Better to almost “equalize” every day or only charge to 80 – 90%?

jeffkruse

I am still adjusting my systems settings trying to find the right spot with my 4 week old batteries.

I now have my Bulk and Absorb voltage at 61.5V and Absorb time set to max. This gets the SG up to baseline (1.275) every day unless lots of clouds.

59V will only get the SG to 1.24 (80%) every day.

It takes a lot more energy to get that last 20 to 10%.

Everything I read says to charge to 100% but to do that is almost like equalizing every day.

My Trimetric battery monitor is in place and I have the charge efficiency set to 70%, it’s only been a few days but I think this will be the right setting. :roll:

I think I’ll end up with my Bulk and Absorb set at 61V to get my SG full every day.

Would it be better to set the Bulk and Absorb lower and only have the SG at 80 – 90% 1.240 – 1.255 every day and then equalize every week or month?

I don’t like having the voltage so high but I also don’t like having the SG so low! :grr

Windsun

Re: Better to almost “equalize” every day or only charge to 80 – 90%?

The single biggest cause of battery failure is to not charge them fully. Batteries that are chroniclally sitting there at only partial charge will sulfate.

hillbilly

Re: Better to almost “equalize” every day or only charge to 80 – 90%?

That's a tricky balance to meet sometimes. It sounds to me like you are charging a bit too high imo, I'd probably drop the voltage back a bit if you're absorbing for that long. Regarding the SG levels, I'd guess that you've got some sulfated batteries and you may not see the SG levels rise quite as high on a normal regular basis. How deeply are you discharging those batteries?
My personal take, although I'm far from being an expert in this area. I'd probably try the voltage somewhere between 59V and 60V (and probably closer to 59V). Check the batteries regularly, and make certain to give them a fuller charge on a weekly basis with a monthly EQ charge.
BTW do not put too much faith in the Trimetric, as they are not an accurate measure of the batteries health or SOC... just a rough estimate. I think under "ideal conditions" the Trimetric can be pretty darn close to telling you what the batteries SOC is, but simply measuring the amps in/amps out is not always indicative of the SOC.

Cariboocoot

Re: Better to almost “equalize” every day or only charge to 80 – 90%?

Do not equalize every day. Fully recharging batteries is not equalizing. Equalization takes place at Voltages above Absorb rate. Too much or too often of equalization will damage batteries. Check them once a month, and equalize only if necessary. I have found that it is only necessary if one or more cells differ by 0.025.

By all means fully recharge every day if at all possible.

You should have taken SG readings with the batteries brand new, to use as a baseline reference for future readings. Your hydrometer ay have only read them at 1.24 to begin with (although that seems low). If you are at higher elevation, SG will read low.

Over-charging is also a significant cause of battery failure.

How's the water usage? How's the wiring? Maybe you're not getting all the power you could to the batteries (i.e. Voltage loss through under-sized wiring).

icarus

Re: Better to almost “equalize” every day or only charge to 80 – 90%?

Agreed with all that has been said. I would add that "over charging" is mostly an issue of using too much water, with the attendant risk of exposing the plates to the air, which will kill the battery.

I would by all means charge the batteries (full) as often as possible, and then check the SG once a month or so, and if the SG varies much between cell, then I would do an EQ.

I have found that the SG in my batteries ALMOST never varies, but I go ahead ad do an EQ a few times a year, but I'm not sure it really does much good. My Pv and battery bank are fairly well matched so that the electrolite gets stirred up pretty well every day. I think that is the "real" reason to have charging capacity ~10% of battery ah capacity.

Tony

PS. If it hasn't been posted in this thread:http://www.batteryfaq.org/
http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

jeffkruse

Re: Better to almost “equalize” every day or only charge to 80 – 90%?

Only charging with 59V will not get the SG to FULL. Charging with/to/at 61.5V will get the SG back to baseline 1.275. It also gets the batteries a little warm and good and bubbly.

Voltage drop on the battery cables under an 80Amp load are 90mV on each of the 10 foot 00 and 12mV on each 1 foot 00 cables.

Discharging about 70 – 100 AH every night (20 – 30%). The bank is 48V 370 AH@20H rate.

Solar collection starts just before 8AM (this time of year) and ends around 4pm (this time of year). From 8 – 12 there are very few clouds. From 12 – 4 it may be partially cloudy. From 8 – 10 I’ll harvest about 2 KWH and from 10 – 12 at least 3KWH. 5KWH’s by noon. Then after that it could be 2 – 5KWH’s. Yesterday I harvested 10.3KWH but normally about 8 (could be more but no place to put them )

With only 8 hours to capture sun light how can you lower the absorb voltage to get the batteries full?

