Battery buffer charging/maintenance
in [Design]
|
Prev: Overloading an LM317
Next: Skype Messenging Question
From: Henrik Nowak on 7 Aug 2010 11:49 Hello, I seek advice on the following: We are designing a computer system based on a ETX computer and Windows Embedded. The power we get (15-30VDC) can disappear suddenly, so we thought about fitting our computer with a small 12V lead-battery and when input power is OK, we charge the battery, and when mainpower disappear, we use the battery to gracefully close files, and shut the system down. The ETX runs off a 5VDC so we can easily design a SMPS for 5V with a 8-40V input range, allowing for a seamless transition between mainpower and battery. So the battery is actually only used maybe once a day or something like that and only for about 2-3 minutes or so. So it never really gets fully discharged. We don't want to do all sorts of fancy charger circuit if it is not neccesary, but it seems that there is a lot of different opinoins about what and how to accomplish what we want. Ranging from full-featured BQ231-based chargers to a simple LM317 constant voltage solution. I have a feeling that the appropriate solutions lies somewhere in between, but I would like to have a few expert opinions on this as well. I dont want to damage the battery and I dont want to find out that it didn't work someday and the system crashed. So I want to be as kind and gentle to the battery as possible, but I don't want to more than what is neccesary. We expect to use a 12V 2AH small sealed lead-acid battery. Preferably this should be a "no-maintenance" product, we dont want to do batterychanges every year or so. Expected lifetime for a unit is approx 5 years. Thanking you all in advance for any comments and pointers. Best regards Henrik
From: Jan Panteltje on 7 Aug 2010 12:19 On a sunny day (Sat, 7 Aug 2010 17:49:18 +0200) it happened "Henrik Nowak" <hno(a)impc.dk> wrote in <4c5d807e$0$56772$edfadb0f(a)dtext02.news.tele.dk>: >Hello, It is very simple, look up the battery specs. Manufacturers give a charge voltage and max current, sometimes different for different applications, like for example alarm system standby or full cycling. Sometimes there is a limit to the allowed charge time too. For example for cycle applications 14.4 to 14.7 V, current limted to a few amperes, until current drops below some (milliamps) value. And for standby (as in your case perhaps) 13.5 to 13.8 V. Again, look up the battery specs.
From: linnix on 7 Aug 2010 12:38 On Aug 7, 8:49 am, "Henrik Nowak" <h...(a)impc.dk> wrote: > Hello, > > I seek advice on the following: > > We are designing a computer system based on a ETX computer and Windows > Embedded. > > The power we get (15-30VDC) can disappear suddenly, so we thought about > fitting our computer with a small 12V lead-battery and when input power is > OK, we charge the battery, and when mainpower disappear, we use the battery > to gracefully close files, and shut the system down. The ETX runs off a 5VDC > so we can easily design a SMPS for 5V with a 8-40V input range, allowing for > a seamless transition between mainpower and battery. > UPS
From: whit3rd on 7 Aug 2010 15:33 On Aug 7, 8:49 am, "Henrik Nowak" <h...(a)impc.dk> wrote: > We are designing a computer system based on a ETX computer and Windows > Embedded. > > The power we get (15-30VDC) can disappear suddenly, so we thought about > fitting our computer with a small 12V lead-battery and when input power is > OK, we charge the battery, and when mainpower disappear, we use the battery > to gracefully close files, and shut the system down. The ETX runs off a 5VDC > so we can easily design a SMPS It sounds like you can use an off-the-shelf DC/DC converter, with some isolation (simplest is two diodes) for the multiple inlets. UPS software can handle the shutdown, you'll want to detect battery drain (voltage drop on the battery's diode will do that) and generate some kind of interrupt or squirt an error code into a serial port. There are a LOT of computers wired this way, in telco offices and in Google farms, I hear.
From: Martin Riddle on 7 Aug 2010 16:34
"Henrik Nowak" <hno(a)impc.dk> wrote in message news:4c5d807e$0$56772$edfadb0f(a)dtext02.news.tele.dk... > Hello, > > I seek advice on the following: > > We are designing a computer system based on a ETX computer and Windows > Embedded. > > The power we get (15-30VDC) can disappear suddenly, so we thought > about fitting our computer with a small 12V lead-battery and when > input power is OK, we charge the battery, and when mainpower > disappear, we use the battery to gracefully close files, and shut the > system down. The ETX runs off a 5VDC so we can easily design a SMPS > for 5V with a 8-40V input range, allowing for a seamless transition > between mainpower and battery. > > So the battery is actually only used maybe once a day or something > like that and only for about 2-3 minutes or so. So it never really > gets fully discharged. > > We don't want to do all sorts of fancy charger circuit if it is not > neccesary, but it seems that there is a lot of different opinoins > about what and how to accomplish what we want. Ranging from > full-featured BQ231-based chargers to a simple LM317 constant voltage > solution. > > I have a feeling that the appropriate solutions lies somewhere in > between, but I would like to have a few expert opinions on this as > well. I dont want to damage the battery and I dont want to find out > that it didn't work someday and the system crashed. So I want to be as > kind and gentle to the battery as possible, but I don't want to more > than what is neccesary. We expect to use a 12V 2AH small sealed > lead-acid battery. > > Preferably this should be a "no-maintenance" product, we dont want to > do batterychanges every year or so. Expected lifetime for a unit is > approx 5 years. > > > Thanking you all in advance for any comments and pointers. > > Best regards > Henrik > > Look at this pico-ups from mini-box, might be just what you need (and a small SLA battery) <http://www.mini-box.com/micro-UPS-load-sharing> Cheers |