Lead overcharging

[scottnj@gmail.com]

For long term storage, is it better to charge at 24vdc, or charge each battery at 12vdc? Victron has some chargers with multiple outputs, but I do not think they can be hooked up to batteries that are wired in series because the charger outputs share a common ground. Charging at 2x12vdc would require 2 chargers.

The ProSport chargers have independent charging banks, too bad they don't have the programability that the Victron ones have. I looked at NOCO and a few others, but they don't have the right charging profiles.

[biscuit]

As long as you have at LEA...
...fixed current for a limited period once current drops to a certain point. (Rather than waiting 8 hours at CV to really low currents).

Can we fix a current? Doesn't the current naturally drop to approximately 0A?

[Burgerman]

With the PL8 you set max current (CC or bulk - which can be up to 40A). At this point the battery will be at a lower voltage if its very discharged. So that giving it 40A or 10A or whatever does not drop away at all until the CV voltage that you set is reached. This will be 28.2 for gel. (And 28.8 to 29.4 for AGM).

When the CV voltage is reached the current naturally falls away if you try to hold the voltage steady as the battery becomes more charged. That last 1A or 2A represents maybe 1 or 2% of the charge only. But it may take another 4 hours or so to achieve. If you rely on a lower float voltage to do this last bit, then it may take another 8 hours to achieve. Maybe more.

So at this point you CAN if time is important begin charging at 1A and no fixed voltage. Or 2A for half the time. Its not as accurate and it puts exactly 1Ah in. Thats about the same as witing a week at a few mA. So it speeds up overall charge.

Read the accelerated finishing here www.wheelchairdriver.com/MK1.pdf
But I dont like doing it... Voltage starts to climb very high. Even though its not for long. And its hard to estimate how long to do it for.


For long term storage, is it better to charge at 24vdc, or charge each battery at 12vdc? Victron has some chargers with multiple outputs, but I do not think they can be hooked up to batteries that are wired in series because the charger outputs share a common ground. Charging at 2x12vdc would require 2 chargers.

The ProSport chargers have independent charging banks, too bad they don't have the programability that the Victron ones have. I looked at NOCO and a few others, but they don't have the right charging profiles.

This is the problem. This is why I use my brain, a bench power supply or a PL8, or a modded charger or whatever. Most chargers do not allow you to even KNOW what exactly they do. They just write AGM/gel on the thing and say its automatic. They inevitably are not! And they murder gel batteries by over voltage as well as undercharging, and then too high float voltage for long term storage while calling them maintainers!

All any lead battery needs and wants is 3 stages.
1 CC at a higher amps than a mobility charger gives.
2 CV at the CORRECT voltage that ends after 8 hours or .3*** of an amp and goes to float.
3 Float at 13.6 to 13.7 complete charge.

***Its better to end at say 750thC and or 8 hours CV whichever occurs first and no float required. As this is faster. But needs individual configuration and fine tuning. And its really best is these voltages are corrected for temperature. Especially in summer.

[Burgerman]

For long term storage, is it better to charge at 24vdc, or charge each battery at 12vdc? Victron has some chargers with multiple outputs, but I do not think they can be hooked up to batteries that are wired in series because the charger outputs share a common ground. Charging at 2x12vdc would require 2 chargers.

Those marine multi bank chargers are fully floating on the output. So the fact that they are 12 + 12V doesent matter. They can be used on a chair. 2 connectors. But beware. The charge current is decieving. A 12A charger is really a 6A charger. Unless you connect both sets of cables to a single 12V battery.

Is it better to charge in series or parrallel? In theory as long as both batteries are healthy and same make/age etc it makes no difference. Because the float voltage of 6 cells or 12 cells is always higher than the fully charged open curcuit voltage. So all cells get pulled up to 100% regardless. EVENTUALLY. If you just buy 2 brand new batteries and fit them. Then they will NOT be at the same state of charge. So for the first half a dozen charges one will be overcharged and one will be undercharged. After a while they will self balance. You may or may not damage them this way. So here charging both in parallel is better. This is why you should connect them together in parallel BEFORE ever fitting in a chair for 24 hours. Or fully charge each one at 12V with a correct charge algo before fitting. You can do that in parallel or individually. Or you can use a dual output marine charger to do that IN the chair.

