Battery Myths and Tips

adas
adas Solar Expert Posts: 136 ✭✭✭✭✭
Aloha, could you verify or comment on the battery charge workings?

Talking about 24v 875AH Heavy duty Electric Forklift batteries

1: Does a weak cell, say 2.01 V bring down the whole other 11 cells?

2: If you are charging 4 of the above batteries in parallel and one battery is of a lower charge, will all batteries equalize out or will the charger controller try to charge the weaker battery and tend to overcharge the more fully charged batteries?

3: Will all batteries draw equally from the controller? ie if your controller is putting out 80 amps, will each of the 4 batteries suck 20 amps if all are in the same state of charge?

4: Any truth to the claim than Potash will rejuvenate a battery?

5: what is the relationship of amps charging verses available amps to draw out. For example if I charge 80 amps for one hour is the 80 amps in the battery? Or is there a rule of thumb, such as 1 in and 1/2 out?

thanks
Frank

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery Myths and Tips

    As is life, the answers are not always easy...
    adas wrote: »
    Aloha, could you verify or comment on the battery charge workings?

    Talking about 24v 875AH Heavy duty Electric Forklift batteries

    1: Does a weak cell, say 2.01 V bring down the whole other 11 cells?

    Weak cell has many definitions:

    A. Shorted Cell
    • Lead or frame short would (at lower currents anyways) make your 12 cell battery look like an 11 cell battery... If in parallel with the other batteries--most likely this battery would "take all of the charge" and overcharge the other 11 cells. When load is applied, the other batteries would supply the load until they are near dead, then the 11 overcharged cells would start to supply current. The shorted cell would probably run very hot (temperature wise).
    B. Open Cell
    • High resistance--more or less, like the battery is not even in the chain.
    C. Electro/Chemically inactive cell
    • Contaminated acid, more Sulfates than other cells--would probably be, more or less, like the "open cell"... Little current flow when charging, quick loss of voltage when discharging.
    2: If you are charging 4 of the above batteries in parallel and one battery is of a lower charge, will all batteries equalize out or will the charger controller try to charge the weaker battery and tend to overcharge the more fully charged batteries?
    • Batteries in other wise identical condition (temperature, amount of use/aging, equal resistance, chemical activity, etc.) would be very close to each other in overall voltage... The difference in charging would be the resistance in the charging path(s). Batteries in a higher resistance path would get (and deliver) less current. Batteries with a lower resistance path would get (and deliver) more current.
    • In electrical design--to get circuits to share well--you would design the distribution network to have a higher resistance (and control it so that each path matched resistance) vs the low resistance energy source/sink (i.e., battery). So, if all of the cables are the same length (and not too heavy gauge), and they all go to the same point (or low resistance bus bar)--then the batteries should receive equal current (and slight differences in battery resistance, chemistry, temperature, etc.) will not have a large effect on the current flow (because the distribution cables have higher resistance--they effectively regulate current sharing).
    • If, however the cables have very low resistance vs the battery resistance, or the cables have different lengths/gauges/etc., then the current sharing to the parallel battery strings is much more difficult to guarantee (minor differences in each battery would affect the charge current distribution)...
    • With parallel batteries--the battery with the lowest current path and the "best chemistry" will tend to source/sink the most current--and will tend to wear out the quickest over time. Which is why it is not recommended to parallel old and new batteries together--the new batteries would tend to cycle most of the load and wear out quickly to match the older batteries in the parallel set.
    3: Will all batteries draw equally from the controller? ie if your controller is putting out 80 amps, will each of the 4 batteries suck 20 amps if all are in the same state of charge?
    • See above... The more batteries you have in parallel, the more difficult it is to guarantee current sharing... Especially if the batteries are of different ages and there is not a balanced electrical distribution system.
    • My personal experience is that I would avoid large numbers of parallel strings and tend towards higher voltage series strings... The absolute number--I don't know--but somebody recommended here about 3 parallel strings maximum--and that would probably be my choice too...
    • To check how far off your matching of distribution is... Place the batteries under heavy load (or even heavy charge) and use a calibrated DVM and measure the voltage drops on the cables and the voltage at each battery terminal...
    • From the Battery FAQ here, the difference between a 90% charge and a 100% charge for a 24 volt bank is 200mV... So, I would probably be aiming at a 20mV maximum differential on a battery terminal to battery terminal difference (that is an accuracy better than 1000:1).
    4: Any truth to the claim than Potash will rejuvenate a battery?
    • Don't know---but there have yet to be any battery additive claims that have been supported by any battery manufacturers (or large users like telephone companies).
    • I read one guy/place that used some sort of caustic to convert a dead lead acid battery to an "Alkaline" Lead Acid battery (rinsed out acid electrolyte and replaced with alkaline electrolyte"... You can read about the process here--I stumbled on the website last week. I have no idea if this is safe or works at all, or if the poster is full of hot air--use at your own risk.
    5: what is the relationship of amps charging verses available amps to draw out. For example if I charge 80 amps for one hour is the 80 amps in the battery? Or is there a rule of thumb, such as 1 in and 1/2 out?
    • For an AGM type battery--they are very close to 100% efficient in Coulomb charge... 100% of the electrons out equals 100% of the electrons back in charging (may be 98%?). The amount of energy delivered vs required to charge is different... The battery's voltage is lower when delivering current, and higher when charging--so, roughly, you end up around ~90% energy efficiency...
    • For wet cell Lead Acid batteries--because of the losses from equalization (and other chemical differences?) the overall energy efficiency is around 80%--at least those are the rough numbers we throw around here when sizing systems. I am sure there are more accurate numbers (based on a whole bunch of variables) if we look around (or ask Jim/Crewzer).
    Well--that is about the extent of my bluffing on Lead Acid battery knowledge...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Battery Myths and Tips
    adas wrote: »
    2: If you are charging 4 of the above batteries in parallel and one battery is of a lower charge, will all batteries equalize out or will the charger controller try to charge the weaker battery and tend to overcharge the more fully charged batteries?

