Upgrading Windlass wire - double up on the wire

[Roy1919]

We recently redid the wiring on our Dickerson 37 sailboat and ran 2awg from the batteries to the windlass. 2 AWG was chosen based on a 5% voltage drop. However appears the cable run is slightly longer than planned and possibly the terminations are adding to voltage drop. Appears the real voltage drop is closer to 10%. We have a battery selector switch so can choose either house or engine batteries. Initially the alternator was on the start batteries, and we normally run the windlass of the start batteries. No problem.

However, we now have the alternator on the House batteries and when running the windlass on the start batteries it appears to be straining more and the 125A MRBF blows at times, never the 100A breaker. I choose 125A MRBF as it was 25% larger than the 100A CB (Bluesea C-series).

No doubt I can safely go to 200A MRBF for the 2 AWG to prevent nusicance blows, but thinking I am better to up the windlass wire gauge. Running 4/0 I guess would be ideal, but that large cable will be problamatic to run through the boat. So I was thinking to just add an other pair (Red/yellow) 2awg wires from the battery posts (see diagram - we have battery posts in the anchor locker for the cable run to terminate at) to the circuit breaker and ground bus bar. Any thoughts, recommendations on this?

 

[dlochner]

The better, easier, and cheaper solution might be to move the windlass cable to the house battery since it worked when the alternator fed the start battery, it should work now with the alternator feeding the house battery.

All fuses are not equal, they all have different trip properties, some trip quickly with an overload, some more slowly. The problem you're experiencing with the fuses may be attributable to fuse characteristics. At any rate, running a motor at less than optimal voltage and current is bad for the motor.

 

[Ralph Johnstone]

Hi @Roy1919 and welcome to the site.

I'm having a little trouble with your logic here.

Initially the alternator was on the start batteries, and we normally run the windlass of the start batteries. No problem.

Why would your alternator not supply BOTH battery banks when the battery selector is set on BOTH ?

However, we now have the alternator on the House batteries

Do you mean that the alt. will only supply the house bank and not the starter bank ?

The ideal procedure before using your windlass is to combine all your batteries together, feed your alternator into the mix and then use the windlass. If your current wiring connections do not allow for this, I would think this would be the simplest solution to the problem.

No doubt I can safely go to 200A MRBF for the 2 AWG to prevent nusicance blows, but thinking I am better to up the windlass wire gauge.

Is your thought that lowering the resistance of the cable to the windlass will lower the amperage draw ? Let's not forget that it was Mr. Ohm who taught us that I=E/R.

 

[dlochner]

I'm having a little trouble with your logic here.

The forumla for measuring resistance in a series is R+R+...= Total Resistance in the circuit where R = the resistance in ohms.

For a parallel circuit the formula for resistance is 1/R + 1/R+...= Total resistance. So using 2 sets of cables wired in parallel should reduce the resistance and hence voltage loss in the circuit.

But that adds a lot of wiring and connections and is certainly a non-standard way of wiring a boat. There are probably other reasons to avoid doing this too.

@Roy1919 may have other reasons for approaching the problem by using parallel wiring.

 

[Davidasailor26]

Nigel Calder says parallel cables are acceptable in a case exactly like that, where the cable is rated to carry the current but the voltage drop is too much. The cables need to be the same gauge and length, and the overcurrent protection still needs to be no more than what one cable could carry.

 

[Ralph Johnstone]

The forumla for measuring resistance in a series is R+R+...= Total Resistance in the circuit where R = the resistance in ohms.

For a parallel circuit the formula for resistance is 1/R + 1/R+...= Total resistance. So using 2 sets of cables wired in parallel should reduce the resistance and hence voltage loss in the circuit.

But of course it is, we all agree with Mr. Ohm. Cables in series increase resistance. Cables in parallel decrease resistance.

Unless I read @Roy1919 wrong, he intends to decrease the chance of blowing the existing 125A MRBF by decreasing the resistance of the existing cables by ADDING PARALLEL CABLES.

No doubt I can safely go to 200A MRBF for the 2 AWG to prevent nusicance blows, but thinking I am better to up the windlass wire gauge.

No, I'm afraid less resistance in the cables is going to increase (although slightly) current flow as shown by Mr. Ohm's law I=E/R.

