using a forklift battery with a charge controller

new2PV · March 2016

Hi when using a forklift battery in a solar application, should I discharge to 80% before recharging? Or does not need to be done when using a solar charge controller?

vtmaps · March 2016

Forklift batteries are designed for daily deep discharges down to 20% SOC. In order to "get away" with such deep discharges they must be recharged immediately. This recharge is from the grid with unlimited time and power. They may take 12 -16 hours to fully recharge.

With a solar setup you cannot duplicate a grid powered battery charger... so try to avoid very deep discharges.

--vtMaps

new2PV · March 2016

Thanks, so what should i set my recharge volts to re enter bulk at., something like 49 volts or 48 volts? The conext mppt 60 150 does not have any other settings to determine when to re-bulk.

BB. · March 2016

In general, lead acid deep cycle batteries like to be be discharged by 20% SOD (state of discharge) or down to 80% SOC (State of Charge). If you discharge by only 5% to 10% a lot, the battery may not last as long.

Try to avoid going below 50% state of charge very often. And avoid going below 20% state of charge ever--For best battery life.

Battery voltage is, at best, a rough estimate of battery state of charge. Under load/under charge, temperature changes, and state of charge all affect the voltage reading. Use a hydrometer to make sure you are correctly managing your battery bank. That can help you calibrate/understand your voltage readings vs state of charge.

-Bill

new2PV · March 2016

Thanks Bill, I do have the midnite solar hydrovolt hydrometer. I am just concerned that some battery manufactures in the forklift world, say that eveytime you charge the battery even if it was 80%SOC and you charge it, they are counting it as a full cycle and cycle life will be cut short if you charge in this manner. Maybe this does not apply in a solar application?

papab · March 2016

BB. said:

In general, lead acid deep cycle batteries like to be be discharged by 20% SOD (state of discharge) or down to 80% SOC (State of Charge). If you discharge by only 5% to 10% a lot, the battery may not last as long.

...

-Bill

I haven't seen this recommendation before, where does this come from? What's the failure mechanism?

Dave Angelini · March 2016

papab said:

BB. said:

In general, lead acid deep cycle batteries like to be be discharged by 20% SOD (state of discharge) or down to 80% SOC (State of Charge). If you discharge by only 5% to 10% a lot, the battery may not last as long.

...

-Bill

I haven't seen this recommendation before, where does this come from? What's the failure mechanism?

It comes from people who have their batteries last over 10 years. If you just get the average of 5 years you are free to do deeper discharges. This is not to say that you can't take your 10 year-old bank down to 50% several times in winter, it is saying you do design your battery capacity for 20% or 30% cycles on a regular basis.You also design the charging source for winter.

I think it came from old sailors who were out cruising the world and buying a battery was very hard in some places and they wanted the battery to outlast the cruise. Ample Power company was one of the first to build charging equipment for these guys and their ladies.

papab · March 2016

I thought you were saying that a shallow discharge was bad, down to 90% SOC.

vtmaps · March 2016

papab said:

I thought you were saying that a shallow discharge was bad, down to 90% SOC.

It is bad. The host of this site has a deep cycle battery FAQ where they explain how shallow discharges cause lead dioxide clumping on the positive plates. Some authorities claim that anything shallower than a 5% discharge is bad, others claim anything shallower than 10% is bad.

--vtMaps

new2PV · March 2016

I think i am going to try watch the specific gravity to recharge at 70% soc and determine the voltage it happens at. Also can you float this type of batttery at. 2.10-2.15 vpc without harm?

Vic · March 2016

new2PV said:

I think i am going to try watch the specific gravity to recharge at 70% soc and determine the voltage it happens at. Also can you float this type of batttery at. 2.10-2.15 vpc without harm?

Hi new2..,

IMO, 2.1 - 2.15 Vpc is really not a Float voltage -- to me, Float is the voltage that will just barely keep a fully-charged battery, fully charged. 2.1 - 2.15 V will not do this for a Flooded battery, especially a Forklift battery (with its generally high-ish SG electrolyte).

Regarding the question about Rebulk voltage, the best voltage for your system will depend upon what you need and expect from the system. Those with a reasonable amount of RE power available for battery charging, and reasonably large battery Capacity, may not need to Rebulk at all. Believe that your system is primarily a Grid Backup, so you may feel that you want RB, but, RB is really an additional charge cycle on a given day, and many of us want to minimize the number of charge cycles.

