12v wiring headache

Slow moe

Likes Bikes
Hi all,
Hoping for some advice about wiring up a dcdc charger and solar setup in my camper trailer. In particular about earthing it.

I am using a redarc bcdc1225d charger with the hope to charge a lifepo4 battery from the car when driving and via solar when camping. The charger needs to be close to the aux battery so will be mounted in the trailer. That also allows me to use the mppt charger for the solar while u am out and about in the car.

The earthing does my head in. I can never quite get my head around earthing to a chassis and then connecting the chassis back to the negative battery terminal. What is the point?

More specifically about the job at hand:

1) Should the negative from the solar panel earth to the trailer chassis? Or is it fine to run it straight back to the negative terminal on the auxiliary battery? In my old setup (charging an AGM battery only fro. Solar) I simply ran the negative cable from the panel to the battery. Was that dodgy AF?

2) I assume where running in a trailer the black lead should run back to the vehicle (planning to use anderson style leads). But what does that mean when the vehicle isn't connected and the system is running from solar and bits j pieces drawing from the battery?

Grateful for any advice. Taking the kids camping and don't really want to electrocute them (not sure they'd appreciate even a mild 12v wake-up)
 

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Dales Cannon

The Olden Dazed
Staff member
Feed from car is easily done through a 50A Anderson plug. Run both positive from battery and negative from battery or chassis, it doesn't matter. Have the positive feed go through a manual circuit breaker so you can isolate the feed if you ever need to.

I run these... 30A for the BCDC in the back of the 4wd (25A) and 60A for the BCDC in the camper (40A).

388959


In the camper run the negative from the Anderson plug to the negative on the BCDC and and also have that run to a good earth on the chassis. I just used a negative post that had cables that run from the car, connected to chassis and to the BCDC. The solar panel can then run direct to the BCDC with the negative lead also going to that earth point.

Something like this... no need for a positive terminal
388958


Make sure the wiring is of a suitable size. Redarc have guides on their site. Solar can be 4mm2 or 6mm2 (note the mm2 and NOT 6mm automotive cable which is shit). For the extra $ now run bigger in case you upgrade to a 40A or 50A dcdc charger at some point.

Consumers in the camper will use the chassis / battery negative as reference earth so make sure your batteries are connected neg to chassis, again that common earth is a very useful way to manage 5 or 6 cables.

On a side note make sure your cables to the inverter are big enough to cope with the current flow and run these direct to the battery. If you have multiple batteries there are guides about connection between the battery to evenly draw from the batteries and not just the first one and rely on some parallel cables to feed back into that.

Our camper sits for weeks at a time camping with only solar infeed to keep the batteries topped up. We have the usual fridge in the camper and lights and also run a rice cooker off an inverter, electric blankets when we camp out west in the dead of winter, fans in summer etc. All work ok. Two 120AH AGMs with a third that can be wired in for extended periods.

Make sense?
 
Last edited:

Slow moe

Likes Bikes
Feed from car is easily done through a 50A Anderson plug. Run both positive from battery and negative from battery or chassis, it doesn't matter. Have the positive feed go through a manual circuit breaker so you can isolate the feed if you ever need to.

I run these... 30A for the BCDC in the back of the 4wd (25A) and 60A for the BCDC in the camper (40A).

View attachment 388959

In the camper run the negative from the Anderson plug to the negative on the BCDC and and also have that run to a good earth on the chassis. I just used a negative post that had cables that run from the car, connected to chassis and to the BCDC. The solar panel can then run direct to the BCDC with the negative lead also going to that earth point.

Something like this... no need for a positive terminal
View attachment 388958

Make sure the wiring is of a suitable size. Redarc have guides on their site. Solar can be 4mm2 or 6mm2 (note the mm2 and NOT 6mm automotive cable which is shit). For the extra $ now run bigger in case you upgrade to a 40A or 50A dcdc charger at some point.

