Renogy 50amp DCDC w/ MPPT - Chassis Ground? (3 Viewers)

[joshik]

Hi. I am installing a Renogy 50A DCDC w/MPPT charge controller to charge my house battery located in the cargo area of my 4runner.

The diagram shows that the both the starter battery (charge source), house battery and solar panel all connect to the controller's common ground.

Could I just connect the common ground of the controller to the chassis of the vehicle instead of running a ground all the way back to the starter battery? I ask because the total length of + and - from the starter battery would be close to 50' +/- a few feet. According to wire gauge calculators at 40amps (max charge my house battery can handle) I would need 2 or 1AWG and I really dont want to run that large of wire. If I shorten the ground and go to the chassis I could easily use 4awg.

Thoughts?

 

[spressomon]

You don't necessarily need to adhere to 1-3% loss for wire length for DC-DC charger circuit; 10%, for instance, allows you to probably go with 4AWG (I didn't do the calc...but 4AWG would be in the general ballpark for feed from alternator to DC-DC based upon your 50'); easier and less $ than 1-2AWG.

After experiencing a couple different issues over the years with using chassis as the ground, my MO is to use wire for ground; YMMV. Other than cost and maybe some physical challenges of where to run the electrical cable, its the 100% surefire way to know you have a good ground path. Do it right, once.

 

[joshik]

You don't necessarily need to adhere to 1-3% loss for wire length for DC-DC charger circuit; 10%, for instance, allows you to probably go with 4AWG (I didn't do the calc...but 4AWG would be in the general ballpark for feed from alternator to DC-DC based upon your 50'); easier and less $ than 1-2AWG.

After experiencing a couple different issues over the years with using chassis as the ground, my MO is to use wire for ground; YMMV. Other than cost and maybe some physical challenges of where to run the electrical cable, its the 100% surefire way to know you have a good ground path. Do it right, once.

Oh. What about risk of the wire heating up and causing a fire?

 

[Tesota]

Could I just connect the common ground of the controller to the chassis of the vehicle instead of running a ground all the way back to the starter battery? I ask because the total length of + and - from the starter battery would be close to 50' +/- a few feet. According to wire gauge calculators at 40amps (max charge my house battery can handle) I would need 2 or 1AWG and I really dont want to run that large of wire. If I shorten the ground and go to the chassis I could easily use 4awg.

Thoughts?

Definitely recommend running a separate ground back to the start battery. 4 AWG should be fine at that length, would be about 5% voltage drop at 50'. It'll get a little warm at 40A but nothing that would cause a fire.

Check these out to compare your options:

Tesota Overland – Wire and Cable Size Table

Use this table to figure out the minimum wire or cable size needed for your equipment in your battery system. Adjust for cable length, cable composition, desired voltage drop and ambient temperature.

www.tesotaoverland.com

Tesota Overland – Wire and Cable Size Calculator

Use this calculator to figure out the minimum wire or cable size needed for your equipment in your battery system. Adjust for current, cable length, cable composition, desired voltage drop and ambient temperature.

www.tesotaoverland.com

 

[joshik]

Definitely recommend running a separate ground back to the start battery. 4 AWG should be fine at that length, would be about 5% voltage drop at 50'. It'll get a little warm at 40A but nothing that would cause a fire.

Check these out to compare your options:

Tesota Overland – Wire and Cable Size Table

Use this table to figure out the minimum wire or cable size needed for your equipment in your battery system. Adjust for cable length, cable composition, desired voltage drop and ambient temperature.

www.tesotaoverland.com

Tesota Overland – Wire and Cable Size Calculator

Use this calculator to figure out the minimum wire or cable size needed for your equipment in your battery system. Adjust for current, cable length, cable composition, desired voltage drop and ambient temperature.

www.tesotaoverland.com

cool thanks for the links!

the links were saying for DCDC you should not exceed 3% voltage drop. But I guess I could just lower the max charging AMPs to 30 which is plenty as well. That should keep things well within spec.

 

[spressomon]

Oh. What about risk of the wire heating up and causing a fire?

Good quality marine grade stranded electrical cable, such as Ancor (vinyl cover, tinned strands), is rated to 221ºF dry / 167ºF wet.

https://www.ancorproducts.com/-/media/inriver/SPEC_Ancor_Primary_Wire_Battery_Cable_TCHDAT.pdf?modified=20200115170052

A little more information here on subject:

 

[joshik]

Good quality marine grade stranded electrical cable, such as Ancor (vinyl cover, tinned strands), is rated to 221ºF dry / 167ºF wet.

https://www.ancorproducts.com/-/media/inriver/SPEC_Ancor_Primary_Wire_Battery_Cable_TCHDAT.pdf?modified=20200115170052

A little more information here on subject:

thanks for the vid! yeh so much varying info out there. 10% voltage drop ok. No more than 3%. etc etc.

