Puzzling electrical question.

[Mad Harold]

Fitted a socket (12v) in the cabin for my vacuum cleaner,phone charger and television.Used 2.5 sq mm 29 amp twin core cable.Length is about 4m.

When I plugged the vacuum cleaner in,it ran at about half speed,the tv didn't do anything.

Checked the voltage at the battery 12.8v,the junction box12.8v,and the socket again 12.8v.

I find it rather strange that the voltage is ok,but stuff doesn't work.

I hope this isn't a daft question,but is there such a thing as amperage drop??

I am finding it difficult to think of anything else.

Look forward to enlightenment.

[Machpoint005]

I bet the cable got hot when you had the vacuum running! 

[ditchcrawler]

You need to measure all those voltages with the vacuum cleaner running including on the cleaner itself as the last link in the chain is the plug and socket

[Tony Brooks]

No but if you suffer volt drop you will get less amps flowing.

What was the voltage at the socket when the vacuum cleaner is running? When chasing volt drop you must always have the circuit under load.

[WotEver]

Assuming that neither the TV nor the vacuum cleaner draw more than 5A (which is a reasonable assumption) then the voltage drop down 4m of 2.5mm² would only be about a quarter of a volt. Therefore one or more of the following must be true...

 

• The cable isn’t 2.5mm²
• The run is much longer than 4m
• There is a bad connection somewhere in the feed. 
   

I’m guessing the latter. Where did you pick up the 12V?  How did you make the connection?
 

[TheBiscuits]

13 minutes ago, Mad Harold said:

cable.Length is about 4m.

Is that 4m from the batteries, so 8m of cable (there and back) or 2m from the batteries so 4m of cable?

 

Also, does the vac have 3m+ cable on it after the plug/socket?

[Mad Harold]

1 minute ago, TheBiscuits said:

Is that 4m from the batteries, so 8m of cable (there and back) or 2m from the batteries so 4m of cable?

 

Also, does the vac have 3m+ cable on it after the plug/socket?

The cable is two core (red and black) length from the battery is about 4m,so total cable length from battery to socket and back will be 8m.

The vac is a Halfords car vac and it does have about 2- 3 m of cable after the socket.

[Mad Harold]

9 minutes ago, WotEver said:

Assuming that neither the TV nor the vacuum cleaner draw more than 5A (which is a reasonable assumption) then the voltage drop down 4m of 2.5mm² would only be about a quarter of a volt. Therefore one or more of the following must be true...

 

• The cable isn’t 2.5mm²
• The run is much longer than 4m
• There is a bad connection somewhere in the feed. 
   

I’m guessing the latter. Where did you pick up the 12V?  How did you make the connection?
 

Thanks for the reply.The cable is two core so the length from battery to socket and back will be 8m.

Checked the voltage at the junction box,the connection from the junction box,the connection to the socket and also the switch terminals. All read 12.8v.

Hence my head scratching.

Will undo all connections tomorrow to check for bad connection.

[WotEver]

2 minutes ago, Mad Harold said:

Checked the voltage at the junction box,the connection from the junction box,the connection to the socket and also the switch terminals. All read 12.8v.

You have to check them with the vacuum cleaner connected and running. 

[Keeping Up]

My 12v vacuum (B&D) takes just over 11 amps. The supplied plug (cigarette lighter type) gets ridiculously hot.

[WotEver]

18 minutes ago, Keeping Up said:

My 12v vacuum (B&D) takes just over 11 amps. The supplied plug (cigarette lighter type) gets ridiculously hot.

That would still only be around half a volt drop down 4m of 2.5. 

[TheBiscuits]

4 minutes ago, WotEver said:

That would still only be around half a volt drop down 4m of 2.5. 

Yes, but it's running down 14+ m not 4.

[WotEver]

1 minute ago, TheBiscuits said:

Yes, but it's running down 14+ m not 4.

You can’t include the accessory’s cable in volt drop calculations so it’s a one-way distance of 4m, or two-way of 8m. Either way, at 11A the drop would be around 0.6V as I wrote. 

[Alan de Enfield]

50 minutes ago, Keeping Up said:

My 12v vacuum (B&D) takes just over 11 amps. The supplied plug (cigarette lighter type) gets ridiculously hot.

Standard cigarette lighter plugs / sockets are rated at 10 amps (Some of the German cars have Bosch types that are rated at 15 amps)

[Tracy D'arth]

Cigar sockets are rubbish, they just don't make a good connection on the plug.

[Keeping Up]

1 hour ago, Alan de Enfield said:

Standard cigarette lighter plugs / sockets are rated at 10 amps (Some of the German cars have Bosch types that are rated at 15 amps)

Indeed, which is why I am surprised that the device came with such a plug fitted. The first time i used it, it melted the socket that i plugged it into.

[Murflynn]

"stuff doesn't work" ..........................  have you tried plugging "stuff" into you car's socket(assuming you have one)?

 

do you have a cigar socket on the DC domestic distribution switch panel?  does "stuff" work when plugged into it?

 

PS:   I gave up on 12v vacs many years ago - they couldn't pull fluff off a day-old chick. 

[Tony Brooks]

FWIW on the basis of info given I am guessing a very poor crimp connection in the new installation.

Oh, and plus the silly socket. If it were mine I would be fitting a small three pin socket as well and the put a three pin plug on the vacuum (as per the wiring method discussed many times before). The TV should not draw anything like 10 amps.

[Mad Harold]

Found the fault.It was a bad connection at the junction box,causing a large voltage drop.

Have taken onboard the comments about cigar lighter sockets.

Many thanks to all who replied.

[Tony Brooks]

Please also take on board the fact that when testing for such faults you need the circuit energised and a load running.