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Rectifier Only Charges 53Ah Battery to Half After 10 Hours - Voltage Readings Inside

Legoo 48345 39
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Why does a 4A rectifier still show half-scale after 10 hours when charging a 53 Ah battery, and are 14.95–15.05 V at the terminals normal?

The charger’s meter does not show the battery’s state of charge accurately, so you should trust a voltmeter on the battery terminals instead of the rectifier’s gauge [#13383719][#13383963] The unit appears to be a very simple charger with no real charge-control circuit, so the indicator can stay active while current is still flowing [#13383963][#13384723] A charging voltage of about 14.95–15.05 V is above the commonly recommended 14.4 V limit for normal 12 V lead-acid charging, so the charger should be supervised and disconnected manually when the battery reaches the proper end-of-charge voltage [#13383719][#13384723] One reply also noted that the measured charging current was 1.15 A, which suggests the battery was still accepting charge, but that does not mean the front-panel meter is a reliable measure of fullness [#13383695][#13384723] The later 12.60 V battery reading after an overnight charge showed the battery voltage, not the rectifier scale, is the meaningful value to watch [#13384689]
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  • #1 13383402
    Legoo
    Level 9  
    Posts: 33
    Rate: 20
    Hello everyone, I have been charging the battery for 10 hours now and the charge indicator on the rectifier is stuck at half scale. 4A RMS rectifier, 53 ah battery, what could be the problem? I will add that when I apply the meter to the connected rectifier, the meter shows a voltage of 14.95 on the terminals. Is it supposed to be like that? at noon the voltage on the terminals was 15.05
    Rectifier Only Charges 53Ah Battery to Half After 10 Hours - Voltage Readings Inside
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  • #2 13383506
    olekt2002
    Level 31  
    Posts: 1867
    Help: 147
    Rate: 500
    Do you have a user manual for this rectifier? If so, what does it say about it? In your opinion, what voltage should be present at the poles of a charged battery?
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  • #3 13383522
    DziadzioMiecio
    Level 27  
    Posts: 1193
    Help: 70
    Rate: 142
    You probably have a meter needle stuck in the charger.
  • #4 13383538
    Legoo
    Level 9  
    Posts: 33
    Rate: 20
    The voltage at which the device operates is limited to 14.1v, which protects the charger against overheating and allows the battery to be charged without the need to constantly monitor this process. That`s what I write in the manual, strange that it limits it to 14.1v and now I have 14.96v on the terminals
  • #5 13383607
    Grzegorz740
    Level 37  
    Posts: 4135
    Help: 313
    Rate: 551
    If you disconnect the rectifier from the battery, will the needle on the rectifier meter move to the initial zero position? That is, to the right. Because maybe the tip actually got hung up.

    There is actually something wrong with this tension. Maybe they made a mistake in the instructions.
  • #6 13383622
    Legoo
    Level 9  
    Posts: 33
    Rate: 20
    With the rectifier disconnected, the pointer is in the full position as in this photo
    Rectifier Only Charges 53Ah Battery to Half After 10 Hours - Voltage Readings Inside
  • #7 13383630
    Grzegorz740
    Level 37  
    Posts: 4135
    Help: 313
    Rate: 551
    Try gently tapping the meter in the rectifier, maybe the needle will move.
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  • #8 13383643
    Legoo
    Level 9  
    Posts: 33
    Rate: 20
    I opened the aperture and tried to move the hand to the initial position, but it automatically returns to the full position.
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  • #9 13383665
    Grzegorz740
    Level 37  
    Posts: 4135
    Help: 313
    Rate: 551
    Legoo wrote:
    With the rectifier disconnected, the pointer is in the full position as in this photo
    Rectifier Only Charges 53Ah Battery to Half After 10 Hours - Voltage Readings Inside


    This is an interesting thing. It should be otherwise. Thinking logically.

    If you have a good multimeter at home, connect it and measure the current while charging the battery.

