12v Boat with 24v bow thruster

[jordanbigel]

So,my boat is all 12v and I have a dead 12v bow thruster (5hp). The unit is over 20 years old and they say they cannot repair it (parts not available).

I can replace it with the same unit, but, they (Wesmar) now offer a new thruster which has 15hp equivalent thrust compared to the old 5hp one I have, but with the same prop size (8") same tunnel (215mm), etc. - except it's 24v only. There are some other possible 12v options I am looking into which might fit the tunnel (SidePower).

Currently, I have a dedicated 4D AGM battery in the forward cabin just inches away from the bow thruster. It is charged by a dedicated alternator (a small-case Balmar 150amp deal with its own MC-614 regulator). This battery also feeds the windlass also 12v (Maxwell).

I'm trying to see if there is a way to run the 24v thruster without spending too much $$ and I don't see any way to do it. I could replace the 4D with a pair of smaller batteries and wire them in series to make 24v, and then I would have to replace the alternator with a 24v alternator - but even if I did that what about the windlass? Maybe some kind of DC-DC step down converter which can feed the windlass 12v from the 24v bank? This is starting to get out of hand!

I wouldn't even be considering this except the current 5hp unit is totally under-powered (at the time it was the largest unit available for the tunnel which was already in the boat with a dead thruster when I bought it) - and I knew it was underpowered, but figured it was better than nothing. In reality, it's been barely better than nothing. It is helpful in a limited set of conditions and circumstances, but a 15hp thruster would be a game-changer in terms of close quarters maneuverability, which is why I am considering it.

Is there a better way? Will this even work? Thanks in advance!

[Jammer]

Cheapest way:


Replace the 4D with a pair of smaller batteries in series as you describe.
Disconnect or remove your bow thruster alternator
Get a pair of 12v-to-12v isolated battery chargers like this. Connect them to charge each of the two batteries in series. Feed them from your main house battery.
Connect your windlass to either of the two new batteries


Inexpensive 12v-to-12v and 12v-to-24v chargers are relatively new on the market and were not available 15 years ago when your setup was put together.


By using two isolated chargers you can keep each battery fully/equally charged so it doesn't matter if the windlass draws some power from just one battery in the series string.

[Jammer]

Alternatively you can get a 24v motor for your windlass, or get a new windlass entirely that is 24v. Then you only need a single 12v-to-24v charger rather than the two isolated-output chargers. But windlass motors are expensive and unless yours is arguably due to a refit anyway it's a hard expense to justify.


Yes you can swap the alternator for a 24v one but that's also an expensive option and unless you anticipate running your thruster for several minutes multiple times a day the actual charging needs for the thruster battery are minimal and easily met by a 10 amp charger.

[goboatingnow]

You have a few simple choices

1. Change the alternator to 24V , fit a 24v battery set , do a 24-12 battery charger to power the windows battery , alternatively run the windlass from one of the 12v batteries. It’s not ideal but it will work.


2. Fit a 24v battery set , split the chargers and charge each better with a 12-12 dc dc charger. One of them must be of the isolated type.

3. Keep life simple and fit a 12v thruster

[noelex 77]

12v is limited as to the maximum power it can deliver, especially for a 50 foot boat, as you have found. You would find a significant increase in the available thrust moving up to 24v.

If you want to use specific batteries for the bow thruster (not my preferred choice) then 24v to 12v battery chargers are readily available. There is no need to necessarily move up to a 24v alternator.

[jordanbigel]

Thanks for the feedback! Some interesting ideas - I didn't realize I could tap 12v from a 24bank just by going direct to one of the batteries.

I am not 100% clear on why this would give you 12v instead of 24v - assuming a 2 battery bank where I have pos from battery 1 and neg from battery 2 going to pos and neg bus bars, I get 24v from the bus - ok, I get that part. But you get 12v if I wire directly to battery1 (or #2) pos/neg and not to the bus - have I got that right?

As for cost, even though a pair of DC/DC chargers (about $550) cost less than a new 24v alternator, which is probably more like $1200 for a high output Ballmar like the 12v one I have now, I might be able to get 300 or $400 for my 12v alternator to offset the cost, and avoid the extra installation and wiring for the DC/DC chargers - plus, I like having the 2nd alternator. I can combine the house+thruster battery so that if the main alternator dies, I can still charge the house bank from the secondary alternator. So I am inclined to keep both alternators running.

