completelycharged said:
.... way back to when telephone/telegraph wires were a single cable with a ground return loop ....
Yeah we forget how far we've come!
completelycharged said:
With low voltage DC the ideal preference would be to leave it ungrounded because any touching of any individual conductor has no risk of electrocution because there is no ground loop.
Yes that's one way to do it.
completelycharged said:
If you have NPN MOSFET switching within your BMS and switches the pack off on low voltage your previously 0V -ve connections are now at 48V looking for a -ve return path because the BMS has disconnected the -ve line. If you then earth anything after the BMS the ground loop created will then bypass the BMS. The effect of using NPN with telecoms and +ve ground eliminates the ground loop issue.
For large systems, typical MOSFETs directly in +ve or -ve the probably wouldn't be good - breakers with shunt trips would be used due to the high currents & possible fault currents involved.
Yes it could probably be done with some of the heavy duty devices.
completelycharged said:
House wiring always has any switching in the positive side,
Agree - a technicality (for other readers): AC mains obviously doesn't have a positive & negative but a "live" or "hot" and a "neutral" or "return"
gregoinc said:
Hey folks... thought I would throw this question in here first.
Am sourcing parts to build my DC busbars and having done some research I am not sure what bolts to use to attach cables to the copper busbars?
Some folks say stainless steel and others talk about something called 'yellow tinned' and others say the bolts should be brass?
Would be interested in the collective thinking from those of you that have experience/knowledge.
Each has it's good & bad...
Stainless bolts probably apply more for lead acid batteries where terminal corrosion is more of an issue.
Corrosion from cell leakage in lithium packs means you've got more serious issues!
Stainless doesn't conduct quite as well as other metals - does this matter? probably not because it's the underside of the lug to battery terminal direct contact path taking the current.
They look nice
"Yellow tinned" is typically = "zinc dichromate" plating used on steel bolts. Not sure if this plating is conductive or not eg alumminium anodising is insulating, but this?
Brass is a good conductor & resists corrosion pretty well but physically it's not as strong & you could shear bolts if muscle applied!
My take is you should have a flat washer + a spring washer under the bolt head. Eg bolt > spring > flat > lug > busbar/battery terminal
Flat washer helps keep the lug flat & make widest contact area with busbar. Spring washer reduces risks of loosening from any thermal expansion changes, etc.
All the commercially made bus bars & switch gear I've used came with either zinc plated steel bolts (silvery looking) or zinc dichromate plated steel bolts (yellow looking)