grounded battery system

[Yuma]

Could anybody please explain what is the effect of having a ground in either the positive or negative wire of a battery system, to the turbine control system? I've heard that maybe the control system gets some digital inputs wrong, i.e.; 1 instead of 0, or vice versa....

Thanks

 

[sslobodan]

You need to have a certain 0 for VCC signal. That is made by grounding one end of a device. In that fashion voltage will not float due to a certain differences in system and for instance 12V will always be 12V and not 16 or 18 0r 9 if you have some other volt signals that may make interference....

 

[GTstartup]

Sslobodan.

Not all DC systems are intentionally grounded. 125VDC systems are typically floating.

To the OP:

If you are referring to a DC system with a ground detection scheme that is made from resistors across the poles with the mid point grounded then the answer is theoretically yes. Not only can inputs get turned on but even external devices such as breakers can close. This is greatly dependant on the value of the ground detection resistors. The lower the value the greater the likelyhood this can happen.

In the real world, battery charger or power supply manufacturers size these resistors so that this won't happen. This means that having a ground on your previously floating DC system is not such a big deal. Another ground on the opposite leg will trip a breaker or blow a fuse and could cause problems so the ground should be located and cleared as soon as possible.

 

[Rodmcm]

The main reason that DC systems were not earthed in power systems was so you could detect the first earth, and hopefullly correct it, before the second earth happened.Large DC systems, and especially those at 220VDC pack a lot of power and hence they are distructive when that second fault happens.
Newer electronic controls are more sensitive to floating earths than older relay based controls so you do need to ask the supplier the implications on this

 

[bacon4life]

See

http://www.eng-tips.com/viewthread.cfm?qid=159915&page=1

for a discussion of positive and negative grounds.