As for the wire, I got some 105C rated pure copper 370strand 4awg wire so following what the video says, i should be in the clear.

 

[spressomon]

It depends on the application: 10% voltage drop for PV panels to MPPT controller might be a deal breaker if, for instance, a 5v threshold isn't maintained to allow the MPPT controller to flow current (minimum 5v differential between resting battery voltage and MPPT output). But, given the variable output of alternators, I suspect feeding a DC-DC charger isn't that critical in terms of voltage input at the charger. Having said that, other than cost and form factor, there isn't a downside to using larger capacity wire/cable to keep the voltage drop to a minimum.

 

[Tesota]

the links were saying for DCDC you should not exceed 3% voltage drop. But I guess I could just lower the max charging AMPs to 30 which is plenty as well. That should keep things well within spec.

As a general guideline 2-3% is what you want for a DC-DC charger but 5% isn't unsafe by any means, just slightly less efficient. The 4 AWG cable you bought should do just fine.

10% voltage drop ok. No more than 3%. etc etc.

Thanks for pointing out the conflicting/confusing guidance, will update to clarify a bit.

 

[sdnative]

Minimizing input voltage drop for DC-DC chargers is also pretty important if the charger is using the main input wires to sense starter battery voltage (vs a dedicated pair of sensing wires). The voltage should be fairly constant over the range of charge current. The charger may go in and out of engine off and low voltage detect as the voltage at the charger input terminals droops with load.

To be safe, size DC-DC wiring for less than 3% voltage drop, less if possible.

 

[spressomon]

Not a fan of anything Renogy and haven't looked at the Renogy DC-DC charger specs but Victron has an input range of 9-17v.

 

[ducktapeguy]

I'd run a dedicated ground wire because you need to run a + wire to the battery anyway. Running 2 wires is the same amount of work as running 1 and it'll be more reliable and save you a lot of headaches in the future.

The DC/DC MPPT controller also has a dedicated voltage sense wire so voltage drop shouldn't be an issue, the controller will automatically compensate for the voltage. Also, If your house battery can only handle 40A most likely you'll never see that much current through those wires and probably only for short periods of time so 4ga should be more than enough.

 

[LandLocked93]

Assuming 2 things:
1) The source batt and target batt for the Renogy are on opposite ends of the vehicle
2) The Renogy is next to the battery it is charging (in the back) and not up front.

If so, then yes a chassis ground (*that is also a frame ground) has been fine in my experience with a RedArc BCDC.
*The bolt in a hole in the body where my BCDC ground is connected (inside the cargo area) is coupled with a short run from the underside of that same bolt (outside the body) to another bolt in a hole in the frame.

It is the Renogy current draw for which you scale the size of the wire run from front to back. Yeah the house batt may have a charge rate limit, but should something go awry you want that wire to handle the full current draw of the Renogy, 50A. Could fuse it to 40A for safety if desired.

Also, an often overlooked/underappreciated aspect of BCDCs is their voltage drop compensation aspect, enabling the use of less expensive wiring.
As another poster highlighted, the Renogy has an input of down to 7V.
So no, v-drop is hardly a concern.
Yes this will affect current flow max were you to use, say 12ga front to back. But the 4ga is plenty sufficient.

And between reality and stated charge limits of the batt being charged, the Renogy output, and average charge level you'll run that target batt down to...it is unlikely that 40A (much less 50A) will ever flow from front to back.

 

[george_tlc]

The chassis/frame is not really a good ground 'path'. Consider that the entire body and engine and transmission are rubber mounted...

Look at how Toyota has done the grounding. The major ground for the starter is via the engine block, the starter/alternator are grounded via bolts to the engine assembly and there's a major ground that runs from the main battery to the engine block. There's a ground connection from the battery to the body near the battery tray area. There are ground straps from the engine to the firewall. All Toyota ground connections (within the vehicle) are to studs in the body. Don't assume the frame is anything but a structural member to hold the vehicle together. Electrical grounds should be made to the body or direct to the battery.

If you run grounds to the battery AND the device you are powering is also making electrical contact to the body, then FUSE that ground wire at the battery end.

cheers,
george.

 

[LandLocked93]

The chassis/frame is not really a good ground 'path'.

What else would you ground to?
The alternator, starter, ECU, everything is grounded to one or the other. Or both.

Consider that the entire body and engine and transmission are rubber mounted...

Which is the point of all the grounding straps, connecting the chassis to the frame.

Look at how Toyota has done the grounding. ... There are ground straps from the engine to the firewall.

Respectfully...right.
After all, the 80's electrical is ground-switched.
And as such, said same requires a vehicle-wide - and connected to - batt neg common ground to nominally function.

