I was sold on doing a 24VDC system for my travel trailer, when I started noticing some high end systems with 4, 6 and 8 12V 100ah batteries in Parallel for the battery bank. I also noticed in one of the videos I watched, He alluded to 2 batteries in parallel are better than more than that? And if you do more than that, you may have problems in about 5 years. I am hoping to understand why. So, if i bought 8 Lithium batteries, and I had the ability to design my system 3 different ways with 3 different bus voltages (In my case 24VDC is probably as high as I would go) Which system is best. So, I can do 12VDC and 800AH if I parallel connect the system. This is the easiest, and makes the most sense for a on the road system, but requires the largest wires, and the largest charge controller (I know that will be a significant savings in the others). I can do 2 series 4 parallel, and run a 24VDC bus, which I like, but then I have 4 batteries essentially in parallel, which he alluded to being a problem long term. Finally, I can do 4 series, 2 parallel, which he alluded to being best, but it creates a 48V bus, which makes some of the components I want to use a little more money than I want. So Why is it that when you go beyond 2 batteries in parallel, you have problems in about 5 years? To me, all these systems are exactly the same, and any one with a weak cell is going to cause problems. Any thoughts?
8 100AH lithium ion phosphate batteries, what is the best configuration bus for the battery bank for the batteries to survive long term?
- Thread starter wcsaddict
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Mudd
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If it was me I would do 48v. What batteries do you have? Even if one of the batteries went bad you can still run your system off four of the batteries. I don't think it would be any more complicated to do a 12 volt 24 or 48. 48 is ideal because it'll cost you the least. I'm a little confused are you trying to buy eight cells or eight batteries?
I am going to buy 8 100AH batteries. What I am trying to understand is why it appears as though the guy doing the videos said that more than 2 batteries in parallel will lead to problems later. I don't understand the difference on batteries between 4 series 2 parallel, and 8 parallel and how it effects long term battery life? the other option would be for me to compare 6 12V 100AH batteries to 2 8D's which are 12V 270AH batteries. essentially the same, although 1 has 6 batteries in parallel, and 1 has 2 in parallel. The videos suggest that the 2 in parallel will last longer than the 6 in parallel.
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
First I think some clarification is required here.... Devil is in teh details.
To make a 12V LFP Battery Pack, it takes 4 LFP Cells, a 24V Battery Pack requires 8 LFP Cells.
Placing Batteries in SERIES increases Voltage: 12V/100AH+12V/100AH=24V/100AH.
LFP Batteries in Series is NOT Recommended because most BMS' will not accept that and it IS risky.
Placing Batteries in PARALLEL increases Storage Capacity: 12V/100AH & 12V/100AH = 12V/200AH
You can have 2-10 Battery Packs in Parallel within a Bank, even more BUT then you are into complex BMS' (Battery Management Systems)
LFP Batteries in Parallel are perfectly fine as each "battery" acts as an "independent agent" if properly designed.
Things do become more complicated as you add more packs (full batteries) into a Battery Bank.
RV's / Campers are mostly all 12V & 120V and so you will need to provide 12V to your existing equipment. If you use a 24V system you will need a good 30V to 12V Step Down Converter (NOT a cheap Buck Converter) and YES, it must be 30V to 12V because when charging the battery bank, it will be just below 29V. And it will have to be able to deliver the Amperage required to operate your RV equipment. Many RV'ers do use 24V very very few go to 48V.
Look at this document I prepared in our Resource Section, on Assembling your own LFP Packs, as well as some other links like the LFP Voltage Chart in my Signature will help you on your path.
diysolarforum.com
Some NOTES: LFP Cell sizes & weight vary by capacity & manufacturer. RV's typically have a dedicated space for the batteries and as such is limited. Get Good Measurements to know the space you have to work with. You can buy LFP cells from 10AH to 1,000AH, currently the most popular are the 280AH cells which are 9" Tall and 8" wide 2-3/4" thick. 8 Cells in a straight line is 23-1/2" long X 8" wide. A "Block" pack is 16" wide X 11-3/4" long. Each 280AH cells weighs 5.2kg/11lbs.
Confusing Point to clarify.
Battery Packs in Parallel are no problem when wired up properly. They will share the Load & Charge capacity and improve the fault tolerance & fail over should anything go awry..
Battery Cells in Parallel within a Battery Pack is done to increase the "pack" AH Storage Capacity. ONLY properly Matched & Batched cells should be used if this is the plan, never Bulk Commodity cells which is what 95% of the Vendors sell. Properly Matched & Batched cells mean their characteristics are the same throughout their operating voltage & load ranges for Internal Resistance & Impedance. They more or less will "March in Step" as they operate. Matched & Batched cells are More Costly but definitely worthwhile for critical systems (like an offgrid residence).
We have a few KNOWN GOOD Vendors and we know of MANY Shlock Floggers selling Bulk Cells as "Matched". What 95% of the vendors will tell you is they are matched, BUT they are only Voltage & Static IR tested - (THIS IS NOT A PROPER Matching).