In addition, the thruster draws like hundreds of amps (I don't have the numbers handy) so having that dedicated alternator keeps the voltage up on the thruster battery/bank while it is being used. Also, I think it is unrealistic to assume it will only be used for 10 seconds at a time. The thermal cutout will trip after about 2 minutes, so anything within 10 seconds and 90 seconds can be considered normal and common, in my experience. At that discharge rate without a dedicated alternator feeding the thruster battery/bank I don't see how you could maintain thrust for more than 30 seconds with just a 30amp DC/DC charger (like the Victron Orion-Tr Smart 12/12-30A linked to above).

Even the windlass alone draws 100amps and is often used for 4 or 5 (or more) minutes at a time - like the thruster, always with the engine running - and so that 2nd alternator is also useful even without the bow thruster IMO. At least, this has been my understanding.

[jordanbigel]

Originally Posted by noelex 77

If you want to use specific batteries for the bow thruster (not my preferred choice) then 24v to 12v battery chargers are readily available. There is no need to necessarily move up to a 24v alternator.

I am not sure I understand what you mean here - I like the part about not upgrading the alternator, so I want to ask you to please clarify!

Is there a way to charge a 24v bank with a 12v alternator, using some intermediary device/charger? A 12v to 24v charger which takes 12v from the alternator directly perhaps?

[noelex 77]

Originally Posted by jordanbigel

I am not sure I understand what you mean here - I like the part about not upgrading the alternator, so I want to ask you to please clarify!

Is there a way to charge a 24v bank with a 12v alternator, using some intermediary device/charger? A 12v to 24v charger which takes 12v from the alternator directly perhaps?

Yes. 12v to 24v chargers are readily available. They will not supply the high current of the bow thruster as this is likely to be around 400A+ @ 24v (for the type of bow thruster you are contemplating), but they will replace the energy in the bow thruster batteries.

The alternative choice is to upgrade to a 24v alternator and then use a 24v to 12v converter to charge the house sytem.

[jt11791]

My boat is set up just like you want. I have a 12V windlass and a 24V bow thruster, and a 12V alternator. The key is the use of a Bosch series-parallel relay switch. The switch puts the two 12V batteries in parallel for charging and in series for the load (thruster). Look here for ideas on how it's wired: https://wiringdiagram.2bitboer.com/b...iring-diagram/


Trucks and heavy vehicles often need higher voltage (24V) for starting big motors and they use these switches.

[sailormed]

If you have 2 12V batteries in parallel for your house bank you can obtain temporary 24V for use with the bow thruster when needed.
I installed this myself a couple of years ago.
Before using the thruster I flip a switch to get 24V, then use the thruster normally, after use switch back to 12V. I have buzzer to remind me of this.
Yo need a 12/24V series/parallel relay commonly used for starting with 24V by heavy trucks.
PM me if you need more details.

Edit: the post of jt11791 just shows up, he covers the details already.

[Jammer]

Originally Posted by jordanbigel

Thanks for the feedback! Some interesting ideas - I didn't realize I could tap 12v from a 24bank just by going direct to one of the batteries.

I am not 100% clear on why this would give you 12v instead of 24v - assuming a 2 battery bank where I have pos from battery 1 and neg from battery 2 going to pos and neg bus bars, I get 24v from the bus - ok, I get that part. But you get 12v if I wire directly to battery1 (or #2) pos/neg and not to the bus - have I got that right?

Yes. Keep in mind that you will then be depleting the charge in one battery, not both, leading to an imbalance. There are various ways to either prevent that or correct it that have been suggested throughout the thread.

As for cost, even though a pair of DC/DC chargers (about $550) cost less than a new 24v alternator, which is probably more like $1200 for a high output Ballmar like the 12v one I have now, I might be able to get 300 or $400 for my 12v alternator to offset the cost, and avoid the extra installation and wiring for the DC/DC chargers - plus, I like having the 2nd alternator. I can combine the house+thruster battery so that if the main alternator dies, I can still charge the house bank from the secondary alternator. So I am inclined to keep both alternators running.

Unless you will be switching your house bank to 24 volts, you would no longer be able to combine it with the thruster battery and charge it with the thruster alternator.

