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Old 04-12-2015, 08:58 AM   #1
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Heavy Load on Battery(s)

Electrical is not my strong suit and so I turn to the experts with a basic question.

When I lift my tender onto the mother ship with my deck crane, I am lifting close to 700 pounds with the 12 volt crane motor.

Which battery "back up" is best during the lift---running the main engines with their 100 Amp alternators or my genny supplying the 40 amp charger. My guess is the engines. Am I correct?

As always, thanks. Howard
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Old 04-12-2015, 09:35 AM   #2
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That depends

Your engines alternators are only at their rated output at a higher than idle RPM.

If you are running your engines at idle then you may not be supplying any more than your AC charger.
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Old 04-12-2015, 10:21 AM   #3
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Quote:
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Electrical is not my strong suit and so I turn to the experts with a basic question.

When I lift my tender onto the mother ship with my deck crane, I am lifting close to 700 pounds with the 12 volt crane motor.

Which battery "back up" is best during the lift---running the main engines with their 100 Amp alternators or my genny supplying the 40 amp charger. My guess is the engines. Am I correct?

As always, thanks. Howard
I run my generator.....But then my crane winch is 120 volts.........
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Old 04-12-2015, 10:27 AM   #4
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That depends

Your engines alternators are only at their rated output at a higher than idle RPM.

If you are running your engines at idle then you may not be supplying any more than your AC charger.
Then can I surmise the that using the engines at an increased rpm, let's say 1,000 would supply more power than the genset and charger?
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Old 04-12-2015, 10:36 AM   #5
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Depends on your alternator and how it's rated. How many amps do you need?
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Old 04-12-2015, 10:46 AM   #6
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Might want to consider a larger dockside battery charger or charger / inverter. Might also want to have someone watch the DC amp draw next time you do a lift to see what the real draw is.

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Old 04-12-2015, 10:53 AM   #7
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Measuring the draw makes good sense. Since we anchor most times, the dockside charger would not be an option.
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Old 04-12-2015, 12:16 PM   #8
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Measuring the draw makes good sense. Since we anchor most times, the dockside charger would not be an option.
My dockside charger will also run off my generator. Is there a reason you can't up size the charger and then run it off your generator for this task? My charger limit set at 120 amps, consumes between 15 and 20 amps 110 AC.

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Old 04-12-2015, 01:00 PM   #9
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If you have a SOC meter, you can see which charging source provides the most juice....genset or main engine at or near idle. My Balmar alternator will put out near 80A at about 1200 RPM. My shore charger run on my generator will produce 50-55A. I know b/c my Xantrex LinkPro told me so.
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Old 04-12-2015, 03:40 PM   #10
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What is the duration of the lift?

Your microwave using the inverter is probably drawing as much out of the batteries to do a bag of popcorn.

Do you know the wattage of the crane winch?

Don't over think this.
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Old 04-12-2015, 04:12 PM   #11
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Psneeld, I will dig out the manual and get the info. Lift is about 15' and it takes about 2 minutes.

I hate to over think it do let me share my biggest concern. What if the winch motor fails with the tender halfway up. Won't go up, won't go down. Any thoughts/suggestions?
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Old 04-12-2015, 04:26 PM   #12
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My plan is two 3 groove pulleys with hooks and 100' of 3/8" rope. 1 pulley on the crane and 1 on the lifting harness. Should yield a 6 to 1 advantage. That means I could lift 600 pounds of dingy while exerting 100 punds of force. Pull, tie off, rest, and repeat until finished. Or you could lift it a little, remove the winch hook, and lower it back down.

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Old 04-12-2015, 04:33 PM   #13
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OMG, that was exactly my thinking. Where would you suggest finding the pulleys? An attachment point on the crane would be nice but I guess I could make a loop over the top of the crane with Amsteel line.
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Old 04-12-2015, 04:55 PM   #14
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A quick Google search found This for $20 but would require longer rope.

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Old 04-12-2015, 04:59 PM   #15
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Sure is cheap enough. I guess for something I hope to never use it might work. I have a friend who is a sailboat rigger. He might have something as well. Thanks
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Old 04-12-2015, 07:55 PM   #16
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This is like the short term high load of anchor retrieval. Muir advise running engines at 1000rpm on retrieving. That`s 2 sources. Are there reasons not to use multiple sources?
I have retrieved with both engines and the genset powered charger running,(my anchor washdown pump uses genset mains power, not 12v),with the solar panels contributing modestly. Wonder what the various regulators make of that, but I`ve had no problem.
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Old 04-12-2015, 08:20 PM   #17
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Quote:
Originally Posted by hmason View Post
Electrical is not my strong suit and so I turn to the experts with a basic question.

When I lift my tender onto the mother ship with my deck crane, I am lifting close to 700 pounds with the 12 volt crane motor.

Which battery "back up" is best during the lift---running the main engines with their 100 Amp alternators or my genny supplying the 40 amp charger. My guess is the engines. Am I correct?

As always, thanks. Howard
I completely agree with not over-thinking this. Just assume the breaker rating for the hoist is the actual current draw and you will be conservative. If your hoist draws 60 amps and it takes one minute (1/60 hour) to lift, thats only ONE AMP-HOUR of your battery capacity! If you like to run something while hoisting, run whatever is easiest i.e. already warmed up. This will hold the voltage up at the hoist and make the lift easier.
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Old 04-12-2015, 10:28 PM   #18
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Thanks. That's comfort.
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Old 04-13-2015, 06:35 AM   #19
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The load will be high while lifting , but minor in terms of discharging the batts as the lift is a short term operation.

I would increase the size of the cables from the house set to the winch, and forget about the rest.
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Old 04-13-2015, 08:50 AM   #20
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Be very wary of block and tackle load estimates....

Every one I have ever used, the effort to do what I wanted seemed double of what I thought it should have been.

The frictional losses on all but the finest blocks must be terrible.

I would suggest a mount for a manual winch and snatch block or a rig with a come-a-long. Definitely something that allows safe stopping without having to tie off.
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