    Added after 1 [minute]:

    The meter in the rectifier may be damaged.
  • #10 13383695
    Legoo
    Level 9  
    Posts: 33
    Rate: 20
    The current is 1.15 Ampere
  • #11 13383719
    zwolmar
    Level 16  
    Posts: 144
    Help: 15
    Rate: 33
    It is only an indicator, not a measure and its accuracy is non-existent. Use a meter and do not charge above 14.4V. You may damage your battery. If possible, check the electrolyte density. In a fully charged and functional battery it should be within 1.28g/cm3 at a temperature of +20C,
  • #12 13383738
    Legoo
    Level 9  
    Posts: 33
    Rate: 20
    Thank you for your comments on the topic. I have a meter, so I will do this, I will rely on the meter reading. If it reaches 14.4 V, I will finish charging.
  • #13 13383739
    Grzegorz740
    Level 37  
    Posts: 4135
    Help: 313
    Rate: 551
    I don`t know what the current was at the beginning of charging, because maybe 1.15 A is an indication that the battery is already charged. And this meter in the rectifier reads incorrectly.

    Does it say in the manual how long it takes to charge the battery? Because it may turn out that 10 hours is not enough.

    You can also disassemble the rectifier, disconnect the rectifier meter and connect a multimeter instead and observe the current on the multimeter.
  • #14 13383748
    Legoo
    Level 9  
    Posts: 33
    Rate: 20
    I write in the instructions to determine for yourself, according to calculations, how long you should land
  • #15 13383800
    zwolmar
    Level 16  
    Posts: 144
    Help: 15
    Rate: 33
    Legoo wrote:
    I write in the instructions to determine for yourself, according to calculations, how long you should land

    It is impossible to calculate the required charging time because:
    -it is not known how much Ah capacity is missing in the battery
    -it is not known how much Ah it received from the rectifier because we do not know the charging current and it varies over time and depends on the state of charge.
  • #16 13383826
    Legoo
    Level 9  
    Posts: 33
    Rate: 20
    Tell me, Grzegorz740, how should I plug in this meter, what did you say, I opened the casing and what next?
    Rectifier Only Charges 53Ah Battery to Half After 10 Hours - Voltage Readings Inside
  • #17 13383963
    zwolmar
    Level 16  
    Posts: 144
    Help: 15
    Rate: 33
    Legoo wrote:
    Tell me, Grzegorz740, how should I plug in this meter, what did you say, I opened the casing and what next?
    Rectifier Only Charges 53Ah Battery to Half After 10 Hours - Voltage Readings Inside

    Do not disassemble anything, connect the meter (voltmeter) to the battery terminals. Will be
    the most accurate measurement, without error due to voltage drop on the cables.

    Added after 16 [minutes]:

    The photo shows that there is no system in the rectifier that controls the charging process. It only contains a toroidal transformer with a symmetrical secondary winding, two diodes (probably 3A), a charging current indicator, a power switch, cables, a housing and that`s all. Unfortunately, you have to use a voltmeter, e.g. a multimeter. There are also special LED voltage indicators - testers - showing battery voltage on sale. Very convenient to use and accurate enough.

    Added after 4 [minutes]:

    E.g. like this:
    http://allegro.pl/listing/listing.php?order=d&string=tester+alternatora
  • #18 13384089
    balonika3
    Level 43  
    Posts: 10926
    Help: 1297
    Rate: 3645
    Legoo wrote:
    With the rectifier disconnected, the pointer is in the full position as in this photo
    Rectifier Only Charges 53Ah Battery to Half After 10 Hours - Voltage Readings Inside
    Do you all think? The "full" position means no current consumption, i.e. with the rectifier turned off, it is rather logical. The drawing of an empty battery indicates the maximum current consumption, so this indicator is an ordinary ammeter calibrated in "kindergarten" units. And also voltage - who said that voltage above 14.4V is harmful to the battery? Does anyone here know what the correct voltage of a charged battery is with the charger connected?
  • #19 13384153
    zwolmar
    Level 16  
    Posts: 144
    Help: 15
    Rate: 33
    balonika3 wrote:
    Legoo wrote:
    With the rectifier disconnected, the pointer is in the full position as in this photo
    Rectifier Only Charges 53Ah Battery to Half After 10 Hours - Voltage Readings Inside
    Do you all think? The "full" position means no current consumption, i.e. with the rectifier turned off, it is rather logical. The drawing of an empty battery indicates the maximum current consumption, so this indicator is an ordinary ammeter calibrated in "kindergarten" units. And also voltage - who said that voltage above 14.4V is harmful to the battery? Does anyone here know what the correct voltage of a charged battery is with the charger connected?

