Cant reach EQ voltage using generator - new batteries

Boohai · September 2021

HI all, we are unable to reach the EQ setpoint on our 48v / 650a/h system using our generator. We had a previous battery bank for 15 years + and never conducted an EQ (We didn't know we needed too and as it turns out, somehow we didn't need too!). I'm wondering if we got away with it due to the quite high Absorb point of: 59.2? It seems high to me and we did have uncontrolled gassing off which seems a strange way to run the system, but hey the folks who rigged it up got our batteries beyond 15 years. Anyway we now have new batteries a direct replacement of 24 x 2V traction batteries /650 a/h and we have been given the following set points: Float: 53.52-54v / Abs: 57.6 v / Bulk: 57.6 and EQ: 62.4 (1 hour each month). So I have tried an EQ cycle through our Outback MX60 and can get the voltage no where near to the EQ setpoint, we managed 58V. We did charge the system first and take any loads off and when we click stop the EQ we see the drop in volts so the system does 'think' it is running and EQ. Many thanks in advance, Scott @ Bron Yr Aur

P.s. our generator does start off by putting in something like 50 amps

RCinFLA · September 2021

You will need to be able to supply enough current to be able to at least initially pull cells to the higher voltage.

If you fully absorb first you will require a bit less current to pull them to equalize voltage. It will likely slowly work it way higher from the absorb voltage to equalize voltage. The greater the charge current the faster it will get to equalize voltage.

Don't go crazy with equalization. It is stressful on batteries. Base your decision to equalize on measured S.G. imbalance.

By controlled overcharging (equalization) you are attempting to breakdown semi-hardened lead sulfate and have it recharge back to lead and return the sulphur back to sulfuric acid in electrolyte. When cell has sulfate locked up up on cell's plates it means more diluted (less sulfuric acid) electrolyte, therefore a lower specific gravity of electrolyte after normal full charge.

Discharging creating lead-sulfate on lead plates. It starts out as a soft brownish moss but left there over time it will crystalize to a hard crust that will not recharge easily.

If it gets totally hardened even an equalization will not convert it. At that point the best you can do is use the vigorous equilation to break off the sulfate from plate surface which eventually makes its way to bottom of battery case and free up the sulfate insulating coating from the lead plate so it can be active in the discharge process again. This will not return electrolyte SG to its normal concentration of sulfuric acid but may improve the cell's discharge capacity.

Vic · September 2021

Hi Scott, welcome to the Forum,

Have you tried EQing, using solar AND the generator?

As RC mentioned, measuring the Specific Gravity (SG) of each cell is the way to tell the state of charge of the battery (on average). For this, you will need a good quality Hydrometer.

Label each battery/cell, to allow you to keep track of the SG trends, and will help you adjust the Abosrb voltage and time. RECORD these SG readings in you Battery Logbook. The variation in SG readings between the cells will help you know, when to EQ.Is your battery a forklift battery? ... what brand/model is it? What is the SG reading for full-charge?
What is the total amount of solar power that you have?
What is the Absorb time setting on the MX-60?

Because you can only reach 58 V during EQ, that probably implies, that the battery was NOT fully-charged, before the EQ was started.

More later, thanks for added info, Vic

BB. · September 2021

Have you measured the current during EQ?

More or less, 5% rate of charge (650 AH [at 20 hour rate] * 0.05 = 32.5 Amp for 5% EQ)... Even down to 2.5% rate of charge can work (16.25 Amps)--Lower charge rate will take longer.

For some batteries (industrial, some Rolls, etc.) can take many hours for several days of EQ (or say a few hours a day over a few days) to fully EQ. Note EQ is "finished" when battery state of charge Specific Gravity stops rising (measured once an hour).

Remember that even at 2% rate of charge (continuous for many hours), batteries can still overheat (energy goes mostly into gassing and heating.

One of the reasons for EQ can be to mix the electrolyte (gassing) and prevent stratification of the electrolyte (dense electrolyte at bottom of cell, less dense at top of cell). This mixing is usually (mostly) required for "Tall Format" batteries. "Short" batteries tend to not stratify--And if you do get a little gassing during normal charging--It is probably enough "mixing".

59.2 volts (14.8 volts @ 12 volt bank) absorb is about standard for Deep Cycle Lead Acid Flooded Cell storage batteries.

If you got 15 years out of the first bank--It sounds like you were doing right by the battery bank.

I guess you are in the southern half of the U.K.... So cool weather/battery banks will last longer. The standard engineering rule of thumb is for every 10C below 25C (18F/77F), the batteries will age 1/2 as fast (i.e., a 7 year life battery if at ~15C should last out through ~14 years). Temperature/Life is separate from Cycle Life (charging/discharging life) of batteries.

