• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Charging batteries in series with 20 amps

Status
Not open for further replies.

SimonTHK

Member
Hello
I have 6 batteries all 6 volts 200 ah connected in series, charged with 24 amp 36v charger.

My quistion:

The charger delivers 24 amps.... will it charge each cell with 24 amps? Or will the amps be shared over the cell´s, delivering 6 amp charge to each cell?

Thanks you in advance


My problem is, that I connected 6 new chargers, 6v, one to each cell, charging 4 amps. This seems to work great, but I now have my doubt´s if I am charging alot slower than the old setup.

best regards Simon
 

JimB

Super Moderator
Most Helpful Member
The charger delivers 24 amps.... will it charge each cell with 24 amps? Or will the amps be shared over the cell´s, delivering 6 amp charge to each cell?
If they are connected in SERIES, the same current will flow through all of the cells. There is nowhere else for the current to go.

However, the voltage across each cell my be slightly different, depending on the state of charge of the individual cells.

My problem is, that I connected 6 new chargers, 6v, one to each cell, charging 4 amps. This seems to work great, but I now have my doubt´s if I am charging alot slower than the old setup.
Yes you will be charging at a slower rate.
The original setup was charging at 24 amps, the new setup is charging at 4 amps.

JimB
 

MikeMl

Well-Known Member
Most Helpful Member
Same system as my EzGo Golf Cart. Using the recommended charge method, the batteries are "equalized" on every recharge. Their charger is voltage limited (poorly, using a ferro-resonant transformer-rectifier) which if that is all there is would taper the charging current downward from an initial ~25A to about 5A as the batteries reach full charge. The 5A current left on indefinetly is what equalizes the charge in the cells, but consumes electrolyte in the process, so must be time limited to no more than about 4h per recharge. Older chargers used a mechanical time clock; newer ones have a solid-state timer.
 

spec

Well-Known Member
Most Helpful Member
Hy SimomTHK,

Your old arrangement was charging each battery at 24A and your new charger will be charging each battery at 4A, which means that the batteries will take six times longer to charge. But having a charger for each battery is a much better arrangement because the voltage across each battery is controlled independently according to the needs of each battery.

If you are not worried about the long charging time that is fine. The batteries would be very happy about such a light charge. If you want a fast charge, six 20 Amp chargers would be ideal.

spec
 

MikeMl

Well-Known Member
Most Helpful Member
SimonTHK ,

Are your batteries flooded-cells, or are they AGMs?

Are you drawing load current from a tap between the series string of 18 cells, or is the load connected only to the entire string?
 

SimonTHK

Member
Hy SimomTHK,

Your old arrangement was charging each battery at 24A and your new charger will be charging each battery at 4A, which means that the batteries will take six times longer to charge. But having a charger for each battery is a much better arrangement because the voltage across each battery is controlled independently according to the needs of each battery.

If you are not worried about the long charging time that is fine. The batteries would be very happy about such a light charge. If you want a fast charge, six 20 Amp chargers would be ideal.

spec
If problem gets big, with charging time. I just needa buy bigger chargers, and make new setup :) I just liked them 4A, small, cozy, silent, cheap chargers.

Thank you that is great to know. I believe for the better charging of each cell (6 chargers), I have an advantage vs the 24 amp quick charge.. The old setup was overcharging some cell´s and some didnt follow in voltage. Some cell´s might have reached high voltage very quickly, tus turning of the 24 amp charger. So for now, the slow charge, might give me more anyway :)
It does seem that my old 24 amp charger does have some off switch when reaching 40 - 41v. Now I havnt used much time on this project at all, so I dont know all details of the charger, but it does turn off.

Generally, as I am working with these kind of cell´s often, and getting more experience. I run into the problem of cells charging very differently, when put in series with 1 charger, and can cause alot of damage. I work with electric bycicle, scooter, etc etc, all kind og electric transportation. Customers quite often seem to change whole battery packs, as when only 1 is damaged, and the cell´s just get damaged way to often, when put in series.
In my experience it can cause:
-Charger never to turn off.
-Charger to turn off too early.
-Overcharging of some cell´s.
-No charging of other´s.
-One damage or worse cell, damage other.

So I like the idea of microprocessor controlled charger´s on each battery. Also it should give give the possibility to only change 1 damaged battery, because they are not dependant of each other´s simultanously internal resistance (or whatever is going on). Atleast not for charging.
 

