MPPT question

System

Hi,

Now that I have all the wonderful information under my belt from having asked about my battery monitor, I have a few questions about my MPPT... thing....

There's snow here today, so this is the first time I've ever looked at my MPPT and not seen any amps coming in during day light hours.

I have it set to show me amps from my pv array.

But, I can also look at either amps or volts from my batteries... since I haven't been looking at that because I thought the battery monitor was telling me everything I needed to know (which it wasn't) I don't know what kind of range of numbers it might display...

Is it possible to use that, the MPPT thing, to monitor my batteries?

It's a bit above 45 degrees in here, which seems pretty comfortable, I suppose because I was so warm in my tent last night, and because I'm always really warm after I've been sleeping.

I'd like to use electric to heat water for coffee, because I don't have many candles left and the ones I have produce a lot of soot... but I'm unclear on the situation with my batteries...

Any thoughts on what I could be learning from my MPPT?

BB.

Re: MPPT question

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).

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.

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.

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.

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.

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

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.

-Bill

System2

Re: 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

Thank you SO much. I'm really keen to try a solar oven... that will be fun.

crewzer

Re: MPPT question

Bill,

Here are the specs on CT's "Deluxe Full-Time Cabin Kit":

Full Time Cabin Kit

For medium-sized weekend places or modest full-time cabins. It will power lights, stereos, TV, laptops and, with an optional inverter, other small appliances like a microwave or desktop computer. The controller delivers maximum power point racking for peak PV output under all conditions; it also provides system monitoring with battery voltage and PV amps. You provide a 4" steel pipe for the PV array mount. The battery pack is optional. Can be setup initially as a 12- or 24-volt system. 2,000+ watt hours.

Includes:

• 4 Sharp 123W PV Modules
• 1 Pole-top fixed rack
• 1 BZ Products MPPT500 Charge Controller
• 1 6-circuit DC Load Center
• 4 Circuit Breakers for above, 1-30A, 3-15A
• 1 110A Class T Fuse

Battery Option:

• 4 98Ah Gel Storage Batteries with Interconnect Cables

Here are links to manuals and specs for the controller and PV modules:

http://bzproducts.net/db5/00461/bzproducts.net/_download/MPPT500Slick.pdf
http://bzproducts.net/db5/00461/bzproducts.net/_download/MPPT500V1INSTALATIONMANUALv2.0.pdf
http://lib.store.yahoo.net/lib/wind-sun/Sharp123.pdf

CT's pix verify the BZ MPPT controller. I'm unable to verify the PV are indeed Sharp 123's. I have a pair of 'em in my system and mine look different. The batteries are not 98 Ah gel batteries. Based on the pix and a description from CT, the batteries are MK 8G4D 12 V x 183 Ah gel batteries.

Here are links to specs and a technical manual for these batteries:

http://www.mkbattery.com/images/MK_Gel_v4_web.pdf
http://www.mkbattery.com/images/VRLA_TechManual.pdf

Note the following battery related issues: correct charge voltage for gel batteries, location, ambient temperature, and temperature compensation.

CT,

A question for you: Are you relying on this system to meet all of your electrical needs?

Regards,
Jim / crewzer

System2

Re: MPPT question

That's pretty similar to what came in my cabin kit.

My panels are Evergreen's made in Germany. They're 120.

Yes, that's the kind of MPPT I have.

When I had my power shut off and began to look at solar, I spoke with a woman salesperson who had me look at my electric bills to see how much electric I was using.

I was SHOCKED to find out I was using a kilowatt a day just leaving the telly on. And another leaving incandescent lights on. Now I leave lights on, because of my lack of balance when it's dark, but they're little day-light flourescents and they hardly use any electric.

I have a small fridge (that I bought years ago, that looks like an old fashioned safe) - it hardly takes any electric, but I don't leave it on because now I cook fresh every day. Only really meals are brough in to me on weekdays because I'm not well enough to be up very much yet... (Pain, but that's boring.)

