Low amps produced by 100 watt panel? Why?

mike74820 · February 2016

the rest for my battery today was 5 hours so how long do i wait to say it at resting voltage?

littleharbor2 · February 2016

SunKing may know a lot about solar (just look at his self given name), but his rude and condescending approach to people trying to educate themselves is really irritating. I'm surprised he is allowed to contribute I any forum and am glad he isn't allowed in NAWS.

westbranch · February 2016

mike74820 said:

the rest for my battery today was 5 hours so how long do i wait to say it at resting voltage?

3 hours is good after charging stops...

Vic · February 2016

mike74820 said:

as a pwm user myself, all i can tell you make sure your pwm controller is adjustable and you should be ok . i can tell you with my 200 watts of solar panels and my c35 xantrex controller set at 14.8 volts for bulk and 14.6 for float my battery's have never been happier. just read handy bob's stuff on pwm controllers and where to set them

mike74820 said:

i just know when i do what handy bob say, my battery voltage settles in around 13 volts, before i doing it the other way it rested at 12.7 volts, and now after i use the battery and wake up in the morning that voltage is usually around 12.65 volts

14.6 volts is NOT a Float voltage, that is far too high, even for Flooded batteries. But on a small system, this might not be the end of the world, especially if the system does not spend many hours per day in Float.

It is important that charge voltages be Temperature Compensated.

AND, it is also important that when we measure battery voltages, that these readings also be temperature compensated.

On one L-16 battery bank, here, really needs about 10 hours of Rest before the terminal voltage stabilizes. And, this is adjusted for the actual battery temperature.

Many Flooded batteries use a temperature compensation coefficient of --5mV per Cell per degree C. This can have a large effect on battery voltages, and needs to be accounted for when taking and referring to battery voltage readings.

IMO, Vic

mike74820 · February 2016

i just looked at the deka page for charge rates and it says my float should be 2.35v per cell and that equals out to 14.1v for float, so is my 14.6v really to high or should i back it down a little?

BB. · February 2016

"Let the battery bank tell you".

Basically, look at water usage--If you have to add water every 1-2 months--The batteries are probably "happy" on average. If you don't add water in 6+ months, you are probably under charging. If you have to add water every 1 month or less, you are probably over charging.

And use a good hydrometer to keep track of the state of charge. Discharging by 25% per cloudy day--A good design point. Avoid going below 50% state of charge very often. And avoid going below 20% state of charge ever.

Get >90% state of charge a couple times a week. Do not aim for 100% recharge every day/every time (that really is EQ territory). And get >90% state of charge before you put the system away for the season. Generally leave the solar panels + charger connected during winter. Turn off the AC inverter and and DC loads.

Some battery mfg. say to equalize every month (do the minimum needed--prolonged EQ is hard on batteries--It is just to get all cells 100% charged--SG not rising after 30-60 minutes--with controlled over charging. Not too much current or get battery too hot).

Adj charging set points and times as needed. You may find in winter that you want "high float" voltage and times simply because there are not enough hours of sun in the day to damage the battery bank anyway--And you need all the energy harvested to get the bank charged. During the summer when you have lots of sun, cutting the float voltage back and changing absorb time to 2-4 hours (instead of 6+ during winter) is good enough.

-Bill

Vic · February 2016

mike74820 said:

i just looked at the deka page for charge rates and it says my float should be 2.35v per cell and that equals out to 14.1v for float, so is my 14.6v really to high or should i back it down a little?

Hi Mike,

OK, so, you might well have Deka Flooded batteries, based on your statement about 2.35 Vpc ... But, if these ARE Flooded batteries, then, the Deka charging specs that I have, state that the Vfloat is 2.30 - 2.35 Vpc, so, 13.8 - 14.1 Volts for a 12 V battery.

Technically, Vflt is usually defined, as the minimum voltage that will just, barely keep the battery charged. On smaller systems, the exactitude of this setting may not be that critical, but, perhaps in Spring, Summer, into Fall, it will be more important, as the odds of spending a number of hours in Float increases.

