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Old 3rd September 2010, 01:57 AM   #1
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Default Battery management system - how complicate is it ?

Hi folks, alike the title says,

I have just some questions to be cleared if anyone experienced member/s is ready to explain for me:

- is it true that SLA batteries can either charged or used but never both actions same time like with the Li-Ion batteries (for example notebook use) ?

- What about battery management systems for SLA batteries ? Is it complicated to build a "voltage monitoring" for 2 batteries and a switch for example ? LED tells you to switch to other battery while you begin to charge the empty one ... of course the most comfortable solution is a full automatic system.

Same questions about the more expensive LIFePo4 batteries ... are these better to handle regarding charging issues ?

Last edited by TheDealer; 3rd September 2010 at 02:00 AM.
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Old 3rd September 2010, 02:14 AM   #2
star882 is offline star882  United States
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It is fine to float charge lead acid batteries and Lithium-based batteries. Nickel-based batteries may need special circuits since varying loads can interfere with voltage slope sensing.

If you have two identical batteries, just connect them in series or parallel and use them as one. The only time a switching system makes sense is if one is the main and the other is the extended. The extended battery should be used first so the user can remove it once it's used in order to reduce weight.
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Old 3rd September 2010, 02:32 AM   #3
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A battery can be charged or discharged. No battery can be charged and used at the same time.

Power can be drawn from the charging circuit and battery. If this is less than the power available from the charging circuit the battery will charge. If the power available from the charging circuit is less than the power being used, then the battery will discharge.

w
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Old 3rd September 2010, 06:57 AM   #4
Mooly is offline Mooly  United Kingdom
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Yuasa's little red book of batteries,
Yuasa - industrial batteries, automotive batteries, motorcycle batteries, golf batteries, mobility batteries.
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Old 4th September 2010, 01:28 AM   #5
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Quote:
Originally Posted by star882 View Post
It is fine to float charge lead acid batteries and Lithium-based batteries. Nickel-based batteries may need special circuits since varying loads can interfere with voltage slope sensing.
Yes but I think that I had read in the past that SLAīs arenīt recommended to charge and discharge same time ... though itīs possible. Í am really not sure how problematic this could be. So here are technical issues and on the other hand audio results to be regarded.

Quote:
Originally Posted by star882 View Post
The only time a switching system makes sense is if one is the main and the other is the extended. The extended battery should be used first so the user can remove it once it's used in order to reduce weight.
What you say here is also senseless if it should be in fact strictly not recommended to charge and discharge SLAs same time.

Are you sure you are getting same audio results then ... ? As I said above I am in the believe that I read something different in the past. Maybe another member could also give a statement.
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Old 4th September 2010, 01:34 AM   #6
star882 is offline star882  United States
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The lead acid battery in a car is essentially charged and discharged at the same time, acting as a filter capacitor and peak power reserve.
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Old 4th September 2010, 01:48 AM   #7
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Quote:
Originally Posted by wakibaki View Post
A battery can be charged or discharged. No battery can be charged and used at the same time.

Power can be drawn from the charging circuit and battery. If this is less than the power available from the charging circuit the battery will charge. If the power available from the charging circuit is less than the power being used, then the battery will discharge.

w
you are speaking for the SLAs, or not ? Exact this is the alternative solution for switching between two batteries. If music plays the BMS discharges the battery but I need a BMS who says for example under 12,5 V voltage + no music plays = charge. I donīt want that every time when I stop music at full battery load that the charging begins ... this is also not good for battery life I think. Not sure what voltage a total full SLA shows ... 13,8 V ?
This means 2,3 V/cell
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Old 4th September 2010, 02:00 AM   #8
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Quote:
Originally Posted by star882 View Post
The lead acid battery in a car is essentially charged and discharged at the same time, acting as a filter capacitor and peak power reserve.
Yes,
but you cannot compare voltage demands in a car with voltage demands in a home audio system. The car battery is charged by moving the car and moving means that energy persistently is needed for the car electric system.

If a battery in an unused amplifer for example can be persistently connected to supply voltage/current - that would be O.K. but I am not sure in this case if these minimum discharge and charge values at same time

a) are good for SLAs life (car batteries are also a bit different you know)
b) have influence on listen qualities
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Old 4th September 2010, 03:15 AM   #9
star882 is offline star882  United States
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Lead acid batteries like to stay charged. Simply supply up to 14.4v current limited to about C/5, then drop the voltage to 13.8v after 14.4v is reached for about 5 hours.
Charging the lead-acid battery
Sense the battery current in order to prevent the load from affecting charging.
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Old 4th September 2010, 05:22 PM   #10
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Some lead acid batteries are designed for very high engine starting current. (hundreds of Amps)
Some deep-cycle lead acid batteries are designed for continuous low current.
If a battery is being used and is re-charged at the same time, then it acts as a large filter capacitor.
I would get two SLA batteries and swap them after a reasonable number of hours.
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