> -----Original Message----- > From: Arjen de Korte [mailto:[EMAIL PROTECTED] > Sent: 27. oktobar 2008 23:54 > To: Zeljko Baralic > Cc: [email protected] > Subject: Re: [Nut-upsdev] Megatec and Batteries > > Citeren Zeljko Baralic <[EMAIL PROTECTED]>: > > >> You can't calculate battery charge of a > >> UPS by looking at the battery voltage alone > >> > >> It physically just isn't possible. > > In order to measure battery charge, knowing how much Watt hours it has > delivered doesn't help much. We want to know the remaining charge > (which is load independent), not the amount of power we already > extracted (which is load dependent). Having said that, the efficiency > of the energy conversion is unknown anyway (depending on size of the > UPS) and so is the charge the battery can hold. Note that NUT won't > remember state/values between restarts, so anything that isn't stored > in the UPS, will be lost forever.
This is a good pint. > > > What is good about megatec is that you can always get Load% and you > > know rated power/voltage out of UPS. > > Not at all. Quite a number of UPS'es will happily report a load of 0% > (or any other fixed number) at all times. The protocol may be able to > deal with this, but many implementations don't. You are right. Here is the real life case: Fenton Lestar MD-800E and Inform Guard Compact 800AP are 90% the same devices from some third manufacturer of controller. In nut they both identify themselves as VT02052N and report constantly 0% load no matter what is connected load. > The power factor is dependent on the load and this isn't reported, so > this value isn't available for most ordinary users. Therefore, I > restate that it is impossible to calculate the battery current from > the values provided by the megatec protocol and hence coulomb counting > is not possible. > > > Anyway Arjen, from my point of view creators of megatec protocol > > where tried to make something in between contact-clousure and > > inteligent signaling and I think that they succeded in this. They > > give some minimal info about a state od device for disaster > > protection. > > Absolutely. I'm not trying to put down the makers. In most cases, > knowing the battery charge is irrelevant, since NUT will only use the > low battery warning signal for shutting down. But in some cases, where > the remaining runtime on battery after signaling low battery is > insufficient for an orderly shutdown of the connected systems for > instance, this is not enough. In that case, a ballpark figure isn't > good enough. It looks like that this needs some deeper consideration. > -- > Please keep list traffic on the list _______________________________________________ Nut-upsdev mailing list [email protected] http://lists.alioth.debian.org/mailman/listinfo/nut-upsdev
