Battery power and capacitors?

[Tim]

I have just ordered a 12V SLA battery for a project to battery power a motherboard in a music server. Not something I have tried before or have any experience with, but does anyone think there is any merit in smoothing its output in any way before supplying power to the server board?

Also, is an oscilloscope the only way you could check to see if there was a measurable benefit?

[Firebottle]

SLAs have very low internal impedance so there's no real benefit in fitting smoothing caps.
Use reasonably thick wire to the motherboard to benefit from the low internal impedance,

:cool:Alan

[Tim]

Many thanks Alan, the SLA should be here by the weekend and I'm looking forward to trying it out.

[tubehunter]

what amp rating is the battery? will it last long before requiring a recharge?

I have built some linear power supplies for pc's and have found they can pull a lot of current.
sound wise benefits can be had by removing the switch mode ps imho.

duncan

[Tim]

Fairly good, 12V - 24.0Ah - the way I have my server configured, the power draw from the board is very low indeed around 12W. The hard drive is powered by it's own 5V supply and the USB output is isolated too, so it should last a reasonable time before needing a recharge. It's just to test SQ at this stage, if I like it I will work out a more permanent solution with 2 switched batteries, so there is always a fully charged one ready to go. I'm just tinkering at the moment ;)

I have a bench linear PSU already, so if there's no real benefit I will work on improving the linear supply instead.

[Mark Grant]

Make sure you fit a fuse as near as possible to the + battery terminal ideally on the battery itself.

Accidentally shorting out a large SLA battery can be 'interesting' :eek:

A 24Ah SLA can deliver about 750 amps if shorted out.:eek:

This webpage shows a picture of how to fit a fuse, ( scroll down a bit)
http://www.prophotonut.com/2010/03/28/sla_battery_care/

Someone having fun on you tube with a car battery: ( dont wear rings when working with spanners and batteries is the idea)

ZfFViY1-zYw

[Ali Tait]

Good advice. A shorted battery will take no prisoners.

[Tim]

Thanks Mark, some really good information on that link you provided :thumbsup:

[Tim]

Thanks for the tips guys, I have been Googling, reading and checking out some Yootoob vidoes and I think I now have the skinny on SLA batteries - don't you just love the internet ;)

Looking forward to seeing what they do for my music server now.

[Tim]

So . . . :lol: . . . (in joke) I want to put together a small box to sort out my power for my music server. Please bear in mind up front I have no practical experience of what I have designed, as up to last week I thought a breadboard was what you cut bread on :scratch: After reading some of Martin's (MartinT) great posts he has given me the inspiration to have a go at this little project myself, thanks Martin. I am a complete novice at this and have never attempted anything like this before, I know its simple, but to me its all new territory.

Anyway, after some Googling I have come up with the below and would appreciate any comments/criticism you may have? What I need to acheive is two 12V rails and one 12/5V combined for a SATA hard drive. All will go in a small plastic project box and needs to have a Blue (of course) LED to show its working, at least the 5V rail to the HDD does.

Hopefully some in the know here can cast an eye over it and see if I have made any glaring errors? Total draw is going to be around 2.5 amps, probably less and will be coming from a 12V 24.0Ah SLA battery, with a fused + wire (thanks Mark)

http://i173.photobucket.com/albums/w63/greatgig/02circuit_zps200c839f.jpg (http://s173.photobucket.com/user/greatgig/media/02circuit_zps200c839f.jpg.html)

Circuit for the 12V to 5V step down.

http://i173.photobucket.com/albums/w63/greatgig/01circuit_zps70f60533.jpg (http://s173.photobucket.com/user/greatgig/media/01circuit_zps70f60533.jpg.html)

Some questions I have;

There seems to be a difference of opinion of the capacitors in this simple circuit, some have a 470 uf cap before the regulator and 1.0 uf after, some have 0.33 uf caps on both sides and there are other mixes as well? Which do you guys think is best?

(check me out casually saying 'caps', before I came to AoS a cap was something you put on yer ed!)

Thanks again chaps :D

[Paul Hynes]

Tim,

Your pics are not showing.

When connecting the battery to your motherboard, or any other load for that matter, you may get arcing at the connector/switch when the connection is made. This is caused by on board capacitors on the item being powered as the capacitors can look like a short circuit to the power source before they charge up to the supply voltage. This arcing can cause considerable surface damage to metal surfaces and degrade the connection. Bad connections = bad electrical performance and ultimately this will affect sound quality. To avoid this happening every time you make the connection you may need to consider some form of soft start circuit when using batteries.

Regards
Paul

[Tim]

Just sent you a PM Paul.