Hello All,
I'd like to have a portable 12 V supply for testing and to run my air compressor (for tyres .... 40 Amp).
I'd thought of a cheapo lead acid battery with a cut out ...... is there a better way?
If you want to draw 40A, then a battery with a trickle charger permanently attached. A 230V AC to 12V DC power supply capable of supplying that kind of current would be rather large.......
You sure you need 40A?
That's getting into small genset territory... :-)
If you had one kicking about, a random car battery would probably be the easiest solution, along with a trickle charger as Gilbert said.
Or a portable jump starter - handy for starting cars with dead batteries, and as a 12v supply. Just keep it charged properly.
I'd be looking at something like this:
They come in various specs and sizes. Proper branded ones would probably cost hundreds, but the chinese ones seem ok for the most part.
The other option you can find are redundant server PSU's which put out lots of current at 12v, theres a big thread here on converting them:
http://www.rcgroups.com/forums/showthread.php?t=1292514
You can often find them cheap on ebay. Much higher quality PSU, and less likely to die like the chinese stuff, but require some "fiddling" to get them functioning.
Thanks for the links.
It could be 20A that the compressor draws (it's a macho off-road jobbie that actually will inflate a RR tyre). I'll check.
if your buying a chinese one, get one rated a decent amount above what you want to draw! The server PSU's are likely a better buy, as they're properly quality items and are pretty cheap. Few DPS-600's on ebay for 15quid.
I've got a 12V 30A power supply that I use to power my LED lights above the work bench, and for all my testing.
It was a cheap (ish) one from eBay, but will has internal overload protection and things like that, even though I've split that out to some fuses for various tasks.
It will power up a P38 EAS compressor on the bench for testing, no problem.
The quality of those (cheap Chinese) switched-mode PSUs is famously inconsistent: Some also have operating frequencies/harmonics that are just beyond the upper range of human hearing - and if so don't use them too close to your head for a long time, unless you want unexplained headaches !! The effect can be worse as you drawn more current... but the noise of an EAS Compressor nearby might mask it.... Actually ignore all/most of that as a P38 can often give you headaches on its own anyway of course.
I have met many P38 owners who (for obvious reasons) permanently carry a spare HD battery around; The other day I saw some small/cheap portable generator/inverters in Lidl (£100) and wondered if one would fit in my boot with all the other obligatory P38 keep-me-going accessories.....
Off the topic a bit, but I wondered some time ago what minimum size battery would turn over the engine (petrol) in warm climates? Just for emergencies, either turn over or charge the main battery enough for it to do it.
Would a motorcycle batt do it? It could be kept somewhere unobtrusively ....
I carry one of those lithium get you started batts which I've yet to use.
My track car has a "12200" wheelchair/golf cart battery and that starts it just fine. Granted thats a little 4 cylinder turbo compared with the big V8, but if its just assisting a flatish main battery, then you'll probably be fine. Motorbike batteries are quite a bit weedier and might struggle.
The most important thing is getting a decent connection between your little battery and the car. I've struggled to jump start my 330d, simply because i couldnt get the jump leads to make a decent connection.