I will recomend Luyuan Tech who is a Very Well KNOWN Good Vendor (Good enough that I wrote the above guide for them, and I do not do such thing unless they are Genuinely Credible).
szluyuan.en.alibaba.com
Good Luck, hope it helps.
Steve_S
To make a 12V LFP Battery Pack, it takes 4 LFP Cells, a 24V Battery Pack requires 8 LFP Cells.
Placing Batteries in SERIES increases Voltage: 12V/100AH+12V/100AH=24V/100AH.
LFP Batteries in Series is NOT Recommended because most BMS' will not accept that and it IS risky.
Placing Batteries in PARALLEL increases Storage Capacity: 12V/100AH & 12V/100AH = 12V/200AH
You can have 2-10 Battery Packs in Parallel within a Bank, even more BUT then you are into complex BMS' (Battery Management Systems)
LFP Batteries in Parallel are perfectly fine as each "battery" acts as an "independent agent" if properly designed.
Things do become more complicated as you add more packs (full batteries) into a Battery Bank.
RV's / Campers are mostly all 12V & 120V and so you will need to provide 12V to your existing equipment. If you use a 24V system you will need a good 30V to 12V Step Down Converter (NOT a cheap Buck Converter) and YES, it must be 30V to 12V because when charging the battery bank, it will be just below 29V. And it will have to be able to deliver the Amperage required to operate your RV equipment. Many RV'ers do use 24V very very few go to 48V.
Look at this document I prepared in our Resource Section, on Assembling your own LFP Packs, as well as some other links like the LFP Voltage Chart in my Signature will help you on your path.
Luyuan Tech Basic Lifepo4 Guide
This document was posted to the forum by Amy from Shenzhen Luyuan and written by Steve S. It was meant to be posted as a resource. Below is her description of the resource: Dear all friends in the forum, This file in the attachment was...
diysolarforum.com
Some NOTES: LFP Cell sizes & weight vary by capacity & manufacturer. RV's typically have a dedicated space for the batteries and as such is limited. Get Good Measurements to know the space you have to work with. You can buy LFP cells from 10AH to 1,000AH, currently the most popular are the 280AH cells which are 9" Tall and 8" wide 2-3/4" thick. 8 Cells in a straight line is 23-1/2" long X 8" wide. A "Block" pack is 16" wide X 11-3/4" long. Each 280AH cells weighs 5.2kg/11lbs.
Confusing Point to clarify.
Battery Packs in Parallel are no problem when wired up properly. They will share the Load & Charge capacity and improve the fault tolerance & fail over should anything go awry..
Battery Cells in Parallel within a Battery Pack is done to increase the "pack" AH Storage Capacity. ONLY properly Matched & Batched cells should be used if this is the plan, never Bulk Commodity cells which is what 95% of the Vendors sell. Properly Matched & Batched cells mean their characteristics are the same throughout their operating voltage & load ranges for Internal Resistance & Impedance. They more or less will "March in Step" as they operate. Matched & Batched cells are More Costly but definitely worthwhile for critical systems (like an offgrid residence).
We have a few KNOWN GOOD Vendors and we know of MANY Shlock Floggers selling Bulk Cells as "Matched". What 95% of the vendors will tell you is they are matched, BUT they are only Voltage & Static IR tested - (THIS IS NOT A PROPER Matching).
I will recomend Luyuan Tech who is a Very Well KNOWN Good Vendor (Good enough that I wrote the above guide for them, and I do not do such thing unless they are Genuinely Credible).
Shenzhen Luyuan Technology Co., Ltd. - Lifepo4 battery, LTO battery
Shenzhen Luyuan Technology Co., Ltd., Experts in Manufacturing and Exporting Lifepo4 battery, LTO battery and 0 more Products.
szluyuan.en.alibaba.com
Good Luck, hope it helps.
Steve_S
Not sure what you mean by this. 12V batteries in parallel will still be 12V. I am not building my own battery with 3.2V individual cells. 8 battereis at 100AH will still be 800AH, not 1000. Do not understand this comment at all.
I do not have access to videos at the moment, but the website is https://www.mobile-solarpower.com/4000-watt-24v-solar-system.html, and he is talking about building a 24VDC system vs a 12V system for RV's. towards the end of the video, is when he makes a relatively quick comment about 4 12VDC batteries in a series parallel configuration to make 2 24VDC batteries is better than 4 12VDC batteries in parallel. He alludes to balancing issues, but I do not understand why, if the same 4 battereis are in the system, how being in parallel is worse than being in series parallel. If a batterey goes bad, or an individual cell goes bad, won't it basically effect the sytem the same?
I believe you can still have balance issues with the 12v lithium in series to have 24+ volts. I have seen some with a communication cable so the batteries can balance with each other. I don't think Battleborn has this option. This is a series issue.
Interesting that he talks about parallel batteries out of balance and then draws the diagram in a bad way. This is a parallel issue.
The main connection (below) comes off one pair. To make this correct the positive connection should come from one set and the negative should come from the other set. The more in parallel the worse it gets as drawn.
