Annoying - S-530 absorb at 57.6V = Low and erratic SGs

YehoshuaAgapao · April 2013

After having reasonable and stable SGs (around 1260) I put the absorption/bulk voltage to the manual recommended 57.6V. Reduce water consumption and increase battery life. That was a bad idea. THe SGs dropped down to 1240-1245 and went all erratic (lowest 1230 highest 1250, averaging 1240-1245) after 3-4 weeks, varying from battery to battery, but consistent in cells within the battery for the most part. Batteries closer to ether inverter cable had higher SGs than batteries in the middle of the string. Both battery boxes were exhibiting similar behavior.

I increased absorption back to 58.8V and increased absorption time to 240 minutes though earlier it took 60V absorption to get the SGs up. Charge controllers with the inverter selling to the grid always run absorption for the full length of time though the inverter tends to run one volt lower than the absorption and float settings. I am using advanced interactive mode. I am not really cycling the batteries at the moment. Could this be why? I do intend to use peak load shave starting May when the summer prices kick in and that should give the batteries their cycles. Wasn't really worth wasting battery cycles on peak load shave with winter pricing.

2 48-V strings of Surrette S-530. Xantrex XW. 6.48 KW of PV (STC). Bi-Modal (grid-tie w battery backup).

Vic · April 2013

Re: Annoying - S-530 absorb at 57.6V = Low and erratic SGs

Hi Y A,

Well Flooded Deep-Cycle batteries really need to be cycled. In my experience, cycling is the thing that reduces the cell-to-cell SG variation. And new banks need cycles to build capacity. A variation in DOD is also good for Deep Cycle batteries, IMHO.

The string ends having different SGs can often mean that there are temperature variations across the string, could be random ...

Hope that you are logging all of the SG measurements in the Battery Log Book. This is a huge help in following variations with the bank.

Bottom line, the batteries need a full charge once or twice per week, and setting Absorb V and time to what is needed to do this is the correct thing to do. Running deep cycle batts in Float service for months is generally not good for them -- these batteries need to be worked even when there is a cost in doing so, that is their job (as well as to reduce ripple I and V when selling to the grid).

Always a balance. Opinions. Good Luck, Vic

YehoshuaAgapao · April 2013

Re: Annoying - S-530 absorb at 57.6V = Low and erratic SGs

Ok. Come May the batteries should get 2-3 hours of discharge every day, for 6 months. That is if I switch back to TOU. On EZ-3 the batteries will only get cycled on cloudy days. I currently greatly overproduce during EZ-3 on-peak so I do want to switch back to standard TOU starting May summer rates (I'm sitting on EZ-3 for now because I only run up 200-400KWH off-peak and the my 4KW of community solar eats that up easily).

Problem is SRP won't let me switch back to EZ-3 for winter as they won't let you return to an abandoned price plan for 1 year. So can't do standard TOU for summer and then EZ-3 for winter. Standard TOU in winter only has a small part in solar production hours (5-9AM, 5-9PM on peak in winter; summer is 1-8PM). EZ-3 is the same 3 hour range all year round (2-5PM, 3-6PM, or 4-7PM). 2-5PM in late Nov-Early Feb would produce some light cycling in the batteries while Late Feb-Late Apr wont cycle much (only on the rare rainy day). I could do partial on-peak load shave in winter (just 8-9AM and 5-6PM) but that seems wasteful on the batteries especially since standard TOUs on/off peak price difference is less than EZ-3.

Vic · April 2013

Re: Annoying - S-530 absorb at 57.6V = Low and erratic SGs

OK, Y A,

I do not know the ins and outs of the TOU vs other Screw You type plans of the Utility, seems that GT is getting less beneficial, and much more complex. Feel for you folks.

The only point that I was trying to make is that FLA batteries need and want SOME cycling. This can be induced manually, hopefully several times per month. Little or no apprecible cycling often causes SGs to diverge. And when the bank is fully charged, can cause measured SGs to exceed the target value. Cycling really helps the SGs of the entire bank to track much more closely together.

