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Noisy power from typical backup generators

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Johnny B Good:

--- Quote from: Johnny B Good on March 03, 2021, 12:34:52 am ---
--- 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.


--- End quote ---

 I can now report on my fuel priming experiments with that priming bulb kit. Sorry for the delay being a fortnight longer than I'd estimated but I do at last have something positive to report even though the upgrade still requires another length of 2 by 3.5mm fuel line to complete the final version.

 I was going to follow my original idea of using the priming bulb kit to refill the carb float bowl via the fuel feed line but this was sidelined by the presence of a mystery clear plastic tube, dangling out of the bottom of the base plate alongside of the float bowl drain tube, connected to a nipple on the carb body which looked temptingly like it could have been a 'priming port'. Succumbing to this temptation, I connected the primer bulb's outflow to this nipple and plumbed the input into a T adapter connection to the fuel tank feed line.

 After priming with a few presses, I was able to start it 'first pull'. Unfortunately, the engine didn't pick up speed after opening the choke obviously running on an over-rich mixture before it eventually died after about a minute or so. Obviously, this 'mystery nipple' wasn't intended for use with a fuel priming bulb as I'd hoped so it was back to my original plan.

 Cascading the priming bulb in series with the fuel tap connection to the carb fuel line was the easiest plumbing arrangement (no need to use a pair of Tee adapters either side of the fuel lift pump which is plumbed in between the fuel tank and the fuel shut off tap). This seemed to work with only some minor bother to start with but after allowing it to run the carb dry and cool down for a couple of hours to retest the "Start from bone dry" stone cold condition, it became obvious that it was suffering fuel starvation due to excessive flow restriction from the primer bulb.

 I had to call a halt on further work for lack of sufficient fuel line and time. It's now finally become obvious that the only viable option that remains is the more complicated plumbing of the primer bulb in parallel with the original fuel lift pump. This arrangement removes any question of flow restriction and the one way valves in both pumps means they should function perfectly fine in this arrangement.

 If I hadn't been tempted by that extra plastic pipe connection to the carb and gone straight for the parallel arrangement, the job would have been done and dusted by now. Still, my experience here may help someone else considering a similar enhancement to make pull starting these cheap inverter gensets as easy as it should have been to begin with. I've placed an order for a metre length of the 2x3.5mm fuel line so it's just a matter of awaiting delivery and some dry warmish weather to resume the modification - it's a task best worked on out of doors rather than indoors for very obvious reasons.

 As for that mysterious plastic pipe connection to the carb, I think it must be an atmospheric pressure equalisation vent tube but why such a plastic tube would be deemed necessary when the more usual system of pressure balancing with a small vent hole into the float chamber above the normal fuel level beats the hell out of me. Presumably there IS a good reason for this bit of extra plumbing. Maybe someone here knows the answer to that question?

 Looking at the long range weather forecast for the UK, it looks like it may be another couple of weeks yet before I can make a final report. Small parts orders from UK sellers rarely take longer than a week to be delivered in spite of the Covid 19 restrictions. Often they will arrive with 2 or 3 days of being ordered, barring Bank Holiday silliness and such like. Even if the fuel line turns up this Saturday, the weather forecast for this weekend and into the following week looks extremely bleak for any such outdoors work so don't hold your breath on my next report. :(

 BTW, I didn't waste this opportunity to connect a DSO to the alternator and a a 3 turn sense winding over the exposed end of the ignition coil core in order to record waveform  traces to let me answer the question "How many stator poles - 18 or 21?". The number is typically 18 or 21 in virtually all such inverter gensets. In this case, as you will see from the attached screen shots, the answer is 21 (with 7 pairs of magnets embedded into the flywheel).

 In this case, there is an ignition pulse every revolution rather than every other revolution. It's not at all surprising since the waste spark is of no consequence and simplifies ignition timing and accuracy - triggered directly from a flywheel sensor without any additional anding with a camshaft derived signal to restrict it to the start of the power stroke.

 Although I have my answer to let me order that TI sensor pre-programmed for a 7 by 3 pole stator BLDC hall sensor emulation (or to DIY a 3 hall sensor array with a 17.143 degree spacing around the flywheel periphery, assuming sufficient leakage flux exists), I rather doubt I will ever bother trying to take my electric starter project any further.

 Looking at those screenshots, I suspect I'd need to provide supplementary battery power to the ignition circuit to get a reliable spark at the 200 to 240 rpm cranking speed I'd hoped to get at best. In itself, such a low cranking speed should still be enough but without a reliable source of sparks, it's a no go as things stand. My best guess, looking at those traces, is that it needs a 500 rpm minimum cranking speed just to generate a reliable source of ignition pulses in the absence of such supplementary battery power to the ignition circuit.

 That low cranking speed ignition issue is the final nail in my DIY BLDC direct drive electric start project's coffin. That's not to say such an electric starting technique couldn't be employed in future models where the manufacture can modify the alternator with additional heavy duty low voltage starter windings to allow a 12v starter battery to directly power the starter windings with a minor modification to the ignition circuit to be powered from the battery/charging generator output. However, that does rather put it out of reach of all bar the most dedicated of DIYers prepared to do whatever it takes no matter the cost.

