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Author Topic: Power Cable Help  (Read 6582 times)
W8JX
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« Reply #15 on: March 23, 2011, 05:08:41 PM »

I am up to speed, Many go crazy with wire size just like they act like 1 db is a deal killer in line loss on HF too. As far as amp draws of radios, that is a nominal rating and is always higher than radio actually uses. It is kinda a CYA in that if rated 21 amp a radio can draw 17 or 19 and still be in spec. As far as efficiency, when I tested my 570, it draw a little over 2 amps in receive and 17 at 100 watts out so 17- 2 = 15 and 15 x 13.8 = 207 so that = 48.3% which is about right. Anyway getting back to wire size, you will not get one more DB or signal or radio performance with over sized wire. 10 is more than enough here but there will always be those that think otherwise just like those that feel hard line is a must for HF feed line runs too. If it makes you feel good fine but is it really needed? No.
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K0BG
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« Reply #16 on: March 23, 2011, 06:16:11 PM »

The question still remains, John, have you actually measured the current draw?
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K1CJS
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« Reply #17 on: March 24, 2011, 03:20:05 AM »

Have you tested your 570 on a simple key down transmit--or when actually transmitting?  When modulating, the radio can and does draw more power, and the voltage drop from insufficient sized wire is what causes bad audio--distortion--just as overdriving the rig will.

Sometimes those extra few tenths of an amp DO make a difference. 
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W8JX
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« Reply #18 on: March 24, 2011, 05:40:56 AM »

Have you tested your 570 on a simple key down transmit--or when actually transmitting?  When modulating, the radio can and does draw more power, and the voltage drop from insufficient sized wire is what causes bad audio--distortion--just as overdriving the rig will.

Sometimes those extra few tenths of an amp DO make a difference. 

The "key down" transmit was tried CW and RTTY and difference was negligible. As far as voltage drop causing problems it is going to take a lot more than a .5 or .8 volt drop to cause problems. The funny part of all of this is that a cars electrical system is not all that stable (ie not like your regulated supply at how) and if radios were as sensitive to voltage as some would lead you to believe,  very few would be able to run mobile successfully. One trick I use and even use at home is I use at least 100,000ufd of electrolytic capacitance in parallel with power source and load. This stabilizes voltage for unit and reduces average power draw on feed which intern reduces any feed line loss. While some might argue the merit of this I have a Astron RS20 that is about 20 years old now with 1000's of hours of hard use on it that I used 24/7 until changing to a 30 amp switch on half its size and 1/3 its weight. That old supply powered a few different HF radios over the years and a VHF/UHF rig too as same time (though I only xmitted on one at a time) and never had a failure. It has had a large cap on it though during this time. Many would say that a RS35 would be needed here to be reliable but such is not the case. Many promote brute force while I use a more logical approach when possible.
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W8JX
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« Reply #19 on: March 24, 2011, 05:45:14 AM »

The question still remains, John, have you actually measured the current draw?

On my rigs yes and none were close to even 20 amps except a old TS 140 on modded years ago for mobile to put out over 150 watts. It drew about 25 amps and used it from many years without issue and with stock power cable (with 25 amp fuses) in mobile too
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KC8IUR
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« Reply #20 on: March 24, 2011, 06:48:26 AM »

15' of powerline is on the short side for anything but a center hump mount. To get to the back seat in my Tundra would need more than 15'.
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K0BG
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« Reply #21 on: March 24, 2011, 08:16:13 AM »

Eric, I never measured the overall length when I did the install in my Ridgeline. I know I bought 60 feet of #2 welding cable, and once I got everything in, it seems to me I had about 12 or so feet left. There's also a second battery, which sits on the right side of the trunk, so about 10 feet was used for that connection. I guess it is about 18 feet from the battery to the amp. The long-term voltage drop is just under .5 volts, so the guess is fairly close.

Measured with a Fluke 353, the IC-7000 draws almost as much current at 65 watts out (19 amps), as it does with 100 (22 amps).
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K1CJS
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« Reply #22 on: March 24, 2011, 09:37:16 AM »

The "key down" transmit was tried CW and RTTY and difference was negligible. As far as voltage drop causing problems it is going to take a lot more than a .5 or .8 volt drop to cause problems. The funny part of all of this is that a cars electrical system is not all that stable (ie not like your regulated supply at how) and if radios were as sensitive to voltage as some would lead you to believe,  very few would be able to run mobile successfully....

You're right--the car electrical system is NOT that stable, and THAT is why you should use larger cable.  Voltages do vary widely when different auto systems come on and go off.  Alternators can't pick up the drop in voltage instantly.  That is why you want the least loss in the wiring, and why some people go the route of a second battery.

In any event, I've said all I can without pushing the issue, and I'm not going to start tossing words either.  Believe what you want to--until something happens that makes you see the light.
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W8JX
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« Reply #23 on: March 24, 2011, 12:18:05 PM »

15' of powerline is on the short side for anything but a center hump mount. To get to the back seat in my Tundra would need more than 15'.

As the "crow flys" it is about 9 feet or less from battery to back seat and 15 would do it easy unless you are taking the "long path" routing here.
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W8JX
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« Reply #24 on: March 24, 2011, 12:26:14 PM »

You're right--the car electrical system is NOT that stable, and THAT is why you should use larger cable.  Voltages do vary widely when different auto systems come on and go off.  Alternators can't pick up the drop in voltage instantly.  That is why you want the least loss in the wiring, and why some people go the route of a second battery.

