Richard Chycoski <rskiad...@chycoski.com> writes: > - They don't actually trip at the rated current. Breakers have a > profile, and will trip quickly if you draw significantly more than their > rated current, but may sit at (or even somewhat above) their rated > current for quite some time.
> - Breakers also get weak if tripped frequently or run near their limits > for a long time. This can take a few years to happen, but it *will* > happen eventually, and your customers will get unhappy if they can no > longer run up to their rated current. Breakers are not meant to be run > at-or-near their rated current continuously. Thanks, this is the sort of thing I need to worry about, and the thing I don't know much about. exactly the info I was going for here. It sounds like what you are saying is that giving the customers smaller breakers won't solve my problem of keeping them away from the limits on my larger breaker. I'm still going to have to hunt them down and pester them about keeping it within 75%, and considering my goals, that might be best done with a metering PDU. Hell, giving everyone a metering/rebooting pdu will set me back one time $200-$400 per customer, but it would also add a lot of value for the customer, if I gave them remote reboot capability. I could charge a one time setup fee, maybe waived or reduced if they pre-pay for a certain number of months. > If you actually want to shut down the circuit based on current limit, > you could use a monitored power bar that also has controlled shutdown > for each circuit, but the cost may exceed your business model. The > advantage to this is that if you can use larger (even 30A) circuits to > feed the power bar, and can choose to warn/charge $ if the customer > exceeds their limit, but not actually shut them down unless the entire > circuit is at risk. > Another reason that breakers are undesirable - you actually have to go > to them and switch them on after they trip. I don't know if this is an > inconvenience for you or not. I don't think this would be a huge deal. You trip your breaker, you go deal with it. SysAdmins are used to a blown circuit being a big deal. Hell, when something blows, you don't just want to reset the breaker anyhow, right? you want to go in and figure out why it blew, and unplug the offending equipment, or it's just going to blow again. I think if I'm up front about it, while it is a inconvenience, it's an acceptable tradeoff for my target customer base. the idea is that I want to sell my customers (SysAdmins, mostly) a product that is as much like the product I buy from the data center is, only smaller, and proportionally cheaper. > What kind of gear are you planning to let your customers install that > will vary in power requirements this much? Normal PC hardware varies quite a lot between 'idle' and 'loaded' - sure, if you do a real careful load and burn in you can get a pretty good idea what it's max draw, but if someone is trying to push it (and many people are) or if they dont' take the 75% rule seriously (you'd be amazed how many SysAdmins don't.) it's not going to work without supervision. but, I have a bigger problem; I want this to be an unsupervised 1/4 rack, so the real problem would be a customer coming in at 4am and, say, replacing a low power server with a high power server. > You might solve the problem > by putting a 'Kill-a-Watt' on their gear and getting them to run the > equipment full-out. Once you know the maximum current requirement, > charge them based on the maximum power usage, and distribute the > equipment on circuits accordingly. (Monitored power bars could also do > this, but the Kill-a-Watt costs about $20.) This is less convenient if > there are frequent equipment changes, but if most customers drop it in > and forget it, it might be practical. (You could have a fee for gear > change, to cover the overhead of doing the power profile.) Again, we're moving away from cheap, if I'm supervising burn in. I wanted an unmanaged "just don't touch other people's stuff" split rack, and depending on people to estimate their own power simply won't work without strong enforcement, either having headroom and charging overages, (and charging appropriate monthlies to cover the headroom) or having some automated thing shut down customers who are over. Higher one time costs (electrician time, advanced PDUs) are acceptable, higher running costs (making me supervise all equipment installs) will jack up prices way beyond what people want to pay. also, an open access 1/4 rack is more value to my target market than something where they need me to dick around with their equipment before they can add anything. I know it looks like I'm both expecting my customers to know what they are doing /and/ then not trusting them to treat the circuit with respect. My goal is to create something where if you 'push it' the consequences fall on you, not on the guy sharing the circuit with you. _______________________________________________ Tech mailing list Tech@lopsa.org http://lopsa.org/cgi-bin/mailman/listinfo/tech This list provided by the League of Professional System Administrators http://lopsa.org/
