Linking just the negatives of two batteries in series

[Montanan]

Originally Posted by 19thol

Geez, everyone is getting their panties in a bunch over your picture of batteries, good thing they can't see mine!! There would be a rush on the emergency room.

Well then just fix your poorly wired system and do everyone in the marina that your boat may cause to catch on fire a favor.

Safety Reference: https://www.boatingmag.com/boat-elec...m-safety-tips/

Boat Electrical System Safety Tips


Select snipets:

Boats make life hell for electrical circuits. The vibration, pounding, salty air, engine-space heat, exposure to chemicals and other rigors of the marine environment put a lot of pressure on the wires that are the central nervous system of any modern boat. In fact, more than half (55 percent) of fires investigated by BoatU.S. were found to have been caused by wiring and electrical problems (with wire chafing found as the most common problem).

Protection, Please
For the most part, fuses and circuit breakers are there to protect your wires, not your equipment. A short circuit can expose a wire to hundreds of times more current than the wire can handle — instantly melting the insulation and starting a fire. An overload (like when too many appliances are plugged into the same circuit) can result in slightly more current than the circuit can safely handle. Fuses and circuit breakers should always be sized below the amp rating of the wires they are protecting. That will prevent short circuits and overloads, big or small, from exposing a wire to too much current.

Simply put, a fuse is a short length of wire or metal designed to melt and separate in the event of excessive current. Normally the fuse wire is encased in a clear sheath of plastic or glass so one can see when it has “blown,” and thus opened the circuit. Blade-type fuses and fusible links, as well as cartridge or “Bosch” fuses, can be found protecting boat electrical systems.

Circuit breakers are mostly thermally operated devices containing a bi-metallic strip that bends when subjected to excessive current. When the strip bends enough, the force created actuates the tripping mechanism. The breaker then trips and opens the circuit.

Chafe Hurts
Chafed insulation is a leading cause of boat fires. Vibration, hull flexing and moving components can quickly result in chafe, which can in turn result in wires being crossed, circuits shorting out and other dangers.

. . .

Here, Not There

Fuses and circuit breakers should be placed as close to the power source as practical (within 7 inches of wire length per the American Boat and Yacht Council). If you put the fuse next to the bilge pump instead of near the battery, the entire length of wire between the battery and fuse is not protected. If there is a short circuit before the fuse or circuit breaker, we want as little wire as possible to burn up.

Can 12-volt electrical equipment really start a fire aboard your boat? Though many boaters think of direct current (DC) electricity, like a boat’s 12-volt system, as “safe” compared with 110- or 240-volt alternating current (AC), 12-volt can create a fire, particularly if the circuit protection (the fuse or circuit breaker) is undersize or installed improperly — as in the wrong location.

Even with properly sized, properly installed circuit protection, an overcurrent situation can develop. For instance, using undersize wire between the fuse and the device could lead to misplaced confidence in having protection. However, an undersize conductor could be heated beyond its temperature rating without activating the circuit protection. Proper fuse and breaker placement is part of a larger system, the parts of which must all work in concert. Call in a pro whenever you are in doubt.

. . .

Size Matters
You need more copper for more current, especially for 12-volt and 24-volt circuits. If you push 30 amps through a skinny wire rated for only 15 amps, it can get hot enough to melt the insulation and cause all kinds of catastrophes. Most equipment installation instructions spell out required wire sizes — be sure to understand and follow closely. Professionals use complicated sizing charts published by the American Boat and Yacht Council. If in doubt, hire a pro.

. . .

Red, Black, White?
Most high-quality boats come with a comprehensive owner's manual. This should include a schematic indicating the wire colors used in building the multitude of circuits that power the equipment installed aboard your boat. Typically, this schematic will have a wire color scheme for positive, negative, ground, hot and neutral on each and every accessory and circuit aboard. This makes troubleshooting, maintenance, and accessory repair and replacement much easier. Most times, you can count on boatbuilders using the “conventional” colors recommended by the ABYC, such as blue for cabin lights, pink for fuel gauges and brown with yellow for bilge blowers. If you are retrofitting or making a repair and find yourself without the right color wire on hand, don’t do your own thing here. The next person working on your boat might get zapped — or worse — not realizing you decided to use white for neutral and hot for that new pump. Also, it’s a very good idea to tag the wire on any new electrical installation with an ID label for ready reference. Another tip you’ll find useful is to create a quick sketch for your files.

[Montanan]

Originally Posted by RigBig

I see a number of circuits coming from those batteries that don't have a fuse at the battery. Bad idea. Plus neither battery seems to have a battery tie-down strap. Again, bad idea.

