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Pacemaker Boats Information exchange on Pacemaker/Aglas Boats
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merwin10 Site Admin
Joined: 11 Oct 2006 Posts: 440 Location: Buzzards Bay, Massachusetts
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Posted: Thu Oct 12, 2006 4:20 pm Post subject: Wire Selector and how to figure wattage - |
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Changeofpace,
Here is how you can calculate the size of the wire!
First you need to determine the length of the wire needed both positive and negative. Since the positive and the negative make up a DC loop your length is times two in other words if the length of the positive wire is 6 feet the total is 12 feet. This length is important as it will specify the size of the cable. Next is the max current of the invertor. Next is the recommended voltage drop across the wire usually 3%. Then if the wire is in an engine space you need to derate for that temperature.
What I recommend is to figure the current at 10.4 volts rather then 12 volts. This is easy to do! First lets say your Inverter is rated at 250 amps. So 250a x 12v = 3000 watts now work it the other way 3000 a / 10.4v = 288.46 amps. Lets call it 290 amps. So now you figure the wire on 290 amps. What you just did is to assure that the inverter can get the proper current with a partial discharged battery.
So with this information you can figure the initial size of the cable. You will be figuring for tinned copper. The formula is below:
amps = 290 = A
distance = 12 = D
Volts = 10.4 = V
voltage drop = 3% =Vd = 3% of 10.4 is 0.312 V
copper resistive constant = 10.75 = R
the formula goes like this.
R x A x D / Vd = CM = circular mils.
In this example the result is CM = 111634.6
Now you need to go to a wire chart and pick the wire in AWG standard.
This is the standard used by the USCG in there regulations. The Reg says if the number of CM is not an even number of AWG wire size you go up to the next highest size. Here is the table of wire size.
Please note that if you use SAE wire the CM is less than AWG so you need to compenstate. All you need to do now is to figure if the wire you chose once derated for temperature will handle the current.
Well that about does it for the wire selection!
Mike -
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Edited by - merwin10 on 03/06/2006 20:33:30
merwin10
OLD SALT
USA
316 Posts
Posted - 03/01/2006 : 10:33:39
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Changeofpace,
Now for wire inductance! Time for another lesson you all have read the discussion here and I have probably written some words that you may not have considered before.
So I thought I would explain the whys and where fors!
One of the failures of inverters is ripple voltage on the dc leads from the battery to the inverter. This ripple voltage causes premature failure of the filter capacitors in the inverter.
So where is this ripple coming from? Well in is induces into the battery cables by the battery cables themselves or by other cables they run parallel too.
Well how does this happen and how can you reduce the effect of this.
First you need to understand how this inductance is produced. When an electrical current (flow) passes thru a wire a magnetic field is created. You all remember your six grade science. Take a normal nail wrap it with some wire attach a battery WOLLA you have a magnet. Well as this magnetic field builds it induces a voltage in any conductor nearby. Thus there is one of the problems. However, the building of the magnetic field also induces a voltage in the original conductor in the opposite direction of the current that produced it in the first place, called self inductance. How much self-induced reverse current is proportional to the size of the loop? This is how transformers work! The larger the loop or number of loops the great the inductance.
So your battery cables aren't making any loops so there is not a problem, wrong! Your battery cables positive and negative makes up one big loop, thus how they are positioned or arranged makes a difference as to how much self induced voltage there will be. The more the distance the more the self induced current will be. Interesting it the magnetic fields in the positive and negative conductors are opposite of each other. So by putting the positive and negative wires together and tapping them every four inches or so the self induced magnetic fields tend to cancel each other out.
This effect can be measured in electronics the unit of measurement is called Henry like resistance is called Ohm. At a foot of separation you will double the number of henries of that of taped battery leads. Of course in reality we measure this in micro-henries, so when taped it measures about 3uH and at a foot 6uH.
Since the induced voltage varies as a rated of change of the current in a conductor, the voltage could be three or four times the original voltage. The induced current works against the applied current which in turn causes loss of inverter performance and reduced efficiency.
All this adds up to needing to apply more current to run the inverter and shortens the battery life and run time. So to sum this all up! Tape your battery leads together right after they come off the battery terminals and keep the runs as short as possible, use large over size cable, avoid running the cables parallel to other wires and keep the battery up to charge.
Hope this helps - I tried to explain this in the simplest form I could!
Mike -
changeofpace
OLD SALT
USA
231 Posts
Posted - 03/01/2006 : 17:06:20
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Mike,
It sure does help, will have to check the calculations before I wire.
I will also make sure the battery cables are taped together. You explained what heppened to my brother-in-laws boat last year when he lost his dc circuit one night. He had run all of the wires together and stuffed them through a tube to make it look nice. Well we were out watching the fireworks and BANG all of his dc shut down, lights, horn, everything. We came in using flashlights. Once back in, we started pulling the wires apart and everything worked. so He put it all back together only to have it go out again after being out for a couple of hours. This time he pulled it apart and left it apart and everything stayed on, no blackout. Must have been some kind of feedback caused by having all of his wires stuffed in one small tube.
Me, I plan on having the battery wires run to the inverter in a different place than the ac wires going to my ac panel. That should hopefully eliminate any of the problems. Wire size I guess would be safe to say the bigger the better, that is If there is any doubt, go with the biggest size as that will not heat up as fast or restrict the power flow right?
Terry
merwin10
OLD SALT
USA
316 Posts
Posted - 03/02/2006 : 08:25:20
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Terry,
Yep! Believe it or not there is a specification and calculation for how many of what type of wires can be put together in a bundle. The calculations take into account the current, type of volts (AC or DC) and temperature. You can find these wiring rules in USCG CFR 183.425, 183.435 and 183.435(a).
