[RE-wrenches] Trojan L-16s

[Larry Crutcher, Starlight Solar Power Systems]

Drake,

When you said, "The batteries usually reach absorb voltage shortly after the sun hits the array", I wondered if you had more of a problem with that system. Glad to hear it's not that way.

Absorb time is an issue I have with the design of most charge controllers: They do not measure current to the battery and use that as the source info to determine if a battery is completely full and when to transition into float mode. Blue Sky Energy does this which, in my book, makes it a great charge controller. If you know how much current any battery draws (they are all different and change with age) when it is completely full, then the charge controller can be programmed to stay in absorb until that parameter is met. It could be 1/2 hour one day and 4 hours the next. Many things affect how batteries charge and this is the only true method I know of to accurately determine when it is full each day.

For your situation, I would go with Trojans recommendation of 2 hours absorb at 29.6. If you see that this is not fully charging each day, you can try increasing the time or choosing a higher voltage. If you have the sun hours available, I would choose longer charge time. There are many areas in the States that simply do not have enough sun hours to completely charge the battery from PV solar alone. In this case, using higher absorb voltage may be a solution.

Larry


On Jul 22, 2013, at 10:04 AM, Drake <drake.chamberlin at redwoodalliance.org> wrote:

Hi Larry,

I will bump up the absorb voltage to 29.6 V. How long do you think the bank should stay in absorb at that rate?  The bank now seems healthy, with the bad battery replaced.  It does accept charge, without going high prematurely.  The max charge rate from the array is around C/10. The system can also be fast charged from a Honda 6500 inverter generator through the Outback 3524 VFX.

We have a Trimetric meter on the system. The discrepancy between the percent charge and the voltage is what demonstrated that we had a problem.

Thanks,

Drake



At 09:30 PM 7/19/2013, you wrote:
> Hi Drake,
> 
> It always concerns me when I hear that a battery bank reaches absorb setting very quickly. It typically means one of two things: very few AH were removed from the bank; the battery bank has sulfated cells due to chronic undercharging. Far too often I find the latter to be true.
> 
> Healthy batteries will accept current and hold the charge voltage down with a fairly linear, slow climb to absorption voltage. Sulfated batteries do not accept current well which allows voltage to climb rapidly as the battery presents little load on the charging system. I'm not sure how this plays into your original post about a bad cell but it seemed worth mentioning.
> 
> My opinion is to aggressively charge, by using higher voltage, large flooded batteries. This is especially true when the PV system is moderate or undersized. 29.6 volts is what Trojan recommends. You can go as high as 32 volts on the L-16's but make sure the temperature compensation is installed properly and working. You will use more water.
> 
> One last comment, I highly recommend that ALL off grid systems have a battery capacity monitor installed. It's kind of like flying an airplane without a fuel gauge…it might not end in disaster.
> 
> Larry Crutcher
> Starlight Solar Power Systems
> 
> 
> 
> On Jul 18, 2013, at 1:11 PM, Drake <drake.chamberlin at redwoodalliance.org> wrote:
> 
> Tom,
> 
> The batteries usually reach absorb voltage shortly after the sun hits the array. The reason the bank wasn't working correctly is that one cell was dead in one of the batteries.
> 
> I could increase the absorb time to 4.6 hours and the voltage to 29.6, especially since the bank has a new battery. That is longer and higher than I'd previously heard recommended. What would be the effect on water consumption?  How did you calculate the absorb time?
> 
> Thanks,
> 
> 
> Drake