Calculating DoD of SLA batteries, with Peukert Effect?

[imorton]

Hi Guys, my questions is regarding how to calculate the DoD (depth of discharge) of SLA batteries with reference to the Peukert Effect.

The reason I ask, I have a 48v motor with four 12v 12Ah SLA's. With my WattsUp meter, if I see that I have consumed 6Ah by pulling 8-10amps cruising around the neighborhood, is that a 50% Dod? (50% of my 12Ah)

I know that the Peukert Effect is coming into play with my SLA's, so in reality my 12Ah batteries are only capable of putting out @ 7Ah when being drawn at @ 8 amps. So the fact that my WattsUp meter tells me that I have consumed 6Ah, does this calculate as using 85% of my battery, or 85% Dod? (12Ah x Peukert = 7Ah, used 6Ah, so 85% usage)

Just curious as to how DoD works with lead acid batteries…

IAN…

 

[Sentionline]

Hi imorton.

I have 6 AGMs (12V/9Ah x 6 = 72V/9Ah). There now 1,5 years old and i have driven now 15.576km (9678.47 miles). I can pick now ~5Ah. You can easy check your State of Charge, if you check the idle Voltage. To prevent damages, i have set the Cut Off Voltage in my controller to 64.7V. Thats a save range from 10.8V for each Battery. You must Set 43,2V Cut of Voltage, to prevent deep cycle damages (sulfation) and take more Lifetime and Cycles. I think you can pick 7~7.5Ah. If you drive safe, you can pick 8Ah.

Most energy consumption flows at approach.
It does not matter how much you consume. Watch out for the voltages! Do NEVER go under 42V at idle!

The Peukerts Law you can easy calculate here;

http://www.csgnetwork.com/batterylifecalc.html
http://www.batterystuff.com/kb/tools/calculator-for-load-specific-run-time-b.html

The Peukert Law Nr for Lead-Acid AGM batterys is 1.24. Gel Batterys have (i remember) 1.21.

Greetings from Germany.

 

[Ypedal]

different brands of lead acid will deliver varying amounts of usable energy at 1h rate ...

example :
http://ypedal.com/sla/sla.htm

 

[imorton]

Hi imorton.

I have 6 AGMs (12V/9Ah x 6 = 72V/9Ah). There now 1,5 years old and i have driven now 15.576km (9678.47 miles). I can pick now ~5Ah. You can easy check your State of Charge, if you check the idle Voltage. To prevent damages, i have set the Cut Off Voltage in my controller to 64.7V. Thats a save range from 10.8V for each Battery. You must Set 43,2V Cut of Voltage, to prevent deep cycle damages (sulfation) and take more Lifetime and Cycles. I think you can pick 7~7.5Ah. If you drive safe, you can pick 8Ah.

Most energy consumption flows at approach.
It does not matter how much you consume. Watch out for the voltages! Do NEVER go under 42V at idle!

The Peukerts Law you can easy calculate here;

http://www.csgnetwork.com/batterylifecalc.html
http://www.batterystuff.com/kb/tools/calculator-for-load-specific-run-time-b.html

The Peukert Law Nr for Lead-Acid AGM batterys is 1.24. Gel Batterys have (i remember) 1.21.

Greetings from Germany.

Thank you very much for your reply. The links you provided help me to see that by using 3.5Ah at for example @ 8amps means that I am actually discharging my 12Ah batteries to 50% DoD. I have at times used @ 6Ah while my scooter used 8amps, which means that I discharged my batteries to 85% Dod.

By using the links/calculators, I see that discharge times really go up fast the more current you use. I can cruise at 20kph and use @ 6 amps, and have a 20km range to bring me at 80% Dod. If I run WOT at 30kph, using @ 12-13 amps, my range drops to 13km before reaching the same 80% Dod.

I guess this is where we see that speed really increases exponentially the current draw which in turn reduce your potential range. hmmmm… information overload..

Again, thanks for your reply and the links, they really helped to visualize the Dod percentages.

IAN…

 

[imorton]

different brands of lead acid will deliver varying amounts of usable energy at 1h rate ...

example :
http://ypedal.com/sla/sla.htm

Thanks for your reply as I had read that page on your site… Very enlightening and really helped to see the real effects of Peukert.

My WATTSUP meter really helps to see the numbers in relationship to amps, voltage, watts,Wh, Apeak, etc….

I just wish I could figure out how to calculate my average current draw. Since the current demands change depending on terrain, wind, stop starts, etc…. Does a Cycle Analyst show the "average current draw"…? Because I seem to use anywhere from 2 amps to 17amps, depending on throttle.

Thanks again for your reply, IAN…

 

[999zip999]

imonron There is no way of knowning the state of charge. Of each battery and cell. Plus some good and some good better. So what lead can work, so know the limits of lead. they can last. I hate lead.

 

[imorton]

imonron There is no way of knowning the state of charge. Of each battery and cell. Plus some good and some good better. So what lead can work, so know the limits of lead. they can last. I hate lead.

I'm sorry, but I'm going to take a guess that english in not your primary language. I am guessing that you passed your reply through a language translator and lose some of the translation?

I can't seem to figure out what you replied. Can you try again and word it a little different.

No disrespect meant in my reply. IAN.

 

[999zip999]

Each battery is 12ah and you have a new battery of said Ah. It from the same company is different. As the same from different battery companies.
So where can we go but bigger or stronger cell to with start. I would not start with sla. *If not on hand.

