Confused on "need" of grounding one thing, but not another

Four wheel driving. Vehicle modifications. Off road driving and recovery techniques. Towing and miscellaneous vehicle topics.

Confused on "need" of grounding one thing, but not another

Post by Lorgar » 02 Oct 2022, 2:29 pm

Hi all,

Long story short, I'm in need of a new MPPT solar control for my 4WD solar.

I'm looking at the Victron units, and am a bit confused about the "need" to ground 1 unit, but not another when they're effectively the same thing.

These are their 'SmartSolar' line of controllers - https://www.victronenergy.com.au/solar- ... -15-100-20

First picture is the 75/15 (being 75v/15a input limit) and the second is the 100/20

Output to either 12v or 24v batteries.

75-15.png
75-15.png (443.14 KiB) Viewed 2094 times


100-20.jpg
100-20.jpg (73.5 KiB) Viewed 2094 times


Same unit, just higher load capabilities for the second.

You'll see on the left of the 100/20 though, the heatsink has a screw for an additional ground cable.

Now, am I correct that neither unit "needs" to grounded in this fashion.

Solar + and - both go to the controller. Battery + and - both go to the controller. Eveything with work fine, long term, and safe.

My understanding for the ground on the heatsink of the 100/20 is in case a live current comes in contact with the body of the unit, it has somewhere to ground to, as a safety measure. To avoid injury / fire.

This is added in the case of the 100/20 as it may be handling more current, but not added to the 75/15 as it is decided that the current is low enough that the additional safety measure is not needed.

Do I have that correct, or have I misunderstood something?

Ultimately I'm looking to use this as a portable plug in/out unit, and obviously having to attach a ground each time would be a huge pain. Want to make sure I correctly understand the impact of not attaching the heatsink ground wire on the 100/20 unit.

Thanks folks.
Last edited by Lorgar on 03 Oct 2022, 10:37 pm, edited 2 times in total.
User avatar
Lorgar
Second Lieutenant
Second Lieutenant
 
Posts: 2156
Victoria

Re: Confused on "need" of grounding one thing, but not anoth

Post by Larry » 02 Oct 2022, 4:13 pm

As they are consumer level products that are 240V any exposed steel parts must be grounded.
Larry
Staff Sergeant
Staff Sergeant
 
Posts: 775
-

Re: Confused on "need" of grounding one thing, but not anoth

Post by Lorgar » 02 Oct 2022, 4:42 pm

Not 240v, mate.

12v / 24v.

(Updated my post with a few extra details for clarity)

That aside, am I to take from your reply that it is, as I queried above, a safety addition, not an operational one?
User avatar
Lorgar
Second Lieutenant
Second Lieutenant
 
Posts: 2156
Victoria

Re: Confused on "need" of grounding one thing, but not anoth

Post by cz515 » 02 Oct 2022, 4:58 pm

I would say it's an extra safety feature that the cheaper unit doesn't have.

Just guessing
When good men and women can’t speak the truth, when facts are inconvenient, when integrity and character no longer matter, when ego and self-preservation are more important than national security — then there is nothing left to stop the triumph of evil
User avatar
cz515
Warrant Officer C2
Warrant Officer C2
 
Posts: 1032
Victoria

Re: Confused on "need" of grounding one thing, but not anoth

Post by Oldbloke » 03 Oct 2022, 8:34 am

Lorgar wrote:Not 240v, mate.

12v / 24v.

(Updated my post with a few extra details for clarity)

That aside, am I to take from your reply that it is, as I queried above, a safety addition, not an operational one?


I know just enough to be dangerous about solar.

My bet is its a safety feature as you said. First time I've seen it.
The greatest invention in the history of man is beer.
https://youtu.be/2v3QrUvYj-Y
Member. SFFP, Shooters Union.
SSAA, the powerful gun lobby. :lol: :lol: :lol: :lol:
Hunt safe.
User avatar
Oldbloke
Field Marshal
Field Marshal
 
Posts: 11192
Victoria

Re: Confused on "need" of grounding one thing, but not anoth

Post by rc42 » 03 Oct 2022, 9:00 am

The maximum DC input voltage on the earthed unit is higher, 100v compared to 75v, most likely this crosses the threshold between 'Extra Low Voltage' equipment that doesn't need to be earthed and 'Low Voltage' equipment which does.

