FLA Battery Charge Voltage Question

MrM1

OK Some may recall I have been having odd battery SG readings with a lagging cell from one of my 6v L16 FLA batteries. More on that in another post as I am still testing things.

The battery with what I supposed was a bad cell went on a road trip, first to the seller and then to the distributor. Long story short, it is home again after testing discharging and returned charged. Seller and Distributor for Trojan Say it is good showing good discharge readings. SG on return was on average at 1270 with a 5 point spread. pretty good. Voltage was 6.35v and it had been sitting off any charger for 2 weeks.

Today my other 3 6v L16's where in service (with a pair of sacrificial 6v golf cart batteries in parallel then all wired in series). Shut everything down. Took out the GC batteries. Put my L16 back into the group. So now I got 4 L16s together again.

Three L16s at 90%. SG readings from 1235 - 1265 with most cells sitting at around 1260. (yes these need an EQ). Voltage is at 6.49v, 6.49v and 6.48v after sitting for an hour off the charger resting and disconnected.

One battery at 99% ish (it had been to the shop and returned charged). SG readings ave 1270. Voltage is at 6.35v resting after not having any charge for 2 weeks.

Question: I just began charging the whole bank with a grid charger (so no cloud variation). I am in the Absorb phase so the charge voltage is constant. Charge voltage for the bank 29.6vAbs (4 L16 435ah batteries wired in series). Why are the 3 batteries that were at about 90% reading 7.3v each and the one that was charged reading 7.9v -almost EQ voltage - while charging the bank ? Clamp meter says they are all getting same amps. I would have thought it would be the other way around, with the most charge battery getting the least volts.

I thought series charging would not see voltage vary so much. Is this because the 1 battery was at a higher SOC than the other 3? The voltage of the highest charged battery was lower than the other 3 when charging began.

mike95490

In a series circuit, the AMPS is the same, but the voltage at different nodes, can / will be different. Take readings at the end of absorb, that's when the batteries are supposed to be full.

As lower capacity cells charge first, their voltage rises first, and as the other batteries charge up, their voltage will rise too. I'd allow for at least 2 good absorb cycles and a very light overnight loading, to get the bank balanced to the point of deciding if you need EQ.

if you can extend or restart the absorb cycle mid-day, that puts more watts into the batteries, and you only need to add more distilled at the end of the day

MrM1

Thanks Mike. That makes sense.

Bank is still charging. But now the one L16 (that I assume has a bad cell) is up to it's Ol' Tricks (well ol' tricks in the past few months) and why i sent it off for testing in the first place. Total bank is now at 95%, Total amps in is at 7.9amps or just about 1.9% of bank capacity (I am shooting for 1%). vAbs is charging at 29.8v ... BUT the 3 batteries are at 7.8v (or would be about 31.2v for the bank) and the one battery that went for testing is at 6.8v. This is what it was doing before it went for testing. It was not charging. At the end of a good day, when the bank got near 100%, this one battery had a cell that read 1123 SG, the other 2 were at 1230, While the rest of the cells in the other batteries were at 1270.

I will do as you say and see how it goes. I have little faith/hope that the one L16 and especially the 1 cell will perform.

extending my absorb cycle is easy with the grid charger, just set float to the same Voltage as absorb, and it will charge at absorb voltage all day and all night until I turn the charger off. (I usually set the charge block feature to block / stop charging so I do not forget)

Dave Angelini

You are following Trojans guidelines for your model right? The other thing is make sure your EQ goes long enough. Schneider sets a 1 hour limit on EQ and you may need 2? And the last thing is it is still winter in many places and temp comp will bring voltages up.

And the very last thing, you may never get them all to balance and as long as they do the job, enjoy life.

MrM1

Thanks Dave,

In Fl. I have found work arounds for the SW's EQ feature. Simply set Bulk / Absorb / Float to 32v (max) AFTER bank is charged, and set the Charge Block feature to control EQ time. works like a charm.

Yes I have followed Trojans guidelines, have full records of SG tests and EQ cycles and results, and was even on the phone with Trojan back a year ago about charging and procedure. Things had been fine until the end of 2018 when i started to notice 1 cell starting to lag. Bank is 17 months old.

MrM1

And the very last thing, you may never get them all to balance and as long as they do the job, enjoy life.

Interesting you say this. I have never heard that before, especially if cells are 1270 but one cells is at 1123. I will continue to test and see what the voltages are for vAbs tomorrow after I have done a light discharge tonight.

Dave Angelini

I started use FLA's for HP in 1978. You may just shift the SG up or down but the balance may not ever be corrected to what one wants.

