Wiring two 6V batteries in series when you have solar panel

[BrucePerens]

I know that's how old auto mechanics said to do it, but that's before cars had Electronics in them. With electronics, you always connect the ground first.

[Bill]

Originally Posted by Bailey'sMom

Thanks Bill!

So what I labeled as #6 in my picture is probably the 30amp fuse, right?

Sorry, I didn't even see the extra pictures in your post. Now that I do, you are right, item 6 is what I called the fuse. In your case, though, the 30-amp fuse has been replaced with a 30-amp circuit breaker, probably self-resetting. This is a good change.

Bill

[Padgett]

Do not try with a Mercedes or Chrysler: always remove the negative battery cable first both for safety and not to confuse the computers (plural). Modern systems have some residual power and if you pull the positive first it will trigger a number of "low voltage" and CANBUS errors.

[Bailey'sMom]

Originally Posted by Bill

Sorry, I didn't even see the extra pictures in your post. Now that I do, you are right, item 6 is what I called the fuse. In your case, though, the 30-amp fuse has been replaced with a 30-amp circuit breaker, probably self-resetting. This is a good change.

Bill

Bill - would you please look at the pictures again. Why do I have 2 wires attached to the positive post? In my image (attached) I labeled them 1a and 2a. What would the second one be for?

I am trying to compare mine to yours and label as clearly as I can. What confuses me is that I have the same number of wires attached to the negative post as you show in your diagram, one is the ground and the other negative.

So why do I have the same number of wires attached to the negative post, but an extra wire attached to the positive post?

The 2 positive wires connect to the 30 amp circuit breaker and come out the other side. I don't know where they go to.

Thanks in advance. Once I get this all straight in my head, I will write up the connecting batteries for dummies version.

[rickst29]

It works, but you found it confusing. The installer did bad things, I think, to cause your confusion, and "he" should have done better

Error #1: From the +12V battery terminal to the circuit breaker "input", someone put two small wires in parallel with each other.

"He" imagined that this would "improve" power distribution, but he was wrong about this. The long wire black wire, going from circuit breaker "output" to the "input" for the TM's 12 Volt "power distribution" Board board (that's the one with all the fuses attached) is only #10 and much longer. The vast majority of "Voltage Drop happens along that wire. Installing anything "bigger" than #10 for the first few inches from the battery, leaving a much longer distance at the small size, accomplishes almost nothing.

Also: If this was house wiring, the inspector would make you rip out the "helper wire" and use ONE bigger wire. They don't allow parallel wires, it's ILLEGAL - for very good reasons. A single big wire such as #8 would be helpful and acceptable, but if (and only if) the long wire to the TM "12V Power Distribution" was also upgraded to #8.
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Error #2: The wire which I'll label as "neutral grounding wire for reset" should absolutely, positively be WHITE in Color. This is a current carrying neutral wire. The lazy installing person didn't have any white wire around, and should have bought some.
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I'm never thrilled to see two wires under the same connector - with the one possible exception of a BTS ("Battery Temp Sensor" for a Solar Controller) and the big current carrying-wire, both on the same battery terminal.

[BrucePerens]

Originally Posted by Padgett

Do not try with a Mercedes or Chrysler: always remove the negative battery cable first both for safety and not to confuse the computers (plural). Modern systems have some residual power and if you pull the positive first it will trigger a number of "low voltage" and CANBUS errors.

How?

I am at a loss to figure out how a car determines which post of the battery is disconnected. Or any two-terminal component with only one connected. No current flows.

The risk of connecting positive first is that negative touches something other than ground, creating an unexpected current path through a signal line. EMI protection diodes used in car control circuitry and other electronics are connected between a signal line and ground, thus they only work properly when ground is connected to the battery negative. They can potentially dissipate positive power on a signal line and blow a fuse, when ground is connected properly. Connect battery negative anywhere else and the protection doesn't work.

Thanks

Bruce

[BrucePerens]

Rick, I think you are wrong about the two wires connected to the same terminal. One is a current wire. The second one connected to the positive terminal is a sense wire and passes under the breaker. And there is also a second sense wire at the negative terminal - I don't think that's a thermal sensor, although they are often attached to a battery terminal. You can't drive the voltmeter or the regulator on a good battery charger with the current wire, because the current wire has a voltage drop in operation due to its non-zero resistance. So, you use a second wire that doesn't carry any significant current to do that.

The thin wire returns the voltage at the battery to the charger and meter, so that the charger can compensate for the voltage drop in the current wires, and so that the meter reads accurately.

If we had super-thick current wires with theoretical zero resistance, we would not need this. Most current wires have a measurable voltage drop.

Sara, you can leave all of that alone. If you ever replace the solar controller (and now is not the time, save this for after you determine that you really need more panels), you would only disconnect the wires from the solar panel to the old controller, and leave the old controller where it is now as a battery monitor.

[rickst29]

N/t.