Generator surging (hunting) when charging sytem thru stacked SW 5548s.

John Sullivan · March 2013

Hopefully someone has solved this problem or at least has some ideas about cause.

I recently moved to an off grid residence with 16 sharp 185 w panels on trackers; two Outback fm 60 charge controllers; a 1450 amp hour, 48v, 24-85-23 traction battery; twin Xantrex SW5548 inverters in series; a 12 kw Kohler propane generator.

When charging the battery bank with the generator the generator will surge or hunt continously. The system will stay within the tolerances allowed by inverters and will continue to charge however it is not stable. Frequency will swing between 56 and 62 hertz, charge rate will fluxuate between 25 and 35 amps and voltage will vary from about 118v to 123v. These fluxuations occur every few seconds.

When running the generator directly to the house loads it is solid and stable. Likewise, the inverters perform all other functions flawlessly.

Generator technician recently gave the generator a thorough once over and could find no issue with the generator. He dampend the governor on the generator to reduce the surging. My solar technician has made a couple of visits, double checked all wiring, and is at a loss. Schneider electric tech support suggested replacing the stacking cable which has been done with no effect.

It appears to me as though some interaction between the stacked inverters is causing the generator governor to surge but I have exhausted all of my ideas about what to do next.

Any help or thoughts are appreciated.

icarus · March 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

What is the genny?
(sorry, just saw, th 12 kw Kohler)

Has it always done it?

Has anything in the entire system changed, so now the surging happens?

Tony

Ps. welcome to the forum

PPS I am WAGing that the genny and the CCs " see" each other, and as the current and voltage rise from the multiple charging sources, each one changes it's parameters slightly, creating a sort of feed back loop.

What charger are you using with the genny?

offgrid me · March 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

You could be overloading the generator. Each SW has a 100 amp charger at 50v this is 5000w. Two of them together is 10kw. Throw in house loads and you are right at the limits of that generator. Try reducing the ac breaker size setting on the inverter. The SW will cut back the charging current and this should help with the surging.
Ned

John Sullivan · March 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

Icarus:

I am charging through the SW5548s with a max charge setting of 30 amps on each inverter. As far as I know the system has done this for quite some time. My solar tech recalled the former owner struggling with the same issue. I recently upgraded the battery bank as it was due but this had no effect on the problem. I am of the opinion also that some sort of feedback loop is affecting the governor on the generator but my education in this area is woefully lacking....John

John Sullivan · March 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

Offgrid me:
I am set up to only pull 60 amps total off the generator when both SWs are charging. This should be well within the capabilities of the generator. I have the ac breaker size set at 60 amps.......

offgrid me · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

Isnt this breaker size based on 220v. This would be 13.2kw. What size breaker does the generator actually have on it. Most of the standby type generators are not designed to produce there rated power for any length of time. This is why their warranties are voided by off grid use. The 12k kohler is probably good for about 7kw of continuous load before the windings get hot and voltage starts to sag.
Ned

John Sullivan · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

The generator has a 60amp 220 breaker on it. The generator is a water cooled stationary mounted. It doesn't even grunt when the inverters start charging.........John

Vic · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

The "Breaker" Terminology is specific to XW Inverter/Chargers (and perhaps others), But the SW and SW+ Inverters do not use this terminology.

There are AC Current settings for the SW Charger, however. And, each SW is 120 VAC outupt and input, not 240 VAC. The charger in the SW 5548 should be 75 DC Amps for each 5548 -- 150 DC Amps total when these two are stacked.

30 Amps for the Charger AC current setting should be right at the maximum capability for the SWs for continuous charging. This represents about 7500 watts, or a bit more load on the genset, accounting for efficiency and battery voltage.

When in bulk, the 5548s should place a fairly constant load on the genset. As has been stated, the PV input could be affecting the behavior of the 5548 chargers, but would exepct that this would only be the case when in Absorb on the CCs -- later in Bulk on the 5548s.

You could try reducing the AC Current settings for each 5548 to see if it stabilizes the genset loading.