Most boaters don't know that there are regulations that you must follow when working on your own boat. The regs are designed to make the boating experience safer. Such as in the case of your BIL. You are both very lucky that all you lost was your lights and DC power. It could have been much worse.
Good idea separating the AC wire from the DC. Always remember not only is the AC a high voltage but it also changes direction of the current 60 times a second, that is why it is call Alternating Current (AC), see inductance. So the magnetic field builds and collapses 60 times a second. Any wires running along side, parallel to, the AC wire will have the the induced voltage from the building and collapsing magnetic field induced into it.
In the case of wire size yep bigger is better! Just remember look for AWG standard copper tinned wire, not SAE. I will tell you now the DC side of your installation is pricey, around $500, by the time you buy all the wire, fuses and switches, never mind the batteries. What is peace of mind and safety worth?
If you have more questions please feel free to ask! You are getting a very good handle on wiring you boat. This is the difference between engineering and a hack job!
Mike -
changeofpace
OLD SALT
USA
231 Posts
Posted - 03/02/2006 : 16:57:34
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Yeah, judging by what I've already spent, $500 is about right for the batteries alone. The inverter was another $400, the AC transfer switch was another $80, never mind the costs for the isolator and the 2 switches for the 2 battery banks. As for the total cost, I'm a believer that money spent well is money in the bank. My boats value will increase significantly if I do it right. It already has gone up judging from some offers I got from members of the club where its stored.
I've got 2 complete new powerplants, new alternators, starters, HEI distributers and ignition, new holding tanks, new head, new windows, The ac and dc circuits will be all new. I have pulled out the original headliner and replaced all of the 12 volt wires for the lights, I'm replacing the fresh water pipes running to the galley and head. I've got new gel coat for above and below the waterline, all new exhaust hoses and all of the rudder and shaft packing kits, new fuel tanks ordered, new VHF radios, new am/fm cd stereo. So far I've put about $8000 into this boat. I've gotten offers already for over $12000 and its not done yet. I tell everybody that when I'm done, I'll know this boat inside out and front to back, wouldnt want it any other way. Yes I could have bought a newer boat with less work, but I love the pacemaker style and plan on keeping this one a long time, so if it costs more but will function better then I buy it, thats why I went to Bob Luther for the tanks and had him coat them instead of the plastic ones. People tell me I'm crazy because of the things I doing to this boat but Hey, its mine and it is a reflection of me. heck, I even got grey gel coat to paint the engine bilge. My freinds say just leave it as is, nope, I'm going to re gel coat the bilge to seal it from the salt water and besides,the grey will ofset the powerplants. They're Crusader blue with aluminum intake and chrome valve covers and spark arrestors. I'm putting in the aircraft style fuel hose (steel braid on the outside) to dress up the engine. Should look real nice. The twin Chevy 350's have been balanced and blueprinted, both have been dyno tuned to each other by 2pc motor sports here in CT. These engines should top out at 330 HP according to Mike at 2PC motor sports. As soon as the weather get better, I'm taking off the flying bridge to replace the wood underneath with the new foamcell material. I replaced the wood around the windows with the plastic wood so no more rotten wood.
All I need now is the anchor windlass and to decide if I really want that swim platform from New Hampshire or buy the fiberglass one here in CT.
Terry
merwin10
OLD SALT
USA
316 Posts
Posted - 03/02/2006 : 17:27:10
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I know another Pacemaker that has had about the same treatment over the years! I would never want anything less! Everytime I go look at new boats I find more things I like about mine. Yea there are some nice things I think about. This year was the fancy popup dash that I saw on a hatty bridge and a hard top! I am working on that! Unfortunately I am partictular and I like some design features from several diffent ones I have seen! Oh well back to the drawing board!
Mike -
changeofpace
OLD SALT
USA
231 Posts
Posted - 03/03/2006 : 13:10:43
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Yeah, I like the idea of a hardtop also, but I also like the idea of being able to take the top down at night and enjoying the view, especially when We're out watching the fireworks
terry
changeofpace
OLD SALT
USA
231 Posts
Posted - 03/06/2006 : 08:53:30
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Mike, Went to the boat yesterday to check wire sizes. I'm having trouble with the formula you supplied above:
Vd x A x D/Vd = CM
In your example you got 111634.6
I checked your formula because I was getting whacky numbers and came up with a different value for the CM than you did.
This is what I get from your formula above
VD (0.312) X A (290) x D (12.0) / Vd (0.312) = 3480
What am I missing?
Terry
merwin10
OLD SALT
USA
316 Posts
Posted - 03/06/2006 : 09:07:24
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I hear what you are saying, mine is so hard to take down that I don't take it down but once or twice a season! So I don't think I will miss it!
Mike -
merwin10
OLD SALT
USA
316 Posts
Posted - 03/06/2006 : 20:47:07
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OPPS My mistake got a typo -
fromula should read R x A x D / Vd or 10.75 x 290 x 12 / 0.312
Problem was the constant for copper was omitted in the calculation.
Thanks for the follow up!
Mike -
Last edited by merwin10 on Sat Jan 27, 2007 10:51 am; edited 1 time in total |
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leokow moderator
Joined: 12 Oct 2006 Posts: 415 Location: Osborn Island, NJ.(Little Egg Harbor)
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Posted: Sun Oct 15, 2006 3:22 pm Post subject: |
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Really glad you saved that work that Mike put on the old site, that ought to keep quite a few people from making mistakes and wiring to small, as that seems to be the most common mistake undersizing rather than oversizing. |
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