[shirley_hkg]

CC, CV, Termination Current, CV Timeout.
If all those were essential, PL8 seems to be the best choice , in this price range, for SLA.
As a bonus , it can also charge Lithium perfectly as well.

[Burgerman]

An 8 hour CV and float works quite well too which the victron can be programed to do wth a fully custom profile. At least for cyclic use. And of course same applies to the ZXD charger when set up properly for your specific battery. With he advantage that it can charge at any current you decide up to 50A. So great for a top up or boost during the day too. And that alone will easily double your battery lifespan.

[Burgerman]

For comedy value this below is a typical mobility charger. A member here used an upright invacare branded charger to charge his chair. He monitored the voltage using the PL8 to watch exactly what it does... This sort of nonsense is what your mobility charger does! And when you have crap range and batteries fail you will wonder why!

The added markings are what he "thought" was supposed to be happening. But non of us can really know! He missed the first few minutes. Battery was about 1/3rd discharged.

This is the charger he used:

Invacare charger used

And this joke and frankly bewildering mess is what it actually did (which is common from a cheap mobility charger) - monitoring VOLTS only:

This is what it actually did...
This is volts, so after 4 hours of absorption at a voltage that reaches 28.85V (too high) it then spent
4 hours dropping lower and lower. And spiking all over. So over volts, and then a too high 27.7V float that starts too soon.

This is what it SHOULD have done, or close to it. CENTRE GRAPH. But with float at the end after some hours at CV. PL8 doesent do float. Its a charger only. But it does that correctly.

This is what we were expecting it to do. Followed by a 13. something volt float... not shown.
This is an ACTUAL charge by the PL8 on my salsa chair via the XLR.

An idealised drawing schematic to show a correct 3 stage charge. Voltages not shown. These depend on actual battery type and usage.

This is a drawing of what is supposed to happen and shows a idealised 3 stage charge. The PL8 only does a 2 stage charge. Because don correctly thats all thats required. This shows volts and amps.

[Burgerman]

The difference?
The invacare charger held the gel battery at too high voltage for around 2.5 hours. So shortens its life severely. Then it went to a too high float level. And did so too soon. So the charger would eventually after around 16 hours fully charge the battery. But it gives the green light and says done where the float part begins after 5 hours! So if you think its done and unplug the charger and so get up and use it. But now its also undercharged. Not by much. But it also shortens lifespan through sulfation from undercharging repeatedly. And that float level is too high for more than a day or so. So leave it plugged in as suggested by invcare and the battery will be overcharged indefinitely. Also causing further damage if left connected long term.

So yes you can use it.
And yes it will result in you getting around half the lifespan from your battery. And decreasing range much faster than need be the case.
Do they know? Care? No idea. But its cheap and safe to use on a mistreated old battery with little risk of thermal runaway. And cheap. So they just keep doing it. Other mobility chargers may vary. They seem to do all kinds of different stuff! I never tested one that I would use though.

I have a 10A sunrise charger here. It is shipped wih chairs using the gel eternity battery. Same as Haze 80A gel. And it sits at 28.8 to 29V solidly, but stops after about 2 hours and goes to a 13.8V float (27.6) and relies on that to do a lot of the charging. So I use that to top up already full AGM batteries for 12 hours if stored. It goes nowhere near gel!

[biscuit]

Is 26.6V a reasonable storage voltage that will allow for self-discharge and parasitic draw on my 35Ah batteries? I usually use the chair a couple of times a week. Sometimes I need less, sometimes more often with no time for filling the battery, otherwise I would not use 28.8V.

[Burgerman]

That is great for long term float. But isnt really enough to charge it. You should tell it to charge normally then long term float.

[scottnj@gmail.com]

Reading through the MK1.pdf I have a couple of questions.

Max time (h) = 1.2 * DoD (Ah) / Avg. Current (A)

1) For calculating the max time for the bulk (CC) stage, what is DoD? I am guessing it is related to C/20 somehow.

2) For calculating the max time for the bulk (CC) stage, what is Avg. Current? I am assuming this is simply what I set the constant charge current to.

