When to charge the acid battery properly?

borko444

100 W
Joined
Aug 1, 2019
Messages
181
I have a question about charging the battery.
When to charge the acid battery properly.
I ask because I have a charging station next to my workplace and I can turn on the motor to charge while I'm at work, but when the battery is exhausted it takes about 7 hours to fully charge. The question is, if it is exhausted at 50%, will it turn on to charge and will it be a problem for the battery if it does not charge at 100% and reaches 90% for example?
My other question is when is a 72 volt battery completely depleted? When without load the voltage is 72 volts or less?
I have a wattmeter attached to the battery.
When the battery was exhausted, I reset the wattmeter.
After full charging indicates that I have 1500 watts of current available. As I start to drive the motor, the watts gradually decrease.
 Now the voltage is 72 volts and I still have about 500 watts left and the battery indicates that it has about 30% capacity remaining, but when I deliver full power the voltage drops to 65 volts. This, in my opinion, is a very exhausted battery, because the traction is very low. The controller is set to 45 amps and when the battery is charged I have this power, but when I apply full thrust at the above values ​​the battery voltage becomes 64 volts and it does not give more than 35 amps because it does not reach amps.
My point is: can I charge the battery whenever I want and as long as I want or always need to drain and then charge to the end.
 
Lead-acid doesn't like being discharged deeply (run right down) and likes to be kept fully charged. That said, 90% charge isn't really a problem.

Bear in mind your batteries will be sealed (VRLA) rather than flooded types - either AGM or Gel-based. The charging requirements are different for these compared "flooded" batteries on car starters or golf carts. You can't add water to a sealed battery so you definitely don't want to do any equalising and you (usually) need to keep the charge voltage lower i.e. 13.8V max. rather than 14.4V for a 12V battery.

There's a bit of charging information on this page: https://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

There's a chart showing (resting!) terminal voltage Vs. state of charge on this page: https://batteryuniversity.com/learn/article/how_to_measure_state_of_charge

The reason it's a wide grey band rather than a thin line is the answer varies a bit based on temperature. You can see though it's completely exhausted by 11.5V even when cold (warm wether boosts voltage and performance). Multiplying out by 6 batteries in a 72V pack gives you 69V to completely dead. Note, voltage under load will sag a lot lower than this. The 69V would be after load removed and ~20 mins to "settle".
 
I only ask if I can partially charge it? For example, I'm going to a close friend, but I won't have the battery to go back. Can I partially load it 1 or 2 hours to get home. It will not charge the battery but the end but I can get home. Is this bad for the battery? :)
 
Yes, you can absolutely do that (partial charge). The battery would prefer a full charge but we must be practical - if you only have 1-2 hrs for a charge then do that. Any charge is better than no charge!
 
Yes... It's not like a nickel cadmium battery... Partial charge is fine... But for sure fully charge it when you get home. Have you been manually balancing the individual batteries? Most lead acid setups don't have a balancing circuit, so unless you go in with a 12v charger to individually even them all out periodically, the voltages will drift apart, leading to some of the batteries undercharging and some of them overcharging, which will shorten the range and kill the lifespan of the batteries quickly.
 
Voltron said:
But for sure fully charge it when you get home.


Of course, once I get home, I fully charge it.

Voltron said:
Have you been manually balancing the individual batteries?

How do I balance them? I didn't do it and is there a device that does it for me?

Voltron said:
Most lead acid setups don't have a balancing circuit, so unless you go in with a 12v charger to individually even them all out periodically, the voltages will drift apart, leading to some of the batteries undercharging and some of them overcharging, which will shorten the range and kill the lifespan of the batteries quickly.


What do you mean,? Do I have to load them one by one? But I have to remove them from the scooter.
This is hard work because I have to disassemble the whole scooter. This is hard work.
Is there an acid battery balancer to do it right and solve the problem.
 
Do not leave sla half charge . The goal is to always keep them fully charged as much as possible. Never let them seat for long time depleted. That's the goal for long life.
Replace with auto grade leaf batteries when no good. Use for now.
 
So I can charge them at any time just so they don't get exhausted. Let's say for 2 days my usage drops to 50% and I can let it recharge in the evening. Right?
Or in the evening when I'm 70% to let it recharge?
 
Yes, one by one charging. I'm sure someone makes something for doing it automatically, but don't know of a specific one. And yes, it's a pain in the ass on some setups. I've had ones where I installed leads coming off the individual batteries to check their voltages without full disassembly, but you have to make sure they don't get pinched and short out.
If you have super high quality batteries they drift apart less, but it dramatically extends the range and lifespan of most packs.
 
Most lead acid battery chargers take care of balancing series strings by using a float or equalization voltage after the bulk and absorption portions of the charge algorithm. With a good quality charger, this should be enough.

With most lead acid batteries you get a 6 cell (12V) jug (case) with does not allow access to individual cells. So at best, any effort beyond the built-in charge algorithm can balance the 12V groups with each other. Which is better than nothing. When I used lead acid packs, occasionally, every 30 to 50 cycles, I'd measure each 12V battery and if significant differences showed, I'd put a quality 12V charger on each individual battery, one at a time until each one was charged properly. No need to remove or disconnect the batteries from the pack if you can safely connect the charger leads.

