Cold Batteries

[ChrisOlson]

We had one of the poorest Decembers for power generation that I can ever remember.  There was about two days of sunshine for the month.  We had good wind, which kept us from burning the gen fuel for much of the month.  But without the solar working my system has no way to regulate the voltage properly to absorb charge the bank.  The power from the turbines is either too much (and dumping), or just enough to meet the loads and keep the lights on.  And sometimes none at all.

Over the last week the performance of my battery bank (24 Rolls T12's, 24 volt) got really bad.  With heavy evening time loads (usually average 1,800 watts with peak load up to ~6 kW when the electric water heater is going), the bank would hold 24.0 volts OK.  But overnight with all of our Christmas lights going (about 350 watts), furnace blower, ''fridge, freezer, night lights, furnace in my shop, and probably some other small parasitic loads, the bank would be down to 23.5 volts by sunup.  I got the "quiet time" for the gen set from 11:00 at night to 6:00 in the morning.  So at 6:00 AM the inverter would immediately start the gen and charge the bank up, if the wind isn't blowing.

Yesterday, over my morning coffee, I punched the calculator keys and figured out the loads and what we're using vs what the bank is supposed to have for capacity.  The bank was delivering less than half of its rated capacity.  I scrolled thru the menus on the master inverter and it said the bank temp was down to 2° C.

The bank is in an insulated battery case in our utility room and the utility room is unheated.  But it normally stays above freezing in the utility room and heat from charging the batteries normally keeps them above 15° C.  The poor power month and not charging them properly let the cold gradually seep in until the whole 1.5 tons of lead in the bank was cold soaked all the way thru.

It took 7 hours with a 45,000 BTU space heater heating the inside of the battery case to get them up to 20° C.  I then put a 6 hour equalization charge on them with the generator and inverter-chargers and got them up to 28° C.

What a difference!

Not a single amp of power coming in from turbines overnight, just another day here with heavy overcast and no sun.  And the wind is just starting to pick up and the turbines are starting to spool up for the day (wind is supposed to blow 30-40 mph later tonight).  But my bank never even dropped below 25.0 volts overnight.

I guess this could be termed Nursing Care for batteries - keep 'em warm and feed 'em   
--
Chris

[TomW]

Almost like it would be effective to put a light warming load on them even tho your incoming is reduced!. Never took my banks temperature but they are in a  heated space well away from the stove on an outside wall.

I suspect it only is an issue in these short days around the solstice. Mine are hovering down in the area I prefer they don't see some over nights. Windy enough to push them up to 28+ many days and dead wind overnight with low sun. Once you get a ton or so of lead chilled down it takes some BTU to get it warmed up much.

A quick check shows mine to be just above 60F here on the last day of 2011.

Tom

[Volvo farmer]

I went through a similar thing earlier this month. Batteries were not at their normal voltage in the morning.  Finally got out there with a hydrometer and found one cell at below 1100 SG. 

I split the two parallel strings and boiled the crap out of it about 4 times. I was pushing battery temperature up over 100F on that string, let it cool down and did it all over again over a couple days. I did manage to bring that bad cell back up to about 1250. 

Even with 4-6 equalizations a year, 2 hour absorb times at 29.2V and 300+ sunny days a year, my cells were all over the place in their SG.  I was shocked to find that one cell could get so far out of balance and still be able to be brought back to life.

[birdhouse]

my batteries are in an unheated space at 4'000 ft above sea level.  it get below zero F often in the winters.  i notice huge loss of capacity at these temps, and try to barely use the juice.  just a few lights and a radio when it's that cold!

i do have my dump load sitting below them, and if windy it seems to help a tiny bit with battery numbness.  

adam

[wpowokal]

Opposite problem here, they sit between 28-33C.

AofJ

[ChrisOlson]

Well frankly, when we put in our new system late last spring and retired the old 12 volt system that served us well for 7 years, we made it all automatic so I don't have to mess with it other than servicing the batteries about four times a year.  It's been a long time since I had this cold battery problem, and I think that was about five years ago, also in the month of December.  The days are short, we get no sun, and the wind turbines aren't voltage regulated other than dumping to the water heater (thru the inverters) when they put out too much power.

So I NEVER bother looking at the battery temp.  They're always above 15 degrees C even in -20F weather  (the Xantrex shows battery temp in C - the confounded thing).

