Dc - Dc Charger Install - Fusing And Wire Gauge Questions

[Steve and Karen]

I might be putting in the Renogy DC-DC charger soon, if the weather holds.

It is rated for 30A. Their install and spec sheet calls for 8-10 gauge and 40-45A fuses on the in (from TV batt) and out (to trailer batt).

Given the amperage the charger will be receiving from the Outback's alternator, and from the 100W panel, and the fact that nothing in the trailer that currently is 12V is fused for greater than 15A and appears to use nothing thicker than 14 ga wire... is this not a bit of overkill? Are the 8-10GA and 40-45 fuse numbers perhaps spec'd to the device's max rating and not what I demanding of it?

My concerns are mainly of charger placement and trying to run four thick 8-10 gauge wires in places where I'd have to be drilling and doing surgery. There's also temp and ignition trigger wires that need some place to go as well. What is the smallest I get away with? Safely?

I haven't settled on the right side bin or the right side cabinet as the charger location. The smallest practical wire gauge and it's bendability around corners and being able to hide under wood trim, and just how much ugly surgery that I may not be able to hide from view will likely determine where this thing can go.

Thanks in advance.

 

[SethB]

Almost all the small camper charge wiring I’ve seen and made is 10ga., including charge lines in tow vehicles installed by shops.

There are certainly stereo installers and overland campers who go down to 6, 4ga, and welding cable; to me that’s over the top. If I had an overlander with 250a alternator and a winch things might be different!

I wired up a CTEK DC/DC with 10ga and have been happy with the results. At the same time I installed a 50a self-resetting automatic circuit breaker, $7 at my local NAPA, and darned if it didn’t protect my batt during install when I shorted something with my screwdriver!

So, I’ve standardized on 10ga for charging on the… um, 3 or 4 chargers (?) I’ve installed over the years on various campers.

Note that you’ll need the big crimp terminals on your new wire. IIRC I needed 3/8” (10mm) terminals for the CTEK, and both red and black “primary” wire in 10ga if you go this direction. As well as some more common sized terminals.

If I recall the temp, ignition relay, etc. wires were all 18ga or smaller.

PS. after years of camper electric installs and experiences the single most valuable has been my recent DC/DC charger. Getting your camper battery on a good charging profile from a TV alternator is a big deal!

 

[fernlane]

PS. after years of camper electric installs and experiences the single most valuable has been my recent DC/DC charger. Getting your camper battery on a good charging profile from a TV alternator is a big deal!

This. We used to drive all day and assume that our battery was fully charged when we got to the campsite. Nope, what we were doing was slowly killing our agm battery by not giving it the charging profile it needed. The ctek changed that. With the trimetric it's kind of interesting to watch the voltage as the phases of charging change. (can't do that riding down the road )

 

[rotus8]

It is rated for 30A. Their install and spec sheet calls for 8-10 gauge and 40-45A fuses on the in (from TV batt) and out (to trailer batt).

Given the amperage the charger will be receiving from the Outback's alternator, and from the 100W panel, and the fact that nothing in the trailer that currently is 12V is fused for greater than 15A and appears to use nothing thicker than 14 ga wire... is this not a bit of overkill? Are the 8-10A and 40-45 fuse numbers perhaps spec'd to the device's max rating and not what I demanding of it?

My concerns are mainly of charger placement and trying to run four thick 8-10 gauge wires in places where I'd have to be drilling and doing surgery. There's also temp and ignition trigger wires that need some place to go as well. What is the smallest I get away with? Safely?

Be careful here. The DC to DC is rated to supply 30 amps. Your alternator can certainly put out 30 amps. Your battery will accept 30 amps if it is deeply discharged. You need to use large enough wire between your alternator, all the way through the tow and the trailer, to the charger and then to the battery, that will not cause a fire if 30 amps happens to flow. #10 is the minimum that is safe for 30 amps, don't use anything smaller for this path. Even this will give some voltage drop on a long run, with some heating of the wire if it actually reaches 30 amps, with some loss of efficiency, but that is probably not a big concern while charging. The important thing is that you never want the wire to get hot enough to start a fire.

