Bow thruster not producing much thrust

[O C Diver]

Took me a bit to come around to the current draw issue, but see that now. Vetus' page for this model includes an asterisk that notes "this model is design to be a compatible replacement for older Vetus BOW75 4.7kW units." Mine might draw more than 500 amps. No way that should be on 110 feet of 2/0 cable.

4.7 KW (4,700 watts) ÷ 12 volts = 392 amps. From recollection, a DC motor running at below rated voltage shouldn't require more amps, it should slow down.

Even more keen to know how much of a voltage drop you're getting.

I would consider taking your start battery up the the bow thruster and wiring it with some 2' cables as an experiment. See if it gives you the push that you want and how much of a voltage drop. Then all you have to do is decide how many boat units you want to invest.

Ted

 

[Jeff F]

If you have space for new batteries forward it's not a particularly expensive proposition. A couple of small starting batteries, a small dc-dc charger and a few short cables are all that's required.

My boat was wired like the OP's when I got it. This was one of my first upgrades.

 

[more]

I burned my bow truster from a factory installed on ex. boat. bow truster to battery bank be 5-meter cable 90 mm2. voltage on truster on work 9-10V factory. for you install 1 starter battery 100-180Ah around 1000+ cca 1 meter from truster and see a huge difference.

 

[Comodave]

4.7 KW (4,700 watts) ÷ 12 volts = 392 amps. From recollection, a DC motor running at below rated voltage shouldn't require more amps, it should slow down.

Even more keen to know how much of a voltage drop you're getting.

I would consider taking your start battery up the the bow thruster and wiring it with some 2' cables as an experiment. See if it gives you the push that you want and how much of a voltage drop. Then all you have to do is decide how many boat units you want to invest.

Ted

I suggested doing a temporary start battery for a test in post #12, I guess that great minds think alike…

 

[HeadedToTexas]

I will be doing the voltage testing this weekend, but I'm going to have to psych myself up to moving the main engine battery. That and eat some spinach. All in due time, of course.

In the meantime, the bottom diagram of these three is what I believe we are talking about. Both the thruster and windlass are currently powered from the house bank through the main busbar. The main engine and generator start batteries are only connected when the Auto Charging Relays meet their voltage requirements.

That bottom diagram shows the installation of new positive and negative busbars that connect the thruster and windlass to the main engine start battery. Both of those motors are behind switches and breakers or fuses, though my diagram only shows the switches. Is that an electrically sound and responsible way to accomplish the rewiring?

 

[O C Diver]

It looks ok to me, but I'm unclear where the alternator senses voltage to make sure both the house and start battery are full.

Ted

 

[DennisB1]

Important in this discussion is voltage drop at the wire to swaged terminal connection and from the terminal to motor post connection.
I wire brush to bright metal before crimping the exposed wire and the inside of the terminal the coat the wire with silicon dielectric grease before swaging. The grease provides a seal and provides a long term low resistant connect.
The connection at the motor post also needs similar treatment. That include the terminal surfaces, the post threads and the nut surfaces and threads. Again seal these with the dielectric grease.
Also the wire sizing and short runs are important.
My thruster is 24v with two group 31 agm batteries and about 6 ft total run with 2/0 cable works great.
The anchor winch is Lofrans 1500w 12 volt off the house bank. The alternator outputs over 100amps at 1100 rpm which makes a very noticable difference in winch operation versus battery only from a 1000amp hour bank.
Message keep all connection clean for best operation

 

[HeadedToTexas]

My plan this weekend is to test volts and amps at the thruster when it is running. I will also inspect the connections as looking clean and tight is not the same as sound continuity.

Also on the list is to confirm how and where the alternator and starter tie into the main engine battery and house bank. I think I know, but you know how that goes. More as I know it. Thanks guys.

 

[BruceK]

My bowthruster ran but was similarly anemic/ineffective in performance. A check of the Optima blue top(90AH)AGM start type battery OEM fitted right next to it showed it was cactus. Replaced with same( even used same securing set screws), improvement was spectacular. Advice is 2 batts are preferable but one seems fine and it`s how the boat was built. The battery gets charge via a connection to one of the dual purpose 8Ds that supply start and house.
As you don`t have a dedicated adjacent battery I think adding one will improve things a lot. But, if it`s how it was built, maybe it did work satisfactorily once, if so, discovering why it doesn`t now could be key.