If this situation occurrs in full sun, you might look at the FM-60 displays of charge Stage, battery voltage and outupt current. If the CCs are in Absorb, this can be a large part of the issue.

One thing that can happen with these inverters, is when the Bulk V setpoint is reached, especially with significant PV input power, the SW may dump some current into the AC input terminals as part of its regulation strategy. This can upset some gensets, and cause "hunting", or some may call it surging.

Kohler gensets are generally fairly stout, and well made. A fuel system problem could also cause surging.

The genset is probably not really overloaded, unless you have have fairly heavy loads on the Inverter output terminals, or you are at a very high altitude, causing the genset to run out of steam.

Done guessing for now, Vic

John Sullivan · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

Vic
Thanks for the response. Max ac current setting for my 5548s is 35 amps. Test ran gen (bulk charge mode) this evening at 35, 30, and 25 amp settings with no appreciable difference in the hunting issue. Typically the generator does not run during solar input times as I will generally run it at night or early mornings. However the same hunting issue occurs while the pv charge controllers are sleeping or charging.

Do the 5548s generate currents from one to the other that could be messing with the electronic governor on the generator? I do see different current values on the 5548s during the absorb stage but during bulk they both hang around the set amphereage except for the cyclic fluxuation I'm trying to solve. If the charge amp setting is 30, during bulk charge the inverters will fluxuate between 25 and 31 amps every few seconds. It seems to me that something is telling the generator the load is changing when it should be relatively steady.

I have experimented by removing all the loads from the system except charging the battery bank which had no effect on the problem. Replaced the stacking cable, with no effect. When I run the generator with all my normal loads while not charging the battery bank (bypass the inverters) it runs very steady and responds to loads as you would expect.

It has me very puzzled...........John

BB. · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

I hope Chris Olson can talk about this issue... He has a lot of experience in this field.

Anyway, checking that the linkage/control(ler) for the auto throttle does not have any rough spots/hiccups in it travel (lubricated if needed with a good oil or something like graphite dust possibly).

Try using a large lamp or electric heater on the genset when it is hunting and see if it changes the behavior. People with smaller genset have found that a 100 watt filament lamp can sometimes stabilize issues like this.

-Bill

ChrisOlson · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

John Sullivan wrote: »

It appears to me as though some interaction between the stacked inverters is causing the generator governor to surge but I have exhausted all of my ideas about what to do next.

You pretty much guessed the problem here. This is a characteristic of SW Series II/SW Plus. They cannot infinitely vary load like you think they would. You more than likely have the amps setting to the charger to the max. The way the SW regulates this when it's pushed right to the limit is to actually overload (go past the setting), then reduce the load by a big step. The result is that the average current will be approximately what you have set for AC Charger Amps. But it varies on each side of the setting and this will make the generator "surge" from the loading/unloading.

With our 5548 I found that adding an aux load (like water heating) will cause the SW to reduce the amps to the charger so the AC2 Input Amps don't get exceeded, and then the "hunting" will stop.

That's the best way to do it.

The second best is to lower the Charger AC Amps setting until the inverter stops "hunting" back and forth on each side of the setting.
--
Chris

Vic · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

Well, on my stacked pair of SW+5548s charging from the largest genset -- 25 Kva -- there is no hunting in early Bulk at Max amps for my batteries, about 130 ADC. When the Bulk V setpoint is reached (would be called V Asorb on Solar chargers), there is the rhythmic battery charge current changes of about 10% or a bit less, and a smaller voltage change. This IS due to regulation of Voltage. Have not seen any real changes in battery charge current prior to Bulk voltage target being met. Having appreciable additional current from a Solar charger can add a bit of hunting.

The SW+es seem to regulate Bulk CURRENT smoothly, but when VOLTAGE regulation is needed, it is a bit rougher. Having a largish genset seems to help stability IMHO.

This is based on my personal experience with two different, but very similar stacked 5548 SW+ systems, with battery banks sized similar to John's. BUT, these are SW+es and not SWs.

Of course, there are two control systems involved -- that of the genset trying to regulate V and speed, plus the the inverters trying to regulate primarliy current OR voltage. Each SW may well not be synced with the other when trying to regulate current of voltage, which could create additional demands on the renset regulators.