[Burgerman]

1) For calculating the max time for the bulk (CC) stage, what is DoD? I am guessing it is related to C/20 somehow.

No its DoD = Depth of Discharge, so unless you measure Ah out and use this to calculate then you cannot use that method. CC time will always vary depending on the actual curret you charge at, battery internal resistance, and condition etc. It ends simply because the battery voltage rises to the level where the CV stage is set.

Think power supply. If I set it to say 20A and 14.1V then the thing will charge the battery at 20A and as its voltage hits 14.1V then the current will drop away naturally so that the voltage doesent exceed what was set. A 2 stage charge is simply that. Nothing complex. All adjustable power supplies are 2 stage chargers. All lead batteries can be charged fully with 2 stages and thats all thats really wanted in cyclic use. Thats all the PL8 does. Although you can also set a "fast finishing" stage too if you are in a mad hurry. But its not as good for the battery and hard to get correct.

2) For calculating the max time for the bulk (CC) stage, what is Avg. Current? I am assuming this is simply what I set the constant charge current to.

Not sure where you read that as it has no context? But it sounds like it.

[scottnj@gmail.com]

Once you mentioned what DoD stood for, it made perfect sense. I don't have the Victron SmartShunt or any other current monitoring, so no way of knowing this besides a ballpark guess.
That equation is on the MK1.pdf that you reference. On the PDF, it is for calculating the max time for the bulk stage for error state.
Thanks

[Burgerman]

The only time that the CC stage will no rise to the CV voltage and automatically reduce current is if in say a boat where the loads on the battery exceed the charge amps or the battery is so destroyed that it cannot charge. So I wouldnt let the error condition here bother you any. Almost no chargers implement this.

The only one that really matters is the case whre th battery is sulfated or been charged badly in the past and the CV voltage absorption stage never drops below the point you set as termination current. So in the case I am charging a typical mobility battery which are never discharged below around 70 to 80% because realistically you cant! Because of an evil frenchman called peukert, then I find that on any AGM or Gel battery that an 8 hour CV limit usually ends at around 1/500th to 1/1000th of the 20h capacity. So a 100Ah battery will end at 140mA, to 70mA as long as there is no significant residual current drain from the system. So you may need to add a little depending on whelchair. But even if it doesent reach this point the 8 hour limit will turn the charge off or drop to a safe voltage anyway (float).

So I set:
1. CC at up to 25A via anderson, 12A via XLR.
2. according to BATTERY temperature (see the charge sheet for actual spec) 13.95V for top up or say monthly top off in storage (when system disconnected from a chair in storage or breaker tripped) Or in daily cyclic use I set the highest allowable 14.1V for gel (28.2 in a series setup).
3. i then set the CV time limit at 8 hours. And the Termination current to whatever the battery seems happy with that doesent fall by 0.1A over any 1 hour period. (on a 100Ah battery). This tends to be around 750th of C . This will drop lower at a lower charge voltage. Wont fall low enough if voltge too high. They vary. At this point no float is required in cyclic use. After this point its done. But it doesent hurt.
4. IF making a general charger that will not be fine tuned you can end charge at say 0.5A and allow a slightly high float such as 13.6 to 13.7V to complete the charge - but this is much slower. And it NEEDS float or battery will sulfate long term with an early cv cut off. This is how most cheap one size fits all 3 stage chargers work. Usually at incorrect and very innaccurate voltages.
5. for long term maintainance storage from days up to years ona full battery set float even lower at 13.30 to 13.35. Or as a secondary lower float level in the victron and then the battery can stay on float indefinitely to good effect.

[scottnj@gmail.com]

I picked up a Victron charger and am looking through the settings and owners manual.

I am putting together an initial general charging profile for MK Gel batteries. This profile is not for nightly charging, so it can take as long as it needs to reach 100%. It also will not be what I use for long term storage.

My profile settings are below, but I have a few questions.

Should battery safe be disabled?

Is 60 mV/C okay for MK Gel? I also noticed that the nominal temp on the MK spec sheet is 20 degrees C and Victron uses 25 degrees C.

What do you set for Re-bulk?

Do you set absorption to automatic or fixed? How long?