To answer your question you can connect both negatives together at the batteries and run one ground to the engine if thats where your common ground is located. It isn't parallel or series. Just a common connection.

Literally every circuit coming from the batteries does not have a fuse within inches of the battery. Yeah, bad idea, like fundamentally flawed.

[DefinitelyMe]

Yes, you can.

Over-sizing the cables can never hurt, but if it works fine as it is then unless you plan to run two large loads at the same time (say, for example, a large inverter load plus starting the engine) your current wire size should be sufficient.

Guys, he may not even have a grounded system so comments relating to that are not helpful.

The question was not related to fuses or safety either.

[Tmacmi]

Originally Posted by Montanan

Question:

Is this bank of batteries:
1) two completely separate battery banks;
or are they
2) two batteries in parallel circuitry?

Answer the above question, then and only then can forum members provide guidance.

Awaiting your response.

This is how I got the boat. I know there are problems with it. That is why I am re-wiring the batteries and asking questions.

I have a plan to address the deficiencies as I understand them. I have mapped it out on at PDF however its too large to post. So I'll do my best to map it out verbally.

The left battery is the starter battery.
The right is the house battery

They are separate.

Plan:

Build a battery box as described in Calder's book.

Starter battery

1. Replace positive cable. Question: should their be a fuse between it at the panel?
   
2. Replace negative cable in parallel as discussed.
   
3. The black and white wires are from the charger. Replace those. Run negative outside the box so as not to cross battery. Question: should there be a fuse on the positive immediately after charger?

House Battery

1. Replace positive cable. Same question as above.
2. Replace negative cable in parallel as discussed.
3. Black and white wires are from charger. Replace. Same question as above.
4. Remove accessory wires on terminal bus and relocate them closer to panel and wired to panel accessory switches using a common buss https://www.bluesea.com/products/502..._Bus_and_Cover
5. Green and red wires are from bilge. Fuse is close to pump switch. Relocate fuse to just outside Box

.

[Montanan]

Originally Posted by Tmacmi

This is how I got the boat. I know there are problems with it. That is why I am re-wiring the batteries and asking questions.

I have a plan to address the deficiencies as I understand them. I have mapped it out on at PDF however its too large to post. So I'll do my best to map it out verbally.

The left battery is the starter battery.
The right is the house battery

They are separate.



Plan:

Build a battery box as described in Calder's book.

Starter battery

1. Replace positive cable. Question: should their be a fuse between it at the panel? A fuse should be within 7 inches of the positive of each battery / power source. All too often fuses / breakers are improperly installed near the load or far down the power source wiring.
   
2. Replace negative cable in parallel as discussed.
   
3. The black and white wires are from the charger. Replace those. Run negative outside the box so as not to cross battery. Question: should there be a fuse on the positive immediately after charger? Yes, a fuse / breaker should be placed immediately after all power sources. Including circuits leading to auxiliaries, such as lights, electronic, bilge pumps.

House Battery

1. Replace positive cable. Same question as above.
2. Replace negative cable in parallel as discussed.
3. Black and white wires are from charger. Replace. Same question as above.
4. Remove accessory wires on terminal bus and relocate them closer to panel and wired to panel accessory switches using a common buss https://www.bluesea.com/products/502..._Bus_and_Cover
5. Green and red wires are from bilge. Fuse is close to pump switch. Relocate fuse to just outside Box

.

Notes above. Sounds like you have identified the issues and a scheme to resolve.

Happy and safe sailing.

[Tmacmi]

Originally Posted by Montanan

Notes above. Sounds like you have identified the issues and a scheme to resolve.

Happy and safe sailing.

Thank you.

I have three follow up questions.

1) How do I size the fuse immediately after the battery?
2) Other than duplicate the existing gauge of the battery cable how do I size the cable?
3) How do I size the fuse from the charger to the battery.

I'm sure you need more information to respond. This in not an arena I am comfortable working in.

Its a small 28' boat. The largest demand will be the starter which is for a simple Yanmar 2qm15.

The from the panel here is the following. Each is served by a 10 amp fuse
8 cabin lights
Nav Lights, including lights for instruments and binnacle
Spreader Lights
Small electric powered shower pump
Accessory 1

Autopilot

Wind Instruments

VHF

Accessory 2

Anderson plug for Costway Refrigerator

Anderson plug unused

Black Tank Level Indicator

Both accessories will be run from the panel switch to a remote bus. There will be individual fuses for each of the accessories.

Thank you very much.

[guyrj33]

On my boat I chose to install a ground post where the ground wires from the engine, batteries and negative buss bar are tied together. That way I can disconnect any of the individual grounds without disabling the entire DC system.