Above just my experience and opinion. Good Luck, Vic

ChrisOlson · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

Vic wrote: »

The SW+es seem to regulate Bulk CURRENT smoothly, but when VOLTAGE regulation is needed, it is a bit rougher. Having a largish genset seems to help stability IMHO.

It all depends on how fast the governor is on the generator. Never had any problems with our Honda on either the stacked 4024's or the 5548. But our backup gen would surge like crazy due to the loading/unloading imposed by the chargers during bulk. Like I said, I always found that adding some aux load to the passthru caused the SW Plus to smooth it out and stop the gen surging. It don't take much load - just enough to cause the SW to dial the charger down a slight amount due to the load.

I've had the clamp-on AC meter on the gen before, charging with with both the 4024's and the 5548 - didn't matter because they both did the same thing - and the amp swing can up to 5-6 amps (2.5-3.0 amps on either side of the setting) with no loads on the passthru. A big generator, or one with a fast governor, won't be affected by the ~500 watt swing in loading. But it affects a small 3 kW generator with a slow governor pretty severe.
--
Chris

Ralph Day · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

My SW4048 does the hunting swing as well. Nature of the beast it seems. Did it with a 10kw diesel genset and also with utility power (both on AC2 input, generator panel controlling which is supplying the inverter).

Even if utility power is supplying and the inverter is floating the batteries it will hunt a bit. Xantrex says that's what it do.

Ralph

ChrisOlson · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

Yep - it's just their method they use to regulate the current based on the amp settings you have entered into it. I found in float it was really bad even with a "tight" generator on it. There is a night and day difference between the SW/SW Plus and the XW-series where this is concerned. The XW is smooth as silk.
--
Chris

Mangas · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

John, I have four SW 5548 Plus inverters (two and two stacked).

I had exactly the same problem you did with my old 1800 rpm water cooled 15 KW genset which I replaced with an higher output 20 KW unit two years ago.

In my case, as the genset's charging cycle neared the end of its timed two hour run the hunting/surging was constant.

After hooking up the larger Cummins/Onan genset the hunting/surging stopped. The engineering guys here will have an explanation for it but I believed it could have had something to do with the older genset trying to match voltages through multiple inverters. For some reason the larger unit handled it better electronically.

That's my best shot from someone who is a complete technical novice in such things. The gurus here will line me out but wanted to pass on my experience.

In a couple of years, I plan to replace the SWs' with the newer generation XW series which Chris mentioned. The older SW Plus' are pretty stout. So far, mine have been running 24/7 for 8 1/2 years pushing two 2.5 ton central air conditioner compressors and two air handlers! Hope the newer XWs' will be as trustworthy.

ChrisOlson · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

Mangas wrote: »

The older SW Plus' are pretty stout. So far, mine have been running 24/7 for 8 1/2 years pushing two 2.5 ton central air conditioner compressors and two air handlers! Hope the newer XWs' will be as trustworthy.

Mangas - I have a propensity for testing things just to see what they got in 'em. While the SW Plus is pretty stout - the XW has proven here to be stouter yet.

I can't say that I saw any real difference between the stacked SW Plus 4024's and the single SW Plus 5548 with this "hunting" issue. I think the bigger the generator is, the less pronounced it will be simply because the larger generator is not bothered as much by a swing in loading. With the stacked inverters we ran the generator on 240V output, with the single inverter we switched it to 120V output. But it still did it, and some days worse than others.

I'm guessing the old Kohler has a slow mechanical governor so it can't react fast enough. Since the loads are in pass thru during charging, very light loads will cause like your CFL's to constantly vary their brightness as the inverter varies the charger amps on each side of the setting.

A newer genset with an electronic governor designed to maintain exactly 60 Hz at all loads will "fix" it. So will adding an aux load with an older generator with a mechanical governor. Before we bought the Honda generator I can't remember the exact settings I used on the stacked 4024's with the EcoGen to "fix" it or minimize it. If it's relevant, I probably got them wrote down in the battery service logs someplace and could look them up.

