[RE-wrenches] Absurd battery question

[Ray Walters]

I think once you compare the cost of 24v battery options ( Rubix, 
Simpliphi) to the 48v (Midnite) it will be worth replacing the 
inverters.  2500 Ah @ 24 vdc is 60 kwh; that's a good sized battery bank 
even for full time off grid, I think over kill for a backup system.  
Just pencil it both ways, my last 24 v system I noticed that LFP was 
almost double $$/ kwh compared to 48v.

Also, I Will reiterate that many on the list, including me, have had XWs 
throw the programming and start charging at maximum DC voltage (32vdc!)  
Many a battery bank has been cooked with fire danger a real 
possibility.   Just another reason to consider going 48v.  I just did a 
24 v LFP upgrade for a client with an Outback 24v inverter.  We too 
decided to keep the inverter, but many lessons learned during install, 
would change that choice next time:

1) Inverter age (10 to 15 years is getting long in the tooth, even if 
its worked perfectly)
2) Battery cost/ kwh  (48v much cheaper)
3) Battery options  (more options)
4) Half amperage on battery cables
5) Inverter can accept full 240 vac charge amps from generator (using a 
newer 120/240 inverter)
6) Charge controllers can operate at double their 24 v capacity
7) More Charge Controller choices, (such as the Midnite Hawke's Bay, 
which very unfortunately do not operate at 24 v)
8) Less parallel batteries for larger banks
9) Everything is wired to your spec, and you're not taking on somebody 
else's workmanship.

I too saw a working system that I didn't want to redo, but I kept 
uncovering crappy wiring that eliminated any cost savings from not 
replacing the inverter.....

You need to look at the full project economics, long term reliability, 
and future expandability.

Ray Walters
Remote Solar
303 505-8760

On 12/22/2025 1:32 PM, Chris Daum via RE-wrenches wrote:
>
> RE:  Closed loop communications…  I have a customer who needs to 
> replace his old AGMs; he’s looking at getting something like 2500ah @ 
> 24V and wants LFPs.  This is a battery based, grid tie system.  His 
> equipment is a pair of XW4024s (Schneider – and he has NO interest in 
> replacing his inverters) and three Classic (Midnite) charge 
> controllers. I’m concerned with integrating the LFPs with his old 
> inverter, but his Classics, I believe, can be reprogrammed to 
> accommodate the LFPs.  This system was installed around 2015 so the 
> equipment is not new – but it’s basically been humming along until a 
> couple of weeks ago, when there was a week of 60 to 90 MPH winds that 
> killed the power for a while.  This is near Boulder, CO (at 9000 ft 
> elevation).  His system worked fine til his old AGMs gave out.  Their 
> power was out for ~3 days, then came on for 2 days, then went out 
> again for a couple of days.  So he realized how undersized and old his 
> batteries were.
>
> If he gets some new LFPs, do you think they’ll work with this vintage 
> equipment?  Any of your wonderful advice to pass along!?   I’m 
> thinking the Classics can dial in the settings he needs.
>
> Thanks, y’all!
>
> Chris Daum
>
> Oasis Montana Inc.
>
> 406-777-4309 or 4321
>
> 406-777-4309 fax
>
>
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