Refurbish process for forklift batteries

[Hedges]

This is a sore subject. My utility is telling me that they consider any "solar inverter" to fall under net metering, and insist I'm not allowed to connect it to grid power without submitting drawings, getting their approval, and having it inspected... even if I have no interest in net metering! This is why I mentioned my bench power supply--I don't have a 48V charger besides the Sunny Island, but the power supply can get the battery up to 60 volts and keep it there indefinitely... I've got it set to do that overnight tonight, in fact.

Configure Sunny Island to charge from the grid, but turn off "sell", and it will not backfeed.

Then plug input into grid and let it do the equalization.

To be even more certain, if you disconnected any AC coupled PV inverters, and disconnected DC coupled coming from midnight, there would be no PV available to backfeed.
Then, the only way that could happen is if you enable "sell" and tell SI you want battery voltage lower than it already is.

I would just do what I needed to do, and make sure it wasn't going to backfeed.

 

[Consumerbot3418]

Just to follow up on my initial post, it looks like I might be making progress. I've seen a marked improvement in the balance of the two batteries, as well as the cells within. (SGs, voltage, and charge/discharge current comparison)

I let the battery spend about a week with my bench power supply hooked up, set to 60V, max of 5A. Initially, that 300 watts (minus the Sunny Island inverters' idle draw of 50W) was enough to hold the battery at 60V. But I was able to achieve an EQ voltage of 63 for a few hours at a time, a few days in a row, and noted that the 5A output of the power supply was no longer able to hold the 60V, as you can see on the evening of Dec 5th:



I'm hoping that means I managed to get rid of some sulfation!

My research indicates that it's helpful to cycle the battery, too, so I let it drop down to 35% SoC (inverter's estimate), and I'll repeat the process a few more times, letting the battery spend plenty of time fully charged, with the 60V/5A PS connected and set to max. I won't worry too much about being unable to achieve a target charge voltage > 63.0 on the Sunny Islands, since the consensus is that's already a pretty aggressive EQ voltage.

@Zwy -- really appreciate your input, and linked video! My understanding is that lead acid batteries are practically a closed loop for recycling, so the environmental impact of scrapping is negligible. My personal motivation is monetary, but I also enjoy seeing things optimized, and hate seeing things wasted. A capacity test would have been a great idea, but unfortunately, I failed to record a baseline. I never have seen the batteries really heat up: even after hours at 63V (over 2.6/cell), only read around 80ºF, although the electrolyte gets bubbling pretty well! I'm thinking this is because it "only" takes about 1000-1500W to hold 63V

@TOU47 -- Thanks for the suggestion. I'm pretty far away from Utah, but I'll consider contacting him...

 

[Consumerbot3418]

I would just do what I needed to do, and make sure it wasn't going to backfeed.

I appreciate your (as always) insightful suggestions. I fully trust SMA's "grid: charge" mode wouldn't backfeed. And temporarily disconnecting PV may provide extra assurance, but I'm adamant about keeping my word, to the point that I'll just purchase a 48V charger, if needed.

But I really don't think it should be necessary. I've seen the SI's dumping 7,000W from AC-coupled into battery, same from the generator. Yet in EQ, regardless of the EQ voltage parameter being set to 65 or more, both sources yield a target charge voltage of 63.0V, which maxes out at around 1,500W. I feel like it must be some parameter I'm overlooking, or the SI is somehow "stuck" in its battery protection mode without giving that indication. I may eventually reach out to them for help, but meanwhile, I'm pretty happy with the progress I've made thus far!

 

[Zwy]

One thing to remember is the battery internal resistance changes as the battery temp rises. The power supply can output 60V at 5A as long as internal resistance remains high. When that level can not be held, then internal resistance dropped for one of two reasons: #1- the sulfation is being removed either by chemical action or new plate material exposed (physical dropping of sulfated plate material) or #2- the battery temp increased leading to lower internal resistance.

 

[shadowmaker]

I have been charging half (24V) of my 48V forklift battery for a week or so now. My smart charger won't do more than 29,2V when GEL-mode. 28,8V when WET or even on CAL-mode, which should go up to 30,5V. I have been adding a half a litre of water every day. What next? Capasity test? Or should I buy some kind of equalizer and try to equalize it? Equalizers seem to do 4 cell only, so I need six of them to equalize all 24 cells? Gravity test? Before gravity test should it be off charger for some time before measuring?

