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scooter1942 09-21-2016 07:13 PM

Another Electrical Thread: Don't let me catch it on Fire!
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I'm about halfway into the buying phase for electrical components. I'm looking to do a very basic electrical system similar to the folks at Sprintervandiaries.com. However, the more research I do, the more I realize I should have paid far more attention in high school and probably should have taken a few extra science classes in college, but alas...I'm an art guy. Electricity...not my forte. Please help me not screw this up.

So here are the specs of what I'm dealing with...my needs, uses, and some components that have already been purchased.

-2016 144" High Roof with 220A alternator
-Renogy 200 W solar with 20A MPPT charge controller and MT-50 tracer meter.
-2 Lifeline 6V 220Ah batteries
-Blue Sea Maxi Fuse 40A
-Blue Sea Fuse Box (12 connections)
-2 Blue Sea 12v plugs
-1 Blue Sea USB plug
-ARB 12v 50 qt fridge
-Maxxair Deluxe vent fan
-Bestek 300W Inverter (for charging camera batteries, laptop, iPhone)
-11-13 LED lights @ 3.5w ea

My goals:
-I want to have my alternator charge my house batteries while driving.
-I want to have my solar charge my batteries while stationary.
-All appliances will run off DC. The inverter will only be needed for charging camera/computer batteries.
-I want to have my house batteries support 3 days of use without any charge. (This seems reasonable given my batteries and anticipated use)

So, here's my first stab at a electronic schematic. Forgive my inaccurate use of the proper symbols, but I think most folks get the idea. Here's what I need to know: Is there anything inherently wrong, dangerous or "iffy" about this design? Can anyone help me with which wire gauge/type to use in each area? Are there missing components that should be added and where? Are there components that should be changed and to what? What should the bus bars be rated at? What the hell is a shunt? And any other wisdom you have to offer. Thanks in advance to all of you seeking to help me from catching my Sprinter on fire.

mikemarmar 09-21-2016 09:45 PM

Re: Another Electrical Thread: Don't let me catch it on Fire!
Every wire coming from the (+) on your house battery bank needs to be fused, as close to the battery as possible. Also, check assets.bluesea.com/files/resources/reference/20010.pdf for a guide to wire and fuse sizing.

Also, running a 300w inverter on a 10A fuse won't work. 300w is 25A at 12v.

scooter1942 09-22-2016 01:34 AM

Re: Another Electrical Thread: Don't let me catch it on Fire!
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Thanks Mikemarmar.

I've added fuses to all wires leading to and from the + terminal on the house battery. So what type & size of fuse should I install?

I've updated the fuse rating for the 300A inverter to 25A at your suggestion. FYI, the inverter has an internal 40A fuse...not sure if that changes things.

Here's version 1.1 of the schematic

gypsybrew 09-22-2016 01:52 AM

Re: Another Electrical Thread: Don't let me catch it on Fire!
interesting this is the same set up I am getting ready to install. No inverter but add an Espar heater. Your schematic looks pretty much identical to the one I have drawn up.....2008 NCV3 I talked to an electrician buddy and asked him about 4 gauge wire as I had seen someone else use it exclusively. He said to use the same gauge wire as comes off the solar panels.....? I haven't looked closely at what I'm dealing with yet but will let you know if I get to it before you do. Shunts act as a type of surge protection only letting a certain amount of current through. .

NBB 09-22-2016 01:57 AM

Re: Another Electrical Thread: Don't let me catch it on Fire!
I mostly used 2 wire sizes and 2 different fuses throughout - 15A on 14 ga wire, 30A on 10 ga wire. Keep it simple. When you look at voltage drops and what-not in that Blue Sea chart, keep in mind those are for full current - which no circuit should come close to. Maintain about 50% max "working" load - ie, the expected normal consumption of the sum of all appliances on a 15A circuit should be less than 7-8 Amps or so. I used 0 or larger for battery, inverter connections.

