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Generator not playing nicely with off-grid system

eldorz

New Member
Joined
Feb 1, 2023
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11
Location
Sydney, Australia
I’m having trouble getting a stable connection between a 3200W DeWalt petrol inverter generator (DXIG3600) and Must hybrid solar inverter (PV18-5K MPK). I have an off grid solar setup with 48V battery. Most of the time I have no need of the generator but it is for when the batteries run low. When I attach the generator to the house the inverter relays click, lights flicker, but no stable connection occurs. No power draw from the generator and no indicators on the inverter to show power to house or battery.

By accident I discovered that attaching my chainsaw battery charger ~250W directly to the generator while it was also attached to the house seemed to stabilise something and a connection was made, power to house and batteries charging. Occasional flickering of the overload light on the generator but otherwise ok. Unfortunately when the chainsaw batteries charged everything stopped working again.

My current theory is that the generator voltage or frequency are not stable enough for the inverter and that attaching a small load to the generator acts as some sort of ballast.

I’ve tried looking at the inverter settings but I don’t have the original manual and they do not match any of the Must manuals I’ve been able to find online.

I could get a new bigger generator but that costs a lot and no guarantee it will work.

I could get a new inverter but $.

Cheapest option seems to be providing some sort of ballast load. I know it works.

So, any ideas on what might be wrong, how to fix it, or if it can’t be fixed, what is a good ballast load to use?
 

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Probably an incandescent light bulb or other purely resistive load of equivalent power rating to your chainsaw charger would help stabilize the generator.

Do you have some kind of voltage / frequency meter that you can check your generator with?
 
Probably an incandescent light bulb or other purely resistive load of equivalent power rating to your chainsaw charger would help stabilize the generator.

Do you have some kind of voltage / frequency meter that you can check your generator with?
OK I have purchased five 60W lights so I can titrate the load needed. I own a multimeter that does frequency as well. It will be a couple of weeks until I can check if this works. Will report back.
 
OK I have purchased five 60W lights so I can titrate the load needed. I own a multimeter that does frequency as well. It will be a couple of weeks until I can check if this works. Will report back.
Have you checked your inverter manual for it's settings to see if it has an inverter generator load limit setting? Some inverters allow controlling the maximum draw from the generator to allow setting it to a value that the generator is happy to provide. Usually something like 75% of generator rated max output is all that can be sustained for continuous loads like battery charging. Generators are usually nameplated for peak short term loads, not sustained loads. Some inverters also allow relaxing the input power qualification limits as well on frequency.
 
Head on over to the Power Equipment forum at:

powerequipmentforum.com/forums/generator-forum.9/

and post the same question, along with Make, model, etc of your generator to those fine folks. The trick of applying a load is a known one, but the real question is why your generator can't put out a stable load (rpm's, frequency, etc) right from the start, after a brief warm-up period. Could be other issues ... these folks will help you sort through the issue, and possibly offer up more solutions for you.

Adjustments to the generator might be possible, or it just might not be sized right for your inverter/charger load ...

Newer inverters are known to be picky about incoming power, associated THD, etc. ... what does your inverter manual say about incoming power from a generator? They may specify an inverter-gen only ...

Hope this helps ...
 
Have you checked your inverter manual for it's settings to see if it has an inverter generator load limit setting? Some inverters allow controlling the maximum draw from the generator to allow setting it to a value that the generator is happy to provide. Usually something like 75% of generator rated max output is all that can be sustained for continuous loads like battery charging. Generators are usually nameplated for peak short term loads, not sustained loads. Some inverters also allow relaxing the input power qualification limits as well on frequency.
Unfortunately, I don't have the original manual and I can't find a copy online. I have emailed the company but no response as yet. Without the manual the inverter settings are somewhat cryptic.

One setting is [03] UTI : 30. I believe this is the utility charging current. I've tried reducing this to 10 with no improvement. And that is with everything in the house turned off. The generator is rated for 3200W continuous at 240V, so should be able to supply 10A no problem?

Another is [05] UTI : Fst/APL/sLo. I think this relates to the allowed voltage range. I have chosen SLO which on the attached data sheet corresponds to 90-280 VAC which seems pretty wide.

The data sheet says the frequency is auto detected at either 50Hz or 60Hz but no range given.

The first setting [01]: UPS/FL/PO has me puzzled as to what it could mean. Currently set on UPS.
 

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Head on over to the Power Equipment forum at:

powerequipmentforum.com/forums/generator-forum.9/

and post the same question, along with Make, model, etc of your generator to those fine folks. The trick of applying a load is a known one, but the real question is why your generator can't put out a stable load (rpm's, frequency, etc) right from the start, after a brief warm-up period. Could be other issues ... these folks will help you sort through the issue, and possibly offer up more solutions for you.

