Voltage

[nelson]

Hello there,

 

I recently replaced batteties as I was getting a very inconsistent volatage to the 12volt mains interior. They were 3 years plus old and I live aboard so It made sense a bit.

Turns out It was not that, when I take a reading from the mains, fine, 13 volts plus. but when I plug an appliance in, such as a laptop adaptor or tv the voltage drops considerably.

Any ideas anyone please?

The lighting is fine, bulbs nice and bright, I checked polarity of the socket and someone said the Isolater, whatever that Is was OK.

It might be a job for an Electrician possibly, does anyone know of one In the Bradford upon Avon area?

 

Kind regards,

 

Nick.

[MtB]

Is this a recent problem or has it always been present?

 

If the latter then the wires are probably too thin.

And some figures would be helpful. Drops from exactly what voltage to exactly what?

[PaulG]

Hello there,

 

I recently replaced batteties as I was getting a very inconsistent volatage to the 12volt mains interior. They were 3 years plus old and I live aboard so It made sense a bit.

Turns out It was not that, when I take a reading from the mains, fine, 13 volts plus. but when I plug an appliance in, such as a laptop adaptor or tv the voltage drops considerably.

Any ideas anyone please?

The lighting is fine, bulbs nice and bright, I checked polarity of the socket and someone said the Isolater, whatever that Is was OK.

It might be a job for an Electrician possibly, does anyone know of one In the Bradford upon Avon area?

 

Kind regards,

 

Nick.

Where are you measuring the voltage?

Close to the batteries or close to the appliance you have plugged in?

If it's the latter, as Mike says above, it's probably poor cabling

[Tony Brooks]

Also well worth checking the cable connections around/inside the main DC fuse/mcb box/panel. Older ones with strip type bus bars with screw connections can have the screws work loose.

 

I agree that if it only does it with a 12V appliance running it sounds like voltdrop.

 

It could also be a faulty domestic master switch (that is if you have one for the engine an done for the domestics).

[alias]

 

Also well worth checking the cable connections around/inside the main DC fuse/mcb box/panel. Older ones with strip type bus bars with screw connections can have the screws work loose.

 

 

I have this bus bar arrangement for fuses, and had the same symptoms. In my case the screws were fine but there was a significant voltage drop across some of the fuses. Cleaning up the metal caps on the fuses with emery paper solved the problem.

[MtB]

Hello there,

 

I recently replaced batteties as I was getting a very inconsistent volatage to the 12volt mains interior. They were 3 years plus old and I live aboard so It made sense a bit.

Turns out It was not that, when I take a reading from the mains, fine, 13 volts plus. but when I plug an appliance in, such as a laptop adaptor or tv the voltage drops considerably.

Any ideas anyone please?

The lighting is fine, bulbs nice and bright, I checked polarity of the socket and someone said the Isolater, whatever that Is was OK.

It might be a job for an Electrician possibly, does anyone know of one In the Bradford upon Avon area?

 

Kind regards,

 

Nick.

 

 

Your post is a little confusing actually. You can either trace and diagnose it yourself (using help and advice from board members) or you can employ an electrician. You seem to have asked for both.

 

Tracing it yourself is going to be cheaper and you'll probably end up with a far more accurate diagnosis, but you'll need to answer a seemingly never ending stream of questions about your system, and what voltages appear where, and when.

 

Which approach re you wanting to take?

[Tony Brooks]

 

I have this bus bar arrangement for fuses, and had the same symptoms. In my case the screws were fine but there was a significant voltage drop across some of the fuses. Cleaning up the metal caps on the fuses with emery paper solved the problem.

 

That sounds horribly like the torpedo shaped fuses that once had ceramic bodies but now come in plastic. Horrible things that give endless problems. If so my advice would be to change the whole thing to use modern auto blade type fuses.

[alias]

 

That sounds horribly like the torpedo shaped fuses that once had ceramic bodies but now come in plastic. Horrible things that give endless problems. If so my advice would be to change the whole thing to use modern auto blade type fuses.

 

Yes, you are correct, and after a few trouble free years they are starting to give problems. Researching making that change I see comments that the old ceramic/plastic (8A) fuses may be rated as the current at which they blow, while blade fuses are rated as continuous current, and will blow at about twice the rating. If that is so, how best can I select blade fuses rated to protect the wiring (most of which is hidden behind the fitout materials)?

[Tony Brooks]

 

Yes, you are correct, and after a few trouble free years they are starting to give problems. Researching making that change I see comments that the old ceramic/plastic (8A) fuses may be rated as the current at which they blow, while blade fuses are rated as continuous current, and will blow at about twice the rating. If that is so, how best can I select blade fuses rated to protect the wiring (most of which is hidden behind the fitout materials)?

 

I know that I have ad modern blade type fuses passing more current than their rating. I also know the the old glass tube type automotive fuses went fro the "blowing" rating to the continuous rating so I suspect the modern ones are rated as continuous. However in a lot of cases this is what is required because of the starting surge of things like motors etc.

 

The cable SHOULD have been specified for the appliance rating so use the fuse size recommended in the manual. I many cases it will be well under the cable's rating because the cable will be specified to minimize voltdrop, not by current.

 

Hopefully another member can throw more light on this.

[Murflynn]

 

 

when I take a reading from the mains, fine, 13 volts plus. but when I plug an appliance in, such as a laptop adaptor or tv the voltage drops considerably.

 

If you have mains power I hope you have more than 13v.

[WotEver]

TonyB is spot on. Modern blade fuses are indeed rated at their continuous load and it will take around double that current to blow them. In theory your boat will have been wired with cable sizes designed to minimise volt-drop in which case they will be considerably larger than they would need to be based on the current they'll be carrying. Therefore replacing a 5A glass fuse with a 5A blade fuse won't be a problem.

