Too shallow depth of discharge?

[Mechanicalbird]

Hi all. I'm a new member here and new to RE and solar in general. Over the last few years I have researched and learned a lot about solar. My system is finally complete and working great. I tend to over engineer most things I build and it looks like I may have done it with my solar setup as well.

I have 740ah @ 24v and 1850w of PV. My question deals with the depth of discharge. I have a Trimetric monitor and a Whizbang Jr. I have had the system operational for about a month now and the most I have discharged the bank is 8%. So in the morning my batt monitors read around 92% and is  usually back to 100% by lunch if it's sunny. I'm wondering if there is any harm in discharging a bank too shallow and then bringing it back to full everyday. Should I re-bulk everyday or set if for every few days instead?

Thanks!

[Vic]

Hi M b,

Like many things,  there can be a fairly broad range of opinions on just how batteries should be recharged and how often,    etc.

Assume that you have Flooded batteries.

For many years,  have tried (and usually succeeded) to fully recharge the batteries here every day.   Then,  it seemed that it would be better to cycle my Flooded batts more deeply before recharging.  Before the advent of the Classic's Skip Day function,  would simply turn off the PV input breaker for 2 - 4 days,  and then switch the PV back on.   That has worked fine.

Now,  with the later versions of Firmware (as you know),  the Classic allows Skipping days.  So,  presently Skip 3 or 4 days on the Classic,  depending on weather and anticipated load variables.  That works fine,  too -- have set Vfloat fairly low to reduce the amount of charge that the batteries can get from just Floating the bank all day.  This chosen Vfloat is currently 50.5 V (down from the Surrette Battery recommended Vfloat of 52.6)  on 48 V systems.

As you may have noticed,  most of the battery Cycle life verses Depth Of Discharge from many manufacturers begin at 90% SOC (or even lower),  and descend to lower SOC values from there.

It is often noted that if batteries are not cycled below at least 90% SOC,  and perhaps even down to about 85% SOC,  that Lead Dioxide can form on the Positive plate in clumps,  which can cause plate bulging, and perhaps mechanical damage of the battery if batteries are not cycled moderately deeply,  at least,  reasonably often.

So,  personally,  I agree with your thought,  that batteries should be forced into deeper cycles,  if they do not experience this from normal daily use.

Furthermore,  especially with Flooded batteries,  one should see less heating and heat retention in the battery bank,  if full recharge happens only a few times per week,  as opposed to daily.   Heat is the enemy of long battery life --  every 10 degrees C increase in battery temperature reduces life by 50%.   Sometimes,  we can do little or nothing to keep a battery cool/cooler,  but it is good to consider the nominal temperature a battery will experience,  when designing the power room,   etc.

All just my opinions ...   YMMV,  so on.   Have Fun with the new system.   Vic