12S power; limited to the fridge?

[JohnI.Stephen]

An obvious means of powering the small (barrel type) rear view CCTV camera whilst towing was to connect it to the 12S circuit, so that it's only powered only when towing and also disconnects automatically when static / on site. Just the job I'd say!

However, I have noticed that when towing (and using the 12S circuit) and the FRIDGE is 'on' (set to 'battery'), the camera's operation is very unreliable - it suddenly turns 'off'. Turning off the fridge completely instantly allows the CCTV camera to work again.

So, whereas I was assured that the camera (the RV29-T130 from Conrad Anderson) would require minimal power it doesn't seem to work when the fridge is also being powered from the 12S circuit.

Any thoughts on how I can resolve this (besides re-wiring the camera to draw directly from the leisure battery)?

John

 

[JeremyClarksson]

You could try an off the shelf voltage stabiliser or regulator or put a large capacitor in parallel with a lowish value bleed resistor (at the equipment) to smooth the supply from influences like the fridge switching on off.

My electronics is a bit out of date (only in the respect that these may have been superceded) but you may also be able to use Zener diodes.

I do not know why the fridge could be switching on/off as I thought they only drew enough to keep the temerature steady, perhaps there is some kind of movement sensitive protection for those larger movements.

The battery should be charging from the car on the same circuit as well and that is in effect one big capacitor.

All of the kit above can be bought at places like Maplins and should cost pennies rather than pounds, if you are lucky they will have someone who would draw you a diagram - you will need appx current draws of the camera equipment in the van.

Have you thought about giving the camera its own supply in the form of rechargeable batteries? it might be the easiest route.

 

[rayc]

John, I think the problem is volts drop in the circuit when the fridge is drawing current. The camera is minimal current but I suspect it needs a healthy voltage to operate reliably. If it were me I would confirm the voltage that it needs to work and then get a suitable 12v DC to DC convertor.

Any chance of you measuring the voltage to the camera when the fridge is On and Off?

 

[rob_jax]

Hi John,

Agree with Garry and Ray - it's either a voltage drop issue or intermittent supply - which could be caused by a poor contact in the 12S plug and socket during towing.

But it's most likely a voltage drop issue since the fridge draws 10 amps. So instead of pin 6 (fridge) you could try pin 2 (aux battery) which should be immune to demands from the fridge

Robert

 

[WatsonJohnG]

Hi John sorry to read you have problems

I haven't had that problem with my camera but my fridge wiring to the 12S socket is my own heavy duty wiring which would minimise voltage drop.

I wonder if they have wired to the fridge output to the element which depending on fridge model could switch off as the thermostat kicks out.

Our current fridge is so equipped but my wiring is to the lead from the 12S before it joins the fridge.

If its voltage drop you could wire direct from the leisure battery and either have a switch to switch off when not needed or have a relay triggered by the fridge circuit so that when the 12S was unplugged the relay would disconnect from the battery.

I swap my feed over to leisure battery on site and plug the AV leads from the camera into the Tv so that I have a view at the caravan rear if needed.

 

[WatsonJohnG]

Pin 4 green wire is also available on tow for battery charging so that could be used instead

 

[WatsonJohnG]

Hi John,

Agree with Garry and Ray - it's either a voltage drop issue or intermittent supply - which could be caused by a poor contact in the 12S plug and socket during towing.

But it's most likely a voltage drop issue since the fridge draws 10 amps. So instead of pin 6 (fridge) you could try pin 2 (aux battery) which should be immune to demands from the fridge

Robert

Pin 2 is now unused(since the advent of habitation relays) as I understand it but pin 4 green would do the job.

 

[WatsonJohnG]

Hi John sorry to read you have problems

I haven't had that problem with my camera but my fridge wiring to the 12S socket is my own heavy duty wiring which would minimise voltage drop.

I wonder if they have wired to the fridge output to the element which depending on fridge model could switch off as the thermostat kicks out.

Our current fridge is so equipped but my wiring is to the lead from the 12S before it joins the fridge.