Cycling will cost you a little bit, but IMHO, you will have fewer battery issues over time, and you will probably have many fewer remedial actions that you will have to take to try to recover from extended periods with few or no real cycles. Again, this is all just Opinion. Good Luck, with the Rate Schedule NOISE. Vic

vtmaps · April 2013

Re: Annoying - S-530 absorb at 57.6V = Low and erratic SGs

Vic wrote: »

The only point that I was trying to make is that FLA batteries need and want SOME cycling. This can be induced manually, hopefully several times per month. Little or no apprecible cycling often causes SGs to diverge. And when the bank is fully charged, can cause measured SGs to exceed the target value. Cycling really helps the SGs of the entire bank to track much more closely together.

I have no personal opinion on the need for cycling, but for what its worth I have seen representatives of Trojan and Surrette (on the wrenches solar installer's forum) claim that cycling is NOT necessary for their FLA batteries. However, they warn that floating causes stratification and that it is important to periodically run the batteries through a bulk-absorb-equalization to stir up the electrolyte, but it is NOT necessary to discharge (cycle) them before running the bulk-absorb-equalization. Obviously, if the batteries are floating the bulk stage will be very short.

--vtMaps

Vic · April 2013

Re: Annoying - S-530 absorb at 57.6V = Low and erratic SGs

Well a new bank needs cycles, as a part of the finishing process, this early cycling buildsand stabilizes capacity (for example if one is trying to use a Battery Monitor as an SOC indicator).

Cycling does keep fresh active material exposed to the electrolyte. Fairly deep cycles helps this.

If one is not going to Float batteries, then cycling is one few alternatives of how to charge a battery bank, short of disconnecting batteries and ignoring them while they croak.

If one looks at the graphs of charge cycles vs DOD, for FLAs like Surrettes, the graph stops at about 90% SOC, at least the ones that I've looked at.

Furthermore, cycling banks here seems to reduce the spread between SG readings for all the cells of the bank. AND, if not to be cycled, there seems little reason to have DEEP-CYCLE batteries.

Just opinions, based on experiences here. YMMV. Vic

vtmaps · April 2013

Re: Annoying - S-530 absorb at 57.6V = Low and erratic SGs

Vic wrote: »

Well a new bank needs cycles, as a part of the finishing process, this early cycling builds and stabilizes capacity (for example if one is trying to use a Battery Monitor as an SOC indicator).

good point. no argument from me. As I stated above, I have no opinion on the matter, I'm just reporting what representatives of Trojan and Surrette have said.

Vic wrote: »

if not to be cycled, there seems little reason to have DEEP-CYCLE batteries.

Some deep cycle batteries are designed to mostly float. They are for standby use. When needed they may cycle deeply, but they are intended to spend most of their lives floating.

--vtMaps

Vic · April 2013

Re: Annoying - S-530 absorb at 57.6V = Low and erratic SGs

vtmaps wrote: »

good point. no argument from me. As I stated above, I have no opinion on the matter, I'm just reporting what representatives of Trojan and Surrette have said.

But if a customer reports to those manufacturers, that there is a fairly wide variation in SG, with some cells reading above target SG value, even with correct water fill, the remedy is often, "Cycle your bank -- ideally to about about 50% SOC -- and recharge. Do this several times per month or more often."

vtmaps wrote: »

Some deep cycle batteries are designed to mostly float. They are for standby use. When needed they may cycle deeply, but they are intended to spend most of their lives floating.

--vtMaps

Yep, but to me these batteries are not called Deep-Cycle batteries, they are batteries designed for Float service. Do not want to get into semantics vollies, but thinking of the batteries that are the subject of this Thread, they are Flooded deep cycle batts.

The above still just my opinions. I have no horse in this race, just spewing opinions ... Good Luck, Vic

Annoying - S-530 absorb at 57.6V = Low and erratic SGs

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