Refueler
Well-known member
Considering the rubbish posted - why not ??
Instruments turn off when starting engine having added extra battery,
- Thread starter sailor211
- Start date
Considering the rubbish posted - why not ??
billskip
Well-known member
It maybe rubbish to you, but there are possibly a few reading this that aren't engaging, some are learning possibly, I imagine many teachers possibly feel/say the same under their breath, but would be dismissed if they were to express it.
bedouin is trying to explain how he sees a possibility of a fault, he is not suggesting for one moment it is the fault.
You are entitled to say and write what you like within the rules, I accept that.
bedouin
Well-known member
Exactly - I am explaining the cause of similar symptoms in my own set up. Not in any way saying that applies here or that other solutions are wrong.
What is shocking is the number of people who can't understand what I am talking about and are absent any understanding of the basics of electrical circuits. So they are trying to tell me that I can't have seen what I see every time I start my engine. There is a certain arrogance in that don't you think?
Refueler
Well-known member
Maybe arrogance - but its based on your stubborness to not appreciate that the two circuits are sufficiently separated by not having common +ve - to be acting as indepedent circuits and your voltage drop cannot affect the other circuit.
The tone of replies has increased due to the persistence of error. I may not agree with 'Paul' at times - but on this he has shown considerable patience and tried to illustrate even.
Basic electrical circuit requires the +ve and -ve to be same circuit for any effect / power / whatever.
Two circuits can have common negative but separate source +ve - such that each circuit will act totally independent of each other. Simple.
bedouin
Well-known member
No Paul has missed the point. I have made it perfectly clear (#15 [see also #17, #34,#37, #62]) the situation I am talking about only applies if there are elements of the wiring of the circuits in common (e.g. the example in #66) and that is the post Paul erroneously contradicts. Paul later comes up with a counter example of a circuit that does NOT have any wiring in common so of course my comments don't apply in that case.
And we have no idea about the details of the OPs circuit.
If you can see anything I have written that isn't 100% correct please point it out.
AngusMcDoon
Well-known member
I did a simulation in CircuitLab using the circuit from #66. Two separate batteries, house and starter, connected grounds and part of that ground side has a common section where both the house and the starter currents flow through. I put a 120 ohm load across the house battery and a 100 mOhm load across the starter battery and gave the common bit of cable a 0.01 Ohm resistance. I then added 2 measurement points across the house load and ran a simulation. The circuit and results are shown here...
What this simulation shows is that the voltage of the ground side of the house load does rise significantly with respect to the ground of the house battery at the battery (1.092 V) and consequently the voltage across the house load drops.
Ohm's Law alone is not sufficient to solve this circuit. Kirchhoff's Laws are needed as well.
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PaulRainbow
Well-known member
This is the system that we've been discussing and is what the OP has, he has clearly stated so in his early posts. I have also explained how it is and even provided you with a schematic.
#66 is no different, still cannot get a voltage drop on the domestic system, as there is no common positive.
Time to stop digging now.
PaulRainbow
Well-known member
My schematic has all negatives connected together but not the positives, exactly the same as the sketch it #66
Yes we do, he has clearly stated that all negatives are connected together, positives are on separate switches and he has a VSR, exactly the same as my schematic.
Too many errors and lack of understanding to even begin pointing them out.
I do this as a day job and i also have a boat myself. All of my negatives are connected together across all systems. That's 2 x 7 litre diesels at 24v, 1 x generator at 12v, basic domestic systems at 24v, several DC-DC converters taking voltage down to 12v for various systems, 2 x DC-DC converters taking voltage down to 5v. All live happily together with no voltage drop between the different systems. Starting 7 litres of Volvo engine does not make any difference to the voltage on the other systems, as it is with millions of other boats with a common negative.
bedouin
Well-known member
No - there is a significant difference. Your schematic shows all the negative coming to a common point - but no (significant) amount of wiring in common. #66 shows a wire carrying common current between the two circuits.- it is the voltage drop across that wire than causes the drop in the domestic
I have repeated said my comments only apply when there is common wiring like that - but no need for any commonality in the +ve
#106 gives concrete figures that prove what I have been saying.