In addition, the thruster draws like hundreds of amps (I don't have the numbers handy) so having that dedicated alternator keeps the voltage up on the thruster battery/bank while it is being used. Also, I think it is unrealistic to assume it will only be used for 10 seconds at a time. The thermal cutout will trip after about 2 minutes, so anything within 10 seconds and 90 seconds can be considered normal and common, in my experience. At that discharge rate without a dedicated alternator feeding the thruster battery/bank I don't see how you could maintain thrust for more than 30 seconds with just a 30amp DC/DC charger (like the Victron Orion-Tr Smart 12/12-30A linked to above).

The group 27 batteries you should be using will deliver, for discussion purposes, around 100 A-h. A 24v thruster will consume approximately 400 amps, which will give you a runtime with full batteries of 15 minutes.


A 30 amp charger will have to charge for roughly 15 minutes to make up for each minute of bow thruster operation. (30 amps * 15 minutes = 450 / 1 minute less 10% for heat losses in the battery gives us roughly 400 amps)

Even the windlass alone draws 100amps and is often used for 4 or 5 (or more) minutes at a time - like the thruster, always with the engine running - and so that 2nd alternator is also useful even without the bow thruster IMO. At least, this has been my understanding.

Sure, you can do that, and you'll be less dependent on the battery being in good shape. But if you're upgrading to a really large thruster then it's going to rely on the battery because the alternator simply isn't large enough to help much, and a good solid battery close to the windlass should do just fine. Again the math is that you've got a 100 Ah battery, and if the windlass draws 100 amps as you state, you'll get a full 60 minutes of runtime from a single battery -- far more than the motor can withstand without overheating.

[goboatingnow]

Originally Posted by Jammer

Yes. Keep in mind that you will then be depleting the charge in one battery, not both, leading to an imbalance. There are various ways to either prevent that or correct it that have been suggested throughout the thread.





Unless you will be switching your house bank to 24 volts, you would no longer be able to combine it with the thruster battery and charge it with the thruster alternator.






The group 27 batteries you should be using will deliver, for discussion purposes, around 100 A-h. A 24v thruster will consume approximately 400 amps, which will give you a runtime with full batteries of 15 minutes.


A 30 amp charger will have to charge for roughly 15 minutes to make up for each minute of bow thruster operation. (30 amps * 15 minutes = 450 / 1 minute less 10% for heat losses in the battery gives us roughly 400 amps)






Sure, you can do that, and you'll be less dependent on the battery being in good shape. But if you're upgrading to a really large thruster then it's going to rely on the battery because the alternator simply isn't large enough to help much, and a good solid battery close to the windlass should do just fine. Again the math is that you've got a 100 Ah battery, and if the windlass draws 100 amps as you state, you'll get a full 60 minutes of runtime from a single battery -- far more than the motor can withstand without overheating.

Leaving aside that a 100Ah battery won’t give you even 30 mins at 100A

[goboatingnow]

Drawing 12v from a battery in series with another to create 24 isn’t optimum. But the imbalance will have little consequence in general for flooded wet acid.

[jordanbigel]

Originally Posted by Jammer

Unless you will be switching your house bank to 24 volts, you would no longer be able to combine it with the thruster battery and charge it with the thruster alternator.

The group 27 batteries you should be using will deliver, for discussion purposes, around 100 A-h. A 24v thruster will consume approximately 400 amps, which will give you a runtime with full batteries of 15 minutes.

A 30 amp charger will have to charge for roughly 15 minutes to make up for each minute of bow thruster operation. (30 amps * 15 minutes = 450 / 1 minute less 10% for heat losses in the battery gives us roughly 400 amps)

Thanks Jammer - I should have realized the first point about no longer being able to combine the 2 banks, which really makes upgrading the second alternator less attractive compared to the DC/DC charger option off the house bank.

I can re-wire the 2nd alternator to the house bank as a backup and disable it via the regulator (a switch to disconnect the field wire?) until it is needed.

I'm leaning in this direction now, definitely seems like the lowest impact way to make this happen. Thanks again.

[jordanbigel]

Originally Posted by jt11791

My boat is set up just like you want. I have a 12V windlass and a 24V bow thruster, and a 12V alternator. The key is the use of a Bosch series-parallel relay switch. The switch puts the two 12V batteries in parallel for charging and in series for the load (thruster).

This is very interesting - I'm definitely going to research this idea more.

But the one thing about this which concerns me - you have to manually flip this switch and then you're in 24v mode, and that means no way to operate both the windlass and the thruster at the same time. Is that right?