Battery equalizing / rotating?

Vic

Re: Battery equalizing / rotating?

Hi VF,

Well, as you asorb, and EQ, the battery terminal voltage drops due to increasing tempeartures. Guess that the OB inverter runs out of current as the temps rise. Think that 32 volts is a bit high for EQ, unless the batteries are fairly cold, which it is prob not due to the Asorb stage. And, most chargers and CCs do NOT compensate EQ voltages, so it might be prudent to manually reduce the EQ voltage as the temps rise On my system, EQ voltages are not compensated, this is my reality.

Previously, BB Bill noted that the max EQ current speced by Surrette was 5 Amps per 100 AH C20 capacity, and recall that the risk of exceeding this current by much was that sulphate crystals could harden on the plates.

In reality, you have made good progress in bringing the lagging cell SG up. My guess has been that this battery was failing, and could not be revived. Time will tell. I should go back and reread this thread. Think that you have about four years on this bank, which is pretty good service for L-16s. More later Good Luck with the struggle. Vic

BB.

Re: Battery equalizing / rotating?

Yea, I probably would be a bit snarky at times too if I was in your situation.

I try not to go off into flame wars when there is probably other explanations available (misunderstandings, stress, language, etc.).

It seems it it getting more difficult to find a charger that would do what you need... Say a charger that can charging anything from 2 volts to 24 volts (actually > 31 volts) at XX amps. One of the very old battery chargers with vacuum tube diodes does exactly that... But it is probably dangerous as heck compared to the new chargers we have today.
nn
The 6-24 volt charger in the second link, here is the PDF for the manual (Northern Tool website):

http://www.northerntool.com/downloads/manuals/1677827.pdf

The Sx 3000 appears to have a fairly wide range of output voltage/current setups... For example, there is a 6 volt high current/12 volt low current setting. So I would guess that you can get the Equalize voltage out of this charger when needed.

And, because you can charge fairly high current at a reasonably low 6 volts--That means the charger uses a relatively low amount of power (VA rating is probably 2x watts due to losses and poor power factor). And will run on a smaller genset (and use less fuel) than your big guy there (again, I realize your choice of genset may be limited by location and available $$$).

You will have to keep an eye on everything--It appears that this charger only has a manual timer--No automatic state of charge/safety shut offs.

And, there is a very good chance that that cell/battery is bad. And even if you get it back to reasonable specific gravity, if it tanks again, you probably need to think about replacing it (vs buying a new battery charger + small genset for "fixing" / experimenting on battery cell recovery).

-Bill

PS: I thought the 5% maximum current limit for equalization was to limit the maximum temperature of the battery bank. Higher current could cause thermal runaway (again, as I recall--could very well be wrong).

Vic

Re: Battery equalizing / rotating?

Bill,

The reference to higher EQ currents than 5%, am certain that several times you mentioned that it was to help limit the hardening/fixing the sulphate crystals onto the plates. I have not seen this elsewhere. It may well be true. Just my recollection, FWIW. Have not googled this Forum.

I have a home brewed single battery manual charger as described earlier. With it, it is important to monitor charge current/voltage and cell temps manually, as NOTHING on it is automatic. But, one advantage of having larger batteries -- 315 Lbs per 4 volts, is that things change fairly s-l-o-w-l-y.

Having misbehaving batteries, especially in off grid settings is very stressful, especially in harsh (almost) Winter environments. I would be a bit cranky, if I had enough energy!

OF VF Best of Luck, Vic

vtmaps

Re: Battery equalizing / rotating?

Volvo Farmer wrote: »

Maybe someone can explain this to me. I have four 6V L16 batteries (800AHR @20 hr rate) hooked to my system @24V ( I split the parallel batteries out). They are maybe 20-40% discharged according to SG. I try and absorb charge them with the generator and the VFX3524. I can easily reach 29.2 V within a half hour and charge amps drop to 15A or so within 30 minutes.

I let them charge another 30 min at 29.2V. Amps in are still 15 or so . Batteries might be 80F or so but no higher at this point. I assume I now have fully charged batteries and might try to EQ now.