Edit:
It wasn't hard to find leafing thru my battery logs from June 2011. AC2 amps 25, charger amps 25. Actual measured gen load amps 23-28. Left AC2 input amps 25, set charger amps 22 per inverter. Actual measured gen load 20-25 amps per inverter with the new setting.
--
Chris

Mangas · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

Chris, exactly right.

You zeroed in one of the biggest contributing factor's in my case. My older generator had a slow mechanical governor. It failed once but the replacement part didn't fix the problem. The new and larger Cummins Onan has an electronic governor and it did fix the problem.

Good to hear about the XWs' durability. Do you think I'll get 10 years out of the SWs'? I'd like to keep them a couple more years. I believe the XWs' have a smoother (my term) sine too.

Blackcherry04 · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

I don't know the age, I have had older Kohler's from the 90's in the that 10-15 KWH range in the Marine environment that had the electronic governors on linear stepper motor in the early days. As long load is constant they were fine, anything on then that has a pulsed power demand, they all hunted. You can fiddle with the gain control till your blue in the face, just a wasted effort. If it uses a RPM sensor on the flywheel, pull it and clean it. They get metal shavings off the ring gear on them and that will throw them off, Also check the gap from the flywheel. Fuel, plugs, spark advance, all play into them.

Believe it or not, sometimes the old fly ball governors can be better to work with, but they do go bad to.

ChrisOlson · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

I don't know that those SW Plus inverters will ever die. After the complete collapse of civilization as we know it, they'll probably be the only thing still left working. They're a tank, and short of running over one with a D9 Cat or zapping it with lightning, I don't know how you could break one.

Mangas wrote: »

I believe the XWs' have a smoother (my term) sine too.

Yes, the XW's output is noticeably cleaner than the SW Plus. Tighter regulation on output voltage too. And more surge and overload capacity. With a 120V inverter at 6,000 watts load all 50 amps has to flow thru one 6 AWG wire coming out of the inverter, and back thru the neutral. With 6,000 watts load on a split-phase inverter you only carry 25 amps on a 6 AWG wire. So the split-phase is more efficient and runs cooler too. With my clamp-on meters here I've measured up to 5% in improvement in power efficiency with the XW vs the SW Plus at lighter loads, and 2-3% at heavy load.
--
Chris

Vic · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

My expeirence is a bit different.

CURRENT regultion seems to be much smoother than is VOLTAGE regulation. When the 5548SW+ es regulte current, before target voltage is reached, much smoother than when the target V is reached. But, all seems to rest on the ability of a genset to accommodate these changes.

Reducing the Charger's AC current setting will also help, but slow the charging process.

Here, the down-stream loads on the Inverter outputs are usually small, but in the Summer, often run the power room A/C during genset charging. This 500 W load seems to have no effect on system dynamics.

In running the second system, using a Kohler 18 Kw genset, the performance is identical to the system with the Diesel genset -- neither are bothered at all during Bulk, of when Bulk target V reached. These two systems are completely independant.

A neighbor has stacked 5548 SWs, and ran it on a Honda 11/10 Kw genset for many years. Believe that he was charging at or very close to the MAX DC current and I have seen no genset hunting (when I was dispatched to recharge from genset), and he has not reproted it as an issue. This Honda was the V-twin powered job.

So, IMHO, the issue may well revolve around the capabilities of the genset and its regulation, and perhaps running very close to its max available output due to other loads, altitude, etc.

It is good to hear that the XW inverter behaves well. It HAS seemed that the way the SW regulates (voltage IMHO) is a bit gross. Will run a test in a month or so, when it comes time to exercise one of the system's gensets.

YMMV, Good Luck, Vic

John Sullivan · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

Chris
Thanks for the info. I will try adding an aux load. Am I right in understanding that the aux load should be applied prior to the feed to the inverters?

We have taken to not operaing loads like washers and dryers with timers when the generator is on as they dont like the surging. It would be nice to find a solution without a major system reconfiguration as the inverters seem quite solid.