YAYS ? NAYS ? Mr. Ohm's law stands.

The mistake has been made. Don't muddy the waters. Live with it. Make the initial voltage at the battery banks as high as possible to start with. House bank + starter bank + alternator. Even with the 10% voltage drop on the cable, you may still be above 12V at the windlass.

 

[dlochner]

No, I'm afraid less resistance in the cables is going to increase (although slightly) current flow as shown by Mr. Ohm's law I=E/R.

YAYS ? NAYS ? Mr. Ohm's law stands.

Not so sure. With undersized cable for the voltage as current increases, resistance increases because the wire heats up which increases resistance, which causes the current draw by motor to increase blowing the fuse (which may not have the characteristics required for this application).

Decreasing the wire resistance will deliver more current to the motor with less loss due to resistance. The motor will only draw what it can, not more. If it is designed to use 100 amps, it will not use 120 amps because of a larger cable.

Perhaps a better way to look at this is in terms of watts. If the motor needs 100 amps at 12v, it will need 1200 watts. If the voltage drops due to smaller cables, to say 11.5v then it will need 104 amps to reach the 1200 watts. That small increase may be enough to trip the breaker. With the alternator supplementing the battery at 14.4v then only 83 amps is necessary.

Remember watts is a measure of work, which is what the windlass motor is doing. Current and voltage are doing the work. Watts = current * voltage.

 

[Roy1919]

Hi @Roy1919 and welcome to the site.

I'm having a little trouble with your logic here.



Why would your alternator not supply BOTH battery banks when the battery selector is set on BOTH ?

We can certainly do so, but no need as the Windlass 1/2/off switch allows us to choose which battery to use, that switch is also conveniently located.



Do you mean that the alt. will only supply the house bank and not the starter bank ? - See above

The ideal procedure before using your windlass is to combine all your batteries together, feed your alternator into the mix and then use the windlass. If your current wiring connections do not allow for this, I would think this would be the simplest solution to the problem.

As above, we have complete control which battery and if we want the engine on and alternator support. Our start batteries are two 850CCA AGM batteries, which are normally always fully charged and ideal for running a windlass. However the windlass should work flawlessly on just the batteries and it appears that is not the case due to probably a 10% or greater voltage drop. So I am trying to address the root cause which is the cable for voltage drop to small.


Is your thought that lowering the resistance of the cable to the windlass will lower the amperage draw ? Let's not forget that it was Mr. Ohm who taught us that I=E/R.

 

[Roy1919]

Nigel Calder says parallel cables are acceptable in a case exactly like that, where the cable is rated to carry the current but the voltage drop is too much. The cables need to be the same gauge and length, and the overcurrent protection still needs to be no more than what one cable could carry.

That is the plan, same length, gauge, and type of cable. 2AWG can handle 200A, so plenty, and will use a 200A MRBF, or less, so that is safe. Two runs of 2Awg would be equivalent to 2/0, not 4/0. I suspect neither 2/0 or 4/0 can be connected directly to the windlass, even the 2Awg was tight to get on. So having the short 1-2' section of 2Awg to the battery posts easily allows me to run larger 4/0 from the anchor locker back to the the batteries (or switches), or multiple cables. Having two 2awg cables also allow me to put the wire from the battery post to the windlass in the middle of the two wires coming from the battery, which I think is probably better than a single 2/0 or 4/0 cable. Half the current coming from the top the other from the bottom, but that is probably pretty minimal benefit. So there are definitely some advantages to two cables (wires). I just want to check if I am missing some thing here, but so far appears no. I am not opposed to running a 4/0 cable, but the considerable larger size, stiffness, and lugs will make it considerably more difficult.

We have two 850AGM start batteries, plenty to run a windlass, so I want that to work flawlessly without the support of the alternator.

Thanks for your reply

 

[Stu Jackson]

We have two 850AGM start batteries, plenty to run a windlass, so I want that to work flawlessly without the support of the alternator.

I don't have a windlass, wish I did.
But every single windlass thread I've ever read said to use the alternator when using the windlass.
Why would you choose not to do so?

And also, Maine Sail has recommended using the house bank for windlass connections for quite some time.

 

[Stu Jackson]

2AWG can handle 200A

Can you link a reputable source for this?

 

[Richard19068]

2AWG can handle 200A depending on voltage drop, length of run, run time and insulation rating.