 

[HeadedToTexas]

I am running out of enthusiasm today and thinking has come easier than crawling around in the bilge. Here's a question for you guys with thruster batteries right next to your thrusters. Do you not have a disconnect switch somewhere readily accessible? Or is there a switch right there close for maintenance?

My boat has a thruster disconnect right by the wheel in the pilothouse. That means the 2/0 cables not only come from the house bank in the lazarette to the main bus, but then go up to that switch before reaching the motor control solenoids and lugs on the motor.

It also means that if I add a dedicated battery for the thruster, I would either have to abandon that switch or run the power to that switch and back. If the switch is important, then the main engine start battery is about as close to that switch as I can get with a battery.

 

[Comodave]

I had a battery switch at the batteries. If you want to be able to turn it off at the helm put in remote controlled switch. I think Blue Seas make one.

 

[HeadedToTexas]

...I'm unclear where the alternator senses voltage to make sure both the house and start battery are full.

The main engine battery switch has two 4/0 cables. One connects to an auto charging relay then on to the main bus. The other connects to the main engine battery. The main engine starter connects to the other lug of that battery switch.

The main engine alternator connects to a 200 amp fuse before connecting to the main bus bar. The means the alternator only charges the main engine when the ACR senses the right voltage inputs. Alternator output is controlled by this Balmar regulator.

 

[HeadedToTexas]

I had a battery switch at the batteries. If you want to be able to turn it off at the helm put in remote controlled switch. I think Blue Seas make one.

The only reason to disconnect the thruster from its power source is to work on the motor or its connections. That isn't going to happen without being up close and personal, so why not have the switch right there by the battery, yes?

 

[Comodave]

That is what I have on our current boat as well as our last boat. The only reason to have a remote battery switch is if the contacts weld together and the thruster won’t shut off, then the remote would be nice.

 

[O C Diver]

The main engine battery switch has two 4/0 cables. One connects to an auto charging relay then on to the main bus. The other connects to the main engine battery. The main engine starter connects to the other lug of that battery switch.

The main engine alternator connects to a 200 amp fuse before connecting to the main bus bar. The means the alternator only charges the main engine when the ACR senses the right voltage inputs. Alternator output is controlled by this Balmar regulator.

View attachment 159036

You have to decide for yourself whether the house battery is getting charged completely. I've never liked 2 battery banks of possibly different chemistries and certainly of different sizes, with very different cable lengths being charged by one alternator. I assume this would only be a cruising problem as the house bank is charged by the inverter / battery charger from shore power.

Depending on how you change the power supply to the windlass and bow thruster, it might make more sense to charge the house bank with the engine alternator and charge the engine battery with a 12 VDC to 12 VDC charger off the house bank.

My personal preference was for 2 alternators, one for the house and one for the engine.

Ted

 

[O C Diver]

I am running out of enthusiasm today and thinking has come easier than crawling around in the bilge. Here's a question for you guys with thruster batteries right next to your thrusters. Do you not have a disconnect switch somewhere readily accessible? Or is there a switch right there close for maintenance?

View attachment 159033

My boat has a thruster disconnect right by the wheel in the pilothouse. That means the 2/0 cables not only come from the house bank in the lazarette to the main bus, but then go up to that switch before reaching the motor control solenoids and lugs on the motor.

It also means that if I add a dedicated battery for the thruster, I would either have to abandon that switch or run the power to that switch and back. If the switch is important, then the main engine start battery is about as close to that switch as I can get with a battery.

It's best practice to have switch near the battery. I never got around to installing one when everything got converted to 24 VDC. Instead, I had a fuse holder that I removed the fuse on.

The other option is a latching relay from Blue Seas. The relay I'm thinking of has 2 coils. Push a button to engage the relay. Push another to disengage. The coils don't remain energized.

Ted