From the battery to the rest of the trailer is fused as appropriate for the wire sizes installed.

There is one way to get away with smaller wire for the charging path and that is to add a circuit breaker in line that will trip at a lower current to protect the wire. But if you do this, the breaker may trip while you are driving and you can get a surprise by arriving at camp with a battery that didn't get fully charged.

 

[SethB]

This. We used to drive all day and assume that our battery was fully charged when we got to the campsite. Nope, what we were doing was slowly killing our agm battery by not giving it the charging profile it needed. The ctek changed that. With the trimetric it's kind of interesting to watch the voltage as the phases of charging change. (can't do that riding down the road )

Quite right. For us that means that when we drive from dry campsite to dry campsite our trailer battery will be fully charged by the alternator via the DC/DC charger. No questions, no worries, no degradation of the battery from low state of charge (SOC). An AGM should consistently have 50% SOC… Ask me how I know!

(Will be updating the lengthy CPAP pony battery thread with um, *learning* experiences from this last season.)

 

[SethB]

Be careful here. The DC to DC is rated to supply 30 amps. Your alternator can certainly put out 30 amps. Your battery will accept 30 amps if it is deeply discharged. You need to use large enough wire between your alternator, all the way through the tow and the trailer, to the charger and then to the battery, that will not cause a fire if 30 amps happens to flow. #10 is the minimum that is safe for 30 amps, don't use anything smaller for this path. Even this will give some voltage drop on a long run, with some heating of the wire if it actually reaches 30 amps, with some loss of efficiency, but that is probably not a big concern while charging. The important thing is that you never want the wire to get hot enough to start a fire.

From the battery to the rest of the trailer is fused as appropriate for the wire sizes installed.

There is one way to get away with smaller wire for the charging path and that is to add a circuit breaker in line that will trip at a lower current to protect the wire. But if you do this, the breaker may trip while you are driving and you can get a surprise by arriving at camp with a battery that didn't get fully charged.

All good points Rotus8! I think I remember that the 10ga standard for these circuits include a safety margin - do you know for sure? My memory *does* agree with R8 that 10ga from alternator to CI battery compartment does typically involve a little voltage drop… which a DC/DC charger compensates for.

One clarification on my story; the 50a self-resetting circuit breaker I installed was not to protect low-capacity wiring. I added it after careful review of late-model CI wiring diagrams showed that they now include it as standard. (I don’t quite remember if that only appeared on the CTEK 12v charger option or all versions.)

A few weeks later I realized that its value is really about sudden catastrophic draws on the battery, aka. short circuits!

 

[Steve and Karen]

Thanks guys. I knew that all of you would chime in. Still learning all this stuff. And I would rather it not be through the school of hard knocks. Frying electricals, that are for the most part inaccessible or difficult to access, is not on my to-do list. 10 gauge and 45A fuses it is.

I was thinking of taking off the right cabinet, like Henry did in this post: Battery And Tv (tow Vehicle) Output but if I am to be handling 10gauge then I think the controler has to go in the right bin and be fed into the foot of the bed and back in again into the battery compartment. Unless anyone has any other location install suggestions. A bin install, I'm thinking, takes up some cooking storage space, but it does make for an easier future fix/replacement of the DC-DC than hiding it in the cabinet.

 

[Steve and Karen]

You need to use large enough wire between your alternator, all the way through the tow and the trailer, to the charger and then to the battery, that will not cause a fire if 30 amps happens to flow. #10 is the minimum that is safe for 30 amps, don't use anything smaller for this path.

Almost all the small camper charge wiring I’ve seen and made is 10ga., including charge lines in tow vehicles installed by shops.

Rotus: Are you suggesting that the existing charge and ground wires in the 7-wire cable that is in both the trailer and my TV may not be sufficient to handle the (additional?) demands that a 30A DC-DC would place on it and that additional heavier gauge wiring through both the TV and trailer may be required? I had assumed that any aftermarket DC-DC install would simply require additional wiring that would be confined to the spaces in and around the battery compartment and where one chose to mount the DC-DC, and not necessarily need to be run end-to-end through both vehicles.

