Recharge Volts setting for 48V Solar system

gridmangridman Registered Users Posts: 18
I have had solar hooked into my system for about a month now. I sometimes run in Grid Support - EIC mode and sometimes no grid, just solar. When I am hooked to the grid, I am not selling back.

For the longest life of the Trojan L16s in a 48v solar system, I wondered if the long-timers could tell me what a good Recharge Volts setting is?

Thanks,

Rod

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Recharge Volts setting for 48V Solar system

    Well Trojan's recommended Absorb setting is 59.2 if I recall. Float would be around 55-56.
  • gridmangridman Registered Users Posts: 18
    Re: Recharge Volts setting for 48V Solar system

    I'm talking about the Recharge Volts setting which is where Bulk kicks in. You can set it on the SCCs and on the Inverter. Right now I have the SCCs set to 50V, but I think that may be a little high.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Recharge Volts setting for 48V Solar system
    gridman wrote: »
    I'm talking about the Recharge Volts setting which is where Bulk kicks in. You can set it on the SCCs and on the Inverter. Right now I have the SCCs set to 50V, but I think that may be a little high.

    In general terms you don't want a 48 Volt system to go below 48 Volts: as a resting Voltage that's about 50% SOC, so under load it's somewhat above that. So yes you could let it discharge lower than 50 without problem.
  • NorthGuyNorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Recharge Volts setting for 48V Solar system
    gridman wrote: »
    I'm talking about the Recharge Volts setting which is where Bulk kicks in. You can set it on the SCCs and on the Inverter. Right now I have the SCCs set to 50V, but I think that may be a little high.

    This setting on SCC is a little bit confusing. If you set it low, it'll still start re-charging in the morning. If you set it high then when the batteries are already in float and the voltage dips below the set value (e.g. high loads and clouds), it'll run a bulk/absorption cycle again.
  • Eric LEric L Solar Expert Posts: 262 ✭✭
    Re: Recharge Volts setting for 48V Solar system

    What you are looking for is affected by several factors including the size of the loads you have and battery age, so there is no single number that is optimum for every case. But here's what I did to find my voltage cut off with different equipment (Magnum inverter and Midnite CC).

    What I did was to start with a higher voltage, let it cut off (= go to bulk on the inverter, although I have my bulk amps set to 0 so all charging comes from solar), then waited a while and checked sg of the batteries with no load. I then systematically lowered the bulk voltage over the next several days. I was looking for a resting sg after cut-off that would correspond to around a 75-80% state-of-charge, since this seems to be a good spot for battery life versus cost.

    The corresponding sg I was looking for was about 1.24 per cell in thecase of my batteries (U.S. Battery, although Trojan are probably similar), which corresponds to a resting voltage of about 50 volts on the bank. In my case, this worked out to a cut-off voltage of 48.8 with new batteries. As the batteries age, I expect that this will go lower.
  • VicVic Solar Expert Posts: 3,177 ✭✭✭✭
    Re: Recharge Volts setting for 48V Solar system

    My guess is that this is called Re-Bulk on other systems.

    The strategy when Grid-Tied may be different than for off-grid. On the systems here Re-Bulk is not used, as there is sufficient battery capacity to supply demands until the next good solar day.

    The exact setting of this (if you are referring to a function that initiates a new charge cycle on a given day) will vary depending upon the system capabilities, weather, loads and when these loads occur etc.

    For many systems, minimizing the number of charge cycles is a good thing for battery life. Opinions, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: Recharge Volts setting for 48V Solar system
    Vic wrote: »
    The exact setting of this (if you are referring to a function that initiates a new charge cycle on a given day) will vary depending upon the system capabilities, weather, loads and when these loads occur etc.

    Vic is right! There is several factors that determine when you should recharge your batteries, and almost none of them apply on the same day. So it's kind of weird that manufacturers put a re-bulk setting in their charge controllers when they roll over at midnight and start a new day, reverting back to bulking and absorbing the bank again, even if it doesn't need it.

    My Classic controllers can get the bank to float, and the battery continues to float on either gen power, wind power, etc.. 12:00 AM comes and the confounded things roll their logs over and start a new "day" - re-bulking and absorbing the battery again when it doesn't need it. Outback controllers do the same thing. The XW inverter is worse. If you charge the battery with it, shut the generator off, the batteries float, restart the generator, it will re-bulk the bank again even though the recharge volts was never reached! So it's like, what do they even put that setting in there for?
    --
    Chris
  • Eric LEric L Solar Expert Posts: 262 ✭✭
    Re: Recharge Volts setting for 48V Solar system

    I may have misunderstood the OP, but I understood him to be running in grid support mode with no sell-back, and to be asking about where he should be setting the voltage cut-off so the the inverter switches from battery power to grid support. I did not understand him to be asking about a re-bulk setting for rebulking the batteries during the day. But if that was what he was asking about though, then I too would agree with Vic too that it's a function that shouldn't be in regular use.
  • VicVic Solar Expert Posts: 3,177 ✭✭✭✭
    Re: Recharge Volts setting for 48V Solar system

    Eric L

    I may well have made an incorrect guess, and without further info from gridman, it will remain an unknown. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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