And bigger cable is going to make it more stable? Brute force will not work here but a little theory and logic by using big electrolytic cap at load will stabilize voltage under load that no cable size and alternator can do on its own.


In any event, I've said all I can without pushing the issue, and I'm not going to start tossing words either.  Believe what you want to--until something happens that makes you see the light.

It is not a question of believing it is a question of practice and theory. I saw light long ago and use caps to stabilize voltage under load in mobile while you cling to bigger wire as cure all here. Put your big wire  solution on a scope watching power feed while talking and then mine and you will plainly see which is better here. And doing it my way you lights in car will never modulate either when talking.  Brute force is not answer here.
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K1CJS
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« Reply #25 on: March 24, 2011, 12:50:53 PM »

And bigger cable is going to make it more stable? Brute force will not work here but a little theory and logic by using big electrolytic cap at load will stabilize voltage under load that no cable size and alternator can do on its own.

It is not a question of believing it is a question of practice and theory. I saw light long ago and use caps to stabilize voltage under load in mobile while you cling to bigger wire as cure all here. Put your big wire  solution on a scope watching power feed while talking and then mine and you will plainly see which is better here. And doing it my way you lights in car will never modulate either when talking.  Brute force is not answer here.

Brute force???  WHAT brute force?  It is not 'brute force' as you put it. It is the lessening of resistance in the feed circuit.  And you're much vaunted capacitance use may well interfere with some of the sensing circuitry used in today's autos.  Have you thought of that?  The circuitry in today's cars is sensitive to the point of additional 'filtering' as you promote may well interfere with its proper operation.  That wouldn't happen in yesterdays cars, but in today's?  It's more than possible. 

BTW, Why don't the professional installers use your way instead of using heavier wiring?  Why don't the car manufacturers document and advise your way of doing things instead of advising the use of heavy wiring?  In short, what makes you think you know more than professional engineers who design these systems.

I think you've mishandled one too many capacitors.

 
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W8JX
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« Reply #26 on: March 24, 2011, 04:21:57 PM »


BTW, Why don't the professional installers use your way instead of using heavier wiring? 

Simple, really professionals that do hard corer audio use CAPS in installation and the wanna be pros keep it simple and cheap and just use wire because they do not understand the function and value of a capacitor here

Why don't the car manufacturers document and advise your way of doing things instead of advising the use of heavy wiring? 

Do not even try to get this dog to hunt, Detroit has long used the smallest wire possible when building a car to cut costs.

In short, what makes you think you know more than professional engineers who design these systems.

Again guys that design hard core audio system that draw a lot of power uses caps. To others they look at oversized wire as the holy grail here but the large wire does nothing to address the instability of a car electrical system.
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K0BG
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« Reply #27 on: March 24, 2011, 04:47:14 PM »

Farad-sized caps, if they are large enough (>1 Farad), will indeed smooth out the voltage fluctuations seen under SSB operation to the point you almost can't see them on an O-scope. However, this is only true if they are connected directly at the input to the transceiver. One may argue to the contrary, but the resistance of the power cable itself is almost two magnitudes greater than that of the capacitor. This said, under steady draw (RTTY for example), they don't do any good at all. One could argue that secondary batteries don't help either, but the capacity (capacitance if you desire) of a battery is far superior to a Farad-sized cap.

John, you can argue all you want, but in this case, Chris is spot on!



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K1CJS
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« Reply #28 on: March 25, 2011, 03:48:52 AM »

Simple, really professionals that do hard corer audio use CAPS in installation and the wanna be pros keep it simple and cheap and just use wire because they do not understand the function and value of a capacitor here....

Again guys that design hard core audio system that draw a lot of power uses caps. To others they look at oversized wire as the holy grail here but the large wire does nothing to address the instability of a car electrical system.

And you know as well as I do, John, that those caps are NOT used to smooth voltage but rather as filters to keep noise out of the amp circuitry.

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W8JX
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« Reply #29 on: March 25, 2011, 05:51:31 AM »

Farad-sized caps, if they are large enough (>1 Farad), will indeed smooth out the voltage fluctuations seen under SSB operation to the point you almost can't see them on an O-scope. However, this is only true if they are connected directly at the input to the transceiver. One may argue to the contrary, but the resistance of the power cable itself is almost two magnitudes greater than that of the capacitor.

Mine have never been directly connected to radio and while in theory they will work best connected as such the will still help a lot when not in car or at home in shack. Resistance is not the reason for cap as much as for providing voltage source stability.


This said, under steady draw (RTTY for example), they don't do any good at all. One could argue that secondary batteries don't help either, but the capacity (capacitance if you desire) of a battery is far superior to a Farad-sized cap.

Never claimed that RTTY would be improved but it could in thoery reduce any ripple of noise in power supply.  As far as a second battery being superior over all, in reserve capacity yes it is but in voltage stability under varying loads vs a big cap, no.


John, you can argue all you want, but in this case, Chris is spot on!

Because I do not just roll on this is a argument? When does a debate become a argument? Is it when you get mad that other party does not ceed? If you want to nix CAPS that is your call but do not e so bold as to suggest that they are in effect wasted effort because they work very well.
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