[VHFcontesting] DC Power Distribution
John D'Ausilio
jdausilio at gmail.com
Wed Aug 29 10:43:50 EDT 2007
One way to avoid the $140 relay is to visit your local boat store and
pick up the very nice rotary switches they carry for controlling
batteries and generators afloat. I've got a single-pole switch between
the vehicle electrical and rover bus, a 1/2/both rotary to select the
battery bank (I run two pairs of T-105s), and another 1/2/both to
select the bank to charge. Since I always run the banks in parallel
anyway, I think I might reconfigure after september to get rid of the
1/2/both stuff ..
These switches are generally in the $15-$25 range
de w1rt/john
On 8/29/07, Stephen Hicks, N5AC <n5ac at n5ac.com> wrote:
> 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 at contesting.com
> [mailto:vhfcontesting-bounces at contesting.com] On Behalf Of Stephen Hicks,
> N5AC
> Sent: Wednesday, August 29, 2007 09:15
> To: 'Matt Patterson'; vhfcontesting at 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 at contesting.com
> [mailto:vhfcontesting-bounces at contesting.com] On Behalf Of Matt Patterson
> Sent: Wednesday, August 29, 2007 06:42
> To: vhfcontesting at 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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