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marco.rc.santos

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Reply with quote  #1 

Hi to all,

I live in Angola and here the public electrical grid have frequent (daily on the last months) power outages. I have a 13kW UPS powering my home and it works with 16 batteries of 12V in series (VRLA gel; 38Ah 20hr; initial current <0.3CA; cycle use: 14.4 to 15.0V), but it is not enough to keep my home powered for more than 12h. When I started using the UPS the batteries were not performing as expected and it was holding less time than a smaller UPS that I had, so I requested the supplier to replace the batteries, as I think they are not working properly. This process is still ongoing and I still have the "faulty" batteries installed. I installed a smoke detector on top of the system as a safety precaution.
I bought solar panels in order to charge the UPS batteries with them. I built a controlling system, that measures the voltage of one of the batteries of the array and if it is below 12V it connects the panels to the batteries, if it is higher than 14.6V it disconnects them. They are 60 cells panels (Vmp=30.7V; Imp=8.15A; Voc=37.4V) and I connected 8 of them in series. Later, after I had the issues I describe below, I connected only 7 in series.
When I first tested the system, the smoke detector started beeping a few minutes after the panels started to charge the batteries. To rule out the control circuit, I isolated the control panel with duck tape and a plastic bag, to make it air tight, and I had the same issue. Thinking that it could have been from the batteries, I connected the panels directly to the UPS, after disconnecting the input power from the electrical grid to the UPS, but still the smoke alarm went off. Then I connected only 7 panels in series (as stated above) and had the same issue. Note that when charging directly from the UPS, the batteries don't make the smoke alarm go off.

Now, I'm thinking about buying MPPT battery charger controllers, to have a proper charging cycle for the batteries. Either 48V controllers (less wiring), connected to 2 solar panels, charging 4 batteries at a time; or 24V controllers (much cheaper), connected to 1 solar panel, charging 2 batteries at at time.

I'd like your advice on the existing problem and on the controller acquisition as potential solution.

You can find attached the as built setup and the potential setups with 48V or 24V controllers.

As built:
PV as built_01.png 

48V controllers:

48V controllers.png 
24V controllers:
24V controllers.png 

Thank you for your support.

Marco

Rick H Parker

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Reply with quote  #2 
Do not charge directly off the Solar panels, get a Charge Controller.

What is the make and model number of the UPS? 

You show a 192V battery bank .... (16 X 12V = 192V) ... voltages in series add.  Are you sure all 16 are wired in series?  This needs to be clarified before we can move on.  If your battery bank is 192V, some UPS battery banks are 192V, your best off getting a 192V Solar Charge Controller, they do make them. Another option is to design a new system from scratch.

MPPT is worth the higher price when Solar panels cost a lot. With the price of Solar Panels dropping, PWM makes more sense then MPPT.
MPPT gets the most out of your Solar panels, PWM gets the most out of your batteries.  Batteries are becoming the biggest expense, getting the most out of them is what makes PWM the better choice.


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Rick H Parker
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stmbtwle

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Reply with quote  #3 
I'd be reluctant to try to charge the batteries in groups at 24 or 48v. It's a complex setup and I'm not sure all the batteries would get the same charge. Your batteries are configured for 192v, so that's what I'd work with. It's simpler and possibly cheaper as long as components are available.

As Rick says there are 192v charge controllers, I googled them and several came up. Here is one, there are others, both pwm and mppt.
http://snatpower.manufacturer.globalsources.com/si/6008834185350/pdtl/Solar-charge/1148360422/192V-384V-50A-high-voltage-solar-charge-controller.htm
I'm not recommending it, it's just an example.

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Willie, Tampa Bay
Rick H Parker

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Reply with quote  #4 
"Your batteries are configured for 192v, so that's what I'd work with. It's simpler and possibly cheaper as long as components are available."

I'm seeing other possibilities but, lets see if we can find out what the capabilities of the 13Kw UPS are first. 
For example, a generator input could not tell the difference between a generator and a pure sine wave inverter.
If the UPS has a DC input, buck the solar panels to the correct voltage.

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Rick H Parker
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stmbtwle

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Reply with quote  #5 
It does have a DC input (the batteries) but I rather doubt it's configured for charging. IF it has a second one you could configure your array to whatever voltage is required.

I'd stick with the charge controller if available; that's what it's designed to do, and you don't have to build or modify anything.

HOWEVER, 38ah x 192v only gives you about 7.3kwh, maybe a bit more (or less) depending on battery condition and losses. If you want more "run time" I think you need bigger batteries. 13kw only means that the unit can deliver that power till the batteries give out.

What size battery bank did the previous UPS have?


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Rick H Parker

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Reply with quote  #6 
"It does have a DC input (the batteries) but I rather doubt it's configured for charging."

