replacing a 12v windlass by a 24v when there's already a 24v bowthuster

[Pelagic]

Originally Posted by Brann-

It seems I have something like this (not this exact model though)

switching to 24v would definitely be more straightforward, but those 12v to 24v converters are quite expensive, aren't they ?

I would price the step up convertor (12 to 24v) first before deciding

Simplest way to bring your default 12v house and charging system into play.

Then all you need is a 24v solenoid to control the new windlass

Originally Posted by smac999

I can't tell from that picture. But I'm guessing you have a relay that puts the 2 batteries in parallel for charging. And in series when you hit the thruster button. Allowing you to charge them from 12v

I would rip the crap out. Make it a 24v bank. Power both devices from the bank. And buy a 12v to 24v dc to dc charger.


Or you have to make it so engaging the windlass also engages the relay to put the batteries in series

[Dave22q]

Originally Posted by Brann-

Actually, in the end, that's what I'll end up doing. I thought the series/parallel switch was wired to a complicated "just-in-time" switching mechanism, but it's not. I have a power switch to change between parallel and series, so I'll just use that and plug the windlass the same way the thruster is plugged in


I don't understand what you're saying. I want to switch to 24v because of the slightly better performance of a 24v windlass vs is 12v equivalent, and also to reduce the voltage drop through the wires. 12v sized wires will be more than adequate for 24v as I would in theory only need a cross section four times smaller, wouldn't I ?

Your existing wires are fine either way. I was was questioning if a 24v windlass would give you better performance.

[Delafontaine]

in reply to Brann- <<to 12v sized wires will be more than adequate for 24v as I would in theory only need a cross section four times smaller, wouldn't I ?>>
No, you need a cross section half as small, it is a linear function. Different if you are talking about wire diameter !

[Meanderthal]

Originally Posted by guyrj33

"This is not an issue for the bowthruster as its use is quite sporadic, but for a windlass, having the battery not being supported by the engine at all for the 5 minutes it takes to retrieve 100m of chain might be an issue, don't you think ?"

let's say your windlass draws 200 amps for 5 minutes,
200A x 5min x 1 hour/50 minutes = 16.66 AmpHours.

17 AH isn't a really big draw on a battery.

Are you neglecting the discharge capacity of the battery bank? A 400ah 12v golf cart battery setup, like I have for a house bank, would be decimated by 200a for 5 minutes, and there'd be a lot of hydrogen offgassing.

Lithium ion house bank of the same size could handle it no problem.

[Brann-]

Originally Posted by Delafontaine

in reply to Brann- <<to 12v sized wires will be more than adequate for 24v as I would in theory only need a cross section four times smaller, wouldn't I ?>>
No, you need a cross section half as small, it is a linear function. Different if you are talking about wire diameter !

You're absolutely right, thanks for pointing that out!
Brann

[guyrj33]

Originally Posted by Meanderthal

Are you neglecting the discharge capacity of the battery bank? A 400ah 12v golf cart battery setup, like I have for a house bank, would be decimated by 200a for 5 minutes, and there'd be a lot of hydrogen offgassing.

Lithium ion house bank of the same size could handle it no problem.

I'm confused by your comments, yes 200 amps is a significant draw that's why I showed the calculation of amp hours used.
Batteries don't out gas when being discharged, they out gas when being charged so there wouldn't be any hydrogen outgassing.

[Meanderthal]

Wow, upon rereading my post I understand your confusion. Ignore the hydrogen sulfide brain fart portion. I'm talking about discharge rate as a function of xC, and it's effect on the remaining capacity.

To clarify, do you still think 5 min@200a is a reasonable load for a cruiser's house bank, if the 200a is 0.5C or 1C of the house bank?

[guyrj33]

I think the point you're trying to make is that amp hour capacity goes down as current draw goes up.
From the NP a battery supplying 1X capacity would be fully discharged in about 20 minutes and about 20% discharged after 5 minutes.
Therefore for a 200 amp hour battery supplying 200 amp for 5 minutes the capacity used would be about 40 amp hours, not the 17 AH I originally suggested.

[noelex 77]

200A @ 12v for 5 mins is a little unrealistic for an anchor winch. Even the largest anchor winch may be drawing 60-80 A while retrieving the chain with a peak of around 90-150 A while breaking out the anchor.

[guyrj33]

I was just using 200 amps as a SWAG, reasoning that a windlass motor would be similar to a DC starter motor. With a current draw somewhere around 100 amps instead of 200 amps the % capacity of the battery used will be of course be less and pushes the analysis back toward the original assumptions.

[noelex 77]

Originally Posted by guyrj33

I was just using 200 amps as a SWAG, reasoning that a windlass motor would be similar to a DC starter motor.

Understood Guyrj. I did not mean to nit pick, but I think this is a case where more realistic numbers may lead to different conclusions.

[guyrj33]

Originally Posted by noelex 77

Understood Guyrj. I did not mean to nit pick, but I think this is a case where more realistic numbers may lead to different conclusions.

no problems, it's always better to have real world numbers to work with.

[Meanderthal]

Originally Posted by guyrj33

I think the point you're trying to make is that amp hour capacity goes down as current draw goes up.
From the NP a battery supplying 1X capacity would be fully discharged in about 20 minutes and about 20% discharged after 5 minutes.
Therefore for a 200 amp hour battery supplying 200 amp for 5 minutes the capacity used would be about 40 amp hours, not the 17 AH I originally suggested.

Yes, thank you.