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Post by TonyDunkley on Mar 1, 2019 10:31:07 GMT
Oh, I do hope you've got your boat wired up with some of the switching in the negative (return) side of your various DC circuits, . . and I hope someone is there to take a photo of it when it goes up in flames ! I see. So when I go away cruising, and I disconnect my car battery so that the alarm doesn't drain it, I'd better make sure I disconnect the right terminal otherwise it will spontaneously combust while I'm away? No, stupid, you're confusing two completely different issues. Disconnecting a battery takes the power source out of a circuit, or circuits, irrespective of which pole on the battery is disconnected, whereas switching the negative side of a (negative earth) DC circuit with the power source (battery) connected, and therefore IN CIRCUIT, leaves a live feed to the piece of equipment the switch controls, and which could develop an earth fault and then go up in flames. If you, or Nick, are still struggling to understand this simple principle after reading this, and JohnV's post above, think about what the word "circuit" means, and the fact that defects and faults which result in dead shorts to earth can and do develop in electrical equipment of any voltage. The clue to understanding any of this is in the word - "circuit'' , and incidentally, spontaneous combustion is NOT an electrical phenomenon, it's an exothermic chemical reaction !
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Post by Clinton Cool on Mar 1, 2019 11:33:34 GMT
Similar theme: I have 375w of solar feeding a 30a Tracer mppt controller. I'd like to introduce a switch close to the controller to isolate the panels from the controller. The controller doesn't have a switch, design flaw imho, given that you are supposed to connect the controller to the batteries first. The only way to achieve this at the moment is to either cover the panels, do it at night or remove a connecting wire from the controller. All Heath Robinson. Anyway, the only 12v switches I can find are big and ugly, isolator type things. I want something relatively small and neat. Would a cooker switch designed for 240v do the job? It's just for occasional use. If so, would a cooker switch accept the cable? I think it's 5mm, solar stuff I bought from Bimble. www.cclcomponents.com/imo-dc-isolator-16a-1500vdc-2-pole?gclid=Cj0KCQiAzePjBRCRARIsAGkrSm6NAPrpotSkw5FTw203XIvJ8zYWDu3lksFBnV48MRFELALhA09-2B8aAk6UEALw_wcBa possibility for you ....... the big problem with ac switches on dc is that the contacts burn when making/breaking contact under load. Many of the old fashioned wiping blade ac switches/isolators are fine on dc but they are mostly large, ugly and ancient. very few modern switches give a dc rating in their spec sheet. With boat lighting circuits domestic types are cheap enough and if they fail early ..... so what. With an isolator you need to make your own judgement call ........ my 1Kw array is isolated by a 240v 60 A rotary isolator and I accept the fact that it running outside it's design spec (I had a couple in my junk box and I objected to paying out for something else when it might only be used once or twice) Cheers John that one seems to be rated at 16a, would it be OK? The current can exceed that the odd time.
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Post by JohnV on Mar 1, 2019 11:56:49 GMT
the current to the battery is not the same as the current supplied by the solar panel. You presumably are charging 12 volt batteries. The solar panel will be putting out a considerably higher voltage than that. The output voltage of the panel is not fixed, it is dependent on the sunlight falling on it ..... typically at full production of it's rated power the voltage will be in the order of 36 volts or so. This means that when the panel is producing maximum power of 375 watts. if the voltage is 36 volts then the current flow through the panel and the switch will be 10.4 amps. this is not the same as the current being provided by the MPPT controller ...... different things ...... think of it like a mains battery charger that gives 100 Amps at 12 volts ..... you don't have a 100 amp fuse in the mains side
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Post by Clinton Cool on Mar 1, 2019 13:11:29 GMT
the current to the battery is not the same as the current supplied by the solar panel. You presumably are charging 12 volt batteries. The solar panel will be putting out a considerably higher voltage than that. The output voltage of the panel is not fixed, it is dependent on the sunlight falling on it ..... typically at full production of it's rated power the voltage will be in the order of 36 volts or so. This means that when the panel is producing maximum power of 375 watts. if the voltage is 36 volts then the current flow through the panel and the switch will be 10.4 amps. this is not the same as the current being provided by the MPPT controller ...... different things ...... think of it like a mains battery charger that gives 100 Amps at 12 volts ..... you don't have a 100 amp fuse in the mains side Thanks for explaining that. I think I get it; at maximum power the controller would be sending 31.2 amps towards the batteries, that being the 10.4 amps you mention x 3, 3 being the sum of 36v/12v. Is that it?
