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 It WORKS! 40 amps DC tripped a 20 amp AC breaker
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MattKarma
Da Kine

USA
326 Posts

Posted - 04/17/2018 :  10:42:24  Show Profile  Visit MattKarma's Homepage  Reply with Quote
40 amp DC circuit breakers are few and far between; I ordered a $60 monster from Amazon, it never shipped so I canceled the order.

Then I did some research:

https://www.youtube.com/watch?v=kRB7Z66brO0

AC breakers will trip with twice the current DC.

Anyhoo the real problem inbound to the controller from the array is lightning, so at worst what you have by using a non-functioning breaker there is a disconnect.

A surge from lightning along the negative wire (I.E. THHN 8 AWG Black) previously upset much equipment to the point of marginal functionality, so we need a double-throw for both positive and negative...

But YEA!!!! Added another rack and Saturday, the amperage exceeded 40 amps ... and she blew!

Bought a 25amp GE breaker at HD for $9, had it installed in 5 minutes, in the standard house box. The controller is 40 amp, but according to the documentation it can take 50 ok. Can't have the damn thing tripping all the time.





Just thought you would all like to know. Off grid engineering... it's about innovation!






***Still can't figure out how to spell 'car' correctly***

Obie
Punatic

USA
3080 Posts

Posted - 04/17/2018 :  12:11:17  Show Profile  Reply with Quote
A youtube video is not really a good source.

Because of the difference in the way they work, a very large surge would weld the contacts on an AC breaker and burn your house down.
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MattKarma
Da Kine

USA
326 Posts

Posted - 04/17/2018 :  12:30:04  Show Profile  Visit MattKarma's Homepage  Reply with Quote
Been struck by lightning, dude. 30 Volts isn't that much.

***Still can't figure out how to spell 'car' correctly***
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MattKarma
Da Kine

USA
326 Posts

Posted - 04/17/2018 :  12:33:23  Show Profile  Visit MattKarma's Homepage  Reply with Quote
Main problem I see is in fact the lower voltage, the AC breaker contacts are cheap and don't conduct as well as a DC magnetic contact. (& @ lightning voltage, Neither are guaranteed to do diddly squat)

***Still can't figure out how to spell 'car' correctly***
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kalakoa
Motormouth

10273 Posts

Posted - 04/17/2018 :  15:41:23  Show Profile  Reply with Quote
40 amp DC circuit breakers are few and far between

Gexpro.

AC breakers will trip with twice the current DC.

Square D.
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MarkP
Punatic

1976 Posts

Posted - 04/17/2018 :  16:34:24  Show Profile  Reply with Quote
I spent a lot of time fooling around with fuses until I found these. Never looked back.

https://www.solar-electric.com/mnepv.html
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MattKarma
Da Kine

USA
326 Posts

Posted - 04/19/2018 :  12:45:51  Show Profile  Visit MattKarma's Homepage  Reply with Quote
Another 'thang... Praises and Hallelujah for the Xantrex C-40 controller. Mine is set at 24V; with bulk charge set to 28.5V (only 2v less than panels at max). This beast is the Jeep of controllers; it's rock solid reliable and survived a lightning strike. I tried an off-brand MPPT controller; the C-40 performed much much better in my humble opinion. The big seller of the MPPT controller is it's ability to convert excess voltage into amperage. I found that this actually is not that useful, the main problem not being use of energy when conditions are optimal but performance when conditions are cloudy. Because the C-40 does nothing period with the power under those conditions it is more efficient, delivering 100% of what power is comming in under low light conditions.

It's also cheaper; you can pick up a C-35 for less than a hundred dollars.

On the downside, you can't monitor your power remotely from the internet or get a composite image of power from all arrays in the area.

Oh well, life is suffering!



***Still can't figure out how to spell 'car' correctly***
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MarkP
Punatic

1976 Posts

Posted - 04/19/2018 :  18:13:04  Show Profile  Reply with Quote
My understanding of solar PV theory is admittedly crude and it goes something like this. Picture photons of light coming in like hailstones and hitting the PV cells like hailstones hitting water. Each photon "splashes" an electron up through an electric field like the hailstone splashes drops of water up into the air against gravity. If a collection device (cup, bucket, gutter) is placed where the droplets of water can be collected before they fall back down to the water's surface from which they started out, then you could run a water wheel and get useful work. Similarly if the electrons are captured somehow they can be used as "electricity" as they attempt to return to the voltage they were originally dislodged from. The million dollar question in each case is how high to you hang the bucket? The higher you collect the droplets/electrons, the more energy to be had per droplet/electron as it rides the waterwheel/motor back down but the fewer make it that high. It's a "how sharp is the bell curve" thing.