It does not mean there is less capacity, just an imbalance built into the battery bank. The nature of the beast.

mcgivor

The internal resistance between the fully charged battery and the other three is different This will cause the fully charged one to increase in voltage because the current is a constant. To compensate in a series charging arrangement a resistive load, such as incandescent light bulb can be placed across the fully charged one, this will allow a portion of the current to bypass that battery resulting in its voltage to drop. The remaining batteries will then begin to rise in voltage, the time it will take depends on the value of the bypass load, naturally there are limitations to this value, too high may result in a reversal, it's all depends on the charging current.

This method will speed up the process, if left alone the voltage should ballance itself, however this may take many hours of equalization The battery which is fully charged will be subject to more stress than the others, remembering equalization is hard on the batteries to begin with. When doing such a procedure always be present to monitor voltages.

Be extremely careful when the load connection is made, it's best to have a switch that is operated away from the batteries to prevent possible hydrogen ignition, ventilation will greatly reduce the possibility but not eliminate it altogether.

MrM1

Thanks Mcgivor

But as I expected, the process actually reversed while charging for several hours today. By the end of the day with vAbs set to 29.9v, the one battery that had been out for testing was charging at 6.89v and the other 3 were at 7.8v - it was now nearly a volt lower than the other 3. If I upped the vAbs to 31.4v, 1 battery went to 8.1v (or about EQ voltage), 2 were at 7.95v +/- and my one suspect battery was at 7.35v. This was after I had been in absorb for 4 hours. The bank was reporting 100% charged. But this is the reason the battery went out for testing in the first place. When the bank is charging at a typical Absorb Voltage, this one battery does not seem to be charging, hardly floating according to voltage. Which is why I believe one cell was at 1123 in early Feb before I sent it out for testing.

But after much observation today, i did detect that 1 out of the 3 cells in this suspect battery seemed to be "boiling" and the other 2 where not ... or not much at all. Which leads me to believe one cell might be charging (and in that cell the SG does indeed rise), but the other cells are not charging much. I expect the SG in the one cell I suspect is failing to decrease over the next few days. It seem when this battery is charged by itself on an "industrial" charger, it will charge, but in series in a bank, it "gives" its charge voltage to other batteries and ends up discharged.

I understand what @Dave Angelini is saying, but is this condition dangerous?

mcgivor

If possible have each L16 fully charged individually, to start on a level playing field, it's easier if all the cells are close to one another, rather than trying to address a few cells within 24. Since each individual battery has only 3 cells ballancing SG is easier.

If the above is not feasible, what I would be inclined to do is set the controller to normal voltage settings as recommended by Trojan with the default 2% of capacity end amps and not discharge for a few weeks, since you have grid power, I assume this would be possible. See what happens during this time.

My lead acid bank started getting unbalanced at 18 months, they were moved to another location with negligible loads, over the course of a few weeks of normal charging everything returned to normal, SG readings, individual battery voltages, ballanced charging and dischargeing current (2 strings). After that they are never discharged more than 10% capacity, everything has been good since (8 months), they do sometimes get used for about 4-6 hours a day when needed due to weather, to allow the LFP bank to catch up, have 2 system interconnected via an auto transfer switch.

Sometimes it just takes time, forcing it may cause unwanted damage.

jonr

Adding electronic balancers (eg HA01 or Victron's) will help with series balance. But if one battery is too far off, I'd replace it.

As you have seen, "parallel causes problems, series is better" is sometimes very wrong.

Estragon

I'd get an IR thermometer and carefully check for any warm/hot spots, particularly in/near the suspect battery/cell.

MrM1

Thanks all

@Estragon when you say hot spots, do you mean on the battery case or at the terminals and connections, as in checking for loose connections.

And @mcgivor I think I will indeed give that a go and just let the batteries charge and float for a few weeks with no loads (except the 25watts of the inverter and normal discharge) and see what happens. Very impractical to send all 4 off for individual charging.

Tecnodave

MrM1,

Infrafed heat guns will see the hot spots through the cell wall, look at the sides of the battery , particularly at the top and bottom of the plates. If the cells that are showing weakness have hot spots then they have a fault internally. The temperature should not show big variations if battery is in good condition.

this has been verified by Steve Higgins @ Rolls battery.

if you can separate the failing battery and charge it by itself. Use recommended adsorb voltage of 2.5 v.p.c. Or about 7.5 volts at 25 degrees C ,77 degrees F. at not over about 10% of 20 hour rating, do a really long charge.

