Connection to starter battery

jmatosp

Member
Joined
Oct 19, 2020
As I wait for some better weather, decided to tackle a bit of electricity.

I'm installing a part electrical, one battery and a DC-DC charger, this is so I can have some lights and a fan to do some work.
I'm not an expert but I think the wiring is sort of correct, although I run out of wire again...

This is a temporary board;
100A Lithium Battery;
All cabling is 110A rated (16mm2);
There's a 16mm2 cable running from a 50A circuit breaker from the starter battery, this should connect to IN on the DC-DC charger;
Missing positive and negative cable to the fuse box;
Should I ground from the negative busbar to the chassis?
I need to connect the DC-DC charger to starter battery to setup and only then turn on the leisure battery;
Battery monitor shunt in place but not the dial thingy, should work without this;
Panel back (+) & (-) cables connect to the battery;
There's a 100A MEGA fuse at the battery (switch first);
40A MIDI fuses to each circuit, at the moment DC-DC charger and Load;

Does this looks OK? Any suggestions?
 

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BigAldo

New Member
Joined
Dec 3, 2020
You ask about grounding the negative busbar to the chassis. If you're using a shunt for the battery monitor, this would normally be in the negative cabling, and all current return paths (charging and discharging) should run through this to ground.
If you then ground the busbar, you will be providing an alternative path to ground, bypassing the shunt. The battery monitor will not read correctly if only part (or none) of the current is going through the shunt.
(and this assumes i've read your explanation correctly.)
 

jmatosp

Member
Joined
Oct 19, 2020
Thanks for the explanation, its now more obvious that negative from busbar should not connect to chassis.
 

mrmoosehead

Active Member
Joined
Sep 28, 2020
Location
Ilkley, West Yorkshire
I still haven't done all my reading about the elektrikery in mhomes yet. Are you saying that all circuits should be made via cabling, and none should use the bodywork to ground (like most other auto electrics?)
 

jmatosp

Member
Joined
Oct 19, 2020
I still haven't done all my reading about the elektrikery in mhomes yet. Are you saying that all circuits should be made via cabling, and none should use the bodywork to ground (like most other auto electrics?)
I think they use the bodywork to save on cabling length and thickness, you just wire the positive and the negative is anywhere in the chassi. Saves on return wire and also cable gage as the return negative is also part of the voltage drop calculation, drop voltage is return lenght. Im sure there's more experienced people then me that can advise.

Anyway it depends what your are installing and where. I used 16mm2, 3.5mm2 and lots of 1mm2 all positive and negative. Also a bit of 240v and audio cable.
 

BigAldo

New Member
Joined
Dec 3, 2020
I take all my twin conductor cables back to the fuse box, and connect the negative to the earth busbar there. This makes troubleshooting so much easier. Never use local body connections for your electrical devices. Finding a bad earth is a nightmare waiting to happen.

If you are using a battery monitor, the shunt usually goes between the Leisure battery negative, and the vehicle ground (but check that yours is the same!! Vehicle ground can be either by a bolt to the vehicle body, or a heavy cable back to the starter battery negative.)

The fuse box busbar is connected to the shunt on the grounded side, not the battery side.
This arrangement requires any current drawn by the electrical devices from the leisure battery to pass through the shunt, and this can be calculated by the battery monitor to judge the state of the leisure battery.
 

mrmoosehead

Active Member
Joined
Sep 28, 2020
Location
Ilkley, West Yorkshire
As previously mentioned, I have the electrical interface box fitted, so some of my connections to the start battery and main vehicle electrics is easier. I hope. :D
I learned about shunts last night after this post, thanks.
 

jmatosp

Member
Joined
Oct 19, 2020
Talking about connecting to chassis is like opening a can of worms I see XD

I followed Victron diagram all looks good, the only difference is that I don't run the negative from the starter battery to the DC-DC charger input negative. I've seen on Victron on support that this is possible, you just connect the negative input to the negative busbar on the leisure side.
 

jmatosp

Member
Joined
Oct 19, 2020
OK, that didn't work.

My DC-DC charger is ISOLATED so the input negative needs to be connected to the negative of starter battery by turn the chassis XD, don't . The DC charge output negative goes to the negative busbar by turn the shunt and then battery negative.

This DCDC charger has two separated circuits, it is now charging bulk happily at 25Ah and I can turn on/off maxxair fan.
The monitor is also working and displaying the amps going through the shunt.

Small victory, I do enjoy this electricity a bit more then the rest.
 
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