If its voltage drop you could wire direct from the leisure battery and either have a switch to switch off when not needed or have a relay triggered by the fridge circuit so that when the 12S was unplugged the relay would disconnect from the battery.

I swap my feed over to leisure battery on site and plug the AV leads from the camera into the Tv so that I have a view at the caravan rear if needed.

If it is Ok with the fridge switched off it can't be wired to the element side of the thermostat so that idea is invalid.

 

[milliesdad]

Hi John,

One of our towcars had a voltage sensing relay to turn on the splitcharge and fridge supply (obviously cheaper than connecting a relay direct to the output from the alternator. It sensed an increase in voltage with the engine running and switched on connecting power to the fridge and van battery. Obviously with the fridge drawing 7ish amps there was now a voltage drop and with ours this would cause the relay to switch off ('cos it thought the engine was off again) and thus a cycle was started as the voltage then increased again switching the relay on. (hope you're still with me!). It could be this turning the supply on and off if you have this type of relay.

They are adjustable but ours was very touchy and took several attempts to get it right. We only found the problem because we could hear a feint click from the rear of the car every few seconds while towing.

Hope this helps - good luck,

Stewart

 

[WatsonJohnG]

Hi md

A good point,I have seen several people on rallies with problems with the voltage sensing relay and when I fitted one to my car the fridge was still on 30 minutes after switching off the engine

I much prefer the older mechanical type of relay myself but this involves extra wiring when fitting as it needs a trigger from an ignition controlled source.

 

[JohnI.Stephen]

Hello all; so it seems that I should perhaps swap the power from that to the fridge to that which charges the leisure battery? You're saying that this is pin 4 (John G)?

I won't personally attempt this but, as I am having a Reich motor mover fitted next week, the helpful Richard Draper may well feel able to sort this out at the same time?!!

Thanks for the great response and suggestions.

BTW The fridge is ALAYS very cold when I switch to 12S battery power. I will usually cool the fridge using A/C power so it shouldn't have to draw too much power in order to maintain the (already) cool temperature?

John

 

[WatsonJohnG]

It doesn't quite work like that.

If the 12V power is on then its on full

If the fridge is not thermostatically controlled on tow as most are (ie not controlled) then as soon as you switch on the engine 10-12amps will be feeding the fridge no matter how cold it is to start with.

 

[JohnI.Stephen]

Oh I see; sounds a 'naff' design to me (but then, what do I know ?!)

Anyway, John you are suggesting that whaetver wire comes from pin 4 on the 12S, this could then be split and used to power the CCTV camera, thus avoiding the power surge of the fridge?

I must say though that the CCTV worked in parallel with the fridge being ON for around 1 hour; then it stopped and wouldn't re-start until I turned the fridge OFF (I just thought I'd see it that was indeed the cause). so if the fridge is ON FULL POWER from the start, it's strange that the CCTV worked at all; but it did .....

More challenges ......!

 

[WatsonJohnG]

Oh I see; sounds a 'naff' design to me (but then, what do I know ?!)

Anyway, John you are suggesting that whaetver wire comes from pin 4 on the 12S, this could then be split and used to power the CCTV camera, thus avoiding the power surge of the fridge?

I must say though that the CCTV worked in parallel with the fridge being ON for around 1 hour; then it stopped and wouldn't re-start until I turned the fridge OFF (I just thought I'd see it that was indeed the cause). so if the fridge is ON FULL POWER from the start, it's strange that the CCTV worked at all; but it did .....

More challenges ......!

Strange but apparently true.

There are all sorts of strange things with the 12S.

Melting round the centre pin of the 12S is quite common and heating up of the pins could cause worse contact.

Have you checked the caravan 12S plug.

Its a good idea to open up the slits in the terminals from time to time(especially the centre one)

 

[JeremyClarksson]

Strange but apparently true.

There are all sorts of strange things with the 12S.

Melting round the centre pin of the 12S is quite common and heating up of the pins could cause worse contact.

Have you checked the caravan 12S plug.

Its a good idea to open up the slits in the terminals from time to time(especially the centre one)

Does sound plausible

I have had a couple of occasions where I thought a car battery was flat because I have had radio, lights etc but could not crank the engine.

