power drop from battery

[sasto]

Re: power drop from battery

Silvertip - do you agree?

I'll Bet he does! I've lost every other bet here, probably not this one.

Anybody?.......but Silvertip.

 

[ajgraz]

Re: power drop from battery

Another vote for never heard of using a fuse or breaker in the power line to the starter.

Also, another vote for assuming you might draw as much as 200 amps on a cold motor. Go at least 2 AWG, 1 or 0 AWG even better, for your 10-foot run.

Heck, 8 AWG is too small for the 3 foot run you currently have, should be 4 AWG or more now.

 

[halas]

Re: power drop from battery

thanks for the replies....that`s why I ask for advise on this ...I ain`t no electrician. I thought that 8 gauge would be big enough cause that is what a lot of booster cables are....now I know that I`ll need at least 4 gauge or heavier and a big fuse as well. .... I will solder and heat shrink as well.

Take off the cowling. Look at the fat cable that goes between the starting solenoid and the staring motor. Determine the size of that cable and buy copper cable one size bigger in diameter. Use that cable to connect your battery directly to the outboard. The inline fuse is not necessary. I personally want to protect all my circuits like I mentioned earlier by fusing. I think it should be a safety code. Most people here never seen it before. The inline fuse however will be the best insurance against burned wires. Look at it as a main disconnect preventing the battery from blowing up. The fuse itself will not restrict current flow. It will protect your system and ensures that you are not using too small of a wire. I install a fuse one size smaller than wire it sized for for added safety. You cannot be careful enough on a boat. Read up on this link for mor info: http://www.rowand.net/shop/tech/wirecapacitychart.htm

 

[sasto]

Re: power drop from battery

I agree on the fuse, is a good thing.....but.....cable size is related to voltage drop. I just don't believe the poster wants any voltage drop to his motor from the battery. I may be able to start that motor with 12ga. wire but the voltage drop will eventually destroy the starter motor...and weaken or destroy the wire. You can put a 200 amp fuse/breaker in there and it will blow/trip if there is a short in the circuit. Are we protecting the starter or the wire?

I do like your thinking though.

 

[halas]

Re: power drop from battery

I agree on the fuse, is a good thing.....but.....cable size is related to voltage drop. I just don't believe the poster wants any voltage drop to his motor from the battery. I may be able to start that motor with 12ga. wire but the voltage drop will eventually destroy the starter motor...and weaken or destroy the wire. You can put a 200 amp fuse/breaker in there and it will blow/trip if there is a short in the circuit. Are we protecting the starter or the wire?

I do like your thinking though.

Sasto, here is a table relating to practical wire length/wire gauge:http://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm

Use one size bigger if you are worried about voltage drop, just to be safe. You are the one paying for all that copper not me. You do whatever you feel safe with. To me it is not as much the cost as it is the added difficulty to run heavy wires under gunwales and so on. But the cost is substantial as well: did you check the price of quality copper cable lately?

 

[sasto]

Re: power drop from battery

Sasto, here is a table relating to practical wire length/wire gauge:http://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm

Use one size bigger if you are worried about voltage drop, just to be safe. You are the one paying for all that copper not me. You do whatever you feel safe with. To me it is not as much the cost as it is the added difficulty to run heavy wires under gunwales and so on. But the cost is substantial as well: did you check the price of quality copper cable lately?

Hi Halas,

I, like yourself, am giving my opinion to help this poster. I am throwing cost out the window, I'm not buying the wire with my money, I'm using his.

But...if I was using my money, or anybody elses, I would go by ABYC standards and not some offroad site that I have no knowledge about.

I have built many boats and bought wire by the boatload...it is expensive..but plays a very small part in the overall cost of construction and maintenance.

If it works for you...then we both are satisfied.

PS: I'm anal sometimes. (only about boating, my livelyhood) Ask the Lady.

 

[halas]

Re: power drop from battery

Hi Halas,

I, like yourself, am giving my opinion to help this poster. I am throwing cost out the window, I'm not buying the wire with my money, I'm using his.

But...if I was using my money, or anybody elses, I would go by ABYC standards and not some offroad site that I have no knowledge about.

I have built many boats and bought wire by the boatload...it is expensive..but plays a very small part in the overall cost of construction and maintenance.

If it works for you...then we both are satisfied.

PS: I'm anal sometimes. (only about boating, my livelyhood) Ask the Lady.

