Want to switch to lithium

[CLeblanc]

I have 4 6V 225ah lead acid batteries and want to switch to lithium because of weight and longevity. How much ah lithium do I need to match the output of my current batteries? I have 300w solar panel on the roof of the trailer, 40amp charge controller and use a 3000 w inverter. We boondock 90% of the time and use inverter and batteries for regular stuff such as coffee maker, tv and sat dish, toaster, etc..., and unplug the inverter system and plug in a generator when we want the a/c. Thanks in advance folks. Really like the info I've read so far.

 

[Steve_S]

4X 6V/225AH Lead Acid configured for 12V provides you with a Gross of 225AH Capacity (at best) if you only discharge to 50% which is what FLA tolerates. Fortunately, LFP does not have that limit and you can use 100% of the capacity. Having Batteries in Parallel divides the Charge & Discharge between them and this can be handy to keep the strain on batteries down while improving the performance.

12V/3000W Inverter is pretty much the Max you can use @ 12V because at 12V/3000W it has to pull just a bit over 250A (accounting for losses).

You have options:
Using 2x 12V/100AH LFP Batteries will provide 200AH and would be capable of delivering 200A for 1 hour. These could also take 100A Charge for 2 hours.
Using 1x 12V/200AH LFP will accomplish the same as above but the form factor will be double the size of the above pair.
There are Many Sizes of "prebuilt" batteries up to 12V/300AH but of course it is reflected in the price.

NOTE: Take Measurements of your battery compartment Length, Width & Height and look at the various battery packs out there and check to make sure it will fit... Some folks forget and that results in Blue Air !

The solar input with one 300W panel is woefully low ! This is certainly something to consider as well. I will also point out that LFP does charge much faster than FLA but it still needs the oomph behind it and of course, it is relative to the size of the battery system.

Here is a link to LFP Batteries reviewed by Will, there are several 12V models.

LiFePO4 Batteries for Offgrid and Mobile Solar

Are you tired of getting scammed by low quality lithium batteries that claim to last forever but die in a few months. Never let that happen again! Check out my recommendations below. I open every...

www.mobile-solarpower.com

Now you "could" build your own 12V LFP Battery and save some cash "IF YOU HAVE THE TOOLS" because if you have to buy tools then the costs add up quick. Nothing crazy is needed but there are basic required tools and basic skills. This guide I wrote a while back will answer many questions: https://diysolarforum.com/resources/luyuan-tech-basic-lifepo4-guide.151/ For 12V you need 4 Cells, a BMS and a Casing/Box to put the goodies in. There are LFP cells available from 10AH to 300AH (larger also but way more $$ also avail). At present the Most Popular cells for Battery Pack building are 280AH & 304AH in general. * ALERT * There are a LOT of Vendors selling cells, there are several Known Good vendors which the membership here has dealt with over the years, DO NOT IMPULSE BUY ANYTHING, Ask First & Check it can save you a crap load of heartache & bux to go with it.

MOST IMPORTANTLY !
BUY Nothing until you have Triple Checked everything and know what you are getting into... If in doubt ASK, there is No Such Thing as a Stupid Question except for the one that is not asked !

Hope it helps, Good Luck

 

[DIYrich]

4 6v batteries is 2s2p for 12v and 550 ah gross, with 225 ah usable. You would need a 12v 280 ah battery to replace capacity.

If you need all 3000 watts on a continuous basis, you need the ability to deliver 250 amps at 12v on a continuous basis. I would recommend two 12v 280 ah packs to keep discharge around 0.5c.

 

[SamDeleted]

I have 4 6V 225ah lead acid batteries

A little be of rough maths...

You've got currently:

6v X 225ah = 1350w

1350w per battery x 4 = 5,400w

As said you can only use the top 50% of a lead acid so you've got 2,700w of battery capacity that you want to replace with LiFePo4


2700w ÷ 12v = 225ah


So you need 225ah of LiFePo4 batteries, possibly 2x110ah ?

 

[SamDeleted]

A little be of rough maths...

You've got currently:

6v X 225ah = 1350w

1350w per battery x 4 = 5,400w

As said you can only use the top 50% of a lead acid so you've got 2,700w of battery capacity that you want to replace with LiFePo4


2700w ÷ 12v = 225ah


So you need 225ah of LiFePo4 batteries, possibly 2x110ah ?

But that assuming you have only been using the top 50% of your lead acids,

If you've been using more than that, then obviously you're accustomed to having more WattHour of battery capacity....

In that case you'll probably want 3x110ah LiFePo4 (or equivalent)

 

[DIYrich]

If he is using more than 50%, then he needs to increase the lead acid when he replaces them next week, or switch to LiFePO4.

 

[CLeblanc]

Awesome! All clear. Thank yous for all the feedback!

 

[defeedme]

4 6v batteries is 2s2p for 12v and 550 ah gross, with 225 ah usable. You would need a 12v 280 ah battery to replace capacity.

If you need all 3000 watts on a continuous basis, you need the ability to deliver 250 amps at 12v on a continuous basis. I would recommend two 12v 280 ah packs to keep discharge around 0.5c.

perfect answer, i'm gonna put two of those new wattcycle mini 300ah lifepo4 batteries in parralellel (replacing the two 6v lead acid) and get some serious wattage on my new 3200 onswi inverter

 

[OTRwSolar]

We transitioned from 6v GC2's to lifepo4 almost 5 years ago. If you're powering small loads, say less than 20a, I could see 4, 225ah 6v GC2's roughly equivalent to approx. 220-240ah's of lifepo4 (assuming the GC2's are only discharged to 50% SOC). However, under high load all bets are off. 6v GC2's are notorious for high voltage drop when under high load. If you're powering a 2000w inverter near max load, it might take 6, GC2's to provide the necessary voltage stability to access anywhere near 220-240ah's.

 

[defeedme]

We transitioned from 6v GC2's to lifepo4 almost 5 years ago. If you're powering small loads, say less than 20a, I could see 4, 225ah 6v GC2's roughly equivalent to approx. 220-240ah's of lifepo4 (assuming the GC2's are only discharged to 50% SOC). However, under high load all bets are off. 6v GC2's are notorious for high voltage drop when under high load. If you're powering a 2000w inverter near max load, it might take 6, GC2's to provide the necessary voltage stability to access anywhere near 220-240ah's.

correct, hence why everyone is migrating to Lifepo4 and now with the new compact, mini 300Ah units - which are roughly the same size & weight as the GC2's - its' almost a game changer.

 

[ocular]

One factor that is seen when changing from Pb Acid to LiFeP04 is the discharge/charge efficiency improvement. For LiFeP04 you need about 102% of what you take to full charge. For Pb acid its 120%+.