If I'm entering it correctly the Blue Sea calculator shows you could use 2AWG for 200A for less than 16 minutes up to a 38 foot round trip.

Circuit Wizard - Blue Sea Systems

circuitwizard.bluesea.com

 

[Davidasailor26]

Can you link a reputable source for this?

Looks like it depends on the temperature rating of the insulation -

(excerpt from Calder’s book)

 

[Ralph Johnstone]

2AWG can handle 200A depending on voltage drop, length of run, run time and insulation rating.

Perhaps a little confusion over wire design and wire AMPACITY.

#2 wire can actually handle 210A (according to ABYC) but only under the following conditions

-it is NOT in an engine room
- it is NOT in a bundle of three or more cables in a sheath
- the insulation is NOT rated for less that 105 deg. C.

However, the wire can be any length desired and used at 210 amps for 100% of the time.

This is the ampacity of the wire. Any greater amperage and the wire risks burning its insulation with the related damage to the surroundings.

 

[Richard19068]

Perhaps a little confusion over wire design and wire AMPACITY.

#2 wire can actually handle 210A (according to ABYC) but only under the following conditions

-it is NOT in an engine room
- it is NOT in a bundle of three or more cables in a sheath
- the insulation is NOT rated for less that 105 deg. C.

However, the wire can be any length desired and used at 210 amps for 100% of the time.

View attachment 196633

This is the ampacity of the wire. Any greater amperage and the wire risks burning its insulation with the related damage to the surroundings.

Thanks for that clarification. I guess I was worried about the voltage drop too.

 

[Roy1919]

I don't have a windlass, wish I did.
But every single windlass thread I've ever read said to use the alternator when using the windlass.
Why would you choose not to do so?

And also, Maine Sail has recommended using the house bank for windlass connections for quite some time.

Hi Stu,

Appreciate your feedback.

Please note I understand electrics, but not necessarily from a boat perspective.
The wire size calculations were done using the Blue Sea wizard and based on a a 5% voltage drop. However the wire length ended up longer then anticipated and it appears relying on Windlass manufactures specs is somewhat precarious. That said I knew that 2awg might be on the low side, and well that turned out to be clearly the case, our voltage drop is closer to 10%. So my only question is can I double up on 2 AWG cable versus a single 2/0 or maybe even 4/0 cable. From a pure electircal standpoint you certainly can, but are there some boat rules or something else I am missing. I need no other input on my setup, it works well for us.

Thought no doubt Maine Sail recommends house bank, every ones system is probably different. In my case I got the boat with two 850CCA AGM start batteries, total overkill, however they are perfect for a windlass, especially as they are always fully charged vs House batteries. I would rather use start batteries that are at 12.8V then house batteiers that are at 12.4V or even lower. Our Windlass 1/2/Off switch is conviently located and allows me to pick which ever battery bank I want, and with alternator support if desired. As to using the alternator, well there are times we just want to sail off the anchor, never start the engine. So having two fully charged (12.8V) 850CC AGM batteries should allow me to that that with our old Muir Cougar 12000 (1000w) windlass. I just need to ensure I have 12V or greater at the windlass, or it appears the windlass well get too strained and the current gets higher and thus voltage drop worse.

Only useful feedback for me so far, was the comment from DavidSailor that Nigel Calder states I can clearly do this. I have not had any response as too why I should not double up on the cables.

I do appreciate everyone's feedback.

 

[Ralph Johnstone]

I guess I was worried about the voltage drop too.

You wouldn't run too much length before voltage loss became unacceptable, especially so when you only start out with 12V. The purpose of the ampacity rating is only to prevent damage.

 

[Ralph Johnstone]

I have not had any response as too why I should not double up on the cables.

Just couldn't let that go by, I've got a few reasons .........................

- money
- useless additional weight
- back-breaking labour getting into all those miserable little places.

Please note I understand electrics, but not necessarily from a boat perspective.

Now that pretty much goes without saying. You've got a bunch of pros with years of 12V wiring experience looking at this. Why not give us some numbers and maybe we can explain why you may not need a second set of cables, all the while using numbers to prove our case. Or maybe you do, but let's PROVE IT rather than using gut feelings. If you look back through the archives for windlass problems, the one problem we most often see is those who have sized their windlass systems based on gut feelings. More often than not, it just doesn't work.

