6 volt battery question......

[NYSail]

hello all,

So now am the proud owner of 4 6volt Trojan T125’s. Have just a basic question for all of you highly knowledgeable people (I did search and didn’t find any prior answers). When you combine two batteries making 12 volts with the neg. from one and poss. from other, what does that connection become? I had no intentions to have anything else attached to either post, however when I was looking at a friends set-up, the yard that installed them put his battery temp sensor on one of the posts.

Thanks
Greg

 

[dlochner]

Battery temp sensors go on the last negative post.

On the last Negative post there will be from bottom to top:

Parallel cable from other battery pair
Negative ground cable to shunt and then to main ground
Negative for Smart Gauge
Battery Temp sensor (charger)
Battery Temp sensor (alternator/regulator)

This violates the no more than 4 connections on the battery post, but, the temp sensors don't count.

 

[jssailem]

Good morning Greg.
Technically it is just “two batteries in series”. Like holding hands with super glue. Alone they are just two 6 volt batteries , but together they are now stronger... 12 volt batteries. Not to get to into the woods but your 6 volt battery is really three 2 volt cells wired together to make a “6 volt battery” that is wrapped in a pretty plastic case. You just took the two 6 volt cases and connected them together.

 

[jssailem]

Parallel cable from other battery pair

Dave... Was he asking about the 4 batteries in the box to the connection of 2 6 volt batteries...
2 6 volts are series = 12 volt battery.
2 12 volt batteries in Parallel give you a bigger 12 volt battery.

But I know you know this Dave.

 

[Stu Jackson]

When you combine two batteries making 12 volts with the neg. from one and poss. from other, what does that connection become?

It becomes Darth Vader in a galaxy far, far away.
Seriously, Greg, have you reread that sentence/question?
If they are connected, they have to be 12V.

 

[Johnb]

hello all,

So now am the proud owner of 4 6volt Trojan T125’s. Have just a basic question for all of you highly knowledgeable people (I did search and didn’t find any prior answers). When you combine two batteries making 12 volts with the neg. from one and poss. from other, what does that connection become? I had no intentions to have anything else attached to either post, however when I was looking at a friends set-up, the yard that installed them put his battery temp sensor on one of the posts.

Thanks
Greg

When two 6 volt batteries are connected to make a 12 volt battery we would say they are connected in series.
If two batteries are connected such that they make one "bigger" one of the same voltage they are said to be connected in parallel.

The temperature sensor just needs a good mechanical connection to the battery so it will be at the same temperature.

I do believe that folks should be allowed to ask any question they want. They should be free to come on the forum and say "have I got this right?" - without being humiliated. The consequences of screw ups are just too severe.

 

[jssailem]

I do believe that folks should be allowed to ask any question they want.

To that.

 

[NYSail]

It becomes Darth Vader in a galaxy far, far away.
Seriously, Greg, have you reread that sentence/question?
If they are connected, they have to be 12V.

Once again sorry for my lack of knowledge.....
Yes I know the bank is 12 volt now...... I am asking what the wire that connects the neg and poss is...... not neg and not poss just a connection? I know it’s the connection between the two to make 12 volts.. I did get that far in my learnin’... but I was confused when I saw my friends bank that was using the connecting wire for his battery temp sensor. I do know where it’s suppose to go..... again just saw something in practice and had a question.

Greg

 

[NYSail]

When two 6 volt batteries are connected to make a 12 volt battery we would say they are connected in series.
If two batteries are connected such that they make one "bigger" one of the same voltage they are said to be connected in parallel.

The temperature sensor just needs a good mechanical connection to the battery so it will be at the same temperature.

I do believe that folks should be allowed to ask any question they want. They should be free to come on the forum and say "have I got this right?" - without being humiliated. The consequences of screw ups are just too severe.

Thanks John...... I always ask even if some people think I’m an idiot. I am very capable in many areas and got this way by asking questions. I hate to do stupid things when there are people around me that have experience and are willing to share.....

Greg

 

[Benny17441]

Greg, a 6V battery has 3 cells combined in series. If you add another 3 cells to that series you end up with a 12V battery. The number of cases is irrelevant. With your 4, 6V Trojans you have the equivalent of 2, 12V batteries. Connecting in series does not double the battery capacity but connecting the 2, 12V batteries in "parallel" maintains the voltage at 12v but doubles the capacity.