So my system meets my electrical needs quite nicely... My batteries are about twice as large... so I think they would be hard to wear out, if I knew what I was doing... that monitor sure let me down, or else the installation of the monitor let me down.

BB.

Re: MPPT question

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

System2

Re: MPPT question

Oh my gosh... You mean I'm CT... I was trying to figure out if that was a manufacturer that I looked into when I was shopping...

I have the specs as a link on my page... there's a panel type box on the pole, which I think is the Outback DC load center, and there was another box that I didn't need or use since I went with 24 volt wiring... or maybe 48, I forget.

And then there's the Eaton box inside with the shut off lever...

I just tried to heat water for coffee, and the inverter shut off. So there's not enough battery power, and there's only an amp from the panels right now. I suppose I could go outside and use a broom to dust the snow off the panels... or, I could wait.

I can't find an MPPT booklet, so I don't know if one came and it wasn't left for me after installation, or if one didn't come.

System2

Re: MPPT question

Hi again... oh... I see, you pretty much copied the specs.

I have this frustrating brain injury.

When I got my kit they had Evergreen panels from Germany.

I was looking at another kit with Sony panels, that sounded really good, but the shipping was free on the kit I got, and it came with the batteries. I thought the batteries were larger, but I may not remember that correctly. I thought they were 168 each... I should go get the catalog I actually used.


Yup... the batteries that came with the kit I ordered are 183 amp hr.

System2

Re: MPPT question

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

Oh... darn. I wonder if I've ruined the batteries, then. Darn it. If I get my condo back, or its value I can replace if I killed them... if not... major Darn it.

I don't use the fridge. I think it's an energy star from a long time ago... I had used my old fridge to freeze the food that I didn't eat that was brought to me each day, I was really looking forward to the frozen fruit in the summer. But all that had to be thrown out when they shut me off without me even knowing ... I thought they should have at least sent a notice, they said sending my bill was notice enough.

I think it's going to take a long time to fill up my batteries again. If I were getting 5 amps an hour, for 8 hours a day, then would that be 40 amps all together between all four of the batteries?

I just put water on over a candle for coffee.

It takes about an hour.

My electric was shut off in April, San Isidro day, but I didn't get a system for about two months. I kept wanting to get a few more panels, but there was no way I could work it out... my money was just too tight.

In between I got one of those little portable PowerPacks, but one of the cells was bad and it didn't give me an hour a day on my laptop... so that was frustrating. Still, even though I didn't know about the bad cell, I thought it would be better to have 16 times that amount of electric and feel safe, than to buy back into the PNM system and never be able to feel safe. I just forget too easily... so for me a notice is something I really need.

BB.

Re: MPPT question

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

Re: MPPT question

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

Ralph Day

Re: MPPT question

I have found a squeege on a telescoping pole (you could wash windows with it too) works well. Just the weight of the pole provides enough force to remove snow with no scraping effort (don't force it). Even when a wee bit of snow, or like yesterday, some ice, will melt off as soon as the sun starts hitting the panels. Minus 8c here and the water was running out from under the ice after a few minutes of sun exposure.

My panels are at a 50deg angle and i'm too impatient to let the sun do all the work, although it has in the past. Too cheap to let all those photons get away too!

ralph

System2

Re: MPPT question

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

I don't understand what you mean about getting me upset about my installation.

I'm sure the battery monitor was installed wrong. They couldn't sell them if they did nothing. Mine did nothing. So I figure it must have been a result of faulty installation.

In terms of my batteries being dead... I think the inverter stops drawing power at a certain percentage down. I don't know what that percentage is. But the booklet says it turns off so the batteries won't be damaged. Clever inverter. But actually, all the inverters I had with the little solar thing did the same thing. More or less. So I think that function is pretty commonly built into inverters for obvious reasons.

I'm glad I got the portable solar thing. It gave me a lot of experience, which came in especially useful with this recent glitch. If not for the portable system I wouldn't have known what the beeps meant and could have thought they related to the cold weather.