SimonTHK

Member
SimonTHK ,

Are your batteries flooded-cells, or are they AGMs?

Are you drawing load current from a tap between the series string of 18 cells, or is the load connected only to the entire string?
The are flooded cell.
I dont understand your last quistion. Why you say 18 cells, it must be because each 6v pack, contains 3 cells? The load is if I understand you correct, drawing current from the entire string. The string of cells are together 36v, and the controller is 36v.
Normally I would never take power from in between a string. Last week I changed a setup that lowered speed of a motor by running over half the battery pack, to using an intelligent controller S-drive.
 

dr pepper

Well-Known Member
Most Helpful Member
If you want to charge 6 batteries with 6 chargers while they are still connected in series there is one very important thing you need to make sure, and that is the charger outputs must all be isolated from each other, if for some reason the charger - o/p is connected to ground then you'll short the batteries out.
 

spec

Well-Known Member
Most Helpful Member
If problem gets big, with charging time. I just needa buy bigger chargers, and make new setup :) I just liked them 4A, small, cozy, silent, cheap chargers.

Thank you that is great to know. I believe for the better charging of each cell (6 chargers), I have an advantage vs the 24 amp quick charge.. The old setup was overcharging some cell´s and some didnt follow in voltage. Some cell´s might have reached high voltage very quickly, tus turning of the 24 amp charger. So for now, the slow charge, might give me more anyway :)
It does seem that my old 24 amp charger does have some off switch when reaching 40 - 41v. Now I havnt used much time on this project at all, so I dont know all details of the charger, but it does turn off.

Generally, as I am working with these kind of cell´s often, and getting more experience. I run into the problem of cells charging very differently, when put in series with 1 charger, and can cause alot of damage. I work with electric bycicle, scooter, etc etc, all kind og electric transportation. Customers quite often seem to change whole battery packs, as when only 1 is damaged, and the cell´s just get damaged way to often, when put in series.
In my experience it can cause:
-Charger never to turn off.
-Charger to turn off too early.
-Overcharging of some cell´s.
-No charging of other´s.
-One damage or worse cell, damage other.

So I like the idea of microprocessor controlled charger´s on each battery. Also it should give give the possibility to only change 1 damaged battery, because they are not dependant of each other´s simultanously internal resistance (or whatever is going on). Atleast not for charging.
Yes, charging batteries in series is fraught with problems. The best way to charge the batteries is independently and to use a smart charger which takes into account the individual battery condition and its chemistry.

There is another issue too. If you are going to charge up a battery and then discharge it to a low level you need deep discharge batteries rather than the automobile type. If you use the ordinary automobile type batteries for deep discharge they will quickly sulfate up and go high resistance. In general, lead acid batteries do not like being in a discharged state.

spec
 
Last edited:

spec

Well-Known Member
Most Helpful Member
If you want to charge 6 batteries with 6 chargers while they are still connected in series there is one very important thing you need to make sure, and that is the charger outputs must all be isolated from each other, if for some reason the charger - o/p is connected to ground then you'll short the batteries out.
Most chargers have a fuse which would take care of that situation.

spec
 

MikeMl

Well-Known Member
Most Helpful Member
The are flooded cell.
Flooded-cell deep-cycle batteries, like the ones in my 36V golf cart, are designed to be "equalized" by charging the entire sting of 18 cells in-series. These batteries will tolerate a moderate overcharge, so by passing the same current through all 18cells at once, and going a bit past the point where the first cells reach full charge, the weaker cells are brought up to the correct Specific Gravity.

As I said in my earlier post, the chargers made for this application accomplish an "equalization" during each re-charge cycle, where the first cells to reach full charge are a bit overdriven so that the weaker cells in the string also come up to full-charge. As long as you add water periodically, these batteries last a long time used this way. This method is used in golf carts, forklifts, scissor lifts, etc...

I think it is a mistake to use six independent chargers. Since each battery has three cells, you are still dealing with the equalization cell by cell, but only three cells at a time. You haven't eliminated the need for it, just made it harder to manage...
I dont understand your last quistion. Why you say 18 cells, it must be because each 6v pack, contains 3 cells? The load is if I understand you correct, drawing current from the entire string. The string of cells are together 36v, and the controller is 36v.
Normally I would never take power from in between a string. Last week I changed a setup that lowered speed of a motor by running over half the battery pack, to using an intelligent controller S-drive.
I have seen golf carts that have 12V lighting (headlamps, tail lights, brake lights, maybe an entertainment radio) which is tapped six cells up from the ground end of the 36/48V string, but this added load on the lower six cells always unbalances them relative to the upper 12 cells, and makes it difficult to equalize the string. Here is a case where you might be tempted to use two chargers, or properly fix the problem by using a buck converter to reduce 36/48V to 12V, and then use a single charger...

