One battery fuse block terminal or two?

[Macboy]

In installing two GC batteries do I want one fuse block terminal or two (one for each positive)?

And all I'm finding on Amazon at the moment are 40, 60, 75 and 100A fuse blocks on the smaller end of the spectrum. I was looking for 90 (can't say why exactly...might have read it somewhere?) but really I guess I'm only concerned with the draw from the starter motor right? I think we'd determined that around 60A? Should I go with he 75A fuse block in that case?

 

[Ward H]

You only need one fuse terminal block. Put it on the red post where you attach your cable supplying whatever it is you are supplying, the Load.
Remember, you are fusing the cable, not the device. What is the maximum current draw you may draw on the battery. Include starting motor, lights, radio, anything electrical. Cable is rated for the amperage it will carry, it's "ampacity". That will determine the minimum cable size you need.
Then fuse 80% of the cable ampacity rating.
Here is a link to a cable chart. http://www.genuinedealz.com/voltage-drop-calculator
There is also a voltage drop calculator. If you choose the smallest cable based on the ampacity and you have a long cable run, you may have a voltage drop that will be unacceptable. You can increase the cable size to reduce the voltage drop. Most try for less than 3% VD.

 

[walt]

The 90 amp fuse may have come from me as that is what I have.

Why... I have measured my outboard starting current (9.8 hp 4 stroke Nissan) at around 35 amps when its warm and up to 50 amps on a cold day. I did this by watching my battery monitor current readout and Im going by memory from a measurement a long time ago but I think these are ballpark.

So I wanted a fuse somewhat larger than 50 amps. You have to pick a wire size both based voltage drop but also based on the fuse size. I chose 4 gauge wire for the run between the batteries in the Vberth and the outboard at the back of the boat and looking at this site https://www.powerstream.com/Wire_Size.htm , 4 gauge wire has a chassis current rating of 135 amps. So the fuse I pick has to be somewhat less than 135 amps but somewhat more than 50 amps. And.. I simply picked 90 amps for the breaker switch. If you have a four gauge run like I do, you could really pick a fuse anywhere between 50 to 135 if you wanted to push things.

Another example (which I did not do) but if a 6 gauge wire run didnt cause too much voltage drop, 6 gauge has a chassis current rating of 101 amps. So in theory, you could pick a fuse anywhere between 50 and 101 amps..

I dont know where Ward got the 80% fuse size for the wire rating but that sounds reasonable. In my case, the four gauge wire has a rating of 135 amps and 80% of this would be a maximum fuse size of 108 amps. The 90 amp breaker I used for four gauge meets this also..

FYI, I also chose four gauge wire because I had a bunch of it. You can run the voltage drop numbers for your wire lenght run and get some percent drop for say 35 amps. I wont bother to try and do this but I will just say that four gauge seems to work just fine for the outboard starter with the batteries all the way forward in the boat and the outboard all the way to the back. Never any issue with starting of false blowing of a fuse. I think four gauge has been a good choice in my case.

 

[Sumner]

How far apart are two batteries from each other? If close then one...

https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A

... on the positive terminal of the one with the charging and load wires. The ones like above can be fused all the way to 300 amps so you would have no problem finding one for your situation. If the batteries are further apart then to meet code you would need one on both. This got me thinking that I should do that on the Mac as one 6 volt is under the sink and the other a few feet away under the V-berth. If you want to meet code then I think you are suppose to have a fuse within 6 inches of the battery.

The same on my two parallel 6 volt banks on the Endeavour. Above you can see there is no fuse on the left bank but there is a cable there that goes to the other bank's positive to the right putting both in parallel. I probably should also have a fuse on the post of the left bank even though the wire from it to the right bank is only over a foot in length. I think I'll add that now. You can see in this case that the 6 volt batteries that are in series are connected by a very short wire from the negative of one to the positive of the other in series. There I wouldn't worry about a second fuse on the second battery as the wire between them is short and not exposed to much so the fuse on the first battery is sufficient.

The fuse on the right bank above is like this ...

https://www.bluesea.com/products/2151/Dual_MRBF_Terminal_Fuse_Block_-_30_to_300A

Sumner
=================================================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...http://purplesagetradingpost.com/sumner/endeavour-main/endeavour-index.html
Mac Trips to Utah, Idaho, Wyoming, Canada, Florida, Bahamas

 

[Ward H]

I dont know where Ward got the 80% fuse size for the wire rating but that sounds reasonable.

Walt, that was Maine Sails recommendation.
Also, since your fusing the wire, not the device, always go with the largest size fuse for the wire. Doing so will also help to reduce voltage drop.
Maine Sail has a very good article on fuse size and voltage drop on his MarineHowTo.com site.
He also has a very good thread in his Musings with Maine Sail section on this site titled Battery Fuse Sizing - How?.

