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Energy/Electricity Storage and Use/Grid Connection => Off-Grid, Batteries & Inverters => Topic started by: stephendv on December 13, 2010, 07:29:45 AM



Title: Voltage settings for forklift batts
Post by: stephendv on December 13, 2010, 07:29:45 AM
Phase 1 of my off-grid install is done  ;D  gen + batts + inverter, no solar yet.  Now I'd like to setup the charger to give my batts the longest life possible, while still not wasting too much diesel.  The Sunny Island has 2 charge modes, "boost" and "full".  Basically it uses the boost charge most often to bring the battery from 60% State of Charge to 85% state of charge, and then only uses the "full" charge once every 14 days (configurable) to bring the battery up to 95% state of charge.  So using these 2 charge modes I can set the absorb voltage and absorb time independently. 

The battery distributor (but not the manufacturer) has recommended 2.4V for absorb because it's the "standard".  But the victron multiplus manual has some specific settings for traction batts as opposed to the regular OPzS.  For "Tubular plate traction batteries in semi-float mode" they recommend 2.45V and for "Tubular plate traction batteries in cyclic mode" they recommend 2.5V.

Since I'll only be discharging to 60% SoC, does that qualify as "semi-float mode" ?  What do the other traction batt users use for absorb voltage?

As for the absorb time, I noticed that when I charged the batts yesterday the generator was only really working hard for the first 5 minutes, then the rest of the 2 hour absorb time was spent only outputting 700W or so as absorb current tapered off.  To reduce runtime, I'm thinking of using 2 hours for absorb in the "boost" mode, and 3 hours for "full" mode, so it'll only do a full absorb every 14 days.  Reasonable?



Title: Re: Voltage settings for forklift batts
Post by: billi on December 13, 2010, 08:43:43 AM
Hi

My absorb voltage varies  from 2.45 to  2.55 Volt  depending on the temp of the battery/weather

The temp-sensor of the solar  charge controller adjust that

In an "only" generator set up one should really fully charge from time to time

I am allays surprised how much more AH (after the Battery monitor says 100% charged)  the PV can push into the battery on a sunny day


Billi



Title: Re: Voltage settings for forklift batts
Post by: stephendv on December 13, 2010, 08:45:54 AM
My absorb voltage varies  from 2.45 to  2.55 Volt  depending on the temp of the battery/weather

The temp-sensor of the solar  charge controller adjust that

Hi Billi, yes mine does temperature compensation too, but what is your programmed absorb setting in the multiplus?


Title: Re: Voltage settings for forklift batts
Post by: rogeriko on December 13, 2010, 09:00:11 AM
I have installed many Sunny Islands and I would just leave the charging settings at standard for flooded batteries. The generator will bring the batteries up to 80% quickly and then gently charge the rest, very slowly. If fuel consumption is an issue this is where solar/wind comes in to play. Charge the batteries to 80% with the generator and then let the panels do the rest. Dont forget the Sunny Island needs a current shunt if you connect panels or wind (ebay 200a 50mv or 60mv) SMA want 90 pounds for this.


Title: Re: Voltage settings for forklift batts
Post by: stephendv on December 13, 2010, 09:21:19 AM
Hi Rogeriko,

Yes, solar is the eventual plan but for the next 6 months I'm going to be running purely on the gen+battery and wouldn't like to damage them with too high an absorb voltage.  The default in the SI is 2.55V which is the highest I've seen in any inverter/charger, it's also the default for all FLA types because the sunny island makes no distinction between different FLA types.  The victron has 2 specific settings for traction batteries which gives me more confidence that there's are more correct than the default in the SI.

I already have the current shunt installed  :) ready for the Tristar MPPT when I do the solar part of the install next year.


Title: Re: Voltage settings for forklift batts
Post by: Stuart on December 13, 2010, 09:24:52 AM
Worth reading through this excellent article for the theory http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

Stuart


Title: Re: Voltage settings for forklift batts
Post by: Justme on December 13, 2010, 09:50:41 AM
I think you are headed for trouble.

Only (almost) fully charging every 2 weeks & then absorbing for 2 or 3 hours is madness.

Bat life reduction would be a given.

I would not call 60% SOC semi float when you 50% SOC is full deep cycle.

A full recharge cycle will take more like 8 to 12 hours MINIMUM.

YES it costs in genny run hours & fuel. But get your other stuff online & correctly sized & then its only for in the winter and poss odd weather periods / extra heavy use.

