How to charge Trojans

stephendv
stephendv Solar Expert Posts: 1,571 ✭✭
in Off Grid Solar & Battery Systems #1
Hi all,

I have a set of tall cell forklift batts and have had 2 different manufacturers recommend a charging curve which looks to be the same as the Trojan recommended curve. But no solar charger controller seems to support the curve. From the trojan manual, the recommended curve seems to be:
1. Bulk up to 2.35V
2. Absorb with a constant 2.35V for an undefined amount of time
3. Rise the voltage to somewhere between 2.45 - 2.79V and stop as soon as the target voltage is reached.

Steps 1 and 2 are easily done with any 3 stage charge controller, but how is one supposed to do the final step 3?

The only partial solution I can think of is to charge using step 1 and 2 normally, then every 5 days or so do a short (e.g. 10 minute) EQ charge. Would this be good enough? or is there a better way to do it?
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: How to charge Trojans

    As a long-time user of Trojan batteries I suggest you try this (as it works with the sort of settings you find on most charge controllers):

    1). Bulk stage. As much current as you can give it up to 13% of the Amp hours.
    2). Absorb threshold 2.4 - 2.5 Vpc. Hold at this Voltage level for the length of the Bulk cycle, up to 4 hours.
    3). Float Voltage set to 2.35

    Equalization done only as needed (SG difference greater than 0.010 between two cells). EQ at 2.5 - 2.6 Vpc for one hour, check SG, repeat until no improvement in SG is seen.

    I've seen those charge curve charts before; they're confusing. As I recall (can't actually see the images on this machine) they are a superimposition of graphs reflecting charge state vs. Voltage and the relevant rise/fall power characteristics. Yeah, as confusing as that. :roll:
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: How to charge Trojans

    i think i am following what it is trojan is saying there. they really wanted it absorb charged at a higher voltage with a current limit, but going straight to the higher single absorb setting voltage would up the bulk charge to that high with unlimited current. they want a small constant current from 14.1v (2.35v/c) to that higher voltage. i don't know of a single charger or controller that meets their requirements either so coot's recommendations are good. eq charges are not current limited so this is not a substitute for that, but use the eq setting as it is intended, that is, for equalizing cells.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #4
    Re: How to charge Trojans
    niel wrote: »
    i think i am following what it is trojan is saying there. they really wanted it absorb charged at a higher voltage with a current limit, but going straight to the higher single absorb setting voltage would up the bulk charge to that high with unlimited current. they want a small constant current from 14.1v (2.35v/c) to that higher voltage.

    Yep, that's the way I read it too and that's the same advise the forklift bta manufacturers were giving.
    niel wrote: »
    i don't know of a single charger or controller that meets their requirements either so coot's recommendations are good. eq charges are not current limited so this is not a substitute for that, but use the eq setting as it is intended, that is, for equalizing cells.

    I believe that EQ charges have to be current limited, else they would damage the batteries severely. Every bat manual that I've read says that above 2.4V current must be limited to max 5% of C20.

    If I could trick the controller to following trojans recommendations it would be to complete absorb at 2.35 and then initiate an EQ at 2.65 which lasts for 1 minute. That should give the same charge curve as trojan provides, but will require some additional external software + hardware to initiate the EQ.... which is why I was thinking that maybe doing a very short EQ every few days might be a compromise. Then do a proper EQ manually to actually equalise the cells as per the usual recommendations, 1-3 months.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #5
    Re: How to charge Trojans

    I think google is going to answer my own question here :blush:

    Came across this manual which recommends different charging regimes for RE or motive power systems: http://www.crownbattery.com/PDF/Safety.First._Deep%20Cycle%20Batteries.pdf

    For RE systems, they recommend the standard IUoU charging curve that 'coot explained above.
    But for motive power applications they also recommend the same modified curve that trojan (and the forklift manufacturers) recommend. So I think that explains the contradiction: the forklift people assume that the batt will be in forklift service and hence the different charging curve. But it's not necessary in an RE system.
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