more MX60 / generator charging [RE-wrenches]

Carl Emerson, Free Power Ltd. freepower at freepower.co.nz
Fri Apr 21 20:54:52 PDT 2006


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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
> > coordinated with the 
> > rest of the system - such as EQ and temp
> > compensation control.  You also
> > 
> > get the metering functions as well displayed on the
> > MATE.  
> > 
> > You will not find a charger which offers three stage
> > charging and 
> > metering for anywhere near the price of a MX60 and a
> > isolation 
> > transformer."    
> > 
>  

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