Why do I only have 11 volts when on mains hookup?

Jul 27, 2020
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Hi again, doing up my old Bessacarr 550GL Cameo (early 90s). Got most things working now, although the old gas boiler thing hasn't been tackled yet (would be lovely to get that working but doubtful!).

I noticed (unlike more modern caravans) that when it's on mains hookup the voltage meter inside says "LOW" in red, or at best "11 Volts". Also, there is nothing at all without a battery connected. Am i right in thinking that it MUST have a bettery in it to get 12v to switches/lights/pump etc? That seems a bit silly to me, but maybe that's how they were designed back in early 90s. If I disconnect battery, we get no voltage (except 240v of course) yet we do have a convertor/invertor thingie which takes in 240 and should push out 12v.

The battery we plugged in is very old and probably had it. So maybe that isn't passing the voltage through if it has a dead cell for instance. But I hoped I wouldn't need a battery in at all to get 12v when on mains, as we will only ever use it on mains anyway.

If anyone has any ideas why this is happening I would be grateful to hear em! thanks
 

Damian

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Mar 14, 2005
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Back when your van was made they only had a battery charger, not a power supply.
A battery must be connected to supply a smooth 12v as the charger cannot cope with sudden demand.

First thing is to check the battery and its voltage and that it can take a charge, if it will not then it is a waste of time even trying to use it.

If the battery is OK, then take a measurement of the voltage with no power connected to the van, then after ensuring the charger is On, check the voltage again at the battery terminals.

If the charger is working you should see 13.8v. if not, the charger is faulty.
 
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Thanks. I see, so it's a charger only. Gotcha. So maybe I could swap that out for a proper 12v invertor, or just get a better battery. Will have to see which is cheaper! On that point.... If i need no CAPACITY (this van will never be away from 240v hookup) then am I right in thinking i could use a small 12v battery instead, even a motorbike battery maybe? That must be able to put out enough current for cranking a small engine, so I would think that's enough for a 12v pump and a few lights? thanks again
 
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Damian

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I dont know why you even mention an Inverter as they convert 12v to 230v, which you do not have.

What you need , if your present charger is not working, is a power supply which will give you battery charging and cope with the heavier demands.

If you dont have a motor mover on your van then an 85Ah battery would be fine, but dont go too small or it just puts extra strain on it. A starter battery does not like the slow discharge required in a caravan, it works best for heavy short term supply, which is why a leisure battery is used in a caravan,

As for charging/power supply, then the one that I like better than most is the Sargent PX300.
It is both battery charger and power supply and is very good, however like any caravan related item it is not cheap, but it is the best.
 
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Thanks for that. It was a vocabulary issue why I mentioned invertor. I never remember all the terms, but yes I meant what you describe, 240 to 12v power supply/charger. I bought one once and may still have it, it was around £50 off ebay second hand and it was cheaper than the same one usually sold for. I suspect it's quite a good one as a friend of mine commented on it (he does know his electrics unlike me!). I will have a look at that model you mentioned if i can't find it.
thanks again
 
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Hello John You have told us that your not particularly familiar with electrics, so I strongly suggest you perhaps ask your friend to help.

A 12V battery can still do quite a lot of damage if its not connected or protected correctly.
 
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Thanks. Not sure what I said, I am no electrical engineer but I do have a better than average understanding of 12V electrics, I rewired my boat a few years back. I tend to be more careful around 240. I can definitely replace a 12v PSU once I know what goes where.

What do you mean by "protect" a 12v battery properly?
 
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Have you measured the battery out of circuit and on its own? It should read at about 13.7v. Many UK caravans will not work without a battery in place to complete the circuit.
 
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What do you mean by "protect" a 12v battery properly?
Physical protection - Correct positioning with the necessary restraints in a room sealed enclosure.
Electrical protection - Principally fusing adn insulation, but also correct conductor gauge, and quality connections.
 