 

[NYSail]

Greg, a 6V battery has 3 cells combined in series. If you add another 3 cells to that series you end up with a 12V battery. The number of cases is irrelevant. With your 4, 6V Trojans you have the equivalent of 2, 12V batteries. Connecting in series does not double the battery capacity but connecting the 2, 12V batteries in "parallel" maintains the voltage at 12v but doubles the capacity.

Yes I fully understand about combining the batteries to make 12 volts....... and my bank will be 480 ah total (4 240 ah) my question I guess is just an odd ball...... the cable that connects in series the two. I know not to use it for anything...... just wanted to know why this other installer did use it.

Thanks

 

[Davidasailor26]

The battery temp sensor isn't pulling any current or have any kind of electrical connection to the battery. It just needs a good thermal connection to see the battery temperature. You could attach it to the plastic case and it would still work, it just wouldn't read the temperature very accurately since it won't have a good thermal connection to the battery core.

 

[NYSail]

The battery temp sensor isn't pulling any current or have any kind of electrical connection to the battery. It just needs a good thermal connection to see the battery temperature. You could attach it to the plastic case and it would still work, it just wouldn't read the temperature very accurately since it won't have a good thermal connection to the battery core.

Thanks David.........

Greg

 

[Ward H]

I am asking what the wire that connects the neg and poss is...... not neg and not poss just a connection?

It is a 6V connection to the positive terminal of the 6V battery. If that battery's negative terminal is connected to your negative bus system, I am sure any wire connection to the positive terminal will have the same requirement as a 12V battery connection, to be fused within 7" of the battery.

For the same reasons, a battery temp sensor should be connected to the negative terminal of the 6V battery that is connected to the negative bus system, not to the positive terminal. (At least that is the requirement for my charger and external alt regulator). Besides eliminating the need for a fuse, I thought if the sensor wire was energized it would harm the device at the other end.

 

[agprice22]

Actually, it is a really cool question... in parallel, the polarity of the cables stays the same, battery 1 amp hours + battery 2 amp hours at the nominal voltage. In series, they cross, so what is the polarity after the cross? The answer is: the battery pole that you are drawing off. Don’t be confused. The poles of the batteries don’t change. Crossing the poles adds the volts of the upstream battery to the downstream battery. The volts are now added at the positive pole of the last battery in the series. The positive pole of the first battery delivers its nominal voltage. Cross the poles to the second battery, and you get battery 1 voltage + battery 2 voltage, and you use the poles of battery 2, or 3, or 4... to power your system. You can test whatever you want at each positive pole.

 

[jssailem]

If I now understand Greg’s question, and please correct me Greg if I miss State it.

The query is about the connection of the Temp sensor to the neg terminal. Since the temp sensor was to the neg terminal between the two 6volt batteries, that were in series, how is the terminal identified- neg or pos or something else.

@Davidasailor26 addressed the question by clarifying that the sensor is just a sensor and is not looking at the positive or negative connection. Dave is correct in that the sensor could’ve been glued to the plastic case and the thermocouple would still work. Just not as good as a direct thermal connection to the internal metal parts of the battery.

I have not used the terminals in the middle of a series as there is the possibility of a short. I connect to the negative side at the end of the batteries in series.

 

[NYSail]

Actually, it is a really cool question... in parallel, the polarity of the cables stays the same, battery 1 amp hours + battery 2 amp hours at the nominal voltage. In series, they cross, so what is the polarity after the cross? The answer is: the battery pole that you are drawing off. Don’t be confused. The poles of the batteries don’t change. Crossing the poles adds the volts of the upstream battery to the downstream battery. The volts are now added at the positive pole of the last battery in the series. The positive pole of the first battery delivers its nominal voltage. Cross the poles to the second battery, and you get battery 1 voltage + battery 2 voltage, and you use the poles of battery 2, or 3, or 4... to power your system. You can test whatever you want at each positive pole.

Thank you..... that was exactly what I was wondering.

 

[Ward H]

Found this in Maine Sail's article on installing a battery charger:
"Any terminal mounted temperature sensor also needs to be connected directly to anegative terminal, and not the positive terminal. The termperature sensor has the ability to fry the charger if connected to the + terminal and also the potential to be accidentally shorted."

While the sensor doesn't need battery voltage to operate, applying battery voltage to it is bad for the electronics on the other end.

 

[NYSail]

Yes I read that..... I will advise my friend about his wrong connection.

Thanks

 

[dlochner]

The last negative post will get the hottest so that is place to take the batteries temperature. Victron makes a sensor that glues to the side of the battery case, however I think it has to be replaced with each new battery. Not very cost effective.