Right on my friend! But remember that the Amperes don't care if they are on dry land or at sea. They will behave consistently. The good old Copper will not get seasick

 

[Fed]

Re: power drop from battery

I had a read of the link you put up halas.
http://www.rowand.net/shop/tech/wirecapacitychart.htm
I'm still laughing at the capacity chart, I hope Silvertip sees this.
Maybe the author thinks that 110 Volt Amps are bigger than 12 Volt Amps.

 

[bruceb58]

Re: power drop from battery

Read up on this link for mor info: http://www.rowand.net/shop/tech/wirecapacitychart.htm

There is way too much misinformation in this guys page to use it as a reference.

For example look at this quote:

"Maybe I'm missing something obvious. Maybe I'm just not understanding this as well I as think I am. Who knows... At any rate, the chart below reflects the difference in 110V AC vs. 12V DC usage, even though I'm still at a loss to explain the details."

It pretty much sums it all up!

 

[jlinder]

Re: power drop from battery

I had a read of the link you put up halas.
http://www.rowand.net/shop/tech/wirecapacitychart.htm
I'm still laughing at the capacity chart, I hope Silvertip sees this.
Maybe the author thinks that 110 Volt Amps are bigger than 12 Volt Amps.

Only read some of this guys site, but from what I saw stay away from it!

His capacity chart starts with the same amperage capacity for 12v and 110v at the smaller gauges then goes to saying that at 12v the wire can carry 3 times what it can at 110v. Holy cow - NO! He says 12 gauge can carry 60A at 12V. If you do, bring the marshmallows so we have something to roast.

There are 2 drivers for wire size - ability to carry the amperage without heating and to minimize voltage drop. Wire heating causes fires, voltage drop causes low voltage to the motors which causes them to strain and work harder.

When concerned with heating it does not matter what the voltage is. A certain size wire will carry a maximum amount of current. I use the old rule of 12 ga = 20A max, 14 ga = 15A max, and you double or half the current every time you go up or down 4 gauges. (12ga=20A, 8ga=40A, 4ga =80A, 0ga=160A, etc.). Good rule of thumb.

For voltage drop you want to talk percentage of the voltage that is lost in the wires. Since the voltage drop in a wire is constant no matter what the supply voltage is, you find the percentage is higher with the lower voltage (12V). Consider that if you have a wire with 1.2 volt drop with a certain current, you only lose 1% of the supply at 120V, but are losing 10% at 12V. Big difference.

 

[Silvertip]

Re: power drop from battery

#8 gauge wire supporting 150 amps is disturbing enough but then he indicates that the current capacities are even higher if the wire is in free air. Yikes!!! At least the fire would be contained if it is contained in conduit. The dude did also say the chart was not prepared by him but rather provided by a friend. So there are apparently two folks to stay away from if they are around electrical stuff.

 

[jlinder]

Re: power drop from battery

#8 gauge wire supporting 150 amps is disturbing enough but then he indicates that the current capacities are even higher if the wire is in free air. Yikes!!! At least the fire would be contained if it is contained in conduit. The dude did also say the chart was not prepared by him but rather provided by a friend. So there are apparently two folks to stay away from if they are around electrical stuff.

I guess in open air he is saying air you can use 8 gauge for what - 200-300 amps? My only hope is they post it on you tube. Be fun to watch.

 

[LippCJ7]

Re: power drop from battery

Here is a better scale that follows more industry information that may be more useful to you guys, it also has a nice calculator on it if your interested. http://www.powerstream.com/Wire_Size.htm

 

[sasto]

Re: power drop from battery

Here is a better scale that follows more industry information that may be more useful to you guys, it also has a nice calculator on it if your interested. http://www.powerstream.com/Wire_Size.htm

Hi Lipp,

I go by this one published by ABYC. I found one online that appears to be the same as their book.

www.sailboatstuff.com/images/Imtra_Wiring Recommendations.pdf

Have a good day!

 

[jlinder]

Re: power drop from battery

Looks like a good chart for voltage drop, but it looks like it only considers voltage drop. That is only one consideration when choosing a wire size.

I think the more important consideration is safety. How much current can the wire carry without over heating (i.e. - causing fires). On this point the chart fails.

Yes, it gives the voltage drop at 10 ft. with 12 gauge wire on a 24v system and 10% drop drawing 100 amps, and I suspect it is accurate, but really? 100 amps on 12 gauge wire? I hope no one thinks they can do that safely.

I would rather see the same chart with the numbers greyed or blocked out for currents that are beyond the safe range for the gauge of wire.

 

[sasto]

Re: power drop from battery

Looks like a good chart for voltage drop, but it looks like it only considers voltage drop. That is only one consideration when choosing a wire size.

I think the more important consideration is safety. How much current can the wire carry without over heating (i.e. - causing fires). On this point the chart fails.

