Battery Placement and Wiring 24v

[Spooner2010]

Just got a 24v 80 thrust Terrova. Plan to wire it this weekend. But I have a few questions. Last summer I restored my 16.5' Aluminum Deep V from the foam up. I added a large livewell (15 gallon ish) under the front casting deck. Thus adding a lot of weight to the front of the boat. Now I have to figure out where to place the 2 deep cycle batteries to run my Terrova. The Terrova install manual says I can run 8AWG wire for up to 15'. If that's the case then I have a compartment in the rear near the transom to put the batteries.

Are there any issues or reasons anyone can think of for NOT putting the batteries in this rear compartment?

Also... What is the typical size fuse or circuit breaker for the starter/accessory batter? I'm running starter, graph, pumps and lights on this one 12v batter.

 

[Spooner2010]

Have I asked a stupid question?

 

[Silvertip]

You actually asked "several" questions. None of them stupid. Stupid questions are the ones that don't get asked. 1) you do NOT want a fuse in the circuit that feeds the starter. Your car doesn't have one, nor your truck, nor have they ever because a starter can draw hundreds of amps over a short period. The fuse would cost as much as the engine (but I digress). You can install batteries wherever they fit but be aware that adding two heavy batteries in the rear of a boat which is typically already stern heavy can have some issues with getting on plane. But then if that's where they need to go, other corrective action can take place if needed. Where you need a fuse for accessories is in the smaller #10 gauge wire that connects to the positive terminal of the starting battery. That wire is what feeds accessories. The big battery cable feeds to the starter and engine circuits. No fuse is used there.

 

[Spooner2010]

Where you need a fuse for accessories is in the smaller #10 gauge wire that connects to the positive terminal of the starting battery. That wire is what feeds accessories. The big battery cable feeds to the starter and engine circuits. No fuse is used there.

Yes Silvertip. What size fuse would I need for that #10 wire? 5 amp?

Thanks btw for the starter info. That narrows my info needs.

 

[PondTunes]

Yes Silvertip. What size fuse would I need for that #10 wire? 5 amp?

Thanks btw for the starter info. That narrows my info needs.

That question kind of depends on some variables.
In general #10 wire can support up to 30 amps provided the wire is no longer than 10 feet.

The size wire you need varies wildly based on the accessories you are using and the length of the run.
The simple method to determining this is looking at what accessories you want to hook to this circuit, and see what size fuse they take. OR calculate the wattages needed.

Already covered was not fusing your starter it should be on its own wire direct to the battery.
Since you have your graph, pump and lights to deal with for your accessories we need to know a little about them.

What type of lights are you running? incandecent? led? LED's will draw far less current but are more expensive than Incandecent halogens. You will need to know the wattages of the lights to figure out how many amps they will draw.
(watts / 12.5 volts = amps) add up all the wattages then divide by battery voltage for an idea of what amp fuse would be required for the lights.
A graph should draw very little, probably 1-3 amps maximum.
Your bilge pump should have a minimum recommended size fuse listed on it, how much it draws is related to how many GPH it can move.

Lets say the pump calls for a 10 amp fuse, the graph calls for a 3 amp fuse and you have 2 50 watt halogen dock lights.
100 watts / 12.5 = 8 amps of draw.

10 a + 3 a + 8 a = 21 amps of accessories, therefore you should go with around a 25 amp fuse.

You can go off of the fuse rating in your accessory as a quick and easy method because that fuse would pop if that accessory ever pulled more than the fuse's rating.

The only other way you may run into trouble is if say you have a lot more lights than 100 watts worth or your run of wire is very long. If the run of wire is say 20 feet instead you will start experiencing voltage drop on a #10 wire past about 15 amps of draw. This means at 16 amps you will get less than battery voltage along the wire while trying to draw this much current over it. The more amperage you try to draw the more voltage drop you'll get.

here is a handy chart that shows what the max length of wire is at a given amperage draw.
https://cdn.sparkfun.com/assets/f/d/...5e3d000002.jpg

 

[Silvertip]

I would disagree with you Pond Tunes. That #10 wire needs a 20A (or 30 amp max) fuse or breaker within one foot of the battery regardless what the accessory load is. That fuse or breaker protects the run of wire from the battery to the distribution/fuse panel at the helm, not the individual devices. It is the same philosophy with the main service panel breaker in your house. Individual fuses of appropriate size are used for the branch circuits (accessories). 5 to 7.5 amp fuses are generally fine for everything except pumps and high power lights, stereo systems.

 

[Spooner2010]

Thanks Pond I like that chart.

So Silvertip you're saying to fuse by size of wire rather than draw by accessory?

 

[Silvertip]

Stop and think. The #10 gauge wire from the battery to the fuse block at the helm carries the current for everything it must feed. If there is a short along the way, the fuse or breaker AT THE BATTERY prevents a burn down. Each circuit (lights, bilge pump, live well pump, radio, and any other accessories) is fed through an appropriate size fuse/breaker to the switch controlling that accessory and then on to the accessory and back to ground. The technical answer to your question is yes and no. If the radio fuse blows for example, it is more than likely the radio had an issue which blew the fuse, not the wiring although that can and does happen. Folks tend to think the fuse protects the device. In effect it protects the wiring. Each device has a maximum current draw so if the device needs a 5 amp fuse, install a five amp fuse even though the 16 gauge wire can carry more than that. The fuse does its job by protecting the wiring. Circuit diagrams showing boat wiring are all over the place.