Any thoughts on the impac of installing a transformer prior to the inverters? This could provide the additional benefit of balancing each leg although currently the system seems well ballanced..........John

ChrisOlson · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

Vic wrote: »

It is good to hear that the XW inverter behaves well. It HAS seemed that the way the SW regulates (voltage IMHO) is a bit gross.

What I've seen with the SW Plus for voltage regulation is that it will actually backfeed the genset and attempt to motor the gen head. That used to kick the breaker out on our Champion 46538 backup unit sometimes.
--
Chris

Vic · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

YES! Chris, that was what I mentioned in a previous post in this thread. This regualtion strategy may work OK for charging from the grid, but takes a genset with an 'attitude' to accommodate this "feature" of the SW series. Vic

ChrisOlson · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

John Sullivan wrote: »

Any thoughts on the impac of installing a transformer prior to the inverters? This could provide the additional benefit of balancing each leg although currently the system seems well ballanced..........John

We had a Trace T240 on the output of our stacked 4024's (balance both inverter and gen loads) and it helped a lot. IMHO, I wouldn't run series stacked inverters without it. With parallel stacked inverters I don't think you'd need it.

We got a Outback PSX-240 on the output of our XW6048. While the XW handles leg imbalances with no issues, without the transformer it would kill our little 4 kVA generator.

John Sullivan wrote: »

Thanks for the info. I will try adding an aux load. Am I right in understanding that the aux load should be applied prior to the feed to the inverters?

I don't think it's necessary to add it before. It won't start the "hunting" until the generator gets pretty heavily loaded. You can't plug the load into the generator itself - it has to be applied to the pass-thru loads to get the SW to dial down the charger a bit and realize that it might be overloading the gen. It took about 1 kW load here to smooth it out, which "steals" some from charging but not a lot with a big genset. If you got the SW you can use the AUX output to activate a load automatically (we used water heating), or with the SW Plus use the ALM module. Or you can turn something on manually too. But it can't be a varying load like a washer. A nice steady load like a water heater element works wonders so the SW "sees" a nice steady draw on the AC pass-thru that's heavy enough to get it to dial the charger down a bit.

That was my experience with it.
--
Chris

John Sullivan · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

Spent an interesting couple of hours this afternoon trying different load application and inverter/charger settings. On my system the "hunting" occurs when the generator is very lightly loaded as well as when it is heavily loaded. I pushed the settings up to AC input 40amps per inverter, set max charge amps at 35 and added load until the generator struggled. Then I worked my way down on the settings and load to AC input 30 amps and max charge amps at 10. The hunting/surging issue never went away with any of the setting changes. I also applied a resistance load while AC input setting at 30 amps and max charge at 30 amps to force the charger to back off the charging amps which it did without issue however the hunting/surging never went away. I also tried some settings with the max charge amps set higher than the AC input amps which resulted in the AC input setting controlling the charge rate. Not sure what I learned except that none of what I tried had any affect..........john

BB. · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

Is this a mechanical or electronic governor? Does the genset surge when the charger is turned off?

-Bill

ChrisOlson · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

It sounds like the governor on your genset is REALLY slow. Any chance you got a backup genset to try?
--
Chris

John Sullivan · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

It's an electronic governor. The genset does not surge with the charger off.........John

John Sullivan · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

I also have an older Kohler 20 KW generator for a backup. It does the same thing to both generators.........John

ChrisOlson · April 2013

Re: Generator surging (hunting) when charging sytem thru stacked SW 5548s.

You've tried everything I did here to minimize it. Unfortunately, it is a characteristic of those inverters. I never got it perfect, but I got it close enough so it was not an issue. It was worse with our EcoGen than it was with the Honda generator too. The EcoGen (with electronic throttle) would vary from 58 to 61 Hz. The Honda held freq at exactly 60 Hz but the sound the generator made as it loaded/unloaded was a bit disconcerting sometimes - I'd say it's about two second or so "swings".

So anyway, I know what you're talking about - BTDT. But short of upgrading to XW inverter(s) I don't know what more to tell you to "fix" it.
--
Chris

Generator surging (hunting) when charging sytem thru stacked SW 5548s.

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