Im using 14 year old Rolls Surette S-530 L-16 I salvaged from failed solar system, that came to me with s.g. Readings so low did not register. I used 84 volts DC at 3.0 amps from old Seimens panels to accomplish cell balance. This process took several weeks but I have a fully balanced L-16 bank that tests as new. I very slowly charged so as to not over voltage the good cells.

Abused batteries take a long time to recover. The technique that I use came from old battery technology where batteries were "string charged" with a "Tungar bulb rectifier" commonly found in 1950's battery shops. The Tungar bulb had a high internal resistance which would allow a limited current to flow but would allow the voltage to rise on the weak cells , therefore "burning off" the sulphates. Tungar bulbs are history now, they are basically a mercury vapor rectifier, much like a Mercury vapor street light......yes I did work in a battery building shop....Alasks Husky Battery at Anchorage,Alaska

Tungar bulb rectifiers are long gone but solar panels have a very similar limited current profile as the Tungar rectifier.

old school for sure but it works!

david

Estragon

I'd check for warm/hot spots pretty much anywhere on the batteries, including terminals, but as Technodave said, especially top/bottom of plates. I'd maybe open the fill plugs and check acid temp as well. They should be pretty consistent from cell to cell.

My concern is the possibility of some shorting turning current into heat instead of charging. The "boiling" cell may just be gassing, but you want to be sure it isn't literally boiling because of a hotspot.

MrM1

I did mean gassing and not actually boiling - my bad. I have 2 temp probes and one is on the upper side of the suspect battery at the cell in most question. Today temp was 65F and that case never rose above 24C. But I'll check it with a temp gun and cell acid temps

MrM1

Thanks @Tecnodave while I do not have an individual charger for 6v, I can put the whole bank on a very limited discharge, and "By the Book" charge for as long as needed.

So with shorts ... shorts will produce heat on the battery case in places. Good to know.

My thought was that the battery was charging at a much lower voltage than the others (sometimes as much as a full volt or more) that for what ever reason (over my pay grade) the battery had built up a higher resistance (or lower whichever).

If I am guilty of anything with these batteries, it is definitely not under charging and Sulfation. If anything I have been guilty of Over Charging. And too many EQs. I have feared Plate Shredding and Shorting. But as I mentioned above, I did speak to Trojan last spring / summer for over an hour. We talked about my whole setup, charging techniques and my test equipment, and they told me If I was NOT hitting 1277 SG in all cells with solar in a day, it was perfectly fine to charge the batteries at upwards of 31.6 vAbs as long as I was not exceeding heat limits. Trojan Said That Golf Courses routinely charged Trojan GC batteries at 32v every day with no problem. But I felt this would shorten battery life. So sure ... a battery manufacture/seller would tell me that.

MrM1

Also, FWIW, the Distributor said they tested my suspect battery and it is good. They put it on a dischasrger at 25 amps and it lasted 325 minutes. They charged it back up and returned it. But I do not know how many cycles they ran it through.

@Tecnodave

Im using 14 year old Rolls Surette S-530 L-16 I salvaged from failed solar system, that came to me with s.g. Readings so low did not register. I used 84 volts DC at 3.0 amps from old Seimens panels to accomplish cell balance. This process took several weeks but I have a fully balanced L-16 bank that tests as new. I very slowly charged so as to not over voltage the good cells

How did actually accomplish this recovery charge? One battery at a time? And when you say slow charged, how did you keep from over volting the good cells? Charging at low over all voltage?

MrM1

Could I use this to slow charge a single 6v battery manually?

Yescom 110V AC 30V 10A DC Power Supply Precision Variable Digital Adjustable w Clip Cable https://www.amazon.com/dp/B00SWK6M0M/ref=cm_sw_r_cp_apa_i_txYNCbYXEDN10

Tecnodave

I used solar panels with no controller, voltage on solar panels will depend on load so when charging 4 6 volt batteries my 4 Seimens SM-55 panels wired in series would be pulled down to the battery voltage very easily. Ope n circuit would be 84 volts and MPP would be about 72 volts, but the batteries would pull the voltage down to where the batteries were charged up to. Within the first few hours I was seeing 2-3 volts at .1 amp. A few days later I was up to the rated current of approx 3 amps and voltage rising slowly. It took 30 days to get to 24.0 volts. I charted specific gravity readings daily. All cells were within .030 or so of each other.

one thing I omitted....stir the acid.....not hard to do...get a turkey baster, they have much more volume than a hydrometer., I would spend 15 minutes every morning stirring acid in the cells. The acid is heavier than the water so sinks to the bottom, stratifies.......this is what kills batteries as the acid concentration is more dense on the bottom of the cells allowing the acid to corrode the plates away.

