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Discussion Starter #1
Hi guys. I have just bought my first generator, not a expensive one though, Bohler 6500W-e 2800watt. I have only used it for about 20 mins and its only had a light load connected to it so far. But I have noticed the voltage constantly changes, about 10-15 volts up and down where it should be at. Is this normal with portable petrol cheap generators? Thanks https://www.amazon.co.uk/B%C3%B6hmer-AG-Generator-6500W-Petrol-Electric/dp/B078W96337
 

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I assume you are generating 230V 50Hz power? Try it with a more substantial load, and also measure the voltage with a digital multi-meter if you have one. The analog meters in generators tend to bounce a bit due to the vibrations.

Also, is the speed of the engine fluctuating? Should be staying very close to 3000 RPM for 50Hz.
 

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Discussion Starter #3
I assume you are generating 230V 50Hz power? Try it with a more substantial load, and also measure the voltage with a digital multi-meter if you have one. The analog meters in generators tend to bounce a bit due to the vibrations.

Also, is the speed of the engine fluctuating? Should be staying very close to 3000 RPM for 50Hz.
according to the specs its 220v and 50hz, but the labels on the plug socket say 230v and I think the engine speed is 3600rpm. The reason I bought the generator was home backup power for when I had power-cuts. I have all my stuff in my bedroom plugged in to a UPS (uninterrupted power supply), so when I have a powercut I only have to plug in 1 plug into the generator to get everything powered up, about 300-400watts in total. The UPS displays the voltage and hertz and thats what I am going by when I plug the generator into the UPS.. The needle slightly moves back and forth on the generator, but hardly anything. I guess if I didnt have the voltage readout on the UPS I wouldnt be worried at all.

Do you think it just needs to get broken in as I have only used it for about 20mins and had about a max load of about 400watts so far, but during a power-cut I'll be using it more then just to power my bedroom?
 

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Discussion Starter #4
Ah yeah the speed of the engine sounds constant not speeding up or slowing down at all.. I was quite impressed when I started it for the first time, all it took was a 1 second turn and hold with the key and it roared into life.. Not bad for a Chinese made generator hey?
 

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according to the specs its 220v and 50hz, but the labels on the plug socket say 230v and I think the engine speed is 3600rpm.
If you're generating 50Hz, the generator speed should be 3000 RPM.
Generator Frequency (f) = Number of revolutions per minute of the engine (N) * Number of magnetic poles (P) / 120
50Hz = 3000RPM * 2 Poles / 120
about 300-400watts in total. The UPS displays the voltage and hertz and thats what I am going by when I plug the generator into the UPS.
That's a VERY light load. Try it with more like 1/2 the rated load and see if it settles down.
Do you think it just needs to get broken in as I have only used it for about 20mins and had about a max load of about 400watts so far, but during a power-cut I'll be using it more then just to power my bedroom?
Yes, I would run it at least an hour with 1/2 load before trying to determine stability. You can use a bunch of light bulbs to get the load up there, and maybe a small motor like a hand saw or something similar that can be locked in the on position.
 

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Discussion Starter #6
I will get it going again the next half decent warmish day I get. and get more of a load plugged into it and see if that makes the voltage more stable, also I will get a light plugged into it aswel to see if the bulb flickers or dims at all..... Also if the generator is cold will that make the voltage not stable, as I havent used the generator longer then about 10mins at a time so far?

This is the spec


  • Maximum Output: 2800W/2.8kW/3.4KVA
  • Voltage Regulator: Automatic voltage regulator
  • Emergency Indicator: Auto breaker overload protection
  • Safety Measures: Low oil automatic shut down
  • Continuous Rated Output: 2600W/2.6kW
  • Rated Voltage: 220V
  • Fuel Tank Capacity: 11 Litres
  • Oil Capacity: 0.6L
  • Oil Type: 10W30 or 10W40
  • Engine Type: Single-Cylinder, 4-Stroke, Air-Cooled, OHV horizontal shaft
  • Engine Output: 8hp
  • Engine displacement: 210cc
  • Starting System: Recoil/Ignition/Electric
  • Continuous Operating Time: 10h
  • Noise Level: 66dB
 

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You said you think it's 3600RPM, but that your UPS also displays Hz. So, was it showing 50 Hz, or 60 Hz? It should be 50 Hz, assuming you're in Europe, or similar.

