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Old 06-06-2020, 12:39   #1
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Lofrans tigress wire size? Voltage drop/wire size calc question..

I installed a lofrans tigress windlass last year. I havenít used it much other then testing that it runs without a load on it. I donít have the chain for it yet..however it does work. I didnít know much about voltage drop etc when I installed it. Now that Iím rewiring the batteries and boat Iíve learned a ďlittleĒ bit. Lofrans says for the tigress 1500 watt 12 volt I should use a 150 amp breaker which I did.and for 50 to 75 feet of cable to use 2awg. Which I did..i figure 12 v and 1700 watts is 142 amps(?)With the wiring size calc I enter voltage 12, load current 142, length of conductor 50ft ,3% voltage drop, 1 wire in bundle, 105; rating and duration in minutes 5, it computes null which means itís either larger theN 4/0 , or some of the input I entered is incorrect..? Does any one know whatís wrong with my figures? I have a 50ft run of 2awg marine cable to a power block then stepped down to 4awg for 5 ft because the design if the motor cover will only fit 4awg. I donít want to ruin the motor by using too small of wire and especially donít want to start a fire.. and lastly donít want to rerun more wires!
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Old 06-06-2020, 15:43   #2
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Re: Lofrans tigress wire size? Voltage drop/wire size calc question..

Not sure,.... why do you think something is wrong with your calcs? Because Lofrans said 2 awg and the calc says 4/0?
The max wattage of the motor is for a stalled motor I imagine. You should likely never see that, or only see it momentarily. maybe Lofrans uses a practical recommendation... and/or more than 3% drop?
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Old 06-06-2020, 15:57   #3
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Re: Lofrans tigress wire size? Voltage drop/wire size calc question..

The measurement for the cable should be double the distance. Is your 50feet there and back?
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Old 06-06-2020, 16:19   #4
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Re: Lofrans tigress wire size? Voltage drop/wire size calc question..

Quote:
Originally Posted by Eastward ho 24 View Post
With the wiring size calc I enter voltage 12, load current 142, length of conductor 50ft ,3% voltage drop, 1 wire in bundle, 105; rating and duration in minutes 5, it computes null which means itís either larger theN 4/0 , or some of the input I entered is incorrect..?

It is not necessary or desirable to limit the voltage drop to 3% for large motor circuits running at 12 volts DC. You're going to lose about 1 volt, around 10%. It's OK.
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Old 06-06-2020, 17:12   #5
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Re: Lofrans tigress wire size? Voltage drop/wire size calc question..

Like Jammer says:

3% voltage drop for a windlass circuit is extremely conservative, and is not needed. If you followed Lofranís suggestion just find something else to worry about.íí
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Old 06-06-2020, 18:19   #6
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Re: Lofrans tigress wire size? Voltage drop/wire size calc question..

Haha there something else to always worry about Did I get enough caulk in that thru hull,are them backing plates big enough,is that packing flooding..haha funny ..yes itís 50 ft round trip. And yes i was wondering b/c the calc says 4/0 which is a hell of a way off from 2. Also since I went lithium and Iím wiring all that up I happened to notice my starter cable Is 2/0 ( factory or po). I donít know the specs of a starter for a yanmar 3gm30f I know bigger wonít hurt so Iíll leave it. That had me thinking. Either the starters over wired big time or the windlass is undersized or a little of both.whatís using mor power my starter or the windlass..Iíd think the windlass uses more and for longer..any how i see 10% not 3% , and max rating of 1500watts is not what itíll be seeing. Let me see what I get for 140 amps ,50 ft, 10% drop ,105 and 5 min duration. Voila 2awg..guess it was the 10% vs 3%. ...now another post regarding length of parallel jumpers...
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Old 06-06-2020, 20:36   #7
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Re: Lofrans tigress wire size? Voltage drop/wire size calc question..

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Originally Posted by Eastward ho 24 View Post
Haha there something else to always worry about Did I get enough caulk in that thru hull,are them backing plates big enough,is that packing flooding..haha funny ..yes it’s 50 ft round trip. And yes i was wondering b/c the calc says 4/0 which is a hell of a way off from 2. Also since I went lithium and I’m wiring all that up I happened to notice my starter cable Is 2/0 ( factory or po). I don’t know the specs of a starter for a yanmar 3gm30f I know bigger won’t hurt so I’ll leave it. That had me thinking. Either the starters over wired big time or the windlass is undersized or a little of both.what’s using mor power my starter or the windlass..I’d think the windlass uses more and for longer..any how i see 10% not 3% , and max rating of 1500watts is not what it’ll be seeing. Let me see what I get for 140 amps ,50 ft, 10% drop ,105 and 5 min duration. Voila 2awg..guess it was the 10% vs 3%. ...now another post regarding length of parallel jumpers...
Interesting, and I am wondering... you come here with a question, we try to help and you come back with an attitude.

