Oh and the other thing is that generators and power supplied work VERY well.
I also run two Honda EU2000i's with a 70A astron and a 50A 28V supply and
that works very well...
Steve
-----Original Message-----
From: vhfcontesting-bounces@contesting.com
[mailto:vhfcontesting-bounces@contesting.com] On Behalf Of Stephen Hicks,
N5AC
Sent: Wednesday, August 29, 2007 09:15
To: 'Matt Patterson'; vhfcontesting@contesting.com
Subject: Re: [VHFcontesting] DC Power Distribution
Great question ... Here's some things I've done that work and don't work:
1. Power cabling -- I have used everything from heavy guage gasoline-proof
wire I bought at Home Depot to the "thumper stereo" 0,4, and 8-guage wire.
Welding wire is another good option. I prefer to not use the wire at Home
Deopt because it tends to be less flexible (fewer strands). I would figure
your max current draw, then lookup the resistance/ft in this table and
calculate the end voltage at your amps and decide what you want to live
with. Some folks use "13.8" or "14" volts for their starting voltage ...
But if you are sitting on the side of the road operating and your alternator
is not putting out 13.8, you might be better to start lower. My
recommendation is to start your car, let it idle or drive it for 10 minutes
unitl the battery is charged and then take a voltage reading. Larger is
always better if you can stuff the wire out of sight. Use ohms/kft of
course
AWG Dia-mils TPI Dia-mm Circ-mils Ohms/Kft Ft/Ohm Ft/Lb
Ohms/Lb Lb/Kft *Amps MaxAmps
0000 459.99 2.1740 11.684 211592 0.0490 20402
1.5613 0.0001 640.48 282.12 423.18
000 409.63 2.4412 10.405 167800 0.0618 16180
1.9688 0.0001 507.93 223.73 335.60
00 364.79 2.7413 9.2657 133072 0.0779 12831
2.4826 0.0002 402.80 177.43 266.14
0 324.85 3.0783 8.2513 105531 0.0983 10175
3.1305 0.0003 319.44 140.71 211.06
1 289.29 3.4567 7.3480 83690 0.1239 8069.5
3.9475 0.0005 253.33 111.59 167.38
2 257.62 3.8817 6.5436 66369 0.1563 6399.4
4.9777 0.0008 200.90 88.492 132.74
3 229.42 4.3588 5.8272 52633 0.1970 5075.0
6.2767 0.0012 159.32 70.177 105.27
4 204.30 4.8947 5.1893 41740 0.2485 4024.7
7.9148 0.0020 126.35 55.653 83.480
5 181.94 5.4964 4.6212 33101 0.3133 3191.7
9.9804 0.0031 100.20 44.135 66.203
6 162.02 6.1721 4.1153 26251 0.3951 2531.1
12.585 0.0050 79.460 35.001 52.501
7 144.28 6.9308 3.6648 20818 0.4982 2007.3
15.869 0.0079 63.014 27.757 41.635
8 128.49 7.7828 3.2636 16509 0.6282 1591.8
20.011 0.0126 49.973 22.012 33.018
9 114.42 8.7396 2.9063 13092 0.7921 1262.4
25.233 0.0200 39.630 17.456 26.185
10 101.90 9.8140 2.5881 10383 0.9989 1001.1
31.819 0.0318 31.428 13.844 20.765
11 90.741 11.020 2.3048 8233.9 1.2596 793.93
40.122 0.0505 24.924 10.978 16.468
12 80.807 12.375 2.0525 6529.8 1.5883 629.61
50.593 0.0804 19.765 8.7064 13.060
13 71.961 13.896 1.8278 5178.3 2.0028 499.31
63.797 0.1278 15.675 6.9045 10.357
14 64.083 15.605 1.6277 4106.6 2.5255 395.97
80.447 0.2031 12.431 5.4755 8.2132
Voltage at amp = Voltage at Battery - (max current * Ohms/kft *
distance-in-feet / 1000)
If you figure, conservatively, 12.8v at the battery while at idle, 30feet to
your electronics and a max current draw of 70A, here would be your
voltage-at-amplifier values:
Battery: 12.8
AWG 0000: 12.70
000: 12.67
00: 12.64
0: 12.60
Two runs of 4: 12.54
4: 12.28
Two runs of 8: 12.14
8: 11.48
I use 0-guage because you can see that after 0, things start to fall off
more quickly, but two runs of 4-guage is almost as good. If you really have
13.8 at idle on your battery AFTER A CHARGE OF THE BATTERY IS COMPLETE, you
can add a volt to these. I believe today's alternators have a feedback
circuit that cuts them back after the battery is charged and I always
observe a drop after I've been driving a while and then sit at idle so it's
good to know what this true number that represents your idle-while-roving
voltage is.
