Help - Battery System Advice Needed

[phstol]

Whatever else, do keep us informed about your spleen .

[exMaggieDrum]

Hi, good detailed, real-world, questions now on the nuts and bolts that we all deal with. Battery placement is one of the toughest. I am struggling with that issue on my boat. I will have to compromise since I can't get 100% of what I want, so I am prioritizing what I need.

First, you absolutely need to be able to get to your batteries on a routine basis. You didn't say outright but it sounds like you have wet cell batteries. You will need (must) inspect the electrolyte/water levels in each cell of each battery often. The level will drop as they are charged. The heavier the charging the faster it will drop. You need to be able to look down in to each cell so you can tell what the level is, so stuffing some of them, or even part of one battery over in a corner where you can't see down in to the cell will ensure you either don't fill it enough, or you will overfill it trying to make sure it doesn't go dry. If the level gets below the top of the lead plates in a cell, it will start destroying that part of the cell and lessen the capacity of the battery.

If you overfill them you will end up having overflow of the excess to the top and then to the sides and bottoms, and then in to your bilge or wherever it can go. It is highly corrosive - which is why you want to provide at least a pan underneath all the batteries. Inevitably, even if you correctly fill each cell each time, some acid will get out and you want to contain that. So a wood-only box/pan will not do. It must be impervious to acid.

You don't need a separate battery box for each battery at all. You can put them in to one or into two boxes/pans no problem. Boxes help to secure the batteries so they can't slide around and move too much. You also absolutely need to secure the batteries so they can't move and get loose. Loose batteries will cause the cables on the posts to loosen over time. And you don't want the batteries to fall out if the boat capsizes (no one expects to capsize their boat but....). So you should strap the batteries down securely or use bars across them that are secured to something strong. There is a lot of mass to a battery and if it gets moving it can hurt something, including its own case, and then pull the cable off which might result in a fire.

Some people build their own battery boxes to custom fit with a wood frame that they epoxy at least the bottoms and some part of the sides. Others use polypropylene store-bought boxes.

One other must is to provide some air space around and between the batteries. 1/4" between is great but anything is helpful. It helps keep them cooler and helps prevent thermal runaway. Heat is not a friend of your batteries. Which is one reason to keep them outside of the engine room but many times that is the only place they can go. You also want ventilation holes if you use boxes, especially if you use a lid on the box. Big holes - like 1" or more and several. It won't weaken the polypro boxes very much. You also need to vent the hydrogen gas that batteries produce (where the water goes as it splits in to hydrogen and oxygen). It is explosive if concentrated.

So - put them where you can see the cell electrolyte - often. Secure them. Provide air flow. Secure the cables close to where they are put on the posts so they can't move and loosen. You can put two batteries away from the other two if needed - just follow the above.

A benefit of AGMs is that they are sealed so you don't have to monitor the electrolyte level and they can be mounted on their sides. But they are expensive and you should be able to find a way to mount what you have (what I would do). My previous boat had two batteries where I could not get to the far cells on them. I could only check the electrolyte level with a mirror and that was hard and error-prone. And I couldn't fill them well.

Don't use the gas-station type filler that you press down and it "auto-fills" the cells. They will over fill over time. There are automatic filler systems but I have not used them. There are also some caps that recycle the gases and let you go longer without refilling the cells. Hydrocaps is one brand. But they need more height as they are put on the top of each cell.

My new boat which I am rewiring has three large 8D AGM batteries. They weigh 155# each. That is definitely spleen busting weight. I want to replace them with either four or six 6-volt batteries - but - I don't think I can fit them in where the others are. Like your problem. I am still thinking it out hoping that I will get a brain-spark and an obvious solution will appear. But I think I will have to compromise - either less total capacity (smaller batteries or fewer batteries) or find another location (last resort).

Regarding cable size: that depends on how much current you need to flow through the cables, i.e. what they will be used for. And then you fuse them so they won't melt and cause a fire if you use more or short them out. You asked about 50mm cables - is that diameter or mm-squared? And the size depends on the length of the cables - positive one way added to negative back. And the temperature rating of the cables. If the cables will go through the engine room you should use wire rated at 105 deg C. And any cable should be fine-stranded and tinned. Good marine grade wire. It's expensive but you only do it once. And use HD heat shrink at each terminal, the kind with adhesive lining. It keeps the corrosive salt and acid air out of the metal inside.