In my limited experience, the voltage shouldn't be unstable just due to the generator being cold. I never noticed that with mine (different brand), even with a small load. Like tabora said, adding a significant load, like a hair dryer, would be interesting, to see how it reacts.
 

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Discussion Starter #8 (Edited)
I dont want to put too much of a load on the generator with it being new, but I really hope the voltage fluctuations clear up on its own. But like I said if I hadnt of seen the digital voltage readout from the UPS I wouldn't of been concerned because the analog voltmeter barely moves on the generator.

The Hz is 50 and I think that goes up and down a bit aswel, I think I have seen it at a max of 52Hz, but I have been more concerned about the voltage.

A totally different question that I dont really understand as I am new to generators... I am guessing that 3000rpm is max speed for a generator and its running at that speed all the time. So where does the power come from when the load increases?
 

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Yes, your generator should always be running at 3000 RPM, to produce 50 Hz electricity.

Horsepower = Torque times RPM.

As you put a larger load on the generator, it needs to produce more amps of current. The engine produces more torque (twisting the crankshaft harder), to meet this added demand. And even though the RPMs remain the same, the extra torque means that more power is being produced by the engine.

An analogy would be riding a bicycle, at a constant speed, in a particular gear. How hard you're pushing on the pedals is torque, and how fast the pedals are turning is your RPM.

On level ground, you don't have to push very hard on the pedals. So low torque, times a certain RPM = low power. But then you start to climb a hill, at the same speed. Now you have to push a lot harder on the pedals. So high torque, times the same certain RPM = high power that your legs are putting into the bike. But you're still going the same speed.
 

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Discussion Starter #10 (Edited)
Ah that makes sense, I see that you can by a 6hp engine that can power the same amount of watts as my 8hp can, but the 6hp will struggle more then a 8hp engine as the load increases to maintain the 3000rpm.

If I can, today I will get the generator going if its not too cold, as it takes me longer todo stuff because I am in a wheelchair...Thats the reason for the generator being outside my door and all plugged in and ready to go, with the extension lead through the door frame. So I just only have to remove the waterproof cover from the generator and start it up.

Anyway heres a picture of it with the waterproof cover removed, all ready and waiting to go
 

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The 6hp will struggle more, and at some point as the load increased, it would be overwhelmed, and would slow down. While the 8hp would stay at 3000 RPM, and support the larger load.

1 hp = 745 watts. So if the generator was 100% efficient (it's not), the 6hp could provide 4470W, and 8hp could provide 5960W.

In reality, you get less than that. My 5500W generator had an 11hp engine (theoretically 8195W).
 

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Discussion Starter #12
So my generator could run the whole 2800watts continuously quite happy then if it was 100% efficient? Just to let you know, Im and its too cold outside for me to play generators today.

Also where the generator sits outside its on a slant slightly, so I will try to level the generator before starting it again. Because I have a oil light thats on, or I think its a oil light anyway, it lights up when I turn on the circuit breaker. It might be because its not level, as I cant get anymore oil in it without it pouring out.
 

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They rated it for 2800W, it should be able to power that without a problem. They should have already taken into account inefficiency, etc.

Make sure it is level when checking or filling the oil, and follow the manual. You need the height to be correct. Too much oil is bad, so don't just put in as much as you can, if that's not the procedure in the manual.
 

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Discussion Starter #14 (Edited)
Yeah I will level it up and check the oil again before starting it again. I have a 3d printer so I'll print out some raisers for 2 of the rubber feet..

The generator will be a life saver as some 3d printouts I do take days to finish, so when the power fails everything or almost everything in my room uses battery power from the UPS and nothing turns off as the switch over is like about 2-3ms, so my printer carries on printing regardless. The battery power last about 1-2 hrs, so plenty of time to get my UPS hooked up to the generator, then when the UPS detects power again it flick back over to mains power,, well generator power.

The weather in the united kingdom is really cold at the moment, so no idea when I'll be able to get outside to the generator. If it was just a matter of starting it up, I could do that in a few mins.. But I need to get it level and check the oil, and thats no easy task for me todo in 5mins.

But thanks for all your help and suggestions and I will report back when I can get outside without being frozen to death.
 

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That sounds like a cool setup! Just test that (if you haven't already), before relying on the generator during a long build.

