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Post by Deleted on Nov 2, 2016 21:41:35 GMT
I've come to this a bit late but I agree with Pete and Nick that you may well be seeing voltage drop down too-small cables. However, I'm unconvinced that the 12.7V you're seeing means that the batteries are fully charged. I suspect you're still seeing surface charge. If you run the TV for about 15 minutes then turn everything off, what's the voltage at the batteries then? How do you determine the batteries are fully charged when you stop charging? Tony I measured the 12.7v after having returned to the boat after 3 days (last run engine on 4 hour trip Sunday). I won't get a chance to do more tests until next week but I'm happy to try a few things out. I've just been using a rule of thumb that 3 to 4 hours engine running per day will replace what I use in the evening (some lights, maybe TV or amateur radio stuff). I also do an off load voltage measurement when I return to the boat after a day or two to check it's settled at around 12.7 to 12.8 volts (and to confirm my rule of thumb works!). However as has been suggested I'm not measuring the voltage at the best place.
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Post by Deleted on Nov 2, 2016 21:45:08 GMT
Wire about the same size as house wiring (2.5mm) is way too small to feed an inverter. I'd still like to know the off-load battery voltage after 15 mins of TV. It's onky a 100 watt inverter though, or is it still a problem?
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Post by tonyqj on Nov 2, 2016 21:46:34 GMT
I've come to this a bit late but I agree with Pete and Nick that you may well be seeing voltage drop down too-small cables. However, I'm unconvinced that the 12.7V you're seeing means that the batteries are fully charged. I suspect you're still seeing surface charge. If you run the TV for about 15 minutes then turn everything off, what's the voltage at the batteries then? How do you determine the batteries are fully charged when you stop charging? Tony I measured the 12.7v after having returned to the boat after 3 days (last run engine on 4 hour trip Sunday). I won't get a chance to do more tests until next week but I'm happy to try a few things out. I've just been using a rule of thumb that 3 to 4 hours engine running per day will replace what I use in the evening (some lights, maybe TV or amateur radio stuff). I also do an off load voltage measurement when I return to the boat after a day or two to check it's settled at around 12.7 to 12.8 volts (and to confirm my rule of thumb works!). However as has been suggested I'm not measuring the voltage at the best place. Could you buy yourself a cheap ammeter? One of those Chinese jobs would be fine, or even a clamp multimeter. It's the only simple sure-fire way to determine when you're approaching 100% charged.
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Post by Telemachus on Nov 2, 2016 21:48:50 GMT
Wire about the same size as house wiring (2.5mm) is way too small to feed an inverter. I'd still like to know the off-load battery voltage after 15 mins of TV. It's onky a 100 watt inverter though, or is it still a problem? That's about 10A. Quite a lot to send right down the boat. That the wiring is too small is evidenced by your reports of voltage drop.
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Post by Deleted on Nov 2, 2016 21:49:33 GMT
Well there is your problem. The wiring is totally inadequate. Compared to 230v, you need roughly 20 times fatter cable for the same voltage drop at 12v. Put the inverter near the batteries and all will be sweetness.. Lol...but the TV is down the other end. I suppose I could put a switch in to switch between an inverter and 5kva generator. Then I could utilise the 240v circuit down the boat.
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Post by tonyqj on Nov 2, 2016 21:50:35 GMT
Wire about the same size as house wiring (2.5mm) is way too small to feed an inverter. I'd still like to know the off-load battery voltage after 15 mins of TV. It's onky a 100 watt inverter though, or is it still a problem? At full load a 100W inverter will draw about 10A. If we say 30 metres round-trip for the cable (15m there and back) then a 10A load with 2.5mm cable will give over 2V voltage drop.
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Post by Telemachus on Nov 2, 2016 21:51:23 GMT
Well there is your problem. The wiring is totally inadequate. Compared to 230v, you need roughly 20 times fatter cable for the same voltage drop at 12v. Put the inverter near the batteries and all will be sweetness.. Lol...but the TV is down the other end. I suppose I could put a switch in to switch between an inverter and 5kva generator. Then I could utilise the 240v circuit down the boat. Sending th power at 240v requires about 20 times smaller cable for the same power loss. This is why electricity is distributed around the country at 330,000 volts!
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Post by tonyqj on Nov 2, 2016 21:53:24 GMT
Well there is your problem. The wiring is totally inadequate. Compared to 230v, you need roughly 20 times fatter cable for the same voltage drop at 12v. Put the inverter near the batteries and all will be sweetness.. Lol...but the TV is down the other end. I suppose I could put a switch in to switch between an inverter and 5kva generator. Then I could utilise the 240v circuit down the boat. Yes absolutely. That's the usual way of doing it. Ever wondered why electricity pylons carry thousands of volts instead of 230? Same reason - dropping a few hundred volts across some fields doesn't matter as a percentage. Does that make sense?
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Post by tonyqj on Nov 2, 2016 21:54:16 GMT
I must stop agreeing with Nick I must stop agreeing with Nick I must stop agreeing with Nick I must stop agreeing with Nick
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Post by Deleted on Nov 2, 2016 21:58:01 GMT
It's onky a 100 watt inverter though, or is it still a problem? That's about 10A. Quite a lot to send right down the boat. That the wiring is too small is evidenced by your reports of voltage drop. Yes, I suppose the 12v circuit is only really designed for lights really. Any resulting voltage drop from switching lots of lights on is just seen as slightly dimmer light from each bulb. I think the 12v sockets were intended for small 12v fans fitted above them. There is another 12v socket in the engine room with the bilge pump plugged into it. Maybe I'm pushing my luck trying to run a 100w tranceiver or 100w inverter off it!
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Post by tonyqj on Nov 2, 2016 21:58:44 GMT
Ain't no maybe π
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Post by Deleted on Nov 2, 2016 21:59:44 GMT
I must stop agreeing with Nick I must stop agreeing with Nick I must stop agreeing with Nick I must stop agreeing with Nick I must type quicker. I must type quicker. I must type quicker. I must type quicker.
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Post by tonyqj on Nov 2, 2016 22:02:57 GMT
I must stop agreeing with Nick I must stop agreeing with Nick I must stop agreeing with Nick I must stop agreeing with Nick I must type quicker. I must type quicker. I must type quicker. I must type quicker. Well yes, but I wrote more π
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Post by Deleted on Nov 2, 2016 22:03:11 GMT
Thanks guys. It's making more sense now. The stupid thing is that I bought a voltage stepper upper for my transceiver as the Icom 706 doesn't like the voltage dropping below 12v. Looks like I tried to fix the wrong problem.....doh!
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Post by tonyqj on Nov 2, 2016 22:06:29 GMT
By the way, that 'over 2V' that I mentioned wasn't a guess, I worked it out at 2.16V π
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