You can use 50 mm2 (our 1 gauge) cable if your round trip wire route is 15 ft or less for 3% (critical systems lowest voltage drop - radios, radar, inverters) or 50 ft or less for any uses not critical (lights, starting engines). But what I would routinely put on 400Ah batteries (yours) is 2/0 cable (70 mm2). It is bloody expensive though. And then fuse them for the wire size - less than or equal to 250 A for the 50mm2 and 300 or 350 for the 70mm2. You can put on smaller but not bigger, and these sizes already are more than the nominal rating for the wires. I doubt you will ever need more than 200A of current though, but that depends on what your max sustained usage would be. If you had a huge alternator, and/or big inverter, then you might use that much. All this is for 105 degree C rated cable.

Good luck with the placement and boxes. Not an easy task sometimes. And none of this is cheap. I have bought about $1000US of cable/terminals for my rewiring so far. Go with smaller (less expensive) sizes where you can but stay safe.

[phstol]

Originally Posted by exMaggieDrum

It sounds like you are making excellent progress in wrapping your head around this. Just starting is the hardest part many times.

Having said that I would encourage you to not set up two redundant house battery banks. They are very hard to manage and keep charged that way. It is easy to forget what setting you have and inevitably you either forget to keep one bank charged well, or you run both as one bank anyway. Much simpler and easier to have one larger house bank and a separate smaller starter battery for redundancy. You can make it work but experience has shown it is easier for you and your batteries to not have two redundant house banks.

Enjoy!

Maggie, I guess each to his own.... I don't find any management overhead from 2 banks, quite the opposite as a recent 2 weeks ago experience shows:
My boat was out of the water for 4 weeks being painted and trucked from Astoria to Seattle. My bilge pumps are wired to #1 bank via a standard fused bilge switch panel. At some time the lower pump float switch failed in the on position, and if anyone heard the beeper, they didn't call me. Depleted the #1 bank over the weeks. When I stepped on board in Seattle, I started the engine on the separate starter battery, switched the house and navionics to #2 bank with the Load selector switch, and the #1 bank to Charge with Charge selector switch, and took off for Port Orchard, about 4 hours including the locks. So, once the ACR ensured that the starter battery was fully charged, it switched to the #2 Bank which then received the full output from the alternator.

Ref managing which bank was last charged, easy enough to log it or keep an eye on the voltage. Often set the Charge selector to Both. Don't overthink it. I have a 12A smart charger for dockside to top off.

Anyway enough on this, if you come to Seattle/Bremerton, be in touch, would love to chat.

[tronic72]

Originally Posted by phstol

Whatever else, do keep us informed about your spleen .

Batteries are installed and spleen is instact..... Only just.

[tronic72]

Originally Posted by exMaggieDrum

Hi, good detailed, real-world, questions now on the nuts and bolts that we all deal with. Battery placement is one of the toughest. I am struggling with that issue on my boat. I will have to compromise since I can't get 100% of what I want, so I am prioritizing what I need.

First, you absolutely need to be able to get to your batteries on a routine basis. You didn't say outright but it sounds like you have wet cell batteries. You will need (must) inspect the electrolyte/water levels in each cell of each battery often. The level will drop as they are charged. The heavier the charging the faster it will drop. You need to be able to look down in to each cell so you can tell what the level is, so stuffing some of them, or even part of one battery over in a corner where you can't see down in to the cell will ensure you either don't fill it enough, or you will overfill it trying to make sure it doesn't go dry. If the level gets below the top of the lead plates in a cell, it will start destroying that part of the cell and lessen the capacity of the battery.

If you overfill them you will end up having overflow of the excess to the top and then to the sides and bottoms, and then in to your bilge or wherever it can go. It is highly corrosive - which is why you want to provide at least a pan underneath all the batteries. Inevitably, even if you correctly fill each cell each time, some acid will get out and you want to contain that. So a wood-only box/pan will not do. It must be impervious to acid.