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Post by JohnV on Mar 1, 2019 13:18:59 GMT
power (watts) is volts multiplied by the amps ...... so amps is power divided by volts
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Post by Clinton Cool on Mar 1, 2019 13:28:12 GMT
power (watts) is volts multiplied by the amps ...... so amps is power divided by volts I see. That explains why 240v appliances are protected by lower rated fuses than 12v ones. Appreciate that, I've learned something today!
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Post by Telemachus on Mar 1, 2019 23:45:39 GMT
I see. So when I go away cruising, and I disconnect my car battery so that the alarm doesn't drain it, I'd better make sure I disconnect the right terminal otherwise it will spontaneously combust while I'm away? No, stupid, you're confusing two completely different issues. Disconnecting a battery takes the power source out of a circuit, or circuits, irrespective of which pole on the battery is disconnected, whereas switching the negative side of a (negative earth) DC circuit with the power source (battery) connected, and therefore IN CIRCUIT, leaves a live feed to the piece of equipment the switch controls, and which could develop an earth fault and then go up in flames. If you, or Nick, are still struggling to understand this simple principle after reading this, and JohnV's post above, think about what the word "circuit" means, and the fact that defects and faults which result in dead shorts to earth can and do develop in electrical equipment of any voltage. The clue to understanding any of this is in the word - "circuit'' , and incidentally, spontaneous combustion is NOT an electrical phenomenon, it's an exothermic chemical reaction ! We are talking 12v circuits. 12v circuits are not “earthed”. The concept of “earth” is meaningless for a 12v system on a boat. So this gives us a clue about your level of competence in matters electrical. If a “dead short to earth” could by some miracle happen, how does a switch help? Or are you mythical “dead shorts to earth” only allowed to happen when the switch is off? Of course if we were talking about mains circuits, your point would be entirely correct. It’s just a pity that we weren’t.
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Post by Clinton Cool on Mar 2, 2019 0:04:03 GMT
I'm going to get a 16a isolator similar to the one suggested when I get home. At the risk of sounding really thick, will I need to cut just one of the cables to install in the switch, or both? If it's not one of them, should I choose the positive or negative? If I were a gambling man I'd go for just one of them, and it doesn't matter, but I could be spectacularly wrong
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Post by TonyDunkley on Mar 2, 2019 1:19:06 GMT
No, stupid, you're confusing two completely different issues. Disconnecting a battery takes the power source out of a circuit, or circuits, irrespective of which pole on the battery is disconnected, whereas switching the negative side of a (negative earth) DC circuit with the power source (battery) connected, and therefore IN CIRCUIT, leaves a live feed to the piece of equipment the switch controls, and which could develop an earth fault and then go up in flames. If you, or Nick, are still struggling to understand this simple principle after reading this, and JohnV's post above, think about what the word "circuit" means, and the fact that defects and faults which result in dead shorts to earth can and do develop in electrical equipment of any voltage. The clue to understanding any of this is in the word - "circuit'' , and incidentally, spontaneous combustion is NOT an electrical phenomenon, it's an exothermic chemical reaction ! We are talking 12v circuits. 12v circuits are not “earthed”. The concept of “earth” is meaningless for a 12v system on a boat. So this gives us a clue about your level of competence in matters electrical. If a “dead short to earth” could by some miracle happen, how does a switch help? Or are you mythical “dead shorts to earth” only allowed to happen when the switch is off? Of course if we were talking about mains circuits, your point would be entirely correct. It’s just a pity that we weren’t. In the improbable event that anyone other than Mr Shit-for-Brains is taken in or impressed by any of the tripe that Nick is spouting here, I suggest that whoever is takes a few moments to look at some internet sites or anything else that covers the subject of 12 and 24 Volt DC electrics on cars, buses, lorries, plant, and industrial and marine engines, where they will find the term 'negative earth', or occasionally 'negative ground', in the common, everyday parlance of those who design, manufacture and service or repair these 12 and 24 Volt DC electrical systems. In addition to the 12 or 24 Volt DC, and usually, negative earth electrics as mentioned above, there is of course the process that was used to construct Nick's pretentious boat and to fix all the fake rivets to it, . . it's called arc welding. The welding current gets from the welding transformer to the work in hand via two welding cables, one of which terminates in an electrode (welding rod) holder, while the other one, the earth cable, terminates in an earth clamp which is tightened onto the work to complete the welding circuit. The welding set operates on either a single or three phase supply, which is itself earthed for safety purposes via the supply's own separate, earth connection. Confusing, isn't it, . . or at least it would seem to be, . . to an argumentative prat with a very overblown opinion of himself.