I got my portable thing to use for my computer, which needs an amp... but it failed to do that and then it turned out one cell was bad... so they refunded my money, but not without effort.

***

are you saying 4.5 days for each battery? or, once they are wired in series, or whatever it's called to get the 48, is it 4.5 days for all of them?

I didn't have any electric last night... and I waited a bit to plug in to it today.

The bold feature won't work... I was going to highlight where my question was...

System2

Re: MPPT question

Ralph Day wrote: »

I have found a squeege on a telescoping pole (you could wash windows with it too) works well. Just the weight of the pole provides enough force to remove snow with no scraping effort (don't force it). Even when a wee bit of snow, or like yesterday, some ice, will melt off as soon as the sun starts hitting the panels. Minus 8c here and the water was running out from under the ice after a few minutes of sun exposure.

My panels are at a 50deg angle and i'm too impatient to let the sun do all the work, although it has in the past. Too cheap to let all those photons get away too!

ralph

Love it! What a clever idea.

I'm getting 7.5 amps now, so I think the snow must have all melted off.

I'm SOOOOO glad it snowed during the night rather than today. I'm delighted with the snow, and especially delighted with its timing.

System2

Re: MPPT question

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

Oh.... Magicians hat for you!

How can that MPPT thing do that? get more amps than it gets?

I am so impressed.

Even with a fairly long pole I don't think I can reach the top of the top panel... so I'm not sure it will do a lot of good as I understand that the photons go to the dark spaces before they will allow themselves to be herded into energy containers...

Anyway, I'm all happy again now that I can be on my computer again.

I'm writing down my MPPT readings... and that's pretty interesting.

(As an aside, for years Santa Fe didn't have any snow removal equipment. When it snowed, the philosophy was that if you just waited, the sun would melt it.)

icarus

Re: MPPT question

Even partially getting the snow off the panels will help speed the melting, as the panels will absorb heat faster.

Icarus

BB.

Re: MPPT question

Karen,

Yes, if your batteries are all connected in one string--that would be ~4.5 days to completely recharge (in full sun).

However, to be more exact, I think you are reading solar panel current. Switching to read battery current is the exact number you want (with MPPT controllers, the battery current can be the same or higher than the Solar Panel current). Using the Battery Current in my previous equation may give you a shorter time to recharge.

About getting making you unhappy with your installation--This was based on your previous comments about installers, power companies, and such. I just want to be clear that I am not there and can only give you suggestions and information. I don't want to give you the idea that your installer messed up (the battery monitor you have, for example, could be wired correctly and still not give useful information--I don't know).

-Bill

System2

Re: MPPT question

icarus wrote: »

Even partially getting the snow off the panels will help speed the melting, as the panels will absorb heat faster.

Icarus

Good to know. thank you.

westbranch

Re: MPPT question

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

System2

Re: MPPT question

BB. wrote: »

Karen,

Yes, if your batteries are all connected in one string--that would be ~4.5 days to completely recharge (in full sun).

However, to be more exact, I think you are reading solar panel current. Switching to read battery current is the exact number you want (with MPPT controllers, the battery current can be the same or higher than the Solar Panel current). Using the Battery Current in my previous equation may give you a shorter time to recharge.

About getting making you unhappy with your installation--This was based on your previous comments about installers, power companies, and such. I just want to be clear that I am not there and can only give you suggestions and information. I don't want to give you the idea that your installer messed up (the battery monitor you have, for example, could be wired correctly and still not give useful information--I don't know).

-Bill

4.5 days is exciting! Way better than what I was fearing...

For a moment I was getting 8.1 amps from my panels.

On my MPPT there isn't a lable that says, "battery current"

I have a choice of Battery Amps or Battery Volts....

Maybe current is amps... those two numbers are fairly similar: the pv and the batteries, I mean...

I don't know ... I think that they couldn't sell those monitors if they didn't show some change from best to no more power for the inverter... mine never changed.

