What is a charge controller with a "positive ground"?

bdl said:

As gnubie noted, it's mainly convention. Switches, fuses, etc are usually conventionally placed on the positive side of any DC circuit (and the Active of an AC circuit), and many people - incl. me, tbh - would assume a switched positive in any given situation. i.e. you stick a meter probe on the chassis and take measurements/etc by poking your positive probe around the place. Also, installing battery management systems with current shunts, etc, that are designed for or assume high-side switching may unintentionally create a path that bypasses a low-side switching circuit. The moral here really is that you shouldn't assume things, but the reality is most people do, and thus there is a market to sell products that satisfy these assumptions.

To paraphrase pierre, if you are careful and understanding of your grounding then you'll be fine in any situation (essentially: if you tie to "ground" in more than one place you may have issues; zero places is of course less than one .

As to case isolation, you'd have to check the manual for your device. In the handful of devices I've played with (Victron and recent Renogy), the case is isolated from all inputs so you can do whatever you like in terms of mounting the device.

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I think you all are talking about exactly what I need to understand for my travel trailers solar install. I have a Renogy solar charge controller and am confused about the grounding as well. Can I share here what I have going on and get some advice? Or do I need to post my own question?

theHouserHouse said:

I think you all are talking about exactly what I need to understand for my travel trailers solar install. I have a Renogy solar charge controller and am confused about the grounding as well. Can I share here what I have going on and get some advice? Or do I need to post my own question?

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If your question has to do with positive ground systems or components this would be a good place to discuss that. If it has to do with general grounding questions or negative (normal) grounding, I think you would be better off (and get more exposure) posting your own question, or posting in one of the other general grounding threads.

We bought a positive ground solar charge controller by mistake. Honestly, I did not even know there was different types of grounding. Before returning it, I thought we'd see if it's something we can use. We are adding solar to our travel trailer. When finished the solar will be connected to both the AC and DC systems. The charge controller we bought is the Renogy Rover PG 60 amp solar charge controller.

From the installation manual: The Rover PG series are positive ground controllers. This means all positive terminals are bonded together. Any positive connection of solar, load or battery can be earth grounded as required. The solar panels, loads and battery will be connected to the Rover PG the same way as a negative ground controller. The difference is when grounding the Rover PG there can only be a single ground point, either ground the positive line of the solar panels, the positive line of the load terminal or the positive line of the battery bank. Do not ground the Rover PG when adding it to a negative ground system.

So, I'm assuming our travel trailer is negative grounded. I honestly don't know how to verify. When reading this statement above, it sounds to me like we could use this charge controller, we just should not ground it. We can ground any one of our other components, but not this solar charge controller. Does that sound right to you?

Also, is anyone aware of any reason we should not use this charge controller?

theHouserHouse said:

So, I'm assuming our travel trailer is negative grounded. I honestly don't know how to verify.

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I think this is a good default assumption in almost any context. It is highly probably your vehicles house system is either negative grounded or ungrounded. Most likely negative grounded.

theHouserHouse said:

When reading this statement above, it sounds to me like we could use this charge controller, we just should not ground it. We can ground any one of our other components, but not this solar charge controller. Does that sound right to you?

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Honestly, I've never really understood the particulars or purpose of positive grounded PV controllers. I've had it explained to me before but it did not penetrate my thick skull . If I recall, it PG controllers may exist mostly to serve the telecom industry or something of that nature.

Personally, unless you understand it well, I would return it, not because it wouldn't work but because it is non-standard and off the beaten track, when I don't understand something fully, I try to stay marginally close to the herd so its easier to get help and find info and not be unsure whether it applies to my situation.

If you do want to stick with it or just learn more, search the forum, this has been discussed in other threads. If a general search doesn't turn up anything, search my username + positive ground, I know I have asked questions about this in the past.

Dzl said:

Personally, unless you understand it well, I would return it, not because it wouldn't work but because it is non-standard and off the beaten track, when I don't understand something fully, I try to stay marginally close to the herd so its easier to get help and find info and not be unsure whether it applies to my situation.

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I did a bit more reading and agree that we should just return it. We can just get the negative ground unit and no worries. I don't need to complicate this project. Thanks.

FWIW, you'll be fine to use the controller you have. It may be worthwhile to totally ignore the term "grounding" when it comes to the controller itself - it's going to be either switched-negative (what you have; positive input+output are bonded together) or switched-positive (negative input+output are bonded together).

So long as you leave the PV inputs floating (both of 'em), which you should do regardless of controller type (*), then you'll be fine. It literally won't make any difference between the two.

(*) note the "PV should be floating" bit is only valid for mobile / low-voltage arrays (say 2-3 series panels max), house PV arrays that run much higher voltages (e.g. 1000V) must be earthed properly per your local regulations.


BTW, switched-negative controllers exist as it's the simplest way of designing the circuitry; the electronics required to drive "low side" negative FETs is much simpler than "high side" / positive FETs. Over time, dedicated high-side drive ICs have come along that have reduced the additional cost, but it's still non-zero.

I went ahead and returned the positive ground solar charge controller and bought a Vectron. Thanks for everyone's input.