I installed a wind turbine on a new off-grid home a few miles south of us a few weeks back.  Those people put in a nice utility room for the batteries, dual Xantrex XW4024 inverters, and power panels, and it's unheated but insulated very well.  The utility room is connected to the house like ours.  He put a small fan in the utility room in the wall between the kitchen area and the utility room.  The little fan (very small - about 60 CFM) has a thermostat on it and when it gets below 60 in the utility room the fan starts and pulls warm air from the house and blows it into the room to keep it at 60.  Plus the little fan draws a small amount of fresh air into the house thru cracks and whatnot, to keep the air exchanged in the house.

That's a very well designed system and I'm going to fire up the Dodge Cummins and go to Menards and get me the stuff to do the same thing before they close up for New Year's.    
--
Chris

[Dave B]

Great information Chris, thank you for posting. I notice the same thing here only on a much smaller scale. I have 8 L-16's running 48 volt and they are in an insulated but vented box outside. My best set up so far is to have the inverter kick on auto charge for a couple hours each day at the same time. Most everyday if it's been a bad energy day before and my demand is low this will bring them to 100%. Like you said though, relying more on the wind and solar for charging they would indicate 100% on the good days but if they are cold the percent drops much more quickly than when warm. Keep em warm and keep em fed, very good advice and the idea of pushing some heat into the box from the house I just might go for that also. Keep us updated, thanks again.  Dave B.

[ChrisOlson]

I rushed to Menards and bought one of those little 4" duct fans like I got on my shop solar hot air panel, plus one of those orange duct stats to turn the fan on and off.  I also found a nice square grille to go over the hole.  I figured there's no sense to heating the entire utility room because the inverters and equipment like it cooler instead of warmer.  When both inverters are charging the bank at 240 amps they put out a lot of heat anyways from the cooling fans running.

Since the battery cases are right up against the outside house wall, and insulated, I bored a hole the thru the wall with a 4" hole saw.  I shoved the duct fan in the hole and put the nice square grill over it.  The hole came thru right alongside the microwave cart in the kitchen, right above the heat register that comes out of the floor.  Perfect.

I set the thermostat on the duct stat to 65° F in "heat" mode so it turns the fan on on temperature drop (the stat has both heat and cool modes built into it - "cool mode" turns the fan on with temperature rise).

The turbines are putting out 160-200 amps now so the batteries are heating from being charged.  The temp was at 18C after overnight, but now shows 19C



I think I got the problem "fixed" and it won't happen again with that fan in there to keep the battery cases warm.
--
Chris

[Simen]

It just shows how important it is for us that have batteries that sits in a place where it could go down to; and below freezing, to have a temperature compensated charging/dumping system...

At around 0 deg. C., a 12V bank should have a absorption charge at 15.3-15.6V to get properly charged... And in my experience, it's not uncommon to have a resting voltage around 12.4V in those temps...

And i think (from memory), at -7 deg. C., a battery bank are closer to 50-60% rated capacity..

Something to keep in mind these days...

[ghurd]

It is a very well known phenomenon.
'CA'  and  'CCA' are listed on the cheapest car battery sticker.
Can anyone remember the last time they changed an in-service car battery in June?  No?
Nov, Dec, Jan?  Yes?

Stupid idea for most people.
Might be something good for you?
Basic concept.  Drill a 4" hole 4' down below the bank.  Drop a couple suitable (for the purpose) resistors, and cover them.
Lets say the math works out to a 1KW resistor using 10W is a good choice?
Most of the time, for you, the 1000W resistor is sending 10W of heat to the dirt under the battery.
From mid Dec to mid Feb, that 10W of 24/7/325 stored heat is keeping the bank warm.

It is not a joke.
There is a family using my stuff to run a DC pump.
The pump sends solar heated water down like 6' deep in coils under a greenhouse.
It runs a couple/few hours a day in summer.
The greenhouse is functional much more of the year than it was before.
If it can make tomatoes in Feb, it can keep an insulated battery warm, right?

[ChrisOlson]

Glen, I agree that some sort of resistive heating load warming the concrete under the battery cases would do the trick.  I got cattle waterers that are ground source heated to keep them from freezing in cold weather.  All those consist of is a concrete pad with the fountain sitting on top of it and the water line coming out of the ground thru a 10" diameter plastic culvert that is buried to a depth of 12 feet below the ground.

The fountains are about the size of a 15 gallon oil drum and they're insulated really well except for the cup on top that holds the water for the beef cattle to drink out of.  The ground heat from down below rises thru that big culvert and keeps those things ice free even in -20°F weather.  If it gets below that there's flip-over lids on the top that you have to close to prevent the water from skinning over with ice.

But those things work with no electricity required to run electric heaters or anything, and I've never had one freeze up solid.

