schneider absorb time

mmag · March 2014

i have a schneider xw mppt 80 600 hooked to 740 amp hours of batteries, i have the absorb time set to 150 minutes but it never absorbs for that amount of time, usually around a half hour, the amps do come down to around 7-10 amps on my trimetric, is this normal?

vtmaps · March 2014

Re: schneider absorb time

mmag wrote: »

i have a schneider xw mppt 80 600 hooked to 740 amp hours of batteries, i have the absorb time set to 150 minutes but it never absorbs for that amount of time, usually around a half hour, the amps do come down to around 7-10 amps on my trimetric, is this normal?

I assume you have flooded lead acid batteries. I don't know how schneider works, but it sounds normal. You are getting down to an absorb current of 1% of your battery's capacity in just 30 minutes. That means something:

1) Your batteries are fine, but barely discharged. It doesn't take long to charge a battery that starts at > 95% SOC.
or 2) Your batteries are not well. Many, many ways this could be. Need many more details to make a diagnosis.
or 3) Your absorb voltage is too low for batteries. Perhaps cold batteries with no temp compensation?

btw, #1 or #3 can cause #2

In general, the best way to charge those batteries is by terminating absorb by 'end amps' rather than setting a timer (150 minutes, in your schneider). You are getting to a 1% end amps. That may, or may not be, appropriate for your batteries.

A question: what is your end amps? You determine this by setting absorb time to 'forever'. When you reach absorb voltage, begin writing down the absorb current (from your trimetric) every 20 minutes. When the current is no longer decreasing, that is your end amps.

Hopefully, when you reach 'end amps' you have also reached 100% SOC as determined by Specific Gravity. This is something you should check.

As I mentioned, I don't know enough about that controller to explain how it knows to terminate absorb in less than the 150 minutes you have set... But its probably good that it does.... 1% is fairly low for end amps, but not out of the question. Tell us much more about your battery bank...

--vtMaps

offgrid me · March 2014

Re: schneider absorb time

The 80 600 uses 2% of the battery bank size as the end amp setting. It also has a maximum time setting in case it never gets to that level because of loads. Did you set your battery size in the custom battery settings. I would check your specific gravities and make sure your batteries are getting fully charged. I found that 2% was not absorbing my batteries long enough so you can get it to run longer by setting a battery size that is smaller than what you have to trick the controller and get it to stay in absorb for the full time period.
Ned

vtmaps · March 2014

Re: schneider absorb time

offgrid me wrote: »

The 80 600 uses 2% of the battery bank size as the end amp setting. It also has a maximum time setting in case it never gets to that level because of loads.

Thanks for explaining.

mmag, if you want to chart out your absorb current, set your battery size to something very small, like 100 ah. Schneider will then try to get the absorb current down to 2 amps. On your bank, that would be the equivalent of setting your absorb time to 'forever'.

--vtMaps

mmag · March 2014

Re: schneider absorb time

Thanks for the replies, i have sixteen trojan l16reb that are two months old, i have temp comp my bts says the batteries are 58 degrees f, my absorb voltage is set at 58.4 but with temp comp it has been absorbing at around 60, after five days of rainy weather and then a full bulk and absorb cycle with the sun, i checked the sg it was around 1.220 so i equalized the batteries, i got them up to 1.260, this is without temp comp i need to get a thermometer today, this got me thinking that something is wrong a have a trimetric tm 2025-a that does history it says my end amps get down to from 7-12 amps, but i need a dc clamp meter to make sure that number is correct, and i have 3540 watts of panels feeding the cc, i will try to adjust the bank size down to see if that helps.

offgrid me · March 2014

Re: schneider absorb time

I played this same game when I first got my system up and running. Constantly seeing low sg after the controller said the batteries were fully charged. You do not want to equalize till the batteries are fully charged. You need to increase your absorb time especially when the batteries are well discharged. Set the bank size to 100amp hr and set time to 3hrs and see what the sg comes up to. Your solar array is a little small for that battery bank. You are looking for around a 10% charge rate after all losses.
Ned

Blackcherry04 · March 2014

Re: schneider absorb time

There has always been two schools of thought on trying to bring your batteries up to a full SG 100% reading everyday. If your achieving 80 - 90% on a daily basis and can reach 100 % every 7-10 days without extended Equalization those batteries do not seem to have as much plate damage as batteries that are pushed to it on a daily basis. Of course a lot depends on the DOD the batteries are taken to.

I have a string of 2 V Rolls, I can do a EQ and when the first battery reaches 1.265 stop the EQ on the string. The batteries will always be .010 -.025 apart. I can then take a 2v charger and bring the other 5 up to the same level individually. If I run them one 50% DOD cycle , recharge and they will be all over the place with the same disparity in their SG levels as they were before I started. Why the difference ? Some must gas more readily, some have more plate exposed, It's just the nature of the beast and can't worry about it.
.
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vtmaps · March 2014

Re: schneider absorb time

mmag wrote: »

my absorb voltage is set at 58.4 but with temp comp it has been absorbing at around 60

I believe that Trojan's recommended absorb voltage is higher than 58.4. If I recall correctly, it's over 59 volts. If your batteries are cold enough to add 1.6 volts (58.4 --> 60.0) of compensation, then you should be seeing temp compensated voltage closer to 61 volts.