These are typical of the batteries used in golf carts, and happen to be the ones in mine...

Typical battery charger (made by Lester) for the batteries above... I have a schematic of one like this if it comes to it... The timer in one I have crapped out, and I built my own using an Arduino....
 
Last edited:

tcmtech

Banned
Most Helpful Member
So I like the idea of microprocessor controlled charger´s on each battery. Also it should give give the possibility to only change 1 damaged battery, because they are not dependant of each other´s simultanously internal resistance (or whatever is going on). Atleast not for charging.
One major oversite in that theory. You are not factoring in discharging rate and energy stored per battery or per cell which will vary greatly between an older battery and a new one and when the load is drawing from all of them in series the ones with the lowest Ah will go dead first and very likely be run in reverse until the higher capacity cells drop off far enough for the system to shut down.
With large multicell battery systems as little as a 5% differnce in Ah between the highest and lowest capacity cell is enough to start doing damage to the whole battery set as its being used and recharged.

Simply put if one battery has a bad cell it it has just as much effect on the discharge and subsequent energy consumption rates from all the other cells as it does in the charging mode.

Your theory of only changing out a bad battery in the set still causes major problems in the end hence the rule of if one battery goes bad all batteries get replaced thusly with your multi charger setup you have in fact gained nothing but made the whole process slower and overly complicated for no good reason or long term measurable gains. :(

If I was dealing with a 36 volt 200 Ah battery bank I would have went with a single properly sized 36-volt smart charger instead of six 6-volt chargers.
 

spec

Well-Known Member
Most Helpful Member
As I said before, charging each battery independently is, by definition, the best for performance and for battery life. There is no reason for thinking otherwise. Serial charging is only done for low cost and convenience. ie you have one charger. But some serial chargers have complex and unsatisfactory balancing circuits to try to correct some of the shortcomings of serial charging. In these cases the charging circuit is far from simple.

Battery charging, with all types of battery, is based on battery voltage not current (the current is limited though).

Plus the fact that the OP has stated that he has had problems with serial charging and has already installed individual charging, presumably for that reason.

Yes, lead acid batteries are made up of individual cells, which is unfortunate because you cannot get at them, but at least the cells are going to be very similar as they are made at the same time, run at more or less the same temperature, and have the same dimensions and chemical composition.

Non-the-less, when a multi cell battery fails it is often because only one cell has failed while the others are OK.

All of the problems listed apply to batteries in series, which is always bad news, not about the charging method per se.

spec
 
Last edited:

spec

Well-Known Member
Most Helpful Member
Flooded-cell deep-cycle batteries, like the ones in my 36V golf cart, are designed to be "equalized" by charging the entire sting of 18 cells in-series. These batteries will tolerate a moderate overcharge, so by passing the same current through all 18cells at once, and going a bit past the point where the first cells reach full charge, the weaker cells are brought up to the correct Specific Gravity.

As I said in my earlier post, the chargers made for this application accomplish an "equalization" during each re-charge cycle, where the first cells to reach full charge are a bit overdriven so that the weaker cells in the string also come up to full-charge. As long as you add water periodically, these batteries last a long time used this way. This method is used in golf carts, forklifts, scissor lifts, etc...

I think it is a mistake to use six independent chargers. Since each battery has three cells, you are still dealing with the equalization cell by cell, but only three cells at a time. You haven't eliminated the need for it, just made it harder to manage...

I have seen golf carts that have 12V lighting (headlamps, tail lights, brake lights, maybe an entertainment radio) which is tapped six cells up from the ground end of the 36/48V string, but this added load on the lower six cells always unbalances them relative to the upper 12 cells, and makes it difficult to equalize the string. Here is a case where you might be tempted to use two chargers, or properly fix the problem by using a buck converter to reduce 36/48V to 12V, and then use a single charger...

These are typical of the batteries used in golf carts, and happen to be the ones in mine...

