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Old 27-03-2010, 06:06   #16
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There's a couple of bad points to your argument. One, the charger is not going to undercharge your battery by .26 volts. Even at float of around 13.2 volts, you would still be at about 13 volts, still charging the battery but at a slower rate. Also, the charger only works at 30 amps for a deeply discharged battery, you might come out of bulk early, but again this is a time issue. Let's say when the charger goes into float mode the battery is accepting 1 amp, that is less than a 0.01 volt drop in this case, so you're down to 13.19 volts instead of 13.2 volts.

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Originally Posted by hellosailor View Post
The trip is 11 feet, so that's 22 feet because you measure it round distance.
With 6AWG cable carrying 30A you will have a voltage drop of about 0.26 volts.

That is equal to a 25% drop in the output from a "12 volt" battery. Or, your charger has to work 25% harder to charge the battery, or the battery will never quite be fully charged. However you want to look at it.

In the best case if your charger has a SEPARATE SENSING LEAD, then you can ignore the voltage loss in the cabling and just let the charger overheat as it works harder than it has to. In the worst case...Well, who cares if a battery is charged to 12.4 or 12.8 instead of 12.6 anyway? (Not!) Undercharged, overcharged, all good ways to sell new batteries before their time.
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Old 27-03-2010, 06:18   #17
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Knowing everyone is tired of facts, I'm glad cal40john, said what I was going to say: when the voltage matters to the charging process the voltage drop error will be very small.

Go with the smaller wire. Save weight. Save money. Sail sooner and faster.

Figures a smart guy would sail a Cal40.
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Old 27-03-2010, 08:23   #18
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mercy boat cup monsoir, but does this mean that having the 6 guage, which I already bought, will hurt me?
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Hola Unbusted! Como esta? Look, take the total wire run round trip. In your case we'll say thats 11 feet. Multiply by total amp output or draw. Total = FAmps, or Foot Amps. Enter the chart under the "12 Volt" heading for 3% volt drop. scroll down 'til you find the FAmps number closest to but higher than the total you came up with using the equation. In your case thats 330 FAmps... 11' X 30 amps = 330 FAmps. Closest higher FAmps on the chart is 348. Now scroll left til you come to the wire size directly across from 348...AWG 10 wire. TAH DAH! For the maximum voltage drop of three percent, you need to use size 10 AWG wire for an 11 foot run. Comprende mi amigo? PS, as you scroll left, make sure your amp requirements are under the ampacity numbers mentioned there. In your case it reads 51 amps if run in the engine room, 60 outside the engine room area. Via con queso, mi amigo!
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Old 27-03-2010, 08:44   #19
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Absolutely not! Go ahead and use it; don't overthink this.

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Old 27-03-2010, 08:50   #20
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Thanks, that's exactly what I was doing. Now if only I could figure out exactly where to put this...
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Old 27-03-2010, 09:07   #21
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mercy boat cup monsoir, but does this mean that having the 6 guage, which I already bought, will hurt me?
Negative my friend! Bigger is ALWAYS better. Now, here's your test: Lets say you have a 40' roundtrip run powering a 20 amp circuit...what's your wire size? NO HELP FOR UNBUSTED FROM THE PEANUT GALLERY! Bet if I asked how I could eliminate high frequency feedback from an overhead drum mic situated close to a monitor you could handle that!
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Old 27-03-2010, 09:48   #22
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That one's easy, you just kill the drummer.

And let's see 40x20+800 FAmps the next size up would be...879 and that is a 6 AWG wire, did I get it?
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Old 27-03-2010, 10:27   #23
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I've found them harder to kill then you might expect
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Old 27-03-2010, 14:35   #24
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John, if you take it literally, yes, they could be bad points. But no matter how you apply the concepts in the larger picture, having less voltage drop in the cables will either give you faster charging times, or less cable heat, or less power wasted by the charger, which will charge in loss time as well. Sure, you'll eventually charge with any kind of cable loss, which is why the salesman told him the chargers use much thinner wires. They don't care if you have to wait an extra two or three hours to cast off with full batteries, or if your charger eats more power, etc.

With a real cable loss of 0.13 instead of 0.26V, I'd call 6AWG plenty good enough.

"Bigger is ALWAYS better." Obviously Christian isn't a racer.<G> On a racing boat where the owner is TRYING TO WIN, every cable will be downsized to save weight and weight aloft and a whole new set of criteria come into play. Thankfully there are LED nav lights so racers can now use thinner lighter cables and still get bright nav lights out the far end of them.<G>
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Old 27-03-2010, 15:16   #25
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OK, now that we've pretty much beat wire size to death, here's something else which really matters: Be sure you put a CPD in the new battery charging positive cable somewhere near the batteries. I'd use a fuse...maybe one of those Maxi fuses and holders that Blue Sea Systems sells. Little red box. Captive positive contact on the fuse lugs. I use 'em all the time for radio installs. WM has them; so does Defender. Use a 40A fuse.

Bill
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Old 27-03-2010, 15:34   #26
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OK, now that we've pretty much beat wire size to death, here's something else which really matters: Be sure you put a CPD in the new battery charging positive cable somewhere near the batteries. I'd use a fuse...maybe one of those Maxi fuses and holders that Blue Sea Systems sells. Little red box. Captive positive contact on the fuse lugs. I use 'em all the time for radio installs. WM has them; so does Defender. Use a 40A fuse.

Bill
Yup I did that. I did the install today and aside from putting a few extra holes in my boat it went pretty well. My only concern is that in the 15 minutes I ran the thing (I had to leave and didn't want to leave a new install plugged in) I didn't hear the fan boot up, is this normal? It was about 55 ambient.
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Old 27-03-2010, 15:39   #27
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Yeah, not to worry. The fan only kicks in when the charger is working hard.

Iotas tend to "hang in there" with high amperage longer than most marine battery chargers. One of these days I'm gonna deep discharge the T-105 bank which powers my radios here at home, then put a couple of recording meters on the DLS-45/IQ4 and see what the charging profile actually looks like over time.

Congratulations on the new install. I'm sure you'll be happy.

Bill
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Old 27-03-2010, 16:04   #28
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And let's see 40x20+800 FAmps the next size up would be...879 and that is a 6 AWG wire, did I get it?
YOU DA MAN!!! Now you can rewire your whole boat! Congrats Unbusted. BTW, what do they call the untalented guy who hangs around with the band? THE DRUMMER! Awe, SNAP!
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Old 27-03-2010, 16:24   #29
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What's the best kind of pickup to put on a bass?
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A chevy!
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Old 27-03-2010, 17:27   #30
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Definition of perfect pitch: The sound made when you throw an accordion into a dumpster and it lands on some bagpipes...
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