Added batteries now have less juice?

FireGirl · June 2018

Hello,

I have a small off grid system. Four 160w panels, Morningstar 45 MPPT charge controller and I started with two 6v Trojan flooded batteries supposedly 220ah.

I use very little power. My cell phone gets charged every day, my laptop gets charged 4 hours a week, my vacuum gets charged 4-6 hours a week, my power tool batteries get charged 2-4 hours a week and I use my sewing machine about 2 hours a week but only during peak sun with full charge on the batteries.

I do run a 0.6amp fan most of the day. The problem was that I wasn't using all my daytime power but I couldn't run my fan all night when I really need it to sleep down here in the deep south. By 10pm my battery meter would read 80% and my charge controller would be at 60%-80% SOC.

Since my batteries are less than 6 months old I thought adding a second set wouldn't be a problem. However, now that I have the new batteries by 9pm my battery meter says 80% and my charge controller reads 35%-60 SOC. The voltage meter says both sets are about 13.5v and the hydrometer reads between 1250 and 1265 at this point and I know that the batteries get to float and equalize states regularly.

I am very new to this and have no idea what is going on. I put the system in myself as a kit purchases from a supposedly reputable solar company...not that they are being helpful now. So I am here asking you nice folks for a nudge in the right direction.

Estragon · June 2018

I assume the fan is 0.6a at 120v through an inverter? What size (wattage) and type (more expensive and heavy pure sine wave or lighter and cheaper modified sine wave)?

Assuming 0.6a@120v via a largish inverter (eg 2000w), this could be part of the issue. 0.6 x 120v = 72 watts. Running 24hrs/day, thats ~1700wtt-hrs/day. Running it via a largish inverter may be relatively inefficient, and a modified sine wave type may have further losses. With ~5000 watt-hours of storage, the fan may be using a significant fraction.

If my assumptions are correct, I have a few thoughts that might help.

In terms of charging, what is your absorb voltage setting (voltage and time)? Does the charge controller have a remote temperature sensor attached to the batteries or internal temp compensation?

mcgivor · June 2018

The Morningstar controller LED 's, which I'm assuming you are using as a reference for state of charge, are in fact an "indication" of voltage during charging only, not thet state of charge of the battery, as soon as the sun sets they may turn to green/yellow or yellow, this has nothing to do with the actual state of charge. The actual voltage would be a better indication, if you are achieving float daily, that would mean the batteries are in reasonably good condition. The voltage meter? Is this a remote Morningstar meter or an add on meter?

FireGirl · June 2018

Thank you for replying so quickly! My inverter is a Magnum MMS 1000w pure sine. The fan is 120vac. The meter is a manual meter that I have to take to the battery box. The charge controller does not have a separate temp sensor, but the manual says you can add one...and I have no idea if it has internal compensation. The absorb. stage is 14.7 v at 180 min which it does get to mid day on most days...even if a little overcast. Should I get a temp sensor?

littleharbor2 · June 2018

FireGirl said: However, now that I have the new batteries by 9pm my battery meter says 80% and my charge controller reads 35%-60 SOC. The voltage meter says both sets are about 13.5v and the hydrometer reads between 1250 and 1265 at this point and I know that the batteries get to float and equalize states regularly. I am very new to this and have no idea what is going on. I put the system in myself as a kit purchases from a supposedly reputable solar company...not that they are being helpful now. So I am here asking you nice folks for a nudge in the right direction.

Sounds like something isn't calibrated correctly with such a large discrepancy between your controller and meter. What is the meter you are referring to? Have you re calibrated both controller and meter since you added batteries?

BB. · June 2018

To clarify your fan's energy usage... Amps is a "partial unit" -- It does not tell the whole story on power (rate like miles per hour) and energy (amount like total miles driven) usage.

When you are using Amps, you need to also take into account the voltage too. For example 0.6 Amps at 120 volts is:

0.6 amps * 120 VAC * 1/12 VDC battery bank voltage = 6 amps nominal battery consumption.

Once we include losses in your AC inverter, it looks something like this:

0.6 amps * 120 vac = 72 Watts
72 Watts * 1/0.85 AC inverter eff * 1/12 volt battery bank = 7 Amps @ 12 volt battery load
7 Amps * 8 hours a night = 56 Amp*Hours of usage @ 12 volts

You have a ~220 AH battery bank, and you should use only 50% of its capacity before recharging:

220 AH * 0.50 usage = 110 AH of "usable" capacity
56 AH used / 110 AH of capacity = 0.51 = 51% of usable capacity

So, just the fan loading (guessing on how many hours per night) uses about 1/4 of your battery capacity (per night). Which is just fine--As long as the battery is recharged the next day or two.