I would ALWAYS use the bat makers charge specs.

Do not use the Victron adaptive charging its pants & reduces charge absorb times far to much.


Title: Re: Voltage settings for forklift batts
Post by: stephendv on December 13, 2010, 10:46:49 AM
Unfortunately the manufacturer hasn't responded about the correct voltages yet, the manual just says that all charging procedures that conform to DIN 41773 and DIN 41774 are acceptable. 
And in another section: charging is complete when the density of the electrolyte and the voltage remain constant for more than 2 hours.  So I guess I could experiment with different absorb times and keep measuring SG and then add another 30 mins to be safe.  How long do think is an appropriate time between full charges?


Title: Re: Voltage settings for forklift batts
Post by: Justme on December 13, 2010, 05:00:50 PM
Time between full charges is a compromise. You should use it & then recharge straight away.
The longer you leave it the less time the bats will live. I try to do it weekly ish. When the charge is about 1% of bank cap at 5c I call it a day.

You dont need or want the victron charger settings to stop the charge, use the VS to turn the genny off when conditions are met.


Title: Re: Voltage settings for forklift batts
Post by: The Slow Old Man on December 20, 2010, 09:06:53 PM
Hi Justme
What settings are you using for your victron if not the adaptive mode?

Brian


Title: Re: Voltage settings for forklift batts
Post by: Justme on December 20, 2010, 09:33:15 PM
I'll just plug it in & see cos it was set up a while ago.


 tumble: tumble: tumble:


Right

Charger settings

Fixed mode
Absorb 14.7v (that contains an adjustment for the accuracy of the Victron & losses in the 120mm2 cable & connectors)
Float 13.8v (but if its in float you should be turning the genny off unless you are using the bulk of the power for a job that you dont want to power via the inverter)
Absorb time 5 hours
Repeat absorb 1 day (but is subject to the genny being on)
repeat absorb 1/2 hour (but in reality never happens)
charge current 120amps
Battery type (personal settings
I dont set the stop after 10 hour bulk as the genny would not be on for that long often & even from as flat as I take it it could not still be in bulk after that amount of time

I also manually force an EQ charge every now & then when I am going to have the genny on for a long time anyway.


Title: Re: Voltage settings for forklift batts
Post by: The Slow Old Man on December 20, 2010, 09:53:46 PM
Hi Justme
Interesting so what about the bulk charge? you say that the absorption charge is five hours at 14.7V does the current decrees over this time?

Brian


Title: Re: Voltage settings for forklift batts
Post by: billi on December 20, 2010, 10:05:10 PM
I was on adabtive , but as far as i know , that over rights your time stings , so on fixed as well

Here the help page from the victron software VE configure


Regards Billi

Quote
  See also   |Where?

Charge curve
With this setting one can choose between three different charge curves:

 

Fixed
Adaptive
Adaptive + BatterySafe
 

The Fixed charge curve will have a fixed absorption time

The Adaptive and Adaptive + BatterySafe curves derive the absorption time from the Bulk time. The maximum absorption time of these charge curves is determined by the absorption time setting.

 

The Adaptive + BatterySafe curve has a special regulation in the absorption phase. The absorption phase will start when the voltage reaches 14.4V (for a 12V battery) regardless of the specified absorption voltage. During the absorption phase the voltage will increase with a fixed ramp until the voltage reaches the absorption voltage or until the calculated absorption time is over. In the latter case the absorption phase will end before the absorption voltage is reached.

 

Please refer to the manual for a more detailed description of the charge process.

 




Title: Re: Voltage settings for forklift batts
Post by: Justme on December 20, 2010, 10:13:18 PM
Hi Justme
Interesting so what about the bulk charge? you say that the absorption charge is five hours at 14.7V does the current decrees over this time?

Brian

I dont understand what you mean, "what about the bulk charge"

The definition of bulk is that the batteries are taking ALL the current (amps) that the charge source can supply at the rising voltage without hitting the point where the absorb set voltage is reached. So its in bulk till the bat charge voltage reaches 14.7v. The current during that time does go down slowly (but as the V is rising the total "power" in is very similar). Then once the fixed V stage starts (thats the absorb stage) the V stays constant at your set point whilst the current (amps) lowers. On my 1550amph 5c bank if I keep the genny on for a long time I can get it as low as 5amps but I more normally stop at 25 or 15amps. Which is about 1% of bank capacity.


