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Post by Deleted on Jul 6, 2017 8:30:54 GMT
Interesting! I can confirm the Crabtree MCB bank is rated for 240//415v (3 phase). I'm not sure how old it is (Model SB6000) or how long it has been fitted, but it does look like more than 10 years, maybe it was installed when the boat was built in 1989. I decided to switch that circuit over to a spare 16A MCB anyway. Initial signs look good but I've been here before! One entertaining thing is watching the voltage drop when the bass on the new stereo is driving hard. Maybe I shouldn't go to eleven? I can't find any data for those (obsolete) breakers but I suspect they are not designed for 12v dc. Still, sounds like it's lasted quite a while. You can get second hand ones from eBay etc if you need to replace it. Well so far it seems that, switching that circuit over onto another spare MCB, has done the trick thanks. The only thing I don't get is why a poor connection on one MCB might cause a voltage drop being measured on a different circuit. I have a permanent voltmeter display wired to the bedroom lighting circuit. It was a way of utilising a couple of bare wires left behind when the previous owners removed a light. Is it possible that a very weak connection might generate a lot of energy in wasted heat (a bit like pushing current through a thin wire) thus showing a general voltage drop?
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Post by Telemachus on Jul 6, 2017 8:35:45 GMT
I can't find any data for those (obsolete) breakers but I suspect they are not designed for 12v dc. Still, sounds like it's lasted quite a while. You can get second hand ones from eBay etc if you need to replace it. Well so far it seems that, switching that circuit over onto another spare MCB, has done the trick thanks. The only thing I don't get is why a poor connection on one MCB might cause a voltage drop being measured on a different circuit. I have a permanent voltmeter display wired to the bedroom lighting circuit. It was a way of utilising a couple of bare wires left behind when the previous owners removed a light. Is it possible that a very weak connection might generate a lot of energy in wasted heat (a bit like pushing current through a thin wire) thus showing a general voltage drop? No. That was why I asked you where you were measuring the voltage - and you said after the MCB in question! Most likely it is just physical disturbance of wherever the bad connection is.
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Post by JohnV on Jul 6, 2017 8:36:22 GMT
Interesting! I can confirm the Crabtree MCB bank is rated for 240//415v (3 phase). I'm not sure how old it is (Model SB6000) or how long it has been fitted, but it does look like more than 10 years, maybe it was installed when the boat was built in 1989. I decided to switch that circuit over to a spare 16A MCB anyway. Initial signs look good but I've been here before! One entertaining thing is watching the voltage drop when the bass on the new stereo is driving hard. Maybe I shouldn't go to eleven? I can't find any data for those (obsolete) breakers but I suspect they are not designed for 12v dc. Still, sounds like it's lasted quite a while. You can get second hand ones from eBay etc if you need to replace it. I just had a dig through some old paperwork and I can't find any info either, A lot of older style mcbs were rated for 50v dc as well as 240/415 ac, with a slightly increased rating
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Post by Deleted on Jul 6, 2017 8:55:16 GMT
Well so far it seems that, switching that circuit over onto another spare MCB, has done the trick thanks. The only thing I don't get is why a poor connection on one MCB might cause a voltage drop being measured on a different circuit. I have a permanent voltmeter display wired to the bedroom lighting circuit. It was a way of utilising a couple of bare wires left behind when the previous owners removed a light. Is it possible that a very weak connection might generate a lot of energy in wasted heat (a bit like pushing current through a thin wire) thus showing a general voltage drop? No. That was why I asked you where you were measuring the voltage - and you said after the MCB in question! Most likely it is just physical disturbance of wherever the bad connection is. Ah, yes. I think I incorrectly read that as being measured after the box. That's a pain, so it may well come back then. So just switching that 'faulty' MCB off and back on again would temporarily fix a voltage drop measured on another circuit. As you say, it may have just been the vibration of flicking the switch which temporarily cured a bad connection on the other circuit. Maybe I should go and check and tighten all the other connectors anyway and keep my fingers crossed.
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Post by JohnV on Jul 6, 2017 10:15:18 GMT
It's a good idea to regularly check electrical connections. Apart from vibration loosening the fixings the heating and cooling due to current flow can also cause the terminals to slacken
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Post by Deleted on Jul 6, 2017 10:29:59 GMT
It's a good idea to regularly check electrical connections. Apart from vibration loosening the fixings the heating and cooling due to current flow can also cause the terminals to slacken I reckon I've had more than one issue causing problems. Firstly my battery terminals weren't that tight which reduced the amount of charging and may have produced some voltage drop issues. Secondly, I'm pretty sure the old car stereo power amp or CD changer was drawing current due to some fault. Thirdly, swapping the MCD seems to have fixed the random current draw issue for now (but I don't understand why when the voltage was measured on another circuit. Maybe it's a bad earth somewhere, who knows?Anyway, until the problem comes back I can't do much. All I can say is that after doing those 3 things the batteries are getting charged quicker and seem to last twice as long.
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