Re: 12V electrics problem


"Woody" <harrogate3@xxxxxxxxxxxxxxxxx> wrote in message
news:NKb8k.44136$7m7.27453@xxxxxxxxxxxxxxxx

Thanks very much for all your advice Woody. Your suggestion that I buy a
multimeter has saved me a few hundred quid

I'm fairly confident that the battery is OK, because since I charged it
up, I've been using it for a couple of days in the caravan without any
problems

That basically narrowed it down to the charger

I rang a few caravan sales / repair companies, and due to the charger
being an integral part of the power supply system, the whole lot was
going to need replacing at around £350 plus fitting. Unfortunately none
of them could do the work this side of August due to them being so busy

I therefore rang a local mobile caravan repairer - Dr Caravan Mobile
Services:

http://www.caravandoctor.bravehost.com

The reason for the shameless plug is that, even though he knew I was
prepared to pay him to do the repair, he gave me an idea that saved me
hundreds of pounds and earned him nothing at all. He suggested I buy a
cheap leisure battery charger and fit it permanently into the caravan. I
suppose I should have thought of that myself, but I didn't!

£35 pounds an an hour later, the problem is fixed

Cheers

Pete



Oh dear, that may actually cause you even more problems.

The power supply in the caravan will probably be a very efficient switched
mode unit no more than about 8"x6"x2" and supplying a stable and clean
supply of about 13.5V and capable of providing 12A or more. This will
provide enough current to feed all of your 12V lights, your pump(s), your
heater fan, your fridge light, your TV aerial amp and your cooker igniter
and still have enough left to provide some charge to the battery and even
supply your (fitted) car radio/CD player if you have one and possibly even
your LCD TV.

The charger you have bought however will be unregulated so could, under
fault conditions (like your battery becomes disconnected) put anything up
to 20V across the power lines. Also it will have no smoothing so will put
a quite large 'ripple' on the supply rails which could cause hum on a
radio or hum and visual patterning on your 12V TV. It's capability may be
4A or so - which really will not power very much.

I think your caravan dealer has possibly be suffering a bit of 'truth
economy.' I would be very surprised if a SMPS (switched-mode power supply
as they are known) is an 'integral' part of the caravan system. Go digging
and look for a box about the size described, possibly with a part vented
or grilled case, and with a mains lead connected to it (usually a wired
connection) and also a '12V' output one wire of which (-ve or earth) will
be white. Mine is mounted on one of the wooden support member of the N/S/F
seat facing the mains RCD/MCB switch box and immediately behind the
external battery box.

If you find it, make sure the mains has been off for at least 24 hours,
and disconnect the cables (it may need the cover to be removed) taking
care to insulate each wire as it comes free - just for safety. Then remove
the unit. As the caravan is British made it will very like have a UK
sourced (though not necessarily British manufactured) unit a replacement
for which you may be able to find on the Internet. The model number may
well give you an idea of its rating - for instance if it is something like
SMPS 12/150 it indicates a nominal 12V output at 150W or theoretically
about 12.5A current. You do not need to buy the same unit to replace it if
you cannot find one - anything that does a nominal 12V at about the same
(or greater) power capability, and has similar connections (i.e. screws
rather than a plug-on connector.) Many SMPS units are multi-voltage (+
and - 5V, + and - 12V, + and - 24V) - DO NOT get one of these as they
require current to be drawn off the +5V rail before the other outputs will
deliver any power at all. Also most of the power capability is at 5V and
the other rails will be relatively low power. If you get a +12V single
supply unit it will also likely have a control (by screwdriver) to adjust
the output voltage. For a 150W supply I would not expect to pay more than
about £60 for a professional unit, or you can get SMPS units that are
commonly available for the amateur radio market that can deliver a
regulated fixed 13.8V at 22A for not much more - look at www.wsplc.co.uk
or
http://www.powersuppliesonline.co.uk/product/12v-12a-caravan-charger/l08ab/default.htm


--
Woody


Thanks for your detailed reply Woody

I'm a bit out of my depth with this, so I'll have it repaired by a caravan
repairer when I get back from my hols

For the duration of this holiday I'll have to recharge the battery every few
days when I'm not using it to power any 12V equipment

Cheers

Pete


.

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