Since you are spending money I recommend making or buying a 24 volt battery. A single 24v battery will balance the series cells as a single group and you will have no issues there. If you need more capacity you can add more in parallel. Two or three you can attach the main charge/load cables to each end of the stack. Four or more in parallel should have equal length cables to a bus and possibly fuse the batteries individually.
Here is more to read on parallel balance: http://www.smartgauge.co.uk/batt_con.html
Interesting that he talks about parallel batteries out of balance and then draws the diagram in a bad way. This is a parallel issue.
The main connection (below) comes off one pair. To make this correct the positive connection should come from one set and the negative should come from the other set. The more in parallel the worse it gets as drawn.
Since you are spending money I recommend making or buying a 24 volt battery. A single 24v battery will balance the series cells as a single group and you will have no issues there. If you need more capacity you can add more in parallel. Two or three you can attach the main charge/load cables to each end of the stack. Four or more in parallel should have equal length cables to a bus and possibly fuse the batteries individually.
Here is more to read on parallel balance: http://www.smartgauge.co.uk/batt_con.html
Sorry, I thought you had 8 cells and was making a joke.
So do you have 8), 100 AH 12V batteries? I didn't get that from your post.
How large of an inverter do you plan on using? If it is over 3K I would definitely do a 24V system.
Under that, put them all in parallel for a 12V system.
What batteries do you have?
Looks like BattleBorn. Decent batteries.
You might want to read about this.
www.victronenergy.com
You might want to read about this.
Battery Balancer - Victron Energy
Equalize the state of charge of two series connected 12V batteries using the Battery Balancer. Find a Victron Energy dealer near you.
Thank you so much, this perfectly explains why and how to do it right. His nodal analysis of each point, had I thought about it, would make perfect sense ans to why the load is not balanced. This answers my question. Thank you!\I believe you can still have balance issues with the 12v lithium in series to have 24+ volts. I have seen some with a communication cable so the batteries can balance with each other. I don't think Battleborn has this option. This is a series issue.
Interesting that he talks about parallel batteries out of balance and then draws the diagram in a bad way. This is a parallel issue.
The main connection (below) comes off one pair. To make this correct the positive connection should come from one set and the negative should come from the other set. The more in parallel the worse it gets as drawn.
Since you are spending money I recommend making or buying a 24 volt battery. A single 24v battery will balance the series cells as a single group and you will have no issues there. If you need more capacity you can add more in parallel. Two or three you can attach the main charge/load cables to each end of the stack. Four or more in parallel should have equal length cables to a bus and possibly fuse the batteries individually.
Here is more to read on parallel balance: http://www.smartgauge.co.uk/batt_con.html
I have not purchased the batteries yet, but I was going to buy 8 Lion UT1300, or 8 Battleborn 12V 100ah heated batteries. Leaning towards the Lion right now, since I believe the heating may not be necessary if I put the batteries inside my trailer instead of outside where they used to be. I am able to get the Lion at $670 each at costco, and I can't find quite the deal on the Battleborn. So, I am looking to invest about $5400 in batteries. I also really like the GC3 Battleborn 270AH battery. I am wondering if 2 of those would be a better solution than the 6 or 8 100ah. Cost is more at $2900 each, and I have 200 less AH for 2 vs the 8 lion. All this may be overkill. My camper is a 30 amp hookup. I live north, so I need a large charge array and battery to compensate for the lack of sun in the Northwest. I am considering 4 bi-facial panels at 410W each to try to boost production per square foot of roof space. I am fabricating mounts that will allow me to tilt them in the fall and winter months which is when I boondock the most. I spend a lot of time off grid hunting and downhill skiiing. running the generator can be done, but then I need to carry a lot of gas. anyway, I digress. I am looking at a 3000KW inverter. I like the victron Multiplus-II 3000VA as an all in one charger inverter package even though I know I am paying a premium. Otherwise, it will probably be a Giandel at 3000W or 4000W. Since the camper is 30AMps x 110VAC, 3300Watts should be enough to power it. I even have a soft starter on the AC, although I know that is a fools quest to try to create enough power for that. I have the RV refrigerator and a dorm refrigerator on the 110VAC system in an outdoor kitchen that I love to use. I am considering all 3 bus voltages. 12VDC is easy, but requires big wires (no big deal), and an expensive charge controller or 2. 24VDC is a little more complicated, but really just requires I use a 40amp 24VDC to 12VDC converter for about $40 to make it work. I save money on the charge controller since it need to be half the size of the other one. 48VDC, seems like it might be too much for this project, although again I save money on the charge controller, but I add a level of danger with the higher voltage in the trailer and young children. No that they should ever be under the cabinets, but 4 and 7 year olds will find a way. So at 3K, would you do 24, or 12. the price is about the same.
Thank you, did not know this existed.Looks like BattleBorn. Decent batteries.
You might want to read about this.
Battery Balancer - Victron Energy
Equalize the state of charge of two series connected 12V batteries using the Battery Balancer. Find a Victron Energy dealer near you.
Smaller capacity cells are more resistant to physical damage. If you are driving on rough roads, you may see a decrease in battery life.
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