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

[Brann-]

Hello,

I'm in the process of replacing my old 12v windlass by a new 24v one.
I already have two 12v batteries nearby my windlass, as I have a 24v bow thruster.
I thought it would be as easy as plugging the two batteries in series, but turns out the reality is not as simple.
Attached is a picture of my bow thruster relay (at least that's what the label says). I've marked each cable I have been able to identify. The bow thruster is also connected to BAT1- (not shown in the picture)

a few questions :
- The windlass is currently connected to BAT1 (both + and -). I guess I can't just connect the two batteries in series and then the windlass to it as it will mess with the bowthruster, but I'm asking just in case

- My battery charger is only connected to BAT1. Nothing is connected to BAT2 except from the two cables shown in the picture. How does the battery ever get charged ?

- If anyone could explain what's going on in the picture, I would be very grateful. I have been scratching my head most of the afternoon.

Thanks in advance !
Cheers,
Brann

[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

[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 ?

[wayne.b]

Originally Posted by Brann-

Hello,

I'm in the process of replacing my old 12v windlass by a new 24v one.
I already have two 12v batteries nearby my windlass, as I have a 24v bow thruster.
I thought it would be as easy as plugging the two batteries in series, but turns out the reality is not as simple.
Attached is a picture of my bow thruster relay (at least that's what the label says). I've marked each cable I have been able to identify. The bow thruster is also connected to BAT1- (not shown in the picture)

a few questions :
- The windlass is currently connected to BAT1 (both + and -). I guess I can't just connect the two batteries in series and then the windlass to it as it will mess with the bowthruster, but I'm asking just in case

- My battery charger is only connected to BAT1. Nothing is connected to BAT2 except from the two cables shown in the picture. How does the battery ever get charged ?

===

It's impossible to give you a definitive answer without an electrical diagram. My guess, however, is that you have a relay circuit that connects the batteries in parallel for 12 volt charging but reconnects them in series for operation of the 24 volt thruster. If so, you could probably duplicate that circuitry for use with your windlass.

[Brann-]

Hi, and thank you for your answer.

It seems your indeed right. The thing with duplicating the circuitry is that switching to a series connection effectively isolates the battery from the alternator. 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 ?

[GordMay]

Greetings and welcome aboard the CF, Brann.

... 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 ?

I would think your concern is justified.

[captstu]

12 volt windless motors are more common and easier to find that 24 volt motors,

What size is your boat? Most manufactures oversize their ground tackle and raise the load on the windless as a result,

You may be able to downsize to HT chain and preserve all or most of the safe working load with a smaller, less expensive 12 volt windless and far less troubles.

[JOHNMARDALL]

As others have said, it's difficult to be positive without a wiring diagram, but if you have a 24 volt thruster and only 12 volt charging from the engine alternator, then the assembly mounted on the bulkhead must be a series/ parallel switch - a device that temporarily rewires the battery bank so that when the 24 volt device is actuated the two batteries are disconnected from the alternator and rewired from a chargeable 12 volt parallel connection to a 24 volt series connection. These switches are actuated by the control function of the thruster or windlass, and if you have both a thruster and a windlass being served by the same batteries, then both the thruster and windlass controls will need to be connected to the series parallel switch. Each device should have completely separate battery connection circuit, each with its own fuse

Both batteries should be connected to the alternator, preferably through an isolating battery splitter, but however it's done, when the batteries are connected in parallel, both will be charged at 12 volts. Be very careful with this series/parallel arrangement, if the negative connection that becomes the middle when the the batteries are temporarily in series, is hard (not switched) grounded, you will have a very high amperage dead short when the series/parallel switch operates.

If you go back to the dock and connect to shore power most evenings, or have a genset, then a simpler and less mistake-prone approach is to have a 24 volt charger for the dedicated thruster/windlass battery bank. If neither of those situations apply, your choices are to add a 24 volt alternator to the engine, use a DC-DC converter or the existing series parallel switch.