I think that same concept could be used to heat a well insulated battery shed and keep it above 50 degrees in the winter time.
--
Chris

[ChrisOlson]

Even with 4-6 equalizations a year, 2 hour absorb times at 29.2V and 300+ sunny days a year, my cells were all over the place in their SG.  I was shocked to find that one cell could get so far out of balance and still be able to be brought back to life.

VF - I check that crap religiously, every time I service the bank.  I have never had cells get that far out of whack unless a battery was going bad.

I got my 24 batteries hooked in 12 series strings.  Then I got two series strings parallel'd at the batteries, with a #2 positive coming off one side of the group, and a #2 negative off the other side, going to the power bus.  So I got six reds and six blacks running from the bank to the bus bars with four batteries on each pair of red/black wires.  My bank is pretty new (about 8 months old now) and I've serviced it twice and every single battery was dead on with virtually zero difference between SG on cells.

If you got cells that get that far out of whack your bank isn't going to last very good.  And I would almost have to say you got a problem with series interconnects or the wiring not keeping the bank balanced somehow.

My new battery bank cost me $10 Grand and if I found something like that when I service it I'd be really worried.  I'd figure out the problem as to what's causing it and fix it ASAP.
--
Chris

[ghurd]

I think that same concept could be used to heat a well insulated battery shed and keep it above 50 degrees in the winter time.

50?  I doubt that.
What is the ground water temp in your area?
I am south of your area, and ours is only around 54F.

In summer, you have plenty of power to spare?
Maybe a ground loop to pump that 80F ambiant heat down below the battery bank?
Get that deep dirt nice and warm.
Could do it with a tiny little brushless 12VDC water pump.
Not sure if it is a great idea... just an idea.
G-

[tecker]

I don't Know your Solar setup but a serial transfer switch will send some voltage to the bank in overcast  conditions .
Also with heavy resistive loads like that you can break the bank in to two subs and use a cap bridge charger on the neutral side of the heavy hitters .
Another thing that works is to match voltage and current to a  dc motor on a Genset placing the resistive loads in the supply circuit with the bank split in two and the load for the dc circuit
patched in between the two banks this works in a wind setup . The motor voltage above the charging cut.

[ChrisOlson]

I don't Know your Solar setup but a serial transfer switch will send some voltage to the bank in overcast  conditions .

What's a serial transfer switch?

We giot one 1,230 watt array with a Morningstar TS-MPPT-60 on it, and another 1 kW array with a Moringstar TS-MPPT45 on it.  The larger array runs at 144 volts, the smaller array at 119 volts.  We get some power from the solar when it's overcast, but not much.  In the winter when there's only 6 hours of useable sunlight we don't get much from the solar even when the sun does shine.

We depend on wind more than solar.  But wind turbines aren't all that great for charging battery banks because the output isn't constant enough.  And you can't hold the voltage at 29.0, or whatever, to properly absorb charge the bank with wind power.  They bulk charge it, then the voltage goes over and it starts dumping.  Using PWM, or some scheme like that, doesn't work very good to try to regulate the voltage when you got 300 amps of turbine power from four turbines.  One instant there's 300 amps, then the next there's only 100 amps and the voltage goes up and down like a yo-yo.  The only two things I got that can properly charge the bank and hold the voltage even is the solar arrays and gen (with the inverter-chargers).

Where there's both solar and wind, then the MPPT controllers on the solar react fast enough to regulate the bank voltage to the constant rate needed for absorb as turbine output changes.  But with just wind power it's impossible.
--
Chris

[tecker]

I see what your saying the solar array is serial connected and the mppt is not processing the lesser voltage .  The solar that I have recharges with out much sun . With the panels serial connected around the controller .I have 1000 AH on 600 watts .
You can reprogram the one Mppt to process the lower voltage .
I'm looking through the manual I don't see the laptop shell  but there are custom battery switches .
Also when you have two mppt controllers on the same bank you don't get feed back impedance .It samples the I think battery reactance o the pulse rate .  Probably a good Idea to make a single amperage test every 6 months anyway to see the low light amperage .
I think the working Shell is   MS view set a hub and check it out .

[kenl]

 Maybe try a snap switch and some kind of heat source in the battery cabinet so heat will come on if
batteries get below a certain temp? You have excess wind could you dump some of that into a resistive heater or maybe something like electric radiant floor fabric in a layer of concrete under your batteries.

 I was considering getting flooded batteries which would have to be put outside due to the weight. I was figuring on a insulated slab
with hydronic heat source or something along that line and a very well insulated shed. Batteries last a long time in cooler climates but sure do lack the reserve capacity of batteries in warmer climates.

kenny

[tecker]

The rs485 connection is the way to connect the two Ts units and the hub connect is to the Pc control shell . Thats kinda wierd the Two aren't talking on the tcpip but they will talk to a serial 485 .
here's a post the manual is a little vague
http://www.greenwired.net/charge-controllers/

[ChrisOlson]

You can reprogram the one Mppt to process the lower voltage .