It has turned out to be a poor battery or earth connection.

Are you sure your fridge was working properly?

 

[JeremyClarksson]

Reply to John G's comment (became invisible on main thread!)

Does sound plausible

I have had a couple of occasions where I thought a car battery was flat because I have had radio, lights etc but could not crank the engine.

It has turned out to be a poor battery or earth connection.

Are you sure your fridge was working properly?

 

[JohnI.Stephen]

Garry said "Does sound plausible

I have had a couple of occasions where I thought a car battery was flat because I have had radio, lights etc but could not crank the engine.It has turned out to be a poor battery or earth connection.

Are you sure your fridge was working properly?"

Well; the fridge has always worked very well, so I assume that it was working. No real way to be emphatic though ??

John

 

[JeremyClarksson]

I think you misunderstand what I meant, are you sure the fridge was still working when the camera was not - after all there is not really any noise indication and the fridge would still stay cool for a long time, this would point to the 12S connection problem that John Watson described.

The battery thing was to indicate that sometimes everything will point to a supply being there when in fact it is inadequate and can not supply the current.

I am not really sure what the "No real way to be emphatic though ??" comment relates to.

 

[WatsonJohnG]

John the fridge is just working in the same way that an immersion heater does.

When the water cools down then the element is switched on by the thermostat at full power in just the same way.

It sounds as though your fridge may be one of the later type with a thermostat.

 

[JohnI.Stephen]

I think you misunderstand what I meant, are you sure the fridge was still working when the camera was not - after all there is not really any noise indication and the fridge would still stay cool for a long time, this would point to the 12S connection problem that John Watson described.

The battery thing was to indicate that sometimes everything will point to a supply being there when in fact it is inadequate and can not supply the current.

I am not really sure what the "No real way to be emphatic though ??" comment relates to.

Garry "I am not really sure what the "No real way to be emphatic though ??" comment relates to."

What I meant is that I know of now way of being able to confirm 100% either way. As far as I am concerned, the fridge is working fine; but whether it is working when the camera is not, is something that I wouldn't have a clue how to test!

 

[JeremyClarksson]

To see if there is a bad 12S connection you could try these.

See if you can measure across the male to female connectors in the 12S plug and socket with everything connected and working you should get little or no reading - 12V would indicate an open cicuit (bad connection).

If this is difficult see if you can locate the supply to the fridge, again with everything connected it should read close to the supply voltage anything significantly below would indicate a bad connection, although not neccesarily at the 12S socket.

I will try and explain my earlier comments about the supply appearing to be OK but not sufficient to run the equipment properly.

Forgetting the camera for the moment if the supply to the fridge is 10A than the power is 120W and the resistance of the fridge would be 1.2 Ohms (Resistance = Voltage/Amps).

If you had a poor connection in the 12S socket equivalent to a 1.2 Ohm resistance you would now have 6V across the socket and 6V across the fridge and of course it will not work properly.

Still with the fault in place you now turn off the fridge and magically you will show 12V across the fridge, this is because the fridge switch is off and all the 12V will now appear across that switch (in theory infinite resistance and if you measured across the the male female 12S connectors you would get 0V because the 1.2 Ohms of the bad connection is now insignificant) - so everything appears to be hunky dory but it is not.

In practice bad connections fluctuate in resistance all the time due to factors like movement and even fluctuations in voltage and cuurrent draw unrelated to Ohms law.

Back to the camera - if it has a fluctuating voltage due to poor connections or even the fridge coming on and off it will not function properly.

The only real way to test the circuits properly is with everything connected and working.

If it is a poor connection you need to sort it out, if it is just a matter of the sensitivity of the electronic camera equipment I would still favour using rechargeable batteries to supply it or perhaps a switchable feed from the battery.

 

[WatsonJohnG]

Just in case its not been mentioned I would check the car wiring to the 12S socket especially any Scotchlocks as they give problems and could cause voltage drop.

 

[JohnI.Stephen]

Guys; many thanks for all of this information. I shall look into this over the next week or so prior to our next trip away in November !

cheers

John