My SG wont go up unless I charge at those higher voltages. Deka recommends a max of 58.8 for absorb voltage. But I also saw a formula to calculate absorb time. That formula gave me a 6 -8 hour absorb time. That doesn’t work with solar (and that’s a lot of power wasted) yet these batteries are sold for use with solar systems. Deka also puts this note with the charging params, “Cut-off parameters per charge and equalize intervals are application specific and will vary dependent upon site specific characteristics such as: temperature, days of autonomy, array to load ratio. Etc…”

So what do I do, get full by almost “EQing” every day or only partially charge and EQ now and then?

mike95490

Re: Better to almost “equalize” every day or only charge to 80 – 90%?

Wow. After all that, I'd go by battery temps, bubbles, and water usage. I've got to follow this, as you have nearly the same configuration I'm going to have, only my winter hours are 9am - 3pm, and then the sun is gone.

niel

Re: Better to almost “equalize” every day or only charge to 80 – 90%?

trojan says to make that 59.2v with a float setting of 52.8v. eq at 62v.
http://www.trojanbattery.com/Tech-Support/tips.aspx

hillbilly

Re: Better to almost “equalize” every day or only charge to 80 – 90%?

Just my own experience here: I was originally very worried about not fully recharging my batteries up to 100% SOC each and every day. Since then, I've heard and read from a lot of folks that with a stand alone or off grid system it's quite common to not reach a FULL 100% SOC each and every day. A battery that is charged up via the PV charge controller is probably only close to full in many cases. I don't think that any real harm comes from this, unless that's all the charging those batteries ever get. Hence a once a month EQ, or a weekly extra charging can help get that last 1%-5% of a full charge. I think that the bigger issue's would be not getting the batteries up above 90%SOC on a regular basis, leaving them for 3-4 days at a 50%-60% SOC, etc... I also think that running what is pretty much an EQ charge on a daily basis would fall into this same category of abuse.
Something is not quite right from the sounds of things; if your SG levels are reading less than 80% from a more "normal" absorb cycle, makes me wonder what's going on there. What were the SG levels like originally, have you seen trends one way or another? Are you certain that the batteries were in good health when you first put them in service? Also those hydrometer readings can be tricky, and not all hydrometers are entirely reliable; if you're getting a reading of 1.255 that may well be "charged", hard to say from here...

jeffkruse

Re: Better to almost “equalize” every day or only charge to 80 – 90%?

The batteries are new. They are a “replacement” set for the first set.
With the first set I only charged to the recommended parameters. With all the data I took I think the manufacturer wanted to just get rid of me and they sent me new batteries.
The first set is only 3 months old and sits unused in my shed with 1.270 SG on each cell. I think if I had 61.5V as my absorb voltage my SG would have been fine for this set of batteries.

The SG of the new batteries after 3 hours of eq was 1.275 – 1.285. They came off the pallet at 1.255

The trend looks like the SG doesn’t like to go that last 10% without using/wasting a lot of power.

I think my Hydrometer is good and accurate. I bought it from this site.

I don’t think 1.255 is full because they can go to 1.275 with effort.

All the numbers I am getting from my new Trimetric just confirm what I already suspected. My usage is as expected, 3 – 5KWH/night and 2KWH in the day

I just hate to not use the extra power my system can deliver when the batteries are still less than 1.275 SG. If I lower the absorb V my extra power just doesn’t get used and my batteries wont be full.

BB.

Re: Better to almost “equalize” every day or only charge to 80 – 90%?

I like Dave Sparks' post:

Dave Sparks wrote: »

I learned this strategy from Dave Surrette (Rolls) in the late 70's. Pretty much the bible on how I design my systems for off-grid.

Assume that the system will never reach more than a 90% state of charge.
Try not to go below 50% SOC, ever! Complete absorption over 90% of the year

Use the energy stored from 70% to 90% SOC for your daily cycles.
Save the energy from 50% SOC to 70% SOC for aging to get long battery life.

I know Surettes has changed their recommendations over the years but I also know they are in the business of selling batteries! If you do the above you will get 10 to 15 years on their batteries with decent maintenance.

The OP is making it complicated by mixing battery types and not really stating a lot of information that would allow decent specific advice.

Oh yea, I am really happy that Surrette and Trojan are making L16's with 1000 AH capacities @20HR. Been bugging them for many moons to do batteries less than 125LB's!

