The mains to 12v power supplied failed in a mate's motorhome, so although he got it replaced I offered to look at it to see if it could be repaired as a spare.
It is branded PowerPart, and is a 20 amp 13.8v device which charges the leisure battery as well as running any 12v things when on mains. Cost about 100 quid.
It was well and truly fried. Only heatsink for the power Mosfets was the thin ally case - and a small cooling fan. Not that much for a device likely mounted inside a cupboard of some sort.
Rectifier was short circuit and a transformer burnt with half the laminations lying loose inside the case, so gave up.
There is a UK after market replacement with a good reputation, at around the same cost. My own PSU was mounted to draw cool air in via the floor. I soon found the disadvantage with that, was that on the road all sorts of muck would be ingested. It had a better heatsink than you described, but the cooling fan had failed due to the muck it had swallowed. New fan and move it to not draw air from the outside and it has been fine since.
It *should* be rather more than a 'simple' PSU as the battery charging circuit needs to have some cleverness to charge a lead acid battery properly.
I think you'd be surprised how expensive that would be, transformers in particular are quite pricey. A PC switch mode PSU would probably be cheaper for that sort of rating (though would likely have lots of
Some stuff sourced for Ham radio operators seem to be quite good for this purpose I think, but they are not cheap if well built with adequate cooling. Most are switch mode these days which may well help with the problems of dissipation greatly, though many have a minimum current as well as a max one.
JOOI do motorhomes separate the battery from the distribution circuits when connected to the mains? I ask only as I wondered if it might work out cheaper to fit (a) a "Smart" battery charger (
They use a system of the battery supplying the load, with a charger/PSU in parallel with the battery - so PSU is able to both source the load and charge the battery. Some of the later PSU are able to act intelligently in their charging of the battery. I seem to recall some have a link able to be set, for the various battery chemistries.
We are 'boatey' people but have essentially similar setup, a large bank of leisure batteries which are used to make us independent of mains electricity when away from moorings with mains power.
We don't ever disconnect the batteries when using shore power, the chargers we have (mains powered, rarely used now, and solar powered which provide most of what we need) are simply left permanently connected to the batteries. So there's no requirement for a separate
12 volt power supply for use when mains is available.
I did have a power supply on a boat in the UK (the above one is in France) which could be switched between 'charger' mode and '12v supply' mode but I assumed the '12v supply' mode was for use when one wanted to disconnect the battery completely for some reason. Otherwise I always left it in 'charger' mode with the battery providing voltage stability.
Not really. A lead-acid battery should be charged to something like
14.5 volts to get it fully charged (and it's important to get them fully charged sometimes). Then, when it's fully charged, the charger should drop back to 13.5 volts or so to maintain the battery in 'float'. Most 'intelligent' lead-acid battery chargers will do something like this, the 14.5 volts guarantees full charge but if maintained long term will make the battery gas. Really clever chargers will occasionally wake up out of float mode and do a sort of battery conditioning sequence.
(All voltages above are 'typical', they're the ones that vary slightly with battery chemistry and temperature)
That will be a switch mode supply I think, no big mains transformer in it. The above is more like the 'PC switch mode PSU' which I said would be cheaper.
There are some switch mode ones around which aren't bad, mainly for the amateur radio market BUT they are power supplies not chargers- which is (hopefully) what was being used to charge the battery in the motorhome. A proper charger will help ensure the battery/batteries are not over heated etc and, assuming the motorhome has a proper smart controller, interface with it to ensure the vehicle battery is also charged when on mains, the leisure battery/batteries are charged by the vehicle when the engine is running, and interface to any solar system.
I think the charger in mine is about £140. Allowing for the extra functions it has, over and about a basic switch mode PSU, and its quality, it isn't a bad price. I'm not sure how expensive the main control unit is- several hundred at a guess.
Sticking in just a transformer, rectifier, etc is a sure fire way to ruin a leisure battery BDQ.
'Ready made' conversions seem to come with integrated 'smart' electronic/electrical systems these days. Mine has a unit which controls the 12V and mains- well the breakers for the mains- and interfaces with the vehicle system and a battery charger. It does everything from controlling the 12V master switches to sensing water levels in fresh and waste tanks. Later ones even interface with your phone.
Those who do their own conversions seem to go for discrete sub-subsystems- you can buy sensors and displays for water levels etc. - and simply install a domestic consumer unit and a battery charger etc.
To comply with the 'construction and use' regs, much of the 'domestic' electrics should be disabled when the vehicle is in motion- the commercial control boxes do this but I suspect most self builds don't bother. No doubt, in time, someone will decide this needs to be checked as part of the MOT ;-(
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