12v circuit problems

[Christophe lamby pie]

Can anybody help me?

 

When we woke up yesterday the newish 12v fridge and shower pump wouldn't work and when the water pump ran all the lights dimmed.

Our batteries are less than a year old and the engine was new in February (Beta 38). The batteries seem to charge up normally when the engine is running but as soon as the water pump runs the power drops right down and the lights flicker.

To make things more confusing even when the gauges state that the battery power is really low, the Victron inverter still works.

I thought the shower pump might have been the cause so I replaced the impellor but still no joy. I've disconned the fridge and replaced a 15A fuse in the engine bay but the wiring looks so confusing I don't know where to start.

 

Please help an electrically challenged bumbler if you can.

[bizzard]

It could be an neg- problem. I'd be inclined to first of all to check out the 12v neg wiring and connections 'usually black cables' from the effected appliances which usually go to a common bus bar. It sounds like the appliances you mention are robbing each other of current.

Edited September 30, 2013 by bizzard

[SamKingfisher]

It would be helpful if you posted a voltage reading from the batteries.

 

My gut feeling is that the batteries are very discharged. The cut off for the inverter would I think be about 10.8v and if your batteries are at or a little above that whilst not under load then they are flatski!

[pistnbroke]

First remember that you must test dont guess ( or it costs time and money) You must put a voltmeter across the battery and read the voltage when the fault exists. 12v or more would be good. Then check across the cables out of the batteries andwork your way towards the pump where you can get access. If the batteries are good and charged it is certain you have a bad connection which is reducing the voltage and causing the light problem.

 

Ignore incorrect statements like the appliances are robbing each other of current ..never happened

[nicknorman]

Yes, expanding on what Bizz said its a bad connection somewhere. The inverter probably will have separate connections to the battery compared to the other domestic services and clearly these are OK. But there is a bad connection somewhere in the domestic wiring. I would get a multimeter and check systematically through the domestic wiring with some load on. Starting at the batteries and with some load on (eg water pump running), check for a good voltage between + and - working through the system - isolator, fuses panel etc until you get to the pump wiring. At some point you will find the (say) 12.5v you could expect from well-charged batteries will drop to below 12v and this should help you to locate the problem.

 

Sometimes the inverter is not wired through the isolator, in which case an easy way to start would be the isolator itself and it might be worth simply cycling the isolator on and off a few times - a bad contact in the isolator can be temporarily improved by this action. Some cheap isolators are renowned for this type of failure.

[bizzard]

First remember that you must test dont guess ( or it costs time and money) You must put a voltmeter across the battery and read the voltage when the fault exists. 12v or more would be good. Then check across the cables out of the batteries andwork your way towards the pump where you can get access. If the batteries are good and charged it is certain you have a bad connection which is reducing the voltage and causing the light problem.

 

Ignore incorrect statements like the appliances are robbing each other of current ..never happened

I know that most boats are double wired unlike most steel bodied vehicles that use the body for the the neg-. Have you never had an old car with say for example has a bad light unit fixing to body connection and strange things happen like when foot brake is pressed the sidelight goes dim or out, or the indicator bulb goes dim or out or the brake light goes dim, can cause all sorts of odd fault combinations because of a dodgy touch and go weak neg connection which is not substantial enough to allow all the light functions to work individually on that particular combined light unit. Well anyway I like to call it robbing each other of the current.

[Tony Brooks]

Look at where your main domestic pos and neg battery cables are connected to the distribution/fuse/circuit breaker assembly. I suspect a loose connection in that area. But do as Pistnbroke says ans TEST. When the fault is present take voltage readings (pos to neg) on the battery lead posts, the metal of the clamps (but as the inverter works I doubt its a terminal problem), the other end of the main cables, in the boat. Also test the voltage ACROSS the master switch when the problem is occurring. It should be all but zero, if its more than about 0.3 V buy a new switch.

 

There is no way the fridge and water pump should be on the same fuse/circuit breaker so if, when the fault is present, you have 12V + between the pos and neg busbars in the box you need to look at the fridge and water pump wiring.

