12 volt two questions

[Rodone]

Hi All

Two completely seperate questions, but both to do with 12 volts.

I've just been away for two weeks and had a hook up. At some point the rocker switch on the electricity supply board got placed in the central (towing) position inadvertantly. Though the charger switch was still on,and lit up, when I came to apply motor mover at the end of the stay, the battery was completely dead,and I read it as 9.7 volts! I have now recharged it, and hope that it will not have sustained permenant damage,but my question is - if the rocker switch is in the central position is the mains charger not charging the battery. The second point is re fridge when towing. When the car engine is running, I get the 12 volt power to the fridge and measured this as over 11 volts when ticking over. Thetford say that.allowing for current loss via the cable, this is adaquate to keep the fridge cold, but it will not work when travelling. Any ideas anyone??

 

[rayc]

Rod, Point 1): On my van with switch in the central position the car will not charge the battery. In the central position the charger will feed the 12v equipment IF the mains is on. For the battery to charge from the car the switch must be in the VAN position.

Point 2): 11 v may be adequate to keep the fridge cold, ( but too low in my opinion), but is to low to get the fridge cold from ambient. Aim for at least 12.5 v at the fridge with the engine running.

 

[Rodone]

Ray, Thanks for your reply.My van, a Sterling (Swift Group) has the ECM supply module, and I know for sure that if I set the rocker to the central position,when towing, the battery will charge with no problem. The is as per the manual. What I wanted to know was if the rocker switch got put into the central position accidentally on site, with a hook up connected, would the mains hook up charge the van battery? Normally, the switch would be in the 'van' poition. Also, how can I up my feed to the fridge - thicker wire?

 

[rayc]

Rod, I do not know what model of ECM you have but in the handbook for my Ace there are instructions for the ECM ( although it is not not fitted to my actual van). I guess you must have adifferent variant if you are sure

It says:-

In caravan position:- DC is available from the caravan battery to power the 12v circuits. If the charger is switched ON the caravan battery will be charged.

Mid position:- In this position with the charger switched ON the van DC circuits will be fed from the charger only i.e. the caravan battery is disconnected and will not be charged.

I guess you must have adifferent variant if you are sure that your battery is charging when in mid position.

Car position:- The van DC circuits are fed from the car via pin 4 of the 12S socket.

As regards the fridge:- yes ideally 2.5mm cables should be used all the way from the car battery to the fridge ( via the car relay of course). I'not sure how long it would take the fridge to cool even then. The general concensus is that it keeps a cool fridge cool not cools it from ambient especially when loaded with food etc at ambient temperature.

Ray

 

[Nigel_374301722]

Ray, Thanks for your reply.My van, a Sterling (Swift Group) has the ECM supply module, and I know for sure that if I set the rocker to the central position,when towing, the battery will charge with no problem. The is as per the manual. What I wanted to know was if the rocker switch got put into the central position accidentally on site, with a hook up connected, would the mains hook up charge the van battery? Normally, the switch would be in the 'van' poition. Also, how can I up my feed to the fridge - thicker wire?

In answer to your questions:

1. No the charger will not charge your battery when in the central position, it will only run the 12v system. It needs to be in the VAN position to charge the battery.

2. The 12V supply on a fridge is only designed to hold the fridge at the temperature it is when you start your journey NOT to cool it from ambient. Always chill the fridge on mains or gas before you fill it and keep it chilled until you set off.

Hope that helps

 

[ProfJohnL]

Hello Rod

I cannot comment regarding the position of the rocker switches, Standards have changed since I was commercially involved.

I do not think you have a 12V problem with your fridge. At tick-over I would expect there to be less voltage available to run equipment. Even modern cars with alternators, still produce less power at tick-over than at normal running speeds. You should recheck the fridge voltage with engine turning at a higher speed, you will almost certainly find the voltage improves.

It is a fact of life that whenever a current flows through a wire, some voltage drop will occur. The bigger the current the greater the voltages drop. Fridges tend to use quiet a lot of current (6 to 8A) so there will be measurable drop when the fridge is running. This is predictable, and providing you have had an approved tow-ball wiring harness fitted, the components and wires will have been designed to cope with the fridge and other loads.

I do wonder if Thetford misunderstood the facts you gave them, or perhaps you might not have understood their reply, but the reported argument is not logical.

Logically, as there is sufficient power to run the fridge at tick-over (albeit not at full performance), then the fridge would continue to run even when travelling. However as the power will increase when travelling, then the performance of the fridge will also improve.