In the case of the hailstones hitting the water I can see less intense hail splashing the rain less high meaning a wider bell curve. If there is a similar relationship between less intense light and less energetic electrons then as the light weakens due to clouds the panels will put out both fewer electrons and less energetic electrons so you should hang the bucket lower.

TL/DR: An MPPT charge controller will allow you to add an extra panel to each string since it automatically adjusts the height of the bucket. The benefit on cloudy days when the panels might otherwise not produce at all more than makes up for the modest penalty for doing so extracted when the light is high. Truest if VOC varies a lot with light intensity. Less true if all electrons knocked loose by each photon are equally energetic (always splash equally high) and vary only in number of electrons produced. The salient point is that there is a rather precipitous cut-off in production as the light dims and the native voltage produced by the panel string is no longer enough to push electrons into the battery bank. MPPT controller lets you design for that worst case.

Edited by - MarkP on 04/19/2018 18:16:22
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kalakoa
Motormouth

10273 Posts

Posted - 04/20/2018 :  08:23:19  Show Profile  Reply with Quote
The big seller of the MPPT controller is it's ability to convert excess voltage into amperage.

Oversimplification of best use case.

MPPT allows your panel array to run at a different voltage than your batteries.

- smaller combiner boxes -- or none at all
- surplus panels with "weird Voc" work great
- reduced power loss and/or wiring expense for distant panels
- freedom to change battery voltage

Several years ago, I picked up some surplus panels that were custom-designed for a specific grid-tie application: they had a Voc of 25V -- useless with a PWM controller. With 3 in series (no combiner box!), an MPPT controller could charge batteries at 12V, 24V, or 48V; the high array voltage made for negligible loss over a long run of #10 wire. In this design, the "expensive" MPPT controller saved way more money than it cost -- and the system still charges (a little) when the panels are in the shade.
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terracore
Punatic

4728 Posts

Posted - 04/20/2018 :  18:43:51  Show Profile  Reply with Quote
The simplistic way I interpreted it was that PWM charge controllers function by limiting the amount of energy that goes to the batteries, and MPPT controllers function by maximizing the amount of energy that goes to the batteries. There are several reasons why but once I got to that level of knowledge it gave me a raging brainer.
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kalakoa
Motormouth

10273 Posts

Posted - 04/21/2018 :  09:38:24  Show Profile  Reply with Quote
MPPT controllers function by maximizing the amount of energy that goes to the batteries

Most MPPT controllers also detect battery voltage drop due to load, and respond by harvesting as much power as they can handle, so you can use the entire panel output.

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MattKarma
Da Kine

USA
326 Posts

Posted - 04/21/2018 :  12:08:18  Show Profile  Visit MattKarma's Homepage  Reply with Quote
The C-40 attempts to maintain charge at whichever voltage it's charging at. It doesn't see "load", it sees the voltage drop and attempts to maintain constant voltage (assuming excess power is coming in). Most panels are designed to operate with 24V controllers, higher voltage goes farther, and it's like "What ... do you live in your CAR?".

lol.

Some loss due to resistance 30 V vs 150V ... lower voltage is safer, for the distance ~ 25ft loss isn't very large.

There may be economics which support using MPPT for larger arrays. Definitely for grid tie.


***Still can't figure out how to spell 'car' correctly***
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kalakoa
Motormouth

10273 Posts

Posted - 04/21/2018 :  15:10:51  Show Profile  Reply with Quote
Most panels are designed to operate with 24V controllers

I have several 18V panels. These might work with a 12V controller. but at the expense of losing 30% of the wattage.

I have several 25V panels. These might work with a 24V controller, but the batteries would never reach float voltage.

Panels have since (mostly) standardized around a Vmp of 30V. Even so, a PWM controller can't make use of the entire output...
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terracore
Punatic

4728 Posts

Posted - 04/22/2018 :  14:30:55  Show Profile  Reply with Quote
"I have several 18V panels. These might work with a 12V controller. but at the expense of losing 30% of the wattage."

You're talking about a PWM controller, correct? A MPPT controller should automatically down-adjust the voltage by increasing the amperage, therefore, no significant loss?
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kalakoa
Motormouth

10273 Posts

Posted - 04/22/2018 :  15:47:59  Show Profile  Reply with Quote
Correct: odd-voltage panels require MPPT to harvest their full output.

The design simplicity is just an extra added bonus.
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microage97
Da Kine

389 Posts

Posted - 04/26/2018 :  18:18:26  Show Profile  Reply with Quote
By a real charge controller, like midnite solar 150. You will want to seiries (sp) the panels so the are almost the max of the charge controller. The controller will drop it to what ever the bank is, but will convert the voltage difference to AMPS.
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