Marine Ac/Dc

Hello,

A quick question about wire type.

I have a autotiller that the previous owner wired with SJ cord (heavy duty extension cord).

Do you see any issues using this type of boat wiring?

Thanks,

Carmen

Hi Carmen,

I am not a huge fan of using SJ cording on boats, but it does work.

I would much rather use a quality, marine grade, tinned copper boat wiring like the product from Ancor.

Kevin

Kevin,

I bought a Sea Nymph 195 Sportfisher with a four-cylinder Mercury I/O last fall and am getting ready to prep for the season.

The current marine electrical setup has a dual battery with an isolator switch controlling them. One is setup for starting and accessories and the other is only being used for the Lowrance navigation and sonor system. Both are charged by the alternator.

I have just bought a 24 volt trolling motor and a 12 volt anchor winch system. I still have to purchase my third battery and might just buy two new for the 24 volt side and pick the best of the two I have for the 12 volt side.

I am trying to identify the most effective way to reconfigure my boat wiring. I don’t have easy access to shore power, so I will not be looking at a marine shore power system right away, but might add one at a later date.

Is there a way to still use my isolator switch with 12 volt on A and 24 volt on B? If so, how would I wire it? Or, should I just trash the isolator and go with a 24 volt VSR since it would allow me to hook up shore power at a later date?

If I go the second route, which battery should I hook up the following accessories to Trolling 1, trolling 2 or starting battery?

• Anchor winch
• Downriggers
• Nav system
• Navigation lights
• Boat horn
• Aerator and bilge pumps
• Marine radio
• Music radio

Thanks

Sam

Sam,

The best solution for this marine electrical system is to have one battery for your engine and normal boat circuits and use the other two batteries for your trolling motor and anchor winch.

Connecting your boat accessories to the trolling motor batteries may seem like a good idea, but as I have mentioned in an Easy Ac/Dc post you can run into some extreme problems.

A normal 12 volt isolator can not be wired to charge a 12 and 24 system. It can be used on a 24 volt system, but your alternator will only put 14.4 volts and your engine is only designd for this lower voltage.

The BEP trolling motor VSR would work great for your application. Since shore power charging is not currently an option, I would use the engine alternator to charge your trolling motor batteries.

If you are concerned about drawing your engine battery down too low with your boat accessories, you may want to consider using a Low Voltage Sensitive Relay. I would normally recommend having a second battery for your house loads, but four batteries in the bilge of a 195 SeaNymph may keep the boat from going onto plane. The LVSR cuts power to the accessories connected to it when the battery voltage gets too low. The battery voltage will still be high enough for your engine to start.

Hope this helps,

Kevin

Kevin,

Thank you for the reply.

I am going to go the VSR route, connecting all accessories to starting battery. I would also like to connect anchor to trolling battery bank like you suggested.

Should I have a fuse on both the positive and negative leads of anchor?

Thanx

Sam

Sam,

If you are connecting the anchor to the 0 to 12 volt battery of your trolling bank, there is no need for circuit protection on the negative lead. If you are connecting the anchor to the 12 volt to 24 volt battery of your trolling bank, then I would definitely put circuit protection on the negative lead to protect against accidental faults to the anchor negative which is actually the 12 volt positive lead of your 0 to 12 volt trolling motor battery.

Kevin

Kevin,

Thanks for the quick reply.

The only question I have left would be which battery in the trolling bank is 0-12 and which is 12-24? Battery A or battery B on the VSR wiring Diagram?

It shows the positive lead from trolling motor on battery A and negative lead on battery B. I am thinking battery A would be 0-12 volt.

Am I correct?

Sam

Sam,

Battery B would be the 0 to 12 volt.

The negative of your trolling motor and the negative of your anchor would connect to the negative of battery B. The positive of your anchor would connect to the positive of battery B.

Let me know if you have any other questions,

Kevin

Hi,

I have read the page on installing a VSR but am still unclear about the issue of grounding.

Following the VSR instructions I have added a second marine battery (in a fiberglass boat) and made the following connections:

• Positive lead from VSR to positive terminal of primary battery.
• Positive lead from VSR to positive terminal of secondary battery.

Now the instructions say to connect a lead from the negative terminal of the secondary battery to the ground.

I have two questions:

1. Can I connect the negative terminal of the secondary battery to the negative terminal of the primary battery? -> i.e. it seems logical to assume the primary battery negative terminal has been earthed correctly already (I have not channged anything on the primary battery and everything was working).
2. The VSR also has a very thin (and short) negative cable which the manual says must also be grounded – should this go to the negative battery terminal or somewhere else?

Thanks for your help

Mark

Mark,

1. “Can I connect the negative terminal of the secondary battery to the negative terminal of the primary battery? -> i.e. it seems logical to assume the primary battery negative terminal has been eartherd correctly already (I have not channged anything on the primary battery and everything was working).”
   
   
   • YES.  Connect the two battery negative terminals together. Connect them with a wire that is at least as large as the engine start cables.
2. “The VSR also has a very thin (and short) negative cable which the manual says must also be grounded – should this go to the negative battery terminal or somewhere else?”
   
   
   • The ground wire needs to go to either battery negative terminal or a ground buss.  The VSR is like a voltmeter that is connected to a battery switch.  It needs to have a wire connected to the positive and the negative of each battery to look at this voltage.  The batteries have a common ground so only one ground wire is needed.

I hope that this is helpful. Please let me know if you have any other questions.

Kevin

Kevin,

I trying to size the wire for my Maxwell 800RC windlass. Every were I look it gives you a different conductor size. The motor is rated at 1000w. I need to run the wiring approx. 25′. What size of wire should I be using?

Thanks,

Mike

Hi Mike,

You can use my wire size calculator or the following equation to calculate your wire size.