If you have a spare small solar panel, does not matter what voltage, connect it to the weak battery by itself , you will not need a charger or voltage regulator, I use only a 5 amp disaster prevention fuse. No regulation of any kind. Keep the current low, wait, chart readings, it takes time.

Right now I'm doing the same with some wet cell Ni-Cd batteries I picked up. Same principle. They were .700 and .800 volts for the 5 cell 6 volt batteries. They are slowly coming up in voltage. The electrolyte in alkaline batteries does not change in specific gravity but remains constant at 1.120 or so, so I monitor voltage only. I have the same 4 Seimens panels connected in series to do this.....no reverse blocking diode so the batteries slightly back feed the panels at night, not a problem. Current is limited to ISC of the panel 3.15 amps

These batteries are built by NIFE battery co. for Edison Battery Co......Thomas Edison...NOT Iron Edison.

If I needed to do this on a string of L-16 that I could not take out of service I would replace the weak one with 2 GC-2 golf cart batteries in parallel to keep my system up and online. 2 GC-2's have roughly the same capacity as one L-16. Not a permanent fix....a patch until you can sort out the bad one.

One key point of the old Tungar bulb string charger is that they had very high internal resistance allowing the voltage to rise if no current is flowing. The voltage would rise to the point of "burning the sulfation" off the plates but when current flowed again it was throttled by the high resistance of the Tungar bulb.......That is what I use the solar panels for......They are NOT a "stiff"source of power but drop down in voltage quickly on load, just like the Tungar bulb.

I built a homemade string charger using a isolation transformer 120 vac to 120 vac, ran this to a single diode 20 amps, 400 volts then to a bank of incadensent light bulbs in parallel, then to the batteries. The incan's have a very low resistance, quickly rising when heated, therefore working as a current throttling device. A bank of 10 100 watt incan's would give a maximum of about 8-9 amps charging current, but the voltage could go up to 80-90 volts easily if the battery had resistance from sulfation. When the battery was accepting current the voltage would be absorbed by the incandescent light bulbs., just screw in the bulbs needed to get the charge current desired, very hands on, very manual control, but no modern charger can do what the old string chargers could do

the solar panels do the same thing very easily and not the shock hazard of what I just described with my string charger. I used salvaged golf cart batteries for quite a few years. My Rolls batteries were going to be cashed in for $20.00 scrap price, been using them 6 years now

good luck with that, it's way cheaper than buying a new bank. One day I'll strike it rich and buy a new enormous set of long life batteries Ni-Fe ar maybe LiFePO4, who knows what is coming next, buckyfullerenes.......lol

MrM1

Thanks for the info @Tecnodave . Wow what a tale and what a wealth of info I continue to gain from this forum. I am doing as you suggest and manually stirring the acid too.

At this point, After 5 days from Thursday to Monday last week to early this week

• I dropped my loads to almost nothing only allowing the bank to discharge between 1-6% each nite.
• Ran the CC at Trojan specs for the batteries: 29.6v vAbs and 27.5v v Float. Have also done some long Constant Voltage / Low Amp charging of the bank by setting float to 29.3v
• Have 2 temp probes (1 controls temp comp for the CC) on the suspect battery: 1 on the post closest to the lowest cell, the other on the side of the case about 5 inches from the top
• Have noticed no unusual heating in the case anywhere. Charging temps have never risen above 25*C
• BUT charge voltage battery to battery is unbalanced in series. There is about 1 to 0.7 volts difference between 3 of the batteries and the 1 suspect battery.
• By Monday the suspect battery (that was fully charged by the distributor Last Thursday and showing good SG numbers) has now declined and the SG was 1245 / 1230 / 1210 when all other cells in other batteries where at 1270-85. Guessing this is due to the 1 to 0.7 difference in charge voltage while charging?

So how do I get this one battery to "KEEP UP" while Series Charging?

And what would anyone recommend for a 6v charger for independent charging of a single L16? Would this Adjustable Power Supply work for manually charging batteries?

jonr

> how do I get this one battery to "KEEP UP" while Series Charging?

See response #11.

Estragon

The power supply might work, but I'd go for an automotive charger with 6/12v capability. About the same price, and more versatile.

Maybe something like:

https://www.amazon.com/Schumacher-SC1281-Automatic-Battery-Charger/dp/B07BLLRM8R/ref=mp_s_a_1_5?crid=AZ0N4MKIX1HL&keywords=battery+charger+automotive&qid=1554389612&s=gateway&sprefix=battery+char&sr=8-5

MrM1

Thanks @Estragon that looks really good. And while it would be more versitle around the house / car ... It would not hold a constant current at whatever voltage I chose. It would do a multi stage/cycle charge terminating when it "thinks" charging is done. Not a bad thing, but a power supply would just hold voltage and current at whatever it was set at until the user turned it off.