Adjustments to the generator might be possible, or it just might not be sized right for your inverter/charger load ...

Newer inverters are known to be picky about incoming power, associated THD, etc. ... what does your inverter manual say about incoming power from a generator? They may specify an inverter-gen only ...

Hope this helps ...
Hi I'll try that forum thank you. I don't have the manual which is a real issue for me. The house inverter isn't that new. The generator has an inverter which I thought would be good but may have just made a purchasing mistake more expensive! I agree it may be underpowered for a 5kW inverter, from what I have read recently. The previous owner said it ran OK with a basic 4kW generator. Maybe should have gone for more power instead.
 
Manuals are indeed hard to find, which seems amazing ...

Only option I can think of at this point is to find a standalone charger, appropriate for your battery bank, hooked up to the inverter-generator. This would bypass the house inverter's built-in charger system, and the standalone charger must have the smarts to correctly charge your battery bank.

Hope this helps ...
 
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Manuals are indeed hard to find, which seems amazing ...

Only option I can think of at this point is to find a standalone charger, appropriate for your battery bank, hooked up to the inverter-generator. This would bypass the house inverter's built-in charger system, and the standalone charger must have the smarts to correctly charge your battery bank.

Hope this helps ...
This does sound like a viable solution. Can the independent charger be operating while the house inverter is attached to the batteries and potentially charging them as well via solar? Or would I have to isolate the house inverter from the batteries (and have no power to the house while charging).
 
Unfortunately, I don't have the original manual and I can't find a copy online. I have emailed the company but no response as yet. Without the manual the inverter settings are somewhat cryptic.

One setting is [03] UTI : 30. I believe this is the utility charging current. I've tried reducing this to 10 with no improvement. And that is with everything in the house turned off. The generator is rated for 3200W continuous at 240V, so should be able to supply 10A no problem?

Another is [05] UTI : Fst/APL/sLo. I think this relates to the allowed voltage range. I have chosen SLO which on the attached data sheet corresponds to 90-280 VAC which seems pretty wide.

The data sheet says the frequency is auto detected at either 50Hz or 60Hz but no range given.

The first setting [01]: UPS/FL/PO has me puzzled as to what it could mean. Currently set on UPS.
Fst:/APL/sLo Sounds like some kind of response time as in Fast / Slow. APL = Auto Phase Lock time (???) as in allowable time to search for synch with generator?
 
Fst:/APL/sLo Sounds like some kind of response time as in Fast / Slow. APL = Auto Phase Lock time (???) as in allowable time to search for synch with generator?
That sounds about right. APL is the one setting I haven’t tried. Another thing to add to the troubleshooting list! Thank you!
 
Probably an incandescent light bulb or other purely resistive load of equivalent power rating to your chainsaw charger would help stabilize the generator.

Do you have some kind of voltage / frequency meter that you can check your generator with?
I tried five 60W halogen light bulbs for a total of 300W but it didn't work.

I tested my multimeter at home on grid supply: 233.0-236.5V, 49.96-50.01Hz

When testing the generator, the voltage remained within 1V of 241V with no load, and with a range of loads. So all good there.

However, the measured frequency was a bit of a surprise. With no load it was reading at 3-4 kHz, with 60W 1.8 kHz, with 180W 900 Hz, and with 300W 650 Hz. I can only imagine that was some sort of harmonic or step being measured. The generator ran a fan motor designed for 50Hz with no problem.

I did eventually get the house inverter to synchronise with the generator but only after plugging in a toasted sandwich maker (2000W). Needless to say this took more generator power than was going to the house. And once the sandwich maker thermostat switched it off, the house inverter disconnected.

So 5 minutes of battery charging for about an hour of mucking around! Better than nothing I guess.

My next plan is to try taking an oil heater, adjustable to 600, 900 or 1500W. It is cold up there at the moment so the power won't be wasted!

Any advice on further steps appreciated.
 
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Forgive me if this is a dumb question but is the generator being attached to an AC input on the inverter, or to the house panel that is attached to the AC output of the inverter?
 
Forgive me if this is a dumb question but is the generator being attached to an AC input on the inverter, or to the house panel that is attached to the AC output of the inverter?
No dumb questions. The generator is attached by 15A extension cord to an inlet on the outside of the house. This inlet is wired to the house panel. I assume that this is then wired, plus fuse, to the inverter AC input. But I would have to check! Will report back next time I go up.

The inverter does report a grid connection at 240V even when not synchronised. Again I’m assuming, but I wouldn’t have thought it would do this if wired on the output side.
 
I'm under the impression that generator attached to output side of the inverter is an incompatible mode for most or all inverters, but I am new and have not used an all in one.
 
