Hey to all, I am new here and looking for help! I live on a boat for the past17 yrs., in that, I've gone through a few batteries (lead-acid).

Rhat Cat

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Ok, so it's close to time in replacing my battery bank on the boat. I'm now looking at the lithium type. My system is 12 volt and having 660amp house. The boat is wired at 12 v and not willing to change. So, I'd like to get 8 200a cells or may-be go with 150a cells. for a total about 400 to 600ah. Does not seem to hard to buy the cells, but, the BMS or Balance units seem to be 24 to 72v. How can I wire in the BMS unit and to find this unit for 12v is the question. I could use some good help to how and what direction to get moving!
If someone wants to know about refrigeration or air conditioning...that is my field for the past 39yrs.
 

HRTKD

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You have a couple options.
1. Build a single 12v battery out of individual cells. Eight 280 Ah, 3.2v cells can be arranged in a 2p4s configuration to yield 560 Ah at 12v. A single BMS can be used for this.
2. Build multiple 12v batteries out of individual cells. Four 280 Ah, 3.2v cells arranged in a 4s configuration yields 280 Ah at 12v. You'll need two of these batteries and each battery will need its own BMS.

For option 1, the battery and BMS would look like the graphic below. The graphic is from the OverKillSolar.com website that sells 4 and 8 "cell" BMS devices.

BMS-wiring-diagram-12v-8-cell.png


The graphic below may do a better job of explaining the 2p4s arrangement.

batterysetup.png
 

Archetype-IS

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You have a couple options.
1. Build a single 12v battery out of individual cells. Eight 280 Ah, 3.2v cells can be arranged in a 2p4s configuration to yield 560 Ah at 12v. A single BMS can be used for this.
2. Build multiple 12v batteries out of individual cells. Four 280 Ah, 3.2v cells arranged in a 4s configuration yields 280 Ah at 12v. You'll need two of these batteries and each battery will need its own BMS.

For option 1, the battery and BMS would look like the graphic below. The graphic is from the OverKillSolar.com website that sells 4 and 8 "cell" BMS devices.

BMS-wiring-diagram-12v-8-cell.png


The graphic below may do a better job of explaining the 2p4s arrangement.

batterysetup.png
Option 2 is for redundancy with two BMS for two 12V individual battery bank. Could take one offline for maintenance. Etc. Safer bet when out at sea.
 

Freep

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If someone wants to know about refrigeration or air conditioning...that is my field for the past 39yrs.

What do you recommend for air conditioning with a 12v system on a truck camper? I've been looking at RV mod where a mini-split replaces the typical rooftop RV AC.
 

Rhat Cat

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Hello, is ture, the mimi's are more eff., but you still need much power. I think you would need to do some checking for 220v and depending on the size (BTU) check the total amp draw and size your solar and batteries as such. Don't forget, the start up amps are greater than run amp. these systems normaly use R-410 which runs much higher pressure than before R-22 systems.
 

Rhat Cat

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You have a couple options.
1. Build a single 12v battery out of individual cells. Eight 280 Ah, 3.2v cells can be arranged in a 2p4s configuration to yield 560 Ah at 12v. A single BMS can be used for this.
2. Build multiple 12v batteries out of individual cells. Four 280 Ah, 3.2v cells arranged in a 4s configuration yields 280 Ah at 12v. You'll need two of these batteries and each battery will need its own BMS.

For option 1, the battery and BMS would look like the graphic below. The graphic is from the OverKillSolar.com website that sells 4 and 8 "cell" BMS devices.

BMS-wiring-diagram-12v-8-cell.png


The graphic below may do a better job of explaining the 2p4s arrangement.

batterysetup.png
Thanks for the return, so when sizing the BMS, the battery amp hr is not as important (100ah to 400h) for the BMS i've seen are mostly mark for 100ah. Because I've looked for a system that will match the 280 - 300ah. Or may-be I'm missing what your saying. I understand the schematic, it's stright forward, it's just the BMS amp rating.
 

Archetype-IS

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Thanks for the return, so when sizing the BMS, the battery amp hr is not as important (100ah to 400h) for the BMS i've seen are mostly mark for 100ah. Because I've looked for a system that will match the 280 - 300ah. Or may-be I'm missing what your saying. I understand the schematic, it's stright forward, it's just the BMS amp rating.
What's the existing inverter model or the 12v @ What watts? BMS could be specified by your inverter draw wattage? For example: 3000 Watts inverter at 12V, will required a huge BMS at 250amp miniumn, so, your looking at 300amp just to be safe. for the option 1 setup.. Where as you run two BMSs in option 2 as I suggested before, you will need 150amp each to meet the 300amp because BMS are running in parallel. I hope you don't plan to run 3000 watts continuously. That will required more than 8 batteries.