 

[Zwy]

SG can be checked while charging. I'd check SG and also battery voltage off the charger with the surface charge removed. Take a small load such as a headlamp and just run it for a few seconds to remove surface charge. Or let it sit overnight.

To get voltage high enough, you have to get thru absorption after bulk charging. If the battery won't hold a charge after bulk and absorption, then it is toast.

If internal resistance is high, the battery will tend to generate heat and would require high amps to move higher in voltage. Most likely you are at that stage. I'd let the battery sit 24 hours, check voltage and SG, if it passes then hit it with the EQ voltage until charger voltage starts dropping. Then move back to absorption voltage and see how many amps it takes. If you start getting down to under a few amps, then let is sit overnight, then run a capacity test.

Each time you do EQ, you need to monitor battery temp. I never run higher than 105F, if you hit 100F then you should stop and let things cool down. Heating/cooling cycle will flex the plates, opening small cracks in the sulfated layer.

With high amp charging, the more water the battery will require. It's the heat generated plus the normal electrolysis consumption.

 

[shadowmaker]

SG can be checked while charging. I'd check SG and also battery voltage off the charger with the surface charge removed. Take a small load such as a headlamp and just run it for a few seconds to remove surface charge. Or let it sit overnight.

To get voltage high enough, you have to get thru absorption after bulk charging. If the battery won't hold a charge after bulk and absorption, then it is toast.

If internal resistance is high, the battery will tend to generate heat and would require high amps to move higher in voltage. Most likely you are at that stage. I'd let the battery sit 24 hours, check voltage and SG, if it passes then hit it with the EQ voltage until charger voltage starts dropping. Then move back to absorption voltage and see how many amps it takes. If you start getting down to under a few amps, then let is sit overnight, then run a capacity test.

Each time you do EQ, you need to monitor battery temp. I never run higher than 105F, if you hit 100F then you should stop and let things cool down. Heating/cooling cycle will flex the plates, opening small cracks in the sulfated layer.

With high amp charging, the more water the battery will require. It's the heat generated plus the normal electrolysis consumption.

All but one are on low-green to mid-green. That one is mid-white and has only 2,07V. Then there's a new cell (one year old) which is 2,15V (still mid-green though). All the rest are 2,10-2,11V. This is measured from half the battery (=12 cells) as I have only 24V chargers. I put the other half charging now.

Don't know how to EQ them with the chargers I have. One is old 60A/24V and the other is new 12,5A/24V. I think even the old one is "smart" as it has big board of electronics inside it. Can I just hook the big one to 8 cells to charge it with 28,8V and monitor closely temp while doing it? Or should I buy a battery balancer instead?

 

[Zwy]

I wouldn't worry about EQ at this point. Either it accepts a charge or it doesn't. You need to see if you can get to full charge voltage at rest, if you can't it probably is toast.

High voltage can blow off sulfation but there has to be lead left on the plates.

The large charger may work if you have electrolyte just above the plates. Water level and temp would need to be monitored while charging constantly. If internal resistance is high, it won't take many amps. If it takes close to full amps and some cells heat up quickly they are probably shorted and junk.

 

[shadowmaker]

After resting for two days the voltage is now 25,3V for the half of the 48V battery. It should be around 25,8V when 100% full??? At least when I calculate according the best cell (new one): 12 x 2,15V= 25,8V. If I calculate according the worst cell: 12 x 2,07V=24,84V

I have an old "dumb" charger 6V/12V which can give like 5A max. Can I "shock treat" the worst 2V cell with it? I'd give 12V/5A to it for a half a minute or so to desulfate it. Of course monitoring it closely while doing so. Repeating treatment for few times after cooling it down first.

After that maybe leaving that new cell out and charging only 11 cells with that smaller charger (28,8V/12,5A) for few days? This way I should get them closer to 2,15V?

 

[Zwy]

After resting for two days the voltage is now 25,3V for the half of the 48V battery. It should be around 25,8V when 100% full??? At least when I calculate according the best cell (new one): 12 x 2,15V= 25,8V. If I calculate according the worst cell: 12 x 2,07V=24,84V

How long it takes to charge a cell or a battery is based upon cell capacity, internal resistance and charge rate (amps). You could be recovering the battery, slowly transforming soft sulfation back to lead and acid. Or you could be just generating heat due to resistance.

It does take time to desulfate, the sulfation did not appear overnight or a few days.