There shouldn't be any voltage on the metal parts of either but if something goes wrong inside them the earth connection will keep the metal parts at the same voltage as the other metal parts of the car ('-' battery terminal), on the non-earthed one the metal could potentially have up to 75v difference to the car, you would probably feel a tingle from that but it shouldn't be dangerous.

Current is not relevant, it's all about voltage.
rc42
Staff Sergeant
Staff Sergeant
 
Posts: 794
Queensland

Re: Confused on "need" of grounding one thing, but not anoth

Post by Lorgar » 03 Oct 2022, 6:21 pm

Hey RC,

rc42 wrote:100v compared to 75v, most likely this crosses the threshold between 'Extra Low Voltage' equipment that doesn't need to be earthed and 'Low Voltage' equipment which does.


This was pretty much my understanding also (albeit my unqualified one).

A "safety standard" requirement, rather than an operational one.

Not concerned with giving myself a zap. Purely operating on the 12v electrical system of the car here, no inverters attached etc.

Just triple checking I'm not inviting equipment failure (or immediately blowing the thing) if that ground were to not be connected.
User avatar
Lorgar
Second Lieutenant
Second Lieutenant
 
Posts: 2156
Victoria

Re: Confused on "need" of grounding one thing, but not anoth

Post by rc42 » 04 Oct 2022, 4:20 pm

That rating will also be based on the maximum input PV voltage that the unit can work with, if your panels output less than 75v (most are in the 30v-60v range) then there's functionally no difference between them and in the event of an electrical fault and PV voltage on the metal case you'd barely feel it.
Unless you put your tongue on it as it's much more conductive and sensitive than skin (note, licking electrical items is never a good idea)
rc42
Staff Sergeant
Staff Sergeant
 
Posts: 794
Queensland

Re: Confused on "need" of grounding one thing, but not anoth

Post by Larry » 04 Oct 2022, 8:35 pm

People have been killed by 12V car batteries. Its not just the voltage and it only takes a few milliamps like 10 to stop a heart.
Larry
Staff Sergeant
Staff Sergeant
 
Posts: 775
-

Re: Confused on "need" of grounding one thing, but not anoth

Post by Lorgar » 06 Oct 2022, 2:32 pm

rc42 wrote:That rating will also be based on the maximum input PV voltage that the unit can work with, if your panels output less than 75v (most are in the 30v-60v range) then there's functionally no difference between them and in the event of an electrical fault and PV voltage on the metal case you'd barely feel it.
Unless you put your tongue on it as it's much more conductive and sensitive than skin (note, licking electrical items is never a good idea)


I'm running a 300w blanket and the output is in the neighborhood of 21v / 13A.

In any case, I ended up going with the 100/20 model, so have some room for growth built in for future upgrades.
Last edited by Lorgar on 06 Oct 2022, 2:49 pm, edited 2 times in total.
User avatar
Lorgar
Second Lieutenant
Second Lieutenant
 
Posts: 2156
Victoria

Re: Confused on "need" of grounding one thing, but not anoth

Post by Lorgar » 06 Oct 2022, 2:38 pm

Larry wrote:People have been killed by 12V car batteries. Its not just the voltage and it only takes a few milliamps like 10 to stop a heart.


I'd dispute this as an old wives tale if I'm honest.

Low amperage to affect a heart, sure. But a 12v battery having the required voltage to push said amps anywhere near deep enough into you to reach anywhere significant? Nah.

If you had a high-voltage inverter in the mix somewhere, maybe, sure, but that's a different story.

In my more reckless youth, I've certainly electrocuted/shorted myself on a car battery, and higher, and had nothing but a burnt fingertip.

( My 2c, IMHO, this is not advice, anecdotal, I take no responsibility for anyone electrocuting themselves :lol: )
User avatar
Lorgar
Second Lieutenant
Second Lieutenant
 
Posts: 2156
Victoria


Back to top
 
Return to Four wheel driving and off road travel