I tried running my APC Smart-UPS on my Generac generator. As I recall, the UPS didn't like the power coming from the generator. I believe it insisted on running from the battery, despite my providing generator power to it. So just make sure that the UPS will consider the generator as acceptable incoming power, and will stop running from the batteries.

You probably did this already, since you've been using the UPS to evaluate the generator's power. But it just seemed worth mentioning.
 

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Discussion Starter #16 (Edited)
Line-Interactive UPS are not great with generators, Im sorry to say. You need either a Online UPS or a "generator compatible" Line-Interactive UPS, normal UPS's dont get along with generators because the volts and hertz are not stable enough and causes the UPS to flick over to and from battery and mains power mode constantly.

Even tho I have a Online UPS I am amazed that its ok because the voltage is constantly up and down atm.. But that makes me wonder if the volt and hertz are suppose to jump around a bit, if this is the reason normal UPS's wont work with generators??

I believe some big companies, hospitals ect, do use this kind of setup.. a huge UPS and a standby generator, so when they loose power, the UPS will keep the building powered while the generator kicks in.
 

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I believe some big companies, hospitals ect, do use this kind of setup.. a huge UPS and a standby generator, so when they loose power, the UPS will keep the building powered while the generator kicks in.
At my former building, I had a 600KVA 3-Phase UPS and a 600KVA Caterpillar Generator to keep it happy when the mains dropped. Way overkill for me now, so I sold them when I downsized. I only have 40 or so CPUs and a half-dozen printers running at a time now...
 

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Discussion Starter #18 (Edited)
I had a belkin 1200va/670watt UPS for a good 9-10yrs, went though about 3 sets of batteries during that time and even though it wasnt a great make, it was a great little UPS and never let me down.

This time last year I decided to buy a new UPS and again I didnt buy a well known one, as I think your paying for the brand and not for the item, if you get me. So I got a PowerWalker Online 2000va/1800watt UPS for a cool £350, hoping that the batteries would lasts hours during a powercut. The UPS lasts about 2-3 times longer then my old UPS, but stll not as long as I was hoping for, it would keep my pc stuff going for about 2 hours . https://powerwalker.com/?page=product&item=10122042&lang=enhttps://powerwalker.com/?page=product&item=10122099&lang=en

Ever since then I have been wanting to get a generator for the UPS, so it would last during long power powercuts, but people kept saying its a waste of money as the power dont do off that often. But it could go off 2-3times a year and the weather is getting more and more unpredictable now, so I dont think its a waste.

So anyway I have finally got one now, and I bet my family members who said its a waste of money, will want to use it during the next powercut we have, and Im going to say "no, tough luck" hehe
 

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Discussion Starter #19 (Edited)
Well. I still havent got it gong again yet , but we had a bit of sun this morning, so I got the generater level, (still may not be perfectly level). Checked the oil again and its over the high line so no more oil will squeeze in. Basically if that light still comes on now, it must be either faulty or its not a oil light.. I am a tad annoyed though as I am using bog standard SAE 30 oil because the manual said 10w30, 10w40 or SAE 30 oil can be used in the generator, and I got the worst, as its not great in cold temps ... I dont know if makes of oil improves anything, as it is Briggs & Stratton oil so its not totally rubbish?

I then just gave it a bit of a clean as I got a bit of petrol spilt in places when filling it up. But hope fully that wont happen again, as I printed out a huge funnel, so the petrol shouldnt splash or spill while filling the generator in future.

Anyway, how do you like the funnels I have printed out for the oil and petrol.........

 

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Ha, very nice :) We have 3D printers at work, it's pretty cool being able to just make whatever you need. And even for simple stuff, I can model it and print it way faster than I could machine it.

How cold is "cold"? I would not use straight 30W oil in cold conditions, personally. Certainly not below freezing. It's too thick, at least at startup, for my comfort. I'd be concerned about poor lubrication. Oil is cheap, compared to possible engine damage.

If you're outside the suggested temperature range, the weight of oil is much more important than the brand, in my opinion.

And yeah, a generator may seem silly to some, but not when you need it! I haven't regretted mine for a minute. They've gotten us through several multi-day outages, in winter (windy, below freezing, etc). Sitting in the cold and dark, on day 3, is no fun.
 
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