I have an old "dumb" charger 6V/12V which can give like 5A max. Can I "shock treat" the worst 2V cell with it? I'd give 12V/5A to it for a half a minute or so to desulfate it. Of course monitoring it closely while doing so. Repeating treatment for few times after cooling it down first.

A better choice would be a power supply with CV/CC. Use the power supply to apply a EQ voltage for a single cell.

As for the dumb charger, you can use a resistor (can be resistor, lightbulb) in series on the 6V setting to reduce voltage and amperage. This would require you to measure with a DVOM for the voltage. At this point I would not apply more than the EQ voltage.

I have seen the videos of people using a DC welder to boil a 12V battery for 5 minutes to blow sulfation off the plates using the 24V output of the DC welder. Uncle Tony's Garage did such a video, it was the most watched and commented video he ever produced. It is extremely dangerous, outdoors only away from any buildings and long cables are a requirement. I have tried it using a cheap inverter style welder (won't use my good welders as it has to be hard on the caps) and found every welder I tried has anti stick and won't run if both cables are connected to a battery. Hasn't worked for me, just wanted to try it on some old automotive batteries I'd use on small engines such as a lawnmower. Nothing I would depend upon for a long trip.

After that maybe leaving that new cell out and charging only 11 cells with that smaller charger (28,8V/12,5A) for few days? This way I should get them closer to 2,15V?

Voltage output of the charger will increase as the internal resistance of the battery rises. With 2 30V/10A power supplies in parallel, you can push in 20A, twice the output you have. The nice thing about using a power supply is the CV can be set to bulk charge voltage and when running the display will show what voltage the power supply is using to put in the CC at full output. As the battery charge increases (internal resistance rises) you will see the voltage reading on the display rise finally hitting the CV setting.

With a CV/CC power supply, you have the ability to work on not only a single cell but a pack of cells up to the voltage limit of the power supply. They do make 60V units too. This might be the way to go, especially if you want the ability to work on a single cell.

 

[Hedges]

If you have access to individual cell terminals, a balancer could keep the cells from getting out of balance.
I think over-charging other cells in series in order to increase SoC of a low cell is considered lesser of two evils.

Since presently imbalanced and requiring equalization, I would think equalizing individual cells with proper voltage/current would be good.

 

[shadowmaker]

Doing capacity tests at the moment. I have 1700W/12V inverter, so I'm testing my 48V 625Ah battery in four 12V segments. Load is a 1000W heater, but @11,94V it is drawing 108,8A so ~1300W. Started about 20min ago.

Battery is rated 30kW/5h, so at 1300W one 12V segment should take ~5h45min.

Am I doing/thinking this correctly?

 

[Zwy]

If you can find the spec sheet for the battery it helps or the label on the battery may give a spec. For the Trojan T105's, the rating at a 20 hour discharge rate is 225Ah. But you have to know what the 20 hour rate is, for that you need the spec sheet and it is 11.25A.

Trojan has other ratings for the same battery, 5 hour, 10 hour, etc, discharge rates. As the discharge current increases, the rating in Ah will decline due to the Peukert's Law. At the 10 hour rate, the T105 is rated for 207Ah instead of the 225Ah.

You can use whatever rate you want, the idea is to be consistent with the discharge rate and conditions (same battery temp each time, rest over the same number of hours after charging are examples). As long as you are consistent and record results each time, then you will know if you are making progress. At some point, you won't see much gain in Ah, it is then you need to decide if EQ will help, if you should accept small increases with each cycle, simply stop and use the battery or recycle it.

 

[shadowmaker]

In the battery it says: "48V, 625ah, 30000W (5hours)".

To me this means if I discharge it as a whole 48V battery with 6kW, it should last 5 hours. But as I don't have 48V inverter (well actually I do, but this 12V is much easier to work with), I have to do capacity test in segments. So if I discharge it in four 12V segments, it should do 1500W for 5 hours (6kw/4=1500W)?

 

[fromport]

Doing capacity tests at the moment. I have 1700W/12V inverter, so I'm testing my 48V 625Ah battery in four 12V segments. Load is a 1000W heater, but @11,94V it is drawing 108,8A so ~1300W. Started about 20min ago.

Battery is rated 30kW/5h, so at 1300W one 12V segment should take ~5h45min.

Am I doing/thinking this correctly?

