[RE-wrenches] offgrid system question

Tue Aug 19 09:12:46 PDT 2008

Peter, that's a very good point.  There are laws of physics involved
with inverter design, and all products have a hard limit in ability to
process Volt-Amps.  One way inverter manufacturers can get higher
starting current is to allow the voltage to sag.  My old DR2424 could
start my 2hp 120v tablesaw, but it darned near turned off the lights in
doing so, the voltage dropped so low.

Unfortunately, there are no published specifications for voltage sag
that I've ever seen, other than some manufacturer provided comparison
curves used in various presentations.  Not exactly fair and unbiased, to
be sure.  Admittedly, the equipment needed to gather this type of data
is pretty spendy; not every wrench is going to have access to that type
of hardware, so we're somewhat at the mercy of the manufacturers.

We had the opportunity here in our training room to play with the major
products side-by-side this past fall, and looked specifically at voltage
regulation when under surge loads.  We focused on voltage stability in
unbalanced conditions - heavy surge loads on one phase, minimal loads on
the other.  Voltage measurements were via two Fluke 87's in Min/Max
mode, current via Techtronix digital scope, clamp meter input.  In
short, the XW had the best voltage regulation and highest surge
capability of the tested products, and the Magnum was impressive in its
ability to start loads well beyond its rated capacity but your client
better not be working on the computer when the well pump kicks on. 

Loaded phase

Unloaded phase

Loaded phase

Unloaded phase

Loaded phase

Unloaded phase

Loaded phase

Unloaded phase

XW6048

Dual VFX3648 OB Stacked

MS4448AE

Dual SW5548

Chopsaw alone

A peak

96 A

110 A

50 A

94 A

V max

122.4

123.2

124

127.2

128.8

132

124

124.8

V min

108.8

112.8

116

116

81.6

87.2

109.6

118.4

V Delta

13.6

10.4

8

11.2

47.2

44.8

2 Electric heaters (not metered), compressor, chopsaw, planer. 

A peak

127 A

128 A

88.5 A

Overload shutdown

V max

124.8

132.8

124

129.6

144.8

142.4

V min

99.2

105.6

97.6

105.6

60.8

72

V Delta

25.6

27.2

26.4

24

84

70.4

2 Electric heaters (not metered), 2 compressors, 2 routers, chopsaw,
planer.

A peak

133 A*

130 A*

93 A

Overload shutdown

V max

125.6

132.8

126.4

131.2

154.6

142.4

V min

96

103.2

92.8

102.4

59.2

70.4

V Delta

29.6

29.6

33.6

28.8

95.4

72

*Circuit breaker tripped

I'm hoping the above clip-n-paste from a spreadsheet transfers over in
this email, now that the Wrenches isn't limited by Topica plain text
format.  However, if this email shows up without numbers in the
paragraph above, please let me know and I'll re-send after re-typing.
:-(

Phil Undercuffler

Director, Battery-based and Off-grid

Conergy Sales & Systems, Americas

Our World Is Full of Energy

1730 Camino Carlos Rey Suite 103

Santa Fe, NM  87507

p.undercuffler at conergy.us <mailto:p.undercuffler at conergy.us> 

Direct | 505.216.3841

Toll Free | 888.396.6611 x4841

Fax | 505.473.3830

www.conergy.us <http://www.conergy.us/> 

________________________________

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Peter
Parrish
Sent: Tuesday, August 19, 2008 8:57 AM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] offgrid system question

I haven't been following this thread carefully, too busy, but my advise
is, don't focus on current capability alone. From Xantrex, find out the
"voltage compliance" as well. By that I mean, "What is the voltage at 52
amps output? Does it vary over time from 1 msec to 5 sec?" Any motor
will need both a voltage and current to operate properly, and they tend
to draw more and more current as the source (inverter) voltage drops. 

- Peter

Peter T. Parrish, President
California Solar Engineering, Inc.
peter.parrish at calsolareng.com 

________________________________

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Phil
Undercuffler
Sent: Tuesday, August 19, 2008 7:40 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] offgrid system question

The XW6048 is rated at 52 amps RMS line to line between 5 seconds down
to 1 millisecond, so if your client's AC has a starting inrush surge of
104 amps at 240v, then yep, I think your biggest problem is not enough
inverter.  Sounds like just one additional inverter will be marginal;
depending upon the additional background loads you may want to consider
expanding to three total.  I think Mick Abraham is right on here, in his
earlier post.

Phil Undercuffler

Director, Battery-based and Off-grid

Conergy Sales & Systems, Americas

Our World Is Full of Energy

1730 Camino Carlos Rey Suite 103

Santa Fe, NM  87507

p.undercuffler at conergy.us <mailto:p.undercuffler at conergy.us> 

Direct | 505.216.3841

Toll Free | 888.396.6611 x4841

Fax | 505.473.3830

www.conergy.us <http://www.conergy.us/> 

________________________________

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Max
Balchowsky
Sent: Tuesday, August 19, 2008 6:45 AM
To: mick at abrahamsolar.com; RE-wrenches
Subject: Re: [RE-wrenches] offgrid system question

You're right Mick, It is an XW 6048, there's only one and I really think
I'm going to find that the biggest problem is that there is not enough
inverter capacity capacity with just one unit (the scematic shows a 60
amp breaker on the output). The system is new ( installed within the
last 4 months and the batteries were new) The AC unit is 240 volt.....

Max Balchowsky

SEE Systems

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