Although I try to recommend systems that don't include a series/parallel switch, sometimes there's not much choice, and we do sell them. If it will help, I can send you the wiring diagrams for our series/parallel switches, which may be useful in understanding what you've got.

Oh - one last comment - if the battery bank is big enough to power the thruster, it will be plenty big enough for the windlass, unless you use the windlass much more frequently and for much longer run times than the thruster.

Good luck
John Mardall
Vetus Maxwell Group

[Brann-]

Originally Posted by captstu

What size is your boat? Most manufactures oversize their ground tackle and raise the load on the windless as a result,

My boat is a 15tons 43ft aluminium sailboat.
My anchor chain is already gr70, so there's not much to gain on that front. My anchor is a Spade S160 which weighs 35kg.

The main reason why I tend to prefer a 24v windlass over a 12v is the lower wire size.

[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.

[Brann-]

Originally Posted by JOHNMARDALL

As others have said, it's difficult to be positive without a wiring diagram, but if you have a 24 volt thruster and only 12 volt charging from the engine alternator, then the assembly mounted on the bulkhead must be a series/ parallel switch

It definitely is a series/parallel switch. The way it's wired, it seems one of the battery is always connected to the alternator, while the other one is connected or not depending on the state of the switch. I have yet to understand why I have 4 small wires connected to the switch (I expected only two). Maybe my bowthruster control panel takes its energy here, this way it has the same ground that the bowthruster power circuit.

Originally Posted by JOHNMARDALL

If you go back to the dock and connect to shore power most evenings, or have a genset, then a simpler and less mistake-prone approach is to have a 24 volt charger for the dedicated thruster/windlass battery bank. If neither of those situations apply, your choices are to add a 24 volt alternator to the engine, use a DC-DC converter or the existing series parallel switch.

I'm almost never connected to shore power. Getting rid of the switch altogether, and charging my 24v battery bank with a DC12->DC14 converter is definitely high on my list of options.

Originally Posted by JOHNMARDALL

Oh - one last comment - if the battery bank is big enough to power the thruster, it will be plenty big enough for the windlass, unless you use the windlass much more frequently and for much longer run times than the thruster.

Unfortunately, I use my windlass way more frequently than the thruster, and for longer run times as well !

I'm currently considering installing a 12v windlass. I would just plug it to one of the batteries (with a fuse of course), et voila ...Besides the smaller wire size, is there another good reason to go for a 24v motor ?

Thank you for the help, it definitely helped clarify things in my mind
Cheers
Brann

[Dave22q]

- The windlass is currently connected to BAT1 (both + and -). I guess I can't just connect the two batteries in series and then the windlass to it as it will mess with the bowthruster, but I'm asking just in case.

The batteries are already wired in series for the thruster. All you need to do is switch one wire to BAT2 so that the thruster and windlass wires go to the same terminals on each battery. But I just don't see any benefit in making the change as the wires for a 12v windlass are in place. Now if you want extra power you would need the batteries wired in parallel and that might involve some complicated and possibly failure prone switching as well as heavier wires.

[Brann-]

Originally Posted by Dave22q

The batteries are already wired in series for the thruster. All you need to do is switch one wire to BAT2 so that the thruster and windlass wires go to the same terminals on each battery.

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

Originally Posted by Dave22q

But I just don't see any benefit in making the change as the wires for a 12v windlass are in place. Now if you want extra power you would need the batteries wired in parallel and that might involve some complicated and possibly failure prone switching as well as heavier wires.

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 ?

[smac999]

I'm assuming the batteries are in the bow? The wire run would be so short. Wire size would be a silly reason for changing.

[Brann-]

Originally Posted by smac999

I'm assuming the batteries are in the bow? The wire run would be so short. Wire size would be a silly reason for changing.

The batteries are indeed at the bow. The current wire length is approximately 4m roundtrip, which I wouldn't qualify as "so short", given the sheer amount of current drawn (160Amps !)