XBox clock backup

Post by **gannon** » Thu May 22, 2008 12:32 pm

Anyone know what the minimum voltage it takes to retain RAM memory? Usually backed up by a 3.3V coin battery, but in the xbox it is only backed up by a capacitor that lasts ~1 hour.
I was thinking of either wiring in a coin battery and relay, or a battery pack and diode. The battery pack I could do with parts on hand, but not sure how much power would get drawn from it vs the psu when power is on. The relay option would only power the chip while the psu was off.

APHawkes · Post by **APHawkes** » Thu May 22, 2008 1:15 pm

The reason they use a capacitor is because of the current drain. See this message for the rationale. Basically, it would kill a button battery in a couple months. I suppose with a large enough battery it would work (or a large enough capacitor), but it's one of those things that must be accepted as a limitation of the machine.

Post by **gannon** » Thu May 22, 2008 2:19 pm

Sure, but a couple of months is way better than an hour. Max I should ever have the unit unplugged at a given time is around 10 hours. But still, seems MS is a cheapskate still

Thanks for the given data though, it'll be helpful in deciding. Maybe using a rechargeable coin battery in the circuit even.

APHawkes · Post by **APHawkes** » Thu May 22, 2008 2:33 pm

I'll agree, MS was cheap on that one. I would think that the difference in price was pennies. Lame.

Any chance you could put a couple NiMH AAs in series? Would they automatically charge when powered?

Post by **gannon** » Thu May 22, 2008 3:08 pm

APHawkes wrote:I'll agree, MS was cheap on that one. I would think that the difference in price was pennies. Lame.

Any chance you could put a couple NiMH AAs in series? Would they automatically charge when powered?

You could, my battery pack idea would be to use 3-4 (depending on the min. voltage needed, the link said 2.5V would work if I read correctly) AA or AAAs. AAAs hold ~750mAh while AAs hold around twice that amount IIRC, so I probably wouldn't even bother with using rechargeables for that. What I'm doing is big anyways, so I could even use D cells and be set

timmeh87 · Post by **timmeh87** » Thu May 22, 2008 10:31 pm

Ive seen 1000mAh AAA and 2700mAh AA batteries.

Anyways, you can get a 1F, 5v capacitor for like 50 cents on digikey. Im sure that would beef it up a bit.