 

[Macboy]

Thanks guys. There's so much more to this than my high school automotive DC days of throwing fog lights and car stereos into the car! Voltage drop back then was what we called it when the stereo drew so much the headlights dimmed ; )

Sumner - the dual fused terminal you show there - would that be suitable to run one lead off to the motor, the other off to the house load wiring or should I run from one fuse block terminal (suitably sized) to a positive load buss and go from there to the motor?

I'll start gathering my load requirements so I get the fusing correct in any case. I'm ordering four wall mount flex neck reading lamps (LED) and some remote 12v sockets so the v berth and the aft berth can be "self contained" for reading and charging iStuff without having to run USB wires everywhere.

The rest of the load will be the running and marker lights (converting to LED), the radio, tiller pilot, iPad for navigation, Fishfinder/depth finder (still not sure if I'll try to run with what I have or just get a dedicated sounder instead), VHF which I want to purchase to replace our handhelds this season, two bigger pumps and the DC TV which may or may not also require a DC DVD player. We get pretty good over-the-air HD reception most anywhere so we may not need the DVD player....especially with the iStuff on board. We're not much of a TV family to be honest but primarily because we're so damn busy all the time - haven't had cable in four or five years because we didn't watch it for four or five years before we cut it. But maybe the sailboat will slow us down enough that we could actually sit and watch the evening news once in a while.

I think that's it? It's a small boat after all.....we don't need to light up the lake and swing from chandeliers.

 

[Sumner]

....Sumner - the dual fused terminal you show there - would that be suitable to run one lead off to the motor, the other off to the house load wiring or should I run from one fuse block terminal (suitably sized) to a positive load buss and go from there to the motor?..

The dual fuse terminal can have different size fuses for the two. If you wanted to run one size wire to the motor and another size wire to the positive load buss you could with fuses sized for the respective wire sizes (I did that, as is shown in the picture above). I think there is a recommended limit to how many wires are stacked on the fuse. I have 3 on each in the picture above and not sure if that is the recommended limit or if two is?

Sumner
=====================================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...http://purplesagetradingpost.com/sumner/endeavour-main/endeavour-index.html
Mac Trips to Utah, Idaho, Wyoming, Canada, Florida, Bahamas

 

[Ward H]

Yep, much different than car wiring.
Try reading Maine Sail’s Fusing thread as suggested above. That will likely give you your answer.
The advantage to a dual fuse is you can run two different size cables, 1 for motor and 1 for house loads. Different size cables need different size fuses. And if you run to a power bus and step down again, you’ll need to fuse again.
With your plan you might want to consider a small panel with a few breakers which work as on/off switches.
On my O’day 25 I had, in order, battery, battery switch, positive post with dual MRBF fuses. One fed the motor and one fed a 6 circuit panel with breakers/switches.
Things like DC sockets, Nav instruments, running lights, anchor light, cabin lights were on separate breakers sized for the wire, which was sized for the load and low voltage drop.
Some suggest to wire the VHF directly to the battery, with its own fuse, so if the panel fails or you blow a fuse and need help you can still use the radio. I didn’t since I sail in an area with good cell service and I would probably leave the radio on and run down the battery.

Have fun.

 

[walt]

Macboy, curious (if you dont mind) where are your two batteries located, are they close together, where do you have the load (radios. lights) distribution switch panel. The only thing known is that your outboard with electric start is on the back of the boat.

Here is what I have

I have two golf cart batteries in the Vberth and both batteries are sitting as close to each other as possible. The wires to the batteries and linking the batteries is all four gauge.

As close as possible to the battery set, I have a single 90 amp breaker / switch. The switch is easy to access so that I can quickly and completely turn off the battery power to the boat. You want this fuse or breaker as close to the batteries as possible as the fuse only protects shorts down stream of the fuse. Since Sumner had his two six volt batteires far apart, he had a long unprotected wire so needed to add a second fuse. My batteires are right next to each other so I only have the one 90 amp breaker/ switch.

The four gauge run goes to a buss in the area under my sink and on the starboard side where I have a general load distribution (radios, lights, fridge, etc). At this distribution area under the sink, the wire gauge goes from four gauge to either ten or fourteen gauge. Any smaller wire from the distribution area must be re - fused because those smaller wires would burn up without blowing the 90 amp fuse right next to the battery.

In that load distribution panel, I have less switches than I do fuses. The reason is that I have one switch that turns on multiple items in the cabin for convenience. But I dont want one fuse blowing taking out multiple items so one switch may be providing power to multiple fuses. Most of the distribution to loads (like stereo, lights etc) is 14 gauge wire and I generally fuse this with 15 amp fuses. And like the fuse near the battery, you wont the 15 amp fuse as close as possible to there the 14 gauge wire run starts as it only protects the wire down stream.

