Positions of inputs & load outputs along auto 12v wiring

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Positions of inputs & load outputs along auto 12v wiring

Post by Lorgar » 02 Feb 2022, 5:27 pm

Hey all,

I currently have an auxiliary battery running my fridge. I plan to add solar to the auxiliary now to charge this battery while not driving, and in future I will likely want to add an inverter.

I have a decent-ish understanding of automotive electrical and know how each individual thing works, but when combining them all into a larger system I have a few gaps when it comes to the wiring position of things.

As you know, when you look at a typical wiring diagram it's all very neat, with all power sources going directly into the battery, and all load being taken directly from the battery.

This doesn't always fit with real life though.

My question is, what happens if the order of these things along the line is changed. What if the solar input connects inline between the inverter and battery, rather than directly to the battery.

What if the inverter sits between the battery and solar panels.

Like so.

automotive-wiring.gif
automotive-wiring.gif (7.52 KiB) Viewed 1979 times


The one point I'm not sure about is the solar pushing power in to the system at different points along the line, before or after load devices pulling power out of it.

Does this matter? Or is the whole system effectively the same 'pool' that is just being filled and emptied, regardless of where in the line things sit?

Thanks all.
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Re: Positions of inputs & load outputs along auto 12v wiring

Post by Oldbloke » 02 Feb 2022, 5:38 pm

"Or is the whole system effectively the same 'pool' that is just being filled and emptied, regardless of where in the line things sit?"

I'm inclined to think that's correct. Assuming the wiring has the capability. (resistance)

Why don't you ask an Auto electrician? Or check out 4x4 forums.
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Re: Positions of inputs & load outputs along auto 12v wiring

Post by No1_49er » 02 Feb 2022, 6:56 pm

From an electrical point of view, those three wiring diagrams are identical. In other words, the same three things drawn differently.
An auto-lecky might be able to unravel your question more thoroughly with direct conversation, to achieve your specific goal.
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Re: Positions of inputs & load outputs along auto 12v wiring

Post by scoot » 02 Feb 2022, 7:13 pm

Same same but different. You can also add to your picture the charge coming from the alternator if you currently run a "conventional" dual battery set-up.
My best advice when connecting multiple sources of feed and draw is to use a specialised unit like the ctek or redarc units. Has inputs for solar and alternator, isolates main battery, charges better (dc-dc), etc., etc. Not trying to upsell but they are relatively simple and they just work.
In theory your diagram will work but most diy jobs will inevitably fail due to sometimes un-predictable outcomes from so many "circuits" being linked.
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Re: Positions of inputs & load outputs along auto 12v wiring

Post by Lorgar » 02 Feb 2022, 7:31 pm

Oldbloke wrote:Why don't you ask an Auto electrician? Or check out 4x4 forums.


Just asking the A-team first... and trying to save myself having to join some 4WD forum I'll likely never read again :lol:
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Re: Positions of inputs & load outputs along auto 12v wiring

Post by Lorgar » 02 Feb 2022, 7:36 pm

No1_49er wrote:From an electrical point of view, those three wiring diagrams are identical. In other words, the same three things drawn differently.


Sorry mate, I'm not sure what you're saying here.

Solar generating power into a battery and an inverter pulling out of a battery (Typical) is not the same, physically, as an inverter being connected mid-line between a solar panel and a battery (B) and having power driven through it, rather than only consuming it. There is obviously a difference of direction(s) here in terms of generation and consumption.

Whether or not this has a practical impact, I don't know. This is my question.

Are you saying, yes, the whole system is effectively the same 'pool' that is just being filled and emptied, regardless of where in the line things sit?

Or is this a grammar nazi-esk lesson on the technicalities of professional wiring diagrams... and you're being unhelpful? :lol:

(Jokes, obviously.)
Last edited by Lorgar on 02 Feb 2022, 7:52 pm, edited 1 time in total.
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Re: Positions of inputs & load outputs along auto 12v wiring

Post by Lorgar » 02 Feb 2022, 7:49 pm

scoot wrote:My best advice when connecting multiple sources of feed and draw is to use a specialised unit like the ctek or redarc units. Has inputs for solar and alternator, isolates main battery, charges better (dc-dc), etc., etc. Not trying to upsell but they are relatively simple and they just work.
In theory your diagram will work but most diy jobs will inevitably fail due to sometimes un-predictable outcomes from so many "circuits" being linked.


I hear you.

To explain my system in more detail, I already in fact have a DC-DC charger, the Redarc BCDC1220 between my start and auxiliary batteries. Charging the auxiliary, isolating the main etc. is all under control. My fridge is currently the only thing connected to the auxiliary battery. All simple.