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Post by patty on Mar 2, 2019 6:51:53 GMT
Confusing about sums it up.... Its why I never touch electrics other than simple stuff...
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Post by Telemachus on Mar 2, 2019 8:30:30 GMT
We are talking 12v circuits. 12v circuits are not “earthed”. The concept of “earth” is meaningless for a 12v system on a boat. So this gives us a clue about your level of competence in matters electrical. If a “dead short to earth” could by some miracle happen, how does a switch help? Or are you mythical “dead shorts to earth” only allowed to happen when the switch is off? Of course if we were talking about mains circuits, your point would be entirely correct. It’s just a pity that we weren’t. In the improbable event that anyone other than Mr Shit-for-Brains is taken in or impressed by any of the tripe that Nick is spouting here, I suggest that whoever is takes a few moments to look at some internet sites or anything else that covers the subject of 12 and 24 Volt DC electrics on cars, buses, lorries, plant, and industrial and marine engines, where they will find the term 'negative earth', or occasionally 'negative ground', in the common, everyday parlance of those who design, manufacture and service or repair these 12 and 24 Volt DC electrical systems. In addition to the 12 or 24 Volt DC, and usually, negative earth electrics as mentioned above, there is of course the process that was used to construct Nick's pretentious boat and to fix all the fake rivets to it, . . it's called arc welding. The welding current gets from the welding transformer to the work in hand via two welding cables, one of which terminates in an electrode (welding rod) holder, while the other one, the earth cable, terminates in an earth clamp which is tightened onto the work to complete the welding circuit. The welding set operates on either a single or three phase supply, which is itself earthed for safety purposes via the supply's own separate, earth connection. Confusing, isn't it, . . or at least it would seem to be, . . to an argumentative prat with a very overblown opinion of himself. Oh dear, you really haven’t a clue. You are so closely resembling your nemesis naughtycal in your wrong advice on a subject you clearly have but the merest smattering of knowledge about, that it is ironic and highly amusing! It’s a shame you don’t understand the fundamental difference between the list of things you quoted (cars, busses etc), and boats. In the former it is common practice to use the metallic chassis and body as one half of the circuit. In boats it is not allowed and a very bad idea. With the former group the term “negative earth” is sometimes quoted by people lacking technical knowledge and unfortunately this results in confusion between the concept of “earth” in a mains circuit, and a chassis return on a vehicle etc, in the minds of people with limited understanding. For the avoidance of doubt I’ll explain that “earth” on a mains circuit is a protective conductor not normally carrying any current, whereas your misused term in the context of low voltage dc systems is the part of the structure and cabling normally carrying current and completing one half of the circuit, and absolutely nothing to do with earth, soil, or a planet. Of course those same people will also talk about “positive earth” for those older vehicle that have the battery +ve connected to chassis, which rather blows your argument out of the water. Never mind, stick to what you are good at (being a curmudgeonly grumpy old git stuck in the last century) and we will all be the better for it.
