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

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.

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.

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

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. .

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.

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,

Cheers

Ross

So does this mean that if you don't use a shunt that your monitor is off in its calculations?

Depends,
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.

Cheers

Ross

nice

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.

1. The maxi fuse shown on the latest drawing can be replaced with one on the pre-fuse block as shown in the MB file pages 13 and 14 which connects to the ACR from the engine battery. The fuse should be rated at around 80 amps. You do not have to buy a 500A ACR. You do not need the fuse on the right of the ACR as the circuit is protected by the fuse nearest to the engine battery. This is the better place for the protection fuse is at the engine battery pre-fuse block.
2. It is best to cable for the capability of your inverter as you may not know what uses it may be put in the future. For best performance and efficiency the cables need to be as short as possible and with the least resistance in the circuit. Each connection to terminals, fuse-holders, fuse ,etc, add to the circuit resistance.
3. The inverter does not need to be hard wired, I am only suggesting it as an option.
4. You can do whatever you want. If you want to know how much is going into and out of the battery which includes all of the items connected to the battery then you will need a shunt.
5. You have all the elements to do the job properly, why not use them. The battery monitor is capable of measuring all the current so long as it is wired as I have suggested in my first post.
Move the ground point to the bottom of the shunt.
6. Move the wire currently shown at the bottom of the shunt to the -Ve bus bar
7. The LED fuses can be 10Amp each
8. The Maxi Fan fuse can be 10Amp
9. The Maxi fuse from the house battery to the fuse panel can be 40Amp.

Cheers

Ross

Great info. Many many thanks.

Here's the latest variation....if I'm understanding that Oldfartt correctly!:thumbs: Admittedly I have some confusion regarding the position/relationship of the shunt, neg bus and ground but hopefully I've followed instructions.

Don't assume you will require the inverter for camera and computer charging. There may be 12v chargers available. We have them for cameras and computers.

Hi Scooter,

Yes very nearly perfect!

The wire drawn from the solar controller to the MT 50 Tracer meter is actually an ethernet type cable and is all that is required to run the meter. The line shown from the meter to the -ve buss can be removed.

Now I have overlooked an important omission. The diagram shows the shunt correctly but there is nothing for the shunt to be used by. There needs to be a battery monitor for the shunt to provide the DC current information. I suggest that you include a Votronic 1262.
The insructions will show you exactly how to wire it. You need to provide a voltage feed ( low current) from the engine battery, the house battery and the current sense wires from the shunt. Then it will show the most important information on the state of charge of the house battery. This gives peace of mind when travelling.

Cheers

Ross

Inexpensive inverters like that Bestek produce "modified sine wave" (actually interrupted square waves) on their 110 vac outputs.
Many devices (such as power tool chargers) do not like that waveform.

Although the USB sockets will be great for your cellphones (etc), the 25 amps (or double that, since their product info says it'll do 700 watts for a short period) is pushing it for cigarette sockets. When you buy your sockets, verify that they can handle that current (the T1N Sprinter's ashtray socket would melt... except it's not fused that high (they still melt)).

--dick

Ross,

Good catch on removing the ground wire from the MT-50. However, that got me to researching all of the functions of the MT-50 and it appears to provide battery voltage, SOC, etc. though interface appears to be cumbersome. With that said, would it be redundant to have a battery monitor?

Could I simply use something like this?: https://www.bluesea.com/products/1733/Mini_OLED_DC_Voltmeter

And I'm confused about the wiring. Reading the Votronic instructions, they clearly state that nothing should be placed between the - battery post and the shunt. So what do I do with my negative buss? And if I need to wire leads back to my battery bank and the starter battery...now I wonder if it is more trouble than necessary...especially if the MT-50 gives me that info?

I've done some research on my USB and 12V plugs and have changed the fuses to match their max/recommended load. Which is only 15A for the 12V plug, but again the Bestek only works from a 12V cigarette lighter plug and cannot be wired any other way...unless I start cutting.

Next I started wondering about what the shunt, + buss and - buss should be rated for? 100A, 150A, 250?

Here's the latest iteration of the schematic

You're opening a worm hole and getting sucked in. Your first schematic looked better than the latest, IMO. You need to think and do the math. If you think advice on this forum combined with marketing literature is going to solve your problem, you're headed for a real mess. Think - a shunt measures current. You need to monitor current in and out of your battery, no shortcuts. Trace the current.

This is how I handled my (-) side. Current comes in through the body, 0000 cable through 2 ground lugs, cut-off switch (important!), shunt, negative battery cables, battery, out the plus side of battery to fuses, through appliances chargers and what-not, and back to the body.

https://sprinter-source.com/forums/showpost.php?p=229724&postcount=67

The bus is just for battery cables. Create another (-) bus elsewhere, probably near the fuse box, for (-) returns from various appliances, battery charger included.

You want a battery monitor. Measuring voltage alone tells you nothing, you need the current.

I am repeating the previous post to some degree in perhaps in simplified form.

Current flowing through the measuring shunt generates a voltage which accurately reflects flowing through current and this voltage is accurately measured by the battery monitor. Different polarity of the voltage will tell the monitor if current flows into the battery or out of the battery.

To connect this measuring shunt correctly all current flow between the negative battery post and consuming devices and charges must flow through it. Your last diagram is not showing it, so make sure:

Negative battery post > measuring shunt > loads/charges

George.

scooter1942 said:

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. ...

Click to expand...

dont have the time at the moment to delve deep here - but IMHO the best way to have the eng-alt throw charge into the housebank is the way its typically done on boats:

with a '1-2-both' switch

now.. a lot of people might tell you that an 'isolator' is a better way to go, but introduces quite a few implications (that i dont have time to get into)

while the best part of a simple 1-2-both switch is that as long as the interconnection conductors are properly sized (for the max output of the eng-alt plus voltage drop to the batteries; ie: not less than #2)?

if your engine cranking battery craps out, all you need to do is put the switch to BOTH and voila!
you have almost endless cranking capacity (since the housebank will typically be much larger than the crank batt)

one just has to pay attention to what position one has the switch, when in discharge mode.

just my .02
(and i've been a DC electrical specialist since mom bought me a trainset for xmas when i was 14

outbound said:

1-2-both' switch

Click to expand...

No production RV on the planet does this. Nobody wants to dick around with some switch several times a day, only to be forgotten at some point.

If you want to "jump" the start battery, insert a manual switch to apply voltage to the isolator - done.

The most common way to combine solar and an isolotor - is to just combine them. Wire each per the instructions.

Solar is just like every other widget you hook into your system - it just happens to push current rather than pull it. Hook the controller up to your fuse box next to the lights, the fridge, whatever. Size your wires as you size all the others. You're done. Few on this forum have demonstrated the skill and experience to consider it beyond that, and they do not need to.