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PV negative and battery negative

rhino

Solar Wizard
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I'm swapping out a Midnite SCC for a Victron and am not sure about the Battery negative and PV-. On the Midnite if I recall they are internally bonded but in the Victron I don't believe this is case. Do I need to wire the PV- directly to the SCC and also have a B- cable now from the negative battery busbar? Right now the PV- is just going to the "ground" busbar where PV-, B-, and chassis are all connected which I am thinking is no longer proper. This is for stationary installation.
 
Do not ground DC circuits. Always + to + and - to -.

The PV is its own circuit that is a closed circuit.

If you understand car speakers think of it like this, would you ever ground the speaker to the chassis ground? Never.

The main reason you do not mix dc circuits is because they are almost never the same voltage.
 
Thanks. That makes sense. Looks like the only change I need to make is as you stated and connect that PV- directly to the SCC. As far as the battery negative and chassis ground I see from the Victron diagrams there is a "central negative busbar" where the Battery negative and chassis grounds all connect to which then connects to your single ground point.
 
I'm swapping out a Midnite SCC for a Victron and am not sure about the Battery negative and PV-. On the Midnite if I recall they are internally bonded but in the Victron I don't believe this is case. Do I need to wire the PV- directly to the SCC and also have a B- cable now from the negative battery busbar? Right now the PV- is just going to the "ground" busbar where PV-, B-, and chassis are all connected which I am thinking is no longer proper. This is for stationary installation.
Normally you should only ground the battery.
PWM SCCs are usually switching the panel and the load from the negative pole, so if you ground them as well, you are just bypassing their logic.
MPPT SCCs usually switch the panel on the positive pole, but some of them may control the load on the low side as well.
So it is never a good idea to ground anything, but the battery.
 
Thanks. That makes sense. Looks like the only change I need to make is as you stated and connect that PV- directly to the SCC. As far as the battery negative and chassis ground I see from the Victron diagrams there is a "central negative busbar" where the Battery negative and chassis grounds all connect to which then connects to your single ground point.

My Victron 100/50 does have a ground screw on the side of the unit. As I recall, the Victron manual was clear that it was to be used.
 
My Victron 100/50 does have a ground screw on the side of the unit. As I recall, the Victron manual was clear that it was to be used.
"Clear" might be overly generous (or maybe I'm just dense :) ) but they do make reference to it (bullet point 2):
3.2 Grounding
  • Battery grounding: the charger can be installed in a positive or negative grounded system. Note: apply a single ground connection (preferably close to the battery) to prevent malfunctioning of the system.
  • Chassis grounding: A separate earth path for the chassis ground is permitted because it is isolated from the positive and negative terminal
  • The USA National Electrical Code (NEC) requires the use of an external ground fault protection device (GFPD). These MPPT chargers do not have internal ground fault protection. The system electrical negativeshould be bonded through a GFPD to earth ground at one (and only one) locatio
  • The charger must not be connected with grounded PV arrays (one ground connection only)
 
Well, preventing malfunction is pretty clear to me!

The fourth bullet point in that list is what has me confused. It comes across to me that Victron does NOT want the panels to be grounded.
 
I always run dedicated negative cables for critical circuits such as charging systems. Other wise I find no problem having the chassis being a common negative.
 
I think a lot of confusion arises from the term 'grounded' vs. 'earthed' and that the way things are in the States is different from most of the rest of the world. In the States (Americas in general) one conductor is connected to earth while this is not so (no conductor is connected to earth) in other places. However, you do have earthing, whereby the non-energized metal enclosure is connected to earth.
 
I think a lot of confusion arises from the term 'grounded' vs. 'earthed' and that the way things are in the States is different from most of the rest of the world. In the States (Americas in general) one conductor is connected to earth while this is not so (no conductor is connected to earth) in other places. However, you do have earthing, whereby the non-energized metal enclosure is connected to earth.
really? I had no idea a grounded conductor was not normal (fits the stereotype I suppose :rolleyes:)
 
really? I had no idea a grounded conductor was not normal (fits the stereotype I suppose :rolleyes:)

Yes, it depends on the earthing network used (note that the wiki article is wrong where it states that "Most modern homes in Europe have a TN-C-S earthing system.[citation needed]").

In the States and Canada, TN-C-S is implemented which means there is a combined neutral and and grounding conductor coming from the distribution transformer, but at the house separate conductors are used - and the neutral must be connected to the earth at the supply side of the disconnect switch at the house.

Over here in (most of) Europe, we use TN-S which has a separate neutral and earth (protective earth, PE) conductors coming from the distribution transformer; these are never to be connected together at the house - the metal cases of devices like washing machines etc. are connected to the PE conductor, the neutral is its own separate entity forming the normal return path of the current in the circuit.

In some occasions TT networks are also employed where the earth electrode is locally provided with rods/loops, and a separate neutral is coming from the distribution system. In these, again, the neutral is not connected to the earthing conductor at the house.
 
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