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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 06-07-2006
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Electrical

If my targeted windlass Muir 1250 has a line speed of 48ft/min (say 30 for chain) and a amp working load of 100/60 (say 70) amps and I have about 60 feet of chain out, then I will consume 70 amps for 2-5 (say 3) minutes or about 3.5 amp hours.

If that's the only draw (all other batteries are fully charged) will my 55 amp OEM alternator (say 45 amp) recharge the windlass battery in about 5 minutes.

Long story short...I don't want to budget for a $2,000 windlass (with all the goodies) and end up having to upgrade my alternator for another $900+
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Old 06-07-2006
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Are you using a dedicated battery for the windlass? You mention other batteries being fully charged, so I would assume you either have a dedicated battery, or are using the start battery. A bit more info on your battery setup might make it a bit easier to determine an answer. As in what size battery are you drawing on, number of batteries, 3 stage charging, etc. Also, why do you need it back up in 5 minutes?

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Old 06-07-2006
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It generally makes more sense to have a dedicated windlass battery, rather than running the very heavy copper wiring all the way forward and trying to run them off the regular battery bank.

Why the need to recharge so quickly?? Also, sizing the windlass battery properly is a major concern. I'd recommend getting a small AGM battery for the anchor windlass.
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I'll try to answer both replies.
It will be dedicated at the bow.
My house and start banks are seperated. The windlass battery will be added to the house side.
My OEM alternator has an internal regulator and I haven't added a more intelligent external reg. yet, so I don't think I get a 3 phase charge unless I'm dockside with the AC charger.
I have flooded cell now and I am not yet convinced to move to AGM but that's another post.
Don't care to bring the battery up that quickly, just wondering if I'm considering all the forthcomming electrical demands.

Thanks for your help.
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The best thing you could do is get a "smart" external regulator. It seems you have a lot of batteries running off of one small alternator. Are you dockside on a regular basis? Your alternator should be 1/4 the size of your battery amps.......ie: 100amp for 400 amp hours of battery, or you won't be getting them charged up very well, windlass or not. Unless you're running the engine for a long time.
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Old 06-08-2006
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Also remember that on a standard OE alternator, it is often so that the regulator will read the voltage from your best battery in the bank that is commonly connected. If you put a windlass battery into the same circuit as your domestics and it is flatter than them because of extensive use, the regulator will take a voltage reading from the better-charged batteries and will downgrade the charge rate accordingly.
So, long story short, if you have 13.6v in your domestics and 11.5v in your windlass battery, it is probable that the regulator will back off to a trickle charge in response to the 13.6 volts it sees and the windlass battery will take forever to get it's charge back.
Best get a smart charger or find a way to isolate the windlass battery so that your OE regulator sees only that voltage.
Hope this helps.
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Omatako has an excellent point. Also, the lower voltage of the windlass battery will drain the house batteries, and may lead to shortening their lifespan.
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It sounds from the coversation that you are a weekend and vacation sailor. If so...I would have no concerns as the current alternator will keep things close enough to "right" for short periods and then your dock power can supercharge everything to float stage when you get back to your slip. 3-5 amps is the equivilent of turning on a cabin light for a couple of hours...Do you worry about that now?? For extended cruising...you really would need a 3 stage and larger capacity alternator anyway.
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A lot of "ifs". First, the windlass battery will need to be installed with heavy cabling or else voltage drops in the cable will cause it to perenially be undercharged. Then, if you expect any battery to be properly charged, you need to switch the alternator "charge sense" lead to the battery you are charging, and it needs to be one sense lead, one battery, no combinations, or else something will be over/undercharged. That's almost unseen unless you have a dual-output alternator and regulator which one charge lead to each battery.
But an automotive type alternator is designed to cut back the output rapidly as voltage in the battery rises, to prevent overcharging on long highway runs. It may in fact never bring your battery back over 90% capacity without extended run times. So, while you only need a couple of amp-hours put back into your windlass battery...it could take a half hour or longer to put them back in, because it will have cut back to 'trickle' by the time your battery has a 90% charge in it!

An external regulator (maybe $200?) is a good compromise, along with proper switching and charge sense leads, and the heavy cables.

It's a "systems" thing, where lots of solutions can be "good enough" but matching up all the parts will pay you back with shorter engine runs times (often HALF) and longer battery life (often TWICE) so if you can, invest up front and try to forget the pain in the back pocket.
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