I think something is wrong with these numbers. Four L16 batteries in series are closer to 400 AH than 800 AH. If your charging current falls to 15 Amps, that is not a good number for a 400 AH battery bank (it should fall to below 8 amps).

You "let them charge another 30 min at 29.2V" and then you "assume I now have fully charged batteries". Generally, 30 minutes of absorb is not enough to charge batteries. If you let absorb go for another 30 minutes, does the current continue to decrease below 15 Amps?
--vtMaps

Ralph Day

Re: Battery equalizing / rotating?

I have 8v Surrette CS25 style batteries. When they get a little sulfated the bulk/absorb setpoint can be reached quickly. Never rely on your charge controller or inverter/charger "knowing" when the battery is fully charged. I check obsessively my SG's, and if absorb is hit quickly the cells might still be only 1.250 or so. After 2 hours, 1.255+, run out of sun before 1.265. SG reading is the best way to find your SOC.

I was shocked to find my SG readings in the mid 1.2__ range when I got my first hydrometer (I've learned a lot since then, especially on this forum). My MX60 and inverter were only charging to 57.6v for 2 hours...woefully deficit charged. Paying for that now with prematurely aging battery bank. I balance my charge parameters (solar, genset or utility) quite closely, watching the weather forcast, and dutifully checking the SG on a pilot cell (daily, and during the day to see SOC).

Ralph

Volvo Farmer

Re: Battery equalizing / rotating?

vtmaps wrote: »

I think something is wrong with these numbers. Four L16 batteries in series are closer to 400 AH than 800 AH. If your charging current falls to 15 Amps, that is not a good number for a 400 AH battery bank (it should fall to below 8 amps).

You "let them charge another 30 min at 29.2V" and then you "assume I now have fully charged batteries". Generally, 30 minutes of absorb is not enough to charge batteries. If you let absorb go for another 30 minutes, does the current continue to decrease below 15 Amps?
--vtMaps

You are correct. The correct number is 400Ahr. My mistake.

Thanks for the target number to look for on the amps. I know that 1 hour is not usually enough to absorb, but I had recently had the whole string at 31+ volts for 1.5 hours and then let it rest with no loads for eight hours before charging again.

Thanks for all the discussion. I have a old Honda EX1000 and a roll around automotive 6v/12v battery charger similar to this http://www.toolbarn.com/solar-4725.html?ref=base. Maybe I'll go and play with them this weekend.

mike95490

Re: Battery equalizing / rotating?

Volvo Farmer wrote: »

....

To equalize a single 6V L16 I need a battery charger that can deliver 8V at approximately 20A and will limit the current at 8V. I would be very interested in learning about an affordable battery charger that meets these specifications. ....

Any cheap, automotive 6/12V 25 amp charger (simple step-down transformer, not smart) would do that. The battery regulates the voltage, to the amps limit of the charger.

And you need to learn the difference between Volts and Current/Amps, or you will be here all the time with questions and problems. Basic electricity or electronics class at a local community college, or maybe even free on the internet.

You bought the gear, now you have to learn the language, or you will completly boil your batteries to death, trying to save one low cell.

vtmaps

Re: Battery equalizing / rotating?

Volvo Farmer wrote: »

Thanks for the target number to look for on the amps.

I wrote "that is not a good number for a 400 AH battery bank (it should fall to below 8 amps)." "8 amps" wasn't meant to be a target number.

You determine your target number for your battery by leaving the charger on absorb for a long time while you monitor the charging amps. After awhile the charging amperage will hold steady without further decrease. Ideally, that would be about 1% of your battery's AmpHour rating, i.e. 4 amps for a 400 AH battery. The lower the number, the better. As batteries age the number becomes higher. When the number gets above 3%, the battery is in pretty bad shape.