You don't need a separate battery box for each battery at all. You can put them in to one or into two boxes/pans no problem. Boxes help to secure the batteries so they can't slide around and move too much. You also absolutely need to secure the batteries so they can't move and get loose. Loose batteries will cause the cables on the posts to loosen over time. And you don't want the batteries to fall out if the boat capsizes (no one expects to capsize their boat but....). So you should strap the batteries down securely or use bars across them that are secured to something strong. There is a lot of mass to a battery and if it gets moving it can hurt something, including its own case, and then pull the cable off which might result in a fire.

Some people build their own battery boxes to custom fit with a wood frame that they epoxy at least the bottoms and some part of the sides. Others use polypropylene store-bought boxes.

One other must is to provide some air space around and between the batteries. 1/4" between is great but anything is helpful. It helps keep them cooler and helps prevent thermal runaway. Heat is not a friend of your batteries. Which is one reason to keep them outside of the engine room but many times that is the only place they can go. You also want ventilation holes if you use boxes, especially if you use a lid on the box. Big holes - like 1" or more and several. It won't weaken the polypro boxes very much. You also need to vent the hydrogen gas that batteries produce (where the water goes as it splits in to hydrogen and oxygen). It is explosive if concentrated.

So - put them where you can see the cell electrolyte - often. Secure them. Provide air flow. Secure the cables close to where they are put on the posts so they can't move and loosen. You can put two batteries away from the other two if needed - just follow the above.

A benefit of AGMs is that they are sealed so you don't have to monitor the electrolyte level and they can be mounted on their sides. But they are expensive and you should be able to find a way to mount what you have (what I would do). My previous boat had two batteries where I could not get to the far cells on them. I could only check the electrolyte level with a mirror and that was hard and error-prone. And I couldn't fill them well.

Don't use the gas-station type filler that you press down and it "auto-fills" the cells. They will over fill over time. There are automatic filler systems but I have not used them. There are also some caps that recycle the gases and let you go longer without refilling the cells. Hydrocaps is one brand. But they need more height as they are put on the top of each cell.

My new boat which I am rewiring has three large 8D AGM batteries. They weigh 155# each. That is definitely spleen busting weight. I want to replace them with either four or six 6-volt batteries - but - I don't think I can fit them in where the others are. Like your problem. I am still thinking it out hoping that I will get a brain-spark and an obvious solution will appear. But I think I will have to compromise - either less total capacity (smaller batteries or fewer batteries) or find another location (last resort).

Regarding cable size: that depends on how much current you need to flow through the cables, i.e. what they will be used for. And then you fuse them so they won't melt and cause a fire if you use more or short them out. You asked about 50mm cables - is that diameter or mm-squared? And the size depends on the length of the cables - positive one way added to negative back. And the temperature rating of the cables. If the cables will go through the engine room you should use wire rated at 105 deg C. And any cable should be fine-stranded and tinned. Good marine grade wire. It's expensive but you only do it once. And use HD heat shrink at each terminal, the kind with adhesive lining. It keeps the corrosive salt and acid air out of the metal inside.

You can use 50 mm2 (our 1 gauge) cable if your round trip wire route is 15 ft or less for 3% (critical systems lowest voltage drop - radios, radar, inverters) or 50 ft or less for any uses not critical (lights, starting engines). But what I would routinely put on 400Ah batteries (yours) is 2/0 cable (70 mm2). It is bloody expensive though. And then fuse them for the wire size - less than or equal to 250 A for the 50mm2 and 300 or 350 for the 70mm2. You can put on smaller but not bigger, and these sizes already are more than the nominal rating for the wires. I doubt you will ever need more than 200A of current though, but that depends on what your max sustained usage would be. If you had a huge alternator, and/or big inverter, then you might use that much. All this is for 105 degree C rated cable.

Good luck with the placement and boxes. Not an easy task sometimes. And none of this is cheap. I have bought about $1000US of cable/terminals for my rewiring so far. Go with smaller (less expensive) sizes where you can but stay safe.

Hi Exmaggidrum,

I have done the following reagarding location:

* the four deep cycle batteries which constitute the house bank are sealed so I have installed them as a group under the floor. This isn't directly below any access points so the most difficult to get to but they are sealed so hoefully won't need moving or topping up.

* the two starting batteries are not sealed so they sit forward of the others towards the engines. These can be accessed when I'm servicing the engines fairly easily.