Consumers in the camper will use the chassis / battery negative as reference earth so make sure your batteries are connected neg to chassis, again that common earth is a very useful way to manage 5 or 6 cables.

On a side note make sure your cables to the inverter are big enough to cope with the current flow and run these direct to the battery. If you have multiple batteries there are guides about connection between the battery to evenly draw from the batteries and not just the first one and rely on some parallel cables to feed back into that.

Our camper sits for weeks at a time camping with only solar infeed to keep the batteries topped up. We have the usual fridge in the camper and lights and also run a rice cooker off an inverter, electric blankets when we camp out west in the dead of winter, fans in summer etc. All work ok. Two 120AH AGMs with a third that can be wired in for extended periods.

Make sense?
Thanks. I think it makes sense. Will check in the morning when I have drunk slightly less. I Don't know much but I'm pretty sure electricity and booze are an interesting combination.

I'm not running an inverter at all so that makes it easier - simply running 12v led lights, 12v fridge and 12v water pump.

Is the point of the earth on the trailer in this case really just a convenience issue?
 

Dales Cannon

The Olden Dazed
Staff member
Thanks. I think it makes sense. Will check in the morning when I have drunk slightly less. I Don't know much but I'm pretty sure electricity and booze are an interesting combination.

I'm not running an inverter at all so that makes it easier - simply running 12v led lights, 12v fridge and 12v water pump.

Is the point of the earth on the trailer in this case really just a convenience issue?
Yes and no, some of your existing wiring might just connect locally to the chassis so you need to make sure it is all connected. The battery chassis earth might be light on for 25A from the car. Best to just hook them all together with good sized cables. If there is 25A travelling in on the red cable you need to get 25A back too.

And I recommend genuine Andreson plugs and not any of the myriad of copies. Have seen some others fail from UV over the years while genuine plugs have lasted. Could be coincidence but they are not expensive.
 

andrew9

Likes Dirt
The earthing does my head in. I can never quite get my head around earthing to a chassis and then connecting the chassis back to the negative battery terminal. What is the point?

More specifically about the job at hand:

1) Should the negative from the solar panel earth to the trailer chassis? Or is it fine to run it straight back to the negative terminal on the auxiliary battery? In my old setup (charging an AGM battery only fro. Solar) I simply ran the negative cable from the panel to the battery. Was that dodgy AF?
Just make sure that the path on the negative side is as robust as the positive side wiring and it'll be sweet. This path can be an unbroken wire or the wiring can take a detour through the chassis, the chassis is the "wire" for that section.
That drawing does kinda make it seem like you have to connect to ground/chassis/earth, but It's just as good, or better, to run a wire all the way to battery negative.
They are showing the most common method, and they use some redundant terms in the process, as earth, ground and negative all mean the same thing in this example.


2) I assume where running in a trailer the black lead should run back to the vehicle (planning to use anderson style leads). But what does that mean when the vehicle isn't connected and the system is running from solar and bits j pieces drawing from the battery?
When you disconnect the vehicle both the positive and negative are disconnected at the same time, so it doesn't matter at all.
It will be an isolated circuit using the battery in the trailer, the negative of that battery is all that is needed.
 

Slow moe

Likes Bikes
Thanks all.
Just to clarify (again, 2 small people I don't want to fry), is there any need to touch the chassis at all if all negative cables are run all the way back to the auxiliary battery? It will be fairly conveniently located and should have a grand total of 3 loads drawing off it so not too many cables on the terminal
 

link1896

Is not a gynaecologist but will look at your fork
completely fine to run a negative cable back to the battery and not connect to the chassis for the current return path.

best you update this thread as you go so the hive mind to help guide you
 

Slow moe

Likes Bikes
completely fine to run a negative cable back to the battery and not connect to the chassis for the current return path.

best you update this thread as you go so the hive mind to help guide you
Give it a week or two and my update will be in the confessions thread
 

Slow moe

Likes Bikes
This is finally starting to take shape - busy at work and cold nights have slowed things down. So Im back here again hoping to pick the brains trust.