It is bidirectional.  How do you think the batteries get charged and provided power? But that DC port cannot be used to connect to a power source ... other then the batteries.




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Rick H Parker
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stmbtwle

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Reply with quote  #7 
My point exactly.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
marco.rc.santos

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Reply with quote  #8 

Hi to All,

Please find below my answers to the several questions/comments that you made.

What is the make and model number of the UPS?
It's a NekSis C15KS (it's rated at 12kW, not 13kW as I previously stated).
It has only: the 220VAC input, the battery DC connection and the 220VAC output for the house supply. It does not have additional power interfaces and it is not prepared for the setup I'm trying to assembly. You can find the specifications attached (single phase 15KS model).

Are you sure all 16 are wired in series?
Yes, the batteries were sold separately and the instructions were to wire them in series, just as the supplier also explained. I did the wiring myself and the UPS setup is assembled as per specifications.

As Rick says there are 192v charge controllers, I googled them and several came up. Here is one, there are others, both pwm and mppt.
I thought of that some time ago, but didn't find any charge controller for that voltage value. I think I was looking more into DC/DC converters, rather than battery charge controllers specifically. It would be a much simpler approach and I will look further into that option. Is there any supplier that you would recommend, off the top of your head?

What size battery bank did the previous UPS have?
I don't remember exactly, but the power rating was 4.8 kW (it was the C6KS). For both, the batteries shall last the same time at full power, so I'd say it was 40% of the new one I have. The aims of having a 12kW UPS are: to cope with the peaks, that the previous smaller couldn't; and having larger battery banks. I acquired 2 sets of batteries, in order to have 2x 7.3 kWh, but only have one at the moment as the other one is partially returned to the supplier for testing. But mainly, my power consumption is around 500 to 700W, when I'm not using any specific appliances (like microwave, electrical oven or such...).

But that DC port cannot be used to connect to a power source ... other then the batteries.
I believe it can't while the UPS is being supplied by the power grid, as it will be charging the batteries. I configured the system to connect the solar panels to the batteries only when there is a power outage (through a normally opened relay powered by the grid, installed between the LVD and the battery). At that point the DC interface is only used to drain power from the batteries and this is when the solar panels will be charging the batteries.
Nevertheless, I installed power diodes between the panels and the battery/UPS terminals, to prevent current "backflow" to the panels.

Thank you for all your support.

Attached Images
jpeg UPS 15KS.jpg (225.68 KB, 22 views)
jpeg UPS 15KS power interfaces.jpg (279.73 KB, 22 views)
jpeg UPS 15KS rear view.jpg (152.54 KB, 22 views)

stmbtwle

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Reply with quote  #9 
Sorry I can't recommend a supplier for the controller, I simply did a search for "192v charge controller" and that's what came up. There were several on Alibaba, all were from China I think. I didn't see any on Ebay. The folks who sold you the UPS might have a suggestion. If they haven't run into this before, they will soon enough.

Even at 500w load, your current battery set is only going to last you maybe 14 hours. If you want more time you'll need bigger/more batteries, or find a way to reduce your load. LED lights are highly recommended if you don't already have them. You could get a second set of batteries and parallel them in with the first set, this should about double your run time.



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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Rick H Parker

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Reply with quote  #10 

It's a NekSis C15KS (it's rated at 12kW, not 13kW as I previously stated). “

I could not find anything on NekSis. I suspect NekSis is re-branded generic products.

If it where mine I would open it and hack the charging section so the batteries charge off the solar panels instead of the grid. I can see you know something about electronics but I don’t know the extent of your electronics skill set.

Here is how I would do it. Locate the DC input to the charging section, disconnect and hook to a buck converter that will accept the solar panels output and and shape it to the correct DC voltage for the charging section. You have 1750 watts a solar panels. That is enough to charge the batteries when the grid is up and supply all your energy needs during the day when the sun is shining. The internal charger should be able to handle all the power that your panels can supply.

 

"I thought of that some time ago, but didn't find any charge controller for that voltage value.”

There are not a lot of 192V charge controllers out there. I did find some on AliExpress and the suppliers do ship to Angola.   Follow this link.

 

I believe it can't while the UPS is being supplied by the power grid, as it will be charging the batteries.”

You can hook more then one charger to a battery bank, however The charging algorithms must match so that they do not interfere with each other. The odds that a solar charge controller is going to match the UPS charging algorithms is astronomical. You would need circuits to disconnect the solar charge controller from the battery bank when the grid is up, do the hack above or disable the charging section in the UPS and use a solar charge controller.

Another alternative is to design a new system using the batteries, solar panels you have along with a new inverter and a charge controller the can accept both grid and solar panels.This would lower your electric bill and give you a backup for when the grid goes down.

 


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Rick H Parker
Kansas, USA
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