aardvarkash10 960 Posted March 14 Share Posted March 14 As an ex auto electrician, it's hard getting over my inherent belief that you leave the "earth" side alone and put all switching on the live side. But a boat is all above ground so it shouldn't matter right? I may not have thought it through so, tell me your thoughts and experience. Existing equipment includes: One house battery, one start battery both lead acid. Alternator Start battery selector switch (off, start, both, house) VSR Solar with mppt controller Capstan with circuit breaker. Go at it team, which side do I put the isolators and why? Quote Link to post Share on other sites
CarpeDiem 430 Posted March 14 Share Posted March 14 It depends on what you want to achieve. But ultimately doesn't matter. Some standards recommend that both sides are isolated. Is the objective an emergency off, that isolates everything in the event of smoke? Or is the objective short term storage (1-2 weeks) to minimise all parasitic loads on a single battery? In a dual battery system, with solar, lithium BMS, voltage senses and all the extras you find hanging off the positive terminal and as close as possible to the battery I recommend a DPST on the negative side, that fully isolates both batteries in the event of smoke. This is easy to do, because it's the only side of the dual battery system that is inherently connected together. You can still put hefty switches on the positive side, but generally these will be upstream of other smaller loads and for a specific use case, eg, winches, starter motor, etc etc... It's getting less and less likely that batteries are fully isolated with an off switch these days, there's too many things that we like to leave connected permanently and if you have solar then you are certainly not fully disconnecting the batteries... eg, 1 Quote Link to post Share on other sites
K4309 261 Posted March 14 Share Posted March 14 I'd put your battery switch / isolator on the positive side. Just cause that is what you do. The negatives go to what ever ground you have. The positives have the control (switches) on them. Helps in the future when you start adding more sh*t, you know which way round everything is. Why would you put switches on the negative / earth? 1 1 Quote Link to post Share on other sites
ballystick 72 Posted March 14 Share Posted March 14 54 minutes ago, K4309 said: I'd put your battery switch / isolator on the positive side. Just cause that is what you do. The negatives go to what ever ground you have. The positives have the control (switches) on them. Helps in the future when you start adding more sh*t, you know which way round everything is. Why would you put switches on the negative / earth? By isolating the negative side through which all circuits commonly use as CD illustrates above, it switches everything off. If you want to individually isolate individual circuuits then put in isolating switches for those circuits. It doesn't matter which side as electrical systems are circuits and won't flow until the circuit is complete. Quote Link to post Share on other sites
harrytom 644 Posted March 14 Share Posted March 14 I have the isolator on the negative side ,why??Last yacht had a wire(presume earth) to the prop shaft. So in my mind ,even though the battery has no earth it self to the outside world.I am picking with salt crystals etc(boat are always damp even though feel dry) that somehow the earth/negative would be connecting to the water and creating a circuit Now comes a problem,auto bilge pump via float switch needs to be hard wired in,if isolator off ho does pump work? 1 Quote Link to post Share on other sites
aardvarkash10 960 Posted March 14 Author Share Posted March 14 2 hours ago, CarpeDiem said: In a dual battery system, with solar, lithium BMS, voltage senses and all the extras you find hanging off the positive terminal and as close as possible to the battery I recommend a DPST on the negative side, that fully isolates both batteries in the event of smoke. This is easy to do, because it's the only side of the dual battery system that is inherently connected together. This was the direction of my thinking, and it's for emergency damage control. But I'm cheap, so it would be two spst "key" devices. 1.743 seconds slower to activate, but only $20 for the pair. The starter selector looks after the +ve side, so hit the two keys and twist the start select and the entire battery bank is isolated, both sides. I'm still a bit with K4309 though. I have a built in hatred of ground loops (building audio gear) and additional switches on the -ve side makes space for voltage drop and its inherent riding partners. Keep it up team, what else have I not considered? Quote Link to post Share on other sites