-Bill

Marc Kurth · September 2021

It would seem that your last sentence may be a critical piece of info: "P.s. our generator does start off by putting in something like 50 amps"

Are you waiting to EQ after the battery bank after being in Float for a bit?

Marc

Boohai · September 2021

Thanks so much all , quite a lot to digest there. I am charging the batteries fully before starting an EQ cycle and I am checking the SG. My main question is why I can't get the voltage to reach a higher point. I'm not looking to get help on when or why to EQ. The batteries are traction batteries /forklift (not at home now so will have to check make , as we used to have FIAMM). We have 1k solar, 2.5 k wind and 0.5 k hydro. Generally we are seeing an input from the generator of 30 amps and even when batteries are full we can't push the voltage higher after some hours. We are based in Wales in terms of cooler climate and all. Thanks so much all , a really good start to unravelling what is going on here! I'll get the info requested asap. Cheers

Boohai · September 2021

P.s. Do any of you folks ignore manufacturers advice on regular EQ's? Seems to me that performing and EQ on new batteries every month is overdoing it?? (Especially if we always keep them at or above 50% capacity).

Marc Kurth · September 2021

Boohai said:

Thanks so much all , quite a lot to digest there. I am charging the batteries fully before starting an EQ cycle and I am checking the SG. My main question is why I can't get the voltage to reach a higher point. I'm not looking to get help on when or why to EQ. The batteries are traction batteries /forklift (not at home now so will have to check make , as we used to have FIAMM). We have 1k solar, 2.5 k wind and 0.5 k hydro. Generally we are seeing an input from the generator of 30 amps and even when batteries are full we can't push the voltage higher after some hours. We are based in Wales in terms of cooler climate and all. Thanks so much all , a really good start to unravelling what is going on here! I'll get the info requested asap. Cheers

What is the capacity of your charging system when running the generator? The only reasons that I can think of, for not reaching your EQ setpoint:

- The setpoints are set too low.

- You don't have the required current available.

Dave Angelini · September 2021

Hey Marc ! In Texas, we had some fun!

Scott, may have a bad battery also.

If the bank is full (correct SG) where is the 30 amps going? Do you have monitoring on your Inverter/charger? What make?

You should do what the manufacturer requires if you are cycling daily. If your discharges are small you can skip a day or so of charging. A 50% discharge is at the limit probably for the make of battery though. They need to get full right after that! Also, new batteries do have to break-in for a few months or so.

Get some data into a post when you get back to the site.

Vic · September 2021

Hi Scott, thanks for some added info.

If you cannot get the EQ voltage above 58 V, after you believe that you have fully-charged the battery after the Absorb stage has ended, then you do not have enough charge current available to cause the battery voltage to rise above that value.

QUESTIONS:
1. Is your Absorb voltage set to 57.6 V ?
2. What is the Absorb time setting?
3. Does your system use the Remote Temperature Sensor for the MX-60? Where/how is this RTS mounted?
4. What is the rated SG for full charge?
5. Approximately, how deeply discharged is the battery, on average?

It still seems to me, that your battery is NOT being fully-charged during the Absorb stage -- normally one would increase the Absorb voltage (Vabs) and probably the Absorb time, to get the basic charging finished.

BB Bill did ask about the battery charge current, during EQ, and it would be good to also know, the battery charge current during the Absorb stage. This is important info.

Does your system have a Shunt, that allows you to monitor the battery charge current?
The MX-60 does have an accurate built-in shunt for its output current, so this can work well, is all other large-ish loads are shut off, and small loads do not fluctuate very much.

You could set the Absorb time to a large number, like 5 hours, then, monitor, and note, the battery charge current during Absorb. It will diminish, as the Absorb progresses. When this current stops decreasing, for 15 - 30 minutes, this is about all of the charge that the battery can Accept, at that particular Absorb voltage.

Most Forklift batteries use fairly high SG electrolyte, in the range of about 1.285 - 1300-ish. This generally means that the required Absorb (and often, EQ) voltage/s need to be set a bit higher than for flooded batteries, with lower SG ... IMO, 57.6 Vabs it too low for Flooded batteries that are cycled daily (Off-Grid), especially forklift batteries.

YES, Scott, you have been peppered with many questions, and you are away from the system site, but please do your best to answer the questions that you can ...

As noted before, EQ, for Flooded Lead Acid batteries, is a controlled overcharge, which overcharges the cells with the highest SGs, in order to fully-charge those cells with the lowest SG. It is a bit hard on the battery, but is really the only way to get t he Sulphates off of the plates of the lower SG cells -- it must be done, and is better for the battery to do this, than allow the sulphates to remain, harden, and NOT be removable after an extended period of time.

IMO, FWIW, etc, Vic

Cant reach EQ voltage using generator - new batteries

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