I've opted to run the earths in the trailer back to the auxiliary battery - figured it wasn't much more effort and given the trailer lives outside and sometimes goes for months without use, doing this should save the connections corroding.

I've come to the black wire from the DCDC charger and am scratching my head which battery this should earth to: the auxiliary battery or the car's battery. I feel like there should be a complete circuit with the auxiliary battery but then feel the same about the car battery.

If the auxillary battery was in the car, earthing to the chassis would create both circuits...
Do I run it to the auxiliary and then connect the negative of each battery to each other?
 

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Dales Cannon

The Olden Dazed
Staff member
Auxiliary should be earthed to chassis and also main battery so either should be the same. I have an aux in the car and two sometimes three aux in the camper. Car aux is charged in the car by bcdc1225. Black wire on the aux is common to the black wire on the bcdc and the neg of the main battery. The bcdc 1240 in the camper is common to camper chassis, aux neg and main battery neg. Main battery obviously connected to car chassis. All common neg when hooked up and common chassis to chassis. When standalone neg is still connected to camper chassis. The black wires are also common with neg on the various solar panels which feed into the bcdcs.

Make sense?
 

Flow-Rider

Burner
If the auxillary battery was in the car, earthing to the chassis would create both circuits...
Do I run it to the auxiliary and then connect the negative of each battery to each other?
If you have both batteries earthed, whatever accessory you have connected with the + terminal to each individual battery is what the circuit will draw from, unless both of the batteries are connected through the + terminal permanently. If you want to waterproof the earth lugs, clean the metal contact surfaces well, bolt your earth lug up tight, and then smear some high-quality silicone adhesive over the top.
 

Dales Cannon

The Olden Dazed
Staff member

These are for vehicle set up so just place a 50A Anderson plug in the red wire and run a black wire from the main battery to the neg side of the Anderson plug and then on to connect to the black wire. The only tricky thing is the blue trigger wire needs to be either connected to a vehicle accessory connection or as I did just join it to the red wire but also fit an sbi12 on the vehicle side of the red wire. This means when the red wire from the battery drops to 12.7V the sbi12 will open and stop draining the main battery. It will close when the engine starts and the battery gets to 13.2V. Like this

.
 

Slow moe

Likes Bikes
Sweet! Getting closer.
About to hardwire the lead for the fridge as I don't trust a cigarette lighter plug not to fall out on dodgy roads. Am I right to think that the 2 prongs are the negative and the other part (on the right) is the positive?
 

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Dales Cannon

The Olden Dazed
Staff member
Sweet! Getting closer.
About to hardwire the lead for the fridge as I don't trust a cigarette lighter plug not to fall out on dodgy roads. Am I right to think that the 2 prongs are the negative and the other part (on the right) is the positive?
Use an Anderson plug for the fridge. If you pinch the lead or it has a problem in the bush are stuck if you have hard wired it. Both mine are Anderson plugs.

Centre is positive but as always check yours to be sure. Merit plugs, the red bit, are OK to use by the way.
 

ozzybmx

call me Cáitín
Use an Anderson plug for the fridge. If you pinch the lead or it has a problem in the bush are stuck if you have hard wired it. Both mine are Anderson plugs.

Centre is positive but as always check yours to be sure. Merit plugs, the red bit, are OK to use by the way.
I rewired my Waeco lead to Anderson nearly 20yrs ago after the dodgy cig plug came out.

Grab a surface mounted plug and mount it in the plastics or drawer unit.

The plastic cover lasts about a week before snapping off.

390337
 

Slow moe

Likes Bikes
Thanks for all your help.
It's certainly not professional quality but I'm pretty happy with the finished product. In due course I will probably carpet the inside of the box to make it look more finished but suspect that'll have to wait
 

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