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Curious about LiFePo4 cells

MkWangus

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Feb 12, 2020
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I've been looking into building a 24v battery for my van conversion using prismatic cells but cant find a reliable seller in Australia.

I have found these and I'm wondering if I run them in parallel pairs in a series of 8 for 24v 480ahr total would these be decent cells to purchase?


If not does anyone have advice on sourcing 3.2v cells and what I should be looking for.
 
8 cells in series = 24V. X2 in parallel doubles the AHrs.

These ARE the best deal going ATM: shipping to Oz is of course always the bugger but play with the various shipping options and Amy @ Xuba may be of help there. Let her know you are coming from DIYSolarForum when you start a chat with her.

 
8 cells in series = 24V. X2 in parallel doubles the AHrs.

These ARE the best deal going ATM: shipping to Oz is of course always the bugger but play with the various shipping options and Amy @ Xuba may be of help there. Let her know you are coming from DIYSolarForum when you start a chat with her.


wow amazing advice! Those cells look great and the price is very reasonable. The site doesn't calculate shipping to Aus so will need to get in contact with Amy to figure those details. especially ordering 16 of them.

Any advice on a BMS for this kind of battery?
 
I use Chargery BUT I am an off-grid cabineer and my needs are such that I require external power handling which the Chargery does with relays. They can be used in a vehicular application as that is what they are designed for. Info link in my signature. The BMS really depends on your particular use case and needs. Typically, BMS' < 120A can use FETS and such internally without relays (that's pretty much the edge) above 120A better to go with external handling.

Case in point, I'm on 24V, if I run the microwave (1200W inverter type) , have 2 LED lights on and the deep well pump kicks on (Grundfos SQ5 soft-start-120VAC) I see 145A pulled from the 24V battery bank. If I was 12V, that would be double, @ 48V it would be half. When you parallel packs properly, they will split the load generally but one must be cautious to get it right.

Very Good Doc to read !
 
I use Chargery BUT I am an off-grid cabineer and my needs are such that I require external power handling which the Chargery does with relays. They can be used in a vehicular application as that is what they are designed for. Info link in my signature. The BMS really depends on your particular use case and needs. Typically, BMS' < 120A can use FETS and such internally without relays (that's pretty much the edge) above 120A better to go with external handling.

Case in point, I'm on 24V, if I run the microwave (1200W inverter type) , have 2 LED lights on and the deep well pump kicks on (Grundfos SQ5 soft-start-120VAC) I see 145A pulled from the 24V battery bank. If I was 12V, that would be double, @ 48V it would be half. When you parallel packs properly, they will split the load generally but one must be cautious to get it right.

Very Good Doc to read !
I had a look at your build and noticed you are making 2 packs with 8 cells each. would this be a better alternative to running 2p then 8 in series to make 1 pack? i know the total will be the same but is one a better way of doing it than the other?
 
I want to manage EVERY Cell, not pairs, and the redundancy if one pack goes down the others are alive + load split / share. I have 1 pack (the ShunBin) which is 16 cells (24V/350AH) and I will likely tear it apart again and convert it to two 8 cell packs @ 175AH ea with their own BMS8T. BTW: Have you ever had to manhandle a 150LB / 70Kg battery pack ? no treat.

In fact I have debating "format" and with my research verified, I'm going for the "Block" format over the "Long" format as well.
PIC from Will's website.
24v-8cell-square.png
 
I want to manage EVERY Cell, not pairs, and the redundancy if one pack goes down the others are alive + load split / share. I have 1 pack (the ShunBin) which is 16 cells (24V/350AH) and I will likely tear it apart again and convert it to two 8 cell packs @ 175AH ea with their own BMS8T. BTW: Have you ever had to manhandle a 150LB / 70Kg battery pack ? no treat.

In fact I have debating "format" and with my research verified, I'm going for the "Block" format over the "Long" format as well.
PIC from Will's website.
View attachment 7294
So an 8 cell 280ahr 24v battery with the cells you recommended would have a continuous discharge of 1c which from my understanding means 280amps. What amp rating would an 8s BMS need to handle this load?
 
So an 8 cell 280ahr 24v battery with the cells you recommended would have a continuous discharge of 1c which from my understanding means 280amps. What amp rating would an 8s BMS need to handle this load?
280 amps for 1 hour = 1C rating yes.

BMS and amp handling varies. Internally managed BMS' with FETS (no relays) don't usually go above 120A although I've seen some advertised higher I personally would not go there. Even then, the general unwritten rule is to get a BMS with a minimum of 20% margin, so a 100A real pull should have a 120A BMS for margin.

I use 200A relays with my Chargery BMS because I can actually pull close to that if I load my system. Now I do NOT have heavy AC appliances... I can actually run my 3HP compressor off the system, even my small 120V MIG Welder (Ohh you wanna see draw !) but I won't abuse my solar gear for that, so I use the GenSet to run those when I need them. I prefer the relays myself and they can be upgraded to higher amps if needed, again it is better to over size the relays and leave a respectable margin. Ultimately the fuses on the battery pack are your last line of defence, the first line of defence is good DC breakers which also need to match up for your loads & what is expected to go through there.