Just not sure which would be better for my particular situation.

Estragon

The battery won't take a constant current in absorb anyway. I don't know how that particular charger transitions out of absorb though; if duty cycle it may not work well for this, if timed it would just want periodic resetting - not such a bad thing. The advantage with the power supply would be you could presumably leave it on a high-ish voltage low current charge indefinitely.

One concern I had with the PS was the size of the leads and how they'd do with sustained 10a over a long time. Hard to tell from the pic though, maybe they'd be fine.

MrM1

Yeah the leads are a main complaint , but I had figured to make my own leads. But there is nothing in that kind of PS that would scream DO NOT USE THIS TO CHARGE BATTERIES?

The advantage with the power supply would be you could presumably leave it on a high-ish voltage low current charge indefinitely.

This was what I was thinking of doing.

MrM1

OK so it has been 10 days of Light duty cycling of the four 435Ah battery bank. Never discharged down below 90% SOC, most days down only to 96% or higher. I have been tinkering with voltages to get the voltage of the suspect battery at least to gassing voltage of 7.4v. but some days I just charged the whole bank at 29.6v

Bank went into float at 1pm today. CC said 100% charged. In checking the cell voltages, When the bank was reading 27.2v, Each cell was at 6.84-.85v but my one suspect battery is at 6.67v. Not much of a difference there. In charging at 29.6v there is about a 0.5v decrease in voltage at the suspect battery from the others.

BUT in check the temps and SG, I filled all cells on Monday 8 days ago. Here a week later, 10 cells are down 1/4 from the fill ring, But 2 cells in the suspect battery had not changed at all, are completely full. 1 cell in that battery also showed a decrease in water.

The SG of 10 cells, including 1 cell in the suspect battery was between 1.277 - 1.295. The SG in middle cell of the suspect battery was 1.275 and the cell on the (+) terminal side was at 1.243 or less than 40% charged.

AND The out side temp today is 86*F ... And the temp with a temp gun of 3 batteries at various places around the battery case was at 27.4*C, BUT the temp at suspect battery is 34.2*C. Moving the temp gun to different locations on the case, the temp is highest near the top of the case at the (+) terminal side, on the cell with the lowest SG (of 1.242) and least amount of water use. On the other side of the battery the case temp drops to 30.3*C . I am temp compensating the charge, and have a temp probe at the hottest spot on the worst battery.

So I am guessing within that battery, 1 cells is seeing over voltage charging (it was using water and SG was 1.280) and at least one cell is not even entering Gassing BUT is indeed heating up - hottest on this side of the battery case.

So it does not appear that I am not going to be able to get a good charge on this battery in series charging via my charging system, regardless of the source, solar or grid charger. I do not know what the battery temp was when it was independently charged at the distributor.

Any ideas, thoughts? how dangerous is this situation? Do I just ride with it, not letting the batteries get too hot (which means decreasing the charge voltage or time) and allowing the under charged cell to remain under charged until it sulfates? Here in FL summer is coming. So 86*F outside temp is pretty low temps. I will see temps of 95* + in the battery box in the summer. The box is vented and fan cooled with air from under the house, so they will not be exposed to full summer heat though.

The bank seems to be handing loads OK.

Tecnodave

Well, you found the problem......and your dealer couldn't .....document...document.....document , then talk to the battery manufacturers public affairs office. A lot of companies have to be encouraged to do the proper thing. If your infrared heat gun has a graphic display of the hot areas , photograph that......evidence of fail mode. If they are decent they will replace the failed battery. No don't accept the situation, it will only get worse. This is just my opinion, but others will concur.

Dave Angelini

If it meets spec for a load test, then there is not a problem. That is what the dealer did, I think.

Tecnodave

If only one spot on one battery is that much hotter than any other spot anywhere on the battery, then that battery is suspect. If that cell is partially shorted it will be very slow to charge, have a low s.g. and be hotter than the rest. There could be other reasons for the hot spot such as a poor battery cable connection and that should be checked. But with the combination of the three signs to me that points to a failed cell.

BB.

Replace the bad battery.

That one cell is limiting that one series string to 40% total capacity (you can only discharge the string down to the AH capacity of the weakest cell).

Long term, the excessive gassing of one cell will errode the plates and cause corrosion in the positive grid. And if it every "boils dry", you run the risk of meltdown or fire.

Bill