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HI all.  I have just inherited a 1970s cadet 10 which I am very excited about and I'm just about to begin a full overhall of it starting with the electrics. I have a 120ah battery (which will soon extend to 2x 120ah) which will power a fridge, tv, stereo, USB sockets and lights. It will be charged via the engine  and eventually solar however I want to keep it topped up via an electrical hookup for now  so I am looking at getting one of these 20a power supplys/chargers: 

 

https://www.ebay.co.uk/itm/203052682276

 

The total current pull with everything on, although unlikely all will be on together, could pull up to 35-40amps. So my question is:

 

If i pull more than the 20a rating of the power supply, will the battery provide the required power and then the supply then replenishes afterwards? Or does only the supply provide the power and I must not exceed 20 amp when its connected?

 

Thanks!

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Yes, absolutely. I do it all the time. Charging the battery and drawing from it at the same time are not a problem. The charger measures the voltage across the battery terminals and adds vol

Not correct At least, not for a ctek charger - see the instruction pdf. There is no "on" button. It is a button to select a different mode. Upon being reconnected and plugged in to the mains

But neither pin 9 nor pin 13 are wired up on the electrical connection of my towcar and yet all 12v lights, water pumps, fridge, etc work while on the move.

The current draw on mains 240V is totally different to the current draw of a 12V system. 

 

Graham

 

Unless otherwise stated all posts are my personal opinion 

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20A @ 14V (the max voltage the charger will operate at)=280Watts, the power used.  At 230 V the power will be about 1.2A (280 divided by 230) add a bit for "inefficiency" and your charger will draw no more than about 2 A.

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First up you will not be able to run your fridge on the 12v supply from your Leisure battery, They are designed (and wired) to run on 12 v only when connected to your towing vehicle and it’s engine is running due to the current required. That facility is to try and keep the fridge cool when the caravan is being towed between sites and is pretty inefficient. 

In addition don’t forget that a 125ah battery will weigh 25-30kg  and that eats into the caravans available payload, and caravan payloads are best described as meagre at the best of times (my year old 4 berth has a payload if just 150kg, and that’s not a lot when you start putting crockery, cutlery, water carrier, waste hog, bedding, clothes, chairs, fridge contents etc into it 

 

A modern TV and stereo don’t draw very much current at all, about 3 amps max, LED lights virtually nothing so where have you got your figure of 20-30 amps from? Remember a three bar electric fire will only have a 13 amp fuse in the plug!!!

 

The most you will get on a campsite is 16 amps and many continental ones just 6 amps. The lower figure is enough to run a caravan providing you don’t try and run too many high wattage items at the same time.  I think perhaps you need to revisit you consumption calculations??

 

By the sounds of it you are new to this caravan malarkey??  There is a lot to learn about it but this forum is an absolute mine of information due to the accumulated years of experience of its members. Don’t be frightened to ask any question at all, we all had to learn at the outset.

 

Oh, and I forgot to say “Welcome to the  forum” 

Experience is an awful teacher who ends up sending you simply horrifying bills

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Not sure where mains current comes into this?  Seems to be a question purely about the 12V system.  Any sensibly designed charger should current limit at its stated charging / output current, and any excess over that would be supplied by the battery.  

 

As Mr Plodd says, if you have a standard 3-way caravan absorbtion fridge, then these should only run off 12V when connected to the car as they pull about 180W / ~15A.  If you want to use this type of fridge off grid, then it should run on gas.  This would be different if you're using either a 12V compressor fridge (expensive) or a peltier coolbox (cheap and poor performance).

 

The current that USB sockets take from 12V is also much lower than the current they put out at 5V, e.g. a 3A USB socket will take about 1.4A from 12V.  Radios also usually take a fairly small current (e.g. ~2A) at sensible volumes.

 

 

 

 

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Thanks for the replies! Yes I was only referring to 12v here but I wasn't aware that camping fridges shouldn't be run permanently on 12v. I will aim to run this on gas or via hookup. My question was largely related to how these 12v supply/ chargers work. I emailed the seller and he said thay they don't restrict the output of the battery (should the draw exceed 20a) and they simply charge the battery below 14v when needed in order to not risk any damage to sensitive 12v appliances. 

 

I've read that smart chargers can provide up to 15v when charging so you should isolate the battery when charging.  I want a charger which i can leave permanently connected when hooked up which will keep the battery topped up but will not affect my 12v appliances. What charger options do I have?