I know that most boats are double wired unlike most steel bodied vehicles that use the body for the the neg-. Have you never had an old car with say for example has a bad light unit fixing to body connection and strange things happen like when foot brake is pressed the sidelight goes dim or out, or the indicator bulb goes dim or out or the brake light goes dim, can cause all sorts of odd fault combinations because of a dodgy touch and go weak neg connection which is not substantial enough to allow all the light functions to work individually on that particular combined light unit. Well anyway I like to call it robbing each other of the current.

 

But actually the current is finding an alternative path to batty negative via other twin filament bulbs with a good "earth" so nothing is robbing current but something is introducing a higher resistance circuit at that point in time. Nothing has robbed any current, the voltage is just not high enough to push enough current through the higher resitance circuit.

 

Definitely not having a pop at you - especially in view of the smiley, but such thinking goes a long way to explaining why people find diagnosing electrical faults difficult.

[MtB]

Can anybody help me?

 

When we woke up yesterday the newish 12v fridge and shower pump wouldn't work and when the water pump ran all the lights dimmed.

 

I suspect this is the problem. Did you have a fridge before? A fridge sucks power out of the batteries and if you didn't have one before you'll need to ramp up your battery charging regime substantially.

 

I suspect your batteries have been getting drained by the fridge a little more than you are charging the batteries every day, and they have finally become fully discharged.

 

MtB

[Alastair]

Take a voltage reading of your batteries with the isolator off.

 

Now turn it on and run the water pump and check the voltage. Tell us the two readings.

[bottle]

While you are doing all the above, check the size of the fridge supply cable and whether you are getting more than 12v at the fridge end.

[Paul's Nulife4-2]

Hi ya,

As already stated Test don't guess,is the way to go,& the preceding posts certainly give you enough information to get you started,,but have you fitted anything new,or different recently,does this problem only happen when say the inverter or other high loads are being used,& are you sure your batterys are in good condition,it might be worth charging them in your usual manner,totally disconnecting them.letting them rest,,,,then testing them in the manor suggested..

It's my understanding a battery can show full,but not hold the capacity or charge.

Hope you find it anyway.

Edited September 30, 2013 by Paul's Nulife4-2

[Tony Brooks]

 

I suspect this is the problem. Did you have a fridge before? A fridge sucks power out of the batteries and if you didn't have one before you'll need to ramp up your battery charging regime substantially.

 

I suspect your batteries have been getting drained by the fridge a little more than you are charging the batteries every day, and they have finally become fully discharged.

 

MtB

 

 

But he says the Victron inverter still works and they are not known for doing 100 Watt jobs. If it was not for that sentance I woudld agree, but I suspect the inverter is wired direct to the batteries whilst the rest, including the voltmeters, go via the distribution box.

 

Maybe the Victron is a combi-unit, he is on shorepower and he does not realise the inverter "working" is only the battery charge part. But even so with a battery charger running it reduces the chances of it being flat batteries.

 

We need some voltage readings.

[sassan]

Could well be inadequate wiring. If the voltage at your batteries is ok, then consider running new wires from the battery to the pump (and nothing else).

[pistnbroke]

but such thinking goes a long way to explaining why people find diagnosing electrical faults difficult.

 

Excellent logic Tony I hate technocrap

[Theo]

I know that most boats are double wired unlike most steel bodied vehicles that use the body for the the neg-. Have you never had an old car with say for example has a bad light unit fixing to body connection and strange things happen like when foot brake is pressed the sidelight goes dim or out, or the indicator bulb goes dim or out or the brake light goes dim, can cause all sorts of odd fault combinations because of a dodgy touch and go weak neg connection which is not substantial enough to allow all the light functions to work individually on that particular combined light unit. Well anyway I like to call it robbing each other of the current.

If your boat isn't double wired then you should do something about it very soon. Using the hull as a return path is a really bad idea and will cause rampant corrosion. Just make sure that all the negatives are connected with copper wire to the battery negative terminal. The negative should be bonded to the hull but the hull should not be the path that by which current returns to the battery.

 

N

I have to say that I rather sigh for the days when Gibbo and Chris W were contributing. In those days any mention of an electrical fault would be good for a couple of days entertainment. Ah me.. How times change. This topic has remained polite and helpful for 16 posts!!