If the battery + charge controller are in the same room and at roughly the same temperature--You do not need a Remote Battery Temperature Sensor.

If they are in different locations/temperatures, and/or you want to recharge the battery as quick/fully as possible, an RBTS is a nice addition.

-Bill

Estragon · June 2018

A 1000w PSW inverter isn't so bad. You might get a bit more efficiency using an inverter like a 300w Morningstar dedicated to running the fan and other small but constant loads, but maybe not enough to make it worth the cost.

Another possibility is replacing the fan with a DC model like:
http://www.backwoodssolar.com/products/fans-large-small/40inch-12-volt-ceiling-fan-white

The fan takes less wattage to run than your AC fan, and avoids the losses (which can be significant) running an inverter constantly for a small load.

MrM1 · June 2018

I'm starting to build this book of "Bill Equations" for future reference.

FireGirl · June 2018

Thank you for the sample math!!!! That really helped.
So since I have now doubled my battery to 440 ah I would only be using a quarter of my battery power which is no problem.
I also looked at the recommended fan...my house is only 160 sq feet so a ceiling fan is a bit much...but they had a DC window type fan. Would I just add another breaker to my DC box and run wires to it directly? I am assuming the wiring is similar to a light switch or outlet?
The meter I am talking about is a midnite solar battery capacity meter.
I can't tell you how much I appreciate all your help and ideas.

Estragon · June 2018

Storage capacity is doubled, but charging capacity hasn't. If you find daytime loads prevent the batteries from getting to float at least once or twice per week, you may want to consider adding some charging capacity.

Yes, for the fan you can just add a breaker to the DC panel and wire to the fan directly, or via a (DC rated) switch. It's much like wiring an AC outlet, two wires and a ground. DC wire is normally red or yellow for positive, black for negative, and green for ground. Unlike AC, which will generally work if wired improperly (ie line and neutral reversed), DC won't, and some DC devices can be damaged by reversing polarity. Regular 14/2 or 12/2 household wire can work (may not be code), but I'd mark the white wire with red tape or marker to avoid confusion in polarity.

FireGirl · June 2018

Thank you again very much! Am going to research dc fans! Will keep my eye on the batteries. I have another panel that matches, but I'd rather save it for another project. You have been way more helpful than the people I bought the system from!

BB. · June 2018

Roughly, near what major city is your system installed (figure out hours of sun per day by season).

Also, how many hours per day do you run the fan?

Only in summer, or loads during winter too?

Bill

Photowhit · June 2018

FireGirl said:
I have a small off grid system. Four 160w panels, Morningstar 45 MPPT charge controller and I started with two 6v Trojan flooded batteries supposedly 220ah.

FireGirl said:

Since my batteries are less than 6 months old I thought adding a second set wouldn't be a problem.

Reasonable, you should be able to provide a bit less than 10% charging rate for a 440 amp hour battery bank. Did you buy the exact same size and brand? Did you equalize before adding the new batteries? Did you install them correctly to be sure they have equal resistance, basically + connected to one string and - to the other?
Image result for 2 x 2 golf cart battery bank

Image result for 2 x 2 golf cart battery bank

Correct!
Wrong!

While I say reasonable, if you are running the fan continuously 24/7, that takes away amps of the amps available to charge, so now you would be 'under paneled' 640x.75=480 So roughly 480(available wattage)/14= 34 amps less @727 amps to charge a 440 amp hour battery bank.

It's hard to imaging you can't make this work, I've air conditioned a 10x16 with a 1000 watt array and 4 GC batteries for 4-5 hours (we gat a bit cooler at night in Missouri so I could sleep 8 hours. Also ran 1 or 2 O2cool fans, they use very little energy, but are a small 10" fan compared to your large fan. They use to be 12 volt, but now are 9 volt.

Looks like Home Depot still sells the 12 volt version, or perhaps they haven't updated their website. Out of my feeble mind I think they used about 8-10 watts on high.

https://www.homedepot.com/p/O2Cool-10-in-Portable-Fan-1071/203121403

Battery voltage is a poor way to measure batteries state of charge. When you say;

FireGirl said:

The voltage meter says both sets are about 13.5v and the hydrometer reads between 1250 and 1265 at this point ...

You are NOT reading the batteries voltage, but a system voltage. Flooded Lead Acid batteries will not 'rest' at 13.5 volts. They are either being charged or have a surface charge. Your SG readings can be trusted.

Most battery monitors that use volt just give bad information most of the time! There are a few that use a shunt to measure the current going into and out of the battery that are somewhat reliable, Like the Trimetric.