Typical battery charger (made by Lester) for the batteries above... I have a schematic of one like this if it comes to it... The timer in one I have crapped out, and I built my own using an Arduino....
You have just made the case for using independent chargers. :)
 

MikeMl

Well-Known Member
Most Helpful Member
...Battery charging, with all types of battery, is based on battery voltage not current (the current is limited though)...
Many modern chargers monitor charging current, and switch modes when the charge acceptance reaches certain limits...
 

spec

Well-Known Member
Most Helpful Member
One major oversite in that theory. You are not factoring in discharging rate and energy stored per battery or per cell which will vary greatly between an older battery and a new one and when the load is drawing from all of them in series the ones with the lowest Ah will go dead first and very likely be run in reverse until the higher capacity cells drop off far enough for the system to shut down.
With large multicell battery systems as little as a 5% differnce in Ah between the highest and lowest capacity cell is enough to start doing damage to the whole battery set as its being used and recharged.

Simply put if one battery has a bad cell it it has just as much effect on the discharge and subsequent energy consumption rates from all the other cells as it does in the charging mode.

Your theory of only changing out a bad battery in the set still causes major problems in the end hence the rule of if one battery goes bad all batteries get replaced thusly with your multi charger setup you have in fact gained nothing but made the whole process slower and overly complicated for no good reason or long term measurable gains. :(

If I was dealing with a 36 volt 200 Ah battery bank I would have went with a single properly sized 36-volt smart charger instead of six 6-volt chargers.
You have also just made the case for individual chargers. :)
 

MikeMl

Well-Known Member
Most Helpful Member
You have just made the case for using independent chargers. :)
Why? The batteries in my golf cart are over ten years old, and still going strong. The secret is replenishing electrolyte, not allowing the batteries to sit discharged, be cognizant of self-discharge in hot weather... Why try to fix something that isn't broken?
 

SimonTHK

Member
Thank you for your many insight´s into this. I also have my own insight´s to add :D
Firstly the cell´s used here, are 1 year old trojan 200 ah 6v flooded cell, that apparently needs to be filled with destilled water from time to time. Great to know this quite an important factor. I am normally just used to use those deep cycle lead acid batteries, closed ones.

I have had experience with another application´s, which I have fixed with independent chargers.

Using cells in in different condition: I have had a situation where 1 out of 4 batteries in a series connection kept getting too high voltage. I tried and change it with another battery, but it kept overcharging the 12v battery to 16v, heating up way to much. I tried 3 different batteries on that place in the string, same happened. I changed to 4 chargers, and now none of the cell´s get overcharged and all of them is charged up to a fine 14,2 v.

The golfcart right now, had the 1 cell bubling with water after 15 minutes of charging time. Batteries are 1 year old.

Also I should mention, that maybe the charger can have an effect on the final output of the golfcart battery pack, since I have made some observations, and now you guys teach me new stuff!!!
The charger is a standard golfcart charger from Huyndai. Now I havnt had much time on the project, but it did seem like it turn´s off charging at only 40v. The batteries are Trojan, and if I read on trojan homepage, it says that the equalize charging voltage per cell should be 8,1v, which is 48,6v, which seems to be alot. Bulk charge is 7,4 v. I wonder if the charger should allways deliver 48,6v for equalizing. Also I was not able to measure more than 40,5v while the 24 amp old charger was connected.

I dunno where I stand right now, I needa do more testing. I cant seem to why 6 chargers should be a bad idea, unless it is because it charges slower. Maybe because it actually does NEED to be equalized to maintain itself, and that doesnt happen with the 6 chargers, they just charge them to a 43,2v.
I think I will try and write to trojan aswell. They must be able to tell me right or wrong on this matter.
 

dr pepper

Well-Known Member
Most Helpful Member
I maintain fork lift trucks amongst other things, as chargers have got more advanced batteries last much longer, I spose batteries have improved too.
Flts vary from 24v to 96v, so far I've never seen one that didnt charge all the batteries in series without any kind of cell per cell feedback or balance charging, later chargers have a compressor built in to degas the cells but thats about it.
I'd be interested to see the day when we have lipo material handlers.
The life of a flt battery if the truck has one responsible driver can be years, if there are a hoard of numpty's using the machine that dont care about it the first winter it sees and its dead.
 

spec

Well-Known Member
Most Helpful Member
Many modern chargers monitor charging current, and switch modes when the charge acceptance reaches certain limits...
I'm not sure what you are saying here. If you charge a battery at a constant current of say C/10 and pay no attention to the battery voltage you will either boil off all the electrolyte or the battery will explode.

spec
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top