I think the main problem is that you need sun to make solar panels work.  Trying to squeeze blood out of a turnip and get decent power from solar panels for a 2,400 ah bank when there's a heavy overcast just doesn't work.

On most heavily cloudy days I get 5 amps or so from the solar arrays.  But that's like a drop in the ocean to a 2,400 ah bank.

With the fan and thermostat I put in the bank is staying right at 70 degrees F.  It was -14F here last night.
--
Chris

[tecker]

I hear what your sayin but 5amps into 24 volt bank is ..
 There has to be a bad connection or setting out or something to not be given you at least half out of your 2k + array even 25 % is  around 20 amps. Got to be a problem in there some where . I'll butt out now

[thirteen]

As a different side note could you install a pipe from the interior of the warm house to the battery storage area and install a thermosat connected to a small fan to take the warm air from the house and put it in the bank arera. It would keep the batteries warm.  I am going to do this to mine and also it will go along the side of my water line that crosses the creek and under the road to my water valve disconnect box. Just an idea. 

[ghurd]

I don't Know your Solar setup but a serial transfer switch will send some voltage to the bank in overcast  conditions .

What's a serial transfer switch?

We giot one 1,230 watt array with a Morningstar TS-MPPT-60 on it, and another 1 kW array with a Moringstar TS-MPPT45 on it.  The larger array runs at 144 volts, the smaller array at 119 volts.  We get some power from the solar when it's overcast, but not much.  In the winter when there's only 6 hours of useable sunlight we don't get much from the solar even when the sun does shine.

We depend on wind more than solar.  But wind turbines aren't all that great for charging battery banks because the output isn't constant enough.  And you can't hold the voltage at 29.0, or whatever, to properly absorb charge the bank with wind power.  They bulk charge it, then the voltage goes over and it starts dumping.  Using PWM, or some scheme like that, doesn't work very good to try to regulate the voltage when you got 300 amps of turbine power from four turbines.  One instant there's 300 amps, then the next there's only 100 amps and the voltage goes up and down like a yo-yo.  The only two things I got that can properly charge the bank and hold the voltage even is the solar arrays and gen (with the inverter-chargers).

Where there's both solar and wind, then the MPPT controllers on the solar react fast enough to regulate the bank voltage to the constant rate needed for absorb as turbine output changes.  But with just wind power it's impossible.
--
Chris

and

I hear what your sayin but 5amps into 24 volt bank is ..
 There has to be a bad connection or setting out or something to not be given you at least half out of your 2k + array even 25 % is  around 20 amps. Got to be a problem in there some where . I'll butt out now

I agree.
Somewhere, something is not right.

"In the winter when there's only 6 hours of useable sunlight we don't get much from the solar even when the sun does shine."
uh... what?

G-

[ChrisOlson]

"In the winter when there's only 6 hours of useable sunlight we don't get much from the solar even when the sun does shine."
uh... what?

That means that in the winter, even when the sun does shine, 2 kW of solar power is like peeing in the ocean to meet our loads and charge the bank.  We get over 85% of our power from wind year 'round.

And no, there's nothing wrong with the panels, there's nothing wrong with the controllers - there's nothing wrong except the sun don't shine.  We get snow, wind, and heavy overcast day after day.  That's just the way it is when you live in the shadow of Lake Superior.  As of today, we have not seen the sun since Dec 18, and on that Sunday it appeared thru a break in the overcast for about one hour in mid-morning.

In really cold years when the lake is frozen over, then we'll get some sun in the winter time.  Otherwise, there's some places where solar power just doesn't work at certain times of the year because the sunlight can't get thru.  And we happen to live in one of them.  tecker says:

"There has to be a bad connection or setting out or something to not be given you at least half out of your 2k + array even 25 % is  around 20 amps. Got to be a problem in there some where"

You just don't understand.  The word "solar" is part of "solar panels".  Solar = sun.  It takes sun to make them work.  When, and if, the sun would come out, those panels will pop right up to 80 amps.  But today they peaked at 18 amps and we only got 1.48 kWh from them.  Which is basically enough power to run the coffee pot in my shop from breakfast to lunch.
--
Chris

[ghurd]

You do not understand it.

I understand it.  I understand what it means.  I understand the implications.

'Solar Insolation'

[ChrisOlson]

By the first of February, when cabin fever has set in bad, I could use some "Solar Insolation".
--
Chris

[ghurd]

Around here, it is not uncommon for the PVs to not reach charging voltage some days.
44062, 44005
That's were I work with solar, mostly.