And I do agree with BB Bill, and vtmaps, that most battery recharges should be done when the battery has been discharged below 90% SOC. Almost ALL battery manufacturer's Number of Discharge Cycle verses DOD Charts , do not plot cycles for discharges that are less than 90% SOC. That is, almost all of those curves go from 90% SOC, downward. IMO, the battery manufacturers know something about their batteries.

FWIW, VIc

new2PV · March 2016

Well, Vic, the way the conext mppt 150 60 works, is if it sees the voltage drop on the battery for 1 minute it will rebulk to the voltage set point. Turn on a heavy load when a cloud rolls by and it will trigger the rebulk, this can;t be turned off. I have no issue setting this to a very low voltage if it will extend the life of the battery.I have enough array to charge at 105 amps presently on a sunny day. I have emailed crown a few days ago with multiple questions, but they have not responded.

Photowhit · March 2016

Hi New2PV,

Looks like you jumped in with both feet!

I would pretty much ignore information from the manufacturers in general as they are speaking to forklift applications.

I would read through the Battery FAQ's here;

http://www.solar-electric.com/deep-cycle-battery-information-faq.html/

Read and understand that voltages will vary while charging and discharging. Typically a fully charged battery will be around 2.12 volts per cell when at rest (No load, no discharge This is not likely to happen very often if ever in a real operating system, and inverter that is on, is a load, if you can see your array, it is likely putting out something!)

While charging, once Bulk and absorb have finished the battery is usually held in 'float'. When charging the voltage is held 15 to 20% above the batteries resting voltage when current is running into the battery. If below that it will allow a small amount of current to pass to the battery but it will not aggressively charge the battery. Float is usually about 2.23 - 2.28 volts per cell. While in this state the charge controller will adjust the voltage for loads to maintain the voltage level.

In essence, once you have reach float, you will be running loads off of the array, provided you have enough array to handle the loads. If you are living off grid, it's common to 'load shift' and do laundry, run air conditioning, cook, run a water heater in my case, once the batteries are in float. Welcome to our world!

You might also take comfort in reading what our sponsor has said about forklift

These batteries are designed for extremely heavy usage. In a typical solar electric system they will normally last for about 20 years or more. We have been selling these for over 25 years and have the utmost confidence in their reliability. Fork lift batteries have a slightly different plate composition from smaller deep cycle batteries in order to withstand industrial usage. The self-discharge is slightly higher and they should be equalized about once a month.

Photowhit · March 2016

If I was going to collect some general information about forklift batteries in a solar application, I might look at information about the HUP Solar One battery, which is pretty much a forklift battery for Solar use (though they say some differences)

http://www.hupsolar.com/

new2PV · March 2016

Great info Photwhit, but even after reading all that info from hupsolar I still don;t know what is the best way to deal with bulk re-entry.

BB. · March 2016

One thing to remember--If your battery is setting much below ~75% (very roughly), the faster the battery will sulfate.

If you are actively charging/discharging when the (lead acid deep cycle battery--just to be exact) battery is below 75% state of charge--That is fine. It is when the battery sets without any charging/discharging activity below ~75% state of charge that sulfation takes place (as I understand the issue).

-Bill

Dave Angelini · March 2016

new2PV said:

Great info Photwhit, but even after reading all that info from hupsolar I still don;t know what is the best way to deal with bulk re-entry.

What do you mean? If you bulk charge more than once a day you are cycling and using your battery up faster than the life curves show for your battery.

It sometimes happens that you bulk more than once in 24 hours, but this is really a symptom of poor choices at the design phase.

When in doubt use the default settings, they were done by folks that were not so new!

mike95490 · March 2016

Generally, in winter, you seldom have enough solar power to spend much time in Float. To fine tune your system, takes frequent SG measurements and tweaking of the Absorb time, so you get a full charge before the Float starts

Dave Angelini · March 2016

Sounds like some more panels Mike?
Many of my clients and myself have less than 20 days a year that we do not float. We do cheat a little by tracking and being able to adjust our usage for poor days. Maybe you are influenced by coastal weather and so ignore this.

new2PV · March 2016

Dave Angelini said:

new2PV said:

Great info Photwhit, but even after reading all that info from hupsolar I still don;t know what is the best way to deal with bulk re-entry.

What do you mean? If you bulk charge more than once a day you are cycling and using your battery up faster than the life curves show for your battery.

It sometimes happens that you bulk more than once in 24 hours, but this is really a symptom of poor choices at the design phase.

