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

[Bartek]

Specifically, what is the difference between these two Renogy 10A charge controllers? They are both identical in appearance, but one is "positive ground".

 

[kernel]

More than likely something you do not need. If you have a positive ground system you would likely know. Mostly vehicl3 systems, old ones but is used still.

If its a traditional power system it will be negative ground* or even ungrounded which is much less likely outside of high voltage controllers.

From the webs.
"A positive ground system works by directly connecting the chassis of a vehicle to the positive side of the vehicle's battery. This system effectively earths the vehicle as the chassis attaches to the battery using a positivebattery cable.

https://www.reference.com › positiv..."

 

[Pierre]

I used to have a + ground British car in the sixties and they were discontinued around then. My mates and I converted our cars to - earth but I am sure there are still a few ‘purists’ out there who kept their collectables standard .

 

[45North]

So, if the Positive Ground controller is only 1/3 the price why not get it instead?

 

[Pierre]

So, if the Positive Ground controller is only 1/3 the price why not get it instead?

You are going to run into a lot of technical issues - stay away.

 

[fat_old_sun]

Specifically, what is the difference between these two Renogy 10A charge controllers? They are both identical in appearance, but one is "positive ground".

A PWM controller switches on/off (modulates) the ungrounded connection between the solar panel(s) (+ in a negative ground system and or - in a positive ground system) and the battery. The electronics required for switching on the positive side is a little more complicated (& hence more expensive) that what's needed for switching on the negative line. Since most vehicles have negative ground electrical system, a positive ground controller won't work. A positive ground controller may be used in small, standalone off-grid installation, as in a small cabin

 

[Bartek]

Yes, so for context, I just have a simple solar setup with a single 100w panel on my shed. The plan is to power some garden lights with it.

 

[bdl]

To expand on @fat_old_sun's comment: a "positive grounded" aka "common positive" controller simply means that the solar panel positive and the battery positive and the controller's load terminal positive are all connected in common; i.e. the controller is using low-side switching using cheaper/more powerful N-channel FETs.



Note the controller grounding does not have anything to do with the chassis grounding - in both the above examples the chassis is negative earth. It DOES matter if both the panels are grounded for some reason (in addition to the battery); i.e. so long as at least one side of the system is floating - as it should be - then either system will work.

 

[Bartek]

Now I'm more confused then ever. I think this stuff goes over my head because I'm just getting started and don't know too much about electricity to begin with. I don't know what the difference between the two diagrams is.

My setup right now is this...

All I have is a single 100w panel on the shed, which feeds into the + and - panel inputs on the controller. From there, + and - get output to the battery. The inverter is not hooked up yet so disregard it.

I want to replace the controller in the photo with one of the two in my initial post because those two have a load output, which this one doesn't. I will be using the load output to power some garden lights.

 

[bdl]

G'Day Bartek,
From what I can tell, you don't have either side earthed / grounded - so you can use either type of controller, it doesn't matter.

Even if you do end up tying your battery negative to "earth" (the metal shed), so long as your panels stay isolated then you'll still be good with both types of controller.

By "panels staying isolated", I don't mean insulating the panel frame from earth/the shed roof (the panel frames should be well earthed!), I mean not connecting the PV negative (or positive!) to earth, which you wouldn't normally do anyway.

 

[Pierre]

You are going to run into a lot of technical issues - stay away.

My comment was referenced to vehicles , RV’s , caravans etc where you are going to integrate into existing electrical systems. Would have been nice if you had all the info up front.

 

[bdl]

@pierre , tbh I'm of the opinion it doesn't matter for vehicles either. The term "positive ground" or "negative ground" doesn't actually refer to the case of the device, rather which side is switched. It's a rather bad choice of labelling if you ask me. They should have used "high side switching" and "low side switching", which is both the more conventional electronics term, is accurate and specific, and not liable to be confused with other separate concepts.

If you refer the figure I posted earlier, you'll see both examples were for a "negative chassis", e.g. a car/van.

The controller case, bolted to a vehicle chassis, would be isolated from all inputs and outputs. (Not saying there aren't examples out there that have the case connected to one of the inputs and/or outputs, but that'd be a pretty poor design.)

 

[Pierre]

@pierre , tbh I'm of the opinion it doesn't matter for vehicles either. The term "positive ground" or "negative ground" doesn't actually refer to the case of the device, rather which side is switched. It's a rather bad choice of labelling if you ask me. They should have used "high side switching" and "low side switching", which is both the more conventional electronics term, is accurate and specific, and not liable to be confused with other separate concepts.

If you refer the figure I posted earlier, you'll see both examples were for a "negative chassis", e.g. a car/van.

The controller case, bolted to a vehicle chassis, would be isolated from all inputs and outputs. (Not saying there aren't examples out there that have the case connected to one of the inputs and/or outputs, but that'd be a pretty poor design.)

I agree , the ‘earth‘ or ‘ground’ part should never have entered the conversation. In a ‘positive‘ ground system in a vehicle the battery positive is tied to the chassis.

 

[Dzl]

@pierre , tbh I'm of the opinion it doesn't matter for vehicles either. The term "positive ground" or "negative ground" doesn't actually refer to the case of the device, rather which side is switched. It's a rather bad choice of labelling if you ask me. They should have used "high side switching" and "low side switching", which is both the more conventional electronics term, is accurate and specific, and not liable to be confused with other separate concepts.

If you refer the figure I posted earlier, you'll see both examples were for a "negative chassis", e.g. a car/van.

The controller case, bolted to a vehicle chassis, would be isolated from all inputs and outputs. (Not saying there aren't examples out there that have the case connected to one of the inputs and/or outputs, but that'd be a pretty poor design.)

So if 'positive ground' / 'low side switching' devices are cheaper to manufacture, and don't effect the design / grounding logic / OCP of the rest of the system, why are almost all controllers 'high side switching'? There must be pros/cons to each approach beyond cost, do you know what they are?

 

[gnubie]

Switching the - side does cause problems for people that aren't aware of what is going on. There was a thread only recently where someone was doing something with an arduino board and a cheapie PWM controller and couldn't work out why the switched output wasn't turning off. He had commoned - via the arduino board effectively bypassing the transistor involved in turned the load output on / off.

Typically we wire switches in the + side so when you throw something odd into the mix people often trip up.

 

[Zil]

You have to mount it so the case is isolated. The case will be neutral to positive and hot to negative.

 

[Dzl]

You have to mount it so the case is isolated. The case will be neutral to positive and hot to negative.

Maybe I'm misunderstanding, but my interpretation of @bdl's comment #8 gave me the impression that this would not be the case. Am I misunderstanding?

 

[Pierre]

That’s why I do not ground anything. Positive is positive and negative is negative and both floating relative to ground.

 

[Zil]

I don't have experience with newer Renogy. But the early Renogy needed to be isolated. They caused many problems when they first were introduce into the USA. I would be safe and keep the mounting isolated.

 

[bdl]

So if 'positive ground' / 'low side switching' devices are cheaper to manufacture, and don't effect the design / grounding logic / OCP of the rest of the system, why are almost all controllers 'high side switching'? ...

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.