MX60 Max Array Voltage? [RE-wrenches]

Tue Jul 1 12:21:58 PDT 2003

Bill Brooks wrote:
> I think in the near term you have a listing issue since it is not listed 
> to 140 volts yet.

Correct - the MX60 is not listed for open circuit voltages over 120VDC 
at this time.  We are planning to relist it at the higher voltage soon. 

The problem is that the circuit breakers we are using with the PSDC 
enclosures and PV-GFP are rated for only 125 vdc.  So we need to address 
this as well before we have a complete solution for the higher voltage 
PV arrays.  Unfortunately - the UL standard requires a minimum of 5000 
amps of interrupt current at 125 vdc for our UL508 approval - even 
though the battery is 48 vdc and the PV array is a current limited power 
source.  We are trying to see if an additional supplementary rating on 
the breakers specifically for use with PV arrays might be a solution.   

> Also, the argument that sunlight and cold don't happen together is not 
> correct. The case in point is a winter cold front that moves through 
> where the array goes from low irradiance and very low temperatures, to 
> very high irradiance (even cloud edge effect) still at very low 
> temperatures at 11:00 am (snow reflectance is another problem in some 
> areas of the country).

The PV open circuit voltage is dependent primarily on the temperature of 
the PV cell itself - increased irradiation due to edge of cloud or snow 
reflection does not increase the open circuit voltage in my experience. 
The PV cells get warm quickly when hit with high levels of irradiance.  

> Breakdown of components can happen in a seconds or minutes--about the 
> time it takes the array to heat up and lower its voltage. 

The MX60 stays off if the PV open circuit voltage exceeds 140 VDC.  This 
helps prevent damage.  The transistors also self protect themselves to a 
degree - they "zener" the PV array to a degree - pulling down the open 
circuit voltage a bit.  So its a battle between the capability of the 
MOSFETs versus the amount of power the PV can produce near its open 
circuit voltage limit... 

> Ultimately it is Outback's call on whether they feel comfortable with 
> this situation if they increase their listed maximum voltage, but using 
> the NEC table 690.7 is the safest bet for not applying too much voltage 
> to your equipment. (42.8V x 3 x 1.25 = 160.5 Volts)

I agree that that is the safest bet - but there are those who want to 
push it a bit and we are trying to walk the fine line between advancing 
the product and not getting people mad at us...  

Christopher Freitas
OutBack Power Systems, Inc.
cfreitas at outbackpower.com  www.outbackpower.com
Tel 360 435 6030  Arlington WA USA

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com
==^================================================================
This email was sent to: michael_welch at sbcglobal.net

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

TOPICA - Start your own email discussion group. FREE!
http://www.topica.com/partner/tag02/create/index2.html
==^================================================================