[RE-wrenches] C-40 question

Brian Teitelbaum bteitelbaum at aeesolar.com
Wed Oct 24 15:49:31 PDT 2012


Allan,

Just to add to Larry's post, a 100W "12V nominal' module would put out about 5.9A, assuming that it's really a 100W module and has a Vmp of 17VDC. So 12 of them should be about 70-71A. The C-40 is not MPPT, so there is no amperage boost.

Luckily, the C-40 is actually rated for a max input of 63A (40A x 1.56 = 62.4A). Whoever designed that unit really did their homework (I can't say the same for the C-60). Assuming less than stellar DYI wiring and installation, as Larry suggested, may just have saved that unit from overload. I wonder what the wiring looks like at this point, since it's likely that he doesn't have the correct overcurrent protection device installed, if he has any OPD at all.

Sometimes, two wrongs do make a right...sort of.

Keeping the system at 12V and adding a second C-40 would be the cheapest alternative, but going to 24V would of course be better.

Funny you should mention that "7000W 12V" inverter. I just received a spec sheet for a "5000W with 10,000W surge" 12V inverter (from China) that a potential customer wants to get for use in third-world counties. Even at 5000W, that's over 400A at 12V, and certainly would be a higher amperage if the battery wasn't large enough to keep it's voltage up with a load like that. It's also more than 4/0 cable can safely handle. Lots of hokum still out there.

Brian Teitelbaum
AEE Solar

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Larry Crutcher, Starlight Solar Power Systems
Sent: Wednesday, October 24, 2012 3:11 PM
To: Allan at positiveenergysolar.com; RE-wrenches
Subject: Re: [RE-wrenches] C-40 question

Allan,

12 100 watt modules are more likely to be about 60-70 amps. With all the losses involved in a poorly designed DIY system (like most of them), I would expect to see more than 25% power loss. Perhaps that is why the controller lasted.

There is no current limiter in the C series controllers.

Great advice about upping to 24 volt. I can only imagine how many strings of batteries they must have at 12 volts. Egads!

Larry Crutcher
Starlight Solar Power Systems


On Oct 24, 2012, at 2:45 PM, Allan Sindelar wrote:

Wrenches,
Sometimes I encounter a situation that I have never encountered, simply because it's so far beyond normal limits that I would never try it to find out what would happen. Here's one.

A did-it-myself customer called me for batteries for his system. I learned he has a 12V system, with twelve 100 watt PV modules and a Xantrex C-40 controller. He has been using this for five years.

Twelve 100W modules is around 80-90 amps - double or more the C-40's capacity. Assuming that what he told was accurate, why is the C-40 still working? Is it current-limited internally?

By the way, since he had a 7,000 watt (yeah, right) 12V inverter from a truck stop, I encouraged him to buy a 24V inverter and rewire everything to 24V; then his C-40 would (just) work.

Thanks, Allan
--
Allan Sindelar
Allan at positiveenergysolar.com<mailto:Allan at positiveenergysolar.com>
NABCEP Certified Photovoltaic Installer
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder and Chief Technology Officer
Positive Energy, Inc.
3209 Richards Lane (note new address)
Santa Fe, New Mexico 87507
505 424-1112
www.positiveenergysolar.com<http://www.positiveenergysolar.com/>


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