2. Fusing ... I have had more issues with fuses than anything else in my
rover. The problems are many, but here are some of them: When the heat
rises in Texas, temps under the hood or in the back of my rover rise and
fuses pop sometimes when they shouldn't. I was told by someone that builds
ambulances that you should not fuse your main power line from the battery
back to the accessories. I originally had a 150 AMP fuse here, but have
removed it. I have tried several solutions including the large, ANL-style
fuses and found them to be absolutely awful. Sometimes the solder that
holds the fusable link to the case gets hot and the fuse fails prematurely.
Sometimes the holder and the fuse are not connected well and they heat up
and the fuse fails (again, solder breaks). I would strongly discourage
using these. If you are under 40A, I have used the square breakers with two
posts and two tabs on a metal can that you can get at the auto store. These
are inexpensive and they reset! So if something blows, you don't have to
disassemble the world...just wait a couple of minutes and it will come back.
I have also used the large blade fuses (see link below) and these seem to
have good contact, etc. Just stay away from those thumper-stereo-plexiglass
fuse holders...bad news
3. Tanner Electronics in Dallas sells the stereo-thumper-plexiglass
distribution boxes and I find these work well. Large metal block with hex
screws to connect to wire and then a plexiglass cover on top of that. No
issues found here.
4. Master cut-off. I prefer to have a master cut-off relay so that
equipment won't kill my car battery. After trying tens of solutions from
starter relays to other large relays, I have found a great solution. What I
have discovered is that many of the relays are not designed to handle
staying energized AND conducting 50A of DC at the same time. The larger
current relays are often designed for intermittient duty. I'll warn you
that they are expensive: A G9EA relay from Omron (Mouser part #
653-G9EA-1-B-CA-DC12). I bought mine over a year ago and paid $130 and they
are now something like $140. Yes, I know it's just a relay, but when I push
ON now, everything always comes on. If you've been doing this a while and
had failures in master switches at the wrong time, you know the
frustration... This relay will switch 150A at 120V 150x per minute so it's
not going to flinch with what I do to it. Read the specs:
http://www.omron.com/ecb/products/pdf/en_g9ea_ec.pdf
5. Alternator: If you want a heavy duty one, Load Boss in Dallas builds a
great alternator and has great service. I got a 275A alternator for my
chevy that is a drop-in replacement and it was about $500. The guy that
owns the place knows a lot about high-capacity DC systems and can do
anything you need also -- want to have two alternators with 12 and 24V or
two 12V alternators? They have all the stuff. Alterstart Systems in Dallas
both manufactures the Load Boss line and sells/services retail: (214)
330-5900 or www.4alterstart.com
6. Batteries are good and bad. They can help, but often they are more of a
pain. If you let them run down and then try to operate, they will drag your
whole voltage buss down. With very low internal resistance, if they are
low, they can draw HUNDREDS of amps along your main batter feed (I regularly
blow a 150A breaker if I have low batteries). The biggest problem I have
had is leaving any equipment on the back batteries when the car not running.
They get low and then everything has to play catchup when the car is
started. I think if you are going to use batteries to supplement things,
you have to do one of two things: 1) never run anything off the batteries
with the car off or you will have catch-up syndrome. 2) If you run things
off of the battery when the car is off, you will need more complex battery
management hardware. I am currently thinking of using multiple relays to
control the three connection points between the alternator, the batteries
and the equipment. If you run the batteries down, I think it would be best
to have a current-limiting charger recharge the batteries while the radio
equipment is now back on just the alternator. This sounds rather extreme,
but believe me nothing draws current from your electrical system like a
run-down battery connected to your buss and if you can't disconnect it, it
makes operating much less fun!
73,
Steve, N5AC
-----Original Message-----
From: vhfcontesting-bounces@contesting.com
[mailto:vhfcontesting-bounces@contesting.com] On Behalf Of Matt Patterson
Sent: Wednesday, August 29, 2007 06:42
To: vhfcontesting@contesting.com
Subject: [VHFcontesting] DC Power Distribution
Hi All,
I'm putting the final touches on my rover for September and I was wondering
if I could get some ideas on what other rovers use for DC power
distribution. I'm especially interested in what you use to distribute power
to your high power amplifiers.
73 Matt
W5LL
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