Mixing lead acid and LIFPO in stand alone solar system

Aussie

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Mar 22, 2020
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58
I have lead acid batteries in my stand alone system. I am going to add LIFPO batteries. I am thinking I will have to run each bank separate. Any ideas on this. How I will be able to wire it up? What additional bits and pieces I will need? How can I charge both sets of batteries using the one set of PV panels. Any thoughts and ideas will be very much appreciated.
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
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Oct 29, 2019
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Rural NE Ontario Canada
That nugget above had made the rounds more than once: OIVEY not again....

I Run a Big Lead Bank (what I started with) and a Big LFP Bank.
Solar Charge Controller & Inverter/Charger have TWO Charging Profiles, one for FLA & one for LFP, as the charging profiles are different and Lead does need regular Equalizing etc which does not apply to LFP ever.

I use one of these BlueSea 9001E switches between my banks
9001e.jpg



While you can do 12V,24V etc with both chemistries the Voltage Curves are different, Close but NOT identical as LFP has a very long flat curve while Lead does not. Side X Side they will be fighting each other and as the lead drops, the LFP will try to back feed it wasting a very significant amount of juice in the process. The way the batteries take the charge is also very different as LFP is 99% Efficient where lead is 85% at best (when healthy).

There has been MUCH FUD but mostly a lot of Misunderstanding when it comes to the chemistries, sadly even old Wives Tales get dragged into it.

BEWARE ! Many Terms used like DOD vs SOC etc have Chemistry Specific Contexts and NOT ALL ARE INTERCHANGEABLE as such. This gets EVERYONE coming from Lead with a History of using it. This is a great source of miscommunication and confusion. IE, Peukerts Laws are irrelevant to Lithium Batteries.

Hope it helps, Good Luck.
Look at the 1st Link in my signature to see "About my System" with diagrams, pics & links for products used.
Steve
 

Northernchateau

Solar Enthusiast
Joined
Apr 14, 2021
Messages
195
Location
Worth, NY
I have lead acid batteries in my stand alone system. I am going to add LIFPO batteries. I am thinking I will have to run each bank separate. Any ideas on this. How I will be able to wire it up? What additional bits and pieces I will need? How can I charge both sets of batteries using the one set of PV panels. Any thoughts and ideas will be very much appreciated.
More input please.
What voltage and how many amp hours of each battery do you have?
How many solar panels and what are their specs?
If your running an inverter what is it?
IMO the simple answer is divide the panels and run 2 completely separate systems.
As noted above the charge profile of those batteries are very different. Optimize each with it's own solar charger.
 

Aussie

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Mar 22, 2020
Messages
58
Thanks for the response Steve. A wealth of knowledge for me to read. The "switch" in the photo is only good for a max 32 volts. I run 48. Could you recommend one for 48v
 

Aussie

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Mar 22, 2020
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Hi Northernchate. I have 24 x 2v x 1025amp hr Batt (sealed lead acid) for 48v system. I have a set of 24 x 80wPanels and two sets of 4 x 200w panels. My inverter is Solar Energy 48v 3.8 k v a A plasmatronic PL60 regulater I live in
Queensland , Australia, so get plenty of sun. I have 16 keheng 280 amp batteries coming soon.
 

Aussie

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Mar 22, 2020
Messages
58
Could anyone recommend a good regulater. I think I will spit up my panels into two sets and run two regulaters for my different batteries, and a manual switch to change batteries to inverter My thinking being , I just need another reg and a switch and away I go? Should be all set?
 

Aussie

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Mar 22, 2020
Messages
58
Can I use a switch rated 48v in a 48 v system? The voltage is often above 48v, up to about 56v sometimes.
 

Aussie

New Member
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Mar 22, 2020
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58
Having trouble finding a switch rated above 48 volts. The switch is for switching between battery banks.
 

wattmatters

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Apr 16, 2021
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Having trouble finding a switch rated above 48 volts. The switch is for switching between battery banks.
I think at these DC voltages you'll need to put each battery on its own DC isolation switch. Something like this:
BDM-125Series_44dd8219-fd2e-4bde-8bd5-462ab5050003_2048x.jpg

rated to the current capacity you require (allow some headroom). DC switching is a bugger and you can't muck about with low rated stuff.
 

Aussie

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Mar 22, 2020
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58
Thanks for that Wattmatters. Can you recommend a good supplier of DC stuff in Australia? I have tried Jaycar but find the quality a bit dodgy.
 

wattmatters

Solar Addict
Joined
Apr 16, 2021
Messages
879
Yeah it's a problem. Some options, in no specific order:
- eBay if you know exactly what you are buying, else it's a crap shoot
and of course for general stuff there's Bunnings or regular local electrical wholesale/supplies stores
 
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