What voltage do you equalize at? It might be the equivalent of an absorb charge.

--vtMaps

mmag · March 2014

Re: schneider absorb time

If I remember right for the Trojan re batteries 58.4 was exceptable for absorb, I equalize at 62 but with temp comp it was over 63. On the scneider there is also a boost charge does anybody use it?

mmag · March 2014

Re: schneider absorb time

I just looked at the trojan brochure for th L16REB and it says the absorption voltage is 2.35-2.45 per cell

vtmaps · March 2014

Re: schneider absorb time

mmag wrote: »

I just looked at the trojan brochure for the L16REB and it says the absorption voltage is 2.35-2.45 per cell

I've seen that. If you look at the Trojan User's Manual they show a charge profile that shows a daily 'finish' charge of 2.45 - 2.79 volts per cell. That's up to 66.96 volts! They also have a chart that suggests a daily charge of 59.2 volts and an absorb charge of 56.4 - 58.8 volts.

Solar batteries are a niche market. Most batteries are charged by battery chargers from the grid. They can take as long as they like and provide current and voltage profiles that are NOT the familiar bulk, absorb, float that solar chargers use.

Bottom line: you have two variables under your control: voltage and time. You need to increase one or both. You are fortunate that you have an hydrometer to guide you. I would suggest that you increase voltage a bit... you need to stir the electrolyte. The results you are seeing with equalization (increased SG) are in part due to breaking up of stratification. Keep at it until you get the SG where it belongs.

One more thing... do you have a DC current clamp meter? It's good to make certain that each of your two strings of batteries is getting the same current while charging. If you don't have a meter (and even if you do) it's a good idea to charge the strings one at a time, especially hard equalization charges.

--vtMaps

mmag · March 2014

Re: schneider absorb time

Thanks for the replies this is good info that I would have a hard time getting without this forum, I am going to change my absorb voltage to 59.2 and tomorrow monitor the absorb stage with the amp hour set at 100, I have a ac clamp meter but I will be buying a dc clamp meter tomorrow if I can find one, I bought a new hydrometer today with a built in thermometer to adjust the sg with but I really want to order a hydrovolt.

mmag · April 2014

Re: schneider absorb time

update; i upped the absorb voltage to 59.2 changed the amp hour size to 100 and the absorb time to 3 hours, my sg has been staying where it should be, my question, is 3 hours to long of a absorb? in my charger manual it lists a shorter absorb time. also trojan is saying to have my float voltage at 52.8, should it be higher also?

Cariboocoot · April 2014

Re: schneider absorb time

You can tell if the Absorb time is too long by watching the current over time. If it drops off to around 2-3% (with no loads) that's about all the Absorb that is going to happen. If there is then still an hour or half an hour left to Absorb time then it is too long.

Float Voltage will probably be better raised to 55.2. You have to judge the practicality of that in terms of being able to maintain said Voltage and not continuing with so much charge activity that you lose too much water over days.

Dave Angelini · April 2014

Re: schneider absorb time

mmag wrote: »

update; i upped the absorb voltage to 59.2 changed the amp hour size to 100 and the absorb time to 3 hours, my sg has been staying where it should be, my question, is 3 hours to long of a absorb? in my charger manual it lists a shorter absorb time. also trojan is saying to have my float voltage at 52.8, should it be higher also?

The manual for the XW-80 charger has absorb as a default 2 hour value. If you have done all this testing and proven that 2 hours is not long enough, why would you want to decrease absorb to 2 hours?

jcheil · April 2014

Re: schneider absorb time

Cariboocoot wrote: »

You can tell if the Absorb time is too long by watching the current over time. If it drops off to around 2-3% (with no loads) that's about all the Absorb that is going to happen. If there is then still an hour or half an hour left to Absorb time then it is too long.

Would End-Amps be confused if in the middle of the cycle, clouds came out and it rained for an hour? Or is it smart enough to know that since nothing is coming into the CC from the array it should not try to base anything on EA at that point?

Cariboocoot · April 2014

Re: schneider absorb time

jcheil wrote: »

Would End-Amps be confused if in the middle of the cycle, clouds came out and it rained for an hour? Or is it smart enough to know that since nothing is coming into the CC from the array it should not try to base anything on EA at that point?

Depending on the particular charge controller there will be a time for End Amps: 'X' Amps for 'Y' minutes before it ends. Usually a passing cloud will not affect it. Change in weather, however, means you'd may end up a bit short on Absorb that day due to lack of power to continue it with. C'est la vie.

Vic · April 2014

Re: schneider absorb time

End Amps only can be satisfied when the CC is in Absorb -- can maintain Vabs. As long as there is enough power available to maintain Vabs, EA CAN cause Absorb to end. If there is too little power available to maintain Vabs, the CC should drop back to Bulk. In Bulk, the EA setting should be ignored by the CC.

On the Outback MX-60, and the MidNite Classic CCs, the time setting is the maximum amount of time that the Absorption stage will last -- if the EA current setting is not reached by this time value set in the CC, Absorb will end anyway.

And mmag, the correct Absorption time for a battery depends upon how deeply it was cycled in the previous discharge. This ideal time will often vary from day-to-day depending on the Depth Of Discharge of the battery.

Vic

schneider absorb time

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