The 'solar insolation' charts are fairly accurate.
Expecting more is a pipe dream based on misinformation from ebay sellers.

Do not blame it on me because you do not comprend the standards.

[tecker]

I saw the snow on the panels It was defiantly covered up but I still have to say something is wrong with a serial setup that is not snow covered and still not giving you at least 25 percent on cloudy days when not covered in 2" of snow of coarse
covered in snow will put you at the bottom for shure
I was close to Wausau last year in Feb the wind coming off the cornfield was blistering and the steam rising from a paper mill there was just not even breaking up .
Good luck with those Mppts they need have the 485s connected to  work right

[ChrisOlson]

Do not blame it on me because you do not comprend the standards.

What?  Did I say I don't understand the standards?  I know perfectly well what my solar panels are capable of with the solar resource I have.  In the summer they work great.  In the winter they don't.  That's why, long term, I have not spent much money on solar power and concentrated on wind instead.  Wind turbines run 24 hours a day.  Solar panels only work for roughly half the day, and sometimes not even then.
--
Chris

[ChrisOlson]

I saw the snow on the panels It was defiantly covered up but I still have to say something is wrong with a serial setup that is not snow covered and still not giving you at least 25 percent on cloudy days when not covered in 2" of snow of coarse

tecker, Wausau is 2-1/2 hours SE of us.  That's the "southerners" that live down there.  We live in the Wisconsin North Woods.

I used to have one array on a ground mount.  But two years in a row that array got buried under a 10-12 foot deep drift.  I worked on it for half a day with my skid steer loader to dig it out and the array collapsed from a couple tons of snow on it.

Since then I've moved them to roofs where I can reach them with a snow rake.  I got four Schott 245's on the shop roof and ten Sharp 123's on the house roof.

BTW - I do have the two Morningstar controllers connected.  And the panels will reach 18-20 amps at solar noon on most days.  But their peak output doesn't contribute much to our total power needs in winter.  I go by kWh production of my equipment, not what it reaches at peak.  It's kind of like the wind turbines - I figure for 167 watts out of a 12 foot turbine as an average output.  Four of them will generate about 16 kWh in a day, on average, year 'round.  Some folks might think that's bad for a 2 kW turbine to only make 167 watts on average.  But that's what they do.  It's a matter of looking at peak output and saying you should get 2 kW from that turbine vs what it actually generates day in and day out.

It's the same with the solar panels.  Their average output, averaged over 24 hours a day, 365 days a year figures out to 188 watts, and I keep immaculate power logging records on my equipment.  I got more money invested in my solar panels than I got in my turbines because I build all my own turbines.  And I get roughly 3.5x more power from the turbines than I get from the solar per dollar invested in equipment.

I'm building a new 3.2 meter turbine with MPPT on it.  That'll be my fifth turbine (actually my sixth because I got a Jacobs 23-10 that I converted to battery charging, but that machine isn't running right now due to some problems with it).  But the point is, for me, spending my time and efforts on wind power has a much higher payback than solar.  And we've come a long way from when we first moved here and used to put 2,500 hours a year on our generator.
--
Chris

[ChrisOlson]

What's that old saying - same s&*t, different day?

Today, at solar noon the Schott panels are putting out 5.4 amps, the Sharp panels 5.5 amps.  2, 230 watts of installed solar capacity has generated a whopping 3.01 kWh over the last 38.1 hours of logging time.  The wind has barely kept up with our loads at ~30 kWh a day and maintained the bank at about 24.5 - 24.6 volts.  But there's a 24 hour timer in the gen controls that starts the gen if the bank has been below 25.0 for more than 24 hours.

When I came in the house for lunch the gen had just started and the inverter was warming it up before putting a load on it   

That little fan that I put in the wall is not as exotic or cool as elaborate schemes like in-floor resistive heaters, or warming the dirt under the shed with something.  But it's keeping the batteries always above 21° C now.  And keeping the bank warmer has kept the voltage up so the gen runs less often.  A maintenance "top off" because the bank was below 25.0 for 24 hours will only put about one hour on the gen.  So it's not terrible.

The little fan has been running, I'd say, 10 minutes on, then 10 minutes off.  Two nights ago when it got down to -14 F outside, it ran just about steady all night.

That little fan draws about 35 watts of power.  So I estimate it's using about .50 kWh per day to keep the bank nice and warm.  With the gen running and bulk charging the bank the temp is at 22 and will probably be at 24 when it gets it topped off.



I think that fan will be a good long term solution, and it has been working totally automatic so I don't have to mess with it.
--
Chris