Grounding my (-) bus bar?

[vansomewhere]

Hey everyone,

Jumping on here to get your opinion. I'm planning out my van electrical setup (see attached), and drawing power from solar panels & an existing power outlet within the van for when it's running (It's 120V with 150W/400W inverter)

Do I need to attach my (-) bus bar to the chassis (for grounding)? My Li-Ion battery is the renogy smart 100a battery, so I'm wondering if that would just keep that 12V voltage difference for me. I also am worried that attaching a ground wire to the chassis could be a safety hazard

Let me know, thank you!

[gahamby]

I'm of the opinion that not grounding to the chassis would constitute the hazard. By not grounding to the chassis you raise the possibility of a potential difference between the system ground and the chassis ground. Use a nice big ground bar and bond it to the chassis.

[vansomewhere]

Thanks! Will make sure to ground the negative bus bar to the chassis. Would a 2 AWG connection be suitable for this?

[gahamby]

Originally Posted by vansomewhere

Thanks! Will make sure to ground the negative bus bar to the chassis. Would a 2 AWG connection be suitable for this?

Not sure, determine the max ampacity of your system. Add a bit for safety and consult a wire capacity table. Going bigger doesn't really hurt, too small does.
I think 2AWG is rated for 100A.

[Scalf77]

I generally just use the same size as my "House Battery" ground, it should be sized for max capacity.

-greg

[vansomewhere]

Thanks, all!

Sorry, just to confirm, would the max ampacity of my system be 100amps (because that is the maximum current that my battery will draw)?

Or would I have to add up the current in all my parallel connections (e.g., 40amp charge controller + 100amp inverter + 100amp battery + 40amp fuse + 10 amp shore power)?

Any guidance would be greatly appreciated!

[Scalf77]

First look at the battery, it list as a 100Ah Battery, Maximum continuous charge current is 50 Amps. Maximum continuous discharge current is 100 Amps. The 100 amp discharge current is an important one. This is being driven by the BMS, actually the FETS in the BMS. It is probably best not to let the BMS be your overcurrent safe guard, so you will need to either fuse or circuit breaker your way out of this.

Now your system has 40 Amp solar controller and a 10 Amp plug in controller that you are driving by the onboard inverter. Maximum charge current will be 50 Amps. So you won't go over the maximum continuous charge current.

For the discharge current, you have a 1000 watt inverter and a fuse panel. The inverter is going to be very close to 100 amps on its own, then you add in what ever loads you are running off of your 12 volt loads. You will possibly be over the 100 amp discharge limit of your battery This is where a circuit breaker would come in handy, you preferably want one that would be sized to go off be for the BMS shut down, but sizing could be a problem.

So the max load current will be the inverter and 12 volt loads. At a minimum add up the always on 12 volt loads, I usually add the fridge in this also even though it has a duty cycle. I would then take the largest load that you might use and add to that. Again use your judgement on what you think will be on at the same time. That ends up being you max current.

If you think you are going to go over the 100 amp battery discharge limit, then you might need another battery in parallel to increase the max discharge current to 200 amps.

Some inverters will let you set the output by percentage, which can be another way of limiting max discharge. The inverter manual should give you some idea on what load and fusing it will require. You need to take into account the conversion efficiency and the lowest operating voltage.

-greg

[vansomewhere]

Thank you for the detail, Greg! Super helpful

So, in order to not overload the battery with more than 100Ah discharge current, I’d need to fuse it (or add another battery, which I would prefer not to do)

If I put a 100Ah fuse off the + terminal of my battery, would this do the trick?

I also plan on putting a 100Ah fuse on the + terminal of my inverter (as recommended by renogy), and a 40Ah fuse on the + terminal of my DC fuse box for the fridge/fan/lights etc. I realize these add up to more than 100, but I would just make sure to only plug one device into the inverter at a time

(I don’t plan on putting any fuses on negative terminals/wires, is this ok?)

Also, one last question, would a 2AWG wire from my - bus bar to the chassis be suitable as a ground wire size?

Thank you so much for all of your help, I really appreciate it

[Scalf77]

I would use a circuit breaker on the battery, or larger fuse then smaller circuit breaker in series with the battery. The BMS will shut down if in overcurrent mode, so you would be fine with just a larger fuse. But I imagine the the BMS is not replaceable so if it were to go bad, you would need to replace the battery. If you feel comfortable knowing that your not going go over then just fuse it. I might try a 187-Series Circuit Breaker - Panel Mount 90A or the 100A version. They have a 5000 AIC rating, making it plausible as a main battery protection. If you wanted higher AIC rating you could move to a Class T fuse of higher and the breaker in series.

Wire ampacity ratings are affected by the sheathing rating, so you need to take that into account, 2 awg Marine Wire is 105°C rated and gives you a ampacity rating of 210 Amps, which would be covered by your fusing. I didn't really look to see if you listed distances, as that would be the only other thing to worry about .

You can use the bluesea circuit wizard or I have one I made in excel you can use if you wish https://docs.google.com/spreadsheets...it?usp=sharing you can also download the calculator here https://www.expo-technology.com/calculators

-greg