Title: Re: Voltage settings for forklift batts
Post by: Outtasight on December 22, 2010, 11:53:32 PM
I think you are headed for trouble.
Only (almost) fully charging every 2 weeks & then absorbing for 2 or 3 hours is madness.
Bat life reduction would be a given.
I would not call 60% SOC semi float when you 50% SOC is full deep cycle.
A full recharge cycle will take more like 8 to 12 hours MINIMUM.

Absolutely!  Car batteries spend their life in semi-float mode (discharged a few times a day by 1% at most, and then immediately put on float charge).  UPS batteries spend almost their whole 5 year life in float mode.  Any off-grid usage will be definitely cyclic / deep-cyclic mode.

Under-charging does more damage than over-charging.  Under-charging causes rapid, cumulative, and permanent loss of capacity from sulphation whereas over-charging causes excessive gassing (water consumption) and positive grid corrosion.  You can limit the damage of over-charging by keeping the water topped right up, as that causes less of the positive terminals to be exposed above the water line.  The pure water reforming on the positive bits of the terminals causes the lead to slowly dissolve away, as well as some other undesirable side reactions below the water line.  The more the cell gasses, the more corrosion occurs.

I also cut absorption at about 1% of bank capacity current (5A going into my 500Ah bank).  For cyclic use, you should use the upper end of the range of the specified float Voltage too.  When you're done with the absorption phase, you'll still only be maybe at ~90% SoC.  The last 10% takes AGES at the float Voltage (more hours than you've probably got before the next discharge cycle), so they recommend increasing the float Voltage a bit.  It allows the cells to fill up a bit faster than at the lower "standby" float level (that you'd use for batteries in a UPS that can be on float for months) but doesn't cause loads of gassing, like it would if you left them on the absorption limit for a few hours.  You can't force the last few % in... It has to be coaxed in.  Bad news when you have to run a generator to do it.  Maybe you could switch to a much smaller generator for the "final push"? 

It may even be worth having a small, cheap 100Ah battery as a "sacrificial buffer battery" that allows the main bank to continue float charge (using a small 250W inverter / charger) after you've switched off the generator.  This buffer battery can supply the small float current to the much bigger (much more expensive) battery, to trickle in the last 50Ah to get it as close to 100% as possible every day.  The cheapo battery will cycle 50% or more per day and will die at regular intervals of maybe every 120 days.  You'd have to weigh the quarterly cost of a 70 battery against the cost of running the diesel generator for the extra hours (fuel, wear and tear, servicing costs). You'd also extend the life of the main bank by minimising the cumulative capacity loss from not charging it to 100% every day.  But then again, a couple of years of blowing money on cheapo "consumable" batteries would needle you into buying those solar panels and the Tristar...

Doing the equalisation charge should be done only after a normal absorption phase and after the battery has had time to cool down a bit and then it should be started only under manual control and supervision (you wouldn't leave a chip pan, on full gas, unattended, now would you?).  The EQ Voltage will cause a LOT of gassing and quite a bit of water loss, so check the water before starting the cycle and after finishing it.  EQ charging also runs the risk of cell thermal runaway in extreme cases, not to mention the risk of all that gas. 


Title: Re: Voltage settings for forklift batts
Post by: EccentricAnomaly on December 23, 2010, 11:16:22 AM
It may even be worth having a small, cheap 100Ah battery as a "sacrificial buffer battery" that allows the main bank to continue float charge (using a small 250W inverter / charger) after you've switched off the generator.

Not cheap but probably not sacrificial either would be to use some sort of LiFe battery for this function.  They like being at least partly discharged.


Title: Re: Voltage settings for forklift batts
Post by: stephendv on December 23, 2010, 12:50:54 PM
Thanks for all the input.  I'm going to stick with pure gen charging - no sacrificial additional battery as I'd rather spend that money towards solar panels in the future.  The batteries will never be float charged, the gen will turn off when absorb is done. 

My initial thoughts about battery usage for the next few months were a bit off.  Since they will only really be used while building the cabin for the odd power tool, there will be very little load.  Usage will probably look like this:
- Full charge on Sunday, with a 5 hour absorb, and I'll check SG periodically, if it stops rising over 2 hours I'll note the absorb time and use this + 30 minutes for the next absorb.  Battery will be at 95-100% SoC on sunday night.
- No or minimal load for the week, inverter completely off.
- Should reach saturday with at least 80% SoC.
- Could draw down to 75% SoC by sunday, do a boost charge to bring it to 90%, shorter absorb, maybe 3 hours.
- As above, no or minimal load during the week so they'll be at 90% ish during the week.
- Do a full charge with 5 hour absorb on sunday, i.e. 2 weeks between full charges.

