DC load on PV side [RE-wrenches]

[matthew tritt]

Yo sunwise,

It's interesting that Todd was the only respondent to your question. Maybe
most wrenches are just in it for the grid connect topics? I sure hope not.
Maybe everybody on the list is at the MWREF? Except us, that is.

This is an interesting question but maybe the answer is to keep all the DC
loads on the load side of the controller? That way all those sensitive
goodies won't get clobbered and fried (as fast).

I just went through a "thing" with an ETA pump and a Wattsun tracker (which
could have been avoided by actually reading the instructions from Dankoff!);
every time the tracker motor started the pump stopped. There was seemingly
plenty of extra Wattage to go around, but the ETA controller didn't like the
action one bit. I also ran a circuit from the batteries (a twelve volt bank
with a DC/DC converter) to the tracker, which is something I usually do
anyway, but the previous Sunrise pump ran fine (until it broke of course)
with the array powered tracker. Who knew?

This is why Dankoff is selling their "ETA Track" system with a passive
tracker.

Matt T
----- Original Message ----- 
From: "sunwise" <sunwise at cheqnet.net>
To: <RE-wrenches at topica.com>
Sent: Tuesday, June 17, 2003 9:52 PM
Subject: DC load on PV side [RE-wrenches]


> Wrenches,
>
> It's late and my mind's getting muddy.  Let's see if I can explain this
> right.
>
> If thru some specific control situation (issue), something like a DC
> attic fan (or water pump) ended up operating off the PV side of a
> battery based PV system with charge control, and assuming the array was
> oversized to the fan load by say 2 or 3 hundred percent......
>
> 1) Would it screw up the various CC's we use in their normal operations?
>
> 2) It would seem that systems with a series regulator would see pretty
> much OCV any time the CC was regulating (on=BV off=PV).  I'm thinking we
> would also see gradually escalating fan voltage over that of battery
> voltage with PWM CCs as the normal solar day advanced?
>
> 3) MPPT systems would have the fans seeing MPPT voltage until CC started
> to regulate and then move up towards OCV?
>
> 4) What about adding to the DC side of a battery-less grid-tie???
>
> 5) Why would anyone ask such questions?
>
> Thanks for any responses.  I may respond too after a good night's sleep.
>
> Kurt Nelson
>
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