Bow thruster bat tie in with house bank

[gpeacock]

Hi everyone
I am about to start wiring up my new bow thruster. Im also about to start setting up a new house battery bank.
After wavering back and forth wrt the different battery types Ive decided on 6V Wet cells for the house bank mostly due to costs. The storage area for the house bank is well secured and ventilated. Im willing to manage the maintenance of them.
Now Im struggling with how to power the windlass/thruster. There is no way to vent up front and being an offshore boat, things are going to get banged around there. Wet cells up front are less than ideal. Voltage drop on the wire run from the house bank would be prohibitive and I could use the extra battery capacity for my house bank. Throwing in some sort of ACR means that extra capacity is wasted and adding in an extra charging system just for the forward battery seems like spending money for the sake of spending money.
There doesn't seem to be a perfect solution here so is the lesser of all evils to just throw an AGM up front tied into house and assume that the charging voltages/characteristics are close enough?
Im not looking for theory here, but surely someone out there has personal experience with this type of setup...
Gary

[rwidman]

....... Voltage drop on the wire run from the house bank would be prohibitive .....

Use large enough cable and the voltage drop will be minimal.

...... just throw an AGM up front tied into house and assume that the charging voltages/characteristics are close enough?....

You would still have to use pretty large cables to connect the batteries and you would have to install overcurrent protection at each end of the cable run to protect the cables in case of a short circuit or a shorted or partially shorted battery.

How much current does your thruster require and how long is the wiring run from the existing batteries to the thruster and windlass?

[gpeacock]

350 Max amps for the thruster, the run to the front is 20ft there and 20ft back... even if they made a cable large enough I still want to add extra capacity to the house bank and using the thruster/windlass battery for double purpose seems like the best option.
1 or 0 awg should be big enough to deal with charging currents with minimal drop. Fusing on both ends is already in place.
Thanks
Gary

[model 10]

I put a group 24 AGM battery up fwd for the windlass. This was inside the cabin of course so you have little choice but to use a sealed battery. I used this battery with a collection of wet and AGM for years. I finally got to about 8 years before every battery kind of died. The up front AGM was in no worse shape than any of the others. Now I am going to buy all new (7) AGM's and hopefully will get another 8 years but with a matched set, we shall see. The scientific guy's will argue that the charge voltage needs to be specific for battery type but you might just get buy with just 1 AGM for your thruster.

[rwidman]

Originally Posted by gpeacock

350 Max amps for the thruster, the run to the front is 20ft there and 20ft back... even if they made a cable large enough I still want to add extra capacity to the house bank and using the thruster/windlass battery for double purpose seems like the best option.
1 or 0 awg should be big enough to deal with charging currents with minimal drop. Fusing on both ends is already in place.
Thanks
Gary

That's a lot of current. Just remember that whatever current the bow battery cannot provide will come through those cables from your other battery or bank. You have to allow for that with the cables and the circuit protection.

Here's a thought - You could connect a relay to the thruster that would disconnect the house bank when the thruster is running and connect it back when you stop using the thruster so it will charge. This would avoid any heavy current flowing through the long cables. And you could use smaller cables.

[gpeacock]

Guy: That's the kind of real world info Im looking for.
Rwidman: I have thought of the relay, but the brief periodic use of a thruster seems like asking it to do too much switching. I could set the relay up to disconnect when the thruster circuit is turned on but then Im asking the battery up front to do too much and the charging current gets higher when things are reconnected. Fuses will protect the wire... if it blows too often I will have to rethink my design.

[rwidman]

It's not too much switching, the thruster itself probably has a relay.

It was just a thought. If your bow battery fails, the house bank will try to run the thruster and blow the fuse.

You can do it the way you plan, that's totally acceptable.

[Andina Marie]

Sufficiently heavy cables from the house battery would be extremely expensive and still lose power in voltage drop. A sealed battery with sufficient capacity to last for your longest thrusting time located as close to the thruster as possible is the best solution.

Once the battery capacity is local, a 10 gauge charging line from the starting battery with a Combiner100 will take care of maintaining charge on the thruster battery. Duty cycles on thrusters are quite low so 30 or 40 amps through the charging line will have adequate time to recharge.

Locate the Combiner100 at the bow end of the charging line. That way if the voltage drop is severe while on charge because your main engine(s) is running, the Combiner100 will disconnect and protect the cables.

