).
Elite
In article <5bm78e$e...@piranha.ianet.net>, adk...@piranha.ianet.net says...
>
>>I sure hope you have a dedicated high output alternator with another
>>battery.
>
>Nah. Just a regular alternator.
>
>
>>Pretty soon junction temps will get critical and GAME OVER.
>>After this its time to buy a new alternator.
>
>I'm hoping that the connection direct to the battery will help
>ease this burden a lot. When I was testing it on my explorer,
>firing up the inverter (when connected directly to the battery
>vi big clips for testing) didn't have any noticible effect on
>the car's idle over a several minute time period.
>
>i.e. I had the car running, fired up the inverter, and then
>put a 450W load on the inverter. The idle didn't appear
>to drop any at all.
>
>
>
>Thanks!
>
>Garry
>
is controlled by the computer, which will automatically
open the throttle as much as it has to to keep the idle
speed from dropping.
SrBwlzalot
<<Not true. As long as the cable is not coiled up or have any kinks around
=
sharp corners, there is no reason why the flexible cables aren't safe. =
I've been running 8 gauge in my setup for my 2 audio amps (about a 4m =
run I think) and I haven't had any problems at all (the amps draw 45A =
all together).>>
On the contrary, the statement is true to a degree. One definately
wouldn't want the cable to bend around anything that may rub on the outer
jacket...I think that's what he meant.
<<Not true again. The ideal grounding for any equipment is the shortest =
(and therefore, closest) point on the vehicle's chassis. Therefore, it's =
unnecessary to run both pos & neg to the battery. I've done many =
installations for people, as well as my own vehicle of course, and have =
never experienced any problems. Anything over 45A would result in me =
using 4 gauge cable instead to supply power to the amplifiers and once =
again, using the vehicle's chassis as an earthing point. Don't know how =
well/poorly made the American cars are up there but I'd imagine that =
they're every bit as good as the Australian and other imported cars! =
This is perfectly safe, and there's no chance of any failures as such.>>
This may be "ideal" for stereo, but not for transmitting amps. The battery
acts as a filter. Grounding the negative wire of a radio or amp to
anywhere other than the battery can and usually will result in squeal and
SWR problems...especially in higher power demand situations.
Another note....these suggestions of large capacitors that are used in
stereo applications are also not practical for transmitter amps. There is
no substitution for amperage supply, battery capacity, and proper wire
size. The only things that stereo and tx amps may share is the fusing
devices and power cable design. Don't pinch on power leads, it will show
(be heard). Running something along the lines of a DX500? Then be smart,
and use 4ga cable with HIGH number of strands.
William