Solar Car Battery Charger

[Macski]

I have taken my MR2 off road for the winter and looking at buying a solar panel to keep the battery topped up. I was about to get a 5W unit when reading through the reviews it was suggested it is not powerful enough to do the job because of short winter nights. Anyone know anything about the subject and advice would be appreciated!

Also could I connect a 12V panel to a 24V mobility scooter?

Thanks for any replies!

[GreenV8S]

Haven't we already had this question recently?

[Tony1963]

Short winter nights? If only!

[Macski]

GreenV8S said:

Haven't we already had this question recently?

I don't know, did a search found nothing on the topic but it would not be the first time I posted and got a link to other posts, so have you got a link.

And to whoever posted and removed their post, thanks for your view, I suppose I could remove the battery but it be a whole lot easier to leave the battery in the car

And OK I made a mistake Short days not nights, I will correct it now if I can

[Mr2Mike]

Macski said:

Also could I connect a 12V panel to a 24V mobility scooter?

You could connect it, but it won't do any charging.

[GreenV8S]

Macski said:

I don't know, did a search found nothing on the topic but it would not be the first time I posted and got a link to other posts, so have you got a link.

How about this one posted by somebody called Macski a couple of days ago?

https://www.pistonheads.com/gassing/topic.asp?h=0&...

[SlimJim16v]

GreenV8S said:

How about this one posted by somebody called Macski a couple of days ago?

https://www.pistonheads.com/gassing/topic.asp?h=0&...

[slybunda]

hi all, i would like to use one of these solar trickle chargers but i read that they all put out 18v and 0.5amp or less. wont 18v cause the battery to overcharge or boil? or does the low current charge offset that?

[E-bmw]

A car battery is a 12.6 volt battery, if a charger only puts out 12.6 volts it will not charge, it has to put out more.

The low current is because it is just a "trickle charger" which by definition will just supply a trickle of charge to top-up the battery.

[Macski]

GreenV8S said:

How about this one posted by somebody called Macski a couple of days ago?

https://www.pistonheads.com/gassing/topic.asp?h=0&...

I really do not know why I posted this twice, I only recall posting this once.

[Dr Doofenshmirtz]

Search eBay for a 10w 12v solar panel.
I have a couple of these...one for my Motorcycle and the other for my Sinclair C5 - they keep the batteries topped up just fine, even in winter.
They cost around £10 from China. If you go over 10w you'll need a charge controller.

[GreenV8S]

Dr Doofenshmirtz said:

Search eBay for a 10w 12v solar panel.
I have a couple of these...one for my Motorcycle and the other for my Sinclair C5 - they keep the batteries topped up just fine, even in winter.
They cost around £10 from China. If you go over 10w you'll need a charge controller.

How much current do those particular batteries need on average in order to stay topped up?

How much current on average is that tiny solar panel actually capable of supplying in real world conditions?

[E-bmw]

GreenV8S said:

Dr Doofenshmirtz said:

Search eBay for a 10w 12v solar panel.

They cost around £10 from China. If you go over 10w you'll need a charge controller.

How much current on average is that tiny solar panel actually capable of supplying in real world conditions?

Just remember (I do realise 12v is a generic term) that if it only supplies 12v it won't charge a car battery as they are actually 12.6v & every 0.1 volt down roughly equates to 20% lost charge so 12v is actually flat if that is what your battery is showing.

Power = Current x Voltage so by transposing that equation, current equals power divided by voltage.

So a 12v 10w cell will give out up to just over 0.8 amps, but that is only if your battery is less than 12 volt to accept the charge.

In reality what you need (yes I know 12 v is still a generic term) is a cell capable of supplying 13 or 14 v and around 8/10 watts to give around 1/2 to 3/4 of an amp, that will be fine.

[Dr Doofenshmirtz]

GreenV8S said:

Dr Doofenshmirtz said:

Search eBay for a 10w 12v solar panel.
I have a couple of these...one for my Motorcycle and the other for my Sinclair C5 - they keep the batteries topped up just fine, even in winter.
They cost around £10 from China. If you go over 10w you'll need a charge controller.

How much current do those particular batteries need on average in order to stay topped up?

How much current on average is that tiny solar panel actually capable of supplying in real world conditions?

In mid summer you'll see about 600mA. In winter on a bright sunny day maybe 200mA.
With solar panels, the voltage stays fairly linear, it's the current that falls off rapidly either side of mid-day. A 10w 12v panel will actually produce up to around 18v but the battery clamps the voltage down to around 13.8v...enough to replenish any self discharge, stop sulfation (which is what kills lead acid batteries) and keep the battery healthy.

[Dr Doofenshmirtz]

E-bmw said:

GreenV8S said:

Dr Doofenshmirtz said:

Search eBay for a 10w 12v solar panel.

They cost around £10 from China. If you go over 10w you'll need a charge controller.

How much current on average is that tiny solar panel actually capable of supplying in real world conditions?

Just remember (I do realise 12v is a generic term) that if it only supplies 12v it won't charge a car battery as they are actually 12.6v & every 0.1 volt down roughly equates to 20% lost charge so 12v is actually flat if that is what your battery is showing.

Power = Current x Voltage so by transposing that equation, current equals power divided by voltage.

So a 12v 10w cell will give out up to just over 0.8 amps, but that is only if your battery is less than 12 volt to accept the charge.

In reality what you need (yes I know 12 v is still a generic term) is a cell capable of supplying 13 or 14 v and around 8/10 watts to give around 1/2 to 3/4 of an amp, that will be fine.

The generic Chinese panels will hit 18v off load. On load the battery will clamp the voltage at around 13.8v

[GreenV8S]

Dr Doofenshmirtz said:

In mid summer you'll see about 600mA. In winter on a bright sunny day maybe 200mA.

I meant on average over a typical 24 hour period.

ETA: Are those real-world current figures, or ones you have calculated back from claimed Wattage divided by nominal Voltage?

Edited by GreenV8S on Tuesday 11th December 18:03

[E-bmw]

Dr Doofenshmirtz said:

E-bmw said:

GreenV8S said:

Dr Doofenshmirtz said:

Search eBay for a 10w 12v solar panel.

They cost around £10 from China. If you go over 10w you'll need a charge controller.

How much current on average is that tiny solar panel actually capable of supplying in real world conditions?

Just remember (I do realise 12v is a generic term) that if it only supplies 12v it won't charge a car battery as they are actually 12.6v & every 0.1 volt down roughly equates to 20% lost charge so 12v is actually flat if that is what your battery is showing.

Power = Current x Voltage so by transposing that equation, current equals power divided by voltage.

So a 12v 10w cell will give out up to just over 0.8 amps, but that is only if your battery is less than 12 volt to accept the charge.

In reality what you need (yes I know 12 v is still a generic term) is a cell capable of supplying 13 or 14 v and around 8/10 watts to give around 1/2 to 3/4 of an amp, that will be fine.

The generic Chinese panels will hit 18v off load. On load the battery will clamp the voltage at around 13.8v

In that case that would be fine assuming around 10 watts load capacity.

[Dr Doofenshmirtz]

GreenV8S said:

Dr Doofenshmirtz said:

In mid summer you'll see about 600mA. In winter on a bright sunny day maybe 200mA.

I meant on average over a typical 24 hour period.

ETA: Are those real-world current figures, or ones you have calculated back from claimed Wattage divided by nominal Voltage?

Those are real world figures that I've seen with my clamp meter at mid-day.