Battery Charging Timing.

[pmmali]

Dear friends,

I have a small question about battery charging. this question I have a long time on my mind.

I wish to know how to calculate any battery charging time
(How long need to charge? what kind of charger/ how many amperes should be on the charger)

examples
let's say I have 60V/28Ah lead acid batteries ( 12V/28Ah x5 series batteries )
how long time this battery will take to charge from a 60V 2A charger?
for a 60V lead acid battery how much maximum voltage i can give it.

 

[harrisonpatm]

1 Ah is one amp hour, meaning a constant use of 1 amp for 1 hour.

You have 60v, 28ah battery. You have a 60v, 2amp charger. 28ah/2amps = 14 hours charge time. If you get a 4 amp charger, it will take 7 hours. If you get a 1 amp charger, it will take 28 hours.

Note that this is all on paper. In a real world scenario, your exact battery capacity and exact charger output will vary.

For lead acid, 12v nominal voltage requires about 14.5v to charge. You have 5 in series. Meaning your max charging voltage for 60v nominal is 72.5v

 

[amberwolf]

Some technical info that may or may not be important, but placed here for future readers if it doesnt' matter to the OP:


I recommend using a charger that is made for lead-acid, rather than one that's for lithium, etc. Some chargers like the http://ebikes.ca Cycle Satiator have programmable profiles that include charging curves/parameters preset for several different kinds, including lead-acid. Note that there are also several kinds of lead-acid batteries, some of which charge differently than others, and will have different lifespans than expected when used with chargers not meant for them.


Each 12v lead acid battery brick should have printed on it's side what charge rate it can accept. Don't charge it at a higher current than it is rated for, or it will begin to outgas it's electrolyte (which you typically cannot put back, so it damages the brick more and more each time you do it).

Any battery that does not have the data printed on the side, you should look up the manufacturer's data sheet or charging guide for that brick's specific model and brand.


A random example from an image search on "SLA battery" shows the charging voltage for either floating (UPS, etc) or cyclic (EV) usages, and the maximum (they call initial) current allowable, which for this specific 12v12Ah SLA is only 3.6A:




Another random example of one that does not have the data printed on it:

but the data is available at their website that's printed on there, by the model that is also printed:
http://www.power-sonic.com
PS-12120 F2
https://www.power-sonic.com/product/ps-12120/
https://www.power-sonic.com/wp-content/uploads/2018/12/PS-12120%20technical%20specifications_US.pdf
View attachment PS-12120%20technical%20specifications_US[1].pdf
which gives charging rate for this one, per the quote below, as "0.25C amps" which means 0.25 x the capacity (in Ah) of the battery. It's a 12Ah battery, so 0.25 x 12 = 3A. It says "less than" that, so 2.99999A would be the maximum charge current. Less is better.

CHARGING
Cycle Applications: Apply constant voltage charge at
2.35v/c – 2.45v/c (14.1 – 14.7v for 12v Monobloc) at 20°C.
Initial charging current should be set at less than 0.25C
Amps. Switch to float charge to avoid overcharging.
“Float” or “Stand-By” Service: Apply constant voltage
charge of 2.25v/c – 2.30v/c (13.5 to 13.8 volts for 12v
Monobloc at 20°C. When held at this voltage, the battery
will seek its own current level and maintain itself in a fully
charged condition.
Temperature Compensation: Charging Voltage for both
Cyclic and Standby applications should be regulated in
relation to ambient temperature. As temperature rises
charging voltage should be reduced to prevent overcharge
and increased as temperature falls to avoid undercharge.
For further charging information including temperature
compensation factors, see Power Sonic Technical Manual/
Power Sonic Charger specifications.

And so on.



How long it will actually take to charge depends on temperature, charge current, amount of capacity used last time, etc.

Since you are using several bricks in series, and presumably a single charger with that series voltage, then as long as all the bricks are in identical condition and state of charge, they'll all charge equally over the same amount of time.

When they are not identical (either becuase they're different kinds, or have aged, etc.) then they won't charge equally, and some may overcharge (and may vent / outgas some of their electrolyte, damaging them) while others may never fully charge. The pack is then unbalanced; at that point it may operate "better" using individual, electrically-isolated, single-brick chargers on each brick in the series set. (if isolated then no connections ahve to be disconnected to charge, if not isolated all series connections must be disconnected first).

 

[john61ct]

Lead batteries used for deep cycling rarely get to 100% Full in much less than eight hours.

No matter how much current the charge source offers.

Of course if the source only offers a C-rate of 0.05C then it can take over 24hours.

Stopping early, before the endAmps spec is reached will shorten lifespan drastically.

 

[john61ct]

Only a few specialized manufacturers in the world make quality lead batteries suitable for deep cycling usage.

They are generally not sold online, it would be stupid to pay for shipping only a few hundred pounds at a time.

They are rarely sold in consumer / automotive retail channels. 99.99% of units on the market are fraudulently marketed and labeled.

Call the mfg to get a list of authorized sellers in your local area.

They publish data sheets with the technical parameters for proper care to get good longevity. Charging profile specs are just the starting point, and can vary widely from unit to unit.

