creating solar charger for compaq cq61

Hello,

looking at my AC wall adapter it states "input: 100-240v  1.6a 50-60hz" "output: 18.5v 3.5a". I measured the output at (19)dcv.

A few panels if I disconnect them  from the 12v controller charge 21v and  and about .3 amps.

Can I just directly connect the solar panels to a new connector? The new connector i would cut from the wall adapter and just splice the solar panelinto the connector.

Is there anything that a should install to protect this? Will a low voltage from lack of sunlight hurt the battery? I assume I could put a 3.5 amp fuse inline? Will I hurt the power supply charging this way?

John

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John

No.
You must have a regulator.

Also your panels are 12V.
Although they can output over 21V, this is at low power/current only and it drops quickly to lower voltages under load.
I doublt tat you would get more than 10% or rated power above 19V from a 12V solar panel.

For 19V, you need a 24V array, or a 12V array with a dc-dc converter.

Both could benefit from an MPPT (which maybe could be reconfigured for 18.5V output - but then you have no battery backup.)


In practice, for 18.5v 3.5A (65W) you'd need an 80W to 100W panel with full output.
This reduces with a battery (to be charged with excess power and supply when not enough solar) and your duty cycles - ie, laptop-on time verses solar-supply time (and its average power) - the solar power must exceed the laptops over a 24 hour cycle (or longer if you expect bad solar days).

oldspark wrote:

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No.
You must have a regulator.

Also your panels are 12V.
Although they can output over 21V, this is at low power/current only and it drops quickly to lower voltages under load.
I doublt tat you would get more than 10% or rated power above 19V from a 12V solar panel.

For 19V, you need a 24V array, or a 12V array with a dc-dc converter.

Both could benefit from an MPPT (which maybe could be reconfigured for 18.5V output - but then you have no battery backup.)


In practice, for 18.5v 3.5A (65W) you'd need an 80W to 100W panel with full output.
This reduces with a battery (to be charged with excess power and supply when not enough solar) and your duty cycles - ie, laptop-on time verses solar-supply time (and its average power) - the solar power must exceed the laptops over a 24 hour cycle (or longer if you expect bad solar days).

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Ok So;

two equal amp 12 v solar panels in series = 24v

connected to

two 12v batteries in series = 24v

then MPPT regulator regulatingdown  at 18.5v on between the batteries and the wall adapter connector to the Compaq CQ61?

Thanks,

John

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John

If you can get 24V MPPTs - I've only seen 12V but ot that I;ve looked for 24V.

But if using 24V, then just a down converter.

But 12V with a 12V up converter may be cheaper - and more usable/transferable than a 24V system. (My 45W converter cost AUD $22. 90W are ~$45. I'd rather that than need to use 2 batteries AND find 24V converters....)

oldspark wrote:

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If you can get 24V MPPTs - I've only seen 12V but ot that I;ve looked for 24V.

But if using 24V, then just a down converter.

But 12V with a 12V up converter may be cheaper - and more usable/transferable than a 24V system. (My 45W converter cost AUD $22. 90W are ~$45. I'd rather that than need to use 2 batteries AND find 24V converters....)

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I had heard from someone that a higher voltage stepped down is more efficient than 12v stepped up. True/False?

Ok so if I get a 12v step up converter how do I adjust it to step up to 18.5v?

Thanks,

John

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John

I'd like that person to explain WHY converting down is more efficient than converting up.
The only reason is higher current from low, hence greater losses, but that is insignificant at this level. (And does not justify going to 24V!)


All the laptop car converters are setable - usually by selecting the correct tip (dc plug) or a selection switch.


And BTW - for battery capacity, use one larger battery than 2 smaller parallel monoblocks. [I'm comparing to having 2 series batteries - not talking about paralleling to other batteries like the main car battery etc (which should have isolation...).]