New Batteries (maybe)

Wanderman
Wanderman Solar Expert Posts: 180 ✭✭✭
Hey All,
Been using my system for a few months now with zero issues. I have quite a bit of excess capacity based upon my daily usage. The current battery bank is 2 x Trojan 27MTX deep cycles. ~230 a/hrs (115 a/hrs to 50%)

I have a very limited and odd shaped battery bay. It looks like I could fit 2 x Trojan 1275 (or Plus) batteries to extend my banks capacity. (300 a/hrs 150 a/hrs to 50%)

My usage has not been higher than 60 a/hrs each day/night cycle.

I have 450 watts of panels feeding a Morningstar TS-45-MPPT controller. Wiring is all oversized and losses are very low.

Two questions, what is the real difference between the T1275 and the T-1275 Plus?

Does the math still give me a healthy safety margin on charging?

Thanks!

Rick

Comments

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: New Batteries (maybe)

    2 batteries are 460ah ?
    Your panels likely max out about 24A. (with real life de-rating)
    The batteries you have, I think, need 23-26a to stay happy, so you are currently at the low end, and more batteries will make it more difficult to de-stratify the batteries. You speak of a battery bay, so I assume an RV, which a drive 1x a week, would help stir up the electrolyte. But if you ever got the 4 batteries down low, they would begin to sulfate before the PV brought them up to charge. You would HAVE to rely on something else to bulk up the batteries daily, till they hit 80%
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: New Batteries (maybe)

    Right now you've got 230 Amp hours of battery. Like Mike said, you probably see about 23 Amps of charge current. That's exactly what Trojan recommends: 10%.

    You're only using 60 Amp hours a day, which is 26% capacity. Another ideal number.

    If you add 300 Amp hours more capacity you'll throw the whole thing out of balance and gain nothing (since you don't need the extra power). Your system is good the way it is. Don't mess with it.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: New Batteries (maybe)

    And, if it is an RV where you spend weekends/part of the year (not year round) in the RV--You can take the batteries down below 50% without too much issue...

    They will not last as many cycles with deeper discharge, however, they probably will "age out" before they cycle out. (500 cycle life, 50 weekends a year, 10 year cycle life--about the age limit for those batteries anyways).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Wanderman
    Wanderman Solar Expert Posts: 180 ✭✭✭
    Re: New Batteries (maybe)

    OK...all points noted. However, perhaps I was unclear.

    I am NOT adding batteries, merely swapping 1 set of two for the other.

    Looking to maximize storage in the extraordinarily small battery box.

    Rick
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: New Batteries (maybe)

    Right now, it sounds like your system is nicely balanced (batteries, panels, and load)... Why try for more batteries (even it they are "free")?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Wanderman
    Wanderman Solar Expert Posts: 180 ✭✭✭
    Re: New Batteries (maybe)

    BB,
    We must have cross posted.

    2 Trojans there now, removed.

    2 New Trojans installed.

    Net/Net

    Rick
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: New Batteries (maybe)

    The 27MTX are 105 AH @ 20hr discharge rate. The 115 AH spec is for 100 hour discharge.

    You would be better off getting BCI class 30H case if you can take the extra length and slight width. 30XHS is 130 AH @ 20 hour.

    I assume your two batteries are wired in parallel for 12v system.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: New Batteries (maybe)

    Sorry, when I typed "more batteries" I really should have said more Amp*Hours/storage capacity.

    I don't see the advantage of more storage capacity for your application... You will be carrying more weight and may need to use the genset less often but longer run-times to bring the battery bank back over 75% state of charge to reduce sulfation.

    You cannot add more panels, right? (out of space).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: New Batteries (maybe)

    Right. Got it. You want to swap the 230 Amp hours for 300.
    If your peak current is 23 Amps that would be 7.6% of the Amp hour rating. Technically still within spec but not at Trojan's recommended 10%. It would work.
  • Wanderman
    Wanderman Solar Expert Posts: 180 ✭✭✭
    Re: New Batteries (maybe)

    OK..so we are on the right path. The new batteries are 82 lbs each..vs 66lbs for the 27s.

    No more panels...I am seriously out of unshaded efficient space.

    Rick
  • Wanderman
    Wanderman Solar Expert Posts: 180 ✭✭✭
    Re: New Batteries (maybe)

    Hmmm..

    Looking at the specs on the Trojan site again. The 27TMX is actually 55lbs and the 20 hr rate is 105a/hr.

    Originally, I was going to replace them with 2 SCS225s. These ARE 66lbs each and have a 130a/hr 20 hour rate.

    The 1275 (plus) are 82lbs and are 150a/hr at 20 hour rate.

    Any suggestions????

    Rick
  • Wanderman
    Wanderman Solar Expert Posts: 180 ✭✭✭
    Re: New Batteries (maybe)

    So,
    What's the final consensus for replacing the 2 batteries I have now?

    Rick
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: New Batteries (maybe)

    What about the "old" batteries? Will you get full credit, have another use for them?

    In the end, your current ratio of solar panel to battery bank is pretty much ideal.

    Why would you want a larger bank?

    In the end, more batteries does not give you more power. Only more panels will do that.

    If you have high peak or surge loads (power tools, pumps, etc.)--More batteries are nice for that.

    However, if you have good sun and the present batteries store enough power for the occasional cloudy day--I would not spend a bunch more money on for a new set of larger batteries.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Wanderman
    Wanderman Solar Expert Posts: 180 ✭✭✭
    Re: New Batteries (maybe)

    BB,
    As usual your observations are astute and on target. The current batteries are simply old. Likely 4 years or so. They were in the RV when I purchased it. They likely have never been charged properly, well until recently that is. Mostly an unknown quantity.

    Maximizing my storage capacity while maintaining a good charge balance via solar is the goal. best system in the limited space I currently have.


    With 450 watts, figuring no more than 105 ah usage per day, worst day is 4 hours (maybe cloudy) what is the maximum efficient storage capacity I should have?

    I will then choose the combination of actual battery models to install.

    The next goal will be a retrofit to lithium phosphate. Prices are and will fall much more.

    Thanks,

    Rick