Anyone for 3-Bank Battery Charger ?

[yurtle]

You've gotten your point across. We're agreeing to disagree whether a series pack of batteries have "ends", that are hit harder whether charging or discharging.

I deal with AC at work, and have no formal electrical training at all, other than what I've taught myself.

I'm waiting to hear from experts whether my understanding with DC theory breaks down in the real world, or whether I'm missing something in my understanding of series circuits.

My contention is that all cells - whether healthy or bad - behave the same regardless of whether they're on the ends.

However, I also respect your empirical proof, based on real world measurements, something I've never performed.

Again, I agree that separate charging circuits are probably superior to just one. The only thing I disagree about is whether "end" cells are harder hit during charging.

[seulater]

No problem. I hope your guy can help. There is allot to batteries than most realize. Some look at it like a capacitor which in a way it is but again far from it. Some issues are in a gray area, by that i mean it depends on how anal the guy is if a point is important or not. Take for instance battery chargers. Does it have an on board temperature sensor. Cold batteries take a different cutoff charge voltage than warm ones do. Does this matter to the average guy in the real world? Will this average guy ever compare a temperature compensated charger on a set of batteries to a non temp compensated charger on another set and do a life lest to see which set of batteries actually lasts longer. Probably not. It all boils down to what we are anal about.

I don't claim to be the foremost expert on batteries. I had 2 jobs to design 2 battery bank chargers. Once for the Rail Road (CTX) and the other for Motorola's battery bank for their comms center. These batteries were stored outside so i had to learn all about temp compensating charging. Hence my reason why i am a anal nut when it comes to batteries .

[yurtle]

I just don't understand how an "end" cell knows it's at the "end". All it sees is the current - the same for every cell - and the voltage across it. Voltage drop across healthy cells will be the same. Voltage drop across a sad cell will differ, regardless of whether it's on the end or middle. The sum of all voltage across each cell will equal that across the whole pack.

I just don't get why "ends" are different, but acknowledge that I could be wrong.

[seulater]

Hmmmm......

I see what your saying and how one could think this way. How about this explanation. Say you have 4 pieces of 1" thick plate steel. Each piece of steel is at 80 deg F. You now take these pieces of steel and place them all together like a sandwich. Stack them vertically. On the right most plate you put a torch to it. After a few minutes that right plate will become hundreds of degrees. Yet the left most plate will probably not have even changed 5 degrees yet.

This is similar to charging series battery's. Eventually all 4 pieces of steel will become the same temp. But its in the meantime for them to get there that the hardest one hit is the right most plate. This is the one that will take all the abuse over the life of heating the plates and will be the first one to be replaced. This can get worse if plate #3 from the right most has corrosion on it, which is impeding the temp to soak through it. If we are monitoring the left most plate (#4) with a temp probe to cut off at a certain temp we will now be inaccurate because plate #3 is corrupting the real temp.

Likewise with a battery charger and batteries. The charger is monitoring total current and total voltage across the "end" batteries. Its not monitoring any of them in the middle. So say one battery is weak and takes allot longer to get to full charge then the rest the charger is not able to know this so it keep applying the "heat" if you will to get it there. the rest of the battery's are up to "temp" but we are waiting for the lazy cell to get to where it needs to be. Meanwhile the rest are gassing when they dont need to.

[yurtle]

Electricity doesn't work that way. Power is simply volts x amps. We already agree that current is the same for each cell. The voltage drop across any cell is dependent ONLY on the resistance of that cell. If one cell is bad and has higher or lower resistance than its neighbors, the voltage drop is pretty much instantaneous, and has no regard for whether it's located on an "end".

[yurtle]

Here's an analogy for you. Take a series of light bulbs, all the same wattage except one. Now hook them up in any order you wish, yet the light, heat, and power consumed for each bulb will remain unchanged. The bulbs don't care if they're located on an end.