So sticking with the original plan of doing a 2 week interval of full charging, but will spend most of their idle time during the week at at least 85% SoC, then drawn down to 75% on saturdays at the worst (very liberal, realistically I think it would be 80%), then full charge every second sunday, and boost charge every other sunday.

Sensible?



Title: Re: Voltage settings for forklift batts
Post by: Justme on December 23, 2010, 02:14:58 PM
The long periods of inactivity at low soc will cause sulphation. Could you not fully charge just before they go inactive so that they stay stored at a higher SOC?

Using the one charge cycle to then calc the other absorb times is also risky. Its what the adaptive charge setting does on the Victron. Basically if you charge for x hours at bulk it will then absorb for Y hours. As the bulk time comes down so does the absorb time.

BUT & its a BIG BUT the faster you charge the longer the absorb needs to be. A lo ng slow bulk phase will need a shorter absorb, a hard & fast bulk needs a long & slow absorb. Adaptive does it the wrong way round.

I would look at solar panels. Do the bulk on the genny & the absorb via the PV. Your not going to get the max kwh out of the PV but you will save on fuel.


Title: Re: Voltage settings for forklift batts
Post by: stephendv on December 23, 2010, 02:22:48 PM
The long periods of inactivity at low soc will cause sulphation. Could you not fully charge just before they go inactive so that they stay stored at a higher SOC?
Yep, that's exactly the idea - maybe I didn't explain it well.  They'll be charged to at least 90% SoC every sunday and left virtually untouched for the week.  Then full charge every other sunday.
I would look at solar panels. Do the bulk on the genny & the absorb via the PV. Your not going to get the max kwh out of the PV but you will save on fuel.

Yeah, will definitely get the PV panels in a few months once the cabin is done.  Don't want to install them yet because the location is quite isolated and it's thieving season.


Title: Re: Voltage settings for forklift batts
Post by: Outtasight on December 23, 2010, 10:59:52 PM
Another small factor to consider is that lead-antimony flooded cells will self-discharge by around 5-10% a week, just by sitting there, doing nothing, with no load on them!  A bit slower in the cold weather but faster in warm conditions.  A small solar panel will at least compensate for the rate of self-discharge.  If they're lead-calcium types then they self-discharge less (more like 3-5% a week).



Title: Re: Voltage settings for forklift batts
Post by: Justme on December 24, 2010, 11:04:10 AM
The long periods of inactivity at low soc will cause sulphation. Could you not fully charge just before they go inactive so that they stay stored at a higher SOC?
Yep, that's exactly the idea - maybe I didn't explain it well.  They'll be charged to at least 90% SoC every sunday and left virtually untouched for the week.  Then full charge every other sunday.
I would look at solar panels. Do the bulk on the genny & the absorb via the PV. Your not going to get the max kwh out of the PV but you will save on fuel.

Yeah, will definitely get the PV panels in a few months once the cabin is done.  Don't want to install them yet because the location is quite isolated and it's thieving season.


I was talking about leaving them at 90% for the week. If they are going to be left then fully charge them. Start at 90% take away the self discharge add in the sulphation and each week you are prob going to permanently loose a % or 2 of capacity & a few charge cycles of life. Once you have the PV it wont be so bad as they will (apart from in winter) if sized right stop the self discharge & finish off the full charge cycle.

Just to be clear, what ever you do with a battery is wrong for its capacity & life time / cycles. Even bats that are on float 24 / 7 die in the end. All you can do is do the least damage possible. Its hard but you need some sort of scale of use over cost over bat life & replacement costs to get a "best" for your install & usage. My target is to use less than 500 of Red per year (mostly in the winter) in the genny & have a bat replacement cost of less than 100 per year (we have spent about 550 on bats [used forklift cells] so far & are at year 2.5 & still on the first bank that cost 127, the other bank that is bigger & for the cabin when its finished gets floated when the genny is on to keep it in good condition). This year will be over budget on Red due in the main to building the cabin which needed the genny on in the summer but also to the extra long winter we are getting.