 

I've believe I've calculated my current draw correctly, I have a lot of heavy pulling audio as I will be visiting festivals and events. Also 7 to 10m of strip lights. However I'm unlikely to ever run everything together! 

 

Thanks!

 

I'm also aware that I cant expect a full charge from one of these chargers so a charger which keeps the battery topped up to 80% which can be permantly wired in and is safe for appliances is what I'm after. The extra charge can be achieved from the vehicle when towing. 

 

Thanks again!

Edited by Willbiker
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Are you planning on towing the said van, as 2x120ah batteries will eat into your payload considerably 

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BMW 520D MSport Touring. ...

 

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Yes I have a van and 750kg of total train weight I can add on between my van and the caravan so I'm not concerned about weight yet however I will keep it in mind. 

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What sort of payload were Cadet 10's allowed? 

I've got nothing to do on this hot afternoon

but to settle down and write you a line.

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I assume your 7 to 10 metre strip lights are LED? If using them off grid that would make a saving in power usage. 

13 minutes ago, JanandJay said:

Are you planning on towing the said van, as 2x120ah batteries will eat into your payload considerably 

If only needing extra power for festivals one battery could be left in the car and attached on arrival

Alan

 

2005 Nissan X-trail 4WD diesel and Swift Charisma 540 2012 Lunar Clubman ES  2018 Lunar Clubman ES

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Yes led strip lights at 60w per 5meters and Yes good suggestion regarding the battery! I'm not concerned about weight currently, I will make sure I'm within limits and distributed accordingly. Can anyone suggest a charger? Can you buy smart chargers which can be left connected when hooked up allowing the battery to be used? Or is my only option a 12v power supply as I linked at the start of the thread?

 

 

Edited by Willbiker
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I'm getting confused.

 

If the van has no built in charger then you can buy one, or a portable smart charger but you'll need a source of mains power to operate the charger. Whilst plugged into mains power you could also run mains sockets and equipment in the caravan. Once off grid then you are reliant on 12V battery or gas as energy forms, the battery might be charged by a solar panel too, if you wish. You can fit an inverter that will turn the 12V battery power into 240V but that transfer from 12V to 240V is relatively inefficient and drains batteries very, very quickly. 

I've got nothing to do on this hot afternoon

but to settle down and write you a line.

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My caravan doesn't have a 12v charger/power supply so heres what I assume is the best approach to my requirements.

 

When plugged into an hookup, I was going to continue to run most of my aplliances on 12v except the fridge which should auto switch to 240v. I will have  240v sockets around the caravan which will be supplied by the hookup when onsite and an inverter when off the grid  but my 12v lights, tv , audio and usb sockets for charging the gadgets will permanently be on the 12v circuit. So when hooked up the the mains, I need a charger which can top the battery up. However I've read that you must not use a normal smart charger as they provide 15v of power and are not designed to be used while the battery is in use. Ive read that a '12v power supply' is needed which detects when a load is on the battery and adjusts the voltage accordingly. Am I wrong? 

 

Thanks 

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Given that modern UK caravans have PSU's alongside built in chargers I'd say you're probably right. If you're going to have 240V available at the caravan, would it make sense to fit a proper caravan charging and power control system? And if you have two batteries charge one somewhere else using a smart charger? 

I've got nothing to do on this hot afternoon

but to settle down and write you a line.

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So I've looked at a few pms, mainly the pms3h and the charging function on it is 13.8v which is good for maintaining charge but doesn't have any smart charging features so may not be good for the batteries health. Surely there is a portable smart charger out there which can be left permantly on when hooked up and not put 12v appliances at risk...

Edited by Willbiker
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Maybe there isn't a solution. A power managment system with 13.8v charging is enough to maintain charge but every so often it may nee to be isolated and charged with a smart charger to restore it to 100% and condition it.  Thanks for the suggestions

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A     ctek mxs 5.0    battery charger is generally reckoned to be about the best there is, and being a smart charger, can be left on permanently. It will do everything you and the battery need. Price c£70.

I am very pleased with mine and have had it for about 4 years now.

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6 minutes ago, daveat92 said:

A     ctek mxs 5.0    battery charger is generally reckoned to be about the best there is, and being a smart charger, can be left on permanently. It will do everything you and the battery need. Price c£70.

