Battery Condition

plongson · December 2011

I've had the new system up for a few weeks now and so far it's running great, but I did have a question...

With winter sun and not wanting to run the genset too much, I'm seeing between 87% to 95% SOC on the BMK. Are there long term battery issues by not reaching 100% very often (if at all)?

Just wanting to get 15 years out of these Rolls Surrette...LOL

Paul

niel · December 2011

Re: Battery Condition

this sounds like the absorb stage is not completing. you could get away with not being 100% soc, but i don't recommend it to be for too long. i would say bring it to full every 3-4 days and at the most it should be brought to 100% at least once a week and more often if you can as time is against you when keeping a deficit charge on them. to keep batteries below 100% soc will cause sulfation to set in and that will ruin your batteries.

westbranch · December 2011

Re: Battery Condition

Paul, I seem to remember reading that reaching100% is recommended once a month for good Batt health. Not a FLA man though...

icarus · December 2011

Re: Battery Condition

I would try to get them to 100% at least once a week. Your options are to increase y our PV to cover mid winter lows, reduce your load to account for mid winter lows,, or adding a bit of genny run time each week, to cover mid winter lows,, possibly the cheapest alternative.

Tony

plongson · December 2011

Re: Battery Condition

Thanks guys, I was afraid of hearing that. With short days, clouds and snow etc. it looks like the chore is going to fall on the genset to pump 'em up. Man, that could take a while too...Should I force an Eq stage somewhere along the way?

BB. · December 2011

Re: Battery Condition

Equalization won't do anything "special" until the batteries are at 100% SOC...

But, remember the battery monitor is just estimating charge... Check the "reset" settings. It might be something like holding 14.5 volts for 3 hours (or something like that) to reset the meter to 100% SOC.

Get the Hydrometer into the battery cells... If the specific gravity does not go up in any cells between 30 minute checks--then your battery is 100% SOC and equalized.

From earlier posts by Dave Sparks and me:

Batteries tend to be less efficient at higher charge/discharge rates (Peukert).

With solar panels, we have a bit of an issue in that there are only so many hours of sun in a day to do the recharging--So higher charging currents for shorter periods of time are necessary, especially during winter (unlike batteries that have utility power for recharging).

Trojan recommends a fairly nominal charging voltage of 2.35 volts per cell until the last 95-100% and finish at 2.45 to 2.7 volts per cell (at 10-13% * C rate of charge as the current limit) until the battery hits around 90% state of charge. (page 12 of this PDF for flooded cell profile).

Flooded/wet batteries will gas (bubble) towards the end of charge to ensure the electrolyte is properly mixed

"Dave Sparks" here has recommended tracking arrays because they not only collect more energy, the extend the charging time too is really good for battery life (if I understand correctly).

Also, from Dave's experience, he has said several times here that (in his opinion/experience) high charge rates are hard on battery life:

Dave Sparks wrote: »

1200 / 10% / 3.5 = 34.3 amps AC

This is the maximum charge amps that you should set the XW to.
Unless you have very big generator your probably fine. Remember you can and should charge at a lower rate if you want more than 10 years on this battery! Just because Surrette says this is fine remember they are in the business of selling batteries. Batteries like the slow charge of a solar day and their life will be shorten by fast generator charges. Good Luck!

But remember Dave also is an advocate of having the battery in a fairly narrow range of state of charge for long life too:

Dave Sparks wrote: »

I learned this strategy from Dave Surrette (Rolls) in the late 70's. Pretty much the bible on how I design my systems for off-grid.

Assume that the system will never reach more than a 90% state of charge.

Try not to go below 50% SOC, ever! Complete absorption over 90% of the year.

Use the energy stored from 70% to 90% SOC for your daily cycles.
Save the energy from 50% SOC to 70% SOC for aging to get long battery life.

I know Surettes has changed their recommendations over the years but I also know they are in the business of selling batteries! If you do the above you will get 10 to 15 years on their batteries with decent maintenance. ...

-Bill

plongson · December 2011

Re: Battery Condition

Thanks for the information Bill, quite a bit to ponder but I see I really need to get the SOC up. I do have a good hydrometer and I'm going to get on this project...

Vic · December 2011

Re: Battery Condition

Hi Paul,

Yes, one of the issues with Bat monitors is that they need to be set, experimenally, on your bank.

