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Old 20-04-2009, 11:05   #1
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Desired Windlass Run Time

Hi all;

I am looking at battery sizing for our to be installed windlass application. Without getting into much about actual battery sizing, I would like to ask the following question.

How many minutes of Windlass run time should I have between battery charging?

I am asking this way to remove the question of windlass power draw, battery type, etc. It does not remove the question of anchoring depths, chain vs rope. So lets say for this question, it would be an all-chain rode, anchoring depths would reach say 40 feet max.

Chris
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Old 20-04-2009, 11:16   #2
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Windlass and microwave

The windlass application is similar to that of using a power inverter to drive a 1200W input microwave. The answer is not so much battery capacity needed it is the internal resistance and specific gravity of the battery used. The higher the specific gravity the higher the voltage. Add to that the concept that you may have a high output alternator which may be operating (if for no other reason than safety when getting out of a tight anchorage) as a supported system for the windlass adding to the current available at a high terminal voltage.

AGM and gel-cel batteries excell in these applications. A good 120 Amp-hour battery will drive a 1200W windlass continuously perhaps until the windlass overheats and thermal's out. But don't buy a battery just for the windlass. Design your house bank to do the job and install 1/0 or larger cable to the windlass to minimize pitching moment of your boat that would occur if you attempt to locate the battery close to the bow. Not worth it.
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Old 20-04-2009, 11:28   #3
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Rick;

I agree about the negative aspects of adding a heavy additional battery in the bow of the boat. I'll spill a little more about why I was asking this question. LIFEPO4 batterys, Lithium Phosphate, are coming down in price. so I am thinking that a very small, light LIFEPO4 battery in the bow might be a new way to do this. To summerize the benefits:

Much more of the total capacity is available for use
weighs maybe 50% of a AGM of wet cell battery
superior cycling - over 2000
Safest chemistry available

Disadvantages:
Cost
Need for Battery management circuitry
Cannot charge as fast as AGM (still researching this)
???

So it MAY be feasible to put a 12v, 40ah battery, weighing in at 15-20 pounds, without heavy cables running. An interesting possibility, as the least.

The Windlass to be installed will be a Maxwell RC800, 1000 Watt motor using 5/16 G4.


Chris




Quote:
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The windlass application is similar to that of using a power inverter to drive a 1200W input microwave. The answer is not so much battery capacity needed it is the internal resistance and specific gravity of the battery used. The higher the specific gravity the higher the voltage. Add to that the concept that you may have a high output alternator which may be operating (if for no other reason than safety when getting out of a tight anchorage) as a supported system for the windlass adding to the current available at a high terminal voltage.

AGM and gel-cel batteries excell in these applications. A good 120 Amp-hour battery will drive a 1200W windlass continuously perhaps until the windlass overheats and thermal's out. But don't buy a battery just for the windlass. Design your house bank to do the job and install 1/0 or larger cable to the windlass to minimize pitching moment of your boat that would occur if you attempt to locate the battery close to the bow. Not worth it.
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Old 20-04-2009, 11:52   #4
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pitching moment

With simple proportion math you can calculate the pitching moment that the battery located forward for a windlass would contribute compared to the distributed mass of cables. It is still unlikely that a battery weighing 50% of a lead-acid one will contribute the same or less pitching moment.

Don't forget to include the cable mass still required from the forward battery to the windlass.
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Old 20-04-2009, 12:14   #5
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You can cut the strain on the windlass motor and I suppose reduce the amps if you let the catenary pull the boat foward so the windlass is not working hard to pull the boat (which is necessary when you begin to retrieve the anchor). Windlasses mfg will give the chain speed up and down and so you can questimate how much time it will take to drop say 150' and retrieve it.
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Old 20-04-2009, 12:26   #6
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Quote:
Originally Posted by witzgall View Post
Rick;

LIFEPO4 batterys, Lithium Phosphate, are coming down in price. so I am thinking that a very small, light LIFEPO4 battery in the bow might be a new way to do this. To summerize the benefits:

Cannot charge as fast as AGM (still researching this)
Good idea. I have used some lifep04 batteries to power a headtorch and they are excellent batteries.
I don't think you will face much of a problem with the charge rate, my small batteries a fine at 2C.
I think you may have some difficulties with the charging, however, they require precise charging conditions that are not the same as lead acid.
Hope you solve the problems. I think they are likely to be the battery of choice for boats in 10 years or so.
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Old 20-04-2009, 12:28   #7
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Assuming 10 minutes of retrieval ( 300 Ft of rode @ 30 fpm rate) at 80 Amp/1000Watt motor load [(10 60) x 80] = 13.33 Amp/Hours of consumption.
Doubling (?) the calculated load, for safety margin, results in 26.66 A/Hr ➛ rounded up to 30 A/Hr.
Since a high powered motor load should be operated at near full voltage, assume a maximum of 25% desired depth of discharge, requiring (30 0.25) = 120 Amp/Hour minimum battery capacity.