I then have another four gauge wire run connected to the four gauge run to the battery (through the high current buss under the sink) that goes to the back of the boat where I have a breakout box that the outboard wire are connected to. FYI, I believe my outboard wires are six gauge and the 90 amp breaker still should blow and protect the six gauge wires coming out of the outboard.

Also in that area under the sink, I have the battery monitor shunt and the solar charge controller. Battery monitor.. a great thing. I monitor voltage, current and amp hours. I dont use the battery percent because it wont be accurate over time. But.. I find the amp hour reading almost as useful as voltage and current readings

 

[Ward H]

Walt, sounds like a good set up.

 

[Macboy]

I'm creating the plan as these threads develop so thank you for describing your layout. Here's the current situation and the plan to this point...

The batteries currently reside in the lazarette alongside the fuel tanks. The A/B switch is in there as well and its the switch more than anything that's the large concern but the overarching concern is to eliminate any source of spark back there and given what I've read about trimming the waterline - the plan was hatched to move the batteries to the locker under the v berth. The PO has already built up a very nice and sturdy three piece floor insert up there (all pieces small enough to insert through the factory opening) so it's literally wide open for me in terms of where to place the batteries. I had planned on placing them about 24" apart - one on either side of the locker. Typing this now I'm wondering if there is any advantage to having those 65lb weights as far apart as possible from the standpoint of heel ballast?

The only other reason I was considering putting them apart from each other was so that I could cut in an access to that space as I saw one here once (reference pic attached). This space would be boxed out for easy access storage stuff.

My VERY crude "organizing my thoughts and shopping list" is also attached. Once I have everything identified and the loads associated I'll start planning the wiring and sizing. Solar panels are roughly to scale - checking sizing if I build an arch somewhat like the one I saw in this month's Good Old Boat.

We don't really have any marine shops around or much access to marine tinned wire that I know of so I'm hoping to do as much shopping as I can on Amazon (might as well get some use out of my Prime membership). The one hold up thus far was a good length of 4 gauge wire. I was only finding inches to 6/10/20 feet. Knowing I can break the wire at the buss bar helps. I suspect I'll want another good 50-60 amp fuse from the buss bar to the starter motor. It also helps knowing I can run to the buss bar and take off to the accessories from there as opposed to using the dual fuse block terminal to a dedicated buss bar. I do however still need the run from the panels at the back to the charge controller(s). Nowhere near knowing enough to size that wire yet.

For the house loads I am ordering the switch panel as shown in the diagram and a fuse block for all of the take-offs from the buss bar. For simplicity, all reading lights will be split on two circuits fore and aft and then likely another circuit for the cabin lighting - haven't decided which style just yet but loved what I saw in this video:

Power outlets again two circuits fore and aft for simplicity. Maybe the same circuit as the reading lamps. I'm contemplating the addition of mast spreader deck lighting - I don't know there is a need so will weigh that thought.

Not showing in the diagram yet are the bilge pumps, the VHF, the depth sounder or fish finder and the tiller pilot. I guess we'll want a light in the head too. And I want to look into a bladder tank (water) for under the v-berth and an electric pump of some sort - there is already a freshwater fill fitting up on the deck and the tube running down into the v-berth. Must have been something up there at one time.

Big project. Yup. But it's what I do. My daughters have determined I'm a tinker. They are correct ; )

 

[Sumner]

If they ship out of country ...

http://www.genuinedealz.com/

... is a good deal and Ward also pointed out that they have a good wire-sizing app that you could use for any of the circuits, especially for the solar.

Good move on getting the batteries and switch out of the compartment where the fuel tanks are. Regardless I'd make sure the fuel tanks are vented out of the space and that the tanks are designed to go into an enclosed space like that.

I'm using the fuse blocks that you showed on both boats and really like them,

Sumner
========================================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...
Mac Trips to Utah, Idaho, Wyoming, Canada, Florida, Bahamas

 

[Macboy]

I'd make sure the fuel tanks are vented out of the space and that the tanks are designed to go into an enclosed space like that.

I suspect they aren't. Not the way they are vented at the very least. They have a little screw top vent in the middle of the filler cap. Is there a fitting that can be attached to or in place of this so they can be vented out of the lazarette? There are two cowl vents into the laz but admittedly we have had days where a fuel smell could be detected in the aft bunk.

They look just like these ones (if indeed they are not these exact ones). https://www.sheridanmarine.com/product/scepter-12-litre-plastic-portable-marine-fuel-tank

 

[Ward H]

There are two cowl vents into the laz but admittedly we have had days where a fuel smell could be detected in the aft bunk.