[guyrj33]

I have three follow up questions.

1) How do I size the fuse immediately after the battery?
2) Other than duplicate the existing gauge of the battery cable how do I size the cable?
3) How do I size the fuse from the charger to the battery.

--------
Fuses and circuit breakers protect the wire not the accessory.
1) Your battery fuse should be the same as the maximum current the smallest of your battery cables can carry. This circuit will need to carry the starting load from your engine, therefore the expected amperage of the circuit could be quite high.

2) Other than duplicate the existing gauge of the battery cable how do I size the cable?
Find the starting current of your engine (I guess it's less than 300 amps). Select a wire size that will carry that current with less than 3%voltage drop. Remember to count both positive and negative cable length when calculating circuit length.

3) How do I size the fuse from the charger to the battery.
First the wire from the charger to the battery must be big enough to carry the maximum current output by the charger plus some safety margin. Again count both positive and negative sides when calculating length.
Then your fuse can be a little bit larger than the maximum output of your charger.
To put some numbers to the answer, if you have a 10amp charger and your wire gauge will support 15amps of current use a 15 amp fuse. If your wire gauge will support 20 amps then you could use a 20 amp fuse as you are protecting the wire, but I would probably still use a 15 amp fuse as the highest current you expect on that circuit is 10 amps.

Hope this helps.

[MerMike]

Originally Posted by Tmacmi

The from the panel here is the following. Each is served by a 10 amp fuse
8 cabin lights
Nav Lights, including lights for instruments and binnacle
Spreader Lights
Small electric powered shower pump
Accessory 1

Autopilot

Wind Instruments

VHF

Accessory 2

Anderson plug for Costway Refrigerator

Anderson plug unused

Black Tank Level Indicator

Both accessories will be run from the panel switch to a remote bus. There will be individual fuses for each of the accessories.

Thank you very much.

Before I built the battery box, I'd make sure that the size of the battery was going to meet my expected needs. I'd take my list of loads (above), find the current requirements, and estimate the amount of time in use at anchor and underway. There are some online tools to estimate your electrical loads. Here are a couple of them:

https://www.emarineinc.com/pdf/vesse..._Estimator.pdf

https://newcontent.westmarine.com/co...r/Elecbugt.pdf

Keep in mind that flooded lead acid batteries should not be discharged below 50%, so a 100AH battery will give you, at best and in top condition, about 50 AH of service before a recharge is needed.

[guyrj33]

"Keep in mind that flooded lead acid batteries should not be discharged below 50%, so a 100AH battery will give you, at best and in top condition, about 50 AH of service before a recharge is needed."

In reality it takes a long time to get from 80% to 100% charge for a FLA Flooded Lead Acid battery. If your planning on extended trips it might be better to use 50-80% and your estimated range of battery capacity.
For a 100AH battery that come out to 30AH (Amp Hours).
30AH might be enough for a small boat that has access to dock power, just something to keep in mind.
Since it looks like you have some extra space for your batteries, I'll suggest you consider building your battery box large enough to accommodate your start battery and 2 6v golf cart batteries. Two 6v Golf Cart batteries would give you a house bank of 200-250 AH and a useable capacity of 60+AH.
For now stick with the two batteries you have. See how they work out.

Many older boats were built without fuses on the battery outputs. I suspect many still are. A fuse in the starter circuit is still an uncommon thing.
I'm not recommending a particular approach, just letting you know that what you have isn't that uncommon.

[MerMike]

Originally Posted by guyrj33

I'll suggest you consider building your battery box large enough to accommodate your start battery and 2 6v golf cart batteries. Two 6v Golf Cart batteries would give you a house bank of 200-250 AH and a useable capacity of 60+AH.
For now stick with the two batteries you have. See how they work out.

By starting with his electrical loads and expected use he can then determine battery size, wire size (accounting for voltage drop, of course) and fusing. Installing larger batteries may increase his charging requirements. That's a significant cost if the alternator and charger are sized for the current setup. Bigger isn't necessarily better.

To the OP, your battery box, whatever size you build it, needs to safely vent the hydrogen gas generated during charging .

[Tmacmi]

Thank you for everyone's suggestions

Regarding Battery sizing. This boat is predominately a day sailor. We have had no problems with capacity. We typically turn off the refrigerator when sailing.

Message received and understood regarding hydrogen gas build up. My intention is to put vents at the bottom of box and do the floating lid Caldwell shows, except with 1/2" of lift instead of the 1/4" lift.