* as I'm unable to use the battery boxes I've installed new pieces of 12 mm marine ply. These are not glued but fastened via some threaded rods glassed into the hull. The sub temporary nature of this will mean I can simply throw it out and replace one it degrades. Not as elegant as the boxes but it ticks a few boxes and considering the previous owner only had them sitting on the hull!!! It's a big step forwards

Cheers.

[exMaggieDrum]

Originally Posted by tronic72

Hi Exmaggidrum,

I have done the following reagarding location:

* the four deep cycle batteries which constitute the house bank are sealed so I have installed them as a group under the floor. This isn't directly below any access points so the most difficult to get to but they are sealed so hoefully won't need moving or topping up.

* the two starting batteries are not sealed so they sit forward of the others towards the engines. These can be accessed when I'm servicing the engines fairly easily.

* as I'm unable to use the battery boxes I've installed new pieces of 12 mm marine ply. These are not glued but fastened via some threaded rods glassed into the hull. The sub temporary nature of this will mean I can simply throw it out and replace one it degrades. Not as elegant as the boxes but it ticks a few boxes and considering the previous owner only had them sitting on the hull!!! It's a big step forwards

Cheers.

Sounds great Tronic. Ready to go. No problem with a "temporary" box so long as it is sturdy enough to secure the battery under any conditions. I do recommend ventilation holes - for cooling and to dissipate gases. Even "sealed" battery will off-gas. Good luck with the rest.

[exMaggieDrum]

Originally Posted by phstol

Maggie, I guess each to his own.... I don't find any management overhead from 2 banks, quite the opposite as a recent 2 weeks ago experience shows:
My boat was out of the water for 4 weeks being painted and trucked from Astoria to Seattle. My bilge pumps are wired to #1 bank via a standard fused bilge switch panel. At some time the lower pump float switch failed in the on position, and if anyone heard the beeper, they didn't call me. Depleted the #1 bank over the weeks. When I stepped on board in Seattle, I started the engine on the separate starter battery, switched the house and navionics to #2 bank with the Load selector switch, and the #1 bank to Charge with Charge selector switch, and took off for Port Orchard, about 4 hours including the locks. So, once the ACR ensured that the starter battery was fully charged, it switched to the #2 Bank which then received the full output from the alternator.

Ref managing which bank was last charged, easy enough to log it or keep an eye on the voltage. Often set the Charge selector to Both. Don't overthink it. I have a 12A smart charger for dockside to top off.

Anyway enough on this, if you come to Seattle/Bremerton, be in touch, would love to chat.

Phstol: Yes, always to each his own. If you can make it work for you that's great. I have been called in to replace too many systems though where the owner was not able to stay disciplined enough to keep the records and manage the batteries well.

There is another reason to have only one larger bank though. E.g., you have two banks of 200Ah deep cycle batteries for a total of 400Ah. If you need to use 100 amps in between charging, you will draw one bank down to 50% SOC (state of charge). This is not good for batteries to be drawn down to that on a routine basis. If you have one bank you draw the whole bank down the same 100A but at 75% SOC. You still have to replace the same amps you used. You can find many threads on the forum which discuss this issue and in many of the DC books out there.

And, there is the issue of why go through all the trouble of managing two banks. There may be some comfort in having two banks as a precaution from not having one go bad, but usually one battery fails prematurely but not all of them at once. And if the whole bank starts to go it is time to replace them all anyway. Your start battery can be used as an emergency backup.

There have been many boats setup the way you propose though. So it is a preference of mine and many others but it is not a requirement. Cheers!

[tronic72]

Hi Everyone,

Heres a quick update. Have installed my new batteries and cables. Electrical system is now "working". I've decided to use the boat for a little bit before I take the step of a rewire.

The main reason for this is I believe that I haven't owned and used the boat enough to know her. In fact, I haven't used the boat at all. Having restored a few cars and two houses I've discovered that using or living in something is the best way to figure out what it needs and where and when these changes should be made.

My last task will be to relocate the shore-powered charger. I know it's under powered. But considering Im not using the boat at the moment and won't be planning any decent trips in the short term, the 10 Amp dolphin will do. I think I will have a better idea of the requirements once I've actually used it and seen how we use it.