That is a portable fuel tank and definitely should not be used in the lazarett for the exact reason you just mentioned. If you can sometimes smell gas, then you have fumes coming into the cabin. A spark is all that is needed for a big boom.
If you don't have a dedicated fuel locker in the cockpit then I think your top priority should be to come up with a proper fuel tank designed for a location like the lazz and then you need a blower system to remove any fumes before starting the boat. I'm guessing this gets a bit complicated.
A dedicated fuel locker for a portable fuel can must only vent to the outside and be sealed such that no spill for fumes can get into the lazz, bilge or cabin.

I don't know your boat details so hopefully @Sumner will chime in on this.

I went back an reread Sumner's post 12. He already addressed it.

Regardless I'd make sure the fuel tanks are vented out of the space and that the tanks are designed to go into an enclosed space like that.

I had planned on placing them about 24" apart - one on either side of the locker. Typing this now I'm wondering if there is any advantage to having those 65lb weights as far apart as possible from the standpoint of heel ballast?

I never heard of "heal ballast". Ballast is normally along the center line of the boat. I would look for the most secure location for the batteries.
You can separate the batteries as far apart as you like but that will require you to have MRBF terminal fuse blocks on each battery. Keep in mind height requirements as the batteries will need to be in battery boxes with lids or boxes with insulated terminal covers. The box is for acid spill containment and if there is any way for anything to touch a terminal a box cover or lid is required. Also, if at all possible orient the battery terminals fore and aft. This helps to keep the lead plates covered with acid when heeling and they last longer.

 

[walt]

Knowing I can break the wire at the buss bar helps. I suspect I'll want another good 50-60 amp fuse from the buss bar to the starter motor.

Just noticed this and I think this is also from something that I did where I have one length of 4 gauge from the Vberth to the sink where it ends at a high current buss. Then another run of 4 gauge wire from the buss under the sink back to the outboard. You would not need a second fuse at the buss under the sink as a short anywhere down stream of the fuse near the batteries will still blow. Its only when you change wire gauge to a new wire size that is not rated for the fuse up stream that you need to add new fuse.

We had been talking about two fuses for Sumners setup both on the four gauge wire but that is a special case where he has the golf cart batteries far apart. Doing this would need a 4 gauge wire that had six volts on it going between series batteries and if that wire somehow shorted, one of the six volt batteries would put out big current.. big problem. When the batteries are very close to each other, you still have this same wire connecting the batteries in series but since its a short wire length, its normally not fused.

FYI, in the past, Ive seen comments about the batteries all the way forward not being good because of more horizontal movement than you would get if the batteries were near the center of the boat.. Well this is correct but I dont think there is a really good place for batteries under the sink and you also have the tube in that area where the centerboard pull up cable comes through. Bust that tube off with a loose battery and your boat sinks. Ive had my two golf cart batteries as far forward in the Vberth as I could get them for almost 10 years now and been happy. Just do a good job securing them. And a bonus.. if you have a single axle trailer (I do), the batteries are in a great location to increase trailer tongue weight which helps with towing.

 

[Macboy]

I never heard of "heal ballast". Ballast is normally along the center line of the boat. I would look for the most secure location for the batteries.

I was making an assumption without thinking it through. I've heard Macs are considered "tender" because of the location and nature of the water ballast. The ballast doesn't really come into play until it's effectively lifted itself up out of the water at least a bit and then the boat seems to settle in. My thought was the added 65 pounds as far to port and starboard as I could get it might help - however little - to take a bit of the tenderness away. But now having typed that out here I see the flaws compounding on that thought - these would be above waterline so would have no positive effect on tenderness. In fact they'd likely have adverse effects. Still, minute though...

 

[Macboy]

And a bonus.. if you have a single axle trailer (I do), the batteries are in a great location to increase trailer tongue weight which helps with towing.

Guilty. And I've been thinking about this as I look around for water bladders that might go up there but I think that's then TOO MUCH weight up there if I haul full. Better to fill when we get where we're going I assume. The boat is already plumbed for the freshwater in (deck filler). I'll have to start a new water pump thread - I'm getting a bit confused and might end up buying something strong enough for a foredeck fire monitor.........

 

[Macboy]

So guess what DIDN'T happen last season? And guess what time it is now again? My ice carving season is drawing to a close and thoughts are returning to the boat which only got wet once last summer. Just a busy busy summer, that's all. We won't let that happen this season.

I was scouring the interwebs trying to remember where I saw the DIY power arch stuff and it brought me here where I found it was an issue of Good Old Boat so tomorrow I'll be digging through my magazine stack to find that issue. But for now it's off to the forums to see what I've missed this winter. Hope to be defrosting the boat in about a month but it'll be snowed in for at least two more.....