If ventilation is a problem for the batteries, an Automatic Battery Vent that runs a small blower while charging is in progress will clear any fumes and it runs for 30 minutes after charging ceases to clear heat and humidity.

[gpeacock]

Rwidman: I hadn't thought of using the relay on the thruster... will check that out when it comes in... I cant imagine right now how that would look.
Andina: Unless I'm mistaken, the combiner (like the ACR etc) doesn't give me the option to add that front capacity to the house bank when not using the thruster. I do like the Battery vent fan relay though, that will work well for the House bank.

[jeremiason]

When Catalina built my boat, they installed a 1200 Windless and a 7hp Thruster, which are both hard wired to the main battery bank, about 23 feet away.

I have no power drop and they perform well...

If you can run the wires, it is one less hassle having a battery up there.

[rwidman]

Originally Posted by jeremiason

When Catalina built my boat, they installed a 1200 Windless and a 7hp Thruster, which are both hard wired to the main battery bank, about 23 feet away.

I have no power drop and they perform well...

If you can run the wires, it is one less hassle having a battery up there.

The West Marine cable size chart doesn't go high enough for his 350 amp thruster.

The West Advisor: Marine Wire

[Andina Marie]

Originally Posted by gpeacock

Rwidman: I hadn't thought of using the relay on the thruster... will check that out when it comes in... I cant imagine right now how that would look.
Andina: Unless I'm mistaken, the combiner (like the ACR etc) doesn't give me the option to add that front capacity to the house bank when not using the thruster. I do like the Battery vent fan relay though, that will work well for the House bank.

Correct, the thruster battery has to be regarded as an independent battery bank with sufficient local capacity to support thrusting jobs.

My bow thruster is run from renewable energy but she hates to get in the cold water.

[rwidman]

Originally Posted by Andina Marie

Sufficiently heavy cables from the house battery would be extremely expensive and still lose power in voltage drop. A sealed battery with sufficient capacity to last for your longest thrusting time located as close to the thruster as possible is the best solution.

Once the battery capacity is local, a 10 gauge charging line from the starting battery with a Combiner100 will take care of maintaining charge on the thruster battery. Duty cycles on thrusters are quite low so 30 or 40 amps through the charging line will have adequate time to recharge.

Locate the Combiner100 at the bow end of the charging line. That way if the voltage drop is severe while on charge because your main engine(s) is running, the Combiner100 will disconnect and protect the cables.

That's probably the best solution.

[twinboat]

Andina said:
Locate the Combiner100 at the bow end of the charging line. That way if the voltage drop is severe while on charge because your main engine(s) is running, the Combiner100 will disconnect and protect the cables.

Question:
If the thruster / windlass battery is low enough to make the combiner cut out due to voltage drop, would'nt it keep cutting out and not charge your battery.

Roger, Slow Churn

[Andina Marie]

Originally Posted by twinboat

Andina said:
Locate the Combiner100 at the bow end of the charging line. That way if the voltage drop is severe while on charge because your main engine(s) is running, the Combiner100 will disconnect and protect the cables.

Question:
If the thruster / windlass battery is low enough to make the combiner cut out due to voltage drop, would'nt it keep cutting out and not charge your battery.

Roger, Slow Churn

Yes and No, Roger.

Our Combiners regulate the load on the alternator by limiting the output diverted to the auxiliary battery to be charged. Even without the bow thruster situation, if the auxiliary battery is very low and the battery on charge is over 13 volts the low voltage load on the Combiner will drag the source battery down which will cause the Combiner to turn off. While it is off the starting battery will recover until it cycles again. On each cycle it transfers about 2 amp-hours of charge to the secondary battery.l

As the secondary battery voltage rises it drags the source battery down less and the Combiner will extend the timing of the cycle untill eventually the load battery gets to around 13 volts and the Combiner can stay on.

This is normal operation and protects the alternator from overload since on average it is never forced to charge a very low voltage, unlike diode isolators that connect the LOWEST battery first. The cycling process can often continue for 5 or even 10 minutes transferring about 2 amp-hours per minute.

In the case of low voltage caused by the bow thruster load, it is a temporary low voltage while running just like you see a low voltage on a starting battery when starting an engine. The drop along the 10 gauge charging line up to the bow will cause the voltage on the Combiner to be low so it will cycle on and off once a minute. With the local thruster batteries being the primary power source the few amp hours delivered makes minimal difference while thrusting but once the process is finished the charging cycles will bring the thruster battery up to full charge.