Did I disable recondition properly?

Victron Blue Smart IP22 Charger - 24 Volt, 16 Amp
General MK Gel Charging Profile

Function: Charger
Charge Preset: Custom
Night Mode: Disabled

Charge Current: 16 Amps
Maximum Current: 16 Amps
Max Charge Current: 16 Amps

Advanced Settings: Enabled
Expert Mode: Enabled
Battery Preset: User Defined

Charge Voltage
Absorption Voltage: 27.9 Volts
Float Voltage: 27 Volts
Storage Voltage: 26.7 Volts
Recondition Voltage: Disabled
Battery Safe: On ???

Voltage Compensation
Temperature Compensation: -60 mV / degree C ??? Is this accurate for MK Gel?

Bulk
Bulk Time Limit: 8 Hours
Re-bulk Method: Constant Current ???
Re-bulk Voltage Offset: 0.2 Volts ???
Re-bulk Current: Disabled ???

Absorption
Absorption Duration: Adaptive or Fixed ???
Max. Absorption Time: 6 Hours
Tail Current: 0.5 Amps
Repeated Absorption: 45 days

Recondition
Recondition Current Percentage: 0.08 ??? I think this stage is disabled above.
Recondition Stop Mode: Auto, on voltage ??? I think this stage is disabled above.
(Max.) Recondition Duration: 1 hour ??? I think this stage is disabled above.

Battery Limits
Low Temp. Cut-Off: Disabled

[scottnj@gmail.com]

I forgot to mention, this is for use with Anderson PowerPole connectors, not through the joystick.

[Burgerman]

Should battery safe be disabled?

Yes.

Is 60 mV/C okay for MK Gel? I also noticed that the nominal temp on the MK spec sheet is 20 degrees C and Victron uses 25 degrees C.

Set it as per the MK charge PDF, dont remember the figure offhand. Add some compensation to the 20C figure to account for the victrons 25C base. But its not that critical anyway unless its 35V in summer...

What do you set for Re-bulk?

I don have a victron. But you dont want rebulk unless something is dragging the battery down. The idea of the float (in 2 stages) is to maintain the battery at 100% long term without adding unessassary addicional charging. If it wont let you turn it off set it to whatever has the least affect and as infrequently as possible.

Do you set absorption to automatic or fixed? How long?

Well in CYCLIC use I would set 8 hours. Or around 100mA on 70Ah batteries whichever occurs first.
Why? Because if I fully 100% discharge a set of healthy MK or Haze gel batteries it requires around an 11 hour CV stage to reach the point where the current falls by less than 0.1A (100mA) and as per the MK PDF sheet). But you never discharge them to 100% DoD in real use. If its a typical days use, you use say 30 to 80% discharged, then they reach that point around 8 hours at the correct CV voltage. If they are already fully charged, and you try to recharge them 24 hours later, then they will reach that same point after 2 to 3 hours. If you actually look at the current at these three different scenarios, it is when the battery has dropped to around 100mA of current. This coincides with the 0.1A drop per hour point. So setting this termination current to 100mA automatically ends charge any time between 2 and 11 hours. But 11 hours at CV is a bit long for health. And the battery may never drop to your 100mA hence a sensible 8 hour limit just in case. That will result in a 99.9% full battery even if it was fully discharged.
We have noidea what "automatic" does. But from experience of automatic on dozens of other chargers both complex and simple they never do anything good. So I dont know. Personally I would set it to ON and test it. If it ends charge and goes to float somewhere around 150 to 200mA then leave it enabled. A much better way would be to set a termination current but the victron cant do that...
If it was cyclic use I would definitely set it to a fixed 8 hours CV. And to 3 hours CV if you are just topping up a full battery that has sat for 2 weeks to a month.

Did I disable recondition properly?

Victron Blue Smart IP22 Charger - 24 Volt, 16 Amp
General MK Gel Charging Profile

Function: Charger
Charge Preset: Custom
Night Mode: Disabled

What is nite mode? Quiet?