To clarify, the "ah" in 280ah is amp hour, nothing to do with the BMS amperage draw.

Please give us more data points on the boat? What are the inverter model? What stuff are you running that will required 3 to 4 days of power(ie. fridge for sure)...any others?

Hope that helps.
 

HRTKD

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Size the BMS for the amount of amps you need to pull. Most people don't pull 400 amps from a 400 Ah battery. They might pull 200 total amps over the span of a day, but never more than 80 amps at one time.

I'm building a 560 Ah battery bank and using a 120 amp BMS.
 

Rhat Cat

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What's the existing inverter model or the 12v @ What watts? BMS could be specified by your inverter draw wattage? For example: 3000 Watts inverter at 12V, will required a huge BMS at 250amp miniumn, so, your looking at 300amp just to be safe. for the option 1 setup.. Where as you run two BMSs in option 2 as I suggested before, you will need 150amp each to meet the 300amp because BMS are running in parallel. I hope you don't plan to run 3000 watts continuously. That will required more than 8 batteries.

To clarify, the "ah" in 280ah is amp hour, nothing to do with the BMS amperage draw.

Please give us more data points on the boat? What are the inverter model? What stuff are you running that will required 3 to 4 days of power(ie. fridge for sure)...any others?

Hope that helps.
Hello, thanks for your input. The inverter is a Cobra 2500w 12v. Most of the boat is set up for 12v operation, that includes boath refer. systems. (14cuft refer., and 5 cuft freezer) combined they draw 12.3amp. @ 45 to 50% cycle so in a 24 hr time = 147ah. thats my largest load! Smaller loads are mostly fans, lights, water pump, transfer pump, radio, nav. equipment at night and washer machine also 2 laptops and 2 cel phones. Soon with the new batteries I would like to install a microwave and that will run off the inverter. The amount of large loads I'll use my gen. set, which I need for the water maker (864 gal per day (24hrs) and uses 18.4 amp a/c, I'll run that every 4 days for about 1.5 hrs or so, also if no sun and no wind I use my battery charger that is 60amp.
So, the loads on the inverter are not every day but, the 12v side is used always. As to living on a boat, over time (17yrs.) you learn to use power wisely and the water too. Normaly we can take showers 2 times per day no matter where we are. The boat is very selfsufficient all we need is diesal. We spend 99.99% of the time at anchor not in a marina too much $$$$. Our boat is a catamaran 47' long and 26' wide. If we went to a marina they charge a catamaran 1.5 times the price of a monohull same size. So you can see we need our batteries.
Hope this helps you to help me knoe what is needed.
 

MisterSandals

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They might pull 200 total amps over the span of a day, but never more than 80 amps at one time.
Probably not helpful to mix amps and amp hours.
combined they draw 12.3amp.
This max draw (with other simultaneous draws) is what your BMS needs to handle. Amps at any one time, NOT amp hours over some period. And sizing 50-100% over your max draw (or some would size for max possible thru your inverter) is a good practice.
 

Rhat Cat

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Probably not helpful to mix amps and amp hours.

This max draw (with other simultaneous draws) is what your BMS needs to handle. Amps at any one time, NOT amp hours over some period. And sizing 50-100% over your max draw (or some would size for max possible thru your inverter) is a good practice.
Ok, so the most draw at one time is how you size the BMS, in my case that should be less than 100amp max..Any other high draw I would use my gen set. Correct?
 

HRTKD

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Ok, so the most draw at one time is how you size the BMS, in my case that should be less than 100amp max..Any other high draw I would use my gen set. Correct?

That's how I do it. If I need the microwave or the air conditioner, I fire up the generator. I suppose I could spend a lot more money on solar, batteries and inverters to run both of those at any time, but my on-board generator is already there and runs for about $3 an hour.
 

MisterSandals

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This is all assuming your loads are going thru your BMS. Some folks have just the charge current thru their BMS (in which case you size the BMS based to max charge current.)
How will your BMS be setup?
 

