Acceptable variance in SG between Surrette cells?
Freewilley
Solar Expert Posts: 228 ✭✭
Can somebody refresh me on how much cells vary before a corrective equalization is needed? Looked around the Surrette site to no avail...
Mate, VFX 2812, FM 60 & MX 60, 2 Full River AGM 400 6v, 1400 watt Solar Array, Yamaha 3000iSEB inverter gen
12 volt Flojet water pump
off grid summer home in northern Ontario
12 volt Flojet water pump
off grid summer home in northern Ontario
Comments
-Bill
Here is a Link to the Surrette Flooded/AGM Battery Manual:
http://rollsbattery.com/uploads/pdfs/documents/user_manuals/Rolls_Battery_Manual.pdf
See Page #16, under Equalization -- Preventive. There it is said that an Equalization should be performed when the variation between cells of a bank is greater than 0.025 - 0.030. Then the EQ should be done for 2 - 3 hours.
On this page, under Frequency, it is noted that an EQ should be performed every 60 - 180 days.
As BB Bill noted, they do recommend that an EQ be terminated when SGs have remained constant for 45 - 60 minutes, generally.
Be certain to set the EQ voltage at or a bit above the minimum specified in the battery manual, and, IMO, the EQ voltage should be Temperature-Compensated. Do so manually, if your charger/ CC will not do this using the Battery Temperature Sensor (BTS).
FWIW, Vic
-Bill
Do you run off of generator during equalization?
Guess that is for me ... Almost always EQ from PV.
and BB Bill, the Finishing EQ current is about 3% of Actual 20-Hr C (Surrette specs Capacity as if the fill SG is 1.280. Actual fill SG is 1.265 for almost all/all of their Solar batteries. Of course, it CAN require 70 - 80 Amps to get on top (reach set EQ voltage) for the largest banks, here. If one needs to EQ in the higher range of Surrette-recommended EQ voltage, the Finishing current would be somewhat higher.
We usually either ramp-up the EQ voltage to limit the current to 5% of C, or a bit lower, or just change the CC output current Limit to 4.5% of C, if time is available, and so on.
FWIW, Vic
-Bill
Well, Bill, in our case, we are NUTSO!
The Power Room is Priority A/C cooled, and do circulate cooled air through the battery box. BUT, as, essentially all of the energy going into the battery bank in EQ (and later Absorb), ends up as heat in the battery, even with fairly aggressive cooling, the battery can still get warm/hot, especially in the Summer months.
When the battery really needs to be EQed, sometimes try of do it over two days -- this does not happen very frequently, thank goodness.
The two largest banks here are 10 years of age, so do try to be a bit gentle with them, but one of the banks is using a bit more water than in years past, and so on.
Thanks, Bill, for all that you do for us here! Vic