And you answer you own question. Whats next...
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Old 07-06-2020, 06:16   #8
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Re: Lofrans tigress wire size? Voltage drop/wire size calc question..

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Originally Posted by Eastward ho 24 View Post
my starter cable Is 2/0 ( factory or po). I donít know the specs of a starter for a yanmar 3gm30f I know bigger wonít hurt so Iíll leave it..

There is a tendency among diesel mechanics to use very large starter cable.


In cold weather (say, 20 F) a large diesel (typical for a box truck or farm tractor) will draw several hundred amps while starting. In colder weather they draw even more because the motor oil on the cylinder walls is thicker and if you're out starting machinery for snow removal or whatever in 0 F then you probably do in fact need 2/0 or 4/0 cable to the starter.


This mindset among mechanics tends to carry over to smaller engines that are only run at warmer temperatures, which is probably why you have 2/0.


The drawbacks of the very large cables (other than cost) are the bend radius and lack of flexibility which can put too much stress on the connector stud for the starter so that after vibration and motion of the engine on its mounts take their toll you can have the nut come loose or break the stud.
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Old 07-06-2020, 06:30   #9
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Re: Lofrans tigress wire size? Voltage drop/wire size calc question..

Less voltage drop in the starter cabling also slightly reduces the required size for the starting battery. Even the gas engines in my boat came with 1/0 to the starters from the factory.
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Old 07-06-2020, 08:48   #10
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Re: Lofrans tigress wire size? Voltage drop/wire size calc question..

Gotcha ...attitude? Ummm....no attitude just grateful for all the help..
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Old 07-06-2020, 10:32   #11
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Re: Lofrans tigress wire size? Voltage drop/wire size calc question..

Yep, just cleaned the battery cables on our little 2.9 Liter International diesel yard tractor, It has 4/0 cables attached to a single 31 starting battery. They are 36" long. Overkill. but extra weight on a tractor is actually a benefit. It is also the jump machine so extra meat in the cables is helpful.
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Old 07-06-2020, 10:53   #12
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Re: Lofrans tigress wire size? Voltage drop/wire size calc question..

I believe your also the guy with the Lithium bank? As Lithium’s voltage drop is less under a load than lead acid that further assists with the total voltage drop.
The windlass only knows total drop, it doesn’t care if it’s from a dead battery bank or undersized wiring, for that reason many of us will crank the engine, let it run at low RPM for a minute or two then run it up to 2000 RPM or so before raising the anchor, this adds the output of the alternator to the banks capacity to lessen voltage drop.
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Old 07-06-2020, 11:11   #13
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Re: Lofrans tigress wire size? Voltage drop/wire size calc question..

Forget it: I had 30 ft AWG 000 with a said voltage drop of 1,8V (calculated)
the Fact was: Battery 12,65V, Net wit alternator 14,2V

and the bowthruster got 8,6 Volts.


So the only bullet proof solution is an bowthruster/windlass service battery in the bow compartment to reduce wire length as much as possible.

Everthing else might burn the motors - like it did at my boat!
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Old 07-06-2020, 17:09   #14
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Re: Lofrans tigress wire size? Voltage drop/wire size calc question..

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Forget it: I had 30 ft AWG 000 with a said voltage drop of 1,8V (calculated)
the Fact was: Battery 12,65V, Net wit alternator 14,2V

and the bowthruster got 8,6 Volts. [...]

Did your battery deliver that with the bowthruster operating? Because batteries deliver less voltage under load.


The voltage drop in the cabling is well understood physics. If you are getting materially more than the chart you probably have connector problems
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Old 08-06-2020, 03:04   #15
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Re: Lofrans tigress wire size? Voltage drop/wire size calc question..

Did your battery deliver that with the bowthruster operating? Because batteries deliver less voltage under load.

I did a "Battery Voltage Drop Check" myself.
12V/225Ah was stressed with 110A

Voltage dropped from 12,65V to 11,9V - this is standard.
Though with an 55Ah alternastor and 14,4V at 1200 rpm I calculated with
14,4 - 1,8 - 0,7V = 11,9V at the bow which I consider not good but quite operable.

And yes, of course all connections have been triple checked.

For me it does not matter I face the fact that there is a problem with loong wires and voltage drop and the best way to avoid it is to reduce the wire length.

So my way "TO KEEP IT SIMPLE" is to mount another 220Ah battery in the bow compartment to minimize cable lenght to < 3 ft. and everything should be fine.

btw: charging - cheaper solution!
I bought a sterling alternator to battery charger 200A (500€) and will buy an
80-250 VAC to 12 VDC 200A converter for around 800€ to avoid the endless row of AC-DC, A2B, DC/DC chargers.

Setup: 7,5 Kw genset and 160A alternator
Batts: 720 / 225 / 225 Ah = 1170Ah x 0,2 = 234 Ah charging (20%) is possible
managed by the A2B charger.
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