Lofrans tigress wire size? Voltage drop/wire size calc question..

[moseriw]

burnt bowthruster - technics:
usually a motor should have a thermal switch to stop the motor when it is overheated.
the Vet... did not stop, enabling the device to set the boat on fire!

When a moter gets enough amps but low voltage the magnetic field does not work as expected any more and most of the amps convert into heat within the motor.

[raedy07]

what formula do you use to calculate V-drop?

[Jammer]

>plonk<

[moseriw]

https://www.wirsindheller.de/spannun...#wshberechnung


Result:
Kabellänge in Meter: 11,00
Leistung in Watt: 6.000,00
Querschnitt in mm: 95,00
Eingangsspannung in Volt: 14,40
Elektrische Leitfähigkeit: 56,00
Widerstand Ω: 0,0178
Temperatur ℃: 20°C
Berechnung
Spannungsabfall: 11,97%
Ausgangsspannung in Volt: 12,68
Leitungswiederstand Ω: 0.0020610526315789
---------
BUT this is GREY THEORY

[sailah]

My Muir Cougar is 1000W and 100A. Have 1/0 cable about 75' total run. Works great.

[raedy07]

@Jammer: what does >plonk< mean?
@ moseriw: thanks for d link! but i'd love to know d formula!

[Franziska]

There is a different way to do this.
Mount a dedicated battery of sufficient capacity close to the windless.
That way you do not need a heavy cable.

Just two small diameter cables.
One for the control relay one to the battery charger.

[rslifkin]

Originally Posted by Franziska

There is a different way to do this.
Mount a dedicated battery of sufficient capacity close to the windless.
That way you do not need a heavy cable.

Just two small diameter cables.
One for the control relay one to the battery charger.

If you're willing and able to install a massive battery (or multiple), this works. But if you've already got a big house bank and the cable run isn't too long, you'll generally have less voltage drop in the batteries (and therefore better performance) if you use the house bank to power the windlass.

In my case, I've got a 1000W Maxwell HRC10-8 (rated load is about 85 amps, breaker is 135). 2ga cable, 50 foot round trip from my house batteries. Performance is quite good and I'm within the Maxwell recommendations for cable sizing / voltage drop. Going up to 1ga probably wouldn't hurt, but my application doesn't stress this windlass anyway, so I'd probably never notice the difference.

[moseriw]

If you're willing and able to install a massive battery (or multiple), this works. But if you've already got a big house bank and the cable run isn't too long, you'll generally have less voltage drop in the batteries (and therefore better performance) if you use the house bank to power the windlass.

############################
exactly what I thought before I installed the bow battery - and it was false
############################
My big house batteries had 720Ah but the capacity is not the problem it is the voltage drop

[rslifkin]

Originally Posted by moseriw

My big house batteries had 720Ah but the capacity is not the problem it is the voltage drop

If you were getting excessive voltage drop with a bank that big, then you weren't using big enough cable for the run you had or you had bad connections somewhere. The drop in my cables at breaker trip load is only about 1 volt, so under 10%.

In most cases, the drop from having a smaller battery to draw from will be worse than the drop from bigger, longer cables.

[moseriw]

Anyway: my final statement is: use a bow battery and keep cable length as short as you can. And I will use AWG 000 too.

[sailingchiro]

12 volt wiring for a windlass is like the anchor, bigger is always better. Mine has 2/0. If you used 4/0, should be OK.

[Franziska]

I'm with you on this.

A second situation were the same approach came handy is our current 2600 Genset with electric starter.
Instead of running a heavy cable from the housebank to the starter, we kept the small starter battery and only added a charging cable.

Works flawless.

Originally Posted by moseriw

Anyway: my final statement is: use a bow battery and keep cable length as short as you can. And I will use AWG 000 too.

[Bycrick]

The idea that you need a "massive" battery for a windlass isn’t true. The Tigress windlass is supposed to have, IIRC, a 135a circuit breaker. So I wouldn’t expect it to draw much more than 100 amps when operating at its rated load. The motor is not rated for continuous duty, my windlass states 15 seconds on and a minute off.

According to the specs, it’s supposed to pull in about 15 meters/minute at rated load. So, with 200 meters of chain, at full rated load, that’s about 12 minutes of constant operation. But you’re unlikely to be running it at full rated load just pulling in chain, so let’s just guess that you’re actually talking about 12 minutes at half- load or about 75 amps. Or, very roughly, 20 amp hours.

An average group 31 STARTER battery is rated at maybe 90 AH. So there’s plenty of capacity. In terms of the intermittent loading, a typical group 31 battery has about 700-800 cranking amps capacity. That means 700 amps for 30 seconds. So at 100 amps, there’s plenty of reserve.

Is there enough to pull up a heavy anchor multiple times from a deep bottom without recharging the battery? Probably not. But a group 31 Optima battery, for example, has ratings well above the numbers that I used for the very rough computations.

[rslifkin]

Originally Posted by Bycrick

The idea that you need a "massive" battery for a windlass isn’t true. The Tigress windlass is supposed to have, IIRC, a 135a circuit breaker. So I wouldn’t expect it to draw much more than 100 amps when operating at its rated load. The motor is not rated for continuous duty, my windlass states 15 seconds on and a minute off.

According to the specs, it’s supposed to pull in about 15 meters/minute at rated load. So, with 200 meters of chain, at full rated load, that’s about 12 minutes of constant operation. But you’re unlikely to be running it at full rated load just pulling in chain, so let’s just guess that you’re actually talking about 12 minutes at half- load or about 75 amps. Or, very roughly, 20 amp hours.

An average group 31 STARTER battery is rated at maybe 90 AH. So there’s plenty of capacity. In terms of the intermittent loading, a typical group 31 battery has about 700-800 cranking amps capacity. That means 700 amps for 30 seconds. So at 100 amps, there’s plenty of reserve.

Is there enough to pull up a heavy anchor multiple times from a deep bottom without recharging the battery? Probably not. But a group 31 Optima battery, for example, has ratings well above the numbers that I used for the very rough computations.

The issue isn't the capacity of the battery, but voltage drop under load. Pull a 75 amp load out of a single group 31 and the voltage is going to dip significantly, even if it's fully charged. I wouldn't be surprised to see 11.5 volts after a minute at that load. A bigger battery bank will dip less for a given load.