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Post by JohnV on Mar 2, 2019 8:33:33 GMT
No, stupid, you're confusing two completely different issues. Disconnecting a battery takes the power source out of a circuit, or circuits, irrespective of which pole on the battery is disconnected, whereas switching the negative side of a (negative earth) DC circuit with the power source (battery) connected, and therefore IN CIRCUIT, leaves a live feed to the piece of equipment the switch controls, and which could develop an earth fault and then go up in flames. If you, or Nick, are still struggling to understand this simple principle after reading this, and JohnV's post above, think about what the word "circuit" means, and the fact that defects and faults which result in dead shorts to earth can and do develop in electrical equipment of any voltage. The clue to understanding any of this is in the word - "circuit'' , and incidentally, spontaneous combustion is NOT an electrical phenomenon, it's an exothermic chemical reaction ! We are talking 12v circuits. 12v circuits are not “earthed”. The concept of “earth” is meaningless for a 12v system on a boat. So this gives us a clue about your level of competence in matters electrical. In proper marine systems the 12v or more usually the 24v system is earthed ..... at the hull earthing point. Ideally all the supplies (and there can be several completely independent supply systems) are all earthed at the same point on the hull, often via a Busbar. ....... but sometimes they are not and this is where some very strange faults can occur. Particularly when the vessel starts to become aged and has the normal rash of "repairs" and "modifications" by the ........ shall we say those of limited competence or limited familiarity with the systems. Sometimes you can find the negative of one system has been used by something fed from the positive of the other .....testing with a meter will show the correct voltage to the installer but when everything is being used some very strange things happen. Especially when, as I have already said, things become "aged" and the earthing points are not quite as good as they might be
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Post by Telemachus on Mar 2, 2019 8:35:06 GMT
I'm going to get a 16a isolator similar to the one suggested when I get home. At the risk of sounding really thick, will I need to cut just one of the cables to install in the switch, or both? If it's not one of them, should I choose the positive or negative? If I were a gambling man I'd go for just one of them, and it doesn't matter, but I could be spectacularly wrong Just one. It doesn’t particularly matter which one, since the aim is just to break the circuit supplying power to the controller, however convention and expectation would be to insert it in the positive.
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Post by Telemachus on Mar 2, 2019 8:38:07 GMT
We are talking 12v circuits. 12v circuits are not “earthed”. The concept of “earth” is meaningless for a 12v system on a boat. So this gives us a clue about your level of competence in matters electrical. In proper marine systems the 12v or more usually the 24v system is earthed ..... at the hull earthing point. Ideally all the supplies (and there can be several completely independent supply systems) are all earthed at the same point on the hull, often via a Busbar. ....... but sometimes they are not and this is where some very strange faults can occur. Particularly when the vessel starts to become aged and has the normal rash of "repairs" and "modifications" by the ........ shall we say those of limited competence or limited familiarity with the systems. Sometimes you can find the negative of one system has been used by something fed from the positive of the other .....testing with a meter will show the correct voltage to the installer but when everything is being used some very strange things happen. Especially when, as I have already said, things become "aged" and the earthing points are not quite as good as they might be That’s called hull bonding, not earthing. Unless you are a vampire, you probably don’t have a lot of earth on your boat!
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Post by JohnV on Mar 2, 2019 8:45:40 GMT
In proper marine systems the 12v or more usually the 24v system is earthed ..... at the hull earthing point. Ideally all the supplies (and there can be several completely independent supply systems) are all earthed at the same point on the hull, often via a Busbar. ....... but sometimes they are not and this is where some very strange faults can occur. Particularly when the vessel starts to become aged and has the normal rash of "repairs" and "modifications" by the ........ shall we say those of limited competence or limited familiarity with the systems. Sometimes you can find the negative of one system has been used by something fed from the positive of the other .....testing with a meter will show the correct voltage to the installer but when everything is being used some very strange things happen. Especially when, as I have already said, things become "aged" and the earthing points are not quite as good as they might be That’s called hull bonding, not earthing. Unless you are a vampire, you probably don’t have a lot of earth on your boat! commonly known as the ground plane ...... or earth ........ You are simply being pedantic over terminology which is common use in standard text books
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