See if you can provide the following details using a digital multi meter:

- What are the specs of the windlass. Include a copy of the cut sheet of the details ?

- What is the measured length of the cables from the battery posts to the windlass motor ?

- What is the voltage at the windlass motor under load* ?

- What is the available voltage to the windlass cables at the battery posts when the windlass is under load* ?

- A little more costly to determine, but what is amperage draw of the windlass under load* ?

* under load refers to all anchor rode being deployed and pulled at one time while hanging free in deep water. All batteries to be combined. Alternator is disconnected from the batteries.

Let's see what's really happening and where we go from there.

 

[Roy1919]

Just couldn't let that go by, I've got a few reasons .........................

- money
- useless additional weight
- back-breaking labour getting into all those miserable little places.

- Money is why I would run a 2nd set of 2 Awg cables, instead of replacing the existing one with 2/0 or 4/0
- Weight is what it is, not much choice here,
- Labour is much easier with the a 2nd set of 2 AWG vs 2/0 or even 4/0. In my case the latter two will not fit through some of the openings / pathways, and could result in actually 4-6 more feet of cable as they would need to routed elsewhere, which I also want to avoid!!

Now that pretty much goes without saying. You've got a bunch of pros with years of 12V wiring experience looking at this. Why not give us some numbers and maybe we can explain why you may not need a second set of cables, all the while using numbers to prove our case. Or maybe you do, but let's PROVE IT rather than using gut feelings. If you look back through the archives for windlass problems, the one problem we most often see is those who have sized their windlass systems based on gut feelings. More often than not, it just doesn't work.

See if you can provide the following details using a digital multi meter:

- What are the specs of the windlass. Include a copy of the cut sheet of the details ?

- What is the measured length of the cables from the battery posts to the windlass motor ?

- What is the voltage at the windlass motor under load* ?

- What is the available voltage to the windlass cables at the battery posts when the windlass is under load* ?

- A little more costly to determine, but what is amperage draw of the windlass under load* ?

* under load refers to all anchor rode being deployed and pulled at one time while hanging free in deep water. All batteries to be combined. Alternator is disconnected from the batteries.

Let's see what's really happening and where we go from there.

- appreciate your help here, but I have already done all that, I don;t need it re-engineered, I simple NEED more wire cross-section area so I can get my voltage drop to <5%. I am not putting batteries up front and I cannot make the cable runs any shorter. Okay, here is some math: start batteries always at 12.8V, so without alternator support, 5% would get me to 12.2 at the Windlass, instead of the 11.4V we get now. 2/0 (or equivalent) cable will do that for me.

With full (or 90% SOC house batteries) than our alternator (Delco Remy 22si - 150amp, though max output so far is 130A) with Balmar MC-618 external regulation and remote voltage sense will be at 14.8V, yes i have measure that too. The Balmar fixed time settings will ensure we stay in Bulk (14.8v) and not switch to float, (though I can manually switch to float with the MC-618 anytime I want) in that case the 10% voltage drop is simply not an issue and windlass works flawlessly. But like I said I want the windlass to work on just the full start batteries without having to run the engine, and our current voltage drop makes it difficult if the windlass has to work hard.

And yes 4/0 would be ideal as that is 3%, though as long as I maintain 12V or more at the windlass I will be fine (5%). So unless there is a reason I can not run a pair of 2awg (equivalent to one 2/0) , I will not go to the expense , weight and labour of running 4/0.

Again I appreciate your help with reviewing the numbers, but I really just need to double my wire cross sectional area, and the simplist is a second pair of 2awg cable, I don;t believe that breaks any code and does have some minor advantages.

 

[Ralph Johnstone]

But like I said I want the windlass to work on just the full start batteries without having to run the engine, and our current voltage drop makes it difficult if the windlass has to work hard.

Odd way to do it compared to most manufacturer's recommended method (Lewmar in my case) but in the end, it's your boat and your choice.

I would however, be interested in seeing the rest of the details requested above to ensure there's not some other problem at work here such as internal battery resistance, excessive cable length, or a bad connection. All we know so far is that voltage at the windlass under load is 11.4V which is not good but it doesn't tell us why.

No one can tell you anything without the numbers.