Should I ground battery negative yes or no?
Just measured the difference between battery casing (grounded) and the battery minus an I measured 20V DC.
The internal 10Mohm of the multi meter is enough to drop the voltage in one minute to zero, so there is none battery current leakage to casing.
Is it advisable to ground chassis ground to keep minus potential the same as chassis?
Should it be hard grounded or by say a 1Mohm resistor to avoid big currents in case you have battery isolating issues?
Maybe connect GX tank input at battery negative to make this way a isolation detection?
In many cases, yes. Sounds like you are talking about a vehicle, so the original eletric system will use a grounded negative already, then you can also ground the secondary system. Theres reasons to keep a system isolated, on some boats or due to radio equipment interference for example.
If its isolated its SELV, if theres a connection to ground on the DC side its PELV.
You can monitor a ground current also in a PELV install. You can limit a fault current by using a resistor. Question is, whats the benefit of this
I own a home battery with 3x Multiplus II and 6x 16kWh EEL DIY boxes.
Quality is real good and the cells are also extra isolated by epoxy sheets, So Iām not afraid for isolation failures.
The metal battery box cases are grounded, but if you also hard ground battery negative ,in case of an isolation defect bad thinks can happen.
You then create a full short, and if there is none fuse in the negative circuit it can be dangerous.
By grounding over a resistor (1Mohm) you will also create zero potential between battery negative and ground and in case of an isolation failure you will see an potential between ground and battery negative.
Maybe an idea to measure this potential by cerbo gx or multiplus and generate an isolation warning error, but do see all analogue inputs do have a 5V 10k pull-up resistor
And by not grounding you could get very high potentials and this could trigger a spark destroying the isolation,ā¦..
Generally, yes, grounding the system negative and fusing the positive leads at the SOURCE of unlimited current flow (e.g, the battery, etc) is a good idea. The concept is that any fault will blow the fuse before burning up wiring. Ungrounded systems risk currents in unexpected paths such as control cables that could potentially burn these small conductors.
In a system with current shunts in the negative lead, ground the SYSTEM side of the shunt, not the battery negative.
The fuses in the positive side will not blow in case of an internal cell isolation failure.
Say #8 from a 16S does have a short to casing and battery negative is hard wired to ground you will get a full short.
Current will flow through casing ground cable and back through the negative battery connection cable, and in this path there is none fuse.
Chances that this happens is very unlikely, but if it happens you will have a very bad situation.
Is the negative side not hard wired the battery is floating and in this isolation fault condition, nothing will happen .
Maybe I found a way to detect isolation failure and keep battery minus pole near ground potential.
You can use the lynx shunt temperature sensor input to do that, see picture.
Have to play with resistor values,but it looks to work, battery minus is around 0,19V and when I make an isolation fault, touch battery + and casing (introducing small leakage), you see direct a temperature increase that can trigger an alarm.
