Anyone for 3-Bank Battery Charger ?

[seulater]

Its a well known fact that charging batteries in series that the end battery takes the hardest hit. Most of the time its that battery that fails first.
This is why its always best to charge them independently if you can.
Since i bought a new set of batteries i want to ensure they will last as long as possible. I just finished installing a 3-Bank On-Board Battery Charger.

Granted its a 12v 3 bank charger, so 2 cells are in series but that if far better then having all 6. Now the charger can charge these 3 cell packs independently from the rest. So if one pack is done charging it still can continue to charge the rest as they need it. The one i used for this is here:

http://www.amazon.com/gp/product/B003JSO1X2/ref=oh_details_o01_s00_i00

http://www.amazon.com/gp/product/B003JSO1X2/ref=oh_details_o01_s00_i00

[yurtle]

Originally Posted by seulater

Its a well known fact that charging batteries in series that the end battery takes the hardest hit.

That's not true. All batteries are connected in series, and moving them around will not affect the current in any way.

If you have a battery that is pulling more or less current than the others, no matter where you put them, they will pull the same current.

I'm not commenting on your setup, just the typical series setup.

[seulater]

That's not true. All batteries are connected in series, and moving them around will not affect the current in any way.

I am talking about charging not discharging.

yurtle, Say you have 2, 12v batteries. One is dead, and the other you fully charged by itself. Then you connected both in series. Now you slap a 24v charger on them and they are charging @ 20A. The "charged" battery has to pass that 20A through itself onto the dead battery where its needed. Yet the charged one needs nothing for itself. There is no way for it to pass that current along onto the other battery without itself taking more of a charge. This is why in all series batteries the end cell takes the greatest hit. Even in your car battery, if you have been around it long enough you will see that its the end cell that goes first most of the time. Same thing with charging Ni-Cad and ni-mh, series packs. After long use, the end battery is shot. typically the rest of the pack is still good.

This is also why ALL laptops, drills with Li-ION, Li-PO, RC toys, cell phones and so on now use this independent method of charging. There is a pair of wires going to each cell in the pack. So it can monitor and charge the cells individually from the rest of the pack.

[yurtle]

I don't disagree that six (or eight, in my case) independent chargers might be superior to just one, but I disagree that whether charging or discharging, the "end" batteries or cells behave any different than any other one in the pack. It is a series circuit, so there is no real "end".

Perhaps other experts can chime in, as there may be something I'm not getting here. Do "end" batteries really fail before others in the pack?

[seulater]

Its cool, we can agree to disagree.

There is an end in series setup. the most - cell and the most + cell are the end points. When you charge a series pack all the current goes from the most + cell all the way through the chain to the most - cell. This becomes even worse for charging when when one cell in the pack self discharge rate increases higher then the rest. What happens then is that particular battery require more to charge it then the rest. So the others become fully charged up sooner while this one still needs a charge. The charger does not know this because it's only looking at total current draw and total pack voltage, so it keeps pumping current into them until that weak battery gets up to snuff. Meanwhile the rest have their cheeks full waiting for the the lazy one to get finished.

Another way to see this is to take a cell reading on every battery 2 hours after a full charge. Let the cart sit 24 hours then check them again and write them down. Then drive it hard. take readings again, you will see that from one end battery all the way around to the other end battery the voltages will get lower and lower as you make your way around to the opposite end.

A final way to observe this in charging is to measure the cell temperatures. While taking a full charge. You If you take a temp reading at the most + cell that will be hotter than the most - cell.

[yurtle]

I too don't mind disagreeing, and even if proven wrong, I've learned something. If you're correct, haven't you now created six end cells, where you used to only have two?

[yurtle]

In a series circuit, current is the same for ALL cells. There is NO end cell.

Voltage drop will vary from cell to cell. The charger will provide whatever the pack wants, until the pack is satisfied. Unless you could provide 18 separate charging circuits - one for each cell - you still have the same problem if there is a bad cell, though perhaps it is less "harmful" with separate and isolated charging circuits.

Discharging will negate any advantage you may gain, if you have a really bad cell.

[seulater]

If you're correct, haven't you now created six end cells, where you used to only have two?

From the carts perspective nothing has changed, its still 2 end points.
From the chargers stand point, there is now technically 6 end points, but they are broken up into pairs. It all about charge current flow. You want to minimize how many cells you go through. Ideally in a 36v cart with 6 batteries, the absolute but not practical method would be to have 18 chargers. 3 for every cell in one battery.

Maybe this drawing will help my poor explanation.

In this example, the 4 charger system works best when cell B2 finishes first, the charge can stop just on that cell and continue charging the rest independently of the others. whereas on the single charger method when B2 get to a full charge the charge cannot stop because the rest still need more, yet the current has to pass through B2 to get to B1.

[seulater]

In a series circuit, current is the same for ALL cells. There is NO end cell.

You are correct for the current part, however there will always be end cells (the point at which the most + and most - terminals in the string to which the equipment is connected to). I don't feel i am getting my point across properly.
While charging if you were to throw a clamp on meter on every point in the cable you would see the same current reading. I do not dispute this. Where this becomes a problem is when a single battery in the pack already has a full charge and others don't. That charged battery still has to pass along the same current to the others. But its already charged and it cannot flick an internal switch to bypass itself out. Thus it will continue to boil when it does not need to. This is another reason why when you check battery levels they are not always equal. Its because that particular cell got charged but had to continue to pass along energy to the rest whom was not. So it continues to gas away.

[seulater]

Did you ever play with high performance RC cars or boats ?
Remember back in the Ni-Cad days when we had the 6-7-8 cell packs and you were charging them @ 20A right after a hot run what often happens.
NOTE: of course we were supposed to wait until the pack cooled down, but in the head of the moment when the race is on who can resist

The most + cell vents. This is because the most + cell charges first and is passing that remaining 20A charge through itself onto the rest who have not charged fully yet. When the pack finally craps out and you separate them to make a new pack that most + end cell is typically the junk cell.

Now that we have moved onto Li-Po packs that all have individual charge leads to each cell in the pack this no longer happens. All cells charge at their own rate, and no one gets hotter than the rest.