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Post by Deleted on Feb 6, 2019 9:53:10 GMT
Attention is turning back towards the pesky positive earth Freeman Just a further thought ..... if all you are running off the domestic is the toilet and the coolbox, would have thought they were floating supplies with no actual connection to the hull earthing point so why not just run all the domestics and the solar charging system as positive earth ? that way it keeps the whole boat as one polarity PS and putup a big sign saying "warning positive earth" keepa da fingas off Trouble is it's not mine - if it were i'd start again tbh, and my friend who's boat it is wants the minimum of buggering about and leaving it as original as possible - bar for the additions! There is now a plaque in the electrical cabinet stating WARNING THIS ELECTRICAL SYSTEM IS POSITIVE EARTH only put there by me after some head scratching when I initially started working on this Freeman! So back to the start - is my theory sound? are the connections correct? |
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Post by Deleted on Feb 6, 2019 9:58:38 GMT
As far as I understand it the reason that early vehicles were positive earth is because that is the way they chose originally and that the change to negative earth came because it reduces body corrosion ...... don't know if it's correct or just someone bullshitted me ..... never bothered to check 'cos never came across a positive earth vehicle. I have been having a bit of a thunk about this ....... as the current flow would be huge, a quick blow fuse in the circuit would protect against the boat going up in flames and is one thought. Unfortunately fuses fast enough to protect electronics usually cost more than the electronics. I can't think of a way you could use the "engine running or not" to switch it in a way that is fail safe, which is obviously what you would prefer. So why not go outside the box totally IF; please note big if ...... the complete;solar charging system has floating negative, why not, when the domestic battery is charged use the vsr to control a double pole changeover relay that disconnects the complete charging system from the domestic circuit and connects it to the engine circuit. My thought was to use a non latching DPDT relay to isolate the solar from the existing positive earth batteries energized by the ignition, it was only really the remote chance of coil failure meaning it would drop to NC that made me think of the PFET solution - straight diodes being too volt hungry to consider, nice and easy to install though  |
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Post by Telemachus on Feb 6, 2019 10:50:48 GMT
So this is a plastic or wooden boat right?
You have an engine that has the battery + connected to its casing? You have some other boat services connected to a different battery? You want to parallel the batteries to charge both from 1 source?
So what? Since one doesn’t use the hull as the current return, and since the hull isn’t even metal, I don’t see what the problem is. I don’t see how a dynamo coming on line changes anything. Maybe I just don’t understand, but are you sure there is actually a problem?
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Post by Deleted on Feb 6, 2019 11:11:11 GMT
So this is a plastic or wooden boat right? You have an engine that has the battery + connected to its casing? You have some other boat services connected to a different battery? You want to parallel the batteries to charge both from 1 source? So what? Since one doesn’t use the hull as the current return, and since the hull isn’t even metal, I don’t see what the problem is. I don’t see how a dynamo coming on line changes anything. Maybe I just don’t understand, but are you sure there is actually a problem? Yes, GRP with no hull bonding I'm beginning to wonder if I've chased myself down a rabbit hole 🧐 This time the VSR will be on a conventional polarity system, sense to negative. I may have the lingering aftermath of the positve earth's setup clouding my view. So paralleling the batteries together won't matter so long as the new vsr is wired correctly? I'll get a sketch up later. Having to do a bit for the firm at the moment 😱 |
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Post by Telemachus on Feb 6, 2019 11:56:04 GMT
So this is a plastic or wooden boat right? You have an engine that has the battery + connected to its casing? You have some other boat services connected to a different battery? You want to parallel the batteries to charge both from 1 source? So what? Since one doesn’t use the hull as the current return, and since the hull isn’t even metal, I don’t see what the problem is. I don’t see how a dynamo coming on line changes anything. Maybe I just don’t understand, but are you sure there is actually a problem? Yes, GRP with no hull bonding I'm beginning to wonder if I've chased myself down a rabbit hole 🧐 This time the VSR will be on a conventional polarity system, sense to negative. I may have the lingering aftermath of the positve earth's setup clouding my view. So paralleling the batteries together won't matter so long as the new vsr is wired correctly? I'll get a sketch up later. Having to do a bit for the firm at the moment 😱 So engine battery and domestic battery connected together by means of: -ves connected by wires. +ves connected by a VSR when charging. Engine battery +ve connected to engine case, -ve to starter motor, Dynamo regulator etc Domestic battery connected to services as per normal practice - with +ve and -ve wiring, not using the hull etc as a -ve return. So long as there isn’t an attempt to connect domestic circuitry to something also connected to the engine (eg making an incorrect assumption the engine casing is a negative return for domestic circuits), I can’t see a problem. |
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