We'd need more info to figure this out.
1) Wire Size
2) Type of charge controller C 60 or new MPPT model
3) use a clamp on meter to measure actual current
4) measure voltage drop across the breaker.
This very well could just be a loose connection at the breaker either
the cable side of the breaker, or where it snaps on to the buss bar.
I've had QOs not work at higher voltage DC. (over 50 v) I'd have to
wiggle the breaker to get good contact on the buss, and it would start
working again. Given the age of the system, there's probably some
corrosion and dust on the contact points. Might just need some sanding/
filing.
The heat described fits with a loose/ high resistance connection.
Switching to a Midnite/ Outback breaker would be the only real way to
reliably make sure it doesn't keep happening though. On old systems,
our job is to exorcise the ghosts from the machine.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 7/9/2013 9:10 AM, jay peltz wrote:
Hi Dan
I'm guessing the wire can handle the 100 amp if they are already
running 60a.
I've had QO breakers go bad, even ones not tortured like that one.
The derate is interesting as it has to do with less atoms of air per
volume. Less air, equals less cooling
Jay
Peltz power
Sent from my iPad
On Jul 8, 2013, at 10:07 PM, Dan Fink <danbo...@gmail.com
<mailto:danbo...@gmail.com>> wrote:
Esteemed Wrenches;
A weird troubleshooting call today for my business partner DanB. I
wish I had been along if only for shock and awe and lessons learned.
A nicely installed vintage 12VDC PV system that someone else designed
and installed over 10 years ago, we replaced a dead/frozen battery
bank a month ago. DanB went back today because customer reported low
battery bank voltage.
He found the PV input breaker tripped, a Square D QO 2-pole 60 amp.
About 600 watts of PV 12vdc nominal on the roof. Reset the breaker,
and a few minutes later it was too hot to touch.
So our working theory -- the 60a QO on *DC* has a 1.2x ampacity
derate, which puts 600w PV right at 60 amps instead of 50. There's
also a bit of a high altitude derate, which I don't understand at
all. And during the battery disaster last year bank voltage was
certainly 11vdc or less, and was a bit over 11vdc on DanB's arrival
since the PV had not been charging. That puts us at possibly 65.5
amps. The breaker was maybe just doing its job correctly, though the
heat was disturbing I am told.Or maybe it got damaged during the
battery disaster......both + and - were connected thru the 2 poles.
In any case, our question --- due to my fuzzy memory and poor
shopping skills, we have a 100 amp QO 2 pole breaker in stock that
needs a home, and it'll plug right in. I have a nice tech bulletin
from Schneider Electric about DC ratings of their breakers that
doesn't show that a 100a QO 2 pole even exists, and a Schneider FAQ
that says it'll work fine:
http://www.schneider-electric.us/sites/us/en/support/faq/faq_main.page?page=content&country=US&lang=en&id=FA125383&redirect=true
Any advice on this? We'd sure love to just drop by and pop in the new
100a amp QO breaker instead of installing a whole new DC rated
Midnite box. But we don't want to leave a fire hazard either. With 15
years service on our local volunteer fire department, It would be
rather embarrassing if a "fix" we made to this old off-grid system
caused a fire. ;-) We are aware of the 5k AIR issue with these
breakers, but the battery bank is small enough I don't think it's
quite up there, and information on AIR interruption from battery
manufacturers is hard to find......and of course it's a weird curve.
Thanks in advance;
Dan Fink,
Executive Director;
Otherpower
Buckville Energy Consulting
Buckville Publications LLC
NABCEP / IREC accredited Continuing Education Providers
970.672.4342
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