[yurtle]

Again, I'm not trying to be argumentative, just to understand. Your triple charger is superior to a single one. If you turn out to be right, it just means that I'll likely rotate my eight batteries every so often.

[seulater]

Electricity doesn't work that way. Power is simply volts x amps. We already agree that current is the same for each cell. The voltage drop across any cell is dependent ONLY on the resistance of that cell. If one cell is bad and has higher or lower resistance than its neighbors, the voltage drop is pretty much instantaneous, and has no regard for whether it's located on an "end".

Yes, i know it does not work this way, i was trying to give you an example of how it kinda works when charging. The + most end cell ALLAYS gets hit the hardest.

Take a series of light bulbs, all the same wattage except one. Now hook them up in any order you wish, yet the light, heat, and power consumed for each bulb will remain unchanged. The bulbs don't care if they're located on an end.

Correct they don't care where they are located. The total filament length is the total resistance, is does not matter where the "thinnest" piece of wire is at in the series. The total resistance will always be the same.

It sounds to me you are getting hung up on discharge vs charge.

I can give it one more shot, you take a discharged 12v battery. you put 14.8V to it. Ever wonder what makes it draw the higher current it does initially and then go down and down. Now imagine this, once that charge current topples down to 300-400ma, you then add a second dead 12v battery in series to the charged first one. Now place a 24v charger to them it again will take a high current draw. This is because the second battery is needing all that current to charge it. But it MUST flow through the first one to get there. Yet the first one does not need anything, so it passes it along to the dead one. In doing so the first charged battery is gassing during the whole process. So in effect, it gassed when it was first charged, then it gassed again when we hooked up the second battery. So it like we charged it twice if you will.


And yes, rotating your batteries is a very good idea!

[bigstik40]

I have been watching this thread with great interest and feel the need to add my $.02 !! I did a google search to find out about the "well known fact" that end cells in a series battery string have higher failure rates. Nothing was found. Any links that discuss the phenomenon would be appreciated.

I have to agree with Yurtle and Mr. Ohm that the voltage across any battery will be a function of the current through it, times its resistance. I also don't think end cells know they are end cells. (I think end cells in automotive applications may show high failure rates because they are the hottest during their lifetime because of direct exposure to high engine compartment temperatures). (my own opinion)

I do agree that multiple bank charging is a very good way to insure a balanced battery pack, which is important for good battery performance and life. A battery pack is only as good as the poorest battery.- RAY

[seulater]

I have to agree with Yurtle and Mr. Ohm that the voltage across any battery will be a function of the current through it, times its resistance.

I am confused why you guys are getting hung up on this statement. Its not about this. That is a function of or rest and discharge. Charging is a whole other matter when it comes to series charging.

As an FYI, for the car battery. The all 6 cells in a 12v battery are subject to the same heat in the engine compartment. So heat is not the factor why the 1'st cell by the + Post typically craps out first.

I am sorry that Google did not show that i do indeed have some insight to what i am talking about. Everything i have discussed here is easily provable.
I have given a few ways to prove it, and have shown other ways why serial charging is not the norm anymore. I have backed up what i said with proof so why else can i do. ;)

The easiest one is to do what i said, drive your cart hard. let it rest for a while to let all cells normalize in temp. Then start to charge it, after 15 minutes or so whip out your non contact temp probe. measure the temp accost the battery from + post to - post. you will see for yourself that all cells are not going to be the same temp. If all things being equal they should be, but i guarantee you they will not be the same temp. There is more to Mr. Ohm when you add chemistry into the mix.

Kinda like these charges for these carts. I am amazed to see that they still would even make and use these old wire wound transformers they weigh in at 20-30 lbs. When i got my cart and saw the charger i was like really? Don't these people move with the times? A 2 pound switching power supply would not only be cheaper, lighter, smaller, and run cooler that any of these old behemoth chargers that i see out here.

I hope i am not taken as being rude or beating a point here. I started this thread to inform people that there are other and better means to charge your batteries properly.