[RE-wrenches] Surrette Battery Question

[Allan Sindelar]

Jay,
You're right about leaving off the post at the bottom - whoops. It's at the
bottom here.
 
About voltage drop: I meant only that by running the array at a higher
voltage than the batteries, there could never be sufficient hot-weather and
undersized-wire voltage drop to prevent the array from exceeding the EQ
voltage of the batteries. This is most often a potential problem with 12V
systems. I mentioned it only to eliminate it as a possible cause of this
situation.
 
The Surrette Tech Bulletin 614 is available for download at
http://surrette.com/files/BU-RS-614.pdf. My understanding is that this
bulletin is the direct result of the complaints on this list about two years
ago about Surrette battery performance and life. 
 
Allan
 
-----Original Message-----
From: jay peltz [mailto:jay at asis.com] 
Sent: Sunday, August 03, 2008 1:41 PM
To: Allan Sindelar
Subject: Fwd: [RE-wrenches] Surrette Battery Question


HI Allan, 


You mention about a Surrette tech bulletin, I can't seem to find it? Can you
tell me where it might be on their site?

Also I"m curious about you saying that hot modules isn't going to affect
voltage drop.
Sure it will.  If the wire is upsized for the lower voltages from hot
weather, then you've compensated for it, but there is still added voltage
drop.

And about the adding new panels to old? I didn't see the link/post at the
bottom?
 Thanks, jay 
 
OK, the story,
This client had started off-grid in the early nineties with a tight budget.
He and his wife would add modules as they could afford them, usually used.
The built a homemade tracker with a Wattsun SA controller and two linear
actuators, using a DPDT momentary switch to adjust elevation seasonally.
Over time the tracker filled out with eight Arco 16-2000s, nine Carrizo
(Arco) M52L 5V Quad-Lams, two BP 275s, and two old square whatsises with 2"
cells from the seventies. 
 
Eventually their income increased and their house and house loads got
bigger. They asked us to upgrade their array, which eventually led to the 8
160W modules I added on a pole-top array. There were several catches,
though:
1. They wanted to keep as much as possible of the original "democracy
tracker" in operation;
2. The house had grown over the years, and the existing tracker had to be
moved 50' farther away;
3. The balance-of-system was still in the original basement, now
inaccessible from the outside, as the house had been expanded bit by bit in
all directions. 
4. The #2 (or 2/0, I can't recall) USE copper array input wires had been
built over and couldn't be replaced; we had to use them.
 
We dismantled the tracker and moved the pole (yep, lifted pole, concrete and
all and set it in a new, larger hole with more concrete). We put a 3R j-box
where the old pole had been and trenched to the new locations. After playing
with different calculations, we changed the old tracked array as follows: 
1. We added two BP 380s (the closest we could get then to the older 275s)
and wired them as one 48V string;
2. We dumped the whatsises, which had low output;
3. Now I'm trying to remember: I think I wired the four 16-2000s (originally
2.2A at 12V) in parallel, then wired this set of four in series with the
nine Quad-Lams (think of M52Ls, originally used in the Carrisa Plains
utility central power plant in California from 1984-1989 or so, as similar
to 16-2000s but with the 3 rows of cells wired in parallel, to make about 7A
at 4 1/2V nominal. That's why they're called Quad-Lams: it took four in
series to charge a 12V battery). 
 
So we ended up with a 17-module array wired at 48V nominal, tied in with the
new 48V array. What made it so special, other than that it's the only
17-module array I ever built? When we were all done and it was charging the
24V battery through the MX60, I alternately turned each array off and let
the MX60 find its MPPT voltage: the two arrays were within one volt of each
other. We got it right, and I have always been especially pleased with that
job.
 
That's all. 
 
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