Battery Connections

[butkus51_]

I run two RV batteries on my 5er. I want my lights to run twice as long. Is the proper connection + to + and - to -? I have been told some applicatios are + to - on both posts of the batteries. Is my wiring correct because my 5er lights do not seem to run twice as long.

[enblethen]

It is also resistance that builds up on the plates within the battery.

[Coach-man]

Water-Bug wrote:

frizzen wrote:
Since the resistance of 8 gauge AWG copper is .0007 ohms per foot, I think we can ignore the voltage drop for a couple of 2 foot jumpers.

Especially since it's usually thicker than that and the wire from the charging inverter is usually 5X longer and 5X thinner.

What about the connections, four connection, and when it starts to corrode? Then do the math! And remember, ALWAYS, the weak battery brings down the strong battery! I admit it is not a LARGE difference, but there is a difference, making the cells (battery) not directly connected a little weaker. This brings down the cells (battery) that is connected. Over days, weeks, months, even years, it will shorten the life of the cells, (batteries)! So its is your money, so go ahead! I will always connect multiple cells, (batteries), with cables on either side of the setup, while not perfect it will balance the charge better accross all cells and lengthen the life of the setup!

[Water-Bug]

frizzen wrote:
Since the resistance of 8 gauge AWG copper is .0007 ohms per foot, I think we can ignore the voltage drop for a couple of 2 foot jumpers.

Especially since it's usually thicker than that and the wire from the charging inverter is usually 5X longer and 5X thinner.

[frizzen]

Since the resistance of 8 gauge AWG copper is .0007 ohms per foot, I think we can ignore the voltage drop for a couple of 2 foot jumpers.

[Timay]

Coach-man wrote:
I am sorry, if you are relying on the extra battery cables to transfer power to the other cells, they have additional resistance, therefore using OHMS law voltage times current divided by resistance, you will have less current gowing to the othe cells if you connect both positive and negative to the same set of cells! Yes you have the same resistance drop across both sets of cells if one positive to one set and negative to the other set, but all cells will be the resistance and receive the same amount of current! But you connect the way you want to, I will connect the correct way!

Whatever you say...

[enblethen]

Telephone battery rooms at 48 volts is similar but not the same as large battery systems used for 120 to 240 volt DC systems for electrical control rooms.
Yes, most use buss bars to tie main runs of batteries together, then to go to next bank or level of batteries paralleled runs of fine strand copper cables are used. These battery rooms are to carry a substantial load while the genset starts and comes on line.
When a battery is taken out of the system a temporary jumper is used around that battery. It is either one or two cables with the same circular mil area as the designed buss bar.

[Coach-man]

I am sorry, if you are relying on the extra battery cables to transfer power to the other cells, they have additional resistance, therefore using OHMS law voltage times current divided by resistance, you will have less current gowing to the othe cells if you connect both positive and negative to the same set of cells! Yes you have the same resistance drop across both sets of cells if one positive to one set and negative to the other set, but all cells will be the resistance and receive the same amount of current! But you connect the way you want to, I will connect the correct way!

[Timay]

Yessir, Mr. Bug! After I got out of the service I became an electrician and had occasion to work in a Mtn. Bell (oldie, huh?) battery room and it was VERY scary carrying a piece of conduit around those buss's! I managed to get my job done without making a large *bang*!

Tim

[Water-Bug]

enblethen wrote:
Coach-man that is correct.
Yes, it is slight difference in resistance.
Timay, look at a large battery room for electrical control systems. They are all wired similar to what I said. This is so you can change out battery or batteries by simply jumpering around the defective or battery(ies) that need servicing.

Actually, the battery banks in large battery rooms are connected with large copper buss bars that are nothing like RV wiring. Nothing is ever jumpered across or around. Any battery can be removed or added to the buss without interupting service.
I'm an at&t retiree. The entire outside plant (telephone lines) are powered by large battery rooms in the Central Office.

[Timay]

enblethen wrote:
Coach-man that is correct.
Yes, it is slight difference in resistance.
Timay, look at a large battery room for electrical control systems. They are all wired similar to what I said. This is so you can change out battery or batteries by simply jumpering around the defective or battery(ies) that need servicing.

My point is that feeding a battery pile from one end to the other to ensure even charging is hooie. Batteries don't charge from one end to the other, all the cells charge at the same time and there is a chemical reaction inside each cell that makes the electricity. Yes, each cell will have different resistances which slightly effect charging - when one cell develops too much resistance the battery is then on its way out. If you have a pile of batteries, i.e. 2 12volters, it makes no difference if you feed the charging voltage from the ends or the sides or wherever, as long as polarity and voltage is observed.

Yes, I worked in those battery rooms you speak of - Chanute AFB Central Office inside plant equipment specialist - ruined many a pair of uniform pants checking the electrolyte levels.

Tim

[frizzen]

In downtheroad's diagram the gray set is wired in parallel and the red set is in series. The series set up will add the voltages of the individual batteries (which do not have to have the same voltage). This is why two 6 volt batteries produce 12 volts.
The parallel set up needs to have batteries of the same voltage and will draw amps from both batteries. Any difference in rate of charge with short connecting cables will be negligible if the batteries are of equal capacity.

[enblethen]

Coach-man that is correct.
Yes, it is slight difference in resistance.
Timay, look at a large battery room for electrical control systems. They are all wired similar to what I said. This is so you can change out battery or batteries by simply jumpering around the defective or battery(ies) that need servicing.

[Coach-man]

Timay wrote:

enblethen wrote:
Downtheroad:
That is correct!
That will give a closer to equal charge and discharge.

Please help me understand how putting the plus and minus on opposite sides will make the first battery get a better (more equal) charge...seems to me that IT DOESN'T MATTER. Electricity runs at the speed of light and putting the plus and minus anywhere on the line that feeds both batteries will accomplish the same charge.

Of course, this is more than my opinion - if it matters I am a master electrician.

Tim

I may be going out on a limb here, I am not an electrician, BUT A/C is one thing and DC is another. Another thing is terminology, we are not wiring two batteries together, we are talking about creating ONE battery with more cells. By connecting the positive to one side of the battery, and the negative to the other, you are forcing the eletricity, (electrons), to flow thru all the cells of the battery ensuring that all cells get charged. If you connect both positive and negative to one side, if there is, and it will be, a differance in resistance between the cells, some cells will receive more current flow than the other. OHM's law anyone?

[Water-Bug]

The whole webpage is BS. If you drain one battery more the others, it's voltage will drop and the remaining batteries will have a higher voltage and supply more current.

EDIT. Maybr batteries work different in England. 🙂