I am very pleased with mine and have had it for about 4 years now.

Thanks dave. I see this pop up everywhere but are you sure its ok to use this product to charge the battery while its in use powering 12v appliances?

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Your only other option is to fit a caravan specific PSU and combined charger unit as that’s exactly what they are designed for. You should be able to source a second hand one. The make doesn’t matter as you are not fitting a replacement. 

Experience is an awful teacher who ends up sending you simply horrifying bills

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1 minute ago, Willbiker said:

Thanks dave. I see this pop up everywhere but are you sure its ok to use this product to charge the battery while its in use powering 12v appliances?

Yes, absolutely. I do it all the time.

Charging the battery and drawing from it at the same time are not a problem.

The charger measures the voltage across the battery terminals and adds voltage at a variable rate (up to c 14.5V) according to the need. Thus, as you draw from the battery, the voltage in the battery drops, the charger sees that drop and puts charge in to bring it back to fully charged, but obviously only as fast as it can deliver it. That's why you need to leave it on, to allow it to continue charging after you have stopped drawing from the battery.

 

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1 minute ago, daveat92 said:

Yes, absolutely. I do it all the time.

Charging the battery and drawing from it at the same time are not a problem.

The charger measures the voltage across the battery terminals and adds voltage at a variable rate (up to c 14.5V) according to the need. Thus, as you draw from the battery, the voltage in the battery drops, the charger sees that drop and puts charge in to bring it back to fully charged, but obviously only as fast as it can deliver it. That's why you need to leave it on, to allow it to continue charging after you have stopped drawing from the battery.

 

amazing! I just looked up the spec and it peaks at 15.8 volts? but if you are saying it won't put out over 14.5 volts when an appliance is drawing from it then perfect! Just for peace of mind, I'll email CTEK and ask. Thanks!

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6 hours ago, Willbiker said:

HI all.  I have just inherited a 1970s cadet 10 which I am very excited about and I'm just about to begin a full overhall of it starting with the electrics. 

These caravans were really nice, and they are extremely saught after. Its becoming difficult to find them without too much damage (Wood rot and accidental). As you are "starting with electrics" I guess the body and chassis must be serviceable. If this is the case, you shouldn't alter it radically as there will be someone out there who would prefer to restore such a classic to original condition. They were really light weight (under 500Kg loaded) and had very little payload, not enough for the 2 batteries you mention which would be around 50KG. They were produced with no internal electrics at all, just basic road lights. A gas mantle should be on one side wall. is yours one of those with the plastic dome roof? or a later one with a small sky light? If you are going to use it as a classic tourer you will be looking for a toilet tent in which to house your Elsan bucket toilet. How about posting a photo or two?

Ern

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I haven't picked it up yet but its my grandads who can no longer use it. And I'm afraid he has chopped and bodged it about very badly so its already a little spoiled however still very pleasing.  I am going to strip out his deadly electrics he has installed and make it usable off grid but thats it. The rest of the improvements will be cosmetic, trying to keep it as standard as possible. Its very light at only 595kg so other than these 2 batteries, it won't have anything else substantial in it when driving.  My van will take the bulk of my stuff. The payload limit will hopefully be on a plate somewhere so if i can't put 2 batteries in it, one or even both can be transported in my van.

 

Luckily it's in great condition underneath however I will wire brush and paint the chassis, service the brakes, grease the hubs and treat it to some new tyres as it has been sat for 10 years.

 

I cant remember the roof style but I will be sure to post some pictures when I pick it up soon!

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3 minutes ago, Willbiker said:

I haven't picked it up yet but its my grandads who can no longer use it. And I'm afraid he has chopped and bodged it about very badly so its already a little spoiled however still very pleasing.  I am going to strip out his deadly electrics he has installed and make it usable off grid but thats it. The rest of the improvements will be cosmetic, trying to keep it as standard as possible. Its very light at only 595kg so other than these 2 batteries, it won't have anything else substantial in it when driving.  My van will take the bulk of my stuff. The payload limit will hopefully be on a plate somewhere so if i can't put 2 batteries in it, one or even both can be transported in my van.

 

Luckily it's in great condition underneath however I will wire brush and paint the chassis, service the brakes, grease the hubs and treat it to some new tyres as it has been sat for 10 years.

 

I cant remember the roof style but I will be sure to post some pictures when I pick it up soon!

This is the rear door one isnt it?

Ern

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