Charge Current: 16 Amps
Maximum Current: 16 Amps
Max Charge Current: 16 Amps

Advanced Settings: Enabled
Expert Mode: Enabled
Battery Preset: User Defined

Charge Voltage
Absorption Voltage: 27.9 Volts

Thats a safe voltage. I use 28V or 28.2V in cyclic use for gel batteries. But as long as you are in no hurry that will work.

Float Voltage: 27 Volts
Storage Voltage: 26.7 Volts

I would set the initial float a bit higher like 13.7V as from memory according to a member here it doesent stay on long...

Recondition Voltage: Disabled
Battery Safe: On ???

That sounds like some magic unknown random behind the scenes thing. What does it actually do?
I would ether want to know details or OFF.

Bulk
Bulk Time Limit: 8 Hours

It will have put back 120Ah by then. So that wont actually do anything on a 74Ah battery which is fine. UNLESS something is draining the battery as you charge. As happens on a boat for e.g.

Re-bulk Method: Constant Current ???
Re-bulk Voltage Offset: 0.2 Volts ???

I would set it to 0V. The CC (bulk) is nly happening if the battery voltage is below the CV voltage as its dragging the battery voltage up. So setting a voltge here doesent seem to make any sense at all.

Re-bulk Current: Disabled ???

Yes.

Absorption
Absorption Duration: Adaptive or Fixed ???
Max. Absorption Time: 6 Hours
Tail Current: 0.5 Amps

Set that to 8 hours (and MK say 12! But thats only needed when 100% discharged) and set that 0.5A (500mA) to whatever the battery reaches in around 8 hours of CV. IF thats the point where it stops charging. Is this a termination current? Isnt there a book that explains their terms anywhere?
The adaptive of fixed thing doesent make sense. Because if that 500mA is the point where it stops charging then what is to "adapt?"

Repeated Absorption: 45 days

Off is better but its not allowed...

Recondition
Recondition Current Percentage: 0.08 ??? I think this stage is disabled above.
Recondition Stop Mode: Auto, on voltage ??? I think this stage is disabled above.
(Max.) Recondition Duration: 1 hour ??? I think this stage is disabled above.

Hopefully!

Listen carefully!
All you want is it to do this:
1. Charge at CC (bulk) at whatever Amps you tell it until it reaches the CV voltage however long this takes.
2, Remain at the CV voltage until current drops to around 100mA or 8 hours, whichever occurs first and stop. (this may vary, and is an analogue for the pint where current falls by less than 0.1A in 1 full hour. As this tends to be pretty much the same thing. You may need to adjust it upwards to 200mA as required.)
3. Float to begin and sit at 13.7V per battery for a few hours. Anywhere from 4 to 8 depending on termination current/time at CV. If it ends early then float longer. Then drop to 13.2V per battery long term. All at 20C.

[Burgerman]

Voltage Compensation
Temperature Compensation: -60 mV / degree C ??? Is this accurate for MK Gel?

To compensate for battery temperature not at 20°C, subtract 0.005 V/cell for each 1°C above 20°C; add
0.005 V/cell for each 1°C under 20°C.

So thats SUBTRACT or minus 0.005vpc per degree. So 0.025V per cell, and 12x that on a 24V battery with a 5 degree change. Or at 25C that would mean a voltage REDUCTION of 0.3V.

Now consider that in a 40C summer day, where the battery has been used all day that it may be 5 degrees warmer than this, and that most mobility chargers are NOT temperature compensated. And that they are typically one size fits all AGM and Gel safe according to the manual...

So you are charging your gel batteries at 28.80 to 29.4V depending on the mobility charger typically.
At 45C in spain or hot bits of the USA you SHOULD be charging at:

Look carefully at temperatures and voltage. Remember that your battery can easily be 40C after
use in summer.

Again a slightly more tech chart showing the rapid recharge safe voltage and the float charge
voltage v temperature in standby use.

And take a look at the damage done by charging a few tenths of a volt too high. And this is ony one type of life shortening damage. Mobility chargers can easily exceed this .7 volt overcharge. Especially in summer. And they cause sulfation in cyclic use by never adequately charging the battery. They stop CV too soon... Further reducing service life. Is it any wonder there are so many battery issues on here?

THIS is what happens when you ignore that stuff...
And this does not include additional damage from ending the charge to soon and allowing sulfation to cause even more damage.

