Motorhome power supply.

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.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 05/04/2018 23:47, Dave Plowman (News) wrote:

Some of the rip-off merchants are asking £145 for it! The leisure market is a right scam. Always buy from elsewhere if possible.
Bill
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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.
Brian
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Dave Plowman (News) used his keyboard to write :

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.
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On 05/04/18 23:47, Dave Plowman (News) wrote:

£100 for a simple PSU - and they still couldn't make it properly? <Jesus wept>
Sounds like a good application for a 200VA transformer, bridge rectifier and nice lumpy heatsink.
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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 5v and 3.3v output as well).
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On 06/04/2018 09:00, Chris Green wrote:

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 (<£20) and (b) a separate 12V PSU (eg LED driver). Also avoids single point of failure.
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Robin used his keyboard to write :

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.
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Yes, our chargers have settings for different battery types (not different chemistries really, they're all lead-acid).
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[snip]

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.
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On 06/04/2018 10:50, Chris Green wrote:

Thanks (and to others who commented). And I can see that allows the batteries to meet peak loads which would otherwise demand a bigger PSU. Anyhow, clearly no turnip for me for my cunning plan :(
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I've been thinking about using a Lidl smart charger with a mobility scooter battery to power a dvr and a couple of security cameras since a local shop in a shed was broken into after the mains supply to the shed was torn out, leaving the cctv useless. The charger seems to cut in and out according to voltage being between 12.5 volts and 14 when used with the battery and a light as load. I'm asking myself if the voltage variations might adversely affect the cctv equipment. Any thoughts?
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Cynic was thinking very hard :

Probably not, but it would be your risk to try it.
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On 06/04/2018 15:27, Cynic wrote:

CCTV equipment doesn't really like voltage variations and switching transients.
Bill
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On 06/04/2018 10:15, Robin wrote:

I was wondering the same thing.
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Blurb with it suggests it's just a regulated 13.8v PS. Which should be OK for the sort of charging use it would normally get.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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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)
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Very odd. SLA batteries have been charged at constant voltage for many many years. What has changed?
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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wrote:

Nothing except it allows the cells to be restored to full capacity quicker and without damage. It's the kind of thing APC haven't been doing for over 25 years.
Page 22 "Two Stage Constant Voltage Charging"
https://news.yuasa.co.uk/wp-content/uploads/2015/05/NPManual.pdf
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First page or so of that says it refers to spill proof wet electrolyte batteries. Which are not gel type SLA. The type I'm referring to.
Didn't wade through the rest as I'm aware different versions of wet batteries need different charging methods for best results.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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