When you have questions, you can communicate directly by phone or email with knowledgeable support techs, often engineers sometimes even the founding family members.

These are all based in North America, so European Australian etc buyers have to accept lower quality, or pay through the nose.

Going to LFP costs lots more up front, but done right can end up much cheaper on a per year, per usable Ah basis.

 

[Hillhater]

by pmmali » Oct 09 2022 9:58pm

Dear friends,

I have a small question about battery charging. this question I have a long time on my mind.

I wish to know how to calculate any battery charging time
(How long need to charge? what kind of charger/ how many amperes should be on the charger)….

A W gave the details above,…
..but i would emphasise that once you establish the charge rate, the biggest factor in estimating the time required will be knowing exactly the state of charge already in the battery before you start charging !

Only a few specialized manufacturers in the world make quality lead batteries suitable for deep cycling usage…….

Who mentioned deep cycle ?

 

[pmmali]

Hi
Thank you very much to everyone who replied. and thank you harrisonpatm for tell me how to calculate it.
now every one is saying divide the battery amperage by the charger amperage to get the charging time. but in real tis timing is totally different. i don't know where is mistake on battery or charger.

for example. i have 12V 9.0AH battery (its written on it) and 12V 10A charger when i charge this battery from this charger it take around 3 hours to charge. So calculation is not matching, now how can i confirm or how to measure, how much ampere this charger really giving to battery. on the same time how can i confirm or how to know what is a exact amperage on the battery
because all these Chinese batteries and chargers are written wrong or manipulated values for selling purpose.

Thank you.

 

[amberwolf]

now every one is saying divide the battery amperage by the charger amperage to get the charging time. but in real tis timing is totally different. i don't know where is mistake on battery or charger.

The actual charging rate is a curve, not linear, and depends on the state of charge SoC of the battery when you start charging, so the math is not completely straightforwardly simple. However, the simple math is an estimate that can come pretty close.

When it doesn't match reality at all, it means something is happening during charge that is not as expected, or the conditions at start or end of charge are not as expected, and you would have to measure start voltage (to guesstimate how much charge it started with), end voltage, charge current during charge, and preferably even Ah going into the battery and out of it.

for example. i have 12V 9.0AH battery (its written on it) and 12V 10A charger

If this charger is not adjustable current limit (like with an easy-to-access knob or switch on it's casing), I'd recommend strongly to use a much lower current charger for a battery that size. The charge rate listed on the battery in your picture is less than 2.7A; charging at a rate higher than that can damage the battery over time. If it's at or near the 10A rate for very long, it may really heat up the battery and boil the electrolyte away, which will damage the battery and reduce it's performance at best, or kill it so it won't hold a charge, or even swell the casing and rupture it.

when i charge this battery from this charger it take around 3 hours to charge.

The *average* charge rate for 9Ah of capacity over 3 hours is 9Ah / 3h = 3A.

(But the average is not the important number for meeting the battery's needs. )

If the battery is completely empty (at whatever the manufacturer specifies as empty voltage, but typically around 10v), then a 9Ah battery taking 3 hours to charge on a 10A charger is probably taking the full 10A at first (almost four times what the battery is designed to be charged at), rapidly dropping to a few amps, then near the end to much less, finally just trickling in.

If the battery is not completely empty, then it's not putting 9Ah in, so the average rate would be lower. Say it's half empty, 4.5Ah, so 4.5Ah / 3h = 1.5A.

But the actual charge rate is going to be different than those, and to know it with certainty you'd need to measure it with a wattmeter or ammeter (or multimeter on DC Amps, if it is designed to handle at least 10A or more).

So calculation is not matching, now how can i confirm or how to measure, how much ampere this charger really giving to battery. on the same time how can i confirm or how to know what is a exact amperage on the battery
because all these Chinese batteries and chargers are written wrong or manipulated values for selling purpose.

If you don't trust the seller specs (I often don't, but I'm sure some are honest) then you can't know what a battery actually is designed to be capable of charging at without going to the manufacturer's website and reading their specifications for the specific model battery you have. If there is no spec available, you can guesstimate what it might be, with lead batteries, by dividing the Ah marked on the battery by four (or more), and charging at a current lower than that.

Some of them may be capable of higher currents, but if you're not sure, you're safer to use lower.

To find out what current and voltage a charger is actually charging at (or how much load a bike, scooter, etc is putting on a battery when using it) you can use a wattmeter. There are many kinds, and which one to use depends on your specific usage needs. You can probably get one for less than $20-40. Some of them can do a lot of things, some only a few, all you really need is one that measures voltage (V), current (A), and amphours (Ah). If it will do Watts (W) and Watt hours (Wh) it's a bonus, and if it will save the data if power is lost even better. ISome use a shunt built into them, and some use an external one for higher currents, the latter is a bit more complicated to wire (the other just goes directly between the battery and charger or battery and controller, + to + and - to -). It must be able to handle the maximum possible current you'll ever put thru it, and the maximum possible voltage you'll ever need to charge the battery to.

 

[pmmali]

@ amberwolf

Thank you very much for your clear reply.

Regards.