I have not seen any post from the OP that says whether or not any -ve wiring is in common, which is why I have stressed so repeated what you seem to have missed - that this is only an issue when there is.
billskip
Well-known member
Well there you go...
Thank you Angus.
bedouin
Well-known member
Yes - and that is what is frightening me
PaulRainbow
Well-known member
Funny, when people can't grasp something they usually resort to taking the piss.
AngusMcDoon
Well-known member
For completeness, here's the same circuit and simulation without the starter motor. The voltage across the house load is almost the full 12 V.
PaulRainbow
Well-known member
From post #1
"Engine battery is separate with its own switch, but all neutrals 0V are connected.
There is a VSR for charging"
Looks like i haven't missed anything, but someone has.
Buck Turgidson
Well-known member
post 66 was for simplification as you well know.
The reality is boats are wired to their individual negatives and the negatives are connected.
so just for fun here is what it looks like with a shared neg but individual returns on each circuit:
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Tranona
Well-known member
Have you not read the original post#1 ? where the OP clearly states that the batteries have a common ground and describes the boat as being wired exactly as per Paul's diagram with the exception of having solar feeding into the VSR. His problem has been solved many, many posts ago - or at least the principles of what to look for with specific reference to the VSR. The simplest solution to eliminate the VSR as an issue is to connect the solar direct to the house bank which is the one that needs it most.
You came in halfway through seemingly having not read the original and try to introduce a scenario that simply does not exist in relation to the OPs boat nor (as Paul says) most other boats Cue dozens of posts at cross purposes trying to "prove" positions that are mutually exclusive. Yours requires both banks to be connected via the +ve as well as common -ve whereas Paul plus many others including the OP are clear that the banks are not connected by design, save for the possibility of the VSR closing when the engine is started because of the feed from solar.
If you are citing experience from your own boat it is presumably not wired the same as the OP if there is a possibility of the 2 banks being connected when the engine is started. For example using a 1,2,B on both or having a BEP switch cluster like mine where the emergency parallels both banks rather than switching to the house bank as in Paul's diagram.
It is clear you are never going to agree because you are both correct under the assumptions you make.
Moral "Read the question first before providing your answer"
Boater Sam
Well-known member
Well done sir for sticking to your guns. I knew that you were correct because I made exactly the same conclusion many posts ago but then the usual arrogant always right posters stepped in and I stepped back as I do not have the patience to argue with these know it alls who are sometimes very wrong.
Any common cable in the negative connections to both batteries will cause the negative in one battery to rise to a slightly positive voltage with respect to the junction of the negatives thereby reducing the voltage available.
Sam.
Sandy
Well-known member
Do you have any research to back up this claim?
If it was possible what sort of voltage change would cause the chart plotter to turn itself off and on again? I know mine is good down to 10.4 volts, I've tested it and once it is off it is off. I need to manually press a button to switch it back on.
AngusMcDoon
Well-known member
The circuit as in #66 can be resolved using Kirchhoff's and Ohm's Laws. Gustav Kirchhoff did his research in the 1840's and published his findings in 1845 (he was born in what is now Kaliningrad). Ohm's Law is from 1827 although he followed on from work done by Fourier and Cavendish. They are both old stuff from the dawn of discovering electricity and pre-date Maxwell's equations (I had a girlfriend at university who is a related to J.C.Maxwell).
Ohm's Law is GCSE stuff. Kirchhoff's Laws are in physics A level syllabus. Finding the potential difference between Node 1 and Node 2 in the circuit in #106 would be a typical physics A level question.
It depends on the minimum input voltage of the power supply. For example, this one, picked at random, is 10.8 V...
https://www.digikey.co.uk/en/produc...&productid=13968668&utm_content=&gad_source=1
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bedouin
Well-known member
Ah - you have seen the light - a new wire has magically appeared and now there is no common wire in the circuits that there clearly was in #66.
Of course R8 is totally redundant as it cannot be included in any circuit.
In my very first post in the thread in #15 I made it clear this was only an issue if there was a wire carry current for both. Those having a go at me clearly haven't understood the significance of that caveat.