The electrician guy was grumbling a lot... so now I think he may have not quite gotten it. I mean to take some pictures of the wires... cuz now that I look at them... they look a little questionable.

I hope my batteries are okay...

Being without electric was not so bad. It was scary, but then in the actual fact it was more boring without my computer than anything else.

I appreciate your information.

If I'd understood the MPPT thing in the first place, I guess I could have not gotten the monitor... I just didn't want to have this happen...

lol

best laid plans...

System2

Re: MPPT question

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

Okay.

I think I've seen it now that I know it increases the amps... if I understand correctly.

After the last set of messages I went and looked, and sure enough, the pv reading for amps was about 3 less than for the batteries... so that extra three amps is courtesy of the MPPT... is that right?

I took readings a few times an hour today, each time I changed what I was using: computer without modem; computer with modem; no computer no modem; no computer, no modem, no inverter... and as a set that activity was really interesting.

I'm torn about using my computer tonight... but I think I will.

If the calculations provided here were from dead to full, then I would think I must be about half way to full from one day since I doubt the batteries were allowed to get lower than 50%... I might be wrong.

Oh.....

I don't quite understand the volts reading from the MPPT... It's not a number I expect. Today it ranged from 223, to 274 at the highest. When I plugged in my computer and modem the volts dropped to 269, but the sun also happened to get clouded right then...

What kind of number is that? I thought it would be, I don't know, maybe the same number as the amp hours, something like 183... but it's never been that low... so... what is it? Can you see what the highest is that it would get? Does it relate to how full the batteries are, or simply to ... I don't know...

icarus

Re: MPPT question

To get a handle on what these readings mean, I suggest that you read and understand, http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries.

This will go a long way to educating you about how reading can and do vary with temp, loads, charging ect.

Icarus

PS And how to keep them healthy and long lived too!

BB.

Re: MPPT question

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:

Temp F Min/Max Charge/Min/Max Float
60 – 69 13.85 14.15 13.55 13.85

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):

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.

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

System2

Re: MPPT question

icarus wrote: »

To get a handle on what these readings mean, I suggest that you read and understand, http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries.

This will go a long way to educating you about how reading can and do vary with temp, loads, charging ect.

Icarus

PS And how to keep them healthy and long lived too!

I've gone to the link.

I have a really hard time reading this "Battery life is directly related to how deep the battery is cycled each time. If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD. If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%." and understanding it. I can't keep it straight. That has to do with my brain injury.

I didn't discharge my batteries very much for about 6 months... so I thought that would be good...

But, one thing I understood was that temperature reduces... I don't quite know how it works, but maybe the low temperature contributed to my problem.

I don't have heat... well, obviously, I guess, since what caused my problem was trying to heat. lol

I was looking at a light in my livingroom a bit ago because it was drooping, and upon closer inspection the metal had broken... I'll take a picture tomorrow and show you... it's rather surprising, and I wonder if it's from the cold.

System2

Re: MPPT question

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

Oh dear, I feel really bad, this is such a beautiful answer and I'm not able to grasp all of it... I've lost some working memory, and that makes it hard to grasp things that aren't sort of linear... I don't know how to describe it, but it's extremely frustrating, and that's why I want people to learn the warning signs... because a vitamin B12 deficiency can cause this, and it can be reversed if it's caught early.

Sorry.

Okay... so what I've picked up so far, is that when I thought the MTTP was saying 274, what it was really saying was 27.4... is that about right?

If that's right, then I understand a bit better because when I was buying the system I noticed that there were these ranges, rather than things being exactly this or exactly that.

***
it was about 48 degrees in here this afternoon, so I expect it was colder than that last night... so that probably affected what the batteries did.

****

I want to go back and read some more of what you wrote.

(Thank you SO Much for writing it!)

System2

Re: MPPT question

BB -- Have a good time while you are gone! I hope you enjoy yourself a lot.
Thank you SO much for your help. It's been dynamite!