And, if you have reasonable PV input, but shortened days, sometimes, setting the Asorb voltage somewhat higher, you can get more charging done in the day -- opportunity charge. You would probably use a bit more water, but perhaps reduce some of the genset run-time.

Your new off-grid Manor house sure looks great! Good Luck, Vic

plongson · December 2011

Re: Battery Condition

Thanks Vic, even in the dead of winter we are really enjoying this place. Water has been a bigger challange than energy right now. I originally built everything to be a fair weather, summer place and now I struggling with the "frozen pump house blues". Dang, when it gets to 0*f it takes lots of effort to keep water flowing...LOl Anyway, this spring, there will be a full overhaul of this system.

Which brings something up. I'll post another thread but maybe you (or anyone reading) have an idea...

I need to monitor the water level in my 550 gallon tank, fill when very low and stop when full (duh...) with the well and pump 600' away and a pressure system already online, I'm after a 120vac 1" valve that can be controlled by a dual level switch?

I've been looking on line but have yet to fond what I'm after. Bennett in Colorado has some stuff online, but still looking...

icarus · December 2011

Re: Battery Condition

Paul,

Pm me if you are interested. I have build a number of systems that allow running water, at temps as cold as -40 with out the use of outside energy.

Tony

mike95490 · December 2011

Re: Battery Condition

Power up the genset in the AM, and let it pump amps in, and maybe after just an hour, the batteries will be partial charged enough that the PV can fill them up the rest of the way, with sunlight. If you KNOW it will be a cloudy day, run the genset anyway for a bit, to keep the batteries from going too low.

samuel · December 2011

Re: Battery Condition

In Northern Michigan where my family has a cabin we usually recharge in the evening.

Recharging from the generator in the evening has several advantages:

nightfall comes early so extra energy not captured by the batteries can be directed toward lighting, TV, cooking supper, pumps, etc
when morning comes around the PV has a headstart and can complete the charge cycle - generators are most effecient under a heavier load and can run shorter hours, PV can then do the light lifting over several hours to finish the charge
regenning at night also frees up daylight hours for outdoor activites - no need to stick around and tend to the generator.

vtmaps · December 2011

Re: Battery Condition

samuel wrote: »

Recharging from the generator in the evening has several advantages

Most of the knowledgeable folks on this forum prefer to run their generators in the morning. It is a much more efficient use of the generator, and it gives the batteries a chance to be fully charged. If you run the generator in the evening, after the sun has partially charged them, the batteries will not accept much energy from the generator (absorb stage). Better to run the generator during bulk stage when the generator's output can be accepted by the batteries, and then let the solar panels charge the batteries during the long absorb stage.
--vtMaps

BB. · December 2011

Re: Battery Condition

But if generator power is needed in the evening, then it is perfectly ok.

You want your system to work for you, not the other way around.

-Bill

samuel · December 2011

Re: Battery Condition

Upon arrival to the cabin we use battery power on day 1, then in the evening of day 2 we use the generator (bulk/absorb) at night, and then day 3 (if sunny) we finish charging. This method is more efficient than charging in the morning due to extra appliances being used at night and follows the general principle of running large loads on a generator instead of off of batteries.

I am also referring to the winter months

westbranch · March 2012

Re: Battery Condition

Bump.... Paul how did the changes work out over the last 3 months?

plongson · March 2012

Re: Battery Condition

Wow, I never reported back but things really look good. Since this thread originally aired, this is where I'm at...

1.) Started out at about 1.225 SG on all 16 batteries.
2.) I did several EQ's a and bumped the absorb on the Classic 250 from (IIRC) 2 hours at 56vdc to 58vdc. this got me to 1.250 pretty much across the board.
3.) I did another 1 or 2 EQ's and bumped the absorb to 59vdc for 3 hours.
4.) Last week all 16 were between 1.260 and 1.275. I was pretty happy with those readings.

This was all over the course of a couple of months.

Water use has not been too bad. I added about a gallon two weeks ago to all 16 batteries. This was the first added water ever since commission.

From what I've read here, 59vdc is pretty hot for absorb but it was the only way I could get the SG up. As long as water use is acceptable and the gravity is up, I'm probably going to leave it alone.

Paul

Battery Condition

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