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Thanks. It turns out my son put a very dead battery in the caravan to begin with (which is reading 8v now out of circuit). I have just put a good battery in (reading 12.8v after a while sat on shelf, it's a good heavy duty one from tractor, albeit not deep discharge/leisure type). I will monitor to check if the caravan charger is doing its job and go from there i think. Ideally i would like to replace the charger with a 12v power supply (240v - 12v zigzag type thing) but i will need some time to find the connections and make sure i do it properly. will report back thanks
 
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Going to tackle this properly tomorrow. Today we found a nice condition leisure battery (13.5v, forgot we had it (on optimiser all this time!))
We plugged it into the caravan, all 12v lights working nice and strong. But I left them on to check if the hookup was supplying charge to the battery. It's dead this evening. Looks like a duff PSU/charher :(

There is a white fused box which has the breakers on, and a switch on top which says "12v". I assumed that should put out 12v, but looks like some aftermarket stuff has been done in there because it has a 240 cable going out to a proper 12v convertor ("Ranger Power Box")for supplying the charge to battery and 12v to caravan, thats the thing I suspect is faulty.
Tomorrow I will check the output from that Ranger box and see, but I have a feeling it won't be putting out 13-14v as it should. If I recall correctly, we had a battery in this caravan and had it hooked up to mains and the battery went dead. Maybe the main white box should put 12v out to the caravan appliances and the Ranger box is just for charging the battery. Will have a look where the wires all go tomorrow. Thanks for the help
 

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Jul 18, 2017
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If you "found" the battery although it was showing 13.5v , there may still be an issue with the battery so why not take it to a battery place to test. Cost nothing and it is one less thing you need to worry about. If only lights on I don't think it should drain the battery in a day unless there is a "short" somewhere draining the battery? Maybe someone else can confirm?
 
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Just an observation, looking at the photograph, the label and the metal casing are showing signs of rust. This is not untypical especially for older caravans, but it does suggest there might well be other corrosion problems that might be waiting to surprise you. Electrical connections in lamp fittings can be a problem.

I would also ask you to pay particular attention to the gas systems, where some appliance's do have exposed steel gas pipes, which can corrode and may need replacing.
 
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Just an observation, looking at the photograph, the label and the metal casing are showing signs of rust. This is not untypical especially for older caravans, but it does suggest there might well be other corrosion problems that might be waiting to surprise you. Electrical connections in lamp fittings can be a problem.

I would also ask you to pay particular attention to the gas systems, where some appliance's do have exposed steel gas pipes, which can corrode and may need replacing.
As suggested earlier by yourself, it may be better for the OP to get a qualified caravan engineer to check out everything. Do you know if there is a possibility if they can they convert the lights in that caravan to LED lights as that may be another thing to look at?
 
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Thanks for the posts. Re "found" the battery - don't read anything into that. It's a good battery I just forgot we owned. I have a battery tester (resistance based). I will be careful with gas, not touching it until our boiler man pops in to check it over, I suspect it's fubar but will let him confirm. Still yet to get to the wiring but yes that rust caught my eye too, will have check every visible contact in the whole system and wiring
 
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Success at last! I tested with a meter and found no voltage coming from the ranger power box. I also noticed some aftermarket stuff has been done under there. I removed the ranger power box, and took to bench, checked fuse and drilled out the rivets to open it up, all looks good as far as corrosion/good contacts go. So it's one of the two components inside. I may try and fix that, will see if my friend can test the two components and see which is at fault. In the mean time I found an old one I forgot I had, actually another "ranger power box". I stuck that in and hey presto, 12v lights etc working without a battery hooked up. So it wasn't connected in series as I suspected. That's progress at least! thanks for the help here
 

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Hello John,

I'm glad you have found a fault, and you can now plan to resolve it.

I note from your picture the internals of the unit are very basic, and it does have a smoothing capacitor but crucially it has no voltage regulation. It will run a few lights, but its output may not be stable enough to safely operate any of the other 12V appliances. This design of charger needs a battery in parallel to compliment the internal smoothing capacitor.

Unfortunately, as it has no voltage regulation it is not suitable for long term charging or optimally maintaining a caravan battery. It really needs to be replaced with a proper modern power supply designed to keep a battery in good condition.
 
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Hello John,

I'm glad you have found a fault, and you can now plan to resolve it.

I note from your picture the internals of the unit are very basic, and it does have a smoothing capacitor but crucially it has no voltage regulation. It will run a few lights, but its output may not be stable enough to safely operate any of the other 12V appliances. This design of charger needs a battery in parallel to compliment the internal smoothing capacitor.

Unfortunately, as it has no voltage regulation it is not suitable for long term charging or optimally maintaining a caravan battery. It really needs to be replaced with a proper modern power supply designed to keep a battery in good condition.

I see, that makes sense. thanks very much again
 

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