| General > General Technical Chat |
| Noisy power from typical backup generators |
| << < (10/19) > >> |
| Johnny B Good:
--- Quote from: G7PSK on March 01, 2021, 04:05:13 pm ---I have built a number of alternator sets over the years mostly using stamford brand of alternator, now part of cummings power, I never had any trouble with noisey power from them and they use electronic AVR's or transformer type regulation on the smaller units. All the rotors have had a slight helical form to the windings which i understand helps with delivering a smoother waveform. --- End quote --- Have you ever tested the effect of connecting a 4.7uF PFC capacitor across the output? You might be shocked by the result. These generators can handle resistive and inductive loads ok but can end up overvolting due to the self excitation effect caused by the leading current produced by a capacitive load which in my case was the 9.4uF's worth of capacitance across the mains input of a SmartUPS2000 line interactive UPS which would be disconnected when it transferred to battery power due to the incoming generator voltage going north of the 240v mark by some 30 volts or more. I couldn't figure whether these caps could be safely disconnected or not and their exact function remains a mystery. It's possible that modern line interactive UPSes may have eliminated the need for such a large amount of capacitance on their mains input circuit (that SmartUPS is well over a quarter of a century old now) so you might not see the overvolting issue I'd suffered with my own setup if you're feeding the generator's output into the mains in socket on a modern UPS. As for my own thoughts on how to add a fuel priming bulb to that Parkside inverter genset, it has occurred to me that I could have saved on the T adapters and just plumbed it into the fuel line (before or after the pulse driven lift pump), assuming the one way valves don't create an excessive pressure drop. I'll test the simple series arrangement first but my original parallel arrangement might well prove to be the only viable alternative to the more usual arrangements. Such arrangements being that it's plumbed into an extra hose nipple on the carb to let it suck the fuel through to prime it and send the excess back to the tank or else simply to squirt extra fuel into the inlet port to make up for a dry bowl and make it easier to start. It seems I've come up with a third alternative that's never been mentioned in any of the youtube videos I've watched (the only source I could track down that offered even so much as a clue as to how these pulse driven fuel lift and priming bulb pumps work) in relation to priming such small engine kit relying on a (crank case pressure) pulse driven fuel lift pump. I'll report my results here in a week or two's time after I've had a chance to work on the generator. John |
| IDEngineer:
--- Quote from: Johnny B Good on March 03, 2021, 12:34:52 am ---I couldn't figure whether these caps could be safely disconnected or not and their exact function remains a mystery... that SmartUPS is well over a quarter of a century old now --- End quote --- APC once made decent UPS's, but by the time we started using SmartUPS in the late 90's and early 00's they were already in decline. Their battery charging circuits were terrible - AFAIK just raw current dumped into the AGM batteries, causing them to swell within a year. I've lost count of the number of SmartUPS I had to mechanically disassemble just to remove the swollen batteries and replace them with new ones, which would themselves inevitably swell within 12 months. BTW, disassembling their 4U SmartUPS was its own precious nightmare with all sorts of interlocking walls to save a screw or two. Given their simply awful battery charging, I wouldn't put too much faith in their AC output design (and their inclusion of those caps you're talking about). |
| NiHaoMike:
--- Quote from: Johnny B Good on March 03, 2021, 12:34:52 am --- Have you ever tested the effect of connecting a 4.7uF PFC capacitor across the output? You might be shocked by the result. These generators can handle resistive and inductive loads ok but can end up overvolting due to the self excitation effect caused by the leading current produced by a capacitive load which in my case was the 9.4uF's worth of capacitance across the mains input of a SmartUPS2000 line interactive UPS which would be disconnected when it transferred to battery power due to the incoming generator voltage going north of the 240v mark by some 30 volts or more. --- End quote --- I wonder if that effect could be put to good use by allowing the generator to run a little slower while still delivering the correct voltage thus saving fuel if the full output rating is not required. |
| james_s:
--- Quote from: NiHaoMike on March 03, 2021, 03:19:32 am ---I wonder if that effect could be put to good use by allowing the generator to run a little slower while still delivering the correct voltage thus saving fuel if the full output rating is not required. --- End quote --- Generators with AVC can easily be slowed down some and maintain voltage, but in a non-inverter generator frequency output is directly tied to engine RPM. Slowing it down will cause motors to run slower, transformers may saturate and some lights will flicker. |
| Johnny B Good:
@IDEngineer, It took a few years before the penny dropped that the13.8v float charging voltage per 12v SLA wasn't the optimum voltage level to maintain SLAs at a relentless 365 days a year for years at a time (at least as far as end users were concerned). It undoubtedly was for APC and other manufacturers in that it allowed the use of undersized and expensive SLA battery packs by maximising the energy storage capacity when brand new and for the first year (or two at most) of their service life before going into a decline over the next year or three if you were very lucky or waited until they eventually failed the UPS's weekly battery test cycle. I'd bought that SmartUPS2000 sans battery box at the Blackpool radioham rally some 15 to 20 years ago (the exact date is now lost in the mists of time) which allowed me the freedom to choose whatever capacity of battery I could afford to buy. I think I started off with a set of four 7AH SLAs supplementing them with a set of 25AH SLAs purchased the following year at the next rally. At some point, I'd managed to cut a deal with a local car parts/salvage dealer for a set of four NOS 36AH SLIs to build the battery capacity to a grand total of 75AH (based on an unwarranted assumption that the two banks of 7AH and the one bank of 25AH, along with those four SLIs I'd managed to blag for a mere 60 quid still had their specified capacity). A test run with some 300W of loading resulted in almost 6 hours of autonomy before the voltage dropped to the cut out point at 40.4v. The SLAs survived this 13.8v abuse for maybe a couple of years of service but the SLIs only lasted a mere 6 months which was to me a surprising result considering the much easier life compared to their normal use as SLI batteries. It took another set of 36AH SLIs and remembering the similarly short life of a 40AH SLI I'd used with a CB radio powerpack to increase the peak current output back in the late 80s / early 90s before I realised that SLIs were simply unsuited to this task. By the time I'd realised the high battery maintenance costs, even when I was paying only a fraction of the full retail price, I'd already gone through two sets of SLIs, one set of 25AH SLAs and a box of sixteen NOS 7AH SLAs I'd purchased very cheaply from my son's best friend plus the first two sets I'd started off with. Mind you, I'd used at least two of the 7AH batteries to replenish the pack in that SmartUPS700 I've given the sack to and at least half a dozen used by the UPSonic 600 (likewise long since retired) which burned through them three or six at a time (36v in one or two banks). At one point, I had a total of five UPSes in service burning a total of 72W in maintainance consumption (32W for the SmartUPS2000, 20W for the SmartUPS700, 18W for the UPSonic600, 7W on an ancient Emerson30 (my very first UPS which was a modified sinewave type) plus maybe another 8 W on a now forgetable UPS I managed to burn out by connecting it to an external 25AH 24v battery to replace its knackered internal 4.5AH SLAs. This was replaced with an APC BackUPS500 (which uses just a single 7AH SLA) about ten years ago. As a result of my experience and research, I've now dropped the per 12v battery float charge voltage down to 13.5v[1] on the two remaining UPSes (SmartUPS2000 and the BackUPS500 which uses just under 3W of maintainance for its 350W/500VA's worth of protection) and stopped wasting money on cheap NOS car batteries. I'd made this decision some three or four years ago when I'd had to replace the single 7AH SLA in the BackUPS500 around the time I gave up satisfying the SmartUPS2000's appetite for eating battery packs by removing it from service as a 'protected supply'. It was only due to the purchase of the Parkside inverter genset that motivated me to invest in a set of four 7AH SLAs so I could verify my hypothesis that an inverter genset would solve the problems I'd experienced with a conventional 2.8KVA PowerCraft generator a few years earlier. The SmartUPS2000 original battery pack is specified to be 18AH so the set of four 7AH SLAs won't offer much autonomy, just enough to run the inverter genset test and provide 5 or 10 minutes on the current 300W load. Recently, I discovered the charm of LFP battery technology which blows away the ancient SLA in regard of every aspect (2000 and more charge/discharge cycle ratings for a 20% loss of capacity when cycled to an 80% DoD and a much flatter discharge voltage curve - improved WH capacity and round trip efficiency compared to even a lightly stressed SLA battery pack limited to 50% or less DoD). The only thing not to like is their capital cost. If you purchase from any of the UK suppliers, you can land up paying two to three times what you can buy them for when using the likes of Alibaba to purchase them directly from the manufacturers in China. Four LFP cells in series conveniently creates a 12.8v battery replacement for the classic 12.6v SLA. You just have to size them so their 1C discharge rating matches the peak current demand by the UPS. In my case, I'd need to build a 16s 50AH battery pack for my SmartUPS2000 which, at UK prices, would be an 800 quid or more investment plus carriage charges. Even at 400 quid delivered from the Chinese manufacturer via the auspices of Alibaba, it's still a large investment although it works out at less than the price of two sets of APC branded 18AH battery packs which, rather obscenely imo, are regarded as a 'consumable' :wtf: Who the hell stood still for this particular scam? ::) The LFP battery makes for a one time only capital investment that's likely to outlive the UPS, totally turning the concept of the battery being a 'consumable' versus the one time investment in the UPS itself which now becomes 'the consumable'. An LFP battery pack replacement is more than worthy of consideration. I'll be investigating the pros and cons of ordering a set via Alibaba. So far it's mostly pro and little to no con but I'm not quite ready to pull the trigger on placing an order for a 16 cell 50AH LFP battery pack just yet. :popcorn: [Note 1] This was a decision backed up by the fact that a secondhand 12AH SLA I'd purchased at our local flea market (which turned out to be 11.95v rather than the 12.5v reading on a borrowed DMM I'd used to assess whether it would be worth its asking price) for just a fiver over five years ago now, had only ever been charged from a pair of 1.2Wpk output solar panels hung outside of the office window for a week or so each summer and then left to rest until the following summer's annual refreshing charge for the first five years of ownership and showing a resting voltage that never dropped below the 12.7v mark. I use it on infrequent occasions as a test battery. One time I even used it to jump start a 1.6litre automatic with a totally knackered battery that had left me stranded outside of our local chippy one winter's night. What this had demonstrated was that a quality made SLA did not need to be cossetted with a battery conditioning charger to avoid the overhyped sulphation risk. It seemed to me that if the resting voltage could be kept above the 12.7 volt mark, this was sufficient to protect against the sulphation risk, suggesting that an unremitting 13.8V float charge voltage was way more than was good. The reduced float charging voltage may knock some 5 to 10 percent off the usable capacity but the elimination of the corrosive wear and tear from float charging an SLA at 2.3v per cell makes such a small sacrifice of performance more than worthwhile. John |
| Navigation |
| Message Index |
| Next page |
| Previous page |