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02-11-2020, 22:36
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#1
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Registered User
Join Date: Jan 2020
Posts: 241
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Converting an anchor winch from 3 phase to single phase. Check my math. 😁
I would like to convert my electric over hydraulic anchor winch from 3 phase to single phase.
Currently the electric motor is wildly oversized for the hydraulic pump at 7.5kw and draws only 5amps regardless of if the winch is reeling or stationary. By my calculations 415v x 5a x 1.732 ~ 3.5kw
Load and direction is determined by manually activating a hydraulic spool valve while the electric motor is running. The electric motor is turned on and off once only during the process. It does not start and stop everytime the winch is moved.
My plan is to replace the motor only with a 5.5kw single phase unit with a soft start to limit in rush start up current while providing headroom over normal power requirements should the anchor become entangled, locked etc.
Is my math correct?
Do soft starts play nicely with electric over hydraulic powerpacks?
Thanks
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03-11-2020, 01:28
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#2
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Registered User
Join Date: Nov 2013
Location: Nice, France
Boat: Hunter Marine 38
Posts: 1,345
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Re: Converting an anchor winch from 3 phase to single phase. Check my math. 😁
Better ask the question in an electric engine forum.
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03-11-2020, 04:30
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#3
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Registered User
Join Date: Sep 2009
Location: Houston
Boat: ‘01 Catana 401
Posts: 9,627
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Re: Converting an anchor winch from 3 phase to single phase. Check my math. 😁
You have 415v three phase power onboard?
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03-11-2020, 04:33
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#4
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Registered User
Join Date: Jan 2020
Posts: 241
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Re: Converting an anchor winch from 3 phase to single phase. Check my math. 😁
Quote:
Originally Posted by Sailmonkey
You have 415v three phase power onboard?
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Doesn't everyone?
Yes. I have everything: 12, 24, 240, 415v. Hence the desire to standardize and not have oversize equipment running for no real reason.
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03-11-2020, 10:19
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#5
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Registered User
Join Date: Jul 2012
Location: North East USA
Boat: 1975 Tartan 41'
Posts: 1,054
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Re: Converting an anchor winch from 3 phase to single phase. Check my math. 😁
"Calculate three-phase motor power consumption by multiplying amps by volts by the square root of three (W = AV (sqrt 3). For example, if the motor is drawing 30 amps at 250 volts, you have 30 x 250 x sqrt 3 (about 1.73) = 12,975 watts)." from the web..
So yes, your calc looks correct...
Damn a 10hp motor for a windlass, I could propel my whole boat with that! Even 5.5kw is huge! This must be some ship you got.
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03-11-2020, 10:33
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#6
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Registered User
Join Date: Jan 2020
Posts: 241
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Re: Converting an anchor winch from 3 phase to single phase. Check my math. 😁
Quote:
Originally Posted by zstine
Damn a 10hp motor for a windlass, I could propel my whole boat with that! Even 5.5kw is huge! This must be some ship you got.
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Thanks. Yep, shes a beast!! A 50t steel converted prawn trawler. New to me but the previous owner was in the industry so everything is surplus off commercial vessels. Not always the prettiest components but rock solid.
I've found the capacity specs of the hydraulic pump so once I put a pressure guage on it, that will give me true hp drive requirements. As I said its drawing ~5a at 415v but 4.5a of that is no load current. It must be running at crazy low hydraulic load and system pressure. I cant even see the lines flex when the windlass is engaged.
Thanks again.
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03-11-2020, 10:44
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#7
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Registered User
Join Date: May 2013
Location: Oregon to Alaska
Boat: Wheeler Shipyard 83' ex USCG
Posts: 3,659
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Re: Converting an anchor winch from 3 phase to single phase. Check my math. 😁
Single phase will draw more amps. You'll need to run heavier wire, bigger breaker, etc.
Why not put a hydraulic pump and clutch on your main engine. Then you don't need to run a generator to lift your anchor. If you're weighing anchor, your main will be running.