I tried five 60W halogen light bulbs for a total of 300W but it didn't work.

I tested my multimeter at home on grid supply: 233.0-236.5V, 49.96-50.01Hz

When testing the generator, the voltage remained within 1V of 241V with no load, and with a range of loads. So all good there.

However, the measured frequency was a bit of a surprise. With no load it was reading at 3-4 kHz, with 60W 1.8 kHz, with 180W 900 Hz, and with 300W 650 Hz. I can only imagine that was some sort of harmonic or step being measured. The generator ran a fan motor designed for 50Hz with no problem.

I did eventually get the house inverter to synchronise with the generator but only after plugging in a toasted sandwich maker (2000W). Needless to say this took more generator power than was going to the house. And once the sandwich maker thermostat switched it off, the house inverter disconnected.

So 5 minutes of battery charging for about an hour of mucking around! Better than nothing I guess.

My next plan is to try taking an oil heater, adjustable to 600, 900 or 1500W. It is cold up there at the moment so the power won't be wasted!

Any advice on further steps appreciated.
Hmmm. That's too bad that it took such a large resistive load to stabilize the genset-inverter pairing.

So: To recap - You have an inverter generator (i.e. typically with non-adjustable output frequency) and an inverter that won't connect to start it's battery charging function.

Probably finding the inverter manual is a first priority to understand it's specified range of input power and settings is important to getting this working.

Attaching a chainsaw battery charger loaded down the generator enough to alter either the voltage, frequency or waveform (i.e. harmonic content aka THD = Total Harmonic Content, Power Factor etc.) enough for the inverter to qualify (accept) the generator output.

So to proceed systematically and identify what the problem is, we need to confirm voltage, freq and waveform

Voltage and Frequency: Inverter generators are usually pretty close to design frequency so probably this is not the problem. However sounds like your multimeter frequency setting is more sensitive to higher frequency harmonics than to the fundamental sine wave of the inverter (50 Hz?) so you got extraneous frequency readings (perhaps cobble up a low pass capacitive filter to block the high frequency chaff). Alternately, see if you can borrow another meter better at frequency testing (suggest purchasing something like a Kill-O-Watt type of energy meter that reads Volts, Current, Power, Power Factor and in some cases frequency and peak readings too - They are about $50 to $90 US online and are hugely useful).

Given that your meter check on grid frequency worked, the odd frequency readings from your generator imply that your inverter power may have a lot of high frequency chaff (switching noise from harmonic frequencies - inverters build up sine waves by adding lots of higher frequencies so isn't surprising). I've put my little US$100 Nano-Oscilloscope (handheld floating input multi channel digital storage scope with X10 attenuation probe to bring VAC down to input level) on a neighbor's Yamaha Inverter generator that was mis-behaving and burning out appliances. I was surprised at the spikes seen on it's waveform, it was sent back to the shop for a new inverter board which solved that problem. Maybe your genset needs to go into the shop for scope testing.

If the genset is working correctly and problem persists, Waveform / Power Factor and THD are likely to be the problem.

Waveform: Within this concept are wrapped up measures such as THD (the percentage of distortion from a pure sine wave as a measure of the presence and relative amplitudes of odd and even higher multiples frequency harmonics that cause a mis-shapen waveform) and Power Factor (the leading and lagging between phases of Voltage (V) and Current (I) flow caused by inductive and capacitive loads respectively).

Fully diagnosing waveforms and power factor requires a dual channel oscilloscope to qualitatively visualize the V and I waveforms and or a spectrum analyzer to measure the harmonic content. However if you are handy electrically, you can experiment with adding or removing various capacitive and inductive loads to see if the inverter works with them (i.e. like your battery charger which is likely a net inductive load - chargers are typically a coil and buck-boost switching power supply). As a test, you might try putting a really long (100 ft) light gauge coiled extension cord between genset and inverter - this often adds just enough inductance and resistance to stablize a genset enough for an inverter. I don't recommend running any significant power through a coiled cord for any length of time but good as a quick test to see if this stabilizes things as well.

Alternately if adding in inductance plus resistance from a light coiled cord doesn't help, you could try the opposite - adding a resistor/ motor run capacitor across the generator supply which may improve things (opposite sense of power factor correction from inductance).

Probably best to seek help from a friendly local electrical engineer or electrician/tinkerer knowledgeable about these things.
 
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Thank you for this detailed and thorough reply! I managed to get the inverter to accept the generator by plugging in a 900W oil heater. That’s a win in winter because I can use the heat generated.

I don’t have all the gear to visualise the waveform unfortunately. Also I contacted the MUST company and they said the inverter is so old they no longer have manuals available for it.

I suspect it was a mistake to buy an inverter generator. You live & learn I guess.
 
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