GTFX 3048 [RE-wrenches]

[Darryl Thayer]

Hi Keith
Ihave heard three reasons.  
first when the battery voltage gets low and a high
surge occurs the current is higher due to both the
battery voltage andthe surge.  (However this is not a
continous current situation and does not need to be
considered in wire rating)

The current to an inverter is in very short pulses
with the instanous current much higher than the
average current.  Heating in a wire is I^2*R, with the
current being in short pulses the heating effect is
higher.  (for example if the duty cycle was 50% and
the actual current would be 2 times the average.  The
heating would be 4 times greater for half the time or
twice the heating for average current)

The third thing I have heard is because the current is
drawn in short pulses with very fast transitions the
inductance is very important.  Larger wire has less
inductance also shorter wire has less inductance.  I
always run my DC inverter leads together back to the
battery to keep inductance to a minimum.  

BTW my 12 inverter system and my 5 inverter system run
on #4 and I have never noticed a heating effect onthe
wires.  Also in regards to tripping, the above systems
are set to the same sell voltage and I never triped a
breaker.  But please do not do as I do.  

Darryl

--- Keith Cronin <kcronin at islandenergy.net> wrote:

> 
> 
> Hello 
> 
>  
> 
> I am trying to understand something. In the GTFX
> manual, it states, we need
> to wire it with 2/0 from the inverter to the big bus
> (about 3' of cable),
> but the highest DC current on the 3048 is 70 amps. I
> recognize the max DC
> input is 150 amps, but we will not hit that with
> this setup. Is this why the
> 2/0 is spec'd?
> 
>  
> 
> A # 1 Thhn is good for 130 amps, per the NEC-
> 310-16, and I know that
> battery cable/marine types have more conductors, per
> circ. mil, so, can
> someone educate me?
> 
>  
> 
> We have 4- 3048's, 4-100 amp dc breakers, 3 MX60's,
> 12-8D batteries on a
> 10.5kW system. 
> 
>  
> 
> So, are we safeguarding against high short term
> current surges?
> 
>  
> 
> We did initially experience the 100 amp breakers
> trip, but I think that was
> because we had both sets of inverters on the same
> sell voltage and amperage.
> We adjusted the sell amps for each set differently
> as well as sell on grid
> battery voltage. This has resolved this situation to
> our satisfaction and I
> think was the contributor to the cascading effect of
> all of the inverters
> trying to sell their maximum ability and when they
> failed (tripped) the next
> inverter was instructed to do the same, per se.
> 
>  
> 
>  
> 
>  
> 
> Keith Cronin
> 
> President
> 
> Island Energy Solutions Inc
> 
> 270 Kuulei Rd. Suite 106
> 
> Kailua, HI 96734
> 
> Electrical Lic C-25221
> 
> 808-262-3268 Tel
> 
> 808-263-0338 Fax
> 
> kcronin at islandenergy.net
> 
> www.islandenergy.net
> 
>  
> 
>  
> 
> 
> [Non-text portions of this message have been
> removed]
> 
> 
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> 


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