    Answer to the question: YES.
    The maximum cell voltage of a lead-acid battery is 2.4V. Therefore, the popular 12 volt battery can be charged to a voltage of 6x2.4 = 14.4V. Is that right or have I made a mistake?
  • #20 13384173
    balonika3
    Level 43  
    Posts: 10926
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    Rate: 3645
    zwolmar wrote:
    Is that right or have I made a mistake?
    Oh, you made a lot of mistakes...
  • #21 13384210
    zwolmar
    Level 16  
    Posts: 144
    Help: 15
    Rate: 33
    Toroids are most often wound with 11.5V at the output, sometimes even more.
    11.5V-0.7V (voltage drop across the diode) x √2 ≈15.3V at max. sinusoids. This voltage can be fatal when the rectifier is connected for a very long time. Unless the battery is epilepsy and has a high self-discharge current.

    Added after 1 [minute]:

    balonika3 wrote:
    zwolmar wrote:
    Is that right or have I made a mistake?
    Oh, you made a lot of mistakes...

    Enlighten me.
  • #22 13384230
    balonika3
    Level 43  
    Posts: 10926
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    Rate: 3645
    Old books gave a voltage of 15.6 - 16.2V. Old batteries lasted up to 10 years. And these old rectifiers actually charged like that. Today, the battery is supposed to die right after the warranty expires, and the rectifier is supposed to help it.
  • #23 13384377
    zwolmar
    Level 16  
    Posts: 144
    Help: 15
    Rate: 33
    I wonder why regulators in alternators ensure that the voltage does not exceed 14.0÷14.2V?
    As for durability: 1- the life of the battery is determined by the number of complete discharge-charge cycles and in the era of a multitude of energy consumers, this number is exhausted faster. It used to be just starting, and now there is an alarm, radio, computer, watches and other gadgets with the engine turned off,
    2-producers are not interested in the durability of anything, because they would have no market. So every 3÷4 years you have to buy a new one.
    3- the users themselves took better care of their batteries, because there was a problem with the new ones. Is anyone nowadays interested in the amount of water or the density of the electrolyte (of course, it is often impossible, but even where it can be checked, no one bothers so much. Why, it says MAINTENANCE-FREE.
  • #24 13384416
    wzagra
    Level 33  
    Posts: 1965
    Help: 224
    Rate: 277
    Quote:
    Old batteries lasted up to 10 years

    ...because the plates in the batteries were thicker - and now, due to cost cutting, they are not.

    Umax=14.4V
  • #25 13384689
    Legoo
    Level 9  
    Posts: 33
    Rate: 20
    After the whole night, I checked the battery voltage and it was 12.60.
    It turns out that this indicator was factory broken
  • #26 13384723
    zwolmar
    Level 16  
    Posts: 144
    Help: 15
    Rate: 33
    It`s not broken. Your charging voltage is too high (more than 14.4V) and therefore the battery was constantly being charged and even overcharged, and the "meter", i.e. the charging current indicator, constantly showed that current was flowing to the battery. The battery no longer needed it, but the rectifier forced further flow. I have already written to you that the charger does not have any protection and therefore you have to supervise the end of the charging process and turn off the charger yourself. The 14.4V battery voltage is one (but not the only) sign of charging.

    Added after 5 [minutes]:

    You yourself wrote that the current was 1.15A, so the indicator showed it, and the fact that this current was unnecessary and overloaded the battery was not his fault.
  • #27 13384768
    balonika3
    Level 43  
    Posts: 10926
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    Rate: 3645
    zwolmar wrote:
    I wonder why regulators in alternators ensure that the voltage does not exceed 14.0÷14.2V?
    Because the alternator is mainly used to power the receivers, not to charge the battery, so it must have a constant voltage. At the same time, it recharges the battery.
  • #28 13385327
    zwolmar
    Level 16  
    Posts: 144
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    Rate: 33
    But in turn, the load voltage is adjusted to the battery voltage. Isn`t it?
  • #29 13385563
    balonika3
    Level 43  
    Posts: 10926
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    Rate: 3645
    zwolmar wrote:
    But in turn, the load voltage is adjusted to the battery voltage. Isn`t it?
    NO. Up to a certain voltage range.
  • #30 13385592
    zwolmar
    Level 16  
    Posts: 144
    Help: 15
    Rate: 33
    An academic discussion began, contributing nothing and taking up time in the style of "which came first, the egg or the chicken". I will contact you when there is something important.
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Topic summary

✨ The discussion revolves around a rectifier that is unable to fully charge a 53Ah battery after 10 hours, with the charge indicator stuck at half. The rectifier outputs a voltage of 14.95V, which is higher than the manual's stated limit of 14.1V. Participants suggest checking the rectifier's user manual, measuring the charging current with a multimeter, and considering the possibility of a faulty meter. Concerns are raised about the potential for overcharging the battery due to the high voltage, and the importance of monitoring the charging process to prevent damage. The conversation also touches on the differences between cyclic and buffer charging, and the implications of modern battery technology on charging practices.
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FAQ

TL;DR: After 10 h a 4 A charger can supply only about 40 Ah, far from fully re-filling a 53 Ah battery, and "use a voltmeter" [Elektroda, zwolmar, post #13383963] Keep voltage ≤ 14.4 V or risk gassing. Why it matters: Correct voltage control doubles battery life by preventing plate corrosion.

