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hi youtubers jeff cote here  we're doing another ask pys and we've  got a question from a fellow boater  named scotty  scotty's got a hans christensen lovely  sailboat um and he's asking a question  regarding a dc panel  he says jeff um when i'm hooked up to  shore power  and my inverter is off i have total  disc i have totally disconnected the  leads from my batteries so  think about this right mode is connected  short power inverter is disabled  but it's not really relevant but it's  important to say  so inverter is disabled and he's even  disconnected the battery leads  and yet here i am measuring dc voltage  on my panel that's that's crazy right  that's crazy how is it possible that you  don't have a battery connected  to your dc panel and yet you have  dc voltage at your panel  it's like not being connected to the  water main and having water flow through  your faucet  if that doesn't freak you out you  haven't really been paying attention  you're disconnected from the city water  main how can you have  water flowing through your faucets if  you're disconnected from the city water  main you can't  well how can someone measure voltage on  a dc panel  without having been connected to  batteries  you know what the trick is here the  trick is this is where the magic of  electrical comes into play  and this is where people take shortcuts  and shortcuts leads to these sort of  problems  and this is the difference between  unswitched distribution  and switch distribution so let's look at  this diagram  so again on switch distribution switch  distribution  notice that the dc panel here right the  dc panel  is connected and should be connected  only to the switch distribution makes  sense so when you turn off the battery  switch  the dc panel should be de-energized and  should have  no voltage reading at all on the panel  that makes sense  now if someone installed a battery  charger and notice where the battery  charger here is  right the battery charger should be  connected to the unswitched side meaning  when you  disconnect or you turn off the battery  switch  the charger should be connected only to  the battery  but if you actually and think about this  if you have your battery charger  connected to the  switch distribution which happens way  too often  effectively your battery charger becomes  a power supply  right and so this connection right here  basically goes now here so your shore  power energizes your battery charger  your battery charger energizes your  switch distribution  and when your switch distribution is  energized  your panel has power so effectively  you're running your battery charger as a  power supply  and that's why the key between unswitch  and switch distribution  and avoid that at your peril because  then you have a magical boat and there's  no magic  i'm not saying magic doesn't exist but  electrically it doesn't  right and so if you want your boat to  act predictably  you want to make sure that your charger  is connected to  and the chargers are here is connected  to the unswitched distribution  otherwise world of magic doesn't make  sense  and so that's why chargers and all and  all chargers that could be  solar controllers right that's really  important a methanol fuel cell  whatever it is has to be connected to  the unswitched distribution so that when  you actually  shut off the battery switch the dc panel  loses power  and that's why you want unswitched and  switch distribution  thank you for watching this pys video if  you've got further questions  ask them down below or go on our website  to fill one of the forms don't forget to subscribe and thanks for  watching  English (auto-generated)