Presently I have some defective batteries which I am replacing with the forklift battery as they only have 30 AH capacity. It is not connected as of yet, so I don;t know its performance. The forlklift battery us 510ah@6hr rate. I can use 60 amp hours sunset to sunriset until the sun comes up and in the winter I am in trrouble by next morning with my present defective batteries.

Dave Angelini · March 2016

You are on grid ?

new2PV · March 2016

Yes, but i tend to use the inverter in off grid mode, as it wastes energy when connected to the grid.

mike95490 · March 2016

Dave Angelini said:

Sounds like some more panels Mike?
Many of my clients and myself have less than 20 days a year that we do not float. We do cheat a little by tracking and being able to adjust our usage for poor days. Maybe you are influenced by coastal weather and so ignore this.

10+ days of solid rain (this was couple months ago, March, we had 13" rain in 13 days) More panels were not the answer. 5 years ago NiFe batteries were the answer. Now it's looking more and more like LFP is becoming viable.

Image: https://us.v-cdn.net/6024911/uploads/editor/0t/3ggnc5f1lh4h.jpg

Photowhit · March 2016

mike95490 said:

Dave Angelini said:

Sounds like some more panels Mike?
Many of my clients and myself have less than 20 days a year that we do not float. We do cheat a little by tracking and being able to adjust our usage for poor days. Maybe you are influenced by coastal weather and so ignore this.

10+ days of solid rain (this was couple months ago, March, we had 13" rain in 13 days) More panels were not the answer. 5 years ago NiFe batteries were the answer. Now it's looking more and more like LFP is becoming viable.

I'm not sure what answer your looking for, but with capacity that costs more, and needing larger capacity for long periods of overcast days... I don't see the answer you're looking for... If he's grid interactive, he needs to read more than he needs batteries, or point out his objectives. He is posting this in off grid, but he's connected and knowing more about his situation would help us to help him reach his goals. I actually think Lithium based batteries, may have real possibilities for hybrid systems (battery back up for grid connected system). They have attributes, such as low voltage drop that may lead to smaller battery banks able to support backfeeding the grid. ...but I have no or minimal experience with back feeding the grid through such a system.

Dave Angelini · March 2016

Mike, those days you showed in the graph don't look that bad to me? There is sun on 7 of the 10?

The beauty of virtual or azimuth tracking in winter is it often happens that the extremes of the solar day are when the sun pokes out. Having an array point and harvest the energy during marginal days is the strategy. Being able to shut down phantoms, vampires, and non-essential loads helps quite a bit.

Dave Angelini · March 2016

" 5 years ago NiFe batteries were the answer. Now it's looking more and more like LFP is becoming viable."

That is quite a shift in thinking! From a doomsday battery to one of the first things that will fail from EMP, the battery electronics on a Lithium bank.

It would help the efficiency of the NiFe, but then almost anything will do that.

kaipo_boy · March 2016

Okay, I'll bite. How many cycles are the LFPs proven to? roughly. I thought when shallow cycled they were still worth only around 5k cycles? has this changed?

Dave Angelini · March 2016

The LFP that I am working with is for 10 years @4000 cycles. Not totally sure that it will get used but it is 172 AH @50V @8.6KWH.
The electronics for the BMS is how this can happen, if it happens...

mike95490 · March 2016

couple of answers - sun peaking behind clouds is mostly only 20 min of harvestable sun

NiFe is not a doomsday battery, the 5-10 yr electrolyte replacement cycle and the steady demand for distilled water times it out.. Keeping winter rain water clean for battery use 8 months later seems sketchy.

I'm pretty sold on LFP, being properly bottom balanced, needs no BMS, if the charge controller & inverter LVD are set properly.

I'll do this years electrolyte swap and then see how I feel about doing another one at 67 yr young with 42, 90# batteries to be inverted and shaken out.

Dave Angelini · March 2016

I think you would be surprised how much energy is out there when you are pointed in the right direction, but enough of that.

I have never owned NiFe but have seen the sales brochures and trade show stuff and Doomsday is how they use to market them.

All the real data from folks selling LFP systems is they need the BMS for long life and deep cycling. They also are not do it yourself friendly/costly at this point so maybe when we are 67.

new2PV · March 2016

No one from crown has responded to my simple question. Do i discharge to 20% SOC before recharging? Or do I discharge to 70% SOC before recharging? Seems odd that they won;t respond. I will just have to take the members advice here and don;t do any deep discharges.

using a forklift battery with a charge controller

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