To support what you may be saying, I see that, depending on the quality of my TV 7-wire cable installation and what CI routinely runs from the 7-pin back to the battery compartment, my existing power and ground wires in both or either could be 10GA, but also as small as 12GA: https://www.etrailer.com/question-31998.html https://www.amazon.ca/Trailer-Harness-Control-10-14AWG-Connector/dp/B07G8R93Z4?th=1

Upon a cursory inspection, none of my 7-wire cable sheathing (TV or trailer) is obviously stamped with gauge sizes. Is there a reliable way to determine with a caliper at the 7-pin connectors whether or not it's heavy enough? I'm seeing wildly varying stranded wire diameters for 10GA in my Google searches.

I hope I'm not misconstruing anything you guys have imparted already.

And if my existing wiring needs no upgrading, then a flexible silicon-sheathed 10 ga like this:
https://www.amazon.ca/gp/product/B0756TDXJ9/ref=ewc_pr_img_1?smid=A2O30CO8D3AY3D&th=1 would play well with my set-up and be the best to work with?

 

[rotus8]

When I did my DC-DC install, I noted that the 7-pin cable from the hitch back to the kitchen has #10 ground and DC feed; the other wires may be smaller as they don't carry as much current.

One would hope that the wiring in the tow vehicle is consistent with the circuit it connects to, If factory wired it will have a fuse or other protection and wire to match. If the hitch was installed after-market, one hopes it was done properly.

 

[Steve and Karen]

the 7-pin cable from the hitch back to the kitchen has #10 ground and DC feed

Good to know. I'll have to tear into my TV wiring then for a caliper inspection. I'm thinking that anything less than 0.10" dia is a good indication that I'm probably dealing with 12 gauge.

The TV 7-pin and brake controller were installed at the same time at a trailer shop; I'm hopeful that the availability and use of 12 gauge wire for 7-pin installs out there is not a frequent choice by installers.

 

[TheSongDogHouse]

Steve, I ran a 10ga wire with 30a fuse at battery to power the CI, via the 7pin connector. At Craigs suggestion after troubleshooting everything including trailer wiring with the Nests unique electrics test bench on wheels...

The 12ga was repeatedly tripping the 15a fuse as a result of the same long wire run, but in 12ga that worked fine in past on a little tent trailer,
And the new but waterlogged ice gunked 7pin harness connectors,

and had nothing to do with the CI and CTEK that draws about 6A. It was just enough resistance all the way from tv battery to hitch that did it.

I ran the replacement wite same as the original; thru firewall, under trim door sill, and thru the various removable body panels, with help of my independent VW mechanic.

This is simple as it bypasses ignition, smart alternator,
But it requires I recollect to disconnect the trailer tow plug, as is generally recommended in the owners manual for an overnight stop, anyway.

So far so good.
I also upgraded the old flooded cell lead acid battery in trailer with an off the shelf AGM.

My Alltrack has the ability to change the charge voltage via the BCM usung VagCom software (aka VCDS) which is commonly used bu independent VW shops for a variety of troubleshooting and coding options.

So the alternator charges the AGM car battery at a higher level to get to 100%, and presumably the CTEK manages that to do same to the house trailer as well.

But I could be wrong as I havent dug down into how it works or checked voltages etc, other than by the charge level on OEM panel, or a plug in volt meter via the DC port in galley.

I have no idea if a comparable shortcut method exists in Subaru's, but my guess is user forums might, and since something like 50% of CampInns are or have been polled as being towed by Subies, perhaps Craig or Cary might know if this simple hack is ok, if another of the cognoscenti does not reply, first.

 

[Steve and Karen]

Thanks Kevin. I haven't been able to dissect the TV harness wiring as yet to see where it's drawing its power from. And through what size of wire. Hopefully it doesn't require a full rewire due to to undersized wiring. If I haven't blown or burned anything yet, chances are it's up to snuff and I can push ahead, with some help along the way.