And, my two cents... If your batteries are using a bit of distilled water per month--you are probably OK. If you are using none, or a lot per month--then you are probably under or over charging.

• Undercharging and operating for long periods (below ~75%) is damaging to lead acid batteries.
• Overcharging is less damaging to flooded cell batteries (at the cost of distilled water and wasted energy).
• Overcharging sealed batteries (AGM, Gel, VRLA, etc.) can be fatal to those types (venting electrolyte).

-Bill

PS: Trojan says to equalize if SG is >0.030 differences between cells--sounds like yours are not.

icarus

Re: Better to almost “equalize” every day or only charge to 80 – 90%?

"Fully Charged" is sort of a relative term. If you get your batteries routinely to 1.265SG I think you can consider them "fully charge" even though you could get the SG to 1.285 or so. I'm not sure in the real world that you would have any greater capacity by doing so however.

I think Hillbilly sums it up pretty well, and I sort of do about what he suggests. If, by estimate or testing, my batteries are >90% by the end of the day, (or are going to be!) I don't worry about them. If by the third day, the are not going to be above 90% then I will throw them on the genny for a couple of hours. I almost never go more than three days, and I almost never go below ~80% and never below 70%.

I still have one set of T-105 that are still humming after 12 years in easy service.

Tony

BB.

Re: Better to almost “equalize” every day or only charge to 80 – 90%?

Add the Trojan recommendations here:

From Trojan's battery manual (PDF):

Equalizing (flooded/wet batteries ONLY) 3.4.2.

Equalizing is an overcharge performed on flooded/wet batteries after they have been fully charged. Trojan recommends equalizing only when batteries have low specific gravity, below 1.250 or wide ranging specific gravity, 0.030, after fully charging a battery. Gel or AGM batteries should never be equalized.

• Confirm that the batteries are flooded/wet
• Check electrolyte level to make sure plates are covered with water before charging
• Check that all vent caps are secured properly on the battery before charging
• Set charger to equalizing mode
• The batteries will gas (bubble) during the equalization process
• Measure the specific gravity every hour. Discontinue the equalization charge when the gravity no longer rises

WARNING: Do not equalize gel or AGM batteries

-Bill

Photowhit

Re: Better to almost “equalize” every day or only charge to 80 – 90%?

Icarus and Hillbilly have it...

I have yet to hear anyone ask if you are compensating for temperatures?

BB's right in listing manufactures recomendations. Trojan has different recomendation from Surrette/Rolls Which is different from Deka.

"Deka recommends a max of 58.8 for absorb..."

Works for me, do you know their battery better than them?

Don't tell me you stop at green lights 'cus your brother might be coming?

jeffkruse

Re: Better to almost “equalize” every day or only charge to 80 – 90%?

Yes I am compensating for temp on the XW charger and when I take SG readings.

Following the manufactures settings got me into trouble in the first place. With the first set of batteries the SG was all over the place and very low. That was with only charging to 58.8V.

Deka doesnt say how long to absorb for. You cant tell people to absorb for 8 hours and also say these batteries work well for Solar PV off grid systems.

sub3marathonman

Re: Better to almost “equalize” every day or only charge to 80 – 90%?

jeffkruse wrote: »

The batteries are new. They are a “replacement” set for the first set.
With the first set I only charged to the recommended parameters. With all the data I took I think the manufacturer wanted to just get rid of me and they sent me new batteries.
The first set is only 3 months old and sits unused in my shed with 1.270 SG on each cell. I think if I had 61.5V as my absorb voltage my SG would have been fine for this set of batteries.

OK, obviously as a beginner I'm missing something, but if "the first set is only 3 months old and sits unused in my shed with 1.270 SG on each cell," why aren't they still working fine?

jeffkruse

Re: Better to almost “equalize” every day or only charge to 80 – 90%?

sub3marathonman wrote: »

OK, obviously as a beginner I'm missing something, but if "the first set is only 3 months old and sits unused in my shed with 1.270 SG on each cell," why aren't they still working fine?

I believe they probably are fine. It took a lot of experimenting to figure out how to keep them fine. I'll have more data in a few weeks now that I have a trimetric hooked up. The little data I have now is confirming my assumptions.

I think with my configuration I'll wind up with 61V and max time for absorption.

Because we get partially cloudy sky's in the afternoon I don't want to "not use" energy in the late morning just because I am at a low Absorb voltage then not have the energy in the afternoon to do a long absorb.