 

HOWEVER, if the boat is old, or a self fit-out, or fitted out by a budget outfit then the above might not be the case.

 

If you are unsure of the size of the wiring then to be safe I'd suggest halving the existing fuse value then taking the next size up. So a 5A would be replaced with a 3A for instance. If experience shows that the 3A blows after a couple of months, then increase it; if it doesn't then so well and good.

 

Hope that makes sense.

[alias]

If you are unsure of the size of the wiring then to be safe I'd suggest halving the existing fuse value then taking the next size up. So a 5A would be replaced with a 3A for instance. If experience shows that the 3A blows after a couple of months, then increase it; if it doesn't then so well and good.

 

Hope that makes sense.

 

It does make sense, and seems a practical and prudent approach. Thanks.

 

 

The cable SHOULD have been specified for the appliance rating so use the fuse size recommended in the manual. I many cases it will be well under the cable's rating because the cable will be specified to minimize voltdrop, not by current.

 

 

All of the circuits appear at the fuse cupboard to have the same size wiring and the same 8A fuse. I suspect that a bit less thought than one might hope for went into the design. Thanks for your help.

 

Sorry for the thread hijack.

[Horace42]

Hello there,

 

I recently replaced batteties as I was getting a very inconsistent volatage to the 12volt mains interior. They were 3 years plus old and I live aboard so It made sense a bit.

Turns out It was not that, when I take a reading from the mains, fine, 13 volts plus. but when I plug an appliance in, such as a laptop adaptor or tv the voltage drops considerably.

Any ideas anyone please?

The lighting is fine, bulbs nice and bright, I checked polarity of the socket and someone said the Isolater, whatever that Is was OK.

It might be a job for an Electrician possibly, does anyone know of one In the Bradford upon Avon area?

 

Kind regards,

 

Nick.

Sounds like a bad connection somewhere. loose joints or terminals in series with all the circuits that cause a voltage drop when a load is plugged in or switched on.. So check for cleanliness and tighten them all.

[Guest]

Hello there,

 

I recently replaced batteties as I was getting a very inconsistent volatage to the 12volt mains interior. They were 3 years plus old and I live aboard so It made sense a bit.

Turns out It was not that, when I take a reading from the mains, fine, 13 volts plus. but when I plug an appliance in, such as a laptop adaptor or tv the voltage drops considerably.

Any ideas anyone please?

The lighting is fine, bulbs nice and bright, I checked polarity of the socket and someone said the Isolater, whatever that Is was OK.

It might be a job for an Electrician possibly, does anyone know of one In the Bradford upon Avon area?

 

Kind regards,

 

Nick.

When you say considerably, what is the recorded drop in volts and where is it measured?

Edited November 16, 2016 by Guest

[WotEver]

OP joined, asked his question, signed out and hasn't been back since.

[Jak]

His loss. I've benefitted from the post!

[MtB]

If you are unsure of the size of the wiring then to be safe I'd suggest halving the existing fuse value then taking the next size up. So a 5A would be replaced with a 3A for instance. If experience shows that the 3A blows after a couple of months, then increase it; if it doesn't then so well and good.

 

 

On the other hand if the cables all catch fire, reduce the fuse size to one size down.

 

[Guest]

OP joined, asked his question, signed out and hasn't been back since.

Might have no signal to be fair? Happens to me often.

Edited November 16, 2016 by Guest

[Tony Brooks]

 

 

 

On the other hand if the cables all catch fire, reduce the fuse size to one size down.

 

 

True (I know its a joke) but -

 

8 amp fuses would imply 1sq mm CCSA cable. Now if the boat was wired in this then we have found a likely candidate for the voltdrop. I find it very hard to believe it is wired in anything less than 2 sq mm CCSA and probably much more so the likelihood of cables burning is very slim indeed.

 

 

 

[Detling]

"All of the circuits appear at the fuse cupboard to have the same size wiring and the same 8A fuse. I suspect that a bit less thought than one might hope for went into the design. ".

 

Fuses are there to protect the wire on a boat not the device on the end, unlike the 240 volt fuse in your domestic appliance although there are only 3 common ratings 3, 5 and 13 amp and a multitude of appliance wattages

[alias]

"All of the circuits appear at the fuse cupboard to have the same size wiring and the same 8A fuse. I suspect that a bit less thought than one might hope for went into the design. ".

 

Fuses are there to protect the wire on a boat not the device on the end, unlike the 240 volt fuse in your domestic appliance although there are only 3 common ratings 3, 5 and 13 amp and a multitude of appliance wattages

 

Yes I understand that. I was picking up on Tony's implication that specifying different (larger) cable for circuits required to carry high currents and/or with longer runs gives the option to reduce voltage drop on them.

[Horace42]

 

Yes I understand that. I was picking up on Tony's implication that specifying different (larger) cable for circuits required to carry high currents and/or with longer runs gives the option to reduce voltage drop on them.

I got the impression this problem came to light only when you changed the batteries. If the cables are too small - then they have always been. If not, then some extra resistance crept into the circuits (it doesn't need much-just 1 Ohm will do.

All connections and joints are suspect.

[alias]

I got the impression this problem came to light only when you changed the batteries. If the cables are too small - then they have always been. If not, then some extra resistance crept into the circuits (it doesn't need much-just 1 Ohm will do.

All connections and joints are suspect.

I'm not the OP

[Horace42]

I'm not the OP

I Beg your pardon. Senior moment.

I wonder if the OP is reading these posts.

[WotEver]

I Beg your pardon. Senior moment.

I wonder if the OP is reading these posts.

I think it's safe to say no he isn't.

 

He joined, made his first post (the OP), signed out and hasn't been back since.