Renogy DCC30S (or 50S) Grounding Question

[beneng_jr]

Curious for those of us mounting the DCC30S in a truck camper, not a modern cargo van, where we would ground it to.

My assumption is that I can drill a hole in the nearest, most convenient place in the frame under the bed and screw off the ground wire there. Or do I need to locate the trucks' (2015 Canyon) Common Ground post which I would assume is closer to the engine compartment?

I was told that I shouldn't run the ground wire all the way back to the starting battery's negative post, that it might create some kind of loop which would mess with the vehicles electrical system.

 

[john61ct]

Any charger should have a home run pair to the target battery.

And loads as well, IMO never rely on chassis ground for anything expensive, important or high-current.

 

[beneng_jr]

Which battery do you mean by 'target' battery (start or house)

 

[DaveInDenver]

Which battery do you mean by 'target' battery (start or house)

The battery that the charger is intended to charge.

That kind of leads to understanding what you're doing in more detail.

Are you charging a stand alone house battery or are you talking about your main starting battery that's serving dual uses? Or trying to charge two batteries?

If you're charging your main battery then you can't completely ignore the chassis ground. You might still want to run all the way back to the negative, though. If it's a house battery powering it's own loads then it's easier to run both a positive and negative between the charger and be done with it. Just use the battery negative as a common point and don't tie to the truck chassis at all.

When you say truck camper is it a slide-in that's basically isolated or are you talking about a camper shell where the loads are actually body mounted (e.g. things like metal cases being actually in contact with the truck body)?

Most likely the engine block is the common ground point for your truck's electrical system and trying to use the chassis as a reference or return for added electrical can come with challenges.

Sometimes you have no choice to deal with it, such as mobile two-way radios with body-mounted antennas. In that case you will have the body tied to electrical returns whether you like it or not.

Other times you go to lengths to avoid it, such as 120VAC systems that must have complete ground isolation from the chassis. Sometimes using the chassis is a convenience and you figure out a way to do it successfully.

In any case you need to be intentional, either commit to it or do not.

What he's suggesting is it's usually easier and introduces fewer issues to provide complete return paths for all your add-on chargers and loads instead of relying on a common one such as your frame and chassis.

The term you're referring to is ground loops or ground sneak paths. These happen when you mistakenly provide more than one way for current to get back to its source. What happens is your normal return/ground develops resistance and that creates problems itself or leads to current trying to find a lower resistance path. This might be lower in resistance but not large enough in size to handle your maximum currents or worse with respect to RF (in the case of radios). It might cause alternator noise on your radio, excessive voltage drop that leads to poor charging or in the absolute worst cases melted wires or a vehicle fire.

By running a dedicated, properly sized negative from your charger to the battery you're charging you just make things more simple.

 

[beneng_jr]

The battery that the charger is intended to charge.

That kind of leads to understanding what you're doing in more detail.

Are you charging a stand alone house battery or are you talking about your main starting battery that's serving dual uses? Or trying to charge two batteries?

If you're charging your main battery then you can't completely ignore the chassis ground. You might still want to run all the way back to the negative, though. If it's a house battery powering it's own loads then it's easier to run both a positive and negative between the charger and be done with it. Just use the battery negative as a common point and don't tie to the truck chassis at all.

When you say truck camper is it a slide-in that's basically isolated or are you talking about a camper shell where the loads are actually body mounted (e.g. things like metal cases being actually in contact with the truck body)?

Most likely the engine block is the common ground point for your truck's electrical system and trying to use the chassis as a reference or return for added electrical can come with challenges.

Sometimes you have no choice to deal with it, such as mobile two-way radios with body-mounted antennas. In that case you will have the body tied to electrical returns whether you like it or not.

Other times you go to lengths to avoid it, such as 120VAC systems and complete ground isolation from the chassis. Sometimes using the chassis is a convenience and you figure out a way to do it successfully.

In any case you need to be intentional, either commit to it or do not.

What he's suggesting is it's usually easier and introduces fewer issues to provide complete return paths for all your add-on chargers and loads instead of relying on a common one such as your frame and chassis.

The purpose of the system is to use the vehicles alternator/start battery to charge a RV (house) battery inside a truck camper. It is basically a topper-style camper, not a slide in, and I was already planning on pulling a fused 4awg wire from the positive terminal of the start battery through the underside of the vehicle and up through one of the ports in the driver-rear of the bed. That wire attaches to the dedicated start/alternator input of the device

The device has positive-out and negative-return posts for attaching directly to the house battery (so that's not in question). That same negative return post also needs to be attached to the vehicles common ground point. I was planning on running that wire out through the same port in the bed, but the question is, after that, what do I actually attach it to (frame, bed, cab, block, start battery neg, or dedicated factory ground)? The manufacturer claims that you can return it the start battery neg but I'm also hearing elsewhere that can cause problems with modern vehicles electrical systems.

.

 

[DaveInDenver]

From the description the least problematic is probably a full run back of the same size (4 AWG in your case) to the starting battery negative.

Then make sure to have a ground bus bar to the house battery negative for all the loads you hang off it and make sure to isolate any cases that happen not to be isolated (like radio bodies are commonly) from the chassis. Alternatively power such things from the starter battery if they must be chassis referenced.

The target battery for your charger is the house battery.

Making any connections to the frame are likely to make your life harder eventually. Let the stock wiring harness do its thing and have yours completely isolated from it with just the two heavy (+) and (-) connections to the starter battery.

 

[john61ct]

There is no real Ground there in the true sense of an Earth reference, as in thick copper buried deep in wet ground. Vehicles are "floating", an isolated system.

As I stated, the negative side should match the positive half of the circuit, to create a clean low resistance return path, same gauge same length.

The chassis can help establish a Common Reference, no problem having your various DC circuits sharing that at multiple points, to

ensure that all surfaces a person can touch are at the same voltage potential,

just do not rely on that for Negative Return.

Your engine Starter batt is the "source side" circuit, the alternator is one actual charge source, no energy should flow from Starter batt, it is just a buffer to absorb spikes / surges etc

Your House bank circuit is the target, and you need to figure out if the Renogy DCDC has ACR/VSR functionality, so that as the only connection between those two sides, it keeps them isolated when there is no active charge source.

Solar being the other one.

If not then you need some sort of automated switch to to so, if not a VSR (combiner) maybe an IGN solenoid will be enough.

 

[DaveInDenver]

Not multiple points. You're trying to avoid creating ground loops.

 

[john61ct]

Maybe you are thinking AC principles.

DC only, in a vehicle, the Common Reference can and should be tied in to multiple points, metal housing points marked "ground" etc wherever you like.

Trailer, camper etc included.

The Negative Return paths are separate and designed to be a much lower resistance, that's for high current.

 

[john61ct]

The car battery (Starter) is not involved.

The House battery is on the target side.

On the source power (engine) circuit, all the energy drawn by the DCDC is coming from the alternator.

These devices are specifically designed to work around the purposefully designed charging limitations of modern systems where everything is controlled through the vehicle computer.

They output a consistent charge profile to the target House bank regardless of input voltage.

They also temper the excessive draw of lithium banks, which otherwise do damage the vehicle charging system.

Sterling makes the best with their BB series, Kisae and CTEK are great, and I'm sure Victron's are good too by now.

Renogy in general is crap, but unless it actually breaks it does do the job.

In general don't get combi units, solar controller should be separate, unless you're just keeping Starter topped up while parked off grid.

 

[dfinn]

I'm about to do this same setup with a Redarc unit and I'm planning to run + and - from the starter battery to the bed of my truck. The ground from the starter and from my "house" battery will then both connect via a Blue Sea bus bar.