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Author Topic: best way to charge 3piece 4v lead acid from 9v 3w panel?  (Read 1386 times)

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Offline dave_j_fanTopic starter

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best way to charge 3piece 4v lead acid from 9v 3w panel?
« on: February 10, 2018, 09:26:54 pm »
i am planning to charge 3no 4v cells keepin in parallel
9v solar panel 3w is the source  source

connection to cells gives 300mA . I am thinking 100mA per cell is ok
just voltage in is 10V
will it make problem

i will add 7  piece 1N4007 as voltage clamper diodes with some reosotor  that will eat away once voltage
crosses 4.7v


any better alternative ?
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Offline dave_j_fanTopic starter

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Re: best way to charge 3piece 4v lead acid from 9v 3w panel?
« Reply #1 on: February 11, 2018, 10:09:35 am »
no reply ?? Anyone
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Offline paulca

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Re: best way to charge 3piece 4v lead acid from 9v 3w panel?
« Reply #2 on: February 11, 2018, 10:39:56 am »
When it's asked, "Can I just connect a panel to a battery?" the answer is almost always, No.  It will work, but it will not do what you think it will. 

If the cells are charged and not pulling current the panel voltage will rise and overcharge them. 

If the cells are undercharged they will pull a  load of current pulling the panel voltage down to the cell voltage resulting in less watts and less charging.

I don't think clamp or dropper diodes will work either.  Panels are not linear, the voltage will vary a lot.

Take a look here.  He has other videos on his channel where he demonstrates what happens if you try and do what you are intending.  It doesn't work very well is the short of it.  You can use a charge pump and PWM with an arduino (Check also Adam Welch videos where he shrinks it to an ATTiny chip)... or you can go full MPPT which is probably overkill for your use case.

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Offline danadak

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Re: best way to charge 3piece 4v lead acid from 9v 3w panel?
« Reply #3 on: February 11, 2018, 03:09:43 pm »
« Last Edit: February 11, 2018, 03:12:34 pm by danadak »
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Offline dave_j_fanTopic starter

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Re: best way to charge 3piece 4v lead acid from 9v 3w panel?
« Reply #4 on: February 11, 2018, 07:21:05 pm »
paulca,
I have been using 4v cell pair in series with a diode on that 9v solar . always charges well
I am using one lantern but it is a bit dim.
 
the  unit LED brightness to be increased but not cost by many factor
so i decided to go by parallel cell method , adding one cell  adds 20cents and possible ( it will be a product )

I have read 3w panels cant overcharge cells if nearby voltage .. coz max current 270mA
if i add a diode clamp as shown i can prevent overcharge



 danadak, task has to be done with lowest cost
« Last Edit: February 12, 2018, 07:02:05 am by dave_j_fan »
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