Boat electrics help with 2x12v batteries

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Hatch

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#228807 23-Jan-2018 15:01

I have a small boat which I am setting up with 2 x 12v batteries for an electric trolling motor, fish finder and a tilt and trim unit.

The previous owner had the batteries set up in series to provide 24v for the trolling motor. The fish finder was connected directly to a single battery for 12v power.

Now I am introducing a tilt trim unit for the outboard which requires a 12v supply.

The current setup has fuses.

What would be the best way to set up electrics with the three power drawing devices?

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#1945475 23-Jan-2018 15:04

how is your understanding of electrics and current draw?

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Hatch

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#1945517 23-Jan-2018 15:18

hsvhel:

how is your understanding of electrics and current draw?

Very basic, but I am a quicker learner (or so I like to think). There are two quality marine grade batteries in the setup. Although i don't have the specs at hand.

The trim and tilt unit and the trolling motor will not be used at the same time, and something could be put in place to ensure current supply is not overdrawn . The fish finder uses only a relatively small amount of power, but a smaller independent 12v battery could be installed to power this is needed.

Hatch

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#1945522 23-Jan-2018 15:32

The trolling motor draws up to max 42A 24v.

I cannot find the power draw of the tilt trim device right now via the internet. The actuator is powered by a 12v supply.

hsvhel

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#1945538 23-Jan-2018 15:55

Whilst its not a huge task i would recommend either speaking with someone knowledgeable near you for sure.

Fires on water are not a good combination

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timmmay

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#1945550 23-Jan-2018 16:12

There's some good information about trolling here.

Hatch

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#1945555 23-Jan-2018 16:20

timmmay:

There's some good information about trolling here.

Thanks I will look at it later.

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MikeB4

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#1945561 23-Jan-2018 16:41

As a boat owner I would like to give some advice that is meant in the best possible way. Unless you are completely confident and skilled you should not do this as your life may well depend on it. The sea takes no prisoners.

Here is a crazy notion, lets give peace a chance.

Hatch

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#1945563 23-Jan-2018 16:44

MikeB4:

As a boat owner I would like to give some advice that is meant in the best possible way. Unless you are completely confident and skilled you should not do this as your life may well depend on it. The sea takes no prisoners.

Thanks, good advice. I am completely confident that I can do this myself, with some assistance. This is really a very simple setup.

Two devices, not used contemporaneously from a single power supply. Fishfinder can be powered independently.

tdgeek

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#1945656 23-Jan-2018 19:21

@MikeAqua

Technofreak

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#1945694 23-Jan-2018 20:07

How are you charging the batteries?

I presume you're using an on board system from the alternator on the main motor, or do you take them away from the boat and charge them up separately?

If you're charging the batteries from the boats alternator then you'd be best to get a 24v-12v converter to run the 12 volt devices. That way both bateries discharge equally. Charging systems do not generally do well at charging batteries that have been discharged to differing levels.

If you're taking the batteries home and charging separately on a 12 v charger then it doesn't really matter.

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Hatch

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#1945708 23-Jan-2018 20:27

Technofreak:

How are you charging the batteries?

I presume you're using an on board system from the alternator on the main motor, or do you take them away from the boat and charge them up separately?

If you're charging the batteries from the boats alternator then you'd be best to get a 24v-12v converter to run the 12 volt devices. That way both bateries discharge equally. Charging systems do not generally do well at charging batteries that have been discharged to differing levels.

If you're taking the batteries home and charging separately on a 12 v charger then it doesn't really matter.

It's a very basic setup.

The boat is really a dingy with a 25hp motor and the previous owner advised there was no point to hooking up the batteries to charge from the outboard because of the limited power output.

The boat is parked on the lawn so I remove the batteries and charge separately on a 12v intelligent charger in the garage. The previous owner provided a 24v charger but I don't use it.

BTW these are the batteries I am using:

http://www.dcpower.co.nz/enex-dc24mf-p-317.html

CCA: 680, 80ah 12v batteries x2.

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Aredwood

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#1945807 24-Jan-2018 02:12

Any idea what the normal running current of the trolling motor is? As if it is 42A continuously, then those batteries will be flat after just 1 hour.

Note that normally you don't discharge lead acid batteries below 50% charge, unless it is a standby type application where the batteries will only rarely get used. And below 50% the output voltage typically starts to reduce quickly anyway.

Any reason why you can't just get a little 2.5HP or so outboard for trolling use? As it avoids the need for big and heavy batteries, and you will then have a backup to your main outboard as well.

Your electric trolling motor has a max output of around 1KW not allowing for motor efficiency losses. For comparison.

MikeAqua

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#1945853 24-Jan-2018 09:29

I suggest sticking with the 24v for the trolling motor. This will be 2 x 12v batteries connected in parallel. If you change from 24v to 12v supply then you double the amps and the wiring may not be set up to accommodate the increased current.

I would use a heavy duty resettable circuit breaker like this one from Burnsco. Position the breaker on the positive lead powering the trolling motor, as close to the batteries as possible. It will also function as an isolation switch when you are not using the boat. The instructions for the trolling motor should specify what amp rating circuit breaker to use. Whatever you do make sure you use marine rated components.

I would definitely install a separate small 12v battery for the fishfinder and power trim. (e.g. a jetski battery).

Do you know how many amps your power trims draws?

Is your outboard electric or manual start?

Mike

nickb800

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#1945860 24-Jan-2018 09:37

If you go for a separate small 12v battery for fish finder etc then you may find that the charge output from the outboard is sufficient to keep it topped up. Then have separate 2x12v for trolling motor that you charge on land

MikeAqua

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#1945865 24-Jan-2018 09:42

nickb800:

If you go for a separate small 12v battery for fish finder etc then you may find that the charge output from the outboard is sufficient to keep it topped up. Then have separate 2x12v for trolling motor that you charge on land

Good point ... do you have charge output from your outboard?

Mike

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