Unfortunately, the 1220 does not support solar input. I've had the above setup for many years now, and at the time I got it solar was not anywhere on my radar as a need or want.

To replace this with the next model up, the BCDC1225, which does support solar, is about a $700 update.

If I was going to have fixed panels that were always connected, the above would be great, however, for other reasons, I will be going with fold-up/portable panels, which will only ever be connected while camped.

As I'm sure you can appreciate, given that I'm plugging in and removing the panels at each stop, can't really justify $700 for a charger upgrade for what's basically a 'neat' feature, when simply determining the attachment position of a few $20 Anderson plug will do the same job. You know?
Last edited by Lorgar on 02 Feb 2022, 8:12 pm, edited 1 time in total.
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Re: Positions of inputs & load outputs along auto 12v wiring

Post by scoot » 02 Feb 2022, 8:07 pm

Look at ctek if cost is a factor. I think it's a ds250 or something. 20a dual input for under $350. Sell the redarc, happy days.
The system will work no matter "where" the panel is linked in (after your redarc dc charger) if that's how you want to roll. Bear in mind you will need a solar controller to regulate voltage and amperage from the panel. Some panels have them "preinstalled", some are rubbish, some have nothing.
Redarc and cteck take care of all that to optimise the charge to your batteries. Kill an AGM deep cycle battery due to over/under charge and you've already paid for the ctek.
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Re: Positions of inputs & load outputs along auto 12v wiring

Post by on_one_wheel » 02 Feb 2022, 8:07 pm

I've often wondered about this and found myself obsessing over it for a while before saying "stuff it" and taking the easy route.

In my unprofessional opinion.
In the absence of switches, relays, inline fuses rated below the input amperage and wiring that isn't up to the task, I agree with no1 49er.
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Re: Positions of inputs & load outputs along auto 12v wiring

Post by scoot » 02 Feb 2022, 8:15 pm

on_one_wheel wrote:In my unprofessional opinion.
In the absence of switches, relays, inline fuses rated below the input amperage and wiring that isn't up to the task, I agree with no1 49er.

Yep, may physically look different but electrically all exactly the same outcome.
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Re: Positions of inputs & load outputs along auto 12v wiring

Post by Lorgar » 02 Feb 2022, 8:45 pm

scoot wrote:Bear in mind you will need a solar controller to regulate voltage and amperage from the panel. Some panels have them "preinstalled", some are rubbish, some have nothing.


Yep, I'm across all that. An MPPT regulator and so on :thumbsup:
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Re: Positions of inputs & load outputs along auto 12v wiring

Post by Oldbloke » 02 Feb 2022, 8:45 pm

"currently have an auxiliary battery running my fridge. I plan to add solar to the auxiliary now to charge this battery while not driving, and in future I will likely want to add an inverter."



"If I was going to have fixed panels that were always connected, the above would be great, however, for other reasons, I will be going with fold-up/portable panels, which will only ever be connected while camped"

If that's the case, just plug into the battery via an Anderson plug.. no more required but panel needs a controller.
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Re: Positions of inputs & load outputs along auto 12v wiring

Post by Lorgar » 02 Feb 2022, 8:53 pm

on_one_wheel wrote:In the absence of switches, relays, inline fuses rated below the input amperage and wiring that isn't up to the task, I agree with no1 49er.


All that side of things is fine.

I'm totally across wire gauge, effects of distance, voltage drop, amperage, appropriate fuses etc.

Installing any one of the above there is no confusion. I've just never done all simultaneously before, which is what brought me to my Typical vs A vs B ponderings.
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Re: Positions of inputs & load outputs along auto 12v wiring

Post by GQshayne » 02 Feb 2022, 9:14 pm

I think if you did a more detailed drawing, then you would see that it sorts itself out a bit. Because as you have drawn it, is not how you will connect it up. Your powered devices will need their own cables with the required fuses etc. So your battery will have a power lead to a fuse box which in turn will have a power lead to each device, fridge, lights, inverter, Travel Buddy etc. You would not connect your solar to any of these, so the connection will be prior to the fuse box. If you do not have a fuse box, then each item will have its own cable from the battery, including the solar.
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Re: Positions of inputs & load outputs along auto 12v wiring

Post by Latitude37 » 13 Dec 2022, 11:46 am

The solar panel fills the battery. The inverter and fridge draw from the battery. Wire it that way. Think of the battery as a water tank, and your devices as taps. Would you run your rain guttering to the taps? No, you fill the tank, and run your taps from that. Anything else is going to cause issues.
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