Going Solar

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Going Solar

Postby MetalFiber » Thu Mar 15, 2018 2:03 pm

Greetings everyone. I'm new here and new to solar...about six months, though I have studied and followed solar for about thirty years. Could never really see the benefit of cost versus ROI until recently. Anyway, I've started using an "off-brand" MPP SOLAR unit and am trying to gather information and reviews on it. There are those who swear by it and those who hate it. I got myself a small 2400W off-brand MPP SOLAR unit to test and so far it's done everything I have needed it to do. That might change as there are those who say after three months they tend to blow up. I guess I'm on borrowed time, but I run a well pump (induction motor 800-1000W) among other things on this inverter and she's still running. When the pump comes on it will "sometimes" send the unit an over voltage error for a split second, but still run the pump. My guess is that the surge from the batteries is a bit much for the inverter. Not sure how to overcome that. Anyway, I'm attaching a video in the hopes that I can gain some constructive criticism in how I set up my system. Any help will be appreciated. I don't work for MPP SOLAR and I don't even ask for subscribers. I really just want to be sure I am getting it right. If I had gobs of money, I'd opt for SMA, Fronius, Selectronic, Outback, SolarEdge and many other respected brands, but again...I'm new and so is my budget. Thanks.

https://www.youtube.com/watch?v=fR9MlnIZcYE

https://www.youtube.com/watch?v=gCFRjU0uY5c
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Re: Going Solar

Postby Gordon-Loomberah » Thu Mar 15, 2018 2:44 pm

Welcome to the Energy Matters Forums MetalFiber :)

Generally when you start a big load you might briefly see an undervoltage event, rather than an overvoltage, due to the very high start load of some motors.
There is no surge from the batteries, rather a voltage drop at the inverter and/or battery, which may be due to small battery capacity, small cable size for the load, or a high resistance connection somewhere. Of course, a dodgy charge controller may not maintain battery voltage very well, which is an added complication, but any effect will be delayed from the initial heavy load voltage sag.

A 1000W induction motor will draw significantly more than 1000W on start-up, especially if it is starting under load- ie a significant head of water that it has to get moving. Depending on the power factor, the inverter will probably see more than 1000VA anyway.
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Re: Going Solar

Postby MetalFiber » Thu Mar 15, 2018 2:52 pm

Thanks for that insight. I was thinking on placing a DC capacitor between the battery and the inverter to see if that helps out and an AC capacitor between the inverter and load to see if that also helps protect the inverter and batteries. Additionally I wanted to put a capacitor between the PV and inverter as I have seen that it helps to keep smoother transition of current and voltage from PV to inverter. Please help me to understand if I am thinking wrong or am on the right track. Thanks.
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Re: Going Solar

Postby Gordon-Loomberah » Thu Mar 15, 2018 3:04 pm

Any capacitor would have to be across the battery or load, ie in parallel, rather than "in between", which suggests in series. Across the battery would have minimal effect unless it had huge capacity.

Putting a cap across the inverter output/load will change the power factor, which is dependent on the particular load, so I wouldn't have any more than say 10uF across the invter output, but that is a job for a qualified electrician (in Australia).

In any case, capacitors wont really be providing any protections as such. The voltage output from PV panels varies very little under a wide range of light intensity, most of the variation is in current.
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Re: Going Solar

Postby MetalFiber » Thu Mar 15, 2018 3:11 pm

Wow! Thanks so much for all of that information. And so quick to respond. Thank you. On the Cap between the batteries and inverter I was thinking about 0.5 Farad or 1 Farad even. There's just too much draw from that motor. It just puts a little scare whenever the error symbol comes on in that split second. This has been quite informative already. Thank you so much.
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Re: Going Solar

Postby Gordon-Loomberah » Thu Mar 15, 2018 3:21 pm

I doubt putting a 1F cap across the battery will have a significant effect, you are better off to reduce the load from the motor, by starting it with no load if possible, or by putting a power factor correction capacitor across the motor. There are calculators online to work out what capacity you might need.

In any case, a brief lighting of the under-voltage light when the pump starts isn't a major problem.

What voltage battery do you have, and what size cables between cells/batteries and also the inverter leads?
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Re: Going Solar

Postby MetalFiber » Thu Mar 15, 2018 3:31 pm

I have 2 12V gel batteries in series to produce 24V. Each is 250aH so in series it should still be 250aH if I'm right. They don't require the higher voltages to charge, but these are the first gels I have ever owned. The leads are ring terminals and the wire gauge is 4AWG at about 2 feet (yeah..English system). My setup right now is fairly simple and straight forward. I am testing, reviewing and experimenting with this off brand MPP SOLAR to determine if I should get a parallel system setup or just spend the money for SMA or some other well known brand. Problem is that those units are 4 or 5 times what I would spend on MPP. And if I design a system (say 10kW with PV, even 3 phase) with MPP, I'd already have PV and would be around the price of SMA or other.
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Re: Going Solar

Postby australsolarier » Fri Mar 16, 2018 8:33 am

you won't get around spending money. generally with the inverter you get what you pay for.
that stuff has been tested hundreds of times.
and yes , if the battery and inverter are undersized, you will get a voltage drop at startup, even with a small motor like a 100w fridge.
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Re: Going Solar

Postby jaahn » Fri Mar 16, 2018 2:43 pm

Hi MetalFiber and welcome :D
I looked at those two videos but was not sure exactly why or what they were demonstrating :roll: ??

That guy had a grinder and something else running but no load on them as far as i could hear. You are starting a pump. These are considered high inertia loads, depending on what they are exactly, and always draw high start currents. Even on the grid they will dim the lights and may trip out a small breaker on 240V. Some pumps(centrifugal) should be started with the outlet valve closed to reduce the start load and current, BUT others must never be run like that or will blow something.

I have put out the main fuse to the main building on 3 phase once with a big pump and had to get the 'leco in to reset the 200A main board breaker, much to the admin peoples irritation as everthing crashed( with a loud bang) :twisted: A slight problem with the old starter sticking !

Three phase motor starters have "stepped voltage" switching to reduce the current at startup for large motors, particularly pumps and similar loads. You can do something similar if your system is being stressed by the start surge. I think Silicon Chip magazine may have had a project to do that some time back. Or there may be other ways. :? A soft start it is called. I would not play with capacitors to solve it.

What is the pump/motor you are running.
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Re: Going Solar

Postby JA2340 » Fri Mar 16, 2018 6:37 pm

From my (long ago) studies in electrotechnology, there are two styles of motor start processes.
1. Direct on line (DOL) - which (from my many years ago) recollection, requires a high start current to get things rolling, and
2. I do not have the name in my head at the moment (dammit!), but the deal is that they start with a boost from a capacitor and require less start up current.

This getting older thing is annoying! I had the words in my head a few minutes ago when I started this reply - gone now! Grrrrr! :oops:
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