 

[george_tlc]

What else would you ground to?
The alternator, starter, ECU, everything is grounded to one or the other. Or both.


Which is the point of all the grounding straps, connecting the chassis to the frame.


Respectfully...right.
After all, the 80's electrical is ground-switched.
And as such, said same requires a vehicle-wide - and connected to - batt neg common ground to nominally function.

^

The alternator and starter are grounded to the engine block. The ground straps from the block go to the body. The battery grounds (2 of them), one thick goes to the engine block - that is THE high current ground for the alternator and the starter, one thin goes to the body/fender. The vehicle body is the ground path for everything electrical that isn't getting its ground directly from the engine/block/transmission/transfer box.

Definitions here:
Frame = Chassis = The big steel structure that the body and engine/transmission/etc is sitting on via rubber bushings/mounts.
Body = The steel thing that sits on top of the frame/chassis that.

The Frame/Chassis (not the body) is NOT part of the grounding system. It 'may' make connection to the ground, but is not purposefully grounded.

Engine/transmission/transfer box are suspended on rubber mounts that do not conduct electricity.

When you want a ground connection, you make it to the body (not the frame/chassis). Note that Toyota connects grounds to studs on the body.

Ground switched has nothing to do with this discussion of whether to use the frame/chassis as a ground path. In fact only a very few things on an 80 (or other similar vehicles) are ground switched - some of the headlight stuff, horn. Tail lights are mostly grounded and positive switched. The ignition switch switches positive and that goes to a lot of stuff including ECU etc.

If you aren't sure about this, go and look at your 80 and try to find ground connections to the frame/chassis that Toyota is relying on to provide ground to all the vehicle electrical stuff.

cheers,
george.

 

[LandLocked93]

The alternator and starter are grounded to the engine block. The ground straps from the block go to the body. The battery grounds (2 of them), one thick goes to the engine block - that is THE high current ground for the alternator and the starter, one thin goes to the body/fender. The vehicle body is the ground path for everything electrical that isn't getting its ground directly from the engine/block/transmission/transfer box.

Not trying to be difficult, but...
...my '93 has a ground strap from the intake manifold to the body.
Beyond that, the aux batt is grounded to both the body and the engine block.
This ensures there are no ground loops, either body or chassis-wide.

 

[george_tlc]

^ Yes, manifold/engine/body etc. NOT the frame/chassis. Manifold is 'part' of the engine - it's bolted to it as is the exhaust system.

Essentially the entire engine/transmission/transfer box/body are suspended on rubber from the frame/chassis. So, if you want a good ground you need to connect to the engine or the body. High current path is to the engine block since that is the path to the starter and alternator. The smaller ground connections (straps etc) are to the body for lower current paths (lights, electronics, etc).

Ground loops are not the issue here either. These are power grounds, not audio stuff.

Again, BIG ground wire from battery to engine block - starter & alternator high current path. Small straps from engine to body and from battery to body for all the other stuff.

My point is that the frame/chassis is NOT where ground connections are made and should not be relied on.

Just trying to be clear for future readers of threads like this about how the ground wiring system is implemented in vehicles like the 80, i.e. body on frame. In your post above my first response, you stated ground connections to frame/chassis. I'm clarifying that is not correct.

cheers,
george.

 

[LandLocked93]

Ok...
...at the very least consider brake lines with metal terminations - OEM or stainless braid- which connect the body to the frame in a metallic fashion. (OEM may be rubber on the outside but there is metal belting inside the rubber)
Beyond that, consider the springs which simultaneously contact the body and the axles.

Or perhaps the driveline itself...from engine to axle...yes there are rubber bushings on all the moving parts but the metal collars inside the bushings through which the bolts are positioned enable a ground between the engine and the frame via the frame/axle ears, again through which the bolts connect.

Ground loops impact more than just audio. One just can't hear it, is all.

 

[george_tlc]

Yes, and tailshaft and bearings to axle etc. The point is that ground is via engine and body. Frame/chassis may have indirect grounding, but is not used as a ground path.

I've got a pretty good grasp of ground loops - my EE work ensures I understand that along with circuit design and board layouts.

Ground loops are not an issue in the vehicle power system.

One does need to understand where the high current paths are and how a failure in one of them can cause another ground (of thinner gauge) to carry more current than it should. Hence fuses and fusible links.

Also, why in my early post I stated if you have a grounded device (through its body to the vehicle body - even say an antenna coax) and you also carry a ground wire from that device (e.g. a Ham radio) back to the battery, you need to fuse at the battery end. That's because if you lose main ground connections to body, engine that Ham Radio will become the 'ground' path for the high currents and without a fuse it can become a fire hazard.

Anyhow, this horse is fairly dead at this stage

cheers,
george.