proper absorb time for deka L16

rkymtnoffgrd · October 2011

Im going over the battery setting on my fathers xantrex system. He has 16 deka L16 (370 amp/hr @ the 20hr rate) and xantrex system is set for 300min absorb time. That seems high to me. I thought is should be around two hours or so. Any thoughts? 16 batts, 48v bank, 2 strings of 8 batts ea, equalize@62.4v. Bulk @56.4v. Absorb@56.4v. Float@52.8v. Thanks for your input,

Vic · October 2011

Re: proper absorb time for deka L16

rky.

I dunno the Daka line at all well, but in trying to see just what battery you might be speaking of, seems that Deka offers an L16 in a number of styles.

To answer the question, it would incrrease the reply accuracy if you specified the exact battery model number.

It may well be Flooded, as you speced the EQ voltage in the range expected for FLAs.

Others may well know more about your batts. Vic

rkymtnoffgrd · October 2011

Re: proper absorb time for deka L16

Good point, that would likely help, Deka 8L16 flooded. I believe that is the model number.

Vic · October 2011

Re: proper absorb time for deka L16

Hi rky,

Well, almost all 8L16s I've seen or owned have been Flooded, but think that the L16 designation may relally be more of a size.

You may want to google " deka 8l16 370 ah " or similar. Did find a data sheet on charging, but the link is via another reseller's web site.

Looks like Vasorb is 57.6 V, as lowest listed for a 48 V bank, 55.2 for Float (seems high to me), and 61.2 as the highest listed EQ V, ( seems a bit low to me). Most of my experience is with Surrettes, and every mfg has a bit different chemestry, which drives the exact charge settings.

The old rule of thumb is that Asorb charge time should about equal the amount of time spent Bulking. But, to me, Bulk time depends upon the amount of current available, and from PV, Bulk is extended as it often begins when the sun is low on the horizon, limiting charge current, and therefore extends Bulk time ... and so on.

Usually, the duration of Asorb is dictated by the Depth Of Discharge, which often is a variable.

Since your batts are probably FLAs, use your hydrometer to determine the SOC of each cell in the bank, and adjust the charger settings accordingly.

Vic

RCinFLA · October 2011

Re: proper absorb time for deka L16

On XW normally you set Exit Current Threshold to terminate absorb charging. The maximum absorb time is just a maximum time safe guard if there is a battery failure.

You can set exit current threshold between 2 to 4% of battery AH rating in current. As batteries get older and have more leakage they may not make the lower 2% current during absorb so the number should be raised a bit.

Joe_B · October 2011

Re: proper absorb time for deka L16

RCinFLA wrote: »

On XW normally you set Exit Current Threshold to terminate absorb charging. The maximum absorb time is just a maximum time safe guard if there is a battery failure.

You can set exit current threshold between 2 to 4% of battery AH rating in current. As batteries get older and have more leakage they may not make the lower 2% current during absorb so the number should be raised a bit.

I can only find a reference to exit threshold modification by changing the battery capacity. It states in the manual that:

The Xantrex XW Series Inverter/Charger transitions to the float stage if either one of the following two conditions are met:

1. The charge current allowed by the batteries falls below the exit current
threshold, which is equal to 2% of the programmed battery capacity (for a
500 amp-hour battery bank, this would be 10 amps), for three minutes.

2. The Xantrex XW Series Inverter/Charger has been in absorption for the
programmed maximum absorption time limit. The default is 3 hours, but the
time limit is programmable from 1 minute to 8 hours.

Since the AH setting of the pack also affects other things, it is not the ideal method for modifying exit current.

Is there another way to do it that I missed?

RCinFLA · October 2011

Re: proper absorb time for deka L16

I reviewed the manual and it looks like the absorb terminate is fixed at 2% AH rating.

Anyway, the time for absorb is dependent on bulk current rate and absorb voltage setting. I would not leave a 5 hour timeout. I would reduce it to no more then two hours.

I don't like the software mutation of the operation funtionally of XW. Bulk charge rate is set by % of battery AH entered (I would rather just set amps directly). A dumb thing that has existed since Trace days is default setting charger to maximum inverter capability. I wonder how many batteries have be cooked before the new user realized that they need to reduce it to account for their battery size.

If you push a bulk charge with a higher current the battery will be at a lower SOC when it reaches absorb voltage (unless you also raise the absorb voltage), therefore needing more time in absorb. At 15% AH rate, the battery should spend about an hour and half at absorb voltage to have current fall to 2% AH rating.

The XW does not have an actual DC current measurement on batteries. Only battery voltage is actually measured. Battery current is a calculated number from the AC currents through the inverter with fudge factor for inverter efficiency. You should have a separate battery monitor on your system.

jeffkruse · October 2011

Re: proper absorb time for deka L16

How many AH are you pulling every night? How many Watts of Panels?

I have 8 of these and if I pull over 70AH I use around 300 minutes of absorb and 58.8 min Absorb voltage.

I found I had to increase my absorb voltage and time if I drew more than 70 AH each night. That also factors in partially cloudy afternoons.

proper absorb time for deka L16

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