Rhat Cat

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That's how I do it. If I need the microwave or the air conditioner, I fire up the generator. I suppose I could spend a lot more money on solar, batteries and inverters to run both of those at any time, but my on-board generator is already there and runs for about $3 an hour.
I agree, if you have it ...use it
This is all assuming your loads are going thru your BMS. Some folks have just the charge current thru their BMS (in which case you size the BMS based to max charge current.)
How will your BMS be setup?
This is all assuming your loads are going thru your BMS. Some folks have just the charge current thru their BMS (in which case you size the BMS based to max charge current.)
How will your BMS be setup?
Well that's why I'm here, to learn what I don't know. All you people have beem kind to someone who knows very little of this type. So when you say to match the charger, which mine is 60amp at 120volt. And my solar I have 2 Morning star MPPT 45, that are always in use. The 120v charger I use only when there is no sun.
 

snoobler

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Sorry... 47' long, 26' wide cat? LOL.. "lived on a boat"

Misleading.

"Lived on a super sweet boat."

For lead acid, charging should be about 10% of cap, i.e., 600Ah needs about 60A, which is about where you are. Haven't seen your specs, but 800W of solar split across your two MPPT 45 charge controllers sounds about right. For LFP, it hardly matters other than you need to be able to fully charge (or to your defined 80-90% upper limit) them in a reasonable time frame via available solar. Most are rated for 50 to 100% of their capacity.
 

MisterSandals

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So when you say to match the charger,
So my point/concern about how you configure your BMS, as shown in post #2 (which is one of the common ways to wire your system) is that its not perfect.
I think of a BMS as a switch, that when conditions monitored by the BMS are met, it turns off the switch. It remains off until the condition is solved (released).
So if wired like post #2 diagram, if BMS detects a low cell or low overall voltage it cuts the negative line until the voltage is restored up to the low voltage disconnect release voltage is met.
The problem is that your battery is disconnected from tour loads (good) but also disconnected from your chargers (bad).

With this situation in mind, some folks only run the charge thru the BMS. The solutions to prevent overdischarge are varied and many and none perfect.
Inverters with low voltage disconnect operate at overall voltage, not able to detect a cell low. Or some voltages unacceptably now and not programmable.
Dedicated low voltage disconnects not compatible with inverters (most anyway) and also operate at total voltage, not cell level.

Then there are separate port BMS’s... this goes on and on. Look at the BMS threads with hundreds of posts. (Sorry, i am in 7th month looking for BMS solution that i like)
 

Cal

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Expansion capability is limited with a fet based BMS. The fets can also be a higher failure point. Not good in a boat.

I suggest using a BMS having external battery disconnects like ElectroDacus or Chargery. No problem operating microwave from battery at a later date. Purchase an inverter that can be disabled by a 12V signal. Do not send 160A through a power disconnect. That’s expensive, prone to failure and pointless when there’s other options.
 

Rhat Cat

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So my point/concern about how you configure your BMS, as shown in post #2 (which is one of the common ways to wire your system) is that its not perfect.
I think of a BMS as a switch, that when conditions monitored by the BMS are met, it turns off the switch. It remains off until the condition is solved (released).
So if wired like post #2 diagram, if BMS detects a low cell or low overall voltage it cuts the negative line until the voltage is restored up to the low voltage disconnect release voltage is met.
The problem is that your battery is disconnected from tour loads (good) but also disconnected from your chargers (bad).

With this situation in mind, some folks only run the charge thru the BMS. The solutions to prevent overdischarge are varied and many and none perfect.
Inverters with low voltage disconnect operate at overall voltage, not able to detect a cell low. Or some voltages unacceptably now and not programmable.
Dedicated low voltage disconnects not compatible with inverters (most anyway) and also operate at total voltage, not cell level.

Then there are separate port BMS’s... this goes on and on. Look at the BMS threads with hundreds of posts. (Sorry, i am in 7th month looking for BMS solution that i like)
well thank you for all your info. it does help much.
 

Rhat Cat

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Sorry... 47' long, 26' wide cat? LOL.. "lived on a boat"

Misleading.

"Lived on a super sweet boat."

For lead acid, charging should be about 10% of cap, i.e., 600Ah needs about 60A, which is about where you are. Haven't seen your specs, but 800W of solar split across your two MPPT 45 charge controllers sounds about right. For LFP, it hardly matters other than you need to be able to fully charge (or to your defined 80-90% upper limit) them in a reasonable time frame via available solar. Most are rated for 50 to 100% of their capacity.
yes my friend, this is a custom cat. The problem I always have is the haul out, for the wells are normaly to fit a boat that is 24' beam max.to be a wide well for haulout. I normally go to St. Kitts there well is 33' wide. There are a few places, but need to find them. In the States is a bit harder to find.
Also the total solar on the boat is 1380w My 4 lg pannel are on the morningstar's 4 sm. 12v on swithes on/ off as needed. I know that is not the best but, it works for me for now. Plus I have 2, wind generators at 400w ea; there is wind at night so I use it, now with the for the new batteries I do not know if they can be used as well.
 
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