These are all MKs own charts and info.
Yet they will still sell you a bad charger, and give out sell sheets that say you can charge at 14.6V... Because they wanna sell more batteries.

[scottnj@gmail.com]

So I played around in Excel with the temperature compensation for 20 & 25 degree C nominal battery temperatures to figure out what the Victron settings should be.

If my math is correct (I had it reversed before, but I think I have it accurate now), it appears Victron chargers with temperature compensation set will ALWAY set the voltages above what MK recommends for their Gel Batteries! Luckily, this is constant across all battery temperatures. If temperature compensation is set, we need to subtract the offset calculated below to the absorption, float, and storage voltages.

I didn't get a chance to verify this with the actual charger yet. These are just calculations based on the documentation.

Victron Battery Chargers

The configured charge voltage is related to a nominal temperature of 25°C and linear temperature compensation occurs between the limits of 6°C and 50°C based on the default temperature compensation coefficient ... as configured.

https://www.victronenergy.com/media/pg/Blue_Smart_IP22_Charger_manual_120V/en/operation/temperature-compensation.html

MK Gel Batteries

To compensate for battery temperature not at 20°C, subtract 0.005 V/cell for each 1°C above 20°C; add 0.005 V/cell for each 1°C under 20°C.

https://www.wheelchairdriver.com/MK1.pdf

Temperature Compensation Coefficient for MK Gel:
12V: 0.005 * 6 = 0.03 V/C = 30 mV/C
24V: 0.005 * 12 = 0.06 V/C = 60 mV/C

Calculate Compensated Charge Voltage
12V: Charge Voltage = Nominal_Charge_Voltage -((Battery_Temp - Nominal_Temp) * 0.03)
24V: Charge Voltage = Nominal_Charge_Voltage -((Battery_Temp - Nominal_Temp) * 0.06)

At first I tried adjusting the Temperature Compensation Coefficient. But the above equation is linear, changing the coefficient changes the slope of our line, which will only allow us to match the correct voltage at a specific temperature. At all other temperatures, the voltages would be higher than what MK specifies.

If you look at the chart below, we want to keep the 0.005 coefficient that MK recommends, and subtract a constant voltage offset. This will shift the blue line (nominal 25 degrees C) down and it will match the red line (nominal 20 degrees C) exactly.

To calculate the voltage offset that we need:
12V: (25-20)*0.005*6 = 0.15 Volts
24V: (25-20)*0.005*12 = 0.3 Volts

So, if you want a 28.2 absorption voltage, you need to set it to 27.9 V.

[Burgerman]

Well its not that critical, as long as its somewhere close. And its a curve... The stated V per degree change on MK s algo page is an aproximation. Since the actual battery temp isnt known, and is estimated, and the thing is really a curve, and theres a range where it is safe and so accuracy isnt too critical, I just charge at 14.1V in deep cycle use, 13.8V in storage when no rush for top up purposes after a month in storage. And if its noticibly warmer than 20C I drop it by a tenth or 2 tenths. Same for long term storage.

If its cold, such as my van in winter then I increase it over the november to march period. Thats sits at a constant (uncorrected) 13.35V via a small wall wart that I modified with a voltage regulator chip. Then I plug in in the house and with a long extention cable connect to a anderson on my van under the wheel arch. It sits for weeks to months at a time in winter. And something drains the now 14 year old (yes its likely destroyed!) Optima battery. But it starts. So I dont worry. Probably half capacity...

If it doesent start I just plug my chair into it. Its got a dual series/parallel connection setup. It will start anything. Martim my carer left his lights on all night some years back. So I started it with my chair. Totally dead. The starter just clicks in and out of mesh. Big old (winter) deisel engine...

The same system charges the chairs battery IN my van as I drive at 50 to 80 Amps... I have an anderson connector under the dashboard. Alternator adds power back fast. Its 14.4V but the current/cable length and battery resistance with 2 in parallel mean it doesent reack that level for the first 90% of the charge. So I just do it for an hour if going a long way. That can put back 40Ah or so. So 20Ah in half hour is a big boost. Around half your range per 30 mins.

https://www.wheelchairdriver.com/gopro/starter.mp4