K4309 261 Posted March 14 Share Posted March 14 I'm sure there are dozens of ways to configure everything, and each way has a logical argument behind it somewhere. But I just like to keep things as simple as possible. Anyway, here is some logic. The isolator switches are always red. So shouldn't they go on the positive? PS, what are these DPST things you speak of? 1 Quote Link to post Share on other sites
tmouse 3 Posted March 14 Share Posted March 14 I assume DPST refers to : Double Pole Single Throw Switch 1 Quote Link to post Share on other sites
Guest 75 Posted March 14 Share Posted March 14 Double pole single throw, switch that functions as name implies. After toing and froing I decided three +ve switches on the three batteries in two banks, and two -ve automatic voltage/current/temperature sensitive switches on the LiFePO4 right next to the -ve post courtesy of bms’s was enough isolation for me and I considered it done. The start battery -ve post could do with one to be consistent but seeing as cars are permanently wired to starter motor without any isolation switch and have multiple earth paths I don’t think I can be bothered. Lithium is another level or two of paranoia though. m2cw 1 Quote Link to post Share on other sites
CarpeDiem 430 Posted March 14 Share Posted March 14 1 hour ago, K4309 said: The isolator switches are always red. So shouldn't they go on the positive? Quote Link to post Share on other sites
CarpeDiem 430 Posted March 14 Share Posted March 14 52 minutes ago, Guest said: Double pole single throw, switch that functions as name implies. After toing and froing I decided three +ve switches on the three batteries in two banks, and two -ve automatic voltage/current/temperature sensitive switches on the LiFePO4 right next to the -ve post courtesy of bms’s was enough isolation for me and I considered it done. The start battery -ve post could do with one to be consistent but seeing as cars are permanently wired to starter motor without any isolation switch and have multiple earth paths I don’t think I can be bothered. Lithium is another level or two of paranoia though. m2cw Most cars have fusible links in the start circuit. I wanted a way to manually isolate. In the event of an emergency it might be the relay controller that's smoking or worse the bms... The switch also isolates the BMS negative. Unless the bms and balancing is cascaded (which is a stupid design) then you can't truly isolate a Lithium. Maybe with a 6pst switch 😂 Quote Link to post Share on other sites
Guest 75 Posted March 14 Share Posted March 14 Are we talking about fuses or isolation switches? Quote Link to post Share on other sites
K4309 261 Posted March 14 Share Posted March 14 13 hours ago, CarpeDiem said: Well, that didn't age well. How many of those are available retail in NZ? I've only seen (and got) red ones, accept for the parallel, which is yellow. PS, I'm only considering lead technologies (lead acid, lead carbon). If you want lithium, then yeah, the requirements and redundancies increase substantially. I'm still to understand the benefits of lithium, esp as retrofits in boats the age of Aardvarks and mine. I'm sure the need for additional isolation is more easily justified in more complex installations you get on these new fandangelled boats. Next you'll be discussing coffee machines and microwaves instead of whistling kettles and kero verse getting a gas certificate 1 Quote Link to post Share on other sites
aardvarkash10 960 Posted March 15 Author Share Posted March 15 2 hours ago, K4309 said: esp as retrofits in boats the age of Aardvarks and mine. About the only benefit I can see is a doubling of the value of the boat! 1 Quote Link to post Share on other sites
K4309 261 Posted March 15 Share Posted March 15 1 hour ago, aardvarkash10 said: About the only benefit I can see is a doubling of the value of the boat! Don't get me started on boat values. What do they say when you want to fix / replace or upgrade stuff? Over-capitalised... As long as you use your boat and enjoy it for it's intrinsic value, rather than it's financial value 2 2 Quote Link to post Share on other sites
Guest 75 Posted March 15 Share Posted March 15 Grand old log 5knota all the usual trimmings, oozes past adventure and old world charm, and with new fangled colour cordinated isolating switches! Um, do they make em half red and half black for the ultimate single throw DP? Guaranteed to solve your loops. 1 Quote Link to post Share on other sites
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