I wish I knew, though, when you say you're not so confident of the 4.5 number, if you now think it should be lower or higher...?

In terms of my wiring... things completely fade in my mind, and while I once knew... I can't be sure now...

Thank you again!

Have Happy Times!

System2

Re: MPPT question

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.

OMG - unless I misunderstand it looks as if I discharged about 90%... I can't remember the numbers I wrote down, though. I should go get the paper but it's so cold ... it's warmer here in my indoor tent.

I'm going to go read from the link, again.

BB.

Re: MPPT question

Yes, the voltage is just missing a decimal point for the voltage...

The reason I am not sure about how long it will take to recharge your system (4.5 days)--is I am not sure of the capacity rating of your batteries and how they are wired.

There is a lack of complete information here... I don't know how your system is wired (voltage), you have given us the solar panel current (amps) but not the voltage (and with a MPPT controller--we need both the voltage and the current). Not sure about the battery capacity (how many gallons is the gas tank?). And now you have given us the Battery Voltage (~26 vdc), but not the battery current (amps) yet...

So, we are getting closer--but some of my earlier guesses were wrong (24 vs 48 vdc battery bank)...

Does not change your system, and you have more information on how to manage and understand your readings from your MPPT controller... All good things.

And, basically, you are correct on the battery... The deeper your discharge it, the shorter its working life.

Also, a cool battery has higher voltage readings. A cool battery will last longer (in years). But does have somewhat less ability to store and supply power.

The link to the battery manual the Jim provided has a whole bunch of information about your batteries.

Karen, you are doing well here. And I wish my English skills were even 1/2 yours (hence, the reason I choose Engineering--I don't have to talk with anyone-- :roll: )... Or at least so I thought until I had to give training sessions (I threatened to quit the first time) and the long reports, manuals, and design sessions... Gotten over the fear--but my writing is none to pretty.

Take care Karen,
-Bill

BB.

Re: MPPT question

Karen,

I think the lowest voltage you gave me was 22.3 volts... Basically, 100% discharged.

But remember, these voltages are very dependent on the temperature of your batteries... And a few 1/10's of a volt make a big difference...

Read Jim's link on the battery and all of this information is there. I cut out just a piece of it (60-69 degrees F) to try and make it clearer to you the first time through.

Sincerely,
-Bill

icarus

Re: MPPT question

I'm sorry to say that I think you are correct in your assumption of draining 90% of your battery. It is quite common for people who are new to RE to not understand that even with "deep cycle" batteries, you can't drain them dead (90%) routinely and expect good longevity from them.

As the link suggests, if you discharge them 20% they will last 10 TIMES as long (as many charge/discharge cycles) than if you discharge them 80%.

Icarus

icarus

Re: MPPT question

I tried to post this as a PS to no avail,

PS. I don't know how big your battery bank, or your panel system is, but the relationship between the two is critical. It is even more important that you (the opperator) understand how much energy you should be using. Just because the lights or the computer is on, doesn't mean there is enough "juice" to safely continue to run them. Most people agree that the battery capacity should be big enough for 4-5 days of average use before the batteries reach 50%. Then you need enough panel capacity to bring them back quickly, as using/leaving them partialy discharge will kill them quickly. Most experts (here) recomend that you have 3-5% of battery capacity in solar capacity. They also recomend that before the batteries get close to 50% (most say 80%) they should be fully charged from either grid power, or from a generator. You might consider, if you are not going to to back on the grid, getting a small generator (Honda eu 1000 or similar) to augment you power. Coupled with a GOOD charger you could keep you batteries up, use the generator for your high draw item such as your coffe/tea pot. I use a Honda eu 1000 to top up my batteries. It costs ~$500, plus a Xantrex tc20 charger ~$250. It burns about a quart of gas every 4 hours whilst charging my battery bank.

I might also suggest that you read through all the threads about "off grid" living on this forum.

Tony