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Running multiple SCC's in parallel and voltage spikes

wwu123

New Member
Joined
Dec 18, 2023
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29
Location
Northern California
Hi all, I have some new LG 435W panels with 48 Voc, that I would like to run 2-3 parallel strings of 3S = 144V. I'm not against quality SCC's like Victron, but their 150/35 and 150/45 leave very little buffer with 150 Voc max, even though temps don't get below freezing in my area. They seem to no longer make 200V models, so the next step up to 250 V is a very pricey upgrade, basically 2X the price. Similarly some of the other reasonable but decent quality brands like Ampinvt also have a 150 Voc max.

I noticed a number of the cheap but at least branded mfrs like PowMr and Easun advertise Voc of 160V, even 190 Voc (a few say they can only handle this for a short while, otherwise 160V). 160V provides a solid buffer vs 150V for my particular panels, so that's why I'm interested in these. Now I read that many of these tend to overheat when pushed to their rate max power, so I would probably only have one 3S string (=1305W) on each controller, and run multiple of these in parallel to a 48V 100ah server rack battery.

Now one of the other knocks against these I read is some people complain they've seen output voltage spikes up to 20V above the settings, which can be harmful to the 48V battery, or possibly trip overvoltage protections in place on the load. My question is - if one has multiple of these controllers in parallel, and only one throws out a voltage spike, will the other units in parallel still putting out the proper set charging voltage (around 55V) mitigate the voltage spike from actually occurring from the misbehaving unit, since they're all wired in parallel on the output to a common bus bar? If the other parallel units don't mitigate the spike, so the voltage on the bus bar is brought up to say 75V by the misbehaving one, does that cause any potential damage to the other units putting out 55V? Does it kill the output from the ones trying to still put out power at 55V while the voltage is spiked to 75V?
 
435W x 6 panels / 54V charging = 48A charger

Is your goal to save money on your first SCC purchase or are you trying to build a reliable and long lasting system? Or something in-between where a budget is involved?
 
435W x 6 panels / 54V charging = 48A charger

Is your goal to save money on your first SCC purchase or are you trying to build a reliable and long lasting system? Or something in-between where a budget is involved?
You make a good point that 48A is greater than the 35A/45A that the Victron 150/35 or 150/45 could output - I should explain I'm overpaneling the charge controller to get more winter production, it's less important to squeeze the most out of summer production. Both units could would be great but just clip at 2000W and 2600W respectively a bit in summer - but the 150 Voc doesn't work for 3S2P.

So yes, trying to save some money, in that I'm looking to pay for quality single unit on the order of the $200-250 of a Victron 150/35 150/45, that has a Voc above 160. Buying two cheap PowMr's is going to cost the same, doesn't save any money, so I'd rather not except they meet the Voc. If there's a Rule #1 on this forum for off-grid solar, it seem to be - never exceed the Voc of your SCC.

But $400+ for a single unit of Victron 250/60 is a big step up in price.

Maybe instead of leading with the question about the voltage spikes, which maybe just leads to bashing of cheap Chinese units, I should ask - are there any decent quality 48V SCC's in the $200 range that have a max 160-200 Voc?
 
But $400+ for a single unit of Victron 250/60 is a big step up in price.
...a big step up in INITIAL purchase price.

If you value not having down time or endless tinkering and worrying, then maybe its only expensive on the initial purchase. I've tinkered with crap for countless hours to save a few bucks. I've had desperate times where i needed power and had to spend quite a bit of money to get temporary power, temporary heat and even stuff expedited shipping. Not cheap or fun.

The bluetooth setup, one button firmware updates, an awesome app for configuring and monitoring. Makes it worthwhile to get something good up front. And, the SCC is the heart and brains of every solar system, NOT the place to skimp.

I have my first quality SCC, a Morningstar Tristar MPPT 45 from 2009. It was $700 bucks and i thought i was out of my mind. Its been a workhorse since then 24/7/365 and showing no sign of letting up. A great investment.

I still have every Victron product that i ever purchased still running today. Everyday.
 
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Mr. Sandals is right, quality gear will continue to put out many years after your cost savings have expired form repeated replacements you want quality? Morningstar, midnite, or Victron any of the three will last you probably (if mine are any example) to way past your desire to mess with them. My oldest that I bought new is a 2011 and its the MPPT 45 that I used on my camper. I have 3 of the 60 amp version running my house and I have two spares that I bought used simply as spares. one of them is from 2006 or so and when tested worked perfectly. the amount of kWh that had ran through it in its former life is staggering as it came from the telecom industry... they do not tend to play around in that domain.
 
Thank you both for your input, I'd not heard much about Morningstar or Midnite. Looking at their specs, for Morningstar, you're suggesting the 600V model would work, and Midnite the 200V or 250V one?

I ran the calculator on the Midnite site, it said my voltage would be "marginal" on the 150V one (I put a lowest ambient temp of 0C as we can get close but never below freezing). Does marginal mean it might be somewhat tolerant of Voc going above 150V (the HyperVoc feature goes to 198V for 48V nominal battery)? Does Morningstar have something similar for their 150V version?
 
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Thank you both for your input, I'd not heard much about Morningstar or Midnite. Looking at their specs, for Morningstar, you're suggesting the 600V model would work, and Midnite the 200V or 250V one?

I ran the calculator on the Midnite site, it said my voltage would be "marginal" on the 150V one (I put a lowest ambient temp of 0C as we can get close but never below freezing). Does marginal mean it might be somewhat tolerant of Voc going above 150V (the HyperVoc feature goes to 198V for 48V nominal battery)? Does Morningstar have something similar for their 150V version?
you would need to use the calculators that are built into the site to check your panels compatibility, but what I was referring to was the fact that any of those manufactures you can trust in a offgrid, must not fail setup to work as they are supposed to regardless
 
Thank you both for your input, I'd not heard much about Morningstar or Midnite. Looking at their specs, for Morningstar, you're suggesting the 600V model would work, and Midnite the 200V or 250V one?

I ran the calculator on the Midnite site, it said my voltage would be "marginal" on the 150V one (I put a lowest ambient temp of 0C as we can get close but never below freezing). Does marginal mean it might be somewhat tolerant of Voc going above 150V (the HyperVoc feature goes to 198V for 48V nominal battery)? Does Morningstar have something similar for their 150V version?
The calculator for Morningstar:


I have the TS MPPT 60A version, I bought two of them used in 2019 for around $350. Not a single problem with them and I like that they have no fans.
 
If you are wondering why some MPPT cost way way more than others check if they are isolated or not. The non-isolated ones like victron and all the cheaper units need a minimum voltage of about 5v over charge voltage. Where isolated ones will typically have a start voltage over 100v being required.

Isolated means the PV inputs are not connected electrically to the battery out side. So a lightning strike nearby can't ride the pv wires in and cross to the inverter and batteries doing more damage... at least that is the theory.

Non-isolated ones are generally a fancy and efficient buck converter that steps down what comes in to battery charge voltage. It also finds the max power point and adjusts voltage to optimize the charge.

Isolated takes more components so it costs more.

I haven't done a deep dive to see which type is better and why yet...
 

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