This is the label on my DC-Solar trailer battery
540 Ah when the discharge current is limited to C(==540) / 6 = 90 Amps
90 amps x 48 Volt = 4320 watt discharge capacity.
Since there are 2 batteries in parallel on this trailer, technically you should be able to discharge with 8640 watts from both your SI inverters.
Take into consideration the converting losses in the inverter (lets assume 10%), you should basically not pull more 7776 watts on the AC side of the inverters to honor the capacity of the batteries.

 

[shadowmaker]

View attachment 126816
This is the label on my DC-Solar trailer battery
540 Ah when the discharge current is limited to C(==540) / 6 = 90 Amps
90 amps x 48 Volt = 4320 watt discharge capacity.
Since there are 2 batteries in parallel on this trailer, technically you should be able to discharge with 8640 watts from both your SI inverters.
Take into consideration the converting losses in the inverter (lets assume 10%), you should basically not pull more 7776 watts on the AC side of the inverters to honor the capacity of the batteries.

Thank you for the explanation.?

My capacity test with the first 12V segment was a mess. With ~1300W total load it went fine for 3,5 hours. I was just measuring draw and it was 11.05V/116,5A when suddenly inverter started some kind of warning sound. I thought it was low voltage level warning (cut-off @10,5V), but after some twenty seconds there was a clear (visible/audible) spark on inverter's positive terminal. After that warning sound stopped and everything seemed to be OK. I suspected that I didn't correctly tighten that terminal so I tried to tighten it some more (no tools, just fingers). It was correctly tightened but at that point I could hear multiple sparks going off inside the inverter (still the positive terminal, but inside the casing) and decided to stop the test.

My friend loaned this inverter to me and it was unused, though some four-five years old perhaps. I'm a little scared of sparks around lead acid batteries, so for sure I'm not going to continue my test with this one.

Uncompleted test result wasn't that bad at all I think, as after dropping quite fast down to 11,6V it slowed significantly. Capacity was ~61% @3,5h, but it would be hard to say how much there was capacity left at that point. Now after sitting for two hours the voltage has raised back to 12,02V, which could mean there is over 40% capacity left according to this voltage chart:

I think that's impossible as 61%+45%>100% and this battery is 18 years old (I got it free because of that). But maybe 70-80% capacity might be possible. Out of six cells in this first 12V segment tested one was new (a year old or so). That can make the result somewhat better than expected. The next segment I was going to test has the worst cell in it, but now I'm not sure how I can do that. At least I need a different inverter.

 

[Zwy]

In the battery it says: "48V, 625ah, 30000W (5hours)".

To me this means if I discharge it as a whole 48V battery with 6kW, it should last 5 hours. But as I don't have 48V inverter (well actually I do, but this 12V is much easier to work with), I have to do capacity test in segments. So if I discharge it in four 12V segments, it should do 1500W for 5 hours (6kw/4=1500W)?

Personally, I'd look at 10 or 20 hour rate. 625Ah/10= 62.5A and 625/20= 31.25A discharge

3000W would be around a 10 hour rate.

The 625Ah rating could be the manufacturer Ah for 10 or 20 hours. Do you have a brand for the battery?

 

[shadowmaker]

Personally, I'd look at 10 or 20 hour rate. 625Ah/10= 62.5A and 625/20= 31.25A discharge

3000W would be around a 10 hour rate.

The 625Ah rating could be the manufacturer Ah for 10 or 20 hours. Do you have a brand for the battery?

These type of batteries are new to me, but it seems that a C5-test is something they do around here, when they sell used forklift batteries. Here's a picture of my battery's label. It's an Exide Tudor.

 

[shadowmaker]

I made a test and my stick welder seems to work with normal 12V car battery. I'm going to try it with this big one (on four segments of course), but I'm not going to do it inside. It means that I have to wait until weather suits my forklift. Also not sure if my welder works with this big battery at all.

I've seen videos people doing it while the battery is still inside the car, so I assume battery being full is not an issue? This way the current is making heat = twisting those plates to knock off sulfation?

 

[Zwy]

Label says Ah/5h so it appears to be 625Ah/5h = 125A discharge rate.

As for the welder, it is possible to blow a plate against another or part of a plate creating a short. This can lead to a battery exploding due to the hydrogen and oxygen being created.

2 things, one it should be off the vehicle and outside, two, the connection needs to be away from the battery as well as your body. Don't become a statistic.