My last question (hopefully) on this subject is where is the best place to mount this unit. It measures about 40 cm high by 20 cm wide by 10 cm deep. The current installation has it literally floating in the breezed between both engines (seriously). If I could post a photo I would show you.

Anyway if you could give me some suggestions on where to mount the unit that would be great. I want to make a frame and attach some marine ply to it as a backboard and mount to that. I plan to make it so it utilises nyloc nuts and bolts to attach instead of screw and will be as big as the biggest dolphin unit available. I plan to use a dolphin again as they seem good quality and are locally supported her in Australia. Any suggestions for alternatives will be gradually accepted (whoops theres another questions...kinda)

Thanks again in advance for all who reply

PS. The boat is a 31 foot cabin cruiser. Engines are located in the middle of the boat (bow to stern and either side of the "spine" running through the centre of the boat.

[exMaggieDrum]

Good idea to use the boat for some time before looking at big changes. There are some things that might be obvious but even those projects will be done in a better way after using the boat and discovering some of the secrets it keeps hidden until the right time to surprise you.

Placement of devices on a boat is a very subjective thing. There is no "best" place. So many variables and each boat model is different and each boat has been changed over time so even that is not a good guide. But here are some general thoughts: the location

- should be dry in all normal situations
- keep wire runs as short and as "good" (wires don't have to go round and round and over, etc - neat and tidy) as possible
- doesn't interfere with access to other stuff
- allow you to monitor the charger if it has operation lights or indicators
- doesn't look "stupid" (in the eye of the beholder)
- should be selected based on potential changes (e.g. bigger charger)
- allow for location of fuses
- as cool as possible with good air flow

You are going to a lot of work for a temporary bit of kit. You will be reluctant to change it in the future. I understand why you want to go ahead with the 10A charger but keep it firmly in your mind that you probably will want to replace it with a bigger one so plan accordingly.

[Stu Jackson]

Originally Posted by exMaggieDrum

There is another reason to have only one larger bank though. E.g., you have two banks of 200Ah deep cycle batteries for a total of 400Ah. If you need to use 100 amps in between charging, you will draw one bank down to 50% SOC (state of charge). This is not good for batteries to be drawn down to that on a routine basis. If you have one bank you draw the whole bank down the same 100A but at 75% SOC. You still have to replace the same amps you used. You can find many threads on the forum which discuss this issue and in many of the DC books out there.

Agree.

Here's an example:

IS IT BETTER TO HAVE ONE OR TWO BATTERY BANKS FOR HOUSE USE?
(By Nigel Calder - I DIDN’T write this!!!)

The popular arrangement of having two house banks alternated in use needs scrutiny before I go any further.

LIFE CYCLES: As we have seen, the life expectancy of a battery in cycling service is directly related to the depth to which it is discharged at each cycle - the greater the depth of discharge, the shorter the battery’s life.

This relationship between depth of discharge and battery life is NOT linear. As the depth of discharge increases, a battery’s life expectancy is disproportionately shortened. A given battery may cycle through 10% of its capacity 2,000 times, 50% of its capacity 300 times and 100% of its capacity around 100 times.

Let’s say, for arguments sake, that a boat has two 200-ah battery banks, alternated from day to day, with a daily load of 80 Ah. Each bank will be discharged by 40% (80 Ah of one of the two 200 Ah banks) of its capacity before being recharged. The batteries will fail after 380 cycles, which is 760 days (since each is used every other day). If the two banks had been wired in parallel, to make a single 400 Ah battery bank, this bank would have been discharged by 20% of capacity every day, with a life expectancy of 800 days, a 5% increase in life expectancy using exactly the same batteries!

But now let’s double the capacity of the batteries, so that the boat has either two 400 Ah banks, or a single 800 Ah bank, but with the same 80 Ah daily load. The two separate banks will be cycling through 20% of capacity every other day, resulting in a total life expectancy of 1,600 days. Doubling the size of the battery banks in relation to the load has produced a 210% increase in life expectancy. The single 800 Ah bank will be cycling through 10% of capacity every day, resulting in a life expectancy of 2,000 days - a 25% increase in life expectancy over the two (400 Ah) banks, and a 250% increase in life expectancy over the single 400 Ah battery bank!