Unless your alternator is capable of at least 80 Amp output, AND your power wiring to the battery and windlass is appropriately sized for that ampacity (4/0 cables ?), a 120 A/Hr windlass battery will not provide the option of multiple anchor retrievals between re-charges.
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Old 20-04-2009, 13:41   #8
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Think of it this way: You usually have your motor running when retrieving the anchor right? Assuming you have a High Output alternator, have been running for a few minutes prior to pulling up, and motor away for 1-15 minutes before you get the main up. You wont have any loss from the windlass retrieval! This assumes you have a good sized bank for cruising... actually, for the first 15 mins or so of running a 100 amp alternator, your alternator will likely be making up the loss as you use it then. Typically starting an electric motor turning takes 3 or 4 times (if I remember right) the amps as when it's spinning, so I would assume an 80 amp windlass breaker is sized for the startup draw?
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Old 20-04-2009, 14:06   #9
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This assumes you have a good sized bank for cruising... actually, for the first 15 mins or so of running a 100 amp alternator, your alternator will likely be making up the loss as you use it then.
Chris is considering a battery mounted near the anchor winch with only small diameter charging cables.
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Old 20-04-2009, 14:27   #10
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I see I missed that in his second post. sorry.
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Old 20-04-2009, 15:18   #11
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Gord;


I think your calculations look good (I would not know, just assuming) up unitl the sizing of the battery. These LIFEPO4 batteries are really different beasts. You don't need to up size them like AGM, Gel or wet cells. I am not sure of what the correct size would be, but you can discharge them deeper without harm. My initial thoughts are that if you wanted to have 20ah of capacity, you would need perhaps 25-50% more capacity.

THe Windlass specs states a retrieval rate of 109 feet a minute
Freedom Range - Rope and Chain

I just cannot imagine retrieving that fast. They even state that as working load, whatever that is supposed to be, as there are no specifications I can see of that.

I have alot more to learn about these batteries.

Chris

Quote:
Originally Posted by
;275733
Assuming 10 minutes of retrieval ( 300 Ft of rode @ 30 fpm rate) at 80 Amp/1000Watt motor load [(10 60) x 80] = 13.33 Amp/Hours of consumption.
Doubling (?) the calculated load, for safety margin, results in 26.66 A/Hr ➛ rounded up to 30 A/Hr.
Since a high powered motor load should be operated at near full voltage, assume a maximum of 25% desired depth of discharge, requiring (30 0.25) = 120 Amp/Hour minimum battery capacity.

Unless your alternator is capable of at least 80 Amp output, AND your power wiring to the battery and windlass is appropriately sized for that ampacity (4/0 cables ?), a 120 A/Hr windlass battery will not provide the option of multiple anchor retrievals between re-charges.
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Old 20-04-2009, 16:05   #12
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it's 4am, you're awakened by the boat starting to pitch up and down, by the time you get outside with your skivvies on it's blowing 35 with 4 ft chop and your 200 feet of anchor chain is snubbing up bar tight with each plunge of the bow. Last night you arrived tired and had to make several attempts at anchoring due to the anchor not digging in with the rocks etc. When you try to retrieve the anchor this am you realize that you used up most of your "special" windlass battery last night. Now you are faced with trying to pull in 200 ft of chain by hand while the chain snubs up tight every 7 seconds......
What's the advantage of not wiring in your windlass with cable from the main bank?
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Old 20-04-2009, 16:27   #13
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Quote:
Originally Posted by witzgall View Post
... These LIFEPO4 batteries are really different beasts. You don't need to up size them like AGM, Gel or wet cells. I am not sure of what the correct size would be, but you can discharge them deeper without harm...
... The Windlass specs states a retrieval rate of 109 feet a minute
Freedom Range - Rope and Chain ...
Chris
My concern is not battery harm, so much as motor performance.
I'm not sure about these batteries either; but don't expect them to deliver any "majic".

The Maxwell RC500/800 specs (linked) state: 14 to 31 fpm retrieval speeds, depending upon rope or chain & model size; but (as you say) don’t specify under what “normal” pull force (Lbs).

Sorry, my hands have turned to claws - cannot type any more ...
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Old 20-04-2009, 17:45   #14
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I've never understood the rationale for putting a small dedicated windlass battery (usually in the bow). The reason give is to save the cost of some thick cables.

What seems to be the most logical approach is to have the largest house bank you can have with high output charging sources (alternator) and use this for the windlass. When you DO use the windlass you ARE running your motor (99.99% of the time) and your alternator is replenishing the amps that the windlass is drawing. If your house bank is paralleled you can add as many batts as you can fit increasing your amp bank.

Then use a separate start batt which is charged by the house bank with an echo charge. so you will always have a topped up start bank.
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Old 20-04-2009, 18:58   #15
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One thing that I don't think has been mentioned --Gord may have touched on it-- is what I've read is the falacy of a dedicated battery in the bow; that with a depleted battery in the bow and a high output alternator at stern, you will still have to have rather large cables to handle the amps.
May be different with these LP batteries if they can't absorb as much charge.
I'd like to hear from others about this, as I know my limitations regarding electricity. But it made sense to me.
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