EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Jiri_L on September 05, 2017, 12:31:49 pm
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Hello All,
my name is Jiri, coming from Europe, my occupation is a teacher/researcher on university, I am dealing with electrochemistry, especially with li-ion batteries.
I would say I have got a knowledge in batteries topic, electrode materials, electrolytes ....just basic research. Unfortunately i have zero practical experience. I decide to star building my own battery boxes for electric vehicles and that is the reason why I sing in to this board.
May I ask you about battery voltage in the pack?
Lets assume that I am using only 3.6 V cells (nominal working voltage) charged to 4.1 V, the difference is 0.5 V per cell.
How many cells in series I need to build up the packs with these nominal voltages:
24 V nominal = 6s or 7s ?
36 V = 10s
48 V =13s or 14s ?
If the nominal voltage of the batt. pack is for example 36 V and we have 10s the charger must reach charging voltage 41 V, am I right?
Thank you for not so cleaver question but I am confused about it.
Thank you,
Jiri
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Yes, the voltages add, so if the nominal nominal voltage per cell is 3.6V and 4.1V fully charged and they're ten in series, then the nominal pack voltage will be 36V and the maximum pack voltage will be 41V.
The same thing is encountered with 12V lead acid batteries. If the nominal voltage of each battery is 12V and 14.5V fully charged, then three in series will have a nominal voltage of 36V and a fully charged voltage of 43.5V.
The electrical system will need to be designed to work from the minimum and maximum battery voltages.
Often cell voltage balancing is required, especially for lithium ion. You will need to design/purchase a suitable charger. There should also be an under voltage warning and disconnect, to prevent the batteries from discharging past their minimum safe voltage.
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Same happens with 9V batteries. The old standard is 6x1.5V primary battery. Then there are rechargeable batteries, some are 6x1.2 some are 7x1.2V and now some are 2x3.7V, which is not even close.
Though, 24V seems to be 7x3.7V, 48V is 13x3.7V and 36 is 10x3.7. Usually packs are mentioning the base cell, like 18650 (size) 2600mAh and then a numbering, like 7S3P, which means 7 in series, 3 in parallel.
And good chargers should have balancing inputs, or the pack should have this built in.