Your C-35 CC may not have too much range in voltage settings, BUT, IMO, it is important that every one of your charge sources be Temperature Compensated, and believe that the C-35 can accept an optional Battery Temperature Sensor (BTS/RTS).

As BB Bill noted, taking and recording the SG of each cell in the battery bank, and noting water consumption are both key indicators of how well a Flooded battery is being charged/overcharged.

FWIW, Vic

Photowhit · February 2016

Mike, if they are flooded batteries, and deep cycle, I'm surprised they can maintain that high a voltage after charging. That would be removed/disconnected from the charger. It's more a factor of what the resting chemistry will maintain.

I hate speaking for someone who isn't here, but I believe Handy Bob's theory is that you have minimal charging time and to maintain as high a level as possible. As Vic said, it's not the end of the world and it makes a lot of sense in terms of usage in a working RV setting. I would suggest reducing settings when the system is inactive. Maintaining such a high voltage would be harder on the batteries (IMO) than when the batteries are in a working environment.

...and as Bill said, let water usage be your guide!

mike74820 · February 2016

my battery is a super start 31dcm battery it is a flooded battery. ill keep and eye on the water for sure, i just got one of those battery fillers that supposed to not let you over fill them. ill most likely turn the float down in a month or so when the sun will hit my panels from 8 am to 8pm. right now i getting bulk charging around 10 am

Photowhit · February 2016

Ouch! Might go back and read Handy Bob's or pretty much any of the back forum posts about batteries that are dual use/Marine batteries. They don't tend to last long in deep cycle use.

Yes, I know it says Deep Cycle as well, but you won't find many friends of this type of battery for true deep cycle uses.

More and thinner plates, might hold a surface charge longer? perhaps that would explain the 13 volts? I don't know just thinking out loud perhaps someone more knowledgeable will jump in...

mike74820 · February 2016

im in the testing phase right now, the one thing i learned from you guys is to burn up cheap battery's 1st. i only paid 94$ new for the 31 dcm, i know a lot you think of weight when it comes to battery's too and this one weighs 60lbs. if it will last a year until next tax season then i switch over to 2 6volt battery's most likely. but around here 2 of them is close to 300 bucks

zoneblue · February 2016

mike49 said:

he recommended 14.8v bulk and 14.6v float for it, right? i looked up the trojan recommendation and it looks like only 13.2v for float, so i guess it's the 14.6v float that is unique with what he is saying? and that works well, eh?

Nah, 14.6V for any 12v lead acid battery is a sure way to kill it. Of course it depends on the ambeint temperature, and whether the charge controller has temp comp, but that high a float voltage will destroy the positive plates by a process called grid corosion.

"The recommended float voltage of most flooded lead acid batteries is 2.25V to 2.27V/cell."
-- http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

Best to take everything you read with a grain of salt.

mike49 · February 2016

Photowit said:
"I believe Handy Bob's theory is that you have minimal charging time and to maintain as high a level as possible"

This is also my grade 1 understanding of what handy bob is saying and what I have read elsewhere:
The idea being that with solar as opposed to an on-grid charger, there is not enough time to complete the entire 3-stage charge cycle needed for a battery to get really full. When using an on-grid charger, it takes lots time at absorb then float stage when used with typical recommendations, because those recommendations assume an on-grid charger with enough time.
But in solar, we only have a few hours of sun to work with everyday (esp in winter) and we need those few hours to be able to get the batteries to be as full as possible.
How to do that from what I have gathered so far is to either oversize your panels and/or set bulk/absorb/float to a higher voltage, based on using a hydrometer to tell you when the batteries are full....

I hope I'm understanding this rationale correctly? (then maybe I can move on to grade2, or am i still stuck in grade1

)

And may I ask the experts/off-grid folks here if they would agree with this kind of rationale and does anyone follow this method with success?

thanks

BB. · February 2016

I would agree... In summer with longer hours of sun and more energy--You might need to pull back on the absorb time and voltage (assuming you have temperature correction for your battery bank by the charge controller).

