Sizing Off-Grid Systems And Using Gen Support

[Alpaca-Meadow]

Solar System not Working

HI All this is my first thread, I am not sure if I should be posting here as I could not find a way of posting back in the main screen.
I have read and tried educating myself over the past 12 months, but unfortunately I have a problem, that is just not clear to me, so if you could help that would be great, thank you in antisapation.

the system
8 x 110amp deep cycle batteries wired in 24 volt configuration
5 205 watt solar panels wired neutral to natural and positive to positive back to the inverter
1 50Amp mppt controller

all I am trying to run is a 150wat inverter which in turn is running a chicken brooder which is 75 watt

I was running a 1kg inverter back in peak summer, but found the batteries were going flat so that is why I changed to the 150 watt inverter.
I live in Southern England and we have had really good sun for quite some time.

the problem is the batteries get up to 26.4 volts in the day, but in the morning it is down to 23.6 volts,

I can't understand why the batteries and panels are not coping with such a low draw of power!

an any one please help

best wishes Derek

[ChrisOlson]

Learned a new one yesterday. Cloudy, drizzle & rain. I'd fired up the diesel, and was running loads and charging batteries, and the sun came out of a break in the clouds and slammed the PV arrays. 5 additional KW hit the batteries, and the generator unloaded.

I've seen 'em do that before. If your charger settings in the XW are correct, it gives priority to the MPPT's for charging. The nice thing is that if you have AGS it automatically shuts the generator down when that happens (assuming it was automatically started due to shortage of incoming RE).

[mapmaker]

I'd fired up the diesel, and was running loads and charging batteries, and the sun came out of a break in the clouds and slammed the PV arrays. 5 additional KW hit the batteries, and the generator unloaded.

There must have been some huge peak currents into the batteries. When I have this problem (sun comes out while generator is running) I can hit bulk charging currents of almost C/4 (not desirable). My system is DC coupled... no regulation of current until absorb voltage is achieved.

--mapmaker

[Mike90250]

I do it a bit differently than Chris does, I load the snot out of the genset (95%), and what it's not feeding into loads, it's changing the battery with. When the toaster comes on, the charger throttles back, and if the big 240V pump comes, on the battery flow on the Conext combox diagram, switches from charge to discharge, and the batteries are aiding the genset while the peak load is on. And when the load reduces, the batteries are back to charging. Very fancy (and fast) sensors in the XW that it can track these events and not disqualify a lugged down genset.

Learned a new one yesterday. Cloudy, drizzle & rain. I'd fired up the diesel, and was running loads and charging batteries, and the sun came out of a break in the clouds and slammed the PV arrays. 5 additional KW hit the batteries, and the generator unloaded. I heard the change in sound and thought Uh Oh - what happened? Got to the generator shed, and read the meters, since the XW thought the batteries were full, it stopped charging and the generator was loafing along with only about 100w of load. So it was all cooled down and ready to shut off by the time I figured it all out.

[ChrisOlson]

This is the one I have.

OTC 4619 Professional Battery Hydrometer

Well, I didn't know that Owatonna Tool Co was building battery hydrometers. And turns out I was right. That's one of those Chinese ones with the paper scale inside the float tube that you have to watch in case the paper slips. OTC (been a manufacturer of specialty service tools for OEM's since 1934, based in Owatonna, Minnesota and now owned by Sealed Power in Muskegon, Michigan) buys and resells that hydrometer from the same Chinese supplier that makes them for everybody else.

[paulcheung]

This is the one I have.

OTC 4619 Professional Battery Hydrometer

[ChrisOlson]

A lot of these cheaper glass float type hydrometers have a float with lead shot in the bottom. Then there's a tube above the lead shot with a scale printed on paper that is rolled up inside the tube. The paper scale ends up at random locations in there when they make it and some of them aren't even glued. The paper scale slides down a bit in the tube and then gives an abnormally high reading. One of those $5.99 plastic Deka hydrometers that has a floating needle that pivots on one side is more accurate than those cheap glass float types that come from China.

[paulcheung]

Well, I always measure the SG reading when they are absorbing in high voltage at about 61 or 62 volt; they hydrometers I have are 3 different ones, one with 4 plastic coins and one with 3 colors in it and one plain, the plain one is so hard to read as the print are so small and I get up to my age. I mostly use the 3 colors. it is easier to determine the reading and it has temperature gauge too, but I don't know how to apply the temperature compensation, guess have to learn it.

The reading is always in the white near to green, the middle of white is 1.250 and the middle green is 1.275; so it is always in the line of white and green so I would say 1.255 to 1.260 there about and if I shake it a little it might go up to green a bit more.

Thank you guys.

[ChrisOlson]

Which is a good argument for keeping some standardized electrolyte mix around to calibrate your new hydrometer.

Yeah, I got a Chinese one around here someplace that claims the specific gravity of distilled water is 1.15

[inetdog]

Have you ever seen those hydrometers that have the red, white and green areas on the scale? Basically if it's in the green she's good because that's about the accuracy limits of a non-laboratory hydrometer that has not been calibrated. I've tested two identical hydrometers bought off the shelf before and get readings 10 points apart on them in the same cell. Which one was right?

Which is a good argument for keeping some standardized electrolyte mix around to calibrate your new hydrometer.

[ChrisOlson]

So if my SG reading is above 1,255 I should not be worry about sulfate problem?
Thanks

No, you're fine at 1.255. I've never seen ours at 1.265 unless they get absorbed many times in a row in summer. Any positive gain in SG means some of the chemistry changed (sulfate going back into solution) to make the electrolyte more dense. But hydrometers are typically not much more accurate than 5-10 points so when you got a reading of 1.260 you're looking at 1.255-1.265 and you're fine. And not applying the temp correction to a non-temp compensating hydrometer throws it off some more.

Have you ever seen those hydrometers that have the red, white and green areas on the scale? Basically if it's in the green she's good because that's about the accuracy limits of a non-laboratory hydrometer that has not been calibrated. I've tested two identical hydrometers bought off the shelf before and get readings 10 points apart on them in the same cell. Which one was right?

[inetdog]

So if my SG reading is above 1,255 I should not be worry about sulfate problem?
Thanks

You should not be worried about new sulfate accumulation and you can be fairly confident that any existing sufation has not reduced your capacity much if at all.

[paulcheung]

Your 1.260 SG is not low. 1.255-1.275 is the normal full charge SG range for 4000-series.

So if my SG reading is above 1,255 I should not be worry about sulfate problem?
Thanks

[paulcheung]

No I just measure it on the hydrometer, I think the temperature is about 90* to 95 inside the battery while absorbing.

[inetdog]

And just to cover all the bases, that is a temperature adjusted SG value you are measuring, right?