Author Topic: Question on wiring my SPD  (Read 360 times)

mickhill

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Question on wiring my SPD
« on: May 18, 2019, 11:16:30 AM »
Hey guys, new here. Just working on an off-grid solar project to run my small chest freezer and possibly fridge. I have 8 - 100 Watt Renogy panels going on the roof and right now, 4 - 125Ah Vmax AGM batteries run in parallel. The components will run down and feed into my utility room where the freezer is. I have a Midnite Classic 150 and a 2000 Watt pure sine inverter/charger. The combiner box Im using is an "Eco-Worthy" 6 string. Pic Attached. My plan is to wire a 115SPD at the combiner box but I guess I dont understand entirely how they work. It looks like it would "pass through" like a fuse but it seems to be wired in parallel. Does it just "eat" the surge? What stops it from going on through the wires to the inverter,etc ?

ClassicCrazy

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Re: Question on wiring my SPD
« Reply #1 on: May 18, 2019, 11:38:09 AM »
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

mickhill

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Re: Question on wiring my SPD
« Reply #2 on: May 18, 2019, 03:09:52 PM »
Yeah, Ive watched no less than 20 videos from all over YouTube. Still not sure how it works but they all seem to be wired in parallel with the PV +/- in combiner boxes, so thats how I wired it. Just got it in the mail today. Hopefully it works if I ever need it to.

ClassicCrazy

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Re: Question on wiring my SPD
« Reply #3 on: May 18, 2019, 11:49:18 PM »
When the voltage goes above a certain threshold - (surge or spike)  then the electronic components in the surge protector send ( clamp) the higher voltage to ground so it won't blast the protected devices on the circuit.

If you want the technical details this will help
https://www.electronics-tutorials.ws/resistor/varistor.html

Larry
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

boB

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Re: Question on wiring my SPD
« Reply #4 on: May 19, 2019, 12:28:15 AM »
Right.  The MOVs in the SPD clamp or keep the voltage spike from exceeding a certain voltage.  Each SPD has two circuits of these with the GND being the common.

A device like the Classic has insulation between all its internal circuitry and ground, such as the chassis.  That insulation will break over when any of the connections coming into or out of the Classic (or whatever product that needs protecting) exceed some voltage.  Every Classic is tested to a high pot voltage.  The main four connections, battery plus, PV plus input and the two negatives are all tied together and treated to 2200 volts DC for one minute.
Other electronics products and even toasters will have this kind of test if it is listed to some NRTL like UL, ETL, TUV, CSA, etc.

So, the SPD is there to keep any of these connections from arcing over through that insulation to CHASSIS GND. 

Lightning is what is called a common mode voltage rise, meaning that both PV positive and negative rise together in reference to ground, which the chassis is tied to.   So, that's why the two SPD circuits are connected to PV minus and PV plus separately.  The SPD tried to keep those voltages from exceeding that 2200 volts.  It should actually keep it quite a bit lower than that but 2,200 V is the legal limit for the Classic.  So, for PV, the SPD 600 or even the SPD 300 should work fine.

Batteries are inside with shorter cables and not as much of an antenna for lightning so typically don't need protection.

boB





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