The bottom line, design your system to be able to handle the Maximum Load Potential you can draw from it. As long as you DO NOT EXCEED the 1C ratings of your cells / battery you should be fine. It is actually more wise to build your system 1 Step above of what you think.... IE: If you think a 24v/3Kw inverter will be sufficient get the next one up... Save yourself the upgrade in advance … BTDT ! Also remember that a 3Kw inverter pulls 125A to delivery 3000W (plus overhead amps) but a surge of 9000 (Low Freq) is possible which is 375A for a surge draw.

Some folks think I'm nuts when I also suggest using larger gauge battery cables (using fine copper Welding Cable) but me reasoning is based on years of playing with heavy DC. Simply put, reduce eliminate deration, potential for heat in the cable (if too undersized it can be a poofdah), future upgrade growth (copper is $$ and ever going to get cheaper) and more...

My EVO-4024 4Kw inverter draws 166A for 4000W output, up to 12,000W so X4 amperage for a momentary surge.
 
280 amps for 1 hour = 1C rating yes.

BMS and amp handling varies. Internally managed BMS' with FETS (no relays) don't usually go above 120A although I've seen some advertised higher I personally would not go there. Even then, the general unwritten rule is to get a BMS with a minimum of 20% margin, so a 100A real pull should have a 120A BMS for margin.

I use 200A relays with my Chargery BMS because I can actually pull close to that if I load my system. Now I do NOT have heavy AC appliances... I can actually run my 3HP compressor off the system, even my small 120V MIG Welder (Ohh you wanna see draw !) but I won't abuse my solar gear for that, so I use the GenSet to run those when I need them. I prefer the relays myself and they can be upgraded to higher amps if needed, again it is better to over size the relays and leave a respectable margin. Ultimately the fuses on the battery pack are your last line of defence, the first line of defence is good DC breakers which also need to match up for your loads & what is expected to go through there.

The bottom line, design your system to be able to handle the Maximum Load Potential you can draw from it. As long as you DO NOT EXCEED the 1C ratings of your cells / battery you should be fine. It is actually more wise to build your system 1 Step above of what you think.... IE: If you think a 24v/3Kw inverter will be sufficient get the next one up... Save yourself the upgrade in advance … BTDT ! Also remember that a 3Kw inverter pulls 125A to delivery 3000W (plus overhead amps) but a surge of 9000 (Low Freq) is possible which is 375A for a surge draw.

Some folks think I'm nuts when I also suggest using larger gauge battery cables (using fine copper Welding Cable) but me reasoning is based on years of playing with heavy DC. Simply put, reduce eliminate deration, potential for heat in the cable (if too undersized it can be a poofdah), future upgrade growth (copper is $$ and ever going to get cheaper) and more...

My EVO-4024 4Kw inverter draws 166A for 4000W output, up to 12,000W so X4 amperage for a momentary surge.
its cool to hear you can run a MIG, i hope to do the same. risky to run it through the inverter off the batteries?

I will 100% be building it above what i need, not gonna skimp on light weight cables.

parts im thinking right now

2, 1 for each array
https://www.outbackmarine.com.au/blue-solar-mppt-100-50-charge-controller-victron-s

4 will be retractable, 8 in total
https://outbax.com.au/maxray-240w-s...tiLyffW6EUydz_dhy5tYLbbJuqM-3ZYcaArJOEALw_wcB

for alternator charging
https://www.outbackmarine.com.au/victron-orion-tr-smart-12-12-30a-360w-isolated-dc~83649


16 cells at 24volts

bms x2



I know im a Victron fan boy but i just want to ensure quality components from a reputable source
 
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If I was building my system today from scratch, I'd more than likely choose Victron as well for a full on solution but alas I built my system 5 years ago and the picture was quite different then. Everything you list is good stuff. The BMS... well that's low fruit in a high end fruit salad. They are a good "basic" BMS with no programmability or control / monitoring per pack / per cell. I cannot recommend these types of BMS, I have to know what it is doing, how it is doing and how the cells / pack are doing and I want to see the status of affairs Real Time...

To that end, you may want to consider the BMS with Bluetooth that Will reviewed & likes. I believe they originate here: https://www.lithiumbatterypcb.com/p...battery-pcb-board/smart-bms-of-power-battery/ I can't be sure, and I forget which thread it got covered.
 
If I was building my system today from scratch, I'd more than likely choose Victron as well for a full on solution but alas I built my system 5 years ago and the picture was quite different then. Everything you list is good stuff. The BMS... well that's low fruit in a high end fruit salad. They are a good "basic" BMS with no programmability or control / monitoring per pack / per cell. I cannot recommend these types of BMS, I have to know what it is doing, how it is doing and how the cells / pack are doing and I want to see the status of affairs Real Time...

To that end, you may want to consider the BMS with Bluetooth that Will reviewed & likes. I believe they originate here: https://www.lithiumbatterypcb.com/p...battery-pcb-board/smart-bms-of-power-battery/ I can't be sure, and I forget which thread it got covered.
thanks for all the helpful advice

I will have to check out which one Will recommends.
 
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