By the way, all of the above pertains to a battery that is well maintained and aging normally. I really don't know what you should expect when there is a bad cell.
--vtMaps

Volvo Farmer

Re: Battery equalizing / rotating?

vtmaps wrote: »

You determine your target number for your battery by leaving the charger on absorb for a long time while you monitor the charging amps. After awhile the charging amperage will hold steady without further decrease. Ideally, that would be about 1% of your battery's AmpHour rating, i.e. 4 amps for a 400 AH battery. The lower the number, the better. As batteries age the number becomes higher. When the number gets above 3%, the battery is in pretty bad shape.

--vtMaps

Thank you for taking the time to explain that to me! I ran through a one hour bulk and two hour absorb with the generator on the full 800Ahr bank last night. I did not get to the point where I saw no further decrease in current, but the last half hour was pretty flat, moving from 20A, to 19. I really need to find the time and fuel to try the same thing for a good 4-5 hours and watch current. I'm hoping to find my end absorb amps (or whatever the proper terminology is) will fall somewhere under 2% which hopefully means I can get a couple more years out of these. On most days, we are only using fifteen percent of capacity, so we might be able to use this bank for quite a while, even as it's capacity diminishes with age.

vtmaps

Re: Battery equalizing / rotating?

Volvo Farmer wrote: »

Thank you for taking the time to explain that to me!

I'm glad to help... I just barely learned this myself and it helps me in my own education to write it out for others. When I write out what I think I know, and nobody corrects me, I start thinking that I must be right ;-)

By the way, I didn't learn this from any of the battery FAQs that I have found on the internet. Forums like this are the source. Unfortunately its hard to find the info without reading a lot of posts. For example, who would expect to find my explanation of "absorb end amps" in a thread titled "Battery equalizing/rotating"?

While on the subject of "absorb end amps", I might mention that my Outback equipment (vfx3524 and fm60) can be set to stop absorb at an 'absorb end amps' that is user adjustable. However, I can't take advantage of it because I have DC loads that the chargers don't know about... e.g. the chargers may know that they are putting out 10 amps, but they don't know that the DC fridge is using 2.5 of those amps and only 7.5 amps are going into the batteries. That is why I manually figure out what my end amps should be (as described a couple of posts ago) and how long it took to get there. Then I program my controllers to stop absorb after a time period that I set.
--vtMaps

westbranch

Re: Battery equalizing / rotating?

Vt and VF, thanks both for digging into the minutia, I too had not put into long term memory, the fact about "amperage will hold steady without further decrease" as being the end point of absorb...
My experience has been similar in not wanting to run the guzzler for an extended period of time, but this summer, during construction, while the PV system was inoperable I hooked up the TC 40 and let it go for 2 full 8 hour days of charging just to top off the unused battery... half way or so into day 2 it finally got to float ( my defn < 10 A) and at the end, down to 2 amps (lowest reading charger shows )
Note: this is an old AGM and this is truly the first time since I got it that it has been charged this fully. I was surprised at how long it took and how low the input amps dropped to. Below 10 A was not expected due to the size of this battery and I had always turned the gen off when it got to 10A, letting the PV 'finish' the charge. Point is that it never got there as the sun doesn't last that long.

VT perhaps this needs to be added to the Definition sticky?

erne

Re: Battery equalizing / rotating?

I have a electro-plating machine that has voltage and amperage adjustments that will charge a single cell or a group. It is completely adjustable and holds selected settings. You might check in your area and borrow one of these devices or have your local installer look into getting one for helping his customers. That way you are not shortening the life of the cells on the batteries that are fine.

Vic

Re: Battery equalizing / rotating?

erne,

You are correct. One of my DC Power Supply kludges started life as a 50 or 60 amp Electroplating Supply. Hacked the AC operated DC supply, and run it into an MX-60 CC. As such, it will not do any battery voltage that the MX does not support.

Also have a Home Brewed Variac/Transformer/FWB/Capacitor bank job as noted earlier here. It is completely adjustable 0-17 volts, at about 50 Amps. It uses jumper cables to clamp onto batt terminals.

Stating the obvious, it is very convenient having 2 volt batteries, or at least batts with access to individual cell terminals.

YMMV, Vic