Matt,
I don't have a lot of experience with undersized generators for the application, but I will share some thoughts about my recent experience.
Having 3 VFX 3648 on a 12 kw Kohler, the math said I shouldn't have difficulty getting 7 kw total charge current which would put 135 amps into the battery.
My experience said the imbalanced load of 2 VFX on one leg and 1 on the other may cause problems. To address that issue I installed an autoformer.
The best compromise/solution so far is one VFX on each leg dialed back to 15 amps maximum charge current. This gives 3.6kw total charge current or about 70 amps ~52 volts. The third VFX (master) is programmed at 0 charge but maximum ac. It's only job is to invert or pass through. The two slaves don't have to worry about adjusting for loads, just charging.
Why can't we get more power? Switching power supplies in the chargers that create harmonics not readable by your standard amp meter, and that inherently, chargers seem to use only a portion of the sine wave presented to them. Harmonics of several orders induce current into the line and the windings of a generator. Some breakers are also susceptible.
In my case, a 70 amp breaker is tripping after a period of time with less than 8kw of charger. I have not yet scoped the line but I suspect the other 50-60% of load is harmonics.
Possible solution: I have found some power correction capacitors (600 Kvar @ 480, should give me 300 Kvar @ 240) that I'm going to put in a box and hang on the wall next to the VFX's. The VFX's will get scared and stop doing that! No, seriously, I'll wire the capacitor bank to the ac input busses of the FW 500 and they'll soak up a lot of the ripples that are trying to get back to the generator.
It may take a week or so to get back up there, but I'll let you know how it works.
Bruce Fiero-RMI
Willpower Electric LLC
-------- Original Message --------
Subject: [RE-wrenches] Outback Chargers
From: m...@solar-energy-solutions.com
Date: Mon, February 10, 2014 4:09 pm
To: "RE-wrenches" <re-wrenches@lists.re-wrenches.org>
Wrenches,
Based on Kevin's comments about Outback Chargers in the HUP thread I am
hopeful that some of you well-versed in the off grid world can assist.
Particularly I am curious if others can confirm deficiencies with Outback
chargers and suggest strategies for overcoming these deficiencies.
I currently have an off grid site with significant charging difficulty.
The site has been online around eight years with a quad VFX3648 stack.
Around six months ago the client began experiencing more generator issues
(he had certainly had occasional problems before but engine overruns
became almost a weekly occurrence which, considering the client is only
there on the weekends except during hunting season, is not good). The
client decided to buy a new generator based on a comment from Outback.
They suggested his old 15 kW Briggs with mechanical governor should have
the governor replaced with an electronic governor. This couldn't be done
so he bought a new GE 20 kW with electronic governor. The GE does not
work with the Outback chargers at all (sounds like immediate overrun) but
will run the home just fine (and pass-thru Outback with chargers off).
I am about at the point of asking the client to buy Iotas. However, we
have a Honda 6500 that has worked as a backup generator for this system
and that has worked for other Outback systems we have installed. The
Honda no longer works well with this Outback system (routinely disconnects
after a few minutes charging and won't charge more than a few amps per
port). Something has obviously changed for the Honda to no longer work
well and I am beginning to think that maybe I am missing something else.
We have checked grounding and switched around inverters to run off dual
stacks without any noticeable difference. The client has tried three
separate generators at this point and none work very well. After eight
years the batteries aren't in great shape but they hold a charge and
should be capable of more years of service (Surrette YS). Outback tech
support seems willing to listen and empathize but incapable of helping me
identify the issue.
Any advice is welcome.
Thanks,
Matt
Matthew Partymiller
Solar Energy Solutions LLC
(859) 312-7456
m...@solar-energy-solutions.com
> "Has anybody scoped ac line to VFX's under full charge load? I'm curious
> about harmonics possibly being the culprit "
>
> Yes, it's pretty nasty. This is why we stopped using Outback products for
> off-grid sites with significant use of generator charging. Not only are
> the chargers really wimpy, we found all manner of harmonics caused by the
> charger circuit. Loads ran fine on inverter; fine on generator but would
> not run at all or reliably with gen running in charge mode.
>
> It took some time to figure this out. Ended up having to tear out several
> new outback systems & replace with another brand to keep customers happy.
>
> What we have done successfully for sites where the customer doesn't want
> to replace the Outback is install a bank of external battery chargers, ie
> the Iota DLS series and use those for gen charging purposes only.
> Sub-optimal in a lot of respects but that's what happens when a client
> buys hardware and says "make it all work". A DC genset would be way more
> efficient.
>
> Another thought have you tried another breaker on the gen? Weak breakers
> do happen, have seen that on brand new gensets.
>
> Kevin
>
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