CV Charge Controller without float option

[steviep19]

I've been using charge controllers that do not have a float setting, on my 24v system I had the voltage set to 28.8.

In the past this hasn't really been an issue because I've never had enough solar to fully charge the battery bank. I recently added panels, and with the summer approaching, I"m regularly getting my battery bank up to high voltage disconnect. Typically by 2:00 PM they hit 28v or so, then stay that way till 6 or 7 PM. I feel like this is not good for the batteries.

I then tried lowering it to 27.2, but found the batteries were charging too slowly. 27.6 was better, but I could still see the charge controllers throttling back down too early in my opinion, and the batteries were not getting to the SOC I was hoping.

I thought about setting my BMS's to cut off at a lower voltage, but I don't like the idea of using the BMS's for this. Am I over thinking this? or should I be concerned about floating the batteries at 28v for 4 to 5 hours a few days a week? Any thoughts would be appreciated.

 

[sunshine_eggo]

I've been using charge controllers that do not have a float setting, on my 24v system I had the voltage set to 28.8.

I have one like that. Bit of a turd. It's my backup. Fortunately, my NMC battery actually works well with one like that, but it sucks for lead acid or LFP.

In the past this hasn't really been an issue because I've never had enough solar to fully charge the battery bank. I recently added panels, and with the summer approaching, I"m regularly getting my battery bank up to high voltage disconnect. Typically by 2:00 PM they hit 28v or so, then stay that way till 6 or 7 PM. I feel like this is not good for the batteries.

Its not.

I then tried lowering it to 27.2, but found the batteries were charging too slowly. 27.6 was better, but I could still see the charge controllers throttling back down too early in my opinion, and the batteries were not getting to the SOC I was hoping.

27.6 is a good compromise. It makes for a good slow charge to full or near full, and it's not so high that it's risking damage.

I thought about setting my BMS's to cut off at a lower voltage, but I don't like the idea of using the BMS's for this.

Your instinct is correct. You should never use the BMS for routine interventions. It should only be utilized when something goes out of spec while your equipment is set to operate inside its limits.

Am I over thinking this?

No.

or should I be concerned about floating the batteries at 28v for 4 to 5 hours a few days a week?

If 27.6V produces acceptable performance, I would not be concerned about dwelling at that level for an average of up to 3 hours per day.

Any thoughts would be appreciated.

TL/DR:
27.6V for 3 hr/day average or replace MPPT.

 

[steviep19]

sunshine_eggo,

First of all, love the username.

Second of all thanks for confirming my suspicions. I'll set it to 27.6 and give it more time. I just know it's going to absolutely kill me those sunny mornings, where the clouds roll in during the afternoon.

Do you have any recommendations for charge controller that'll allow me to set a float?

 

[sunshine_eggo]

sunshine_eggo,

First of all, love the username.

Second of all thanks for confirming my suspicions. I'll set it to 27.6 and give it more time. I just know it's going to absolutely kill me those sunny mornings, where the clouds roll in during the afternoon.

Do you have any recommendations for charge controller that'll allow me to set a float?

It's hard to find a MPPT that doesn't allow float these days.

Will recommends several:

DIY Off Grid Solar Charge Controllers

Building a vehicle mounted solar power system? Let me help.

www.mobile-solarpower.com