Solar panel earth point?

Submitted: Sunday, May 21, 2017 at 18:35
ThreadID: 134916 Views:4713 Replies:8 FollowUps:5
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Hi,

Okay, so I have a silly question. I have a redarc 1225 BCDC charger in my motor car to charge the second battery and wish to use the MPPT function to regulate a solar panel when we are camped up for awhile.

The diagrams I have looked at show the positive cable from the panel back to the relay and the negative earthing next to the panel.

What I would like to know is where to earth the panels negative cable, do I attach it to the chassis or to the negative terminal of the second battery?

I'm normally pretty good at doing this sort of thing but this is my first go with a solar panel and I don't want to stuff it up! LOL.
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Reply By: IvanTheTerrible - Sunday, May 21, 2017 at 19:01

Sunday, May 21, 2017 at 19:01
Yes. I would run it back to the controller though and earth all the neg wires to the same place
AnswerID: 611276

Reply By: Member - Phil G (SA) - Sunday, May 21, 2017 at 19:05

Sunday, May 21, 2017 at 19:05
Your auxillary battery should have a good earth to the chassis. So it is fine to earth the solar panels to the chassis.
AnswerID: 611277

Reply By: RMD - Sunday, May 21, 2017 at 19:45

Sunday, May 21, 2017 at 19:45
All solar regs and bcdc units require the negative wire of the panel to go directly to the regulators PANEL NEGATIVE connection.
Connecting it's negative to the vehicle ground will mean No regulation action because the solar negative line is what is switchedon and off or modulated to do the regulating.

Having ALL negative wiring to the same point does not seem at all correct or wise.
AnswerID: 611280

Follow Up By: IvanTheTerrible - Sunday, May 21, 2017 at 20:04

Sunday, May 21, 2017 at 20:04
The positive is regulated is most solar. Most mppt regulators have the solar in Neg and the battery Neg directly connected internally
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Follow Up By: Nomadic Navara - Tuesday, May 23, 2017 at 15:17

Tuesday, May 23, 2017 at 15:17
RMD, that only applies to regulators like the Plasmatronics, Steca and many of the cheap evilbay models that were designed for positive earth systems. The communications systems were the first to use solar systems and they are all positive earth systems (your telephones work off 50 V pos earth.) If you are wiring in one of the above regulators in negative earth systems you have to be careful how you wire them in. You have to decide which part of the system you wish to earth, you have to decide whether you want the battery terminal, load terminal or solar panel negative earthed, you can not earth more than one of them.
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Follow Up By: HKB Electronics - Wednesday, May 24, 2017 at 10:47

Wednesday, May 24, 2017 at 10:47
Sometimes this is not as easy as it sounds, the Projecta solar controllers are an example, they are positive earth which if only a regulator is not such a big deal, but in this case they also have an inbuilt BMS which for it to work correctly means all accessories must be have their negatives only connected to the solar controllers load negative terminal so that the controller can monitor current drawn by the loads as well as current into and out of the battery. This also means the negative battery terminal can't be grounded else the controller will not see the current they are drawing.

Sounds strange why not just monitor current in and out of the battery you ask, well actually it works very well you can see what current the solar panels are generating, how much is flowing in and out of the battery as well as monitor the actual current being drawn by the loads, and by a simple press of a button you can turn the power off to all accessories. All in all very comprehensive, only issue is the battery negative terminal and solar panels negatives must be isolated from the van chassis for all this to work, which they are.

The problem is if you connect the van to the car and try to charge the van batteries either directly off the alternator or via a DCDC charger where the negative passes straight through as you then have the vans battery negative terminal grounded to the cars chassis, which of course then grounds the van chassis via the tow hitch or chains etc.

With these units you would need a fully floating earth system for them to work correctly if direct charging off the vehicle is to be used.

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Follow Up By: Nomadic Navara - Wednesday, May 24, 2017 at 11:36

Wednesday, May 24, 2017 at 11:36
Thanks for that. I will add that one to my list of controllers not to recommend. Collyn Rivers had several articles in the CMCA magazine about problems whit these pos earth regulators incorrectly wired by people including licensed electricians. Switched on people can work around their difficulties but they are a big headache for lesser people to install.
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Reply By: Member - Westcoast Mark - Sunday, May 21, 2017 at 19:59

Sunday, May 21, 2017 at 19:59
So in the attached image I should run the panel earth to the relay earth or the chassis where the unit is earthed?
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Follow Up By: IvanTheTerrible - Sunday, May 21, 2017 at 20:06

Sunday, May 21, 2017 at 20:06
Relay neg is not as important so any neg will do
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Reply By: Allan B (Sunshine Coast) - Sunday, May 21, 2017 at 20:17

Sunday, May 21, 2017 at 20:17
Mark,

All your negatives should be connected to the vehicle "chassis" as per the Redarc Figure 2.8d as shown below. I have marked each such connection with a blue circle.
Of course, each negative wire does not require a separate chassis connection, they can share connections as suits the cable layout. So you could connect the panel neg cable to the second battery terminal as that is also connected to chassis but in general it is good practice to not connect multiple wires to the battery terminal ---- connect them to the chassis stud where the main wire from the battery connects.

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Reply By: Member - Westcoast Mark - Sunday, May 21, 2017 at 20:21

Sunday, May 21, 2017 at 20:21
Thanks Allan, Thats what i was thinking but not having actually hooked one up before I just wanted to be sure. I appreciate your time as well as everyone else who answered.

Cheers,

Mark
AnswerID: 611287

Reply By: Member - Phil G (SA) - Monday, May 22, 2017 at 10:04

Monday, May 22, 2017 at 10:04
Just an additional suggestion for getting good earth connections, I sand off the paint and run a tap through any hole I'll be using for earth and smear vaseline on it to prevent corrosion.
AnswerID: 611294

Reply By: The Bantam - Monday, May 22, 2017 at 23:26

Monday, May 22, 2017 at 23:26
it is important to understand that there is no earth connection in a DC system on a vehicle ....... people persist with talking about "earth", this causes much confusion.

safer to talk about "battery negative" and "vehicle chassis"

In most casses and in most positions there is absolutly no necessity to connect to vehicle chassis ...... it is best and easiest to wire positive and negative with a figure 8 or twin cable ........ the only necessary vehicle chassis connection is at the main cranking battery ..... and only then because the car manufacturers are tight asses and use the metal body as a negative battery return path because it is cheaper than wiring one.

cheers


cheers
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