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03-11-2020, 10:50
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#8
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Registered User
Join Date: Jan 2020
Posts: 241
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Re: Converting an anchor winch from 3 phase to single phase. Check my math. 😁
Quote:
Originally Posted by Lepke
Single phase will draw more amps. You'll need to run heavier wire, bigger breaker, etc.
Why not put a hydraulic pump and clutch on your main engine. Then you don't need to run a generator to lift your anchor. If you're weighing anchor, your main will be running.
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I hadn't considered this but I like your thinking. It's worth investigation.
Thanks
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03-11-2020, 11:00
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#9
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Registered User
Join Date: Aug 2016
Location: Long Island, NY
Boat: Cal 33-2
Posts: 505
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Re: Converting an anchor winch from 3 phase to single phase. Check my math. 😁
One thing missing from the equation for 3-phase power is the power factor. Unlike for pure resistance, with a motor, the volts and amps are not in phase. One good thing is that you have a number based on a power factor of 1.0, so the actual power is less.
__________________
S/V First Tracks
1985 Cal 33-2
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03-11-2020, 11:04
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#10
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Registered User
Join Date: Aug 2016
Location: Long Island, NY
Boat: Cal 33-2
Posts: 505
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Re: Converting an anchor winch from 3 phase to single phase. Check my math. 😁
One thing missing from the calculation of power is the power factor. Unlike for pure resistance, the volts and amps are not in phase for motors. However by not including it, your number is based on a power factor of 1.0. So actual power is actually a bit lower.
__________________
S/V First Tracks
1985 Cal 33-2
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03-11-2020, 11:11
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#11
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Registered User
Join Date: Oct 2019
Posts: 772
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Re: Converting an anchor winch from 3 phase to single phase. Check my math. 😁
I would stay with the 3 phase as it was installed for a reason. More power.
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03-11-2020, 11:20
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#12
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Registered User
Join Date: Nov 2015
Posts: 54
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Re: Converting an anchor winch from 3 phase to single phase. Check my math. 😁
I would seriously consider removing the hydraulics altogether and go with a 3-phase supplied variable frequency drive.
Many advantages: no oil, no pump, no hydraulic motor, no valves, infinite speed control with constant torque, minimal maintenance.
The current and torque limit parameters on the VFD can be set to ensure that the motor and mechanical load are protected.
Consult an electric drives sales engineer before proceeding.
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03-11-2020, 11:21
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#13
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Registered User
Join Date: Aug 2015
Location: SW Florida
Boat: Grand Banks 49
Posts: 572
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Re: Converting an anchor winch from 3 phase to single phase. Check my math. 😁
Quote:
Originally Posted by Stewie12
I would stay with the 3 phase as it was installed for a reason. More power.
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===
Exactly, and if it's not broken, why fix it?
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03-11-2020, 13:17
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#14
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Registered User
Join Date: Sep 2007
Location: Queensland, Australia
Boat: None at present--between vessels. Ex Piver Loadstar 12.5 metres
Posts: 1,476
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Re: Converting an anchor winch from 3 phase to single phase. Check my math. 😁
Well, as the man said, if it ain't broke why fix it?
But if it were I faced with a FAULTY motor, I would remove it and make the whole thing hydraulic, using a pump driven from either the main engine (which will always be running when the anchor is being raised) via an electric clutch so it is only drawing power as required. If I HAD to have an electric motor I would much rather have a DC for the same reason elevators and trolley-buses used DC traction motors--they are very smooth and controllable in operation. For that you would also need a rectifier--and that can be solid state.
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03-11-2020, 13:18
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#15
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Registered User
Join Date: Nov 2014
Location: Sydney
Boat: Mummery 34
Posts: 77
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Re: Converting an anchor winch from 3 phase to single phase. Check my math. 😁
Exactly,
If its not broke don’t fix or you’ll “F” it.
This all about load, the power required is the same for both 3ph and single phase. 3ph gives a balanced load single phase adds new problems you don’t need.
High start current for one but since its hydraulic theres no load starting in your favour. So why add high starting Current?: 
I say don’t go there unless you’ve got loads of cash, loads of time, to waste and have a professional on stand by ready to sort it out in the end. Buy some nice new other thing.
Cheers
Woody
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