• CM (wire size)= (K*I*L)/E

Where:

• CM = Circular mil area of conductor.
• K = 10.75 (constant representing the resistivity of copper)
• I = Load current in amperes
• L = Length of conductor from the positive power source connection to the electrical device and back to the negative power source connection, measured in feet.
• E = Maximum allowable voltage drop at load in volts (e.g., for a three percent voltage drop at nominal 12V, E= 0.03 x 12 = 0.36; for a 10 percent voltage drop at nominal 12V, E = 1.2)

The current draw of a maxwell 800 RC at 12 volts is 83.3 Amps
The conductor length is 25*2=50 feet

• At 3%, the CM is 124,371 or 2/0 AWG battery cable
• At 10%, the CM is 37,311 or 4 AWG cable.

It is very common to see 4 AWG cable used on 1000 watt windlasses. A larger wire will reduce the voltage drop at load and the windlass will perform better.

Please let me know if you have any questions,

Kevin

Kevin, 

One more quick question.

So the windlass will operate ok on #4 AWG. The only time this will make a big difference is when it is under high load? And as to my calculation the battery output from my batteries is 13.8 V. So this would also help if I choose to run the #4.

Also thank you so much for your help. 

Mike

Hi Mike,

Yes. The windlass will operate ok on 4 AWG. The only time you may notice it struggle is under very high load.

In reality, your highest load will be when you are trying to retrieve your windlass. Start your engine before reeling in the windlass (probably a good idea anyway). This will increase the battery voltage which will decrease the current draw, decrease the voltage drop in the windlass wire, and increase the windlass retrieval speed.

Happy boating,

Kevin

Kevin

I have a 27’ boat with shore power, a Heart Freedom 1500 inverter charger, two group 31 AGM Lifeline batteries and a battery switch that has four settings.

The battery switch settings are Off, Battery 1 , Both, and Battery 2. The Battery 1 portion of the switch has the wire from the Charger portion of the Freedom unit connected to the lug.

When I leave the boat hooked up to shore power the Freedom unit is operating and supposed to charge the batteries. The remote panel indicates it is working and the batteries condition shows green or “float” on the remote.

Since I have owned the boat I have gone through three batteries hooked up to the Battery 1 position.

My questions are as follows.

• What position should I leave the battery switch when hooked to shore power and I am away from the boat?
• Is the Freedom unit defective and burning up the #1 battery by overcharging it?
• What is the correct wire routing for the system especially the connection from the Freedom charger portion to the four way battery switch?
• What is the most likely cause of battery #1 going dead ?

Thanks John

Hi John,

In my opinion, the best way to connect a battery charger is at the battery switch on the battery posts of the battery switch instead of the common post. When you connect the charger to the battery side of the switch it doesn’t matter what position the switch is in. The charger will always charge the battery.

Boiled batteries are usually caused by the charger staying in the bulk stage of charging. Large draw devices can trick the charger into thinking the battery still needs more charge. Refrigerators are notorious for this. They draw 5-10 amps when it is warm out. The battery charger never shuts off. Most new chargers have a timer on the bulk stage to prevent this from happening.

If no devices are connected to the battery and the inverter is still boiling the batteries, I would replace the charger/inverter.

Hope this helps,

Kevin

Hi Kevin,

I’m an airplane guy who’s redoing the boat wiring on my brother-in-law’s 1972 22’ Reinell.

I have a couple of questions.

We ordered a boat horn and a Smart Battery Switch from EzAcDc yesterday. However, we only ordered the VSR thinking it was all we need but after looking closer I’m not sure.

The boat has two batteries and a manual 1/both/2 switch. Should I change our order to the complete Smart Battery Switch System?

This boat has an original one-wire Delco alternator. I want the following but I’m not sure how to achieve it:

• The ability to disconnect the alternator from the battery when the alternator fails (if this is not important than I’ll forget about it)
• The ability to turn on a warning light when the alternator fails (we removed the original ammeter but the 3 in 1 gauge we installed does have a volt meter)

Do you have any suggestions i.e relays or any other components I can use to achieve the above results? I wouldn’t mind upgrading to a more modern alternator if that solves the problem.

Any direction you can give would be greatly appreciated.

Kevin

Hi Kevin,

A VSR works best when you have a dedicated engine battery and a dedicated house battery. The VSR makes the connection between the two systems.

A conventional battery selector (Off, 1, 2, Both) controls which battery the engine is connected to but does not control which battery the house is connected to.

The key to our partner’s complete Smart Battery Switch System is the dual pole On/Off battery switch. This acts like two on/off battery switches combined into one body.

• When the switch is Off, only emergency devices are connected to the house battery.
• When the switch is On, the engine is connected to the engine battery and the house is connected to the house battery.
• When the engine is running, the alternator first charges the engine battery. When the engine battery hits 13.7 volts, the VSR connects the engine battery and house battery together and begins charging the house battery.
• When the engine is off, the VSR keeps the batteries connected until the battery voltage hits 12.6 volts. When it drops below 12.6 volts, the VSR breaks the connection and allows for enough reserve in the engine battery to start again.

I would not worry too much about a way of disconnecting the alternator if it fails.

In the event of an alternator failure, your system voltage would begin to drop. With the complete VSR system, once 12.6 volts is reached, the VSR will open the connection between the engine and house batteries. Your engine will continue to run until the battery voltage is below 10 volts. When the engine dies due to low voltage, you can turn the battery switch to the COMBINE position. This will manually parallel the batteries and allow you to start your engine and continue running until your battery voltage is to low to run the ignition system.

You will probably run out of gas before you completely drain two batteries running only a simple ignition system on a single stern drive.

Thanks

Kevin