-Bill

zoneblue · February 2016

PNJ has suggested something to this effect previously. (setting Vabs = Vfloat).

However the thing is that PV prices have dropped, and now arrays are/should be much bigger. My bank for example is in float prior to noon most days, and in the long summer days, can look forward to float times of over 8 hours, Thats not something you want to do to an AGM battery, itll destroy the battery from positive grid erosion and catalyst exhaustion. On the contrary i use skip days to only absorb every 5 days in the summer.

The logic does however make lots of sense, if your array is undersized, your climate nasty, and your bank flooded.

Really if you want to pick this apart some more, you come back to our basic tenets:
- designing for 25%DOD daily cycles
- designing for 0.1C charge rates.

For lead banks, this has the side effect that you can recover the overnite DOD with = 0.25/0.1/0.8 = 3.125 sun hours which just about everyone can get access to most of the year. Youll need the genset from time to time in the off months.

By using AGM, 15% DOD and 0.15C, you get = 0.15/0.15/0.9 = 1.1 sun hours, considerably easier to muster that up on a year round average.

Photowhit · February 2016

Yes, it's more involved and we are simplifying things. RV systems tend to be under sized for the recommended charging %. This both makes taking advantage of the available charging hours more important, and the higher voltage, at least somewhat, less damaging. Note that in a standard off grid installation, I would NOT (and do not) use his recommendations.

We are all learning, and often things taken out of context sound wrong and can get an immediate knee jerk response. I don't really have an issue with Marine batteries, so long as their limitations are understood. Heck I ruined my battery bank a decade ago, by leaving the inverter running with no to minimal charging while away for 3 months. Since I was running a minimal system a friend offered me an old trolling motor battery which I used over the winter when I had very minimal loads. It made it until spring, when I switched to a 24 volt system in preparation for a move... It was a used battery to begin with and pretty much worthless when I replaced it, but saved me from a lot of expense for 2-3 (maybe 4) months.

mike74820 · February 2016

you guys made me a little nervous running at 14.6v for float, so i backed it down to 14.1v which is deka's highest set point for float on their battery's. but i did keep bulk at 14.8v

Hassan · October 2017

Hi am Hassan from Liberia am kindly seeking an assistance on a system I setup at my home I do have 4 panel rated at 6.5amp they are all in parallel my expectation is that the combined strings should put out 24amp plus but on a real Sunny day the highest output of current is 8ahms and all the panel don't have any diode in them.

BB. · October 2017

Hassan, welcome to the forum.

Just to confirm, with solar charging systems, the maximum current is a combination of low battery state of charge (typically under 80% state of charge), a charge controller that thinks the battery needs full charging current (typically, charger is set to ~14.75 volts and the battery bus is at or below 14.5 volts and accepting all the charging current it can), and the solar panel(s) in full sun around noontime (must be pointing to within 10 degrees of the sun, clear skies, an no shade on panels--even a little shade from an overhead rope or a few leaves from a bush can kill solar panel output to near zero current).[

Next--Have you tried one panel at a time and see how much current each panel produces on its own? If you get within 80% of Imp (current maximum power) per panel, then probably all is OK at the piece part level.

If placing all of the panels together in parallel, you don't get (0.80 * 4 panels * 6.5 amps Imp) ~20.8 amps typical maximum on average good day with discharged battery bank (and/or DC loads).

What is the battery bank voltage when you are trying to measure maximum noon-time current flow? You can have too small of diameter wiring, too long of cables (cables should be short and heavy between charge controller and battery bank to keep voltage drop low), and/or bad electrical connections in your battery wiring (corrosion, loose/dirty connections, do not use "alligator clamps").

-Bill

mcgivor · October 2017

Best to start a new discussion, outlining exactly what you personally have, this way answers are directed to your particular queries, there are so many variables which may pertain to your particular situation which would otherwise be lost in the conversation of other people's issues. Tell us more, include as much detail as possible, don't be shy or reserved to start a new discussion.

Low amps produced by 100 watt panel? Why?

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