using a forklift battery with a charge controller

Photowhit

Off grid, deep discharges happen. I, at least, don't have a clue what your goals are since you are connected to the grid, if not grid interactive. 

What are your goals?

Save money?

Save the planet?

Have a huge expensive UPS?

Are you back feeding the grid?

I would not have chosen a forklift/traction battery for 99% standby... Which I would figure your system to be... Of course we can NOT read your mind.

mike95490

Generally, batteries need a couple of conditioning cycles, of fairly deep discharges, and immediate recharging. This is also called Plate Forming.  Done right, it prepares the battery for a long life.  Done wrong, and you get short life or/and low capacity
There should be something on the Crown site on proper forming for your model.

new2PV

Photowhit,  I feel bad for not giving you more info.  The goal is save some electric bill costs, have some backup power and have some independance also.  I do understand there might not be much savings unless I can also reduce the heating bill, with a heat pump.  However, that being said I doubt I would have  enough power to run that at night. Thanks for your info.

I have set bulk to 2.45vpc
absorb to 2.45vpc
absorb to float transition @ 2% =16A (510A x 1.57=800ah )  1.57 is the conversion to the 20h rate (not sure if that is accurate)
float 53.5v
temperature compensated to 100mv/C
Recharge or rebulk voltage 48 volts
Eq volts =2.60 vpc

Photowhit

The dilemma is that using the battery costs more than using the grid. So to save money you would want to never use the battery unless you have an outage.

The math works out that if you had 100kwhs of energy coming from your array. if you store the energy and use the inverter later you get to use @65 - 70Kwhs of electric, due to losses in charging the battery and creating a sine wave. If you back feed the grid, you will likely (I don't know how efficient hybrid systems are) get to use 90-92 Kwhs. So for best outcome dollar wise, you don't want to use the battery.

Problem is Batteries like to be used...

Personally I would run it hard once a week when You know you will have a sunny day following, for the first 6 months. While the battery is being 'formed'. Then maybe once a month, and just keep it in float and equalize once a month. Other batteries are better designed for this type of backup application.

new2PV

Just out of curiousity how much is the cost per kwh using a forklift battery?

Photowhit

With out knowing your situation and costs, it would be hard to hang a dollar figure on it. I don't know of any hybrid solar systems that are cheaper than the grid, though I would think some of the expensive grid areas could be.

If you don't understand my previous post,  I'd guess some where between 30% and 50% more than just back feeding the grid from your system.

If it makes you feel better, pure off grid systems require roughly 3 times the array size for the same delivered kwh, and must be wasteful for a healthy battery.

Dave Angelini

I am glad this got made clear.  I was thinking that medical help was needed here more than energy help.
We generally do not run heat pumps at night offgrid BTW, and not up north. 
If we do, it takes even more array sizing.
I will say that some may think it is wasteful but the side benefit besides good charging in winter is the homeowner can shift away from propane use and cook/bake electrically. The need is still there for propane for deep winter but it is cut by 2/3 or so.

Photowhit

new2PV said:

Just out of curiousity how much is the cost per kwh using a forklift battery?

I just re-read this and see that you might be thinking that using the battery, since the system exists, is 'free' but it will account for as much as 1.5Kwh that you won't be back feeding the grid.

Maybe that statement will clarify my earlier calculations.

BilljustBill

In all this good and thoughtful information I've read in this thread, both the OP and I are needing one thing: 
Where is a good, or "the best", vendor to purchase a forklift battery?

A long while back I looked into a 24 volt forklift battery and remember that one vendor was including shipping and off loading in the delivered price to Texas.  My system will be a 4kw or 5kw array with dual GFX 3524 Outback inverters. 

Thanks for the help,
Bill

Photowhit

Our sponsor sells Crown batteries and they are a very high quality traction battery.

I purchased mine through GB Battery. They are NOT as reputable a company. It has been discussed here a couple times that they over rate the 20 hour ratings of their batteries. So my 12-85-13 "804 amp hour battery" is more likely closer to 670 amp hour. This make cost comparisons and calculation a battery for your needs more difficult, but they are a bit cheaper and they did deliver in a timely fashion. They did NOT pay all applicable taxes as they failed to pay the Missouri sales tax stating that I was liable for that. Not sure why that's not an applicable tax?

http://gbindustrialbattery.com/Forklift_Battery_Sizes_and_Specifications_Zone15.html

new2PV

Photowhit, lets not worry about the selling to grid right now, I will have 2 3kw heat pumps and there won't be anything left to sell back. I need to concentrate on the charging settings of a forklift battery and how to get the max life out of it vs dollar spent.   Ok I have scanned many websites and they say to convert from 6hr to 20hr rate X 1.57 so 510ah would be 802 ah.  to convert 20hr rate to 6 hr rate take the 20h rate and multiply 802 ah x.84= 673 ah.  However doing the math like this the two numbers don;t match, so I tend to belive that the 1.57 multiplier is just not right.