There are two immediate conclusions to be drawn from these figures:

1. For a given total battery capacity, wiring the (house) batteries into a single high capacity bank, rather than having them divided into two alternating banks, will result in a longer overall life expectancy for the batteries.

2. All other things being equal, any increase in the overall capacity of a battery bank will produce a disproportionate increase in its life expectancy (through reducing the depth of discharge at each cycle).

FOR BATTERY LONGEVITY, A SINGLE LARGE (HOUSE) BANK, THE LARGER THE BETTER, IS PREFERABLE TO DIVIDED (HOUSE) BANKS.

[tronic72]

Originally Posted by Stu Jackson

Agree.

Here's an example:

IS IT BETTER TO HAVE ONE OR TWO BATTERY BANKS FOR HOUSE USE?
(By Nigel Calder - I DIDN’T write this!!!)

The popular arrangement of having two house banks alternated in use needs scrutiny before I go any further.

LIFE CYCLES: As we have seen, the life expectancy of a battery in cycling service is directly related to the depth to which it is discharged at each cycle - the greater the depth of discharge, the shorter the battery’s life.

This relationship between depth of discharge and battery life is NOT linear. As the depth of discharge increases, a battery’s life expectancy is disproportionately shortened. A given battery may cycle through 10% of its capacity 2,000 times, 50% of its capacity 300 times and 100% of its capacity around 100 times.

Let’s say, for arguments sake, that a boat has two 200-ah battery banks, alternated from day to day, with a daily load of 80 Ah. Each bank will be discharged by 40% (80 Ah of one of the two 200 Ah banks) of its capacity before being recharged. The batteries will fail after 380 cycles, which is 760 days (since each is used every other day). If the two banks had been wired in parallel, to make a single 400 Ah battery bank, this bank would have been discharged by 20% of capacity every day, with a life expectancy of 800 days, a 5% increase in life expectancy using exactly the same batteries!

But now let’s double the capacity of the batteries, so that the boat has either two 400 Ah banks, or a single 800 Ah bank, but with the same 80 Ah daily load. The two separate banks will be cycling through 20% of capacity every other day, resulting in a total life expectancy of 1,600 days. Doubling the size of the battery banks in relation to the load has produced a 210% increase in life expectancy. The single 800 Ah bank will be cycling through 10% of capacity every day, resulting in a life expectancy of 2,000 days - a 25% increase in life expectancy over the two (400 Ah) banks, and a 250% increase in life expectancy over the single 400 Ah battery bank!

There are two immediate conclusions to be drawn from these figures:

1. For a given total battery capacity, wiring the (house) batteries into a single high capacity bank, rather than having them divided into two alternating banks, will result in a longer overall life expectancy for the batteries.

2. All other things being equal, any increase in the overall capacity of a battery bank will produce a disproportionate increase in its life expectancy (through reducing the depth of discharge at each cycle).

FOR BATTERY LONGEVITY, A SINGLE LARGE (HOUSE) BANK, THE LARGER THE BETTER, IS PREFERABLE TO DIVIDED (HOUSE) BANKS.

Yayyyyyy! I chose the best solution based on sheer luck. ��

[tronic72]

Originally Posted by exMaggieDrum

Good idea to use the boat for some time before looking at big changes. There are some things that might be obvious but even those projects will be done in a better way after using the boat and discovering some of the secrets it keeps hidden until the right time to surprise you.

Placement of devices on a boat is a very subjective thing. There is no "best" place. So many variables and each boat model is different and each boat has been changed over time so even that is not a good guide. But here are some general thoughts: the location

- should be dry in all normal situations
- keep wire runs as short and as "good" (wires don't have to go round and round and over, etc - neat and tidy) as possible
- doesn't interfere with access to other stuff
- allow you to monitor the charger if it has operation lights or indicators
- doesn't look "stupid" (in the eye of the beholder)
- should be selected based on potential changes (e.g. bigger charger)
- allow for location of fuses
- as cool as possible with good air flow

You are going to a lot of work for a temporary bit of kit. You will be reluctant to change it in the future. I understand why you want to go ahead with the 10A charger but keep it firmly in your mind that you probably will want to replace it with a bigger one so plan accordingly.

Thanks EmD.