Fuses protect wire from shorting, melting and staring a fire. The fuse belongs at the beginning of a wire run - ie, the fuse box.

Whatever fuses exist in or near your appliance are different. They are there to protect the appliance alone - not the wire that leads to it. This fuse will have a rating based on what is necessary to protect internal components in the appliance from catching fire or getting damaged - with little consideration for the circuit it's connected to.

Oldfartt 09-22-2016 02:21 AM

Re: Another Electrical Thread: Don't let me catch it on Fire!
1 Attachment(s)
Hi Scooter,

Generally your diagram is OK, but needs extra protection and adjustments.

Firstly, All sources of energy should have a fuse in series with the supply as close a possible to the batteries. This is to protect the wiring.
Now in your van you will find a Prefuse fuse block attached to the + terminal of the engine battery in front of the drivers seat (USA Lefthand drive) . There is a spare position on the fuse block for an additional circuit. See attached file on pages 13 and 14. You can use this position to feed the ACR which can be placed under one of the seats. Use a heavy cable similar to that going to the engine starter.

By the way, in case you have not found it, there is a battery disconnection point under the dash by your right drivers foot. Just pull that before you do any wiring work. Make sure the the engine is not running and the key is out of the ignition before disconnection.

Place the maxi fuse the +ve lead in and near the house battery. You do not need a fuse in the solar panel lead as the panels are designed to accept a short circuit. However it is good practice to have a means of isolating the panels for maintenance purposes. Suggest another maxi fuse of the same rating as the other maxi fuse, then you have a spare!

The Shunt is used to detect the current going into and out of the battery. It is made of a block of metal which has terminals at each end and the block has a very small resistance. When current flows through the block, a small voltage can be measured across it. This voltage is used by the battery monitor to work out how much power is going into and out of the battery.

Currently the drawing shows the -ve terminal of the fuse distribution block going to the negative buss which is OK but the shunt should be installed in the lead from the negative buss and the ground termination. That then allows all current to and from the battery to be monitored.

The inverter should be connected to the house battery maxi fuse output using a heavy cable. No need to run it through a connector or separate fuse. If there is a need for a connector an Anderson plug could be used.
The -ve lead from the inverter needs to be connected to the -ve buss bar or to the non ground side of the shunt and not directly to ground. (the non ground side of the shunt can be used as your -ve buss bar).

Hope this helps,



gypsybrew 09-22-2016 02:37 AM

Re: Another Electrical Thread: Don't let me catch it on Fire!
So does this mean that if you don't use a shunt that your monitor is off in its calculations?

Oldfartt 09-22-2016 02:47 AM

Re: Another Electrical Thread: Don't let me catch it on Fire!
If you have a solar controller and all the circuits are fed from the "load" connection, it will read correct, but if you connect any other device directly across the battery, like an inverter then the current drawn by the inverter will not be measured.
Because the inverter can draw much more current than the solar controller can allow, that is why it is normal to use a separate battery monitor with a shunt.



gypsybrew 09-22-2016 03:38 AM

Re: Another Electrical Thread: Don't let me catch it on Fire!

scooter1942 09-22-2016 04:05 PM

Re: Another Electrical Thread: Don't let me catch it on Fire!
1 Attachment(s)
Oldfartt, Thanks for the info.

A couple of follow up questions:

1. Just to be clear...you're suggesting putting the 40A Maxi Fuse between the house battery and the ACR, not the other way around? Most other schematics have the Maxi Fuse between the starter battery and ACR. My ACR is rated for 120A and my thinking was that the 40A Maxi Fuse would prevent too much power from the alternator/starter battery from getting to the ACR. If I do as you suggest, do I need to buy the 500A ACR?

2. My inverter will only be used for charging camera batteries and phones. Additionally, I believe it only has an option for a 12V plug. Given that, do I really need to hardwire it? Secondly, if I don't hardwire it, is there really a need for me to have a shunt? Could I simply ground to the negative bus?

Here's a new schematic based upon the info received.

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