more MX60 / generator charging [RE-wrenches]

Darryl Thayer daryl_solar at yahoo.com
Fri Apr 21 21:54:29 PDT 2006


Hi
I would like to reinforce what Chris said about the
small generator yet large loads.  The example where
the 1200 AH battery set is used, a large 7.5 Hp motor
is powered by a quad stack. the use of the large motor
is very intermittent, the small generator just needs
to recharge, during power outages, but the quad stack
has to be able to carry the big load.  If my memory is
correct the large motor drew 130 amps 240 volts surge
on start on the grid.  And 30 amps 240 volts running,
this is by memory.  

Also I was talking with a farmer, in a similar
situation, and he would like to use a larger
generator.  I had the idea to place two X240s with
rectifiers and two MX60s in hopes of handleing a 4kW
generator.  Just preliminary at this point.  
Have a nice day
Darryl

--- "Carl Emerson, Free Power Ltd."
<freepower at freepower.co.nz> wrote:

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> 
> Chris,
> 
> If the generator and the PV are both active will the
> MPPT not be confused ??
> 
> Carl Emerson
> Free Power Ltd.
> Auckland NZ
> 
> 
> 
> ========================================
> Yes - the same MX60 can be used to both step down
> the PV array and the 
> back-up generator.  If both sources are available at
> the same time than 
> the source with the higher DC voltage will provide
> the most power. 
> 
> Putting an additional diode "in series" with the PV
> array (i.e. in the 
> positive conductor) is not necessary as long as the
> DC voltage produced 
> by the rectified back-up generator does not exceed
> the open circuit 
> voltage of the PV array.  If it did - then current
> will flow "back" into 
> the PV array - which is probably not a good idea.  A
> series diode will 
> eliminate this from happening - it will not cause
> much power loss but is 
> an additional part and is not free...  So if you
> have a 48vdc PV array 
> or higher it should be OK.  
> 
> Using the X-240 autotransformer does work - I just
> have some concerns 
> about the possibility of a ground fault since most
> small AC generators 
> are internally bonded neutral-to-ground.  With an
> isolation transformer 
> this is eliminated.    
> 
> This is actually a very nice solution as the
> customer ends up having 
> their AC loads always powered from the clean,
> true-sinewave power of the 
> inverter while the generator is running.  They also
> can operate loads 
> larger than the generator's rating for short time
> periods (up to the 
> ability of the inverters).
> 
> Christopher Freitas
> OutBack Power Systems, Inc.
> cfreitas @ outbackpower.com  
> www.outbackpower.com
> Arlington WA USA
> Tel 360 435 6030  
> 
> 
> kirk at vtsolar.com wrote:
> > 
> > Thanks Darryl.
> > 
> > From your experience, it looks like the pv &
> generator/xformer/rectifier
> > output can be paralleled. I don't understand the
> "rectifier in 
> > series with the PV", though.
> > 
> > Kirk Herander
> > Vermont Solar Engineering
> > 802.863.1202
> > fax 802.863-7908
> > NABCEP(tm) Certified Solar PV Installer
> > Xantrex Certified Dealer Charter Member
> > NYSERDA-eligible installer
> > VT Solar and Wind Partner
> > 
> > 
> > -----Original Message-----
> > From: Darryl Thayer [mailto:daryl_solar at yahoo.com]
> 
> > Sent: Wednesday, April 19, 2006 7:11 PM
> > To: RE-wrenches at topica.com
> > Subject: Re: more MX60 / generator charging
> [RE-wrenches]
> > 
> > HI Kirk
> > I have done two such and it looks like I might do
> a
> > third. In both my cases the generators are small,
> 1.8
> > to 2.2 kW, the third one I might do is also small,
> > less than 3 kW for sure, perhaps a 2 kW. ( the
> owner
> > has not purchased as yet) In my case it is just
> for
> > emergency recharge of the battery set.  One
> battery
> > set is 48 volt 1200 AH and the second is 48 volt
> 400
> > AH.  The third one will be a 48 volt string of
> L16s
> > (about 400 AH). 
> > 
> > I have used the Outback X240 and put the 120 volt
> > generator into the 240 volt side and taken 60
> volts
> > out of the 120 volt side.  So I did not use a
> > isolation transformer.  (Chris used an isolation
> > transformer)
> > 
> > I have had no problems with either setup.  I set
> the
> > max MX 60 charge rate to limit the generator
> current
> > to values the generator can handle.  The 2.2 kW is
> set
> > up with a 1.2 kW PV array in parallel with the
> > generator-transformer-rectifier circuit.  I placed
> a
> > rectifier in series with the PV array also, but I
> am
> > not sure that I needed to.  I had to set the MX
> limit
> > for the generator to about 1.8-1.6 kW (I do not
> > remember the exact amount).  The generator seemed
> as
> > if it could not handle full rating.  Also the MX
> 60 at
> > times seemed to squel slightly ( a high pitch
> maybe
> > 3000 hz).  Both systems have functioned as
> expected. 
> > If perchance the generator and the PV were to
> operate
> > at the same time the load on the generator would
> be
> > reduced.
> > Darryl
> > 
> > --- Kirk Herander <kirk at vtsolar.com> wrote:
> > > Chris F.,
> > > 
> > > You mentioned that the MX60 could be used for
> both
> > > PV and generator
> > > charging. I'm wondering if the output of the
> > > rectifier can be paralleled
> > > with the PV inputs without causing harm - due to
> > > overloading the MX60 or
> > > just in general - or if some switching is
> necessary
> > > to isolate the array
> > > when the generator is charging through the
> > > transformer/rectifier/mx60.
> > > 
> > > And I assume generator charging through the MX60
> > > voids its warranty,
> > > right?
> > > 
> > > 
> > > 
> > > "We have also played around with the MX60 and a
> > > isolation transformer 
> > > with rectifier - and it does work pretty well -
> just
> > > keep in mind that 
> > > its limited to around 800 watts at 12vdc, 1600W
> at
> > > 24vdc and 3200W at 48
> > > 
> > > vdc.  
> > > 
> > > You can also use the same MX60 controller for
> the PV
> > > array if the 
> > > back-up generator is only used at night or
> during
> > > poor weather 
> > > conditions (which is almost always the case).  
> > > 
> > > This solves a couple of problems - such as poor
> > > quality generator 
> > > waveform and the grounded-neutral of nearly all
> > > portable generators.
> > > 
> > > Using the MX60 allows the charging process to be
> 
=== message truncated ===


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