And yes, opportunity charging is recommended. Throw in a few Ah whenever you can.

Regards,

major
 
Sla's have trickle chargers that people leave on to keep batteries always fully charge at all times. So best to try and keep them fully charged every time and instant you have. To the best of your ability .
 
The proper way to charge lead acid to is get rid of it and replace with lithium. Unless the vehicle is a submarine.
 
No charger without balance leads can keep a lead acid string in balance. And lead acid goes out of balance constantly.

In a normal string of 6 for 72v, the charger just sees the total voltage, but one or two charge slower than the others and stay low in voltage, which isn't great, but then one or two will go to very high voltage fast, like over 15 volts, then pop the seals and cook themselves dry, and then maybe catch on fire. But the charger thinks everything is ok as it just sees the total voltage.

When I had to run lead acids for a while, I made a tester from an electric clock with hands, a lamp, and 12v to 110 inverter. When the lamp and the clock (with the hands at noon) are plugged in, it will run until it hits the low voltage cutoff of the inverter, then shut off, but the clock still shows the run duration without having to stand around watching it, which is why one with hands is better.
Then you can select ones with similar run times which minimizes the pack unbalancing.

Also many sealed lead shouldn't be trickle charged. They don't constantly self discharge as much as the flooded type, which is the point of trickle charging.

And don't mind flat tire... He's a parade rainer.
 
Re total voltage, during charging the voltage might peak at 84-85ish volts, then sag down to around 81ish (13.6 x 6) after the charger cuts off. It actually makes a noticeable speed bump using the battery hot off the charger.

70 volts is pretty empty. (11.5 x 6)
 
Here's a paper on lead acid charging explaining the algorithm including float and equalization stages. You should check with your particular battery manufacturer for his charging recommendation.

https://chargetek.com/images/pdfs/equal.pdf

major
 
What I understood was that they were better charged than standing empty. Up to 50% is no problem, but if they fall below 50% they need to be loaded and not leave them for the next day after I get home from work because then they will drop to 30%. So looking every 3 days in the evening I have to let them load.
The other thing I didn't like is that they say I charge them individually, which is very difficult because I have to dismantle all the plastics on the bike to get to the batteries. And how do I charge them one by one? As I charge the last battery, the first battery will lose some of its voltage and by connecting them together it will be crucial for the whole circuit, which is not abnormal again. The other good thing is to buy 6 chargers and charge them at the same time but this is also abnormal. I'm going to make pins on each battery but they are connected together and can I go with 6 chargers. This is not an option.
First, I either have to find a balancer or keep the batteries always charged and hope they don't get damaged in the next year, and then I'm thinking about buying lithium, but for now it's about 800 euros too expensive.
My bike is new at 1 month and the batteries are at a month old at frequent charging.
The manufacturer gives my battery life about 300 charge cycles, but how do they count?
A little thought: If I charge the batteries every 3 days and say that I will not have 300 charge cycles but only 150. It will then have about 400 days of battery life which is good for 1 year except winter and maybe a year and a half can endure.
How long do I need to charge the batteries one at a time, and is it a problem when they are connected to each other, or do I have to separate them beforehand so that they do not connect with the other batteries?
 
You don't need to separate them, or worry about the first one being different than the last one. You don't 6 simultaneous chargers.
Maybe it's not worth it to you with the hassle of getting to them, but I can almost guarantee that with heavy use, they will drift apart a lot in voltage.
And don't be confused by the the difference between equalizing the 6 internal cells that make up one 12v battery, and balancing the 6 whole batteries in your 72v string. The first is done automatically by a good charger, but not the second.
 
I do not use batteries extremely. I even limited the power consumption to 35A.
To slow the bike slower, but for me this is enough for me here in town. It's as if I've activated ECO mode. I also have a sports mode but I never use it. I did it if I needed to move fast from lane to lane or to traffic light but I don't use it. It is set to 55 A in just 10 seconds. When I activate it, I have more thrust for 10 seconds,

I have the original charger that comes with the bike, but there are so many on the internet, starting from 15 and going up to 150 euros, but there is no guarantee of their quality. How to choose? I guess mine is still good, but it's not a bad thing either. What would you recommend to me?
But what do I think about charging them more often before they drop below 40% is it good or not? And what will you tell me about the charge cycles.
 
My batteries are 6 x 12 volts 72V/20 amps.
Can you suggest me a good quality charger and how good amps are for my battery 2.5 or 3 or 4 or 5 amps
 
A charge cycle usually means taking them to empty and then back up. The more you avoid deep discharge the better, so don't wait to charge until they're way down.
 
You probably mean 20 amp hour which is different than amps. I would go at least 5 amp charger.
I don't know if you're familiar with c rate... On your 20 amp hour (ah) battery, taking 20 amps in or out of the battery is 1c. Safe charging rate for sealed lead is usually c/3, or one third of 20, or 6.6 amps.
 
this is my original charger I got with the bike
 

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