FireGirl · June 2018

I am near Pensacola Fl. The fan runs during the day, but I made insulated shades so I would like to run the fan at night when it is cool then close up the house to keep the sun and heat out during the day. There are going to be shade arbors finished on 3 sides of the house by July to help...
I did wire the batteries correctly (I checked 3 times before turning the panels back on!) and they are the exact same as the 1st set. I let the old set rest for a few hours and then tested each one and they all tested the same 6.3 to 6.5 and the hydrometer gave readings that were very close as well. Once they were hooked up and I knew I had enough light I ran the "equalize" on the charge controller. Was there something else I was supposed to do?

Photowhit · June 2018

That sounds pretty good, usually like to equalize the old set before adding new and a commissioning equalizing is usually a good deal!

You are a brave person to deal with Florida heat and humidity without 'air' I was raised and lived in Tallahassee for many years.

FireGirl · June 2018

My jobs involve being outside and playing with fire...a/c seems too cold to me any more. But I will admit it is a far cry from Illinois where I was raised!😊
How do I equalize a new set before adding them?

littleharbor2 · June 2018

I have bought 3 of those fans at Wal Mart. They are a 8 D cell battery fan with a 12 volt power inlet. great personal fan. I have also had great results with 12 volt radiator fans too. The generic ones are about $20.00 on eBay. Been running all day every day in Baja for over 3 years now without a whimper.

mcgivor · June 2018

My bedroom fan setup is a 12VDC table fan, connected to a 45Ah battery with a 60W panel charging via a cheap PWM controller. Fan draws 1.1A runs for 8 hours, battery is charged before noon on a clear day. Using a 120VAC fan requires the inverter to be powered which runs inefficiently at low output, driving the net battery current up to a point where the inverters current needs could exceed the useage of the fan itself.

Thom · June 2018

We use ryobi 18v fans at night and turn off the inverter.

FireGirl · June 2018

I love all the fan alternative ideas! Thanks. But I still don't understand how doubling my battery bank makes the same load drain the batteries faster...

Estragon · June 2018

It doesn't.

It may, however, make batteries *appear* to drain faster, depending on how the initial condition and present state of charge are defined by the device (or person) making the determination of each state.

It also makes me wonder a bit about the wiring and connections between the two strings of batteries. Suppose, for example, one string is fully charged and floating at ~13.6v with SG at 1.27. The other is partially charged (because of bad connection, too small wire or whatever) with SG at 1.20. The high string makes the charge controller go to absorb & float, while the low string struggles. When charging stops, the float surface charge gets taken off the high string by both the loads and the low string. In other words, the high string is both supplying loads and charging the low string, making it appear as if loads are drawing the overall bank down faster than with a single string alone.

Just a thought.

FireGirl · June 2018

Well after reading this last comment I've checked my connections and they seem fine. All the wires are the same size as the 1st string. I am going to turn off the whole system and test the batteries in the morning before they have had any more charge or load. I just don't know what else to do!

Estragon · June 2018

My suggestion would be to check the batteries when the controller reaches absorb voltage. If there's a connection issue, it will show best when there's more current going to or from the bank (which there typically would be in the bulk stage of charging before reaching absorb voltage). Testing them after resting overnight with little load and no charging lets them level out, and may give misleading results.

Do you know what size the wires connecting the batteries are? They should be about the size of your little finger or larger.

BB. · June 2018

Just to give you an idea of how much power you can harvest/support:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Tallahassee
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 63° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.66	5.39	5.80	6.11	5.98	5.38
Jul	Aug	Sep	Oct	Nov	Dec
5.08	5.06	4.96	5.27	4.85	4.51

So, for 4x160 watt panels or 640 Watts

640 Watts * 0.61 DC solar system eff * 4.55 hours of sun (Dec average) = 1,776 Watt*hours typical max for average December day for DC loads
1,776 WH / 12 volts = 148 AH @ 12 volts per day

If you are taking most of your power from the AC inverter:

640 Watts * 0.52 AC Battery based solar system eff * 4.55 hours of sun (Dec average) = 1,514 WH per December day at 120 VAC

Remember these are long term averages. Actual harvest will vary based on weather conditions. And you should not plan on using 100% of your generated power every day. If you have fixed daily loads (like a refrigerator), you have to over size your system to support a few days of bad weather (not using too much genset+fuel).

-Bill

Added batteries now have less juice?

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Tallahassee
Average Solar Insolation figures

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Added batteries now have less juice?

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TallahasseeAverage Solar Insolation figures

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Tallahassee
Average Solar Insolation figures