Yes, it gives the voltage drop at 10 ft. with 12 gauge wire on a 24v system and 10% drop drawing 100 amps, and I suspect it is accurate, but really? 100 amps on 12 gauge wire? I hope no one thinks they can do that safely.

I would rather see the same chart with the numbers greyed or blocked out for currents that are beyond the safe range for the gauge of wire.

I'm not sure as to which chart you are refering to but....resistance thru a conductor causes voltage drop which in turn causes heat. They are related. Current is measured in amps, if you are loosing amps, it must go somewhere. That would be what causes heat.

That said..I havn't been to school in years, If I'm mistaken, let me know.

 

[jlinder]

Re: power drop from battery

I'm not sure as to which chart you are refering to but....resistance thru a conductor causes voltage drop which in turn causes heat. They are related. Current is measured in amps, if you are loosing amps, it must go somewhere. That would be what causes heat.

That said..I havn't been to school in years, If I'm mistaken, let me know.

They are related, but each has a consideration that must be addressed.

Consider this - a wire of a certain gauge has a maximum current that it will carry before it gets too hot. (This number is also affected by the conditions - open air vs. being in conduit for example). This maximum safe amperage is not affected by distance or voltage. A 12 gauge wire can carry about 20 amps safely whether it is supplying 120 volts or 12 volts, running 1 ft. or 100 ft. You never want to exceed this rating. This is the safety consideration

The second consideration deals with whether or not the wire can supply the power to the load. This is the voltage drop. The consideration here is how much voltage (and hence power) is lost in the supply wiring? This is usually discussed in terms of the percentage of the supply voltage that is lost.

To get the voltage drop you need to look at the wire gauge, current, and distance of the run (both to the load and returning). For example, using the second link and the calculator there, if you have 12 gauge copper wire, a 20 amp load, and are 50 ft. from the battery you have a 3.265v drop in the wire.

While 12 gauge will carry 20 amps without overheating, on a 12v circuit you would only have 8.7 volts delivered to the load. Think of how a light, electronics, or a motor would run with this voltage. (From the calculator you would see this is a 27% voltage drop on a 12 volt circuit.)

Under this condition you would want to go to something like 6 gauge to be able to supply enough voltage.

Why does this work on 120v extension cords? That is because while the voltage drop is 3.2v that is only 2.7% of the 120v supply, so it is much less of a factor.

Does this explain it?

 

[bruceb58]

Re: power drop from battery

Does this explain it?

Perfect explanation.

 

[halas]

Re: power drop from battery

I'm not sure as to which chart you are refering to but....resistance thru a conductor causes voltage drop which in turn causes heat. They are related. Current is measured in amps, if you are loosing amps, it must go somewhere. That would be what causes heat.

That said..I havn't been to school in years, If I'm mistaken, let me know.

Sasto, that is absolutely correct! Any more said would over complicate a simple but universal concept! Mr. Ohm laid the law out many moons ago. No one I know disputed the Ohm's Law until Iboats came along with a few self righteous folks.

 

[halas]

Re: power drop from battery

They are related, but each has a consideration that must be addressed.

Consider this - a wire of a certain gauge has a maximum current that it will carry before it gets too hot. (This number is also affected by the conditions - open air vs. being in conduit for example). This maximum safe amperage is not affected by distance or voltage. A 12 gauge wire can carry about 20 amps safely whether it is supplying 120 volts or 12 volts, running 1 ft. or 100 ft. You never want to exceed this rating. This is the safety consideration
The second consideration deals with whether or not the wire can supply the power to the load. This is the voltage drop. The consideration here is how much voltage (and hence power) is lost in the supply wiring? This is usually discussed in terms of the percentage of the supply voltage that is lost.

To get the voltage drop you need to look at the wire gauge, current, and distance of the run (both to the load and returning). For example, using the second link and the calculator there, if you have 12 gauge copper wire, a 20 amp load, and are 50 ft. from the battery you have a 3.265v drop in the wire.

While 12 gauge will carry 20 amps without overheating, on a 12v circuit you would only have 8.7 volts delivered to the load. Think of how a light, electronics, or a motor would run with this voltage. (From the calculator you would see this is a 27% voltage drop on a 12 volt circuit.)

Under this condition you would want to go to something like 6 gauge to be able to supply enough voltage.

Why does this work on 120v extension cords? That is because while the voltage drop is 3.2v that is only 2.7% of the 120v supply, so it is much less of a factor.

Does this explain it?

That is correct but only in longer runs of wire here we are only dealing with 10-15'.