[RE-wrenches] Outback Chargers

Wed Feb 12 09:41:20 PST 2014

Hello Esteemed Wrenches,

First, I apologize for the delayed reply. There are lots of great replies and a lot of good information in this email thread and everyone’s suggestions will help to remedy the problem.

One piece of information that might be crucial to get the overall sense of the installation is that the system that Bruce is working on has a 1.5kW load. The system has resistive loads as well as several small pumps. If we also consider that, when charging, the inverters are essentially full wave bridge rectifiers than we will have to take into account the displacement power factor and the distortion power factor of the system. Typically, single phase generators are rated at a power factor of 1, so his 120/240V-12kW generator is able to source up 50A per phase with a load that has a power factor of unity.

If we also take into account that we typically do not want to load a generator beyond 80% of its capacity, and account for power factor and sea level then we would have to significantly derate the generator. Following that logic, and assuming a total power factor of 80%, would mean that he can only load the generator with a 7.68kW load (7.68kW = 12kW x .8 (derate) x .8 (TPF)). This would translate to a current of 32A per phase. However, since his loads are already consuming 1.5kW (6.25A), he would end up with an available current of 25.75A from the generator.

Admittedly, inverters have a tough time with generators because of the way their synchronous clock and electronic speed control react to load disturbances. The inverters try their best to keep up with the constant shifting of the AC signal from the generator, and sometimes they are not successful. This is true of any power conversion system that is fed from a generator. Having inductive loads (however small) and having non-linear loads does not help the situation.

While charging, the VFX3648 inverters are essentially full wave bridge rectifiers and the master does not control the slaves. Each slave will follow its own charge parameters like the Grid input AC limit (in Amps) to limit the overall AC current that goes into the inverter,  and  the Charger AC limit (in Amps) to limit the AC current that goes into charging and the DC voltage set points. In that sense, each inverter simply becomes a current source. The actual amount of DC current that the inverters can source to the batteries depends on the AC source as well as the battery voltage.

Adding capacitors to improve the power factor will help while the inductive loads are on, but will also introduce a leading power factor when the inductive loads are removed and that has its own set of problems. The best and probably cheapest approach to obtain more charge current would be to use a load transfer switch to remove some of the inductive loads from the generator while charging. This will not only improve the power factor but will also reduce the load current on the generator.

As for the breaker tripping, I will work with Bruce to run a controlled test to find out why the breaker was tripping.

Best Regards,

Ronald Paredes
Manager, Product Quality and Test Engineering
OutBack Power Technologies
17825 59th Ave NE, Suite B, Arlington, WA 98223
360.618.4316 direct | 425.903.0680 mobile
www.outbackpower.com<http://www.outbackpower.com>
[Description: Outback-Power-color-TAG-2010]

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of bruce at willpowerelect.com
Sent: Wednesday, February 12, 2014 8:53 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Outback Chargers

Steve,
Good reminders and very practical. I realize that the core of my frustration was in attempting to get a full charge on a recently watered battery that had a huge capacity for charge current, with an undersized generator that was carrying running load plus the occasional chopsaws from other trades on the job. An impossible environment for making sensitive adjustments. More fine tuning to come...

Bruce Fiero-RMI

[cid:image003.jpg at 01CF27D6.95BA4190]

Willpower Electric LLC

-------- Original Message --------
Subject: Re: [RE-wrenches] Outback Chargers
From: Steve Higgins <steve at surrette.com<mailto:steve at surrette.com>>
Date: Tue, February 11, 2014 7:59 am
To: RE-wrenches <re-wrenches at lists.re-wrenches.org<mailto:re-wrenches at lists.re-wrenches.org>>

Hey guys,

The FX's have always been rough to generator waveforms, back some 9-10 years ago there was a case in Alaska that identified that they (FX's) don't play well with capacitive coupled regulators.  We brought in several generators and the guys in engineering worked on a fix but never found one other than a $500.00 dollar tank circuit filter that most of the time didn't work.

At that point anything with a capacitive coupled regulator would have to be backed way off, and would cause a really nasty flicker of the Lights/loads when the inverter was charging the battery bank.

Electronically regulated regulators work better, but the way the inverter measures ac input amperage can also be way off.  I've seen the metering display 7 amps when indeed the actual current pull was closer to 10-11 amps.   This is most often the cause of the mystery breaker tripping.

One of the things I always did that worked pretty well was.

Turn the charge rates down to zero.

Start the Genset, wait till connection.

Edge the charge rates up 1 amp at a time to see how much the genset can handle.

I've usually found that at about 60-70% of the rated current is where the sweet spot is.

Another issue that I've seen come up affect multiple stacks of inverters regardless of their manufacture.  Most inverter/chargers in this market are Voltage Controlled chargers.  This means that current follows voltage, if voltage is low then current is high... once voltage get to say Absorb voltage the combination of the inverter seeing the absorb voltage and the battery no longer is accepting max current the amount of current flowing drastically drops.   This tends to drive customers/installers crazy on how to maximize the amount of current flowing into the battery.  Remember, once you get past the Bulk Charging stage you cannot force current into a battery, it's only going to accept what it can.

A secondary issue to this is when you have multiple chargers connected to the same battery bank. Very often if you have a quad stack of Outback's you will see on or two inverters charging while the rest of the inverters are sleeping, this is normal as nobody's products to my knowledge share charging information that will equally divide charging current between the sources.

Just something else to chew on.... Altitude will also affect how well the generator operates, as the higher you go the thinner the air the less efficiently the fuel burns.

Steve Higgins

Technical Services Manager

P: 800.681.9914

M: 206.790.5840

F: 902.597.8447

Surrette Battery Company

http://www.rollsbattery.com

Steve Higgins

Technical Services Manager

M: +1.206.790.5840

F: +1.902.597.8447

Surrette Battery Company

Exclusive manufacturer of

________________________________________

From: re-wrenches-bounces at lists.re-wrenches.org<mailto:re-wrenches-bounces at lists.re-wrenches.org> [re-wrenches-bounces at lists.re-wrenches.org] on behalf of Doug Wells [dwells at thesolarspecialists.com]

Sent: Tuesday, February 11, 2014 11:03 AM

To: RE-wrenches

Subject: Re: [RE-wrenches] Outback Chargers

Kevin,

I am curious about what you are seeing on the Outbacks as well.

Have dozens of these out in the field.  They have been pretty reliable for me.

The biggest issue that I have had with them is when the inverters are transferring from generator charging back to inversion.

If you leave this at the factory default, 1 s, you will see light flicker, and sensitive electronics will go into error.

This transfer rate can be adjusted down and has cured most of the power quality issues with the battery charging.

A different issue than harmonics under load, but it might help.

Doug Wells

The Solar Specialists

Morrisville, VT 05661

(p) 802-223-7014

(c) 802-498-5856

www.thesolarspecialists.com<http://www.thesolarspecialists.com>

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