 

[Ypedal]

Just to clarify a detail about your observation on DOD.. ( Depth Of Discharge )

A 12ah battery, used on your scooter, at say 10 amps ( imaginative number... just for the example ) .. delivers aprox 7~8ah before the voltage of the brick drops to 10v .... this is 100% DOD

the same 12ah battery, drained over the course of 20 hours, will deliver 12ah, also 100% DOD

If you know your 12ah brick can deliver 8ah at your discharge rate ( on your scooter ), and your watt's up meter says you used 4ah worth, then that... is 50% DOD. :wink:

 

[Ypedal]

Each battery is 12ah and you have a new battery of said Ah. It from the same company is different. As the same from different battery companies.
So where can we go but bigger or stronger cell to with start. I would not start with sla. *If not on hand.

I think, not really sure, that what he's trying to say is that batteries vary from brick to brick, even if they come from the same batch, 3 bricks purchased at the same place, same time, will have slightly different capacity/weight etc....

 

[999zip999]

Yes there can be used for a bike.But using them for ebike is difference between ah in lead batteries for use in the demands from ebbikes. As sla are not meant for this use.
They are best as a high amp demands of a battery of a starter motor and then recharge for the next drain of a starter motor to start the gas engine. And for a draw of an ebike motor. They work great as a one time start up of a gas engine and not for the draw of an ebike motor. They just drain in a down hill way. In being use this way to full ah just waste them.
I do know of people getting 2yrs from them (sla's) but they do light drain and recharge and keep at a high state of charge. They can work if you work in there working zone.

I hope this clears up my veiws. Yes sla's do and can work if you work in there limit's. As with all batteries.

I

 

[Ypedal]

not true...

they make starter batteries, and they make EV deep cycle batteries.... just like all other types.. lithium nimh etc... some for low drain devices, others for high drain...

 

[999zip999]

Yes they make them and label them but there are better batteries. Plus there are heavy. And if not charged will loose ah. . plus need to be gotten fresh.

 

[999zip999]

Different battery manafactors have different quality and with one or some not being rotated or keep charged can get a little flat. It's like buying a Yugo, you could get a good one. It's always best to buy from a vendor who has high volume. To get a fresh battery. Always best at full charge and keep at full charge.
I would like to buy a desultor charger for testing.

 

[imorton]

@999zip999, you are right, fresh batteries are very important and like you said, SLA's like to be kept fully charged and not discharged to 100% DOD.

@ypedal, your example of a 12Ah discharged at @ .5amps will reach 100% DOD after using @12Ah, but just the same as a 12Ah discharged at example 8amps, will be 100% discharged after using @ 7-8Ah. This is what I was trying to understand.

My scooter has a speed switch (eco/high) which limits current. In high mode, I can do 32kph on flat but will use 12-13amps, which only gives me a range of @15kms. If I use the "eco mode", it uses @ 5-6 amps and still does @ 20kph, but gives me a range of @ 22kms. hmmmmm…. interesting…..

So this tells me that SPEED is a very BIG FACTOR on overall consumption, thus range.

Thanks for all you guys explanation, you're all very kind for taking the time to help a newbie…

IAN.

 

[Ypedal]

mostly due to wind resistance, the faster you go, the more wind you push, costing precious energy in the process..

 

[Sentionline]

Important is to charge the Battery(s) every time after use it. Plug the charger in every time, so fast u can. psychological factor...Train it! Thats the best way to prevent sulfation!

Sulfation can be avoided if the battery is fully recharged immediately after a discharge cycle.

http://en.wikipedia.org/wiki/Lead_acid#Sulfation_and_desulfation

@ypedal, your example of a 12Ah discharged at @ .5amps will reach 100% DOD after using @12Ah, but just the same as a 12Ah discharged at example 8amps, will be 100% discharged after using @ 7-8Ah. This is what I was trying to understand.

I did read many over Lead acid batterys. If you discharge the 12Ah battery fast, the chemical process will give you in this time not the full capacity. After this time (8A discharge), you did pick the 7~8Ah. There is about 4~5Ah in the battery, it isnt away. You can pick the rest, if you very slow (~0.5A) discharge the 4~5Ah. Then you have finish the 100% DoD.

8Ah only? Yes. Why? But you pick the energy too fast from the lead chemical.

Lifepo4 isnt realy better. BMS Stress...Discharge over 100% DoD without BMS, battery dead. Lead Acid can be charged everytime in this scenario. BMS did pick every time Energy from the battery and it can over discharge the Cells, that you cant charge again, if there deeply discharged. If the BMS didnt work correctly (recuperation), cells will be damage.

I do charge my 6 batterys with Delran Battery Tender 4x and 2x Version. Every battery charged separately individually (IUoU characteristic). Thats the best way, what you can do to correct charge Lead Acid batterys. Charge it separately.

And again;

The battery's open circuit voltage can also be used to gauge the state of charge.

http://en.wikipedia.org/wiki/Lead_acid#Measuring_the_charge_level
http://www.windsun.com/Batteries/Battery_FAQ.htm#Battery Voltages

Greetings from Germany

 

[imorton]

I hear that often, charge after every use.

Charge after use, does this mean I can use the scooter intermittently during the day and CHARGE IT at the end of the day. Or should I charge it even for 30mins or 1 hr during the day if there is a plug?

Hmmm…?

 

[999zip999]

Sla's like to live at 12.86v or above. They are made to give a burst of energy. As lifepo4 give a strong even discharge line. We are talking about a lighting bolt in a box and you are taking out just some of the lighting bolt as needed. Math and lighting bolts don't mix well.

 

[Sentionline]

Charge after use, does this mean I can use the scooter intermittently during the day and CHARGE IT at the end of the day. Or should I charge it even for 30mins or 1 hr during the day if there is a plug?

Both is correct. If you always pour the flowers, there will have long time rays...