Back to charging, my forklift guy states that if I do not do a full discharge to 1.140 SG the battery will not accept enough charging current to shake off the sulphation and prevent acid stratification is this true? I just don't know my controller goes to bulk each day as soon as the sun comes up regardless of battery volts, does this count as a cycle? Other sites say it is better only to recharge at a 1.240 SG level.

Photowhit

Well, I was hoping someone else would respond, so I don't look like the bad guy here.

I don't think you need to fully discharge, and I wouldn't do it and don't think it's necessary. Solar isn't like a standard battery charger. I don't know the size of your array, but I do know the sun doesn't shine every day. If you discharge to 20% of capacity and the sun doesn't shine, and the battery sits at 20% SOC(State of charge) the battery WILL Sulfate and you will loose capacity. In a warehouse batteries that are taken down to 1.140 or 20% of capacity only last 5-7 years! and that is with prompt recharging! (Please note VTMaps has already stated this)

It is important to properly 'form' your battery. So they need to be used for the first 6 months. I would be sure to draw them down 20% daily (80% SOC), and perhaps 40-50% once a week when you know you will have a sunny day following and can fully recharge them. Please note I say fully recharge them, I don't know the size of your array or orientation so I can't make this calculation for you.

Be sure to equalize at least once a month and some recommend more often. Heavy use and equalizing help to mix the electrolyte.

I'd keep talking with your "forklift guy" only if you have a fork lift or you want to run your battery down daily and recharge with a large battery charger daily from the grid. That is what they know. 

Pretty much every lead acid battery will spend at least a short time in bulk every morning. The array, if oriented south, isn't putting out much current, start with less than the inverter in idle is using. Once the array starts producing meaningful current above what the system is using, the voltage will rise. Once it reaches your set point, the charge controller will maintain that voltage and switch to the absorb mode. It will stay there depending on how your charge controller is setup, for a prescribed time, or until the current reaches your set end amps, then switch to float. Float is a lower voltage that is above the batteries natural resting voltage, but not enough above to force current to flow into the battery.

Equalizing cycle is a higher voltage cycle that comes after the battery is fully charged, with the higher voltage current is flows into the battery, this does several things. A battery is a electrochemical reaction, when equalizing it is forced into a very active state, the current running through the plate tries to convert the sulfates on the plate back into solution, reducing the buildup on the plates. The battery is already fully charged so most of the sulfate is already in solution, so the electrolyte must do something with the energy. The temperature rises and the electrolyte breaks down and releases hydrogen and oxygen. This 'boiling' helps mix the electrolyte. It's important to have a temperature sensor so the battery doesn't get too hot.

Equalizing in short case batteries is primarily to 'equalize' the cells, some cells will have all of the sulfates mixed into solution and have a higher SG (Specific Gravity) than other cells which will still have some sulfate on the plates. You will see some manufacturers recommend only equalizing when the SG is out of balance. This is not true of forklift batteries. They need the equalizing regularly, some recommend every 2 weeks or 10 cycles. I really hate the term cycle when used in solar applications, but understanding why is important. This is why when in an off grid situation, and you have had your battery sitting at a low state of charge for a long time, like 2 weeks of fall storms, that you fully charge and equalize ASAP.

I've never read maintaining a 1.140 SG, I think if that represents the minimal SG at which you won't have sulfating, thinking that this will preserve long battery life. It is just bad thinking and has no bearing in a lift/traction battery world.

Photowhit

I guess I should say something about my approach to equalizing, though I'm sure I have heard others with the same approach.

Equalizing comes in 2 categories; Maintenance equalizing and Corrective equalizing.

Maintenance equalizing is primarily to mix electrolyte and secondarily to equalize the cells.

Corrective equalizing is when you have cells out of balance and you are trying to regain balance (and capacity)..

In general, I'm happy allowing the charge controller do maintenance equalizing, 1 or 2 hours. Just keep an eye on the water levels and check the SG monthly. It is primarily to mix electrolyte. If you see cell considerably out of balance, you need to do a corrective equalizing.

Corrective equalizing, is when one or more cell has low SG. It is done while watching the SG and until the cells are all reading near the same SG or until there is no change in the SG for 2 hours checked on hour or half hour intervals.

new2PV

Wow,  that is alot of info to absorb. Thanks for taking  your time to explain your methods, and I will try and follow your suggestions.  Right now I have 7 kw of array and on a bright sunny day I can charge at 100 amps, and it temperature compensated also.  I have set the end amps to about 7.5 amps as this seemed the point where the SG did not seem to rise anymore around 1.280. My charge controller goes to float when the absorb time runs out(set for 3 hours) or the current drops to 7.5 amps for 1 minute. I have changed the float to 2.18 vpc , bulk to 2.40 and absorb to 2.45V.  Do you think these settings are OK?