 

N

[Paul's Nulife4-2]

& Silence descends...!

Edited October 1, 2013 by Paul's Nulife4-2

[Tony Brooks]

I have to say that I rather sigh for the days when Gibbo and Chris W were contributing. In those days any mention of an electrical fault would be good for a couple of days entertainment. Ah me.. How times change. This topic has remained polite and helpful for 16 posts!!

 

N

 

Wot, you want me to call Bizzard a pillock or some such? No way, if one can not help best either to keep very quiet or be 100% sure of your facts before starting something.

 

Actually I think on the basis of the information we were given there are many posts that need disregarding at this time but they are all trying to help and all new and fairly new members need to learn to sort out who to trust, who to use a guidance, and who to ignore. There is just no point in attacking people.

[Paul's Nulife4-2]

Well whatever the problem is, I do hope it get sorted for the OP. & we all get an update on both what it was,& how it was rectified from them...anyway...after all,that's how us newbies learn,by standing in the shadows of giants !.

It is very evident,that there are some VERY knowledgeable,electronic based guru's on here,& thank god for that...

But surely even a newbie can be right,,occasionally.(not suggesting I am though).

[Tony Brooks]

You may well be correct because we have no real idea how much the OP actually knows and as I said his idea of the Victron working could be that its just charging or has some random light on. However an inverter of the size that Victrons tend to be really need their own wiring and fuse direct from the master switch. This being so and taking the OPs message at face value a working inverter suggests (no more than suggest) that the batteries are OK, that is turn points to a problem in the fridge and pump wiring. Good practise indicates that both those appliances should be on separate circuits which in turn point the finger at a poor connection on the main pos or neg busbar.

 

None of this is certain because the OP has not come back to clarify the situation or told us what they found. We are just playing probabilities at present.

[Paul's Nulife4-2]

He is probably asleep !.WAKE UP !!.

[MtB]

& Silence descends...!

 

I see the OP was last online at 6.15pm yesterday, so let's hope he was reading the thread and today is doing a bit of testing in order to post some battery voltage data.

 

Until he does this, little more constructive can be written.

 

 

MtB

[jonathanA]

maybe he's sat in darkness with no power for his laptop/smartphone unable to read the pearls of wisdom that could help him...

 

Lets hope not of course...

[Christophe lamby pie]

Thank you everyone for your posts.

 

Sorry not for replying sooner but been off the interweb for a while.

We managed to find the problem after much probing into small dusty and dirty alcoves - it was as suggested by Bizz as the first reply. The main negative connection to the isolation switch was loose, causing the wiring to move about when the engine was running (to recharge the batteries) and arc/disconnect.

All tightened and sorted now - thanks again for the helpful (and a few off track!) posts

[George94]

As Tony B said, you learn after a while whose advice to take!

 

And for those of us who aren't electronics engineers, I like the idea of appliances robbing each other of current. It's what happens when there isn't enough to go round. As in this case.

 

BTW, Tony B has a wealth of knowledge, but Bizz has been "hands-on" since the late Pleistocene. If you ignore what he says you are probably pissed and will probably soon be broke.

[bizzard]

As Tony B said, you learn after a while whose advice to take!

 

And for those of us who aren't electronics engineers, I like the idea of appliances robbing each other of current. It's what happens when there isn't enough to go round. As in this case.

 

BTW, Tony B has a wealth of knowledge, but Bizz has been "hands-on" since the late Pleistocene. If you ignore what he says you are probably pissed and will probably soon be broke.

Why, thank you George for the kind and uplifting words. You surely meant the late PlasticIne period. I'm a bit of a Fred Dibnah really, what looks right is right, well almost. My reference to appliances ROBBING each other which was ridiculed by some due to faulty connections or wiring was in my experience the simplest way to explain to a customer what might be happening with their electrics, which they seem to understand rather than by waffling away, showing off, blinding them with science and getting too technical about high and low resistances and all the other technical facts figures, laws and goodness knows what appertaining to the mysterious and invisible force called electricity. By the way I'm not an electrician by trade, just call me a Sparks.

And Theo old bean, of course my boat is double wired.