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In Reply to: RE: Which capacity batterie for cMP HTPC posted by hanssatink on June 20, 2009 at 06:05:23
Hans,
congrats for deciding on batteries! :-)
The proper capacity for listening for 4-5 hours without charging depends I'd say on a number of factors:
- What parts of the PCs power supply are you willing to power with batteries? Only P4, or also P24, or even the "dirty supplies" etc.?
- You write "cMP HTPC" - how close is your system to the "recommended" setup, i.e. what CPU / RAM / PCI cards / software do you run, and which file formats do you use etc.? I assume that the "HT" (=Home Theatre) part in "cMP HTPC" might require additional calculation ontop of a "standard" cMP setup's power consumption.
For a "standard/recommended" cMP setup, you could use two methods of calculation to get the current draw:
- A rather exact one for every line involved, looking at the various measurements that have been made on P4 and P24 consumption. Here you have ~350mA @ 12V on P4 = 4.2Watt, and ~140mA @ 12V plus ~300mA @ 3.3V plus ~4200mA @ 5V on P24 = 1.7 + 1 + 21 Watt = 23.7Watt, or 27,9Watt in total. Once you power all that with 12V batteries (e.g. P24 through a picoPSU), you have a current draw of 27.9Watt / 12V = 2.3A
- In cics' currently recommended setup with parameters set as specified, he says "power consumption will be below 20Watt", so 20Watt / 12V = 1.7A
Now you have to consider the discharge characteristics of the batteries you intend to use. If you e.g. take Panasonics 7.2Ah 12V VRLA model (LC-R127R2P), it will provide a terminal voltage of ~12V for ~60mins / ~90mins at 2.3A / 1.7A . So in case of these batteries you could use 5 or 6 of them in parallel and be quite safe for 4-5hrs, plus reducing the overall internal resistance to acceptable levels.
I myself tend to extreme solutions ;-) so I would recommend to use just 2 of Panasonics 28Ah 12V batteries (price ~100EUR, so still acceptable) - their terminal voltage falls below 12V at ~2A discharge current after ~600mins, so you're really safe plus you get a decent internal resistance - which I would strongly recommend to combine with proper capacitance following the batteries anyway!
Hope that helps
Robert
Follow Ups:
Robert,Thanks.
I use the GA-EG45M-UD2H mobo with 1 gig mushkin em2-6400. HDD's are external. Feeding Juli@ with dual Lipofer and using M4-ATX picpsu for 5 and 3.3V. All lines buffered with 10.000uf (Panasonics FM/FC). I have planned to feed all the 12 volt lines (P4+p24) direct analog from the batterie with use of a a low drop voltage regulator. (see attachment). I am building it all together in one desktopcase. Its pretty hard to make an easy switch between listening and charging.
You talk about dirty lines. What do you mean by that? Are the 12, 5 and 3,3 volt seperate lines not internally connected on the mobo?
Edits: 06/21/09 06/21/09 06/21/09
Hans,looks interesting! Although I would not want to go for the picoPSU since it is just another switching PSU (although a good one) for 3.3V and the main workhorse 5V, so nothing much gained, this certainly is a good solution. But please take care: From the MIC29502BT's datasheet I see that it needs a "voltage difference" of 350-370mV, so when you want to output 11.93V as has been recommended for optimal SQ, the batteries' terminal voltage needs to stay over 11.93V + .37V = 12.3V. Unfortunately that's a figure the datasheets for the batteries' discharge rates usully don't give you clearly. So with the above mentioned 2 x 28Ah or your suggested 50Ah battery, when using them fully charged you surely get decent playtime until they hit the 12.3V limit, but I doubt that this will be 4-5hrs. Unfortunately datesheets don't really help, I'm afraid you've got to try out. For this reason I use batteries with a total of 18V and a THEL regulator that needs a (quite high) minimal voltage difference of 2.5V which I have plenty, so I'm safe for a long time.
As Theo has explained, with "dirty supplies" I meant supplies like the Granites for HDDs, USB, LCD etc., so everything else than P4 and P24. Since you say that HDDs are external, I have understood that you do not want to power them with the same 12V battery source.
And yes, all the separate wires for the respective voltages (12V, 5V and 3.3V) are connected internally on the MoBo, multiple wires are just used to reduce cabling issues like internal resistance and heat and such.
Regards,
Robert
Edits: 06/21/09 06/21/09
Hopefully robert won't object to my attempt at an answer---dirty was a term originated by cics to collectively describe power supplies for sata drives, displays, dvd/cd drives, powered mice or peripheral items that 'dirty up' the power supply for major items like cpu/sound cards.
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