    I'll try to address this one

    An EQ charge cycle, DOES overcharge all the cells, in an attempt to fully charge 1 weak cell.

    This will mildly "bubble" or gas the batteries, and consume water, which needs to be checked after each cycle. This also "mixes" the acid inside, by using the bubbles to stir it up. (I can shake a single T-105, but not a forklift pack, or bank of 8 T-105s)

    If you check after each EQ cycle, and the overall health is getting better, after cells cool down, you can run another EQ, till you either decide you have a bad cell, or it comes back to life. If the latter, you have a battery that has a single, chronically undercharged cell, which has likely become sulphated, and is on it's way out. You might get a month, or 6 out of it, but at the same time, it reduces, by 2 volts, the observed voltage of the battery pack, and a charger is going to spend a lot of time trying to overcharge the rest of the bank, consuming more water, and habitual overcharging can't be really good.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • adas
    adas Solar Expert Posts: 136 ✭✭✭✭✭
    Re: Battery Myths and Tips

    Aloha, thanks for all the info!! One more thing...

    What is the best way to minimize the fuzzy growth on terminals? Using a liberal amount of grease to cover? What about the a spray or brush-on rubber material?

    Frank
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Battery Myths and Tips

    Fuzzy growth is a result of off gassing of the batteries. If it is excessive, it is often a sign that the batteries are about to go south. Can also be caused by bad cable connections.

    I wash my batteries twice a year with clear water and never get any "fuzzy growth. I'd test my bank pretty carefully if you have a continuing problem.

    Tony

    PS Excess gassing can be a result of higher than normal charging voltages, or a bad cell boiling trying to charge. Some boiling and bubbling is normal and serves to keep the electrolite stirred up.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery Myths and Tips

    For cars, I just use those little rings (usually red/green) loaded with anti-corrosives--you can also get the same stuff in a can+brush for protecting terminals.

    And, as said earlier, you are probably getting lots of acid mist from charging (maybe OK, maybe overcharging)...

    You might look at these Hydrocap/Water Miser battery caps and see if they fit and reduce your battery water usage (one is passive--just captures the mist--the other has a catalytic metal and recombines the H2+O2 back into water; the second should not be used when equalizing because of overheating).

    If your water usage is normal--not a big issue--however, if lots of misting--you are not only losing water but Sulfuric Acid too--which you normally do not replace.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset