MPPT question

BB. wrote: »

Using the meter on the Solar Charge Controller (MPPT) would be a good start. Take a few readings and see what they say (charging, under load charging, resting and no sun--like early in the morning with no loads).

Okay. Yes. I think this is the way to go. (I was getting 1 amp or a fraction of 1 amp from my panels the second time I took a look.)

Might help get a handle on what your system is doing. Knowing actual voltages from your batteries is easier to understand than trying to figure out what the LED power meter box is doing.

Well... the LED thing isn't doing anything... which was misleading. I thought it was genuinely saying that I had 90% of my stored energy left. That was easy to "understand" -- to understand the MPPT numbers I'll have to do as you say... get to know them. Thank you for helping me see the way with this.

You can also check your battery load current too to figure out how much power you are using. For example, after dark turn on one appliance at a time and measure the "Load Current" from the battery. From there, it is pretty simple math to workout how long you can run each load (or combination of loads) on a day's worth of solar charging.

My MPPT thing only has three readings: pv amps, battery amps and battery volts... I think it's volts... If it were a sunny day, I'd try several things now... but without much sun and not knowing what state of charge my batteries are in... I best be patient. I doubt I'll do the math... my math score years ago when I took the SATs was in the 22nd percentile, as opposed to English comprehension which was in the 98th percentile. (Now much reduced due to the impact of the brain injury and damage from low vitamin b12 -- the last being really hard to believe that something so innocuous sounding could have such a HUGE affect.) I know from experience what things I could use everyday. I just don't know now that there are fewer sunny days quite what the situation is.

I would highly recommend not using electric heat until you get a better idea of how well the batteries are being charged. If you can do anything else for cooking/heating (such as a camping stove--obviously, be very careful of fire/fuel spills) would be better.

I can't use it mainly because I'm afraid my inverter would start beeping again. It's been several years since I drove, due to having had tetanus -- it caused seizures in the beginning -- so I can't just pop out and get an alternative heat source. Luckily the tent thing is really cozy inside.

By the way, MPPT is a type of solar charge controller. It means Maximum Power Point Tracking--basically a electronic power supply that is more efficient at taking power from solar panels (especially during bright, cold, weather). Older PWM (Pulse Width Modulation) solar controllers are generally not as efficient as the newer style MPPT type.

I think it keeps my batteries from getting overcharged. It's the thing that has the Float light, which comes on during peak hours of sunny days. (and may not be seen lighting up again till next spring or summer).

By the way, do you know what Brand/Model of Solar Charge Controller (MPPT) you have?

I don't... I looked a bit ago and then came in here and couldn't remember what it said. It's not the nifty Outback one.

By the way, since you do have good sun there, have you looked into building a home made solar oven. There are instructions all over the web and it can be a good way to cook stews, beans, and other "oven type" dishes. They can be very simple, Styrofoam or cardboard boxes with insulation, aluminum foil, and a glass cover.

I've been thinking about them. I was using candles which work quite well, and are a lot cooler in the summer than using appliances. I put some tin foil in my garden to test a thing I read in Square Foot Gardening... and was amazed!

http://www.health-boundaries-bite.com/Tinfoil-in-the-Garden.html

So, I put the end of my tinfoil roll up in my livingroom where the sun hits the wall... and I'm going to get more foil and put it up as if there were wainscotting on two of the other walls. I'm thinking my avocado and other plants will like that. I'm very curious to see if it increases the heat at all. The only window I have (to speak of) in my livingroom is the clerestory.

-Bill

BB. wrote: »

Thank you Jim and Karen,

I don't have time to look at the manuals right now--but some quick replies.

Yes, Karen is using solar full time right now because of problems with the utility and her power has been disconnected (since April?).

Regarding the small fridge--I would tend to avoid it unless you are sure you have enough electric power... One surprising thing is that the small fridges use almost as much power as a modern Energy Star full sized fridge/freezer.

If you can find a used chest freezer and just use a small fan with an industrial 120 VAC thermostat--can use 1/4 or so of the power of a regular fridge. Look around this forum and you might get some ideas for one of your own.

Karen, please note that storage batteries are very sensitive to miss-use. No matter how many you have (or how few), over discharging or over charging can kill them pretty quickly.

If you can get a few battery voltage readings from your solar charge controller (MPPT), folks here can probably get a good handle on what to recommend next.

Take care,
-Bill

BB. wrote: »

Karen,

Assuming your 4x 183 amp*hour batteries are in series (4x12vdc=48 vdc) then how long it would take to recharge you pack from "dead" (we don't want dead--but for the sake of the math):

183 amp*hours / (5amps * 8 h/day) = 4.575 "sunny" days to recharge a "dead" pack (any power you take out for lights/TV will lengthen the recharging time)...

Normally, if your "MPPT" solar charge controller is properly programed and working--seeing the "float" light should indicate that you have pretty much fully charged the batteries.

The fact that your inverter is "beeping" (depending on brand/model) could indicate that the battery voltage is low or your drawing too much power--or that you have some other issue.

And, I cannot tell anything, for sure, about your installation and usage--or whether or not you have damaged the batteries or have other problems. I am just trying to education and provide some cautionary verbiage to help prevent battery damage if it has not already happened.

Those little "portable battery packs"--pretty much just a waste of money unless you have specific application where one make sense. Batteries (especially small ones) just don't store that much energy. I have seen ones with an attached 500/something watt inverter--sounds cool until you cruch the numbers and find out that running 500 watts will kill the battery in about 20 minutes (and somebody was planning on running their refrigerator for a 3 day power failure with one).

So, don't let me get you upset you about your installation--I am taking very big guesses here. Just trying to be safe.

-Bill

westbranch wrote: »

Hello CT just a quick note about the snow on your panels...

Get it off as soon as you can.

It will maximise the input to the batteries when the panels get full sunlight especially on a cool day. Without getting into the techie stuff an MPPT Charge Controller (CC) will give your batteries more amps than the panels are rated for IF there is LOTS of light hitting the panel. I am sure Bill can tell you (much) more.

So ... keep the panels clean if you can do it SAFELY... that pole is a bit of a problem.

Cheers
Eric

westbranch wrote: »

Karen, further to Bill comments and mine. It would be beneficial to record all 3 readings from your MPPT hourly, {volts, panel amps and amps to battery}, as a set, that way you can see when the MPPT is working and relate it to the time of day and the amount of light needed to get the 'MPPT effect'. It (MPPT) is not necessarily 'there' all day long.

SO... for parts of the day you will get the max output from your panels that they can produce, at that time of the day,
and for other parts of the day the MPPT may be operational and you would get 'more' than the max rating of the panels... this of course asssumes a clear sunny day,
cloudy or partly cloudy days will be different and deceiving as to their input to your batteries. At this time: record, record, record...
once you see what is coming in and going out (calculated or estimated) you can figure out the state of your batteries by watching the battery voltage drop at night. there will be more on that later I am sure.

cheers

Eric

BB. wrote: »

To use an analogy, an MPPT type Solar Charge Controller is like the transmission for your car... The Motor (solar panels) have a particular range of voltage/current that they work best in (supply the most power). However, the wheels need to move at other speeds (0-80 mph). The MPPT Solar Charge Controller basically just matches the Panels to the Battery bank voltage (i.e., engine speed to wheel speed). In the case of the solar panels, their "Maximum Power Point" changes with temperature. In the battery's case, it's voltage changes with temperature, level of charge, and amount of load (if any).

You can drive your car around in only first gear or high gear all of the time--but you will not be getting the most "power" or best fuel economy if you were to do this.

And yes, you are correct. Amps and Current are basically the same in our conversation. Current is the flow of electricity through the wire, and Amps (really Amperes) is the electrical unit used to measure that flow.

Volts is like water pressure (pounds per square inch). And Amps are like water flow (Gallons per Hours).

Your reading of "274" for battery voltage is probably 27.4 volts DC (range from 22.3, to 26.9, to 27.4 VDC)...

That is great, now we know (probably) what battery bank voltage you have. And from the Battery Manual Link that Jim/Crewzer supplied, we see the proper voltages for your VRLA batteries are:


At 60-69 degrees F (cool home), you should be charging your 12 volt batteries at 13.85 to 14.15 volts (yours is a 24 volt system, so double those numbers). And long term storage (after fully charged) 13.55 to 13.85 volts...

So, your battery bank should read (nearing full charge) 27.7 to 28.3 volts. Once your battery bank has reached that voltage range, and you see the current start to go towards zero amps (even though there is still lots of sun), eventually your float light should come on, and the battery bank will drop to around 27.1 to 27.7 VDC (fully charged, no load from your inverter).

Also, from the battery manual, if you let your battery sit for awhile (no load, no charging--the manufacturer says 24 hours--but you can at least get an idea from over night--and measuring the voltage before the sun rises) (edited for your 24 VDC battery bank):



Now, I would still need to see the wiring of your battery bank, and if possible, for you to confirm the model number of your batteries...

I guessed that this was a 48 VDC bank, and your meter seems to be indicating that this is a 24 VDC bank...

Not a problem, but depending on the exact wiring and size of the batteries, I am not confident in my 4.5 days to recharge (all things being equal--this is still a reasonable number if the system is designed correctly).

I am not going to get back to you for a week--because of a bunch of other stuff I need to do--so I am not ignoring you. Others here should be more than capable of helping you further.

Reading through the battery manual, it is designed to support 100% discharge--but if you can keep your discharging to only 10-50% of battery capacity (see pdf file), your batteries will last much longer.

Please ask any questions--this can be confusing trying to understand all of these things at one time.

-Bill

Open Circuit Voltage vs. State of Charge Comparison*
% Open Circuit Voltage
Charge 12 VDC Gel / 24 VDC Gel Battery
100% 12.85 or higher 25.6 or higher
75% 12.65 / 25.3
50% 12.20 / 24.4
25% 12.00 / 24.0
00% 11.80 / 23.6

NOTE: Divide values in half for 6-volt batteries.
* The “true” O.C.V. of a battery can only be determined after the battery
has been removed from the load (charge or discharge) for 24 hours.