Here are follow on questions. Thank you for your patience

Starting Battery

I found this from an earlier post someone made:

https://www.youtube.com/watch?v=8hX7NMiV_Gc

That shows an on rush of 316 amps. Based on a 13 foot circuit length (out and back) the circuit wizard on Blue Sea is suggesting 2/0 cable. I am guessing that the correct size terminal block fuse would be 300 amps.

Does this sound right? The cable gauge is substanially larger than what is currently in the boat, which I estimate to be 4 gauge.

House Battery

I am at a completely loss on how to size the cable or the terminal fuse. I don't know how to calculate the length of the circuit. The positive cable runs to the switch, then to the panel where there are 10 fused switches, each with a 10 amp fuse. The grounds from all the various fixtures on the boat are grounded to the back of the panel and thence to the common ground. The circuit from panel to battery is also about 12', How does that get sized?

Battery Charger

Earlier I asked about installing a fuse between the charger and batter immediately after the charger.

After rechecking my notes I was reminded that there was a fuse in the charger. Please confirm that this will addressing the fusing. I apologize for the upside down photo.

Thanks as always for your help.

[guyrj33]

battery fuse sizes
300 amps is probably ok for your starting battery, i'd put the same size on your house battery, remember you want to be able to start your engine with the house battery too.

Hydrogen is lighter than air and vents easily from the top of a battery box.
If you have vents at the bottom of your box it won't be able to contain an acid spill.
The battery in my car vents through a 1/8" vent tube.

[MerMike]

Originally Posted by Tmacmi

The cable gauge is substantially larger than what is currently in the boat, which I estimate to be 4 gauge.

I think you mentioned the round trip distance as 13ft. 2/0 will certainly work. If you can determine the load for the starter motor you can likely go smaller. I don't think you mentioned your engine make and model.

House Battery

I am at a completely loss on how to size the cable or the terminal fuse. I don't know how to calculate the length of the circuit. The positive cable runs to the switch, then to the panel where there are 10 fused switches, each with a 10 amp fuse. The grounds from all the various fixtures on the boat are grounded to the back of the panel and thence to the common ground. The circuit from panel to battery is also about 12', How does that get sized?

You want to know the approximate draw of each load. Most often, it can be found on the device itself or in the manual.

Size the wire for each branch circuit based on current draw, length and the minimum voltage drop required. Non-essential loads can have up to 10% voltage drop. Essential loads can have up to 3% voltage drop. From ABYC E-11:

Conductors used for panelboard or switchboard main feeders, bilge blowers, electronic equipment, navigation lights, and other circuits where voltage drop should be kept to a minimum, shall be sized for a voltage drop not to exceed three percent. Conductors used for lighting, other than navigation lights, and other circuits where voltage drop is not critical, shall be sized for a voltage drop not to exceed 10%.

The length is the round-trip distance from the battery to the load and back. It's doesn't have to be precise. Just grab a tape measure and estimate it as best you can, then round up. This is where the list of loads that you prepared comes in handy . Enter the length of wire for each load. For cabin lighting on the same circuit for example, it's the distance from the battery to the farthest light and back.

Once you have the total loads of all branch circuits, you can calculate the size of wire from the battery to the panel board, allowing for some growth. Calculate the size of the fuse or trip-free breaker at the battery based on the wire size.

Use the calculator at bluesea.com to calculate your wire and fuse sizes.

Battery Charger

Earlier I asked about installing a fuse between the charger and batter immediately after the charger.

After rechecking my notes I was reminded that there was a fuse in the charger. Please confirm that this will addressing the fusing. I apologize for the upside down photo.

What is the output of the charger? that determines the size of the wire. Wire size determines the correct fusing.

[Tmacmi]

Originally Posted by MerMike

I think you mentioned the round trip distance as 13ft. 2/0 will certainly work. If you can determine the load for the starter motor you can likely go smaller. I don't think you mentioned your engine make and model.

Its a Yanmar 2qm15. The manual says that based on a voltage drop of .2volts/amp with a cable with a cross section of 20 mm squared (approx 4 gauge a circuit length of 2.5 meters is acceptable.

The description of the starter says the no-load current is 60 amps or less.

But then there is this that suggests the in-rush amps are 300!

https://www.youtube.com/watch?v=8hX7NMiV_Gc

There is a significant disparity between the sizing recommended in the manual and what would be calculated at a 300 amp inrush

[/QUOTE]

Originally Posted by MerMike

You want to know the approximate draw of each load. Most often, it can be found on the device itself or in the manual.

Being very conservative (i.e. assuming that each light bulb is an old fashioned 25 volt incandescent bulb) I figure that if everything was turned on at the same time it would draw approximately 75 amps.

I then estimate the average length of the lines to be 30 feet. I know estimating isn't optimal, but I am not able to measure each line.