Quick Facts

• Cyclic-charge voltage: 14.4 – 15.6 V; some manuals allow 16 V [tzok, #13404690 ; 514242, #13385660] • Float/buffer voltage ceiling: 13.8 – 14.4 V [tzok, #13404690] • Recommended current: 0.1 C (≈5 A for 53 Ah) [tzok, #13404690] • Fully charged open-circuit voltage: 12.6 – 12.8 V @ 20 °C ["Battery University"] • Lead-acid charging efficiency ≈ 85 %; restoring 53 Ah needs ≈ 62 Ah input ["Battery University"]

Why did the rectifier’s pointer freeze at half scale?

The panel ammeter’s spring sits reversed: with no current it points to “full,” confusing the scale. Users saw the needle jam even after tapping [Elektroda, Legoo, post #13383643] The meter likely left the factory mis-calibrated or warped by heat, so readings are unreliable [Elektroda, Grzegorz740, post #13383665]

Is 15 V normal while charging a 12 V lead-acid battery?

Momentary 15 V is common during cyclic charging, but sustained 15 V overheats plates and boils electrolyte. Most alternators cap at 14.0–14.2 V [Elektroda, zwolmar, post #13384377] Stay below 14.4 V for float service [tzok, #13404690].

What voltage shows a 53 Ah battery is full?

Resting voltage of 12.6–12.8 V at 20 °C indicates ≈100 % state of charge ["Battery University"]. During charge, end the cycle when on-charge voltage holds 14.4 ± 0.1 V for 30 min and current falls below 0.05 C (≈2.5 A).

How long to recharge 53 Ah with a 4 A transformer charger?

Divide missing amp-hours by charger current, then add 15 % losses. Example: from 50 % (≈26 Ah missing): 26 Ah ÷ 4 A × 1.15 ≈ 7.5 h. A full 0–100 % recovery needs about 15 h (statistic) [tzok, #13404690].

Is voltage above 14.4 V always harmful?

Not always. Cyclic chargers finish at 15–15.6 V to equalise cells [tzok, #13404690]. Yet leaving a simple unregulated charger at >14.4 V for days causes water loss and plate sulphation [Elektroda, zwolmar, post #13384723]

How do I accurately measure charging current?

Insert a multimeter in series with either battery lead. How-To:
  1. Set meter to 10 A range and break the positive lead.
  2. Connect meter probes in series (red to charger, black to battery).
  3. Power ON and read current. Stay below meter limit [Elektroda, zwolmar, post #13383963]

What’s the difference between cyclic and float charging?

Cyclic: battery repeatedly discharges then recharges; finish at ≈15 V, current 0.1 C, 14–18 h max [tzok, #13404690]. Float: battery stays connected permanently; hold 13.8–14.4 V, tiny maintenance current ≤ 0.01 C [tzok, #13404690].

What happens if I overcharge this battery?

Over-voltage accelerates corrosion and vents hydrogen. One study shows capacity can drop 20 % after 50 hours at 15.8 V ["Battery University"]. Edge-case: sealed VRLA may swell or rupture because gas cannot escape safely.

How does cold weather change charging rules?

At −20 °C internal resistance rises; raise finish voltage by 0.03 V / °C, so 14.7 V is acceptable [Elektroda, zwolmar, post #13422419] Charging time also extends about 30 % because chemical reactions slow ["Battery University"].

How can I judge state of charge without a hydrometer?

Measure open-circuit voltage 12 h after charging: 12.8 V ≈ 100 %, 12.4 V ≈ 50 %, 12.0 V ≈ 0 % ["Battery University"].

Why does the alternator charge lower than 15 V?

An alternator mainly powers electrical loads; it must stay within 14.0–14.2 V to protect electronics while still topping the battery [Elektroda, balonika3, post #13384768]
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