cheapest source for 10/20 watt solar panel

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floydie

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#156022 16-Nov-2014 21:26

looking for a 10 or 20W solar panel to keep my rarely used sportscar battery charged and possible a 12v backup battery for emergency light etc... looking for a cheap source for a panel and regulator.
jaycar etc seem very expensive??

Aredwood

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#1177079 17-Nov-2014 00:27

Have a look on Aliexpress.com And consider using youshop for the shipping.

Fred99

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#1177430 17-Nov-2014 15:53

4w solar panel should do the trick - ie from Supercheap Auto.

There's a potential problem with a 10 or 20 watt panel used for maintenance charging of car batteries etc. They may destroy the batteries unless used with a charge controller.

floydie

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#1177483 17-Nov-2014 17:23

ive got a supercheap one at the mo and it doesnt keep up in the winter. was looking to use a charge controller with it. wondering if the charge controller and cars voltage regulator in the car will play nicely together. dont want to be disconnecting battery all the time

Niel

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#1177574 17-Nov-2014 20:37

Either the battery has a weak internal short or the car has something draining the battery or the car is stored in a very cold place. Car batteries sitting on the shelf needs top-up charging only every 3-6 months, and that is only about 5% charge needed. If it is a classic with an electromechanical clock, then that is one source of likely discharge.

You can clip the solar regulator to the battery without disconnecting the battery, or some plug into the cigarette lighter socket (but only works if it is not a switched socket). Don't run the engine with the solar charger connected, typically it is a shunt regulator which will try and limit (but not very long!) the battery voltage by shunting the alternator current...

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Fred99

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#1177575 17-Nov-2014 20:40

As I understand it, the car's voltage regulator is from the alternator, connecting a solar charger (with or without charge controller) direct to the battery won't be a problem.
I'm unsure about quality of cheap charge controllers. The one I use on my boat has several options depending on type of battery it's charging - deep cycle, regular lead-acid, or calciium/lead (sealed). I know when I connect a voltmeter when first connected, it gradually steps up the voltage over quite a few minutes. I use that with a 20W panel when we're staying on the boat, but leave it with a 5W panel over winter and that keeps up the charge just fine. With a car however, there may be something leeching a tiny amount of current - stereo, keyless entry etc.

floydie

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#1177658 17-Nov-2014 22:21

my car has the stereo and alarm pulling current. its only a small battery so after just a few weeks its flat. ive lunched 3 batteries over the past 4 years because theyve been over discharged... need to stop that happening again.

any hoo..... anyone know a good cheap source for the panels? the charge controllers all seem to be around the $70 mark but the panels seem to vary greatly in price.

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floydie

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#1177661 17-Nov-2014 22:23

richms

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#1177666 17-Nov-2014 22:30

$70 is a crazy amount for a charge controller.

I would ebay the lot. 10w panels are cheap as out of china, as are charge controllers.

Just check the float voltage is right once its full with a decent quality digital multimeter as the metering on the charge controllers that have it is not always spot on accurate. Neither are $30 multimeters so dont bother comparing cheap stuff with other cheap stuff.

Richard rich.ms

Fred99

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#1177679 17-Nov-2014 23:05

richms: $70 is a crazy amount for a charge controller.

Not all charge controllers are equal - and batteries are (much more) expensive.

floydie

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#1178048 18-Nov-2014 17:19

ive heard lots of negative feedback on those $20 ebay regulators. woul drather just get a proven $70 one.

Niel

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#1178137 18-Nov-2014 21:03

A solar regulator simply connects a load to pull the voltage down to 13.8V once the battery is fully charged (and not pulling the voltage down any more). The components to do this is worth about $1 retail.

Solar chargers can just be connected across the battery while connected to the car, but need to be disconnected before starting the car or else the alternator will charge to 14V while the solar charger will try and pull it down to 13.8V... Cycle charge is to 14V, float charge is to 13.8V.

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Fred99

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#1178144 18-Nov-2014 21:14

Niel: A solar regulator simply connects a load to pull the voltage down to 13.8V once the battery is fully charged (and not pulling the voltage down any more). The components to do this is worth about $1 retail.

Solar chargers can just be connected across the battery while connected to the car, but need to be disconnected before starting the car or else the alternator will charge to 14V while the solar charger will try and pull it down to 13.8V... Cycle charge is to 14V, float charge is to 13.8V.

Sorry - that's not correct.
The better charge regulators (PWM and MPPT) are not simple voltage regulators.
In fact - simple voltage regulator circuits are inherently unsuitable / inefficient for this purpose.

Niel

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#1179675 19-Nov-2014 16:14

Fred99:
Niel: A solar regulator simply connects a load to pull the voltage down to 13.8V once the battery is fully charged (and not pulling the voltage down any more). The components to do this is worth about $1 retail.

Solar chargers can just be connected across the battery while connected to the car, but need to be disconnected before starting the car or else the alternator will charge to 14V while the solar charger will try and pull it down to 13.8V... Cycle charge is to 14V, float charge is to 13.8V.

Sorry - that's not correct.
The better charge regulators (PWM and MPPT) are not simple voltage regulators.
In fact - simple voltage regulator circuits are inherently unsuitable / inefficient for this purpose.

Let me rephrase that, a low power (shunt) solar charger for the OP's application of standby charging simply pulls the voltage down when the battery is charged. Using a PWM/MPPT regulator for this application is an overkill, with 50+ components instead of 5 to charge a battery with an estimated 1Ah per day (guess 30Ah over 4 weeks) so about 100-200mA is a reliability issue and a waste. The PWM/MPPT charger will most likely have trouble tracking the optimum point with such a low current, except for the first time the battery is charged.

You can never have enough Volvos!