 Since I'm not quite into that class of extreme DIY, that now puts an end to any further work on my BLDC direct drive electric starter folly leaving me to concentrate upon fixing the unconscionable lack of a priming bulb pump perpetrated by the manufacturer, Parkside.

 As it happened, it was rather fortuitous that I'd spotted the opportunity to wrap three turns of a croc clip test lead around the ignition coil core to save using a microphone by the vacant spark plug hole to detect a timing reference as I'd originally intended since it let me spot the low revs ignition issue in time to avoid expending any more effort on what had threatened to become a rather more complex modification than I'd ever originally imagined it would ultimately turn into.

 Considering the poor or unreliable ignition pulses at low cranking speeds, it seems surprising that a kickback risk should still be present but I think just enough voltage must be getting generated to produce a possibly mis-timed spark if a poor technique is employed to pull start it. I would say all that ignition circuit needs is an undervolt lock out with a power ramp up ignition retardation set to a few degrees past TDC for the first two or three power strokes in order to eliminate the kickback risk of a fixed advanced ignition timing optimised to the eco and max output engine speeds without any consideration for the pull start kickback hazard this presents to the end user. Just adding a priming pump goes a long way to mitigating this rather spiteful shortcoming.

EmptyHead:

--- Quote --- As for that mysterious plastic pipe connection to the carb, I think it must be an atmospheric pressure equalisation vent tube but why such a plastic tube would be deemed necessary when the more usual system of pressure balancing with a small vent hole into the float chamber above the normal fuel level beats the hell out of me. Presumably there IS a good reason for this bit of extra plumbing. Maybe someone here knows the answer to that question?
--- End quote ---
Sometimes, the atmospheric pressure equalization vent will allow fuel to exit the carb:
A) when unit is tipped over it will allow gasoline to exit
B) if carb float or needle has an issue it will allow gasoline to exit carb without flooding engine(if engine is sitting level)
Many "suitcase" type generators route the hose to exterior of the generator to prevent gasoline from collecting inside the housing.

Johnny B Good:
@EmptyHead,

 Thank you very much for that answer. It makes good sense to provide such a vent/drain tube with a 'suitcase' type generator now that I think about it. The open frame types don't really need such a tube but it's all too painfully obvious now you've reminded me of the distinction. :palm:

 BTW, I've added a couple more paragraphs to that post (I was only going to slightly improve my phrasing of the final paragraph but got a little carried away). I think I can resist any more tinkering now. ::)

Johnny B Good:
 Well, the parts arrived over a week ago but the weather didn't didn't permit any outdoors work until yesterday when I was finally able to install the priming pump bulb in parallel with the original fuel lift pump. As expected, I didn't have any fuel starvation issues with this more complex arrangement and, joy of joys, starting is now a less arduous task after a long lay up with a drained down carburettor float chamber (typically done by shutting the fuel off to let it run dry).

 I tested by allowing it to cool down after my first test run and draining the remaining 2 or 3 cc of fuel from the float chamber having let it run dry to terminate the test run. Since I'm using the priming bulb kit in a non-standard way to refill the carburettor float chamber from bone dry, it seems to need about 6 to 10 pumps rather than the more usual 2 or 3 when it's used as originally intended simply to squirt a bit of neat fuel into the venturi. I'm fine with this since those extra 4 to 7 presses are a damn sight easier to apply than pulling on the starter cord 4 or 5 times with kill switch operated to inhibit the ignition until I'm ready to chance my arm (literally!) to give it one good full strength yank to fire it up.

 I can now (at long last!) conserve my energy for a full strength pull that's guaranteed to fire it up first go and worry less about just how much life remains in that much abused pull starter cord. :)

IDEngineer:
Had our first power outage (due to high winds) last night since getting the large inverter generator. It fired right up, and after warming up for a few minutes I powered the house with it.

Worked perfectly! Economy mode worked as intended, keeping the engine RPM's (and fuel consumption) down during lighter loading. But when a refrigerator fired up, or another large load kicked on, there was none of the UPS beeping and other complaints by electronics in the house. The engine would adjust its RPM's to accommodate but otherwise such things were non-events. As intended!

I had my wife use the ~1000W microwave oven a couple of times while I monitored the generator's behavior. I could tell when the load came and went, but nothing in the house complained at all.

The layout of this unit is interesting. The inverter is mounted directly below the fuel tank and above the engine (?!?) with a nice large heat sink on the engine side. The thing is, heat sinks work both ways... they lower thermal impedance in BOTH directions, and the way this one is mounted appears like it would absorb waste heat from the engine directly below. I didn't check the heat sink temperature, but I will next time.

